EEVblog Electronics Community Forum

Products => Test Equipment => Topic started by: bryanp on January 08, 2018, 12:21:24 am

Title: EEVblog 121GW Multimeter Issues
Post by: bryanp on January 08, 2018, 12:21:24 am
Hi Dave (and everyone else),

I have done a search on the forums for a dedicated 1212GW support thread but could not find one, apologies if I have missed it.

I just received my 121GW and it is awesome. I was looking over the set up menu to set the date and time etc but am having a few issues.

1. If I change the year (it defaults to 2016), the day, month, hour or minutes the setting does not stick/save. Changing (and having them save) other set up menu items works fine. I have tried cycling the power on the meter after making a change but that has no effect.

2. Is it possible to disable the beep please, at least for button presses and any time the rotary switch is changed? The beep is loud which is great for continuity etc but after trying to figure out how to change the date/time it is starting to annoy.

3. There appears to be a set up menu option between item 7 (Hour-Minute) and item 8 Logging Interval. This set up menu item is not mentioned in the manual, and it is present on at least the Low Z, V and Ohms ranges. The set up menu item consists of 5 digits, it seems to default to 5 zeros but these numbers can be changed from 0-9 and once you hold down the setup button to edit this option you can use the set up button to switch between each digit. I do not know what these numbers/digits mean. I changed the last digit (on the right hand side) to a value and saved it but this seemed to have no effect.

4. An erratum for the manual in regards to changing the Hour-Minute and Month-Day set up menu items should include some mention of a long setup button press to switch between month and day for instance and a short setup button press to save and move on. This functionality seems to be the opposite to the five zeros set up menu item (mentioned above) as a short press switches between zeros/digits and a long press saves and switches to the next set up menu item.

Please let me know if I am being an idiot and have missed something obvious.

Thanks and the meter really is a beast.
Title: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 08, 2018, 08:59:09 pm
This is a thread for discussion of bugs and issues found with the 121GW meter.
Please state your version number.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 08, 2018, 09:54:50 pm
Hi Dave!

On my "U-1.01" low z doesn't work until voltage reaches 11V. Then it works fine (but shows only one digit after dot (like 11.3V), intentionally low resolution?).

Update rate is like 0.5samples/s. Tried to change "In x" (by default it's ln 0), no luck.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 09, 2018, 12:03:29 am
1. If I change the year (it defaults to 2016), the day, month, hour or minutes the setting does not stick/save. Changing (and having them save) other set up menu items works fine. I have tried cycling the power on the meter after making a change but that has no effect.
Just got my meter today, and I am very impressed. Calibration is pretty much spot on.

The time/date works fine on my meter (version U-1.01). It arrived with the correct time and it seems to keep correct time even after changing the batteries. 

After changing a time/date field, are you pressing the setup button for about two seconds until the beep to save the change?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DrGeoff on January 09, 2018, 12:12:53 am
1. If I change the year (it defaults to 2016), the day, month, hour or minutes the setting does not stick/save. Changing (and having them save) other set up menu items works fine. I have tried cycling the power on the meter after making a change but that has no effect.

Confirmed. I have 2072-06-12 as the default date and changing it does not save.
Time does not save correctly either.

2. Is it possible to disable the beep please, at least for button presses and any time the rotary switch is changed? The beep is loud which is great for continuity etc but after trying to figure out how to change the date/time it is starting to annoy.

Yes please!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bryanp on January 09, 2018, 12:15:14 am
Thanks amspire for the help, I tried the long setup button press and the date and time etc changes were saved. Could have sworn I tried that yesterday but thanks.

My version number BTW is also U-1.01

Still not sure what the five digits thing is in the set up menu between the Hour-Minute and Logging Interval is. Does anyone else have this extra set up menu item?

Title: Re: EEVblog 121GW Multimeter Issues
Post by: DrGeoff on January 09, 2018, 12:19:17 am
After changing a time/date field, are you pressing the setup button for about two seconds until the beep to save the change?

I missed that, not in the manual, just 'press setup'. Date/time appears set OK now that I hold setup down for an extended time.

Thanks!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 09, 2018, 12:23:12 am
1. If I change the year (it defaults to 2016), the day, month, hour or minutes the setting does not stick/save. Changing (and having them save) other set up menu items works fine. I have tried cycling the power on the meter after making a change but that has no effect.

Confirmed. I have 2072-06-12 as the default date and changing it does not save.
Time does not save correctly either.
Are you saying that if you change the year to 2018 and hold the setup button down till the beep, then if you check the year again, it is back to 2072?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DrGeoff on January 09, 2018, 12:28:48 am
1. If I change the year (it defaults to 2016), the day, month, hour or minutes the setting does not stick/save. Changing (and having them save) other set up menu items works fine. I have tried cycling the power on the meter after making a change but that has no effect.

Confirmed. I have 2072-06-12 as the default date and changing it does not save.
Time does not save correctly either.
Are you saying that if you change the year to 2018 and hold the setup button down till the beep, then if you check the year again, it is back to 2072?
Yes, I cycled through all the date/times and set them. Then cycling back to the year again it was unchanged. There must be a difference between pressing the Setup button to cycle to the next setup option and holding it for longer to save the current value. The manual was not clear on this.

Quote
To change the date items:
1. Navigate to the menu item.
2. Hold SETUP
3. Press UP and DOWN to configure the date/time item.
4. Press SETUP again to save
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 09, 2018, 12:32:03 am
Yes, I cycled through all the date/times and set them. Then cycling back to the year again it was unchanged. There must be a difference between pressing the Setup button to cycle to the next setup option and holding it for longer to save the current value. The manual was not clear on this.

Quote
To change the date items:
1. Navigate to the menu item.
2. Hold SETUP
3. Press UP and DOWN to configure the date/time item.
4. Press SETUP again to save
You have to hold the setup button for 2 seconds until the beep to change the date/time settings. Otherwise it is not changed. I don't think it does clearly say that in the manual.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DrGeoff on January 09, 2018, 12:40:16 am
Also, as an aside, if you hit 'Setup' in the AC volts display you get dBm in the smaller top display.
Very useful.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 09, 2018, 11:26:02 am
Looks like full scale of the 121GW is 54999 and not 49999 - which is fantastic.  :clap: The specifications in the manual probably should be updated to mention this.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 09, 2018, 11:45:14 am
BTW, is there a source code so I could try fix some problems by myself? (sorry if this was asked before)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 09, 2018, 12:00:44 pm
The source code for the Bluetooth 121GW App is available. The code for the Multimeter will likely never be open source according to Dave.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mikeselectricstuff on January 09, 2018, 12:06:36 pm
The source code for the Bluetooth 121GW App is available. The code for the Multimeter will likely never be open source according to Dave.
But I suspect someone will disassemble it at some point...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Fungus on January 09, 2018, 01:09:16 pm
The source code for the Bluetooth 121GW App is available. The code for the Multimeter will likely never be open source according to Dave.
But I suspect someone will disassemble it at some point...

IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

If you want to mess around with it, that's your problem, not theirs.

(And I hope you make people aware of this problem if you start uploading modified firmware somewhere)

Edit: The best course of action if you want something "fixed" is to ask here. Dave could maybe pass sensible requests along to the manufacturer...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 09, 2018, 05:55:29 pm
IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

Is it a law or requirement? Or they try to be on a "safe" side?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 09, 2018, 05:59:23 pm
Opened the manual, it says "This meter is hackable, go for it.". Challenge accepted  :box:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mikeselectricstuff on January 09, 2018, 08:45:50 pm
The source code for the Bluetooth 121GW App is available. The code for the Multimeter will likely never be open source according to Dave.
But I suspect someone will disassemble it at some point...

IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

Do the IEC test equipment standards actually cover software funcitionality ( e.g. not under-reading)?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on January 09, 2018, 10:49:41 pm
FYI
Possible bugs in User's Manual (Rev 11 December 2017):
1.  No mention of input impedance for any V inputs.
2.  No mention of Low Z position on dial.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on January 10, 2018, 12:30:36 am
Slow Auto Ranging.

Manually set Range response time is great. So if you are testing a batch best to lock it in.

Without knowing how the code is written but checking out the bottom of the display shows it start at MOhms then cycle down through the ranges until it get into limits, it then seems to run a stepped routine to decide where to place the decimal point before displaying a value? Remove display indicators and anything not absolutely necessary to make the auto range work well and safely to improve the speed. So some firmware code optimization needed if possible?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on January 10, 2018, 03:55:51 am
Minor update for the next manual revision; The main photo needs updating to show the 500mA text over the 'A' terminal and the Bluetooth symbol is missing between the 'SETUP' an '1mS PEAK' buttons.
Manual I am looking at was last revised 11th Dec.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: VK5RC on January 10, 2018, 08:23:10 am
+1 re the relative slowness of auto-ranging, otherwise very happy :-+
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on January 10, 2018, 08:42:42 am
Yes, I cycled through all the date/times and set them. Then cycling back to the year again it was unchanged. There must be a difference between pressing the Setup button to cycle to the next setup option and holding it for longer to save the current value. The manual was not clear on this.

Quote
To change the date items:
1. Navigate to the menu item.
2. Hold SETUP
3. Press UP and DOWN to configure the date/time item.
4. Press SETUP again to save
You have to hold the setup button for 2 seconds until the beep to change the date/time settings. Otherwise it is not changed. I don't think it does clearly say that in the manual.

Just playing with the settings on mine and yep. Manual needs to use the words "Long Press" or similar to save and to jump from the hours set to minutes.

Minor on the manual but the Index and Pages are out of step as no doubt more content has been added and will be :)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: blueskull on January 10, 2018, 08:53:31 am
IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

Dave maybe can sell a version with open source firmware as DMM development kit? As a dev kit, you can basically bypass any certification requirements.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 10, 2018, 09:00:44 am
BTW, I found the problem of slow updates. My meter came with "AC+DC" mode activated. In this mode it is very slow :(. And yeah, beeping sucks.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BBBbbb on January 10, 2018, 09:00:51 am
IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

Dave maybe can sell a version with open source firmware as DMM development kit? As a dev kit, you can basically bypass any certification requirements.
I do believe that it's not his to do this, it's up to UEi, as they hold the IP. Dave gave up a lot of his rights regarding the meter as a part of the deal between them, from what I understood. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: idpromnut on January 10, 2018, 12:53:01 pm
Dave has said that the issue with open sourcing the firmware is that it is UEi's source code, but they don't own all the rights to the code (i.e. they don't have the right to re-distribute the source code in its entirety). Getting this sorted out seems like it will be more trouble than it is worth for UEi, so they are unlikely to do it.

I think Dave mentioned that UEi /might/ be willing to opensource certain bits of the firmware (the LCD driver for instance); he would need to confirm that however.

If you are going to go hacking around, remember a couple of things:

- The STM32 line of mcus offer "read out protection", so directly reverse engineering the firmware from the meter might be tricky (but the protection has been weakened, see paper referencing this https://www.aisec.fraunhofer.de/en/FirmwareProtection.html (https://www.aisec.fraunhofer.de/en/FirmwareProtection.html)),
- Even if a firmware update blob is released (say a v1.02), it will likely not include at least one of the boot loaders, and may not include any bootloader. That means using the existing bootloader as-is might be tricky (i.e. reverse engineering the application might be possible by looking at the firmware update blob),
- There is a JTAG header on the board IIRC, but you can't use it when read-out proctection is enabled (if I'm remembering correctly). But that means re-writing a new firmware from scratch is totally possible (and I am pretty sure this is what the "Hack away!" sentence in the manual refers to).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mikeselectricstuff on January 10, 2018, 03:50:59 pm
From a video in another thread, it seems it takes 7 seconds to autorange from open to zero ohms - how can Dave have considered this remotely acceptable ?
Any more than 1 second is too slow.
The bargraph seems to respond quickly, so why isn't it using that conversion for ranging?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on January 10, 2018, 04:23:14 pm
From a video in another thread, it seems it takes 7 seconds to autorange from open to zero ohms - how can Dave have considered this remotely acceptable ?

He couldn't have, hopefully a last minute change that can be easily fixed, the delay is agonizing. 

Joe might be able to comment on how the pre-production 121 behaved?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: gnavigator1007 on January 10, 2018, 04:46:07 pm
That autoranging is really atrocious lol. Just raced it against every handheld meter I had nearby (BM235, U1252A, U1273A, UT61E, & a UT210E just for kicks). UT210E was the next slowest, but still seems like a rocket next to the 121GW. Others were all reasonably close with the the BM235 & UT61E appearing slightly faster than the Agilent/Keysights. One of the reasons I was eager to get an early 121GW was for the fun of finding issues like this. Not sure how this slipped past Dave & UEI, but hopefully it's a fairly simple fix.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 10, 2018, 06:49:00 pm
Okay, we'll not see FW released for opensource, I got it. But I want to roll my own. Please post information how to do this or a minimal buildable example. Like, a zip-archive with a Makefile inside.

UEi's source code, but they don't own all the rights to the code (i.e. they don't have the right to re-distribute the source code in its entirety).

Alright, let them ship without that pieces. I can try to write open-source equivalent of that pieces.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: markb82 on January 10, 2018, 07:25:23 pm
Anyone else have a lot of play (loosy-goosy) in their rotary switch?

Also my meter flashes the backlight when first turning on (firmware issue?) and beeps every time you switch settings (ie rotate the rotary switch) which is very annoying.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: gnavigator1007 on January 10, 2018, 07:46:04 pm
Anyone else have a lot of play (loosy-goosy) in their rotary switch?

Also my meter flashes the backlight when first turning on (firmware issue?) and beeps every time you switch settings (ie rotate the rotary switch) which is very annoying.

I actually like the feel of the switch quite a bit. Definitely easier to turn on one handed than others. On some of my meters with stiffer switches I'll occasionally use so much force that I turn past the selection I intended. The beeping doesn't bother me, but should definitely have have an option to turn it off. I've been wondering about that backlight flash too. Flashes briefly turning on from either off position. Went back and rewatched one of Dave's videos to make sure others did it. Hard to see in the video, but they did it too.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: VK5RC on January 10, 2018, 09:16:38 pm
Switch on mine is good.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DrGeoff on January 10, 2018, 10:09:22 pm
I am sure Dave will do a full review of the meter in one of his videos after the holidays.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 10, 2018, 10:15:44 pm
I do believe that it's not his to do this, it's up to UEi, as they hold the IP. Dave gave up a lot of his rights regarding the meter as a part of the deal between them, from what I understood.

Just to be clear, I have ZERO legal rights to this meter apart from exclusive distributorship.
I did not pay a single cent for its development.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: markb82 on January 11, 2018, 01:44:50 am
Just to be clear, I have ZERO legal rights to this meter apart from exclusive distributorship.
I did not pay a single cent for its development.

How about the open source-ness of the schematics?  It was on the feature list of the Kickstarter.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ez24 on January 11, 2018, 02:10:06 am
Watching
Title: Re: EEVblog 121GW Multimeter Issues
Post by: floobydust on January 11, 2018, 02:54:21 am
For people modifying the firmware, I'd say that invalidates the 61010 agency safety approvals.
A multimeter is expected to function a particular way, i.e. display hazardous voltages correctly after test scenarios and who would re-test those after adding a super-fast autoranging hack?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 11, 2018, 05:11:20 am
IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

Dave maybe can sell a version with open source firmware as DMM development kit? As a dev kit, you can basically bypass any certification requirements.

There is absolutely nothing stopping anyone writing their own firmware and making it open source.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 11, 2018, 05:30:36 am
mVA Problem: (Confirmed by DrGeoff)

I seem to have a definite measurement problem on the mVA range in DC. Can anyone confirm this on their meters?

If I have a test setup with a power supply and a precision 100ohm resistor and I am putting 5V across the resistor, then as long as the current flowing into the mAuA socket is positive, I get 5.0000V across the resistor, 50.000mA current and 250.00 mVA. All good. Just using absolute numbers here - not worrying about the +/- polarities.

If I swap the power supply polarity - nothing else changes, I get  5.000V, 0.0368mA and 55.215 mVA. The current is wrong and the mVA product makes no sense.

The configuration I used was the mAuA socket to the power supply, the multimeter common to one side the resistor load, the V/Ohms input to the other side of the load that also connects to the other power supply output. I am using this configuration so that the multimeter is measuring the actual voltage across the load. The problem happens whether or not the v/Ohms input is connected or not, so my meter just cannot measure negative currents over exactly 10mA in the mVA/VA mode.

The problem occurs exactly when the current reaches 10.000mA. It works perfectly at 9.999mA with both power supply polarities. At 10.000mA, it fails. This makes it look like a software bug.

The mAuA input works fine in A/mA switch setting. This is only a problem in the mVA/VA mode.

The same problem does not occur using the A input for current instead of the mAuA input - at least at up to 100mA.  The problem might be there using the A input at higher currents, but I cannot test that right now.

I have not tested this in AC mode, but assuming the RMS converter is only supplying positive voltages to the measurement chip, I would guess that AC mVA mode probably is fine.

UPDATE:

The same problem happens with the A input when measuring VA. If the current into the A socket reaches -1.0000A it wraps around to zero. -0.9999A is fine. Same thing happens with the mAuA socket at -10mA. Both inputs work perfectly in the mVA/VA modes with positive input currents.

The problem seems to be connected to Autoranging with negative currents - if you use the range button, you can get the right numbers with negative currents. So it seems that the current measurement autoranging for mVA/VA measurements does not work properly for negative currents. It works properly for positive input currents. If the firmware can be fixed to get the measurement chip in the correct range for the applied negative DC current, this problem should be fixed.

It would seem that with negative currents, the mVA get stuck in the 5.4999mA range. It actually seem to keep measuring up to 9.9999mA  - that is 80% overrange before rolling over to 0.00000 at 10mA. It then continues to measure correctly to 11mA (with the lost first digit) which is 100% overrange!. After that, I think the poor current input has had enough. At some point, the current input totally overloads and just produces rubbish numbers. The multimeter does not change to the 54.999mA range with mVA negative currents or to the 5.4999A or 10A ranges for VA negative currents at all if Autoranging is enabled.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DrGeoff on January 11, 2018, 05:52:05 am
mVA Problem:

I seem to have a definite measurement problem on the mVA range in DC. Can anyone confirm this on their meters?

If I have a test setup with a power supply and a precision 100ohm resistor and I am putting 5V across the resistor, then as long as the current flowing into the mAuA socket is positive, I get 5.0000V across the resistor, 50.000mA current and 250.00 mVA. All good. Just using absolute numbers here - not worrying about the +/- polarities.

If I swap the power supply polarity - nothing else changes, I get  5.000V, 0.0368mA and 55.215 mVA. The current is wrong and the mVA product makes no sense.

The configuration I used was the mAuA socket to the power supply, the multimeter common to one side the resistor load, the V/Ohms input to the other side of the load that also connects to the other power supply output. I am using this configuration so that the multimeter is measuring the actual voltage across the load. The problem happens whether or not the v/Ohms input is connected or not, so my meter just cannot measure negative currents over exactly 10mA in the mVA/VA mode.

The problem occurs exactly when the current reaches 10.000mA. It works perfectly at 9.999mA with both power supply polarities. At 10.000mA, it fails. This makes it look like a software bug.

The mAuA input works fine in A/mA switch setting. This is only a problem in the mVA/VA mode.

The same problem does not occur using the A input for current instead of the mAuA input - at least at up to 100mA.  The problem might be there using the A input at higher currents, but I cannot test that right now.

Can confirm this.
I repeated the experiment using a bipolar supply, leaving the 0V cable intact and switching from the +ve supply terminal to the -ve supply terminal. Same results as you see.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 11, 2018, 09:14:56 am
I discovered more details of the DC mVA/VA problem and added it to post (2 posts back). It is an Autoranging bug.

No wonder people want to hack this multimeter - the measurement chip keeps working to the 99999 count and actually keeps working till the 109999 count with the slight problem that the first "1" digit is lost - the 5 digit counter just wraps around. The overload display at 55000 is just a firmware thing.

Until this bug is fixed, you can actually get the meter to read currents to 9.9999mA and 0.99999A right now.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nidlaX on January 11, 2018, 09:54:58 am
One person on Kickstarter reported a poorly soldered connection to the LCD backlight.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mikeselectricstuff on January 11, 2018, 10:05:20 am
IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

Dave maybe can sell a version with open source firmware as DMM development kit? As a dev kit, you can basically bypass any certification requirements.

There is absolutely nothing stopping anyone writing their own firmware and making it open source.
Are the formats of the calibration data, and the firmware update file public yet ?
Those would be prerequisites for a proper OS alternative FW implementation.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: flano on January 11, 2018, 10:42:19 am
Found something interesting on the low Z range with a 100khz squarewave, 5Vpp and 5V offset.

I get a reading of 158V?

Edit. Firmware is 1.01

Mike.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chriz2600 on January 11, 2018, 03:50:12 pm
Hi Dave,

I received my unit today, and had some problems with continuity test.
From time to time there seems to be a contact problem related to the rotary switch, which occurs when switching from off to continuity mode. I made a short video showing this problem:
- inputs are shortened.
- version is 1.02

https://youtu.be/cERpnZiUjV4 (https://youtu.be/cERpnZiUjV4)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 11, 2018, 05:15:52 pm
Hi Dave,

I also got my meter today. Thanks for your effort. I like the probes and the build quality. I have no equipment to test its precision.

Firmware version is: U-1.02

Here are the things I don't like or consider a fault:


I would be most glad if the logging features could be improved. Please add at least sub-second precision time stamps to the SD-card logfile. I don't care if they are absolute or relative value to the start of the logging but just a counter is not enough. This is the point I care about, since I have no other meter with this capability.

All other points would be nice to have but are not important to me.

A higher bluetooth speed would be second, but I have a meter with a real serial Adapter, so I could live without it. At least a deterministic logging interval would be a win for bluetooth.

Anyway, thanks for the meter, it's fun to play around with.

Quote
mm@ovid:~/121gw$ ls -l
total 232
-rwxr-xr-x   1 mm mm  39189 Feb  9  2006 18011100.CSV
-rwxr-xr-x   1 mm mm 117848 Dez 29 07:17 EEVBlog.bin
drwxr-xr-x   2 mm mm   4096 Dez  4 08:31 System Volume Information

Quote
time (s), Power DC (VA)
0.66214, 10.04
2.319854, 10.04
3.587273, 7.41
5.342622, 135.58
7.682192, 10.04
8.947719, 135.58
10.70679, 7.41
12.94711, 6.66
14.21456, 6.47
15.48118, 102.93
18.74924, 131.67
20.99118, 7.3
21.77326, 9.65
25.52709, 138.36
27.76692, 7.41
28.54338, 10.04
30.30227, 7.41
31.5711, 7.41
32.78831, 135.57
33.56652, 10.04
34.25069, 7.41
37.56762, 7.41
38.34549, 7.4
40.53939, 9.89
40.83278, 6.72
41.61178, 6.46
42.87929, 103.97
44.63388, 7.03
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on January 11, 2018, 06:15:19 pm
Did anyone checked the quality of the contacts in the rotary switch?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 11, 2018, 07:13:09 pm
Hi joeqsmith,

yes, I can handle line voltages and do so regularly.

Do you think it's related to spikes on the mains? I usually use a 0-300V 6A insulating transformer for tests like this, but if you think it makes sense I can test directly on mains but have only 230V available then. So your request would be >50VA for >6h logging to SD-card? Resistive load would be fine (they are more quiet)?

I will run it over night and hope it doesn't burn down the house. :-)

Just tell me if with or without the transformer.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 11, 2018, 07:48:09 pm
Hi firewalker,

yes, I took it appart after I noticed the issue.

Contacts look fine there are 4 of them, two on each side of the axis, each with two contact points.
They look "goldish" the pcb also looks like ENIG finish. All looks good, so I have no idea why it happens.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 11, 2018, 07:51:31 pm
They look "goldish" the pcb also looks like ENIG finish. All looks good, so I have no idea why it happens.

May be they don't reach well the pcb?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on January 11, 2018, 07:54:00 pm
Hi joeqsmith,

yes, I can handle line voltages and do so regularly.

Do you think it's related to spikes on the mains? I usually use a 0-300V 6A insulating transformer for tests like this, but if you think it makes sense I can test directly on mains but have only 230V available then. So your request would be >50VA for >6h logging to SD-card? Resistive load would be fine (they are more quiet)?

I will run it over night and hope it doesn't burn down the house. :-)

Just tell me if with or without the transformer.

I was checking the power using an arb, amplifier and transformer coupled.  It seems like it was limited to 50V when I started to turn it up.  You don't need a lot of current.  Obviously the meter has no problems reading just voltage.  It was tied to the power measurement.   

The data logging problem I don't think was mode specific.  I was wanting to run a stability test and had the input pins shorted or some voltage reference attached to it.   I tried recording  24 hours and when I checked it, the card only had a few points.  I tried different sample rates and such but it seemed like there was maybe a delay and timeout when recording to the card and it would just stop recording.   I want to say I tried to narrow down how long it took to fault out and it was maybe two hours.   

So just a quick test at for the AC VA mode and a short or something for the long term so we don't burn down the house. 

Thanks again for looking into this.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 11, 2018, 08:30:29 pm

I was checking the power using an arb, amplifier and transformer coupled.  It seems like it was limited to 50V when I started to turn it up.  You don't need a lot of current.  Obviously the meter has no problems reading just voltage.  It was tied to the power measurement.

You are completely right. The display switches to OFL when I exceed a voltage of 55V AC.

I can't test with DC as my power supply has max 32V.

Can someone else please check VA mode with more than 55V DC?

I will run the logging over night.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 11, 2018, 08:49:59 pm
They look "goldish" the pcb also looks like ENIG finish. All looks good, so I have no idea why it happens.

May be they don't reach well the pcb?

I don't think so. In that case the meter would also show odd behavior during operation when you touch the switch which is not the case.
I'd rather guess it might be an debouncing issue in the firmware.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 11, 2018, 08:58:11 pm
If you change to mVA/VA to manual ranges, you realize there are only 4 combinations available:

mVA mode:
5.5V + 5.5mA
55V + 5.5mA
5.5V + 55mA
55V + 55mA


VA mode:
5.5V + 550mA
55V + 550mA
5.5V + 10A
55V + 10A

Definitely the whole VA feature is underveloped. If I was logging VA, I would definitely want to use a manual range to avoid any autoranging during logging.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 11, 2018, 09:20:06 pm
In lowZ mode the meter only starts to display a value >0 when the voltage rises to around 11.5V. When the voltage is lowered from 12V it works down to around 3V. If this is expected behaviour, it should be documented in the manual.
I haven't had a meter with a Low Z mode so I am not familiar with how it is meant to work. It seems to be trying to autodetect whether the input is AC or DC and it needs at least 12V to do this. It has no ranges so I assume the 550V range is fixed. The Low Z input resistance looks to be about 2.7K ohms which would dissipate 112W at 550V!

To limit dissipation to, say, 5W, then you are limited to around 110V maximum. At 240V, the dissipation would be 21W which is a lot of heat to be contained inside the meter. You could do a quick measurement, but a long term measurement would be really cooking the insides of the meter.

I think I will be replacing the 2.7K resistors with something much larger. 27K or higher. This seems like a dangerous feature as it is right now. Like the VA mode, very underveloped as you can see from the lack of documentation and specifications in the manual.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: idpromnut on January 11, 2018, 09:32:01 pm
In lowZ mode the meter only starts to display a value >0 when the voltage rises to around 11.5V. When the voltage is lowered from 12V it works down to around 3V. If this is expected behaviour, it should be documented in the manual.
I haven't had a meter with a Low Z mode so I am not familiar with how it is meant to work. It seems to be trying to autodetect whether the input is AC or DC and it needs at least 12V to do this. It has no ranges so I assume the 550V range is fixed. The Low Z input resistance looks to be about 2.7K ohms which would dissipate 112W at 550V!

To limit dissipation to, say, 5W, then you are limited to around 110V maximum. At 240V, the dissipation would be 21W which is a lot of heat to be contained inside the meter. You could do a quick measurement, but a long term measurement would be really cooking the insides of the meter.

I think I will be replacing the 2.7K resistors with something much larger. 27K or higher. This seems like a dangerous feature as it is right now. Like the VA mode, very underveloped as you can see from the lack of documentation and specifications in the manual.

My Aglient U1232A has an impedance of 3.6kOhm on its LowZ mode. I think 2.7kOhm on the 121GW is fine.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 11, 2018, 09:43:03 pm
In lowZ mode the meter only starts to display a value >0 when the voltage rises to around 11.5V. When the voltage is lowered from 12V it works down to around 3V. If this is expected behaviour, it should be documented in the manual.
I haven't had a meter with a Low Z mode so I am not familiar with how it is meant to work. It seems to be trying to autodetect whether the input is AC or DC and it needs at least 12V to do this. It has no ranges so I assume the 550V range is fixed. The Low Z input resistance looks to be about 2.7K ohms which would dissipate 112W at 550V!

To limit dissipation to, say, 5W, then you are limited to around 110V maximum. At 240V, the dissipation would be 21W which is a lot of heat to be contained inside the meter. You could do a quick measurement, but a long term measurement would be really cooking the insides of the meter.

I think I will be replacing the 2.7K resistors with something much larger. 27K or higher. This seems like a dangerous feature as it is right now. Like the VA mode, very underveloped as you can see from the lack of documentation and specifications in the manual.

My Aglient U1232A has an impedance of 3.6kOhm on its LowZ mode. I think 2.7kOhm on the 121GW is fine.
But how does it work? Is it a PTC thermistor and not a 2k7 resistor? I was just looking at the Fluke 114 manual and its LowZ goes to 600V and has about a 3K impedance. It better be a PTC thermistor, because 120W of heat inside a multimeter is a massive problem.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 11, 2018, 09:45:43 pm
In lowZ mode the meter only starts to display a value >0 when the voltage rises to around 11.5V. When the voltage is lowered from 12V it works down to around 3V. If this is expected behaviour, it should be documented in the manual.
I haven't had a meter with a Low Z mode so I am not familiar with how it is meant to work. It seems to be trying to autodetect whether the input is AC or DC and it needs at least 12V to do this. It has no ranges so I assume the 550V range is fixed. The Low Z input resistance looks to be about 2.7K ohms which would dissipate 112W at 550V!

No! That's not how this meter or any other Low-Z meter works.
The "resistor" is actually a PTC themristor, it's resistance increases when it heats up.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 11, 2018, 09:48:48 pm
I think I will be replacing the 2.7K resistors with something much larger. 27K or higher. This seems like a dangerous feature as it is right now. Like the VA mode, very underveloped as you can see from the lack of documentation and specifications in the manual.

No, the lowZ mode seems fine apart from the low sensitivity. It consumes around 5mA at 12V AC input voltage.
If I ramp up the voltage very quickly to 310V AC it consumes a maximum of 245mA for a very short time and drops immediately to around 3mA which is a power consumption of about 1W.
So I guess everything is save.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 11, 2018, 09:53:03 pm
In lowZ mode the meter only starts to display a value >0 when the voltage rises to around 11.5V. When the voltage is lowered from 12V it works down to around 3V. If this is expected behaviour, it should be documented in the manual.
I haven't had a meter with a Low Z mode so I am not familiar with how it is meant to work. It seems to be trying to autodetect whether the input is AC or DC and it needs at least 12V to do this. It has no ranges so I assume the 550V range is fixed. The Low Z input resistance looks to be about 2.7K ohms which would dissipate 112W at 550V!

No! That's not how this meter or any other Low-Z meter works.
The "resistor" is actually a PTC themristor, it's resistance increases when it heats up.
Thanks. Even Fluke didn't bother to explain that in their manual. I guess it is one of those things that you are just meant to know.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 11, 2018, 10:01:34 pm
NOTE: Can we please limit this thread to reporting and confirmation of bugs and issues, any discussions should be on the discussion thread.
Thanks.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 11, 2018, 10:09:28 pm
NOTE: Can we please limit this thread to reporting and confirmation of bugs and issues, any discussions should be on the discussion thread.
Thanks.
I think we have been doing that. If I crossed a line by not understanding the undocumented low Z mode, I apologize.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: massivephoton on January 11, 2018, 10:19:06 pm
I haven't had a meter with a Low Z mode so I am not familiar with how it is meant to work. It seems to be trying to autodetect whether the input is AC or DC and it needs at least 12V to do this. It has no ranges so I assume the 550V range is fixed. The Low Z input resistance looks to be about 2.7K ohms which would dissipate 112W at 550V!

To limit dissipation to, say, 5W, then you are limited to around 110V maximum. At 240V, the dissipation would be 21W which is a lot of heat to be contained inside the meter. You could do a quick measurement, but a long term measurement would be really cooking the insides of the meter.

I think I will be replacing the 2.7K resistors with something much larger. 27K or higher. This seems like a dangerous feature as it is right now. Like the VA mode, very underveloped as you can see from the lack of documentation and specifications in the manual.

The 2k7 impedance seems to be pretty standard. Fluke 115, 116 and 117 LoZ specs indicates 3k with 500pF, as the datasheet states:
http://media.fluke.com/documents/2793260_6116_ENG_A_W.PDF (http://media.fluke.com/documents/2793260_6116_ENG_A_W.PDF)

As already suggested at least here...
Probably some thermistor or similar.

Instruction Sheet for Fluke SV225 says:

Specifications
Voltages up to 1000 volts continuous can be safely applied to
the Adapter without damage.
Operation Temperature
-20 °C to +55 °C (-40 °F to 131 °F)
Altitude
2,000 Meters Operating
Humidity
90 % at 0 to 35 °C (32 °F to 95 °F), 70 % at 35 to 55 °C
(95 °F to 131 °F)
Nominal Resistance
3,000 ? @ 25 °C (77 °F)

... and here ...

I would think it uses a PTC thermistor, so it draws a semi constant power over the voltage range. You find a similar one in the cheap voltstick devices.

... and way hotter here ...

https://www.google.com/patents/US8480301 (https://www.google.com/patents/US8480301)

thermistors are used to limit the power.


Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on January 11, 2018, 10:38:50 pm
NOTE: Can we please limit this thread to reporting and confirmation of bugs and issues, any discussions should be on the discussion thread.
Thanks.
I think we have been doing that. If I crossed a line by not understanding the undocumented low Z mode, I apologize.
I think part of the problem as well is that it's not always cut and dry if the perceived problems were not that way by design.   To me, the slow auto range was by design.  It's known and not really a bug.  For the most part, the feedback appears to be going in one of two places.   

Strange on the VA mode.   I guess I just assumed it would allow for a wider voltage range.  Keep us posted on the data logging.     
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 12, 2018, 10:21:23 am
Keep us posted on the data logging.   

I did run VA logging for about 9h over night.
It produced a logfile with  130662 entries, which is about 4 lines per second.
So this seems fine.

It has a small display glitch during logging. The "k" symbol behind the record counter in the upper display is flickering.

As I stated in my previous post the bargraph is also flickering some times when two values are measured, so I guess there are some race conditions in the display update code of the firmware or they didn't use double buffering for the display.

Quote
mm@ovid:~/121gw$ head -10 18011200.CSV ; echo "[...]" ; tail -10 18011200.CSV
START,2018/01/12,01:48:47,
ID,170800000,
INTERVAL,000,sec,
,MAIN,,,SUB-1,,,SUB-2,,,Remark,
No. ,Func. ,Value,Unit,Func. ,Value,Unit,Func. ,Value,Unit,
1,DCVA,00000.0,mVA,DCV,00.0001,V,DCA,-0001.41,mA,,
2,DCVA,00000.0,mVA,DCV,00.0001,V,DCA,-0001.41,mA,,
3,DCVA,00000.0,mVA,DCV,00.0001,V,DCA,-0001.41,mA,,
4,DCVA,00000.0,mVA,DCV,00.0001,V,DCA,-0001.41,mA,,
5,DCVA,00000.0,mVA,DCV,00.0001,V,DCA,-0001.41,mA,,
[...]
130656,DCVA,01292.9,mVA,DCV,03.2999,V,DCA,0391.83,mA,,
130657,DCVA,01292.9,mVA,DCV,03.2999,V,DCA,0391.83,mA,,
130658,DCVA,01292.9,mVA,DCV,03.2999,V,DCA,0391.81,mA,,
130659,DCVA,01292.9,mVA,DCV,03.2999,V,DCA,0391.81,mA,,
130660,DCVA,01292.9,mVA,DCV,03.2999,V,DCA,0391.81,mA,,
130661,DCVA,01292.9,mVA,DCV,03.2999,V,DCA,0391.81,mA,,
130662,DCVA,01292.9,mVA,DCV,03.2999,V,DCA,0391.81,mA,,
MAX,49,DCVA,01294.1,mVA,
MIN,1,DCVA,00000.0,mVA,

Should I try something else?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 12, 2018, 10:30:37 am
I found something else with logging.

If you long press [MEM] in Ohm mode (no matter if AUTO or MANUAL range) the meter crashes immediately.
Only turning it OFF and ON again brings it back.


Forget  it. It was my stupidity. I had the SD-card still in my desktop.
So the bug now is:

The meter crashes if you enable logging without a SD-card present.

And another one:

Autoranging doesn't work when logging to SD-card and it stays disabled even after you switch off logging but it is displayed the whole time on the display as enabled. You have to long press the RANGE button to get it working again.

I added both issues to post https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1397729/#msg1397729 (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1397729/#msg1397729)
Title: EEVblog 121GW Multimeter Issues
Post by: fanOfeeDIY on January 12, 2018, 12:14:58 pm
I am not sure this is the how it is designed or a bug.

When I was reviewing the 121GW meter, almost every time I turn the knob from OFF to Low-Z, the back-light flickers.

The back-light going on for about 0.1 sec seems to consume battery every time start using the meter.

The firmware version is 1.01.

I uploaded the video of back-light flashing at the bellow link.
https://youtu.be/7Plq4HR34cI
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 12, 2018, 12:25:51 pm
When I was reviewing the 121GW meter, almost every time I turn the knob from OFF to Low-Z, the back-light flickers.

The back-light going on for about 0.1 sec seems to consume battery consumtion every time start using the meter.

Confirmed with Firmware U-1.02.
It blinks always when it is switched on from any of the "OFF" positions, but it doesn't blink when turning on again from auto power off.

I guess it's related to the micro controller initialization on a cold boot.

The power consumption for this should be negligible, so I'd say it'a purely cosmetic issue, if at all.
Title: EEVblog 121GW Multimeter Issues
Post by: fanOfeeDIY on January 12, 2018, 12:27:52 pm
Another point I found was when I was doing the overnight SD card data logging.
one of the file had garbled data in the file, when I was testing for the thread in the forum.

https://www.eevblog.com/forum/testgear/new-eevblog-branded-multimeter-coming/msg1398530/#msg1398530 (https://www.eevblog.com/forum/testgear/new-eevblog-branded-multimeter-coming/msg1398530/#msg1398530)

The data is corrupted as bellow in the middle of the data.
59625,DCV,049.997,V,,,,,,,,
59626,DCV,049.997,V,,,,,,,,
59627,DCV,049.996,V,,,,,,,,
59628,DCV,049.997,V,,,,,,,,
59629,DCV,                                                                                                                                                                                        59641,DCV,050.001,V,,,,,,,,
59642,DCV,049.996,V,,,,,,,,
59643,DCV,049.996,V,,,,,,,,
59644,DCV,049.998,V,,,,,,,,
59645,DCV,049.996,V,,,,,,,,

The garbled line only happened in one line out of four files of data logging.
The other three files had no issue.

The firmware is 0.01 and the SD card is the SunDisk which is included in the meter as a factory default.

I attached the original file with zip compression to work around the file size limitation on the forum.

Hope these report help improving the meter.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on January 12, 2018, 12:32:26 pm
Maybe a self test thing? Like show all segments and test the back light?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on January 12, 2018, 01:02:58 pm
I did run VA logging for about 9h over night.
It produced a logfile with  130662 entries, which is about 4 lines per second.
So this seems fine.

Should I try something else?


Thanks for running these longer tests!  I know a bit of a pain.   Glad to hear they have it working.   It's been some time since I did anything with the prototype and I can't remember any other real major functional problems with it.  I remember most were simple problems.   If you check my main thread where I post my results, some of the problems were discussed there but my guess is they have been corrected.   

What's the open circuit HV diode test putting out now? 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 12, 2018, 01:16:04 pm
What's the open circuit HV diode test putting out now?

17.332V
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on January 12, 2018, 02:43:50 pm
What's the open circuit HV diode test putting out now?
17.332V
That's interesting.  I think the prototype was under 17.   I was a bit concerned with the mux they were using had an absolute max rating.  It looked like they stayed with the same part in Dave's close up video showing the board.   Maybe they came up with a better way to protect it.   From what I saw, the mux was the weak point as far as the transient tests I run.    That mux is an HEFxxxx  located near the edge of the PCB if you wanted to pull the datasheets to have a look.   I think its an absolute max of 18 on that one.  You can drive it a little above the rail.   Easy enough to trace the path to the input pin to see how it is being protected.   Again, hard to say if you would call it a bug or issue anyway.  Maybe just something to be aware of.   
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on January 12, 2018, 02:59:55 pm
What's the open circuit HV diode test putting out now?
17.332V
That's interesting.  I think the prototype was under 17.   I was a bit concerned with the mux they were using had an absolute max rating.  It looked like they stayed with the same part in Dave's close up video showing the board.   Maybe they came up with a better way to protect it.   From what I saw, the mux was the weak point as far as the transient tests I run.    That mux is an HEFxxxx  located near the edge of the PCB if you wanted to pull the datasheets to have a look.   I think its an absolute max of 18 on that one.  You can drive it a little above the rail.   Easy enough to trace the path to the input pin to see how it is being protected.   Again, hard to say if you would call it a bug or issue anyway.  Maybe just something to be aware of.   
Good question, it was claimed to be 15V, so if it has the room maybe a good TVS diode could go in and even with the voltage drop it would still be above 15V. But I don’t know if a TVS diode would even stop your transients Joe. But it would be better then nothing.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on January 12, 2018, 03:02:20 pm
What's the open circuit HV diode test putting out now?

17.332V

000063 = 16.3V
000061 = 17.8V
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mikeselectricstuff on January 12, 2018, 03:04:49 pm
What's the open circuit HV diode test putting out now?

17.332V

000063 = 16.3V
000061 = 17.8V
Is it significantly dependent on battery voltage ?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on January 12, 2018, 03:09:57 pm
Bug, FW 1.01.

Switching to diode test mode, the secondary display continues to show temp, not 3/15v like it should, until the Range button is cycled.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on January 12, 2018, 03:17:50 pm
What's the open circuit HV diode test putting out now?

17.332V

000063 = 16.3V
000061 = 17.8V
Is it significantly dependent on battery voltage ?

From 5-6.5V battery voltage has no impact.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: hwti on January 12, 2018, 03:30:27 pm
What's the open circuit HV diode test putting out now?

17.332V
Here 15.45V (and 3.23V for the 3V mode), FW 1.02
Title: Re: EEVblog 121GW Multimeter Issues
Post by: hwti on January 12, 2018, 03:44:49 pm
  • The range switch is unreliable, you sometimes need to poke it a bit until the meter behaves properly.
  • The inability to disable the excessive beeping or at least lowering the volume get's annoying fast.
  • Autoranging speed in Ohms is way too slow.

I just had the range switch issue : after switching from V to Low-Z, it stayed in volts mode, I had to move the switch a little bit.

+1 for the annoying beeps and slow autoranging
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lewis on January 12, 2018, 05:08:02 pm
Beep beep. Beep. Beep. Beep. Beep!

FOR THE LOVE OF GOD....

Skip to 6min 32sec

https://www.youtube.com/watch?v=bKvyoZa5J8Q&t=6m32s (https://www.youtube.com/watch?v=bKvyoZa5J8Q&t=6m32s)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on January 13, 2018, 12:38:51 am
What's the open circuit HV diode test putting out now?
17.332V
That's interesting.  I think the prototype was under 17.   I was a bit concerned with the mux they were using had an absolute max rating.  It looked like they stayed with the same part in Dave's close up video showing the board.   Maybe they came up with a better way to protect it.   From what I saw, the mux was the weak point as far as the transient tests I run.    That mux is an HEFxxxx  located near the edge of the PCB if you wanted to pull the datasheets to have a look.   I think its an absolute max of 18 on that one.  You can drive it a little above the rail.   Easy enough to trace the path to the input pin to see how it is being protected.   Again, hard to say if you would call it a bug or issue anyway.  Maybe just something to be aware of.   
Good question, it was claimed to be 15V, so if it has the room maybe a good TVS diode could go in and even with the voltage drop it would still be above 15V. But I don’t know if a TVS diode would even stop your transients Joe. But it would be better then nothing.

I assume 15 would be the minimum.  It really would not matter to me anyway, if it ran a little hot (higher).  Actually, I would prefer it.   It the part has an absolute max of 18 and they are running it a bit over 17, there is not a lot of wiggle room.  You don't want it to leak and you don't ever want to exceed that absolute value.   I don't know if they made improvements to the released meter or not and am only assuming it's the same based on the comments.   They may have found a better way to protect it.   

There was a third video of my final mods as well. I damaged that prototype a few times before settling in on part selection.  I don't remember how high I went up to with it before calling it good enough.  I can tell you I never put the grim reaper on it with 14KV or bust.   :-DD       
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on January 13, 2018, 11:58:53 am
Received mine on 12th Jan in Netherlands. Auto ranging is ridicuously slow. None of my other DMM’s 869, 235 and an old Metrixc 53c are so slow. Is this an issue or by design?

Apologies.  Just noticed it has been mentioned already many times. V 1.02 is my firmware. Will do more tests later.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mikeselectricstuff on January 13, 2018, 08:03:35 pm
Has anyone checked to see if they still limit the frequency counter to 1MHz?   Again, not really a bug perhaps but more a slight oversight.
Or maybe there are issues like jitter or miscounts that make higher frequencies subject to errors?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: hwti on January 13, 2018, 08:47:21 pm
Has anyone checked to see if they still limit the frequency counter to 1MHz?   Again, not really a bug perhaps but more a slight oversight.
It's still limited.
It's in the manual : "99.999 Hz to 999.99 kHz" ranges.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: The Soulman on January 13, 2018, 09:29:59 pm
NOTE: Can we please limit this thread to reporting and confirmation of bugs and issues, any discussions should be on the discussion thread.
Thanks.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on January 14, 2018, 12:21:52 am
NOTE: Can we please limit this thread to reporting and confirmation of bugs and issues, any discussions should be on the discussion thread.
Thanks.
I didn’t know we were keeping score.
One point to you!
Who is winning?

Wait, that’s your signature, not your post. That doesn’t count then.
So if this is the bugs only (some know about before the release and never fixed?) the What thread is the shipping only? Does anyone know, I tried searching but their is so many threaded mentioning the 121GW in then. Most old threads before the Kickstarter even launched.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: The Soulman on January 14, 2018, 12:48:24 am
Well maybe this one is actually monitored by Dave and he gets a notification for every single reply here so he can gather data
to form statistics and eventually can act accordingly?
Don't pollute it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on January 14, 2018, 01:15:35 am
For those looking for another place to post, there is a discussion thread up and running on the meter here!
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/ (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Kal on January 14, 2018, 01:49:01 am
I can aslo confirm that v1.02 autoranging is very slow, especially measuring low ohms or higher voltages. Compared to BM235 its about 16 times slower worst case (0.5s vs 8s, short circuit measurement) which makes those modes basically unusable at the moment. I'm expecting this should be easily fixable in firmware so not too worried, just looks like it's always measuring at full precision starting from Mohms range and not doing fast range checking measurments at first.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: idpromnut on January 14, 2018, 03:49:15 pm
@Dave: when you get the chance, can you see about getting the firmware update v1.02 published for those of us that have only v1.01?  Thanks!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nuclearcat on January 14, 2018, 05:26:48 pm
BLE data corruption issue:
Code: [Select]
#!/usr/bin/python
from bluepy import btle
from bluepy.btle import UUID, Peripheral,DefaultDelegate
import binascii
import array
from struct import *

def parse_data(x):
    xlen = len(x)
    for offset in range(0,xlen):
        if (ord(x[offset:offset+1]) == 0xF2):
            # Process accumulated data
            print ("Accumulated data(%d): %s" % (len(parse_data.accumulated_data), str(parse_data.accumulated_data)))
            parse_data.accumulated_data = array.array('c')
        else:
            parse_data.accumulated_data.append(x[offset:offset+1])

class MyDelegate(btle.DefaultDelegate):
    def __init__(self):
        btle.DefaultDelegate.__init__(self)

    def handleNotification(self, cHandle, data):
         parse_data(data)


parse_data.accumulated_data = array.array('c')
 # Put your multimeter mac here
p = btle.Peripheral("88:6B:XX:XX:XX:XX", btle.ADDR_TYPE_PUBLIC)
p.setDelegate( MyDelegate() )

print('Ready!')
p.writeCharacteristic(0x9, "\x03\x00")

while True:
    if p.waitForNotifications(1.0):
        continue

    print("Waiting...")

with this script it is easy to reproduce data corruption over BLE, length is changing and bits are flipping.
For example:
Code: [Select]
31373038303030303030313031343041451b34303130304537303130383038343030303030300a
3137303830303030303031300c343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453607303834303030303030303030303030303030300a
31373038303030303030313031343041450d74373031303830383430303030303030303030300a
3137303830303030303031303134304145360a
31370638303030303030313031343041453634303130304537303130383038343030303030300a <-- here is a "06" at pos 5,6 where I expected "30"
31373038303030303030313031343041453634303130304537303106383038343030303030300a
31373038303030303030313031343041453634303130534537303130383038343030303030300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
3137303830303030303031303134304145360c304537303130383038343030303030303030300a
3137303830303030303031303134304145360630303030303030303030303032440d0a
313730383030303030303130313430414536343031300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453634300330304537303130383038343030303030300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453681303030303030303030303030303030303030300a
313730383030303030303130313430414536303032440d0a
3137303830303030303031303134304145363430313030453730313038303834300a
31373038303030303030313031343041453634303130304537303130383038343030303030300a
31373038303030303030313031343041453634303130304537303130383038341830303030300a
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on January 14, 2018, 05:53:25 pm
The data is corrupted as bellow in the middle of the data.
59625,DCV,049.997,V,,,,,,,,
59626,DCV,049.997,V,,,,,,,,
59627,DCV,049.996,V,,,,,,,,
59628,DCV,049.997,V,,,,,,,,
59629,DCV,                                                                                                                                                                                        59641,DCV,050.001,V,,,,,,,,
59642,DCV,049.996,V,,,,,,,,
59643,DCV,049.996,V,,,,,,,,
59644,DCV,049.998,V,,,,,,,,
59645,DCV,049.996,V,,,,,,,,

The garbled line only happened in one line out of four files of data logging.

It looks to me as if samples 59629 through 59640 are missing from the file? So it's not just a garbled line, it's some dropped data.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: fanOfeeDIY on January 15, 2018, 03:07:35 am
The data is corrupted as bellow in the middle of the data.
59625,DCV,049.997,V,,,,,,,,
59626,DCV,049.997,V,,,,,,,,
59627,DCV,049.996,V,,,,,,,,
59628,DCV,049.997,V,,,,,,,,
59629,DCV,                                                                                                                                                                                        59641,DCV,050.001,V,,,,,,,,
59642,DCV,049.996,V,,,,,,,,
59643,DCV,049.996,V,,,,,,,,
59644,DCV,049.998,V,,,,,,,,
59645,DCV,049.996,V,,,,,,,,

The garbled line only happened in one line out of four files of data logging.

It looks to me as if samples 59629 through 59640 are missing from the file? So it's not just a garbled line, it's some dropped data.

Good comment, I should have attached the raw data of the log file from the beginning why I thought it was a garbled line.

I just opened the file with binary editor.
Attached is the screen shot when opening the log file with binary editor.
0x00 is not in ASCII code.

This is my pure guess based on my software engineering experience. The firmware is trying to write the data to SD card however it could be it has memory writing over flow, memory leak or improper locking between other threads.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=386620)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: iainwhite on January 15, 2018, 04:07:31 pm
My issues:

1. The manual is not very clear on the type of Setup button press that is needed e.g. long press to save a value after editing it.
2. The constant beeping is driving me mad. Please can we have an option to turn off the beeper.

I realize that both these issues have already been reported.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 16, 2018, 06:03:06 am
Seems like YOU are the one polluting it.  Have anything technical to add?

I'll be very clear again.
This thread is for REPORTS of bugs and issues and CONFIRMATIONS of those bugs and issues.
DO NOT discuss them here, PLEASE!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 16, 2018, 06:36:11 am
Addition to Dec 11th Manual:

Firmware Version 1.01 has an extra setup field "00000" not mentioned in the manual. It is between the hour-minute setting and logging interval setting.

I gather it is a programmable Serial number or ID number used in Bluetooth communication to identify a meter.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on January 16, 2018, 09:11:46 am
Seems like YOU are the one polluting it.  Have anything technical to add?

I'll be very clear again.
This thread is for REPORTS of bugs and issues and CONFIRMATIONS of those bugs and issues.
DO NOT discuss them here, PLEASE!


I did not realize you were censoring posts in this area.   I resubmitted the post you removed twice because I literally thought I had forgotten to press the send key, not because I was trying to be a dick about it.     
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lewis on January 16, 2018, 01:24:12 pm
...CONFIRMATIONS of those bugs and issues.

I can confirm the meter beeps and beeps and beeps and beeps and beeps and beeps and BEEEEEEEPPPPS which makes it basically unusable, because I BEEP, I mean keep, wanting to throw it at great BEEP, I mean speed, across the workBEEP, I mean workshop. I've taken back off and covered the sounder in many layers of tape but it's still annoying as hell.

I can also confirm It also takes about 9 seconds to measure a low resistance. The fuse rating printed on the back label does not match the fuse inside (440mA 1kV vs 400mA 600V). Update rate on the bluetooth app is abysmal, and the connection keeps dropping out. I don't know if the measurement displayed on the smartphone is what the meter is actually measuring, or if the connection has died.

If I remember correctly, there is also a large-ish offset under an open-probe condition on AC and DC voltage ranges (will edit this post later when I have the meter in my hand to confirm). Nope! mV range was showing on display, but selector switch was set to V! Had a -0.5mV DC offset, thought it was -0.5V. I think I had a dicky selector switch, very difficult to reproduce now the switch has had some (ab)use.

Dave, I can't see how you would have approved the prototype and thought it acceptable.

Beep <shudder>
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 16, 2018, 04:10:27 pm
Firmware Version 1.01 has an extra setup field "00000" not mentioned in the manual. It is between the hour-minute setting and logging interval setting.

I thought it's a logging interval or screen refresh interval in ms... Or a sample number... Uhm...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: MatthewEveritt on January 16, 2018, 04:59:15 pm
It's apparently a sort of 'serial number' that gets added to the bluetooth data to help distinguish multiple meters [source] (https://www.eevblog.com/forum/testgear/121gw-bluetooth-protocol/msg1401360/#msg1401360).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 17, 2018, 04:14:05 pm
While I consider the autoranging speed not particularly good, it is at least correct and works.

The fails in the adnvanced functions, that distinguish this meter from the rest of the market are much more annoying. They are not just "slow", they are plain unreliable and broken.

After fanOfeeDIY showed the broken logfile I decided to do a test to the maximum extend the meter logs.

I don't get why there is a limitation on 600k lines, but well, maybe Dave will explain some day or it's extended.
The 600k lines don't even last 48h.
I know I could reduce the log interval, but why?

I got the corrupt logfile in my first try.

The data is corrupted as bellow in the middle of the data.
59625,DCV,049.997,V,,,,,,,,
59626,DCV,049.997,V,,,,,,,,
59627,DCV,049.996,V,,,,,,,,
59628,DCV,049.997,V,,,,,,,,
59629,DCV,                                                                                                                                                                                        59641,DCV,050.001,V,,,,,,,,
59642,DCV,049.996,V,,,,,,,,
59643,DCV,049.996,V,,,,,,,,
59644,DCV,049.998,V,,,,,,,,
59645,DCV,049.996,V,,,,,,,,

The garbled line only happened in one line out of four files of data logging.

It looks to me as if samples 59629 through 59640 are missing from the file? So it's not just a garbled line, it's some dropped data.

Good comment, I should have attached the raw data of the log file from the beginning why I thought it was a garbled line.

I just opened the file with binary editor.

I can confirm the file corruption. I let the meter log for almost 2 days in VA mode and have several corrupted lines in the log.

I ran a small awk script on the file to find lines where the line counter didn't match the actual line number of the log lines.

Code: [Select]
awk -F, '/^[0-9]+,/{if ( c != $1 ) { printf("%6d %6d %s\n", l, c, $0); c = $1 } c++; l++; }BEGIN{l=1;c=1}' < 18011500.CSV
It prints the real line number, the line number it expected and the line from the logfile. The result is this:
Code: [Select]
61501  61501 61502,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
139554 139555 139562,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
243949 243957 243962,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
267167 267180 267182,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
344797 344812 344822,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
356188 356213 356222,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
412106 412140 412142,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
431304 431340 431342,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
478699 478737 478742,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
523695 523738 523742,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,

So there are 10 errors in just one logfile.

Here are the errors:
Code: [Select]
61499,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
61500,DCVA,01959.5,mVA,DC^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@61501,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
61502,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
139553,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
139554,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,044^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@139561,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
139562,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
243956,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
24395^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@243961,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
243962,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
267178,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
267179,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@267181,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
267182,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
344810,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
344811,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@344821,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
344822,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
356212,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
35621^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@356221,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
356222,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
412138,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
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412142,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
431338,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
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431342,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
478735,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
478736,DCVA,01959.5,mVA,DCV,0^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@478741,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
478742,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
Code: [Select]
523736,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,
523737,DCVA,01959.5,mVA,DCV,04.4482,V^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@523741,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,
523742,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.52,mA,,

The last logline in the file is:
Code: [Select]
600000,DCVA,01959.5,mVA,DCV,04.4482,V,DCA,0440.53,mA,,

So logging stops after the meter thinks it logged 600k lines, but in reality it logged only 599956 lines.

Interestingly the display counted to more than 600.00k lines. The highest value I saw on the display was 602.xxk lines (I don't remeber the xx).

So on the display it either kept counting after it stopped logging or didn't number and write all lines it actually thought it logged.

In the end there was "SDend" displayed and the "MEM" LCD-segment was not active anymore.

I can't attach the logfile since the forum says it's too big (even zipped it is 1.7MB). But I can send it to anybody who is interested.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on January 18, 2018, 03:14:37 am
Bug/mechanical issue in the Diode test mode. When selected if you jiggle the plugs at the meter you get the short double beep and sometimes a continuous beep which requires further lead or switch jiggles to stop. So the switch seems to be very sensitive mechanically to trigger the continuous beep. Also via some PCB flexing (i guess), due to the test lead plugs will also trigger the beep.

Others can test to confirm.
As Dr diesel noted the temperature display is on until the range button is pressed for either 3 or 15v test.

Also to note that continuity function sometimes does not work either(similar switch issue?).
Ohms appears unaffected by any mechanical jiggling.

firmware 1.01
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 18, 2018, 04:22:00 am
Bug/mechanical issue in the Diode test mode. When selected if you jiggle the plugs at the meter you get the short double beep and sometimes a continuous beep which requires further lead or switch jiggles to stop. So the switch seems to be very sensitive mechanically to trigger the continuous beep. Also via some PCB flexing (i guess), due to the test lead plugs will also trigger the beep.

firmware 1.01
I do not get the jiggling issue, but for some reason, when the diode mode senses any change (like a 10K resistor or anything else), it double beeps and then a second later double beeps again. Not sure why that is wanted. If the probes are shorted, it beeps continuously just like the continuity test mode.

Also in diode mode, the bar graph seems to be not normalised for the measurement. In the default 3V diode mode, the bar graph is at 60% on open circuit. For the 15V mode, it is at 33% on open circuit. These correspond to the positions the bar graphs would be in the 5V and 50V DC ranges respectively. A minor issue, but it probably should be tidied up.

Edit: Looking closely at the bar graph and it goes from 0 to 5. So it is on 3 for the 3V range and 1.6V (16V) on the 15V diode range. I guess that makes sense.

firmware 1.01 Diode Mode
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on January 18, 2018, 04:43:12 am
By jiggling I mean moving the lead plugs intentionally forward and back "a bit" in their sockets causes the continuous beep to engage with out shorting the probes together. And further to this once the continuous beep has started I can remove the probes from the meter and it carries on beeping until I "wiggle" the selector switch a little bit then it will stop followed with the 2 short beeps.
Unfortunately I cannot do a video which would make it very clear whats going on.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Kean on January 18, 2018, 04:47:30 am
I tried to reproduce this "wiggling" problem in diode mode, but I can't.  Sounds like you have an intermittent internal short.  Strange if you cannot also reproduce in continuity mode.
edit: FW 1.01
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 18, 2018, 04:59:12 am
By jiggling I mean moving the lead plugs intentionally forward and back "a bit" in their sockets causes the continuous beep to engage with out shorting the probes together. And further to this once the continuous beep has started I can remove the probes from the meter and it carries on beeping until I "wiggle" the selector switch a little bit then it will stop followed with the 2 short beeps.
Unfortunately I cannot do a video which would make it very clear whats going on.
Sounds like you have an intermittent supply of 3V and 15V to the sockets. Could be a poor contact on the switch or a broken trace on the board. Can you connect a voltmeter to the probes and see if the voltage drops when you wiggle?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on January 18, 2018, 05:54:57 am
Okay checking the output with a voltmeter still gives 3 or 15V when continuous beep is going, also when this condition has started the display also goes to all '0' from OFL so no short at the input terminals it would seem.

Just tried a short drop of a few inches height to my desk (no probes) and that can also trigger the continuous beep. This is with no holster BTW.

When the Diode function is not doing the odd behaviour it does measure a diode correctly.

edit: The drop test is not as repeatable as the movement of the probes in the input jacks. I still get the feeling its related to the switch. 
 I will crack it open and take a look tomorrow  to see what movement on the PCB can be induced from the probe jacks.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 18, 2018, 06:12:48 am
Okay checking the output with a voltmeter still gives 3 or 15V when continuous beep is going, also when this condition has started the display also goes to all '0' from OFL so no short at the input terminals it would seem.
So it looks like the intermittent connection is somewhere between the measurement IC and the point at which the 3/15v is connected. I still think a switch connection is the most likely cause. You probably should contact Dave directly, unless you want to just Take-It-Apart yourself and have a look.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: maukka on January 18, 2018, 07:32:48 am
This was already reported by mattselectronics (https://www.eevblog.com/forum/testgear/new-eevblog-branded-multimeter-coming/msg1400505/#msg1400505) in the other thread, but the VA mode reports voltage wrong. On 5V range it is too high, on 50V range is much better but a bit too low. Gets worse with higher voltages. Tested with a resistor and a Rigol DP811A with remote sense active. No problems when only measuring voltage, only max 1 digit off. Current is spot on.

(https://i.imgur.com/tmm43n5.png)

(https://i.imgur.com/4QiTdJD.jpg)

(https://i.imgur.com/cLBp6NJ.jpg)

EDIT: Did the same test with a Mooshimeter (https://moosh.im/mooshimeter/) which also has VA (and real power) measurement and it is even more off

Actual measured with a 34401A from DMM terminals: 1.0008V
112GW 1.0133V
Mooshimeter 1.02022V

The Mooshimeter shows 2.0% more than it should, but it is consistent regardless of voltage while on the 112GW error gets larger with increasing voltage.


Title: Re: EEVblog 121GW Multimeter Issues
Post by: maukka on January 18, 2018, 01:51:46 pm
How much burden voltage do you guys have on the 10A range? Mine is 0.035V/A measured externally while the manual says 0.02V/A. The 112GW itself reports 28.7mV/A.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 18, 2018, 11:08:15 pm
How much burden voltage do you guys have on the 10A range? Mine is 0.035V/A measured externally while the manual says 0.02V/A. The 112GW itself reports 28.7mV/A.

Latest edition of the manual has this revised to 0.03V/A, will upload this when I get back tomorrow.
The previous one didn't include the fuse resistance.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: cpposteve on January 18, 2018, 11:25:18 pm
Hello mr Jones..!!
Just curious as to when people will get their answers to these on going faults? I’m in the second batch of meters not yet shipped and wondering if all these faults will or most likely be able to be fixed in software?
Hope you had a great holiday.

Steve
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on January 19, 2018, 01:58:51 am
 I created a Youtube acc. and uploaded a very short video clip of the Diode test mode continuous beep after giving the probe plugs a wiggle in the meter sockets.
I then removed the probes from the meter to show no external short circuits being the cause and then how a light press on the range switch will stop the tone.

https://youtu.be/rABVuzqzLXQ (https://youtu.be/rABVuzqzLXQ)

I hope this clarifies my earlier posts.

(I will open the meter to investigate this after a weeks holiday)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 19, 2018, 02:33:54 am
I created a Youtube acc. and uploaded a very short video clip of the Diode test mode continuous beep after giving the probe plugs a wiggle in the meter sockets.
I then removed the probes from the meter to show no external short circuits being the cause and then how a light press on the range switch will stop the tone.
(I will open the meter to investigate this after a weeks holiday)

I can confirm this. I also experienced the switch to be unreliable some times.

I fixed it by mounting two small sheets of 0.25mm telson below the snap ring of the switch.

I'll attach a photo.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on January 19, 2018, 04:24:07 am
I created a Youtube acc. and uploaded a very short video clip of the Diode test mode continuous beep after giving the probe plugs a wiggle in the meter sockets.
I then removed the probes from the meter to show no external short circuits being the cause and then how a light press on the range switch will stop the tone.
(I will open the meter to investigate this after a weeks holiday)

I can confirm this. I also experienced the switch to be unreliable some times.

I fixed it by mounting two small sheets of 0.25mm telson below the snap ring of the switch.

I'll attach a photo.

Hmmm, looks like it requires some form of spring/wave washer type tension device included. Case may not be rigid enough to provide consistent tension for the contacts without a simple spring tension device being fitted!

Wave washer info here http://www.globalspec.com/learnmore/mechanical_components/springs/wave_washers (http://www.globalspec.com/learnmore/mechanical_components/springs/wave_washers)

That's not a good indicator for the construction robustness of the meter and hopefully a simple mechanical fix will be found. Well documented and fixed Iagash, we all benefit from your faulty switch investigation.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 19, 2018, 08:53:46 am
I can confirm this. I also experienced the switch to be unreliable some times.
I fixed it by mounting two small sheets of 0.25mm telson below the snap ring of the switch.
I'll attach a photo.

I do not understand this.
That fix is on the case of the meter, not on the carrier that holds the switch contacts which is a different assembly mounted and clipped to the PCB that has it's own tension with the plastic insert clip.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 19, 2018, 08:54:23 am
Hello mr Jones..!!
Just curious as to when people will get their answers to these on going faults?

When I know, you'll know.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 19, 2018, 01:44:44 pm
I can confirm this. I also experienced the switch to be unreliable some times.
I fixed it by mounting two small sheets of 0.25mm telson below the snap ring of the switch.
I'll attach a photo.

I do not understand this.
That fix is on the case of the meter, not on the carrier that holds the switch contacts which is a different assembly mounted and clipped to the PCB that has it's own tension with the plastic insert clip.

Yes, but the effect is the same. The range switch is pressed a little more to the pcb by the clip ring. With this washer the plastic insert clip is relieved. It seemed easier that way as you can see in the video poking the range switch makes the meter switch the mode. When poking the range switch from the top, you also apply pressure via the clip ring to the switch and move it a bit more to the pcb.

Edit:
Since there are only very little reports here about the switch, it might be a tolerance issue which only affects a minority of meters.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 19, 2018, 04:41:11 pm
I think the switch problem may be due to two things:

The wobble in the knob is wobbling the switch on the PCB from side to side. Probably not good if you want to maintain the tension in the spring contacts in the switch.

The looseness of the clip spring combined with the tapers of both the knob and the case knob recess all combine to allow for this wobble. If the knob was moulded with a reverse taper so it is wider at the top then the bottom, it could have a far more snug fit and would be less affected by any clip ring looseness.

As an experiment, I added a spacer between the knob and the nylon detent spring to raise the knob so that the clip ring groove was just above the inner case plastic, but the clip ring was not tight against the plastic. This is different from the approach Iagash took. I also added a couple of layers of Kapton tape around the outside of the knob to stop the wobble a little. It now seems that pressing on the knob never depresses the switch, and the wobble is much less. I think the switch has a better feel now.

Basically what I am saying is if the knob moulding was tweaked a bit, the switch could possible be more reliable and feel much more solid. It is just out here and there by fractions of a millimetre and that is all it takes.

Don't know what the best advice is for people with contact issues. I would probably want to inspect the contacts to see if any had been deformed a little. You should not need to have the clip ring pushing the switch down by perhaps 0.1mm. That does not feel like a real solution.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on January 19, 2018, 10:02:31 pm
I should emphasize that the diode tone issue I have starts from the probe movement
In their sockets and not from switch movement. But once started both probe and gentle
pressure on the switch will stop it, as shown in the short video.
BTW it was too hard to video and show wiggled that probes (mobile phone in one hand).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 19, 2018, 11:11:33 pm
Basically what I am saying is if the knob moulding was tweaked a bit, the switch could possible be more reliable and feel much more solid. It is just out here and there by fractions of a millimetre and that is all it takes.

Switch wobble confirmed on the two remaining meters we have here.
We (as in David2 + me) also suspect it's some slight difference in production tooling process, although the pre-production was obviously supposed to be the same.
The pre-production units were fine.

REMINDER, please keep discussions in the discussion thread:
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/ (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 3db on January 20, 2018, 09:58:39 am
IIRC the point of not open-sourcing it is that messing with the firmware could affect the safety of the meter so there's no way they can officially sanction that or help people to do it.

Dave maybe can sell a version with open source firmware as DMM development kit? As a dev kit, you can basically bypass any certification requirements.

There is absolutely nothing stopping anyone writing their own firmware and making it open source.

Does that include YOU Dave ?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 20, 2018, 10:16:31 am
There is absolutely nothing stopping anyone writing their own firmware and making it open source.
Does that include YOU Dave ?

No, the ridiculous amount of time spent on the open source app taught us not to touch the firmware.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on January 20, 2018, 10:46:14 am
Confirmed issues (or annoyances) from what I've (re)-tested so far.

1. Slow auto-ranging: Ohms, Voltage, Capacitance
2. double double double beeps constantly going on when in diode mode
3. measuring any resistance (short or higher value) in diode mode gives a constant and loud beep
4. Wobbly selector/range switch: back an forth (vertical) when in diode mode it will even blink the back-light or completely switch off.
5. Strange to me is that when in diode mode a small green LED has a Vf of 1.79 in the 3V mode and a Vf of 1.98 in the 15V mode. And also is a bit brighter then.

Hope this helps,

6. on the lower current fuse is rated 600V and 400mA from ASTM. Which is different from the manual: 440mA and 1000V. I believe this was somewhere posted already?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 20, 2018, 11:18:44 am
3. measuring any resistance (short or higher value) in diode mode gives a constant and loud beep

That feature was requested by people.

Quote
5. Strange to me is that when in diode mode a small green LED has a Vf of 1.79 in the 3V mode and a Vf of 1.98 in the 15V mode. And also is a bit brighter then.

Expected, as they result in different test currents.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 20, 2018, 11:25:23 am
Manual Correction Dec 11:

The manual specifications is a bit vague on diode test currents. It mentions 1.4mA and 7mA short circuit but they don't really line up with the 3V range and 15V ranges.

It seems the actual currents are different on my meter (v1.01):

3V    0.7mA short circuit
15V  4.6mA

Page 44 mentions the Diode Test current is limited by a resistor + PTC totalling about 2.2K. Has this changed?

ChrisG: Your point 5 is not an issue - the two diode tests are at two different currents. The voltages are meant to be different.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Fungus on January 20, 2018, 01:38:01 pm
The manual specifications is a bit vague on diode test currents. It mentions 1.4mA and 7mA short circuit but they don't really line up with the 3V range and 15V ranges.

It seems the actual currents are different on my meter (v1.01):

3V    0.7mA short circuit
15V  4.6mA

Short circuit current is a maximum. It will be less when there's no short circuit.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 20, 2018, 03:12:29 pm
The manual specifications is a bit vague on diode test currents. It mentions 1.4mA and 7mA short circuit but they don't really line up with the 3V range and 15V ranges.

It seems the actual currents are different on my meter (v1.01):

3V    0.7mA short circuit
15V  4.6mA

Short circuit current is a maximum. It will be less when there's no short circuit.

Huh?  I am just mentioning a case where the specifications for short circuit current and the actual meter are different. Also the formatting of the specifications does not have values lining up correctly. It may be the resistor in the final meter are different from the prototype meter. That is all. Dave has mentioned that he wants to soon release an updated version of the manual. It is part of the product.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mikeselectricstuff on January 20, 2018, 03:34:04 pm
I wouldn't expect a low to mid-DMM diode check function to have particularly constant current.
Some quick checks on my meters over the reading range :
Fluke 87 (i and III) 0.8 to 0.15mA
Fluke 287 1mA up to 2V, then down to 0.8mA at 3v
Agilent 36641A 1mA constant
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 20, 2018, 04:25:48 pm
No one is suggesting constant current. I have done a report on short circuit currents of my meter because they are different from the spec. It would be useful if you can confirm my numbers, or if your 121GW meter matches the spec.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: hwti on January 21, 2018, 12:16:06 am
No one is suggesting constant current. I have done a report on short circuit currents of my meter because they are different from the spec. It would be useful if you can confirm my numbers, or if your 121GW meter matches the spec. O miss
0.7mA on 3V range
4.25mA on 15V range
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on January 21, 2018, 01:39:50 pm
No one is suggesting constant current. I have done a report on short circuit currents of my meter because they are different from the spec. It would be useful if you can confirm my numbers, or if your 121GW meter matches the spec. O miss
0.7mA on 3V range
4.25mA on 15V range
0.71 mA on 3V range
4.61 mA on 15V range

Measured through a BM869s.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 22, 2018, 03:48:27 am
UPDATE:
UEi are aware of the various issues and are working on them.
The autoranging as you might expect is not necessarily trivial and will take a few more days to test this.
For the range switch they are waiting on a slightly modified part to see if that can solve it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on January 22, 2018, 04:14:45 am
If UEi are fixing the Autoranging, it might be a good opportunity to fix the non-working DC mVA/VA autoranging with negative currents.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: borealis on January 22, 2018, 02:50:08 pm
Hi Dave

On my meter pins PE13 (SPI1_SCK/FSMC_D10) and PE14 (SPI_MISO/FSMC_D11) of the STM32L1 are shorted together (continuity tested). The attached file has the best focused image I could get of this. Should I do anything about it?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zaoka on January 23, 2018, 09:57:44 pm
Metal parts in range switch will make it more enjoyable to use...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 23, 2018, 10:39:06 pm
On my meter pins PE13 (SPI1_SCK/FSMC_D10) and PE14 (SPI_MISO/FSMC_D11) of the STM32L1 are shorted together (continuity tested). The attached file has the best focused image I could get of this. Should I do anything about it?

That's VSSA and VREF-, they should be connected.
Looks like they used a direct track in-between pins which trapped the solder.
Nothing to worry about.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: benst on January 23, 2018, 11:51:59 pm
The switch on my meter (#000499) is also wobbly and has the problem described here.

I took it apart, and contacts and pcb looked ok. After I put it back together it worked allright for a while, but now it's back and I have to fiddle with the switch again to get it to display correct readings. :-BROKE

Dave, once UEi figures out a fix, will you send out a replacement part?

Thanks,
Ben
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 24, 2018, 12:06:08 am
The switch on my meter (#000499) is also wobbly and has the problem described here.
I took it apart, and contacts and pcb looked ok. After I put it back together it worked allright for a while, but now it's back and I have to fiddle with the switch again to get it to display correct readings. :-BROKE
Dave, once UEi figures out a fix, will you send out a replacement part?

Yes we'll have to do that for those existing shipments who have problems.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on January 24, 2018, 12:38:35 am
Minor Issue:

I just opened my 2nd set of leads, note the positive lead, recessed threaded portion, and it's broken internally.  Slightly flexing the break in the 2nd photo to accentuate the area.

It's electrically connected however.  (Replacements not necessary, I got a zillion of them)

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on January 24, 2018, 12:59:14 am
Minor Issue:

I just opened my 2nd set of leads, note the positive lead, recessed threaded portion, and it's broken internally.  Slightly flexing the break in the 2nd photo to accentuate the area.

It's electrically connected however.  (Replacements not necessary, I got a zillion of them)

It happens in large numbers. My BM235 with the same probes has done that the inside spins on when I screw on the banana jacks. So I’ve just been carful to not torque that one since I fear the wire might eventually twist to much and break off. I even had one probe new with the fluke 289 that was bent, they did replace that one since they reached out to me. I guess they saw it on the unboxing video.
I never bothered to mention it since I have the probematers and a few fluke probes. Like you, I have enough of them, but sometimes I have to run three meters and I usually use the probes they came with.

That brings up a good question, I know Brymen is responsive to fixing and communicating with customers to fix issues. So if the probes have an issue, who do we contact since Brymen makes the probes but UEI made the meter? Do we contact UEI, Brymen, or EEVBlog (Dave)?

Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on January 24, 2018, 01:04:30 am
inside spins

This one is tight, perhaps just in the wrong position when molded.

I suspect the wire lead is terminated at the break in my case above, which means it probably wouldn't last long in the field.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Kean on January 24, 2018, 03:38:52 pm
Just confirming an issue reported by Joe Smith on the prototype unit he tested still exists on my production unit.
As posted in the discussion thread at https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1408767/#msg1408767 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1408767/#msg1408767)
And confirmed by maukka in a followup post https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1408768/#msg1408768 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1408768/#msg1408768)

I wonder if someone could check the meter in the LowZ mode.   In the early unit, if I applied a 1VRMS 60Hz signal, the meter would read zero as expected.   However, when I would increase the frequency to 389KHz, the meter was displaying 181.3 volts even though there was still only a volt being supplied.   There was something strange going on with it that I never looked into.  I reported the problem when I discovered it but with as many problems that the meter still has, I wonder if this was addressed in the released version.

Joe, I can confirm this issue is still present in FW1.01.
I generated a 2.8Vpp 60Hz (& 1kHz) sine wave with my MSO1104Z-S and it read 0V in LowZ mode.
When I upped the freq to 389kHZ and I got a reading of 189.2Vac.  See photo...

Edit: and it correctly read ~1V AC without LowZ up to maybe 100kHz, but that dropped to 0.773V AC at 389kHz
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on January 24, 2018, 05:04:21 pm
Confirmed... Though it does too vary a bit when changing frequencies.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on January 24, 2018, 10:19:27 pm
Does this LowZ issue happen in the ACV's highest (600V) range? The two are calculated virtually identically in the software. If there's an issue with the routines or calibration data for that ACV mode, they should be broken in the same way. Of course, I'm not saying that them not behaving the same means it has to be fixed in hardware.

Edit: the calibration tables are also only specified up to 10KHz. Perhaps the 10KHz correction factor becomes invalid at such a high frequency? Can anyone dump their calibration data (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1406163/#msg1406163) (requires firmware 1.02) for me?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on January 24, 2018, 11:32:19 pm
Edit: the calibration tables are also only specified up to 10KHz. Perhaps the 10KHz correction factor becomes invalid at such a high frequency? Can anyone dump their calibration data (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1406163/#msg1406163) (requires firmware 1.02) for me?

Here you go, I attach it zipped.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on January 25, 2018, 04:16:14 am
So I toyed around in Python and got some interesting results. There is a routine which takes the measured input frequency and value, then calculates an offset based on these two factors. It is possible for a large negative calibration value to produce the behavior, but the required value seems kind of crazy (though the firmware would accept it as valid). See here (https://i.imgur.com/s7s7Pw8.png) for a graph of that result.

Some other notes:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on January 25, 2018, 08:26:44 am
I re-tested in my early morning and in the LowZ position I could not change the range and it indicated 1000v in the lower right hand corner. So assume yes this is the highest 600V then too. Upping the Vpp to 5.0v at 389Khz the result was a staggering 367v on the display.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Kean on January 25, 2018, 02:35:01 pm
@ChrisG What tpw_rules was suggesting I believe was to input the 1Vrms 100+kHz input into the VAC mode (instead of LowZ), and then manually select 1000V range.  And thus see if the same wrong readings were displayed as in LowZ.

Well I just did that, and got some interesting - but not consistent - results.

With 2.8Vpp (~1Vrms) sine at 300kHz:
LowZ AV 1000V range read 161V - consistent
VAC auto range (5V)  read 1.63V 299.9kHz - once only, see below - otherwise ~1V 299.9kHz
VAC 5V range read 1.63V 299.9kHz - once only, see below - otherwise ~1V 299.9kHz
VAC 50V range read 12.6V 299.8kHz - once only, see below - otherwise 0V 0Hz
VAC 500V range read 149.2V 299.8kHz - once only, see below - otherwise 0V 0Hz
VAC 1000V range read 149.3V 299.8kHz - once only, see below - otherwise 0V 0Hz

I actually tried going through these VAC ranges (and back and forth to LowZ) several times.  The first time gave the 0V 0Hz on the AC 50V ranges and above (can't recall the 5V range reading).  The second time the above high readings.  And all subsequent times back to the 1V or 0V.

Then tried 1kHz and 10kHz inputs, and got slightly low readings in the higher ranges (1V in 5V range dropping down to 0.6-0.7V in 1000V range), but also interesting was that it couldn't display the frequency any more in the 50V and higher ranges.  It then just showed 0Hz.  The meter is specified to 5kHz in the VAC mode, but I guess in those manual ranges the attenuation is too high for the frequency measurement.  But how does it "work" then in LowZ mode (i.e. measures correct frequency, but incorrect voltage) if also using the 1000V range attenuation?

I tried several things including increasing my output to 5Vpp and I couldn't get those strange readings again.  The fact it happened once does point to tpw_rules theory about the whacky adjustment for frequency being potentially correct.  Or I could have been hit with the rotary switch wobble issue that one time.  Or maybe there is a specific sequence needed to reproduce...   |O

While doing this I noticed another strange reading on AC mV manual ranges too.  Same 2.8Vpp 300kHz sine wave.  On 50mV range it read 23.0mV, and on 500mV range OFL.   :-//  At 10kHz both showed OFL.  Limited bandwidth coming to play here I guess - way beyond the 5kHz spec, and not as worrying as the weird LowZ readings.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on January 25, 2018, 06:31:35 pm
If the switch is wobbly, but the measurements are not affected by moving it, is this still a defect?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on January 25, 2018, 06:37:55 pm
If the switch is wobbly, but the measurements are not affected by moving it, is this still a defect?

I'd argue the wobbly switch has a questionable longevity. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on January 25, 2018, 09:37:48 pm
I'd argue the wobbly switch has a questionable longevity.

Possibly, but it could be by design. There should be some slack between the switch knob on the case and the switch mechanism on the PCB, so that rotating the switch does not put excessive stress on the PCB.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on January 25, 2018, 09:54:11 pm
@ChrisG What tpw_rules was suggesting I believe was to input the 1Vrms 100+kHz input into the VAC mode (instead of LowZ), and then manually select 1000V range.  And thus see if the same wrong readings were displayed as in LowZ.

...

I tried several things including increasing my output to 5Vpp and I couldn't get those strange readings again.  The fact it happened once does point to tpw_rules theory about the whacky adjustment for frequency being potentially correct.  Or I could have been hit with the rotary switch wobble issue that one time.  Or maybe there is a specific sequence needed to reproduce...   |O

You are correct about what I intended. I've been calling it the 600V range because that's what it's referred to in the calibration chart.

As for the behavior, ...huh. I'm not sure what to make of that, if it proves or disproves my theory. I've made another patch which removes the software frequency compensation entirely. If you can't replicate the behavior in any mode, that compensation must be the problem. If this is what happens, can you dump your calibration (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1406163/#msg1406163) data using the patched firmware and upload it for me? I don't know much about the meter circuit, so someone else will have to take over if that doesn't fix it. It may end up being fixable in software though.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on January 27, 2018, 04:57:04 pm
With the patched no frequency compensation 1.02 version I have identical behavior as with the 1.02 (autorange patched) version and as described by Kean.

And for the frequency thing:
At about 15Vpp/1kHz I can switch between 5V and 50V range without OFL in 5V range. Then I get correct Hz reading on both ranges. Going to 500V and 1000V range voltage reading stays ok but Hz again is 0.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on January 27, 2018, 06:14:29 pm
you patched the firmware or which patch did you apply? If you're still in version 1.02 of the firmware what would be different then?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on January 27, 2018, 08:01:37 pm
I tested the tpw_rules 1.02 with removed frequency compensation (see one post above my last one).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on January 28, 2018, 12:13:00 pm
you patched the firmware or which patch did you apply? If you're still in version 1.02 of the firmware what would be different then?

Apologies, I now see the download firmware link..  :-//
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 31, 2018, 01:28:53 am
With 2.8Vpp (~1Vrms) sine at 300kHz:
LowZ AV 1000V range read 161V - consistent
VAC auto range (5V)  read 1.63V 299.9kHz - once only, see below - otherwise ~1V 299.9kHz
VAC 5V range read 1.63V 299.9kHz - once only, see below - otherwise ~1V 299.9kHz
VAC 50V range read 12.6V 299.8kHz - once only, see below - otherwise 0V 0Hz
VAC 500V range read 149.2V 299.8kHz - once only, see below - otherwise 0V 0Hz
VAC 1000V range read 149.3V 299.8kHz - once only, see below - otherwise 0V 0Hz


I don't understand why you are testing at 300KHz? That's way outside the frequency spec.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on January 31, 2018, 02:30:22 am
The Low-Z reading problem at high frequencies is confirmed and has been reported.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on February 01, 2018, 02:10:39 pm
all, has it been pointed out here on this list the duty cycle:


Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on February 02, 2018, 04:50:51 am
121GW Manual revision 24 Jan 2018 (minor issue):
http://www.eevblog.com/files/EEVblog-121GW-Manual.pdf (http://www.eevblog.com/files/EEVblog-121GW-Manual.pdf)

On page 57, the description of the Setup Option Multimeter ID has been added, but it was not added to the list on page 53.
The correct order should be:
Quote
1. Temperature
2. Battery Voltage
3. Auto Power Off (APo)
4. LCD Contrast
5. Year
6. Month-Day
7. Hour-Minute
8. Multimeter ID
9. Logging Interval (ln 1)
10. Additional settings dependent upon the function selected.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on February 08, 2018, 08:20:43 am
I made some measurements with my FeelTech FY6600 and RD JDS6600 function generators concerning the phantom voltage to earth. Both of them use simple SMPS and I can measure about 80Vac to earth in normal mode.

In LowZ mode I would expect only some Vac. I checked with my Brymen 235 and the 121GW. Both behave like expected but with the 121GW, when I wait some seconds suddenly it measures about 70Vac in LowZ mode but only with the FeelTech FY6600 not with the RD JDS6600?

The Brymen 235 (and a labeled UNI-T the Voltcraft VC890 from Conrad Electronic in Germany) always give me the correct(?) LowZ behavior.

Can someone confirm this and does anybody know why the 121GW behaves like this?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on February 08, 2018, 08:41:01 am
LowZ is often a PTC that draws current, depending on the current it will heat up and increase resistance. It sounds like the PTC in the 121GW heats up faster or at lower current.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: amspire on February 09, 2018, 12:32:56 pm
Capacitance in Manual Ranging not properly detecting Overflow
121GW Ver 1.01

In Auto Ranging mode, if you attach a 100uF electrolytic capacitor, the meter steps through the ranges to the correct range in less than 5 seconds, so the meter can detect the OFL state on a range fairly quickly.

However in manual ranging modes, if you step through the ranges with the same 100uF electrolytic capacitor attached, the period can be 10s of seconds to show OFL to never showing OFL in the low ranges.

It seems the oscillator measuring the capacitance has no timeout, and so it will happily wait forever for the capacitor to charge. With electrolytic leakage, it may never reach a voltage on the lowest ranges to complete a single reading. There is no sense in this in that in all ranges, there is a maximum possible time for a reading, and so there is no reason not to time out the reading and show OFL.

While you are waiting, the meter shows the last successful reading - usually zero.

For the same reason, if you short the leads in capacitance mode with manual ranging, the meter just shows the last reading forever. Usually zero.

In autoranging, a short will cause the display to blank and it will autorange to the maximum range, but it may be that it has no timeout in this maximum range either. At least the display is blank rather then zero.

The problem with this is that you cannot tell whether you are reading something that has no capacitance or something that has a lot of capacitance when in a manual range. I would expect to see OFL if the capacitance is too big for a manual range.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on February 20, 2018, 08:27:34 am
Hello all, it's been quite the time there has been a post here, 11 days. I'm just wondering if there isnow an overall issue or backlog list. HW and SW related. I assume there must be and is Dave able to share it then here?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bitwelder on March 04, 2018, 03:23:23 pm
I hope this thread would work also for issues regarding the documentation.

Regarding the manual (revision 24.1.2018), I would suggest:
- add a reference to the meter f/w version, not only the manual revision date (e.g. setup menu has a paragraph about buzzer on/off, but that option doesn't exist in fw v1.01)
- the Auto Power Off function is mentioned, but it doesn't describe after how many minutes it triggers.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on March 08, 2018, 02:23:14 am
 In diode test mode the temperature display still remains on instead of showing the currently set test voltage. Pressing the RANGE button will toggle to the test voltages,  but switch to another function then back to diode test and the test voltage is replaced with temperature again.
 Also when the beeper is disabled and you select the continuity mode the beeper symbol on the LCD is on but the beep is off. As others have noted in the discussion thread the beep mode should have multiple options for the functions that actually need the beep.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on March 08, 2018, 02:25:48 am
Minor manual correction, the 500mA text on the front cover picture is still missing next to the A text over the current input jack.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on March 14, 2018, 12:39:37 am
 When in Ohms (auto range) mode and shorting the probes the display will show some random numbers for a short time before ranging down to display the value of the shorted probes.
So 95 % of the time the random numbers come up instead of blanking the display while changing ranges. It only occurs on the top M Ohm range and will blank as soon as the auto ranging starts.
Do others see this effect on theirs with firmware version 1.07. ?.
Not a major issue, but hopefully will be corrected at some point.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: morrone on March 16, 2018, 05:09:42 pm
So 95 % of the time the random numbers come up instead of blanking the display while changing ranges. It only occurs on the top M Ohm range and will blank as soon as the auto ranging starts.
Do others see this effect on theirs with firmware version 1.07. ?.

Yes, I see the same thing with 1.07.  When the probes are applied to a resistor the screen blanks for a moment, then shows a random bad value and pauses for a second or two with no sign that it is still working to find the correct value, then it blanks again briefly before showing the correct value with relatively rapid updates to the lest significant digits.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on March 29, 2018, 04:41:51 pm
minor Manual, 07 March 2018,

Page  kind  description
7  spelling 'VERION'
29 grammar (twice), 'for the is jack'
59 grammar, 'and is can be'

Starting to look pretty good !
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on April 07, 2018, 11:33:02 am
I already posted in the discussion thread about a problem I have with Vac readings. Now I will switch to the correct place for this.

In 5Vac mode I get wrong readings.

Today I checked the ZERO OFFSET CALIBRATION and had to find out, that only in 5Vac range mode with shorted inputs I get a reading of 0,499xVac. With open input I get nearly the same value of about 0,5Vac.

In all other Vac (and Vdc) ranges I get 0,0xxV. So I tried to calibrate only the zero offset in Vac 5V range mode. During the count down it displays the 0,499xV and after the calibration I still have this offset with shorted inputs on the 5Vac range. At the end of the calibration countdown I see "OFF-E" for about half a second what is not mentioned in the manual.

I have two references from voltagestandard.com. The 121GW is spot on for all voltage measurements I can do (Vdc 0,350V up to 10.000V and Vac 5V).

So there must be something wrong with the 5Vac range mode of my 121GW.

Another thing happened today while testing for the first time. When I switched from left side off to V mode the meter did not turn on. I taped on the mode switch still in this mode and it turned on. So there must be another problem with my 121GW.

You can read my postings and realted answers if you want to get the complete story:
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1446232/#msg1446232 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1446232/#msg1446232)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447697/#msg1447697 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447697/#msg1447697)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447957/#msg1447957 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447957/#msg1447957)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1465469/#msg1465469 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1465469/#msg1465469)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469130/#msg1469130 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469130/#msg1469130)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469890/#msg1469890 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469890/#msg1469890)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on April 09, 2018, 12:53:54 am
I already posted in the discussion thread about a problem I have with Vac readings. Now I will switch to the correct place for this.

In 5Vac mode I get wrong readings.

Today I checked the ZERO OFFSET CALIBRATION and had to find out, that only in 5Vac range mode with shorted inputs I get a reading of 0,499xVac. With open input I get nearly the same value of about 0,5Vac.

In all other Vac (and Vdc) ranges I get 0,0xxV. So I tried to calibrate only the zero offset in Vac 5V range mode. During the count down it displays the 0,499xV and after the calibration I still have this offset with shorted inputs on the 5Vac range. At the end of the calibration countdown I see "OFF-E" for about half a second what is not mentioned in the manual.

I have two references from voltagestandard.com. The 121GW is spot on for all voltage measurements I can do (Vdc 0,350V up to 10.000V and Vac 5V).

So there must be something wrong with the 5Vac range mode of my 121GW.

Another thing happened today while testing for the first time. When I switched from left side off to V mode the meter did not turn on. I taped on the mode switch still in this mode and it turned on. So there must be another problem with my 121GW.

You can read my postings and realted answers if you want to get the complete story:
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1446232/#msg1446232 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1446232/#msg1446232)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447697/#msg1447697 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447697/#msg1447697)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447957/#msg1447957 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447957/#msg1447957)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1465469/#msg1465469 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1465469/#msg1465469)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469130/#msg1469130 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469130/#msg1469130)
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469890/#msg1469890 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469890/#msg1469890)

Thankyou for your message we are aware of your issue, the issue with the on-off is almost certainly due to the shim fix (this will be shipped to you at some point soon, it will resolve the issue if that is an issue). It does sound like your 5V AC range has an issue, there is a new firmware update coming out. It might improve the situation for you and if you did want to recalibrate it would be better to do it after the next update.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on April 09, 2018, 05:47:06 am
Thank you for the response. I will try to calibrate with the next firmware update. I really wonder what the problem is. In all other ac/dc ranges the zero offset is ok so it hopefully is something that can be fixed with a firmware update.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Doctorandus_P on April 14, 2018, 09:22:06 pm
Source code not available.
To me this was the biggest bug of them all and enough reason to not buy this meter.
I really would have liked to be able to add some customized measurements, without too much effort, but having to rewrite all firmware from scratch would cost me far too much time.

Maybe I'll revise my opinion when a "community" alternative version of the software for this meter becomes available.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: morrone on April 26, 2018, 03:03:58 am
Bug in firmware 1.10:  If you try to start logging to the SD card while there is no SD card in the slot, the meter locks up.  Granted, user error, but it would be nice if the meter displayed an error rather than locking up.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on April 26, 2018, 06:17:24 am
Source code not available.
To me this was the biggest bug of them all and enough reason to not buy this meter.

Name another commercial meter on the market that has open source firmware?

Quote
Maybe I'll revise my opinion when a "community" alternative version of the software for this meter becomes available.

We encourage that.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on April 27, 2018, 11:47:32 pm
I already posted in the discussion thread about a problem I have with Vac readings. Now I will switch to the correct place for this.

In 5Vac mode I get wrong readings.

Today I checked the ZERO OFFSET CALIBRATION and had to find out, that only in 5Vac range mode with shorted inputs I get a reading of 0,499xVac. With open input I get nearly the same value of about 0,5Vac.

In all other Vac (and Vdc) ranges I get 0,0xxV[...]

Thankyou for your message we are aware of your issue, the issue with the on-off is almost certainly due to the shim fix (this will be shipped to you at some point soon, it will resolve the issue if that is an issue). It does sound like your 5V AC range has an issue, there is a new firmware update coming out. It might improve the situation for you and if you did want to recalibrate it would be better to do it after the next update.
Ok the new firmware is out. I flashed v1.15 and tried again. But it is still the same. In 5Vac range I have an offset of about 0,5V (shorted or opened port is nearly the same). I tried to calibrate the zero offset for the 5Vac range but it did not help. So there must be a problem with the 5Vac range of my 121GW.

What can I do? The shim fix did not arrive up to now bot I don't think it will help with this.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on May 02, 2018, 08:17:59 pm
Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on May 03, 2018, 01:13:30 am
Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.

That is unlikely as the Bluetooth is basically a UART-BLE bridge module and it hasn't been updated. It is more likely an update to windows or android that caused the issue, otherwise i'm not really sure how this could have happened.

One important thing to know is that if you simply minimize the app it is still using the bluetooth device until it is properly closed this means if you opened another instance it will not connect as the bluetooth device is already in use.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 03, 2018, 01:31:41 am
Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.

That is unlikely as the Bluetooth is basically a UART-BLE bridge module and it hasn't been updated. It is more likely an update to windows or android that caused the issue, otherwise i'm not really sure how this could have happened.

One important thing to know is that if you simply minimize the app it is still using the bluetooth device until it is properly closed this means if you opened another instance it will not connect as the bluetooth device is already in use.

Sounds  logical. As and admin do you have the power to modify the fist post in this thread?
I was thinking somehow of informing people when reporting issues to include as much details as posable. As with most trouble shooting issues or working on replicating the same issue the more details the better.
Like the OS or remote device being used to connect to the meter via Bluetooth. What app was used, and what version of the app used? And so on?
It’s usualy a time saver and others besides admins and EEVBlog employees can try to replicate the same issue and help confirm if it’s an issue that affects all or just one persons systems from an bad registered driver or older app version.
Just a thought?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Iagash on May 03, 2018, 10:12:10 am
Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.

That is unlikely as the Bluetooth is basically a UART-BLE bridge module and it hasn't been updated. It is more likely an update to windows or android that caused the issue, otherwise i'm not really sure how this could have happened.

I did some more tests and I guess it's the decreased data rate, that seems to cause a longer time to be able to reconnect. It just needs a lot longer until a reconnect is possible. I guess the BLE module resets the connection, when some buffer overflows when it couldn't send the data for some time making a new connection possible.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on May 05, 2018, 11:26:11 pm
Didn't I already read about this? I am not sure so I post it here in the issues thread.

When I turn off the beeper and afterwards go to diode test I get a nonstop beep with firmware 1.15.

PS: On 19th april I got a message telling me that the repair parts for the 121GW have been sent to me. They still not arrived ;-(
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on May 07, 2018, 01:19:39 am
Didn't I already read about this? I am not sure so I post it here in the issues thread.

When I turn off the beeper and afterwards go to diode test I get a nonstop beep with firmware 1.15.

PS: On 19th april I got a message telling me that the repair parts for the 121GW have been sent to me. They still not arrived ;-(

That is another strange issue your meter has, do you have steps to reproduce? I've tried a few things and couldn't get it to hold on beep.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: knapik on May 07, 2018, 01:30:10 am
I believe that I used to have the same issue, and it was due to the wobbly knob not making correct contact with the pads.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on May 07, 2018, 07:15:23 am
Ok so I will go on waiting for the replacement parts and hopefully they will solve bot problems I have. I think I can remember that I already read about someone having this issue too here but could not find the post.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on May 16, 2018, 07:40:25 am
@ Candid

Did you receive your shims and whatnot, any update with the issue you were having?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on May 16, 2018, 01:23:18 pm
@ Candid

Did you receive your shims and whatnot, any update with the issue you were having?
No, I did not receive anything up to now. And no update to the issue except that it is getting worser. Very often from off to any position the meter stays off or resets/starts from time to time and still having the +0,5V with shorted leads on ac 5V-range.

I got the mail about the delivery on 19th May but without any tracking Url. Maybe you can track something but not me:
Your order is on its way!

We are pleased to confirm that your order has now been shipped.

    Our Reference: 11633

    Your Reference:

    Carrier: Plain Labels
    (Australia Post for within Australia)

    Carrier's Reference:

    Tracking Url:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on May 17, 2018, 11:24:03 am
Today I got the switch and shim and installed them. So now the known issue seemes to be fixed.

But the fault concerning my 0,5Vac offset with shorted input in the 5Vac range still exists. So there must be something else with my meter.
I have firmware 1.15 installed and I just tried ZERO offset calibration of the 5Vac mode and it is still at about 0,5Vac with shorted input. When I open the input it is slightly higher (about 0,499xV against 0,515xV). The other Vac ranges are ok this only applies to the 5Vac range.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 19, 2018, 10:30:46 am
Has anyone reported or noticed when you zero out the meter on voltage or resistance (I think all settings) and use the auto hold at the same time, the auto hold results ignore the zero out value when it displays the auto hold results.

Then if you turn off the Auto hold the relative triangle symbol is still displayed on the meter, but it’s not the truly zeroed out value being displayed. It’s the normal value ignoring the relative value it should be doing math with like you didn’t zero it at all. But the triangle is still displayed on the LCD. So I pushed the relative button again, instead of the triangle turning off it blinks on and off real fast and sets a new zero value.

Or, once you get the Auto hold reading without the relative value calculated into the Auto hold reading displayed, then turn off the relative set value by pressing the button again the triangle on the LCD does turn off and the Auto Hold is still displayed on the LCD. But it’s not doing any auto holding despite the LCD showing Auto hold being displayed, the meter will display the live readings with no holding at all or beep indicating it’s captured a hold.

Seems these two functions just don’t know how to work together or play nice with each other.

The other thing I noticed with Auto hold is it seems to have difficulties capturing changes in values when the meter is set in a manual range instead of auto ranging. I set the meter to a manual range, and probe the DUT like voltage from my power supply or voltage reference so I know it’s a steady contact source. No beep, not auto hold after maybe 5 to 8 seconds. So I remove the probes and try again, sometimes it will work the second time, sometimes it won’t. Then I try again if it doesn’t work and eventually it will beep and display the hold value captured. This issue seems intermittent. I tried it also changing the voltage when it didn’t work and still had the same intermittent issue, and I’m not talking about small changes in the value. I tested this with 2.5VDC differences or 5VDC differences in the voltage.

And then also Auto hold might capture a value and beep, but if you don’t immediately remove the probe from the point being measured really fast it will display a lower value as you disconnect the probes from the source.
Example, let’s say I’m measuring a 5V source. When it does a hold and then beeps, if I hesitate and wait a second before I remove the probe it will change from 5V to a lower value like 3.856V as I remove one of the probes. So I have to take a reading again and wait for the beep, and remove the probe from the points I’m messing really fast for it to keep and hold the 5V measurement on the display. The voltage source doesn’t change and stays powered on the whole time.

And it doesn’t detect small changes like mV or uV changes even when it’s set to the highest resolution using auto range or selecting a manual range. I think it’s looking for pre-set amount of change in the value it’s measuring before it will display a new hold value. I’m not sure how much difference it needs to see before it captures and display the new hold value? I think it’s between 35mV and 40mV?
I found myself reversing the probes between each reading before taking probing the next reading. This way I forced it to the negative value before taking the next reading so it would capture even the smallest change in the next reading in case the next reading didn’t have a big enough change in value that would result in dillaying the same reading as before. No new beep if the value change isn’t big enough, or you start to think it’s just not working on the next reading you take.

And I know this is common with some meter, so maybe I shouldn’t mention this next one. But like some other cheap meters the reading are more accurate if you don’t use auto hold compared to the auto hold results. This might be from the meter displaying the results to fast before the measument settles all the way or not taking a few samples before display the hold number?

As I type this I’m starting to realize the auto hold might be the main issue from the fist thing I wrote about using auto hold with a zero set relative value first. I think Auto hold needs a little code tuning in the firmware.

Latest firmware 1.15, just recveied it today.
Scott
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 22, 2018, 09:45:06 pm
(i moved this here from the general discussion, was not aware this was a thread)
Got my multimeter today and it arrived with problems, the ohm mode is reading a constant 0 ohm, diode mode reads 1 volt, high Z mode gives an over range, wont read AC volts, 15v diode mode reads overload
anyone else having these same problems? any fix?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 22, 2018, 10:40:18 pm
Video of the issue is still being processed but the link is down below
https://youtu.be/sZZliqPRBJ4
my serial number is #420 (heh)

EDIT: i should add that AC and DC volt reading in the standard (non-lowZ) mode read fine (not sure about accuracy but it looks good enough compared to my UT61E)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Mickatroid on May 23, 2018, 12:15:51 am
My meter arrived a couple of days ago followed by an email from Kick-starter telling me it was my last chance to update my shipping details :)

Mine arrived with an immediate problem.  The screen contrast and viewing angles were weird and touching the screen even very lightly caused various segments to come on.  The packaging was largely OK, some bumps and bruises.

Anyway I gave the meter a bump on my bench (just on the top edge of the rubber surround) front and back.  Problem solved.  Not sure if the screen suffered a squish in transit or if it was pushed to hard front or back during assembly but I am thinking it was one or the other.  If you have this problem you can try giving the thing a bump.  Worked for me but, as they say, YMMV.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 23, 2018, 04:44:40 am
I thought i would give a small update on my problem
The current ranges all work fine, the 1v in diode mode does appear at the output, the 0ohm on resistance does not, and it does output current that differs depending on range
inside all of the protection appears fine and intact with quick diode and resistor measurements
impedance reads what i would expect it to, but the 10mohm hybrid is sorta flapping around in the breeze, its still connected

im at a lost as to what it might be, but definitely appears to be a hardware fault, i have not looked under the switch or removed the PCB
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 23, 2018, 12:28:08 pm
Video of the issue is still being processed but the link is down below
my serial number is #420 (heh)

EDIT: i should add that AC and DC volt reading in the standard (non-lowZ) mode read fine (not sure about accuracy but it looks good enough compared to my UT61E)
It thinks your probes are closed. When you crossed continuity it sounded off.
I had some solder splash on one trace by the flux capacitor, at first it looked like the trace was broken or scratched. This is from the manual soldering of the jacks and fuse holders. You might have some solder splash causing this probe short?
Also check the 2 resistors by the 2 jacks that are used for probe detection,

It is a EEVBlog meter, encouraged to take apart and don’t turn it on. If you feel comfortable enough I would take a quick look, general visual inspection of the board to see if an solder splash is causing this. If so, might be an easy fix. It should just swipe off with a little pressure using a plastic tool. Theirs s lotmof flux left over on the manual soldered parts so of the solder splash short is under the flux you may need a little rubbing alcohol to clear the flux first. I wouldn’t bother cleaning all the flux, just the one you might see solder causing a short.

I also have a bodg hand soldered capacitor at the top of the open whole were the middle screw post comes through, C23. It also caused a resistor behind it to move off slightly.
I don’t know if this was changed or added after the board were processed. Or if this was just something they noticed that the cap was loose when they installed the shim? Either way if it is a change after then maybe to much solder their is causing a short. I can’t say it’s the best soldering job I’ve ever seen, actually it fairly bad. But I don’t want to re-do this since I don’t want it to affect the calibration.

And U17 had flux and burned flux around the chip, I think it was added later or reflowed manually.

Those would be the thee spots I would check first.
Scott
Just a thought.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on May 23, 2018, 12:44:21 pm
My meter arrived a couple of days ago followed by an email from Kick-starter telling me it was my last chance to update my shipping details :)

Mine arrived with an immediate problem.  The screen contrast and viewing angles were weird and touching the screen even very lightly caused various segments to come on.  The packaging was largely OK, some bumps and bruises.

Anyway I gave the meter a bump on my bench (just on the top edge of the rubber surround) front and back.  Problem solved.  Not sure if the screen suffered a squish in transit or if it was pushed to hard front or back during assembly but I am thinking it was one or the other.  If you have this problem you can try giving the thing a bump.  Worked for me but, as they say, YMMV.

Probably an assembly tolerance or some crud on the zebra strip. First report of that, thanks, will keep an eye on it.
The screen is protected by a strong polycarb window, so pressing on that does not, AFAIK, translate into pressure on the LCD itself.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 23, 2018, 03:13:34 pm
Hi Dave, you did this video a while back with voltage. I’ve been :palm: trying to figure this out, and I think I finally figured out why my resistance testing is gettting such large differences in readings.

I haven’t had time to check the voltage and temperature change but it also didn’t jump out at me during basic testing so I’m assuming it’s probably ok.
What I have noticed is the resistor mensrment range being severely affected by the internal meter temperature. I’m going off what the internal temperature is showing on the meter.

Can you run this again in the resistance mode? Specifically the 50M resistance mode maybe with a 10M resistors? Although I’ve noticed the temperature affecting all resistance modes, the 50M ohm range seems to be the worse and most sensitive. The ambient temperature in the lab did not change more then 1C but the internal temp on the meter with backlight on went from 21.1C to 26.1C.

My Caddock 10M resistor at 0.1% tolerance is a 15ppm temp coefficient but as I mentioned the lab room temperature hardly changed at all. At internal meter reading temp it showed 10.005. By the time the meter internal temp reached 26.1C the resistor was reading 10.158. And the day my air con was off the lab was at 24.4C and the internal temp on the meter reached 28.9C and the reading was much higher at 10.356.

Despite the 10M resistor being 15ppm I also testing with Vishay that are 2ppm at 0.025% tolerances and those are affected also with all ranges I own 1, 10, 1K, 10k, 100k ohm resistors.
I will also note the 50M range seems to be the most sensitive jumping around a lot just going to push a button on the meter or waiving your hand around it.
I just want to know if this is mine only, or if you can repeate the test with the resistance mode and see if this is a common thing? And maybe the sensitivity can be adjusted in the firmware, it reminds me of your 2016 mV range video showing it being so sensitive that I believe was corrected with firmware or maybe a hardware change? If it not just mine maybe theirs a specific component this resistance mode uses that can be changed to something that has better temperature coefficiency?

The sweet spot for internal meter internal temperature seemed to be about 21.1C for all ranges.

https://youtu.be/Wwz_fdU17aQ
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on May 23, 2018, 04:15:03 pm
From preliminary testing I find the resistance mode to have some issues.

When I short the probes to null out the lead resistance I get very variable resistance readings. Sometimes the display shows 0.000 with the leads shorted, sometimes 0.002 (I expect some 10's of mΩ -- 0.000 Ω seems unlikely). Also the display is unstable and doesn't settle. If I move my hand to the Rel button to null out the reading the display seems sensitive to the proximity of my hand. Just moving my hand near the meter with the leads shorted (with croc clips) makes the reading jump around.

The 1 mΩ precision is nice, but I think the measurement is not stable or repeatable enough for this to be useful.

Also resistance measurement shows quite odd display behavior. If I try to read a 100 Ω resistor I often see the display jump from OL to some number of MΩ, then to blank, then finally to the expected resistance reading.

Footnote: Retesting again today with shorted leads gives a reading of about 0.035 Ω, so I do not know why I kept seeing readings close to 0.000 Ω yesterday. There is somehow a lack of repeatability.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 23, 2018, 05:08:52 pm
From preliminary testing I find the resistance mode to have some issues.

If I move my hand to the Rel button to null out the reading the display seems sensitive to the proximity of my hand.

Yes I'm having this as well, meter go way out of spec when touching or nearly touching buttons.

Finger just above REL button (almost touching) or lightly touching any of range-hold-rel buttons causes resistance value to change, 0.5ohm+ on mine. Same with light taps.

Also similar in the mVDC ranges.  Touching / lightly depressing the range/hold (or both) buttons causes mater to go way out of spec, 0.5mv+

v1.15
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 23, 2018, 06:08:05 pm
i took it fully apart except for the LCD and found really nothing out of place, some bodges that look fine and some flux here and there but no solder blobs or lifted components, i attached some high res photos of both sides, see if you can see anything
i also checked out under the switch and found nothing out of place

my next course of action is tracing down both signal paths and see if anything is a miss

EDIT: no attachment, too big, i placed both images here https://imgur.com/a/vHISAb5

EDIT2: I traced down what i could, PA9, PLD and PB0, none of these show a short or anything below what looks normal as referenced to agnd
i also looked at u16 and that also appears to be functional
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 23, 2018, 08:33:36 pm
Thought I should report that the knob on mine felt way too tight, with a squeaking grind. Opened it after about a day of use and found the shim installed at Kane (from delayed batch) had been installed upside-down.
(https://i.imgur.com/PMQt9YR.png?1)

Title: Re: EEVblog 121GW Multimeter Issues - Diode test bar graph range indication
Post by: Mag748 on May 23, 2018, 09:30:40 pm
In using the Diode test function, there is a discrepancy in the bar graph voltage reading and the bar graph voltage range indication.

Without any input:
In the 3V range, the bar graph indicates roughly 3 volts, and a full scale range of 5V.
In the 15V range, the bar graph indicates roughly 16V, although still displays a full scale range of 5V, which I believe should read 50V.

See images attached for your reference. Btw, I currently have FW version 1.15

Thanks,
Marcus

Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on May 23, 2018, 09:42:59 pm
Thought I should report that the knob on mine felt way too tight, with a squeaking grind. Opened it after about a day of use and found the shim installed at Kane (from delayed batch) had been installed upside-down.

Interesting. I wouldn't say the action on my meter feels silky smooth. I might open it up and have a look.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 23, 2018, 09:50:47 pm
Thought I should report that the knob on mine felt way too tight, with a squeaking grind. Opened it after about a day of use and found the shim installed at Kane (from delayed batch) had been installed upside-down.
(https://i.imgur.com/PMQt9YR.png?1)
UODATED;
Well at least it’s not just just mine that was tight. I did finally confirm the routed are is supposed to face up, or at the PCB when re-assembled. But I think removing those three mold break points made the biggest difference. All three of them stuck up high, and without a fourth one it caused it to turn unevenly.
Scott
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Mickatroid on May 23, 2018, 10:21:28 pm
Thanks Dave. I suppose one of the good bits about selling meters to people like us is that many of us are prepared to have a go at some minor adjustments. If I have further problems I will try reseatting the zebra strip.

While the window is clearly very strong, as I said touching it lightly would at first cause some segments to come on. Perhaps the edges of the display were a bit jammed. Either that or I have discovered the secret touch screen option :)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on May 24, 2018, 04:35:01 am
Due to it becoming a little disorderly and difficult to manage I have added a form on the product page to report issues with the multimeter.

https://www.eevblog.com/product/121gw/ (https://www.eevblog.com/product/121gw/)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on May 24, 2018, 04:42:44 am
i took it fully apart except for the LCD and found really nothing out of place, some bodges that look fine and some flux here and there but no solder blobs or lifted components, i attached some high res photos of both sides, see if you can see anything
i also checked out under the switch and found nothing out of place

my next course of action is tracing down both signal paths and see if anything is a miss

EDIT: no attachment, too big, i placed both images here https://imgur.com/a/vHISAb5

EDIT2: I traced down what i could, PA9, PLD and PB0, none of these show a short or anything below what looks normal as referenced to agnd
i also looked at u16 and that also appears to be functional

Hello,

Could I get your kickstarter details, backer number etc.

Kind Regards,
    Seppy
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 24, 2018, 06:13:06 am
I will PM you my information
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 24, 2018, 03:33:53 pm
Anyone test the 1khz LPF? On my unit, attenuation begins somewhere around 30hz (sine).

1.15
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 25, 2018, 07:38:44 am
From preliminary testing I find the resistance mode to have some issues.

If I move my hand to the Rel button to null out the reading the display seems sensitive to the proximity of my hand.
Yes I'm having this as well, meter go way out of spec when touching or nearly touching buttons.
Finger just above REL button (almost touching) or lightly touching any of range-hold-rel buttons causes resistance value to change, 0.5ohm+ on mine. Same with light taps.

Also similar in the mVDC ranges.  Touching / lightly depressing the range/hold (or both) buttons causes mater to go way out of spec, 0.5mv+

v1.15
I can confirm this also. Since I don’t believe the meter is capable of reading mili Ohms (like most meters can’t) it probably why other meter remove the least significant digit in this range.
I have not tried relative in the mV mode yet.
Work around:  I find if you manually change it to the next range it’s a lot easier to zero out the resistance of your probes.
Scott
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 25, 2018, 07:46:42 am
Has anyone reported or noticed when you zero out the meter on voltage or resistance (I think all settings) and use the auto hold at the same time, the auto hold results ignore the zeroed out value when it displays the auto hold results.

Then if you turn off the Auto hold the relative triangle symbol is still displayed on the meter, but it’s not the truly zeroed out value being displayed. It’s the normal value ignoring the relative value it should be doing math with like you didn’t zero it at all. But the triangle is still displayed on the LCD. So I pushed the relative button again, instead of the triangle turning off it blinks on and off real fast and sets a new zero value.

Or, once you get the Auto hold reading without the relative value calculated into the Auto hold reading displayed, then turn off the relative set value by pressing the button again the triangle on the LCD does turn off and the Auto Hold is still displayed on the LCD. But it’s not doing any auto holding despite the LCD showing Auto hold being displayed, the meter will display the live readings with no holding at all or beep indicating it’s captured a hold.

And then also Auto hold might capture a value and beep, but if you don’t immediately remove the probe from the point being measured really fast it will display a lower value as you disconnect the probes from the source.

And it doesn’t detect small changes like mV or uV changes even when it’s set to the highest resolution using auto range or selecting a manual range. I think it’s looking for pre-set amount of change in the value it’s measuring before it will display a new hold value. I’m not sure how much difference it needs to see before it captures and display the new hold value? I think it’s between 35mV and 40mV?

Latest firmware 1.15, just recveied it today.
Scott

Has anyone been able to confirm any of these issues? To make this easier since it might not come across clear in text I’ve attached a video. Maybe someone can try the same things I do in the video and see if you can replicate this including taking a hold measument, turning off auto hold, then returning to Auto hold and reading the same source and it will not show anything (or maybe the wrong number if it changes when removing the probes).
Thanks,
Scott

https://youtu.be/l7hBJh_NMOo
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 25, 2018, 09:36:30 am
1,2,3,4:yes
5: The threshold depends on the range selected I believe. Not updating until some threshold is the behavior defined in the manual though. 

I've been keeping rough track of fw issues I've come across as well. Maybe check these?

Code: [Select]
1. set max/min active, -> range button does not function

2. set max/min active, set hold, unset hold -> readings change as if max/min off, but shows max/min as on

3. set a-hold, press max/min button (note  min/max mode change is not displayed), turn off a-hold, -> max/min mode change suddenly displayed but not in min/max mode

4. set hold, press max/min button (note max/min mode change is displayed), set a-hold -> a-hold works as if max/min is off, even though max/min is displayed as active

5. In mvDC press range and immediately press REL -> REL sets before ranging completes, leaving error in offset. REL should delay until range completes

6. Short v-com, set VAC mode, set manual range other than 1000v, turn on 1ms peak, select 1000v range -> meter flashes high voltage warning symbol

7. Set a VAC mode, set a manual range, turn on 1ms peak, turn off 1 ms peak, -> meter forgets manual range set and reverts to auto range

8. Short v-com, set mVAC mode, set manual 50mv range (shows ~0mv), turn on 1ms peak, set range to 500mv-> suddenly large offset appears. Similar in Vac mode

9. Short v-com, set VAC mode, set range to 1000V, activate 1ms peak, set range to 5v -> takes over 10 seconds to switch into 5v.

10. Open v-com, set mVAC mode, set 1ms peak, switch to VAC -> mater never ranges - infinite blank

11. VAC or maVAC, set a manual range, turn on 1ms peak, turn off 1 ms peak -> meter goes to auto-range, forgetting it was in manual
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 25, 2018, 10:47:38 am
Thanks.
As for 5, I know the threshold is between 45mV and 50mV, I was going in 5mV increments. I could probably narrow is down more if I had a better mV power supply that was more accurate. It probably 50mV if I had to guess.
I need some sleep for now, but I’ve sent your tests to myself in email.
Did you check these on 1.15 or 1.17 for the things you want to me check?
I’ll check it once I wake up.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 25, 2018, 11:03:33 am
I have one more for you I forgot about, but also probably related to the hold code.
In Amp if you measure current, hold the reading and pull the probes out the reading stays displayed.
In the mA/uA jack if you do the same thing when you pull the probe out, the screen goes blank. And if you had it set to a manual range it changes over to Auto range when you pull the probe with the reading on hold.
Some flukes do this from the jack detection warning, but when you put the probe back in the measurement is displayed again on the LCD. When I plugged it back in the mA/uA jack I was hoping it would display again but it didn’t. Then I realized it’s becjase it reset to Auto ranging also.
Scott
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 25, 2018, 11:07:15 am
My meter arrived a couple of days ago followed by an email from Kick-starter telling me it was my last chance to update my shipping details :)

Mine arrived with an immediate problem.  The screen contrast and viewing angles were weird and touching the screen even very lightly caused various segments to come on.  The packaging was largely OK, some bumps and bruises.

Anyway I gave the meter a bump on my bench (just on the top edge of the rubber surround) front and back.  Problem solved.  Not sure if the screen suffered a squish in transit or if it was pushed to hard front or back during assembly but I am thinking it was one or the other.  If you have this problem you can try giving the thing a bump.  Worked for me but, as they say, YMMV.
Mine has a weird viewing angle also, straight on is dim compared to looking up at it. But looking at a down angle it get worse, almost unreadable.

If you hold the RANGE button down when you turn it on, it will display all the LCD characters so you can check the LCD or see if some of the zebra connections are not making good contact.
Scott
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on May 25, 2018, 03:52:57 pm
Thanks for the testing.  Haven't received mine yet.
Mine has a weird viewing angle also...

Have you tried the LCD Contrast adjustment?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 25, 2018, 06:24:01 pm
Thanks for the testing.  Haven't received mine yet.
Mine has a weird viewing angle also...

Have you tried the LCD Contrast adjustment?
Yes, contrast doesn’t change viewing angles. It just adjusts the dark and light between the displayed numbers and the background.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 25, 2018, 07:23:32 pm
Did you check these on 1.15 or 1.17 for the things you want to me check?
I checked on both 1.15 and 1.17

In Amp if you measure current, hold the reading and pull the probes out the reading stays displayed.
In the mA/uA jack if you do the same thing when you pull the probe out, the screen goes blank. And if you had it set to a manual range it changes over to Auto range when you pull the probe with the reading on hold.
Same behavior on mine on 1.17

Mine has a weird viewing angle also, straight on is dim compared to looking up at it. But looking at a down angle it get worse, almost unreadable.
The view angle bias seems ok on mine - viewable flat on a table or looking straight on at meter (contrast does fade a little bit straight on but it's not bad). The default contrast setting on mine (4) was way too low though, I have mine set at max (7) and do wish it would go a little higher.

Noticing input jack warning doesn't function if both plugs are in the current jacks (one in A, other in uA). If in mV AC, and set 1ms peak, then input jack warning is not displayed. Similarly if one sets hold, then jack warning not displayed.   1.17
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 26, 2018, 12:43:37 am
A little update on my meter, the problem looks to be at least partly software as i cannot update the firmware, i checked out the mcu and there was some gunk over some pins as seen in attached but this appears not to be the issue, i cleaned it up and hit it with the rework station and the problem persists

when i attempt to update the firmware it looks like the micro locks up (with both 1.15 and 1.17 firmware) as some segments stay on and appear to build up and loose charge as it sits, i let it sit for an hour to no avail

at this point i have basically given up trying to repair it and hope for a replacement, i sent my details off to Seppy (i think i have, its not appearing in my sent messages)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 26, 2018, 01:35:17 am
Bummer, but you tried

For sent messages to appear in outbox, you have to make sure "Save a copy in my outbox" is checked before sending. If you go to preferences there's a "Save a copy of each personal message in my sent items by default" option too.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 26, 2018, 01:49:33 am
Bummer, but you tried

For sent messages to appear in outbox, you have to make sure "Save a copy in my outbox" is checked before sending. If you go to preferences there's a "Save a copy of each personal message in my sent items by default" option too.
Oh okay, thanks for the heads up ill keep that in mind
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nidlaX on May 26, 2018, 02:06:25 am
I noticed a potential quality issue with the rubber boot. On the right side, the lip is a bit deformed and doesn't adhere to the contour of the meter. Based on videos I've seen of the production meter, my problem doesn't seem to be a one-off (didn't notice it with Joe's pre-production meter though).

Any thoughts?

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=441463)
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=441469)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on May 26, 2018, 02:08:51 am
I noticed a potential quality issue with the rubber boot. On the right side, the lip is a bit deformed and doesn't adhere to the contour of the meter. Based on videos I've seen of the production meter, my problem doesn't seem to be a one-off (didn't notice it with Joe's pre-production meter though).

Any thoughts?

mine does the same thing, but does slowly pull it self back together after an hour after pulling it out of its sheath
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 26, 2018, 02:35:28 am
Pulled away a bit as well on same side, but higher up near LCD/buttons; out of box. Not as bad as yours though, but enough to notice immediately when holding first time.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nidlaX on May 26, 2018, 03:31:07 am
I noticed a potential quality issue with the rubber boot. On the right side, the lip is a bit deformed and doesn't adhere to the contour of the meter. Based on videos I've seen of the production meter, my problem doesn't seem to be a one-off (didn't notice it with Joe's pre-production meter though).

Any thoughts?

mine does the same thing, but does slowly pull it self back together after an hour after pulling it out of its sheath
Mine is probably permanent, it was like this out of the box. I'm guessing it's either an issue with the way they're pulled out of the mold or with how the meters were handled when they were opened up to install the shim.

Not sure if this is worth a warranty inquiry though. Maybe if many other customers have the same problem.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on May 26, 2018, 06:30:00 am
Burden voltage function doesn't seem to work? Set current range, then change bd.off->bd.on - doesn't seem do anything (unless not understanding something?) v1.17
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Mickatroid on May 26, 2018, 11:12:34 pm
Mine has a weird viewing angle also, straight on is dim compared to looking up at it. But looking at a down angle it get worse, almost unreadable.

As I said in my original post a bump on the bench appeared to fix mine properly. Whether the problem will come back I cannot say. Our symptoms were about the same. You will see Dave thinks it could be the zebra strip.

Edit: thanks mod :) sorry about the quote pebcak
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 26, 2018, 11:39:26 pm
I noticed a potential quality issue with the rubber boot. On the right side, the lip is a bit deformed and doesn't adhere to the contour of the meter. Based on videos I've seen of the production meter, my problem doesn't seem to be a one-off (didn't notice it with Joe's pre-production meter though).

Any thoughts?

mine does the same thing, but does slowly pull it self back together after an hour after pulling it out of its sheath
Mine is probably permanent, it was like this out of the box. I'm guessing it's either an issue with the way they're pulled out of the mold or with how the meters were handled when they were opened up to install the shim.

Not sure if this is worth a warranty inquiry though. Maybe if many other customers have the same problem.
Does anyone know the material that the outside boot is made of? Ifs it TPU, or some combined mix of stuff?
Sometimes depending on the material a little heat like a blow dryer on low can help re-shape it back to normal.
Do it use high heat like a 1,000 watt har dryer on high, or a hot air soldering station. This could melt or burn it. But that’s why the type of material is important to know the limits for temperature durring it’s original molding.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bitwelder on May 27, 2018, 07:21:40 am
Does anyone know the material that the outside boot is made of? Ifs it TPU, or some combined mix of stuff?
That's a piece of information that if it's not already in the manual, I think it should be added there, also for ecological disposal purposes.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 27, 2018, 10:35:31 am
Does anyone know the material that the outside boot is made of? Ifs it TPU, or some combined mix of stuff?
That's a piece of information that if it's not already in the manual, I think it should be added there, also for ecological disposal purposes.
Nope, it’s not in the manual. Unless I missed it both times I gone over the manual.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on May 27, 2018, 09:57:55 pm
I noticed a potential quality issue with the rubber boot. On the right side, the lip is a bit deformed and doesn't adhere to the contour of the meter. Based on videos I've seen of the production meter, my problem doesn't seem to be a one-off (didn't notice it with Joe's pre-production meter though).

Any thoughts?

I might suggest to immerse the boot in hot water and see if it "relaxes" back to the correct shape? Proceed carefully though in case anything bad happens like shrinking or greater deformation.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: drtaylor on May 27, 2018, 10:11:09 pm
Regarding the material the boot is made from:

Those kinds of boots are almost always made of "Elastomeric Rubber" which actually is a form of Silicone. Same stuff that insulates very flexible test leads. Available in many viscosities.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on May 28, 2018, 04:11:55 am
Hi Dave, you did this video a while back with voltage. I’ve been :palm: trying to figure this out, and I think I finally figured out why my resistance testing is gettting such large differences in readings.

I haven’t had time to check the voltage and temperature change but it also didn’t jump out at me during basic testing so I’m assuming it’s probably ok.
What I have noticed is the resistor mensrment range being severely affected by the internal meter temperature. I’m going off what the internal temperature is showing on the meter.

Can you run this again in the resistance mode? Specifically the 50M resistance mode maybe with a 10M resistors? Although I’ve noticed the temperature affecting all resistance modes, the 50M ohm range seems to be the worse and most sensitive. The ambient temperature in the lab did not change more then 1C but the internal temp on the meter with backlight on went from 21.1C to 26.1C.

My Caddock 10M resistor at 0.1% tolerance is a 15ppm temp coefficient but as I mentioned the lab room temperature hardly changed at all. At internal meter reading temp it showed 10.005. By the time the meter internal temp reached 26.1C the resistor was reading 10.158. And the day my air con was off the lab was at 24.4C and the internal temp on the meter reached 28.9C and the reading was much higher at 10.356.

Despite the 10M resistor being 15ppm I also testing with Vishay that are 2ppm at 0.025% tolerances and those are affected also with all ranges I own 1, 10, 1K, 10k, 100k ohm resistors.
I will also note the 50M range seems to be the most sensitive jumping around a lot just going to push a button on the meter or waiving your hand around it.
I just want to know if this is mine only, or if you can repeate the test with the resistance mode and see if this is a common thing? And maybe the sensitivity can be adjusted in the firmware, it reminds me of your 2016 mV range video showing it being so sensitive that I believe was corrected with firmware or maybe a hardware change? If it not just mine maybe theirs a specific component this resistance mode uses that can be changed to something that has better temperature coefficiency?

The sweet spot for internal meter internal temperature seemed to be about 21.1C for all ranges.

https://youtu.be/Wwz_fdU17aQ

Hello scott!

Just did some long term logging of 10MR. Don't see the same error you discuss, is there any specific things I missed with my tests?


Test 1: Simply connected 10M resistor to the multimeter and logged for an hour.
Test 2: Placed multimeter in a thermal chamber starting at 26.6 degrees and raised it to 35.6. The 121GW measured a 10M resistor that was outside the thermal chamber (so it was unaffected by rising temperature or humidity), logging for an hour.

NOTE: There are some glitches in my logging, thats just when I bumped the leads with my computer mouse, try not to move wires when measuring such high impedances.

The next test starts at 26.6 and raises to 35.6. These were logged using the windows app over bluetooth. At about 2000 I left the room for lunch and the erroneous readings stopped entirely, again high impedance readings are very sensitive.

Are you able to show something similar? I recommend using the Windows App for this is as it will make saving and posting the data a little easier.

 




Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on May 28, 2018, 12:42:52 pm
did this thread get unpinned by accident? - it no longer appear at the top of the thread list.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on May 28, 2018, 01:01:20 pm
did this thread get unpinned by accident? - it no longer appear at the top of the thread list.

Yeah, no idea how it got unpinned, fixed.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on May 28, 2018, 09:36:12 pm
Hello scott!

Just did some long term logging of 10MR. Don't see the same error you discuss, is there any specific things I missed with my tests?


Test 1: Simply connected 10M resistor to the multimeter and logged for an hour.
Test 2: Placed multimeter in a thermal chamber starting at 26.6 degrees and raised it to 35.6. The 121GW measured a 10M resistor that was outside the thermal chamber (so it was unaffected by rising temperature or humidity), logging for an hour.

NOTE: There are some glitches in my logging, thats just when I bumped the leads with my computer mouse, try not to move wires when measuring such high impedances.

The next test starts at 26.6 and raises to 35.6. These were logged using the windows app over bluetooth. At about 2000 I left the room for lunch and the erroneous readings stopped entirely, again high impedance readings are very sensitive.

Are you able to show something similar? I recommend using the Windows App for this is as it will make saving and posting the data a little easier.
Nope, no difference. I didn’t log the results, I just watched it change.
I’ll have to find my wondws laptop and install the software.

Speaking of apps, do you know what happened to the iOS app for Apple devices? I had it downloaded and it controls thing like ranges, hold, but doesn’t display any numbers. Then I realized it was removed from the iOS App Store, do you know when we can expect this to be returned?

I also took into the consideration based off Dave’s video showing a grounded ESD mat affecting mV readings and moved it to another room that is latterly empty. Still the same results.
I’ll try to log it if I find the computer, It might just be my meter?

Thanks for checking and running the tests,
Scott
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 01, 2018, 01:18:07 am
Hello scott!

Just did some long term logging of 10MR. Don't see the same error you discuss, is there any specific things I missed with my tests?


Test 1: Simply connected 10M resistor to the multimeter and logged for an hour.
Test 2: Placed multimeter in a thermal chamber starting at 26.6 degrees and raised it to 35.6. The 121GW measured a 10M resistor that was outside the thermal chamber (so it was unaffected by rising temperature or humidity), logging for an hour.

NOTE: There are some glitches in my logging, thats just when I bumped the leads with my computer mouse, try not to move wires when measuring such high impedances.

The next test starts at 26.6 and raises to 35.6. These were logged using the windows app over bluetooth. At about 2000 I left the room for lunch and the erroneous readings stopped entirely, again high impedance readings are very sensitive.

Are you able to show something similar? I recommend using the Windows App for this is as it will make saving and posting the data a little easier.
Nope, no difference. I didn’t log the results, I just watched it change.
I’ll have to find my wondws laptop and install the software.

Speaking of apps, do you know what happened to the iOS app for Apple devices? I had it downloaded and it controls thing like ranges, hold, but doesn’t display any numbers. Then I realized it was removed from the iOS App Store, do you know when we can expect this to be returned?

I also took into the consideration based off Dave’s video showing a grounded ESD mat affecting mV readings and moved it to another room that is latterly empty. Still the same results.
I’ll try to log it if I find the computer, It might just be my meter?

Thanks for checking and running the tests,
Scott

Due to the Packet change of the 121GW the iOS app stopped working. We are porting our app to the iPhone now, it won't be available immediately as I need to do a whole song and dance to get Apple to approve Apps, not a show stopper just a slow process.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: iainwhite on June 06, 2018, 01:33:37 am
Still waiting for my missing 121Gw yellow shim that I was promised twice in the last 3 weeks.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on June 06, 2018, 09:26:49 am
Hi all, Dave, Seppy, I've received my shim and selector switch and installed it. The internal selector with the wipes is still causing abrasion to the PCB by the looks of it. Initially the selector knob could not be operated with one hand and I had to fix the 121GW with my left-hand. I've loosened the internal 2 screws and this helps (a bit). What remains now is that when the selector is in the ohms range and I wiggle or pull the V+/Ohm cable the 121GW goes into black/reset mode. I loved the 121GW from the on-start due to the crowd funding, the discussions, the feature set and specifications. But I need to come to the conclusion that this is not workable for me and need to revert back to my trusted BM869s. I can inspect the socket on the PCB but suspect it's the wipes and internal selector which causing the issue since it only happens when in the Ohms range. A genuine pitty it is.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 07, 2018, 02:47:50 am
Hi all, Dave, Seppy, I've received my shim and selector switch and installed it. The internal selector with the wipes is still causing abrasion to the PCB by the looks of it. Initially the selector knob could not be operated with one hand and I had to fix the 121GW with my left-hand. I've loosened the internal 2 screws and this helps (a bit). What remains now is that when the selector is in the ohms range and I wiggle or pull the V+/Ohm cable the 121GW goes into black/reset mode. I loved the 121GW from the on-start due to the crowd funding, the discussions, the feature set and specifications. But I need to come to the conclusion that this is not workable for me and need to revert back to my trusted BM869s. I can inspect the socket on the PCB but suspect it's the wipes and internal selector which causing the issue since it only happens when in the Ohms range. A genuine pitty it is.

Please ensure that shim's routed cutout faces downwards into the plastic rotary selector assembly. The cutout is NOT for the circlip, a lot of people have had that issue with upside down shims.
There is also chance that some burs on the plastic are causing the shim to raise up too far, you might want to remove the injection molding burs if possible. It is a shame that the shim was needed.
It might also be worth opening up the device and removing the selector switch, carefully (this can be pretty tricky), making sure the PCB underneath it is fine.

It could be that the brushes aren't perfectly housed, or that one of the brushes has two spring contacts stacked on-top of each other (happened once in pre-production, but thought this was sorted out).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on June 07, 2018, 06:22:26 am
..
Please ensure that shim's routed cutout faces downwards into the plastic rotary selector assembly. The cutout is NOT for the circlip, a lot of people have had that issue with upside down shims.
...
Up, down, into selector assembly?  A picture of the proper installation by the seller would be worth 1000 posts. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on June 07, 2018, 06:43:14 am
..
Please ensure that shim's routed cutout faces downwards into the plastic rotary selector assembly. The cutout is NOT for the circlip, a lot of people have had that issue with upside down shims.
...
Up, down, into selector assembly?  A picture of the proper installation by the seller would be worth 1000 posts.

Its already been done, available as a pdf and on youtube!
https://www.eevblog.com/files/How%20to%20Replace%20121GW%20Rotary%20Switch-180411.pdf (https://www.eevblog.com/files/How%20to%20Replace%20121GW%20Rotary%20Switch-180411.pdf)

https://www.youtube.com/watch?v=Kok7VJft3vs (https://www.youtube.com/watch?v=Kok7VJft3vs)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on June 07, 2018, 08:29:19 am
Hi all, Dave, Seppy, I've received my shim and selector switch and installed it. The internal selector with the wipes is still causing abrasion to the PCB by the looks of it. Initially the selector knob could not be operated with one hand and I had to fix the 121GW with my left-hand. I've loosened the internal 2 screws and this helps (a bit). What remains now is that when the selector is in the ohms range and I wiggle or pull the V+/Ohm cable the 121GW goes into black/reset mode. I loved the 121GW from the on-start due to the crowd funding, the discussions, the feature set and specifications. But I need to come to the conclusion that this is not workable for me and need to revert back to my trusted BM869s. I can inspect the socket on the PCB but suspect it's the wipes and internal selector which causing the issue since it only happens when in the Ohms range. A genuine pitty it is.

Please ensure that shim's routed cutout faces downwards into the plastic rotary selector assembly. The cutout is NOT for the circlip, a lot of people have had that issue with upside down shims.
There is also chance that some burs on the plastic are causing the shim to raise up too far, you might want to remove the injection molding burs if possible. It is a shame that the shim was needed.
It might also be worth opening up the device and removing the selector switch, carefully (this can be pretty tricky), making sure the PCB underneath it is fine.

It could be that the brushes aren't perfectly housed, or that one of the brushes has two spring contacts stacked on-top of each other (happened once in pre-production, but thought this was sorted out).

The shim is installed as it should be no worries there (but will triple check). The selector switch on the PCB is very difficult to take out as the three (3) plastic prongs are super difficult to squeeze and thereby remove the switch. I did this once and it already damaged the plastic prongs from the outside. I guess that if I start to remove this once more, or you have a smart tip, I will start to ruin more and more of the selector PCB switch. As a last request to you I would like to request a new one if possible and then will take the old one out. Is this an idea?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 15, 2018, 06:56:22 am
Hi all, Dave, Seppy, I've received my shim and selector switch and installed it. The internal selector with the wipes is still causing abrasion to the PCB by the looks of it. Initially the selector knob could not be operated with one hand and I had to fix the 121GW with my left-hand. I've loosened the internal 2 screws and this helps (a bit). What remains now is that when the selector is in the ohms range and I wiggle or pull the V+/Ohm cable the 121GW goes into black/reset mode. I loved the 121GW from the on-start due to the crowd funding, the discussions, the feature set and specifications. But I need to come to the conclusion that this is not workable for me and need to revert back to my trusted BM869s. I can inspect the socket on the PCB but suspect it's the wipes and internal selector which causing the issue since it only happens when in the Ohms range. A genuine pitty it is.

Please ensure that shim's routed cutout faces downwards into the plastic rotary selector assembly. The cutout is NOT for the circlip, a lot of people have had that issue with upside down shims.
There is also chance that some burs on the plastic are causing the shim to raise up too far, you might want to remove the injection molding burs if possible. It is a shame that the shim was needed.
It might also be worth opening up the device and removing the selector switch, carefully (this can be pretty tricky), making sure the PCB underneath it is fine.

It could be that the brushes aren't perfectly housed, or that one of the brushes has two spring contacts stacked on-top of each other (happened once in pre-production, but thought this was sorted out).

The shim is installed as it should be no worries there (but will triple check). The selector switch on the PCB is very difficult to take out as the three (3) plastic prongs are super difficult to squeeze and thereby remove the switch. I did this once and it already damaged the plastic prongs from the outside. I guess that if I start to remove this once more, or you have a smart tip, I will start to ruin more and more of the selector PCB switch. As a last request to you I would like to request a new one if possible and then will take the old one out. Is this an idea?

Could you take a photo of the abrasion and post it here. Just take a photo of everything actually :)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: BiOzZ on June 15, 2018, 07:30:28 am
Just an update, new meter arrived and it works flawlessly, slight blip on the shroud but nothing to write home about, switch is fantastic, tested well in cal, firmware updated perfectly
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 15, 2018, 07:31:17 am
Just an update, new meter arrived and it works flawlessly, slight blip on the shroud but nothing to write home about, switch is fantastic, tested well in cal, firmware updated perfectly

Very glad to hear.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 16, 2018, 05:38:24 am
I noticed the meter will auto-power off while in BT communication mode. I noticed this while logging some data and I wondered why the screen and graph froze. I suspect that auto-power off should be suspended while BT communication is enabled?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 17, 2018, 12:46:41 pm
I noticed the meter will auto-power off while in BT communication mode. I noticed this while logging some data and I wondered why the screen and graph froze. I suspect that auto-power off should be suspended while BT communication is enabled?

This is an option, at least manually, you can disable APo in the settings menu.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 17, 2018, 04:27:49 pm
This is an option, at least manually, you can disable APo in the settings menu.

I appreciate this is an option, however it is a permanent setting, one way or the other.

The manual says, "APO is disabled in data logging mode." I suggest it would be an idea to disable APO during Bluetooth communications too, to facilitate Bluetooth data logging.

Also, some other meters have a way of temporarily disabling APO one time only, for example by holding down the MODE button when turning the meter on. This kind of feature would be useful.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 17, 2018, 05:44:28 pm
Long time reader first time poster. Received My 121gw (Thanks), and was playing around and found the burden voltage with firm ware V1.17  to be less than spot on, and totally not working with the new V1.21 firmware, only tested dc amps, (all ranges) so far.  Finger problems? On the plus side found Auto Hold to be working as well if not better than my Fluke 87V.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 17, 2018, 06:05:04 pm
Some Pic's.... Sorry limited by pic size due to under 25 posts
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 17, 2018, 06:40:26 pm
Long time reader first time poster. Received My 121gw (Thanks), and was playing around and found the burden voltage with firm ware V1.17  to be less than spot on, and totally not working with the new V1.21 firmware, only tested dc amps, (all ranges) so far.

I have never been able to make the burden voltage appear. How did you achieve that?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 17, 2018, 07:17:32 pm
With "bd.OFF" in upper display, hold setup till display blinks , select "be.ON" with REL or 1ms PEAK , hold setup button again till display blinks (beeps if you have that on) then press setup one more time to display "b  0.0 mV"
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on June 17, 2018, 07:38:17 pm
Quote from: Bugsyson on Today at 01:44:28 pm (https://www.eevblog.com/forum/index.php?topic=101807.msg1614049#msg1614049)
Long time reader first time poster. Received My 121gw (Thanks), and was playing around and found the burden voltage with firm ware V1.17  to be less than spot on, and totally not working with the new V1.21 firmware, only tested dc amps, (all ranges) so far.

I have never been able to make the burden voltage appear. How did you achieve that?
With "bd.OFF" in upper display, hold setup till display blinks , select "be.ON" with REL or 1ms PEAK , hold setup button again till display blinks (beeps if you have that on) then press setup one more time to display "b  0.0 mV"
There is a bug (I think) in 1.17 and 1.21 where if you go from bd.off, switch mode to bd.on, and then press setup to apply without holding for some length (1/2-1 second), then i goes in to a weird state where it says bd.on but never actually displays burden voltage. Must hold setup button for some period.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 17, 2018, 08:08:29 pm
With "bd.OFF" in upper display, hold setup till display blinks , select "be.ON" with REL or 1ms PEAK , hold setup button again till display blinks (beeps if you have that on) then press setup one more time to display "b  0.0 mV"

Thanks, got it.

I did a quick test and the voltage measurement looked reasonable. Did you remember to make a link between the VΩ terminal and the mA terminal? That link is needed to connect to the voltage measurement circuit inside the meter.

The 121GW measured 11.1/11.2 mV and the reference said 11.29 mV.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=458521;image)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 17, 2018, 09:01:35 pm
Ah yes seems I forgot to put that jumper back in after updating to 1.21. Its seems more accurate than 1.17, also noticed it defaults to what ever mode you were in last, AC,DC when turning back on, instead of always DC, or like the fluke87V AC (bad). Thanks again for catching my finger problem.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 17, 2018, 09:55:29 pm
There seems to be a problem with auto-ranging up from the 5 mA range to the 50 mA range. The meter seems to get confused and cannot lock into the reading. See video linked, where I have slowly ramped the current up from around 3 mA to around 30 mA. This is with firmware 1.21. Does anyone else see this?

https://youtu.be/AOJ8776Qg5Y
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on June 17, 2018, 11:04:43 pm
Quote from: IanB on Today at 05:55:29 pm (https://www.eevblog.com/forum/index.php?topic=101807.msg1614499#msg1614499)
There seems to be a problem with auto-ranging up from the 5 mA range to the 50 mA range. The meter seems to get confused and cannot lock into the reading. See video linked, where I have slowly ramped the current up from around 3 mA to around 30 mA. This is with firmware 1.21. Does anyone else see this?
Yes, but only when burden volt mode is on; meter tries to switch out of the 5ma range to the 50ma range but gets stuck   edit FW V1.21
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 17, 2018, 11:58:25 pm
Had the same auto ranging issue, also seem to have locked my meter up, reading 50mv all the time now (in A/mA rang), removed batteries no help, only thing that will make it go away is to put a banana plug into the mAuA jack.  Fuses good, never went above 100mA while playing around with the burden voltage. Went back to 1.17 also no help...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on June 18, 2018, 12:10:00 am
 Is there a change log for the new firmware 1.21?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on June 18, 2018, 12:26:16 am


Had the same auto ranging issue, also seem to have locked my meter up, reading 50mv all the time now (in A/mA rang), removed batteries no help, only thing that will make it go away is to put a banana plug into the mAuA jack.  Fuses good, never went above 100mA while playing around with the burden voltage. Went back to 1.17 also no help...
If software, there must be someway to do a factory reset? Settings seem to persist after pulling main and rtc batts and across firmware updates.
Is there a change log for the new firmware 1.21?
not yet afaik
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 18, 2018, 12:33:11 am
There seems to be a problem with auto-ranging up from the 5 mA range to the 50 mA range. The meter seems to get confused and cannot lock into the reading. See video linked, where I have slowly ramped the current up from around 3 mA to around 30 mA. This is with firmware 1.21. Does anyone else see this?

https://youtu.be/AOJ8776Qg5Y

Could you attempt the same test without the burden voltage measurement?
This is because when burden voltage measurement is switched on the multimeter alternates between voltage and current, this might be reseting the auto-ranging.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on June 18, 2018, 01:00:54 am
Could you attempt the same test without the burden voltage measurement?
This is because when burden voltage measurement is switched on the multimeter alternates between voltage and current, this might be reseting the auto-ranging.
I am seeing it too, but only when burden volt mode is on
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 18, 2018, 01:05:15 am
Had the same auto ranging issue, also seem to have locked my meter up, reading 50mv all the time now (in A/mA rang), removed batteries no help, only thing that will make it go away is to put a banana plug into the mAuA jack.  Fuses good, never went above 100mA while playing around with the burden voltage. Went back to 1.17 also no help...

What happens if you manually range to a different range?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 18, 2018, 01:39:23 am
Had the same auto ranging issue, also seem to have locked my meter up, reading 50mv all the time now (in A/mA rang), removed batteries no help, only thing that will make it go away is to put a banana plug into the mAuA jack.  Fuses good, never went above 100mA while playing around with the burden voltage. Went back to 1.17 also no help...

What happens if you manually range to a different range?

See video, having a read through the cal procedure, do you think it may be possible it was cal's with a lead in the mA/uA jack?
https://www.youtube.com/watch?v=NqbcHCiH5Ew (https://www.youtube.com/watch?v=NqbcHCiH5Ew)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 18, 2018, 02:13:05 am
Had the same auto ranging issue, also seem to have locked my meter up, reading 50mv all the time now (in A/mA rang), removed batteries no help, only thing that will make it go away is to put a banana plug into the mAuA jack.  Fuses good, never went above 100mA while playing around with the burden voltage. Went back to 1.17 also no help...

What happens if you manually range to a different range?

See video, having a read through the cal procedure, do you think it may be possible it was cal's with a lead in the mA/uA jack?
https://www.youtube.com/watch?v=NqbcHCiH5Ew (https://www.youtube.com/watch?v=NqbcHCiH5Ew)

Hmm, it seems that it flipped from manually ranged to auto ranged when you plugged in the jack. Can you manually range after the lead is plugged in.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 18, 2018, 02:51:38 am
Yes can manual range in both cases, every time you cycle a plug into the jack it goes into auto range.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 18, 2018, 02:54:23 am
Yes can manual range in both cases, every time you cycle a plug into the jack it goes into auto range.

It still displays 50 mA in both cases?
I suspect at some point your full scale range calibration for that range was calibrated while open circuit. Is this possible?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on June 18, 2018, 02:59:54 am
Yes can manual range in both cases, every time you cycle a plug into the jack it goes into auto range.
I can confirm this, it does reset to Auto when you cycle the plug. It’s also the reason that Auto Hold messed up with one of my tests. But I don’t know if the auto hold issues was worked on in the new firmware 1.21 since I came across a different error specifically to my meter in the 50M  \$\Omega\$ range. I sort of gave up on testing for now since this one is a hardware issue. That’s why I was wondering if a change log was published for 1.21 firmware.
Scott

Edit:
I guess I should check that auto hold and 1.21 since I did promise to delete the video once it was resolved. I guess I’ll load the firmware tomorrow if I can.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 18, 2018, 03:02:44 am
Yes can manual range in both cases, every time you cycle a plug into the jack it goes into auto range.
I can confirm this, it does reset to Auto when you cycle the plug. It’s also the reason that Auto Hold messed up with one of my tests. But I don’t know if the auto hold issues was worked on in the new firmware 1.21 since I came across a different error specifically to my meter in the 50M  \$\Omega\$ range. I sort of gave up on testing for now since this one is a hardware issue. That’s why I was wondering if a change log was published for 1.21 firmware.
Scott

Change has not been added to manual, version was released over weekend haven't gotten to that yet, at the moment working on the iOS app with the Beta testers. The key change in 1.21 was that F and C were added to the bluetooth packet.
1.20 had some changes too I'll add that to the manual ASAP.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 18, 2018, 03:39:23 am
Yes can manual range in both cases, every time you cycle a plug into the jack it goes into auto range.

It still displays 50 mA in both cases?
I suspect at some point your full scale range calibration for that range was calibrated while open circuit. Is this possible?

Have definitely not been in the cal mode, and it really thinks there is 50 extra mA, but only when plugged into the Amp Jack, readings are all good when using the mA/uA jack.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 18, 2018, 04:06:19 am
What mode should I try and calibrate? Meter reads correct in all ranges and amp jack position except in "A" jack and in 500mA range which it auto ranges to, but reads the same when manually ranged.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 18, 2018, 04:54:01 am
Yes can manual range in both cases, every time you cycle a plug into the jack it goes into auto range.

It still displays 50 mA in both cases?
I suspect at some point your full scale range calibration for that range was calibrated while open circuit. Is this possible?

Have definitely not been in the cal mode, and it really thinks there is 50 extra mA, but only when plugged into the Amp Jack, readings are all good when using the mA/uA jack.

Thats super weird but the solution seems it could be offset error calibration. I suspect somehow this did get calibrated incorrectly.
If you have something to verify the reading after this then you can try zero the offset calibration setting. The steps are in the user manual. Make sure you are in the bad range, very important.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 18, 2018, 05:07:01 am
So what range is the bad one? The 50mA or 500mA, or should I just try and cal both, best I have is an 20 year old fluke 87 ( been calibrated every year) and a 87v never cal'd. Should be alright eh...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 18, 2018, 05:14:15 am
So what range is the bad one? The 50mA or 500mA, or should I just try and cal both, best I have is an 20 year old fluke 87 ( been calibrated every year) and a 87v never cal'd. Should be alright eh...

500mA? Thats the one with the error right (getting worried)?
Only calibrate Offset.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 18, 2018, 08:22:33 am
There seems to be a problem with auto-ranging up from the 5 mA range to the 50 mA range. The meter seems to get confused and cannot lock into the reading.

Could you attempt the same test without the burden voltage measurement?
This is because when burden voltage measurement is switched on the multimeter alternates between voltage and current, this might be reseting the auto-ranging.

Yes, without the burden voltage turned on the meter jumps smoothly between the two ranges.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bugsyson on June 18, 2018, 10:58:39 pm
So what range is the bad one? The 50mA or 500mA, or should I just try and cal both, best I have is an 20 year old fluke 87 ( been calibrated every year) and a 87v never cal'd. Should be alright eh...

500mA? Thats the one with the error right (getting worried)?
Only calibrate Offset.

Left it all night and day, came home from work to do the cal and it was working?? Did the 500mA cal anyway, no noticable change in readings. Noticed I could not select 50mA range when in the calibration mode ( no leads inserted) and the same when operating normally, manual range cycles 500mA, 5A and 1000A, it's not until I insert a lead into the mA/uA jack that it will cycle through the 5mA and 50mA ranges, seems right. Still very weird it was out and reading exactly 50.00mA high, I'll let you know if it does it again. Thanks for your help and suggestions everyone.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: iainwhite on June 20, 2018, 01:48:24 pm
Still waiting for my missing 121Gw yellow shim.     5 weeks now.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: qmif on June 20, 2018, 02:32:07 pm
Hi Dave,

Today, I was very glad to receive the 121GW multimeter, but when I opened it, I found some welding troubles.
Although the functions are well tested and the accuracy is perfect, I still have some concerns.

The attached picture shows the problem I found. It looks like something is wrong with SMT process.

Please let me know if the components are not lost, I only need to welding them.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on June 20, 2018, 04:01:41 pm
It looks like there is a solder bridge on AD8436.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanJ on June 20, 2018, 05:20:21 pm
Also, U3 pin 6 shorted to pin 7....?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Gyro on June 20, 2018, 05:59:07 pm
Did those burns on the casing and L? come from careless hand soldering of J2?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on June 20, 2018, 08:19:31 pm
It looks like there is a solder bridge on AD8436.
It's probably fine as the schematic shows the two pins shorted; bridging ok in another spot https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1408213/#msg1408213 (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1408213/#msg1408213)

Also, U3 pin 6 shorted to pin 7....?
Does look kinda iffy

The attached picture shows the problem I found. It looks like something is wrong with SMT process.
Please let me know if the components are not lost, I only need to welding them.
Nothing is missing from what I can tell; unpopulated locations seems to be same as mine
Title: Re: EEVblog 121GW Multimeter Issues
Post by: baoshi on June 23, 2018, 07:16:13 am
Not sure if anyone encountered this or I just unlucky.
I found my meter reading for voltage rather unstable for some time until today I find it is actually the probe problem.

The black probe jumps around 40-500kohm and after playing for a while it is completely open circuit now.


(https://uploads.tapatalk-cdn.com/20180623/9212a7874d01c204550346d65bfe1ae9.jpg)

The probes came with the meter is really nice and I can’t find a replacement source for it. Any tips how can I get this fixed?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: iainwhite on June 23, 2018, 11:15:42 am
For info:  the probes are made by Brymen and they are available on eBay (https://www.ebay.com/itm/Brymen-Silicone-Gold-Plated-Test-Leads-Probes-for-Multimeters-CAT-IV-1000V-/171162377470), although you should be able to get yours replaced for free if they are defective.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on June 24, 2018, 10:42:26 pm
Not sure if anyone encountered this or I just unlucky.
I found my meter reading for voltage rather unstable for some time until today I find it is actually the probe problem.

The black probe jumps around 40-500kohm and after playing for a while it is completely open circuit now.


(https://uploads.tapatalk-cdn.com/20180623/9212a7874d01c204550346d65bfe1ae9.jpg)

The probes came with the meter is really nice and I can’t find a replacement source for it. Any tips how can I get this fixed?

Please PM me your Kickstarter backer number and email address and I'll organise a replacement.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on June 28, 2018, 04:32:17 pm
Mine does this with v 1.22 (and did it with 1.17 and 1.21). When set to Ohms almost every time I short the probes it will display a random reading in the MOhm range for about a second then it will start autoranging and giving me accurate readings.

It's just cosmetic but I really don't like it, because for a moment it sure looks like it thinks it's giving me an accurate reading.

Do they all do this?

So 95 % of the time the random numbers come up instead of blanking the display while changing ranges. It only occurs on the top M Ohm range and will blank as soon as the auto ranging starts.
Do others see this effect on theirs with firmware version 1.07. ?.

Yes, I see the same thing with 1.07.  When the probes are applied to a resistor the screen blanks for a moment, then shows a random bad value and pauses for a second or two with no sign that it is still working to find the correct value, then it blanks again briefly before showing the correct value with relatively rapid updates to the lest significant digits.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 28, 2018, 04:38:09 pm
Mine does this with v 1.22 (and did it with 1.17 and 1.21). When set to Ohms almost every time I short the probes it will display a random reading in the MOhm range for about a second then it will start autoranging and giving me accurate readings.

It's just cosmetic but I really don't like it, because for a moment it sure looks like it thinks it's giving me an accurate reading.

Do they all do this?


Yes, mine does this. I have been debating whether to log this as a formal issue. I think I may do so.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on June 28, 2018, 09:11:22 pm
Mine does this with v 1.22 (and did it with 1.17 and 1.21). When set to Ohms almost every time I short the probes it will display a random reading in the MOhm range for about a second then it will start autoranging and giving me accurate readings.

It's just cosmetic but I really don't like it, because for a moment it sure looks like it thinks it's giving me an accurate reading.

Do they all do this?


Yes, mine does this. I have been debating whether to log this as a formal issue. I think I may do so.


I think it's related to the fact that the update frequency is much slower in the 50 MOhm range. If the timing is such that it picks up a reading in that range as the connection is being made it hangs on it and delays the autoranging by the 50 MOhm update interval.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on June 28, 2018, 11:20:34 pm
Mine does this with v 1.22 (and did it with 1.17 and 1.21). When set to Ohms almost every time I short the probes it will display a random reading in the MOhm range for about a second then it will start autoranging and giving me accurate readings.

It's just cosmetic but I really don't like it, because for a moment it sure looks like it thinks it's giving me an accurate reading.

Do they all do this?

Yes, mine does this. I have been debating whether to log this as a formal issue. I think I may do so.

Mine with v1.22 only does this sometimes, mostly it's straight to ohms range.
I think if I tap the probes slower or with less force then it happens more, but I'd have to do controlled tests to really see that.
Are you touching the probes with your fingers?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on June 28, 2018, 11:41:02 pm
Mine with v1.22 only does this sometimes, mostly it's straight to ohms range.
I think if I tap the probes slower or with less force then it happens more, but I'd have to do controlled tests to really see that.
Are you touching the probes with your fingers?

I think it happens less often if I tap harder but it hard to tell. I've been very conscious to keep my fingers off the probes. I think it's also pretty important that the meter is stabilized on OFL with a full bar graph before making the connection in order for it to happen.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on June 29, 2018, 12:27:05 am
Mine with v1.22 only does this sometimes, mostly it's straight to ohms range.
I think if I tap the probes slower or with less force then it happens more, but I'd have to do controlled tests to really see that.
Are you touching the probes with your fingers?

No, not touching the probes with my fingers.

It happens with auto-ranging turned on, measuring a low value resistor ~100 ohms. What happens is when I touch the probe to the resistor lead the display flashes up some 10's of MΩ first, then it goes blank while ranging, then comes back with the right resistance.

A similar thing happens in reverse when I disconnect the test lead. It again shows some 10's of MΩ on the display, then goes blank, then shows OL.

It seems to me that the auto-range feature is trying to be "too quick" to latch on. It sees a momentary contact resistance, and without waiting for it to stabilize, puts it on the display.

I can avoid this happening if I am really quick touching and removing the probe, but it takes an effort to be quick enough.

This is particularly noticeable if using the auto-hold feature. It will latch onto the MΩ value instead of the expected value. In my estimation, auto-hold with resistance is only useful if you manually set the expected range first.

I can maybe make a video of this later, when I get home from work.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on June 29, 2018, 12:30:29 am
Mine still does this most times , no touching the the probe tips with fingers either !. Its largely cosmetic but I think it would have a more polished look without that random reading showing.
Just blank display briefly at the start of the auto range sequence.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: iainwhite on June 29, 2018, 02:07:52 am
Dave & David,
I got my replacement shim & knob today!  Thanks for sending these.    :-+
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Yannik on July 04, 2018, 08:26:17 pm
I have still not received the shim.

I emailed dave, david and susan multiple times about this, yet never got a reply back.

I'm pretty disappointed how this is being handled by dave..
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on July 04, 2018, 10:44:08 pm
Same experience with emails.

BTW, has anyone tried Low Z measurements? Can somebody check for me if it works for voltages below, say, 5V? It doesn't work for me even on latest firmware (but I think I destroyed calibration data, so can be my bad if it's fixed). It would be great to have a list of bugs somewhere to see what's fixed and what is not.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: iainwhite on July 05, 2018, 03:02:37 pm
has anyone tried Low Z measurements? Can somebody check for me if it works for voltages below, say, 5V?

I tried with my 121GW meter hooked to a power supply and I have to turn the voltage up to about 12V dc to get a reading in Lo-Z mode.
I can then turn the supply voltage down to about 3V before the meter stops showing a value.

Re: Shim etc.  I had to send several PMs and emails over 4-5 weeks, but I did get one!  I suspect Dave & David are buried with work and some support issues are falling to the floor.   
Given the huge success of the Kickstarter, I guess it is not surprising.
 
By the way, I made a shim from .040" plastikard (styrene sheet) while I was waiting for the official one from Dave... it worked fine, although it didn't have the hex hole that the 'official' one does.. didn't seem to matter.

Edit:  .040" is about 1mm
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 06, 2018, 04:02:38 am
Same experience with emails.

BTW, has anyone tried Low Z measurements? Can somebody check for me if it works for voltages below, say, 5V? It doesn't work for me even on latest firmware (but I think I destroyed calibration data, so can be my bad if it's fixed). It would be great to have a list of bugs somewhere to see what's fixed and what is not.

Low Z is not designed for low voltages. It is designed to eliminate ghost voltages (usually on higher voltage AC lines).
It is not expected that this range work below around 12V.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on July 07, 2018, 08:14:03 am
Low Z is not designed for low voltages. It is designed to eliminate ghost voltages (usually on higher voltage AC lines).
It is not expected that this range work below around 12V.

Got it. May it's worth mentioning in the docs for noobs like me. BTW, why is it only for high voltages? For me it would be useful for low ranges as well.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Welectron on July 10, 2018, 10:39:30 pm
I have still not received the shim.

I emailed dave, david and susan multiple times about this, yet never got a reply back.

I'm pretty disappointed how this is being handled by dave..
Please leave us a PM, we will take care of it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 12, 2018, 12:01:43 am
Another point I found was when I was doing the overnight SD card data logging.
one of the file had garbled data in the file, when I was testing for the thread in the forum.

https://www.eevblog.com/forum/testgear/new-eevblog-branded-multimeter-coming/msg1398530/#msg1398530 (https://www.eevblog.com/forum/testgear/new-eevblog-branded-multimeter-coming/msg1398530/#msg1398530)

The data is corrupted as bellow in the middle of the data.
59625,DCV,049.997,V,,,,,,,,
59626,DCV,049.997,V,,,,,,,,
59627,DCV,049.996,V,,,,,,,,
59628,DCV,049.997,V,,,,,,,,
59629,DCV,                                                                                                                                                                                        59641,DCV,050.001,V,,,,,,,,
59642,DCV,049.996,V,,,,,,,,
59643,DCV,049.996,V,,,,,,,,
59644,DCV,049.998,V,,,,,,,,
59645,DCV,049.996,V,,,,,,,,

The garbled line only happened in one line out of four files of data logging.
The other three files had no issue.

The firmware is 0.01 and the SD card is the SunDisk which is included in the meter as a factory default.

I attached the original file with zip compression to work around the file size limitation on the forum.

Hope these report help improving the meter.

Thanks for the report, good to know.
Can you upgrade your multimeter firmware to the latest then see if the error still occurs, we didn't attempt to deal with that issue some time back with a firmware upgrade.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on July 12, 2018, 01:36:19 am
My meter has been working great, but I have noticed another cosmetic issue I think is worth mentioning.

I find the red ink for the alternate modes on the labels around the selector knob really hard to read in anything but fairly bright lighting. If you're going to produce any more I think it would be a big improvement to find a hue that pops better off the charcoal.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: galleno64 on July 12, 2018, 06:55:52 am
Hello.  I'm backer #1063.  I got my 121GW meter today and was super excited.  That is until I tried to turn it on, and nothing happened...  I've checked the factory installed batteries and they're fine.  Can any one help me either get this one fixed or tell me if there's a reset button I could try?

Thanks
Title: Re: EEVblog 121GW Multimeter Issues
Post by: comeau on July 15, 2018, 04:44:07 am
Got my meter today. Worked great first time I turned it on. Then I went to monkey with it later and found that the date and time wouldn't save no matter what I did. Anyways I kept messing with the settings and next thing I know nothing works. The light started turning on and off and it switched from AC/DC reading. I think it must be the mode button. This makes sense because when I turn it on it starts the cal process and displays "Cal.1" . I took it apart to try to take a look but nothing obvious is wrong. Tried updating the firmware, no luck.

Anybody else having these issues?

Where do I go to actually report this so I can get a replacement?

Edit: After looking at some pictures I took, it seems the pull-up resistor R3 is not populated. (I'm guess the X in the diagram means do not populate so thats fine) That means they're doing the pull-up on the STM32. Any chance this may be the cause of my issues? Issue is frustratingly intermittent. Firmware U-1.22
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on July 15, 2018, 09:03:36 am
That black plastic molding for the switch is either cracked or malformed. I would ask for a replacement part for it, but I'm guessing they will replace the meter with one that works.
I really thought the quality of this UEI manufactured meter would be better than this! Having said that, my meter works fine and I'm loving it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: comeau on July 15, 2018, 03:40:42 pm
That black plastic molding for the switch is either cracked or malformed. I would ask for a replacement part for it, but I'm guessing they will replace the meter with one that works.
I really thought the quality of this UEI manufactured meter would be better than this! Having said that, my meter works fine and I'm loving it.
Are you talking about the rotary switch? It is perfectly fine, it may look worse because of the lighting.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JonM on July 15, 2018, 04:44:52 pm
Dave or David - It would be good to have a version or date for the manual on the 121gw page. Today I got the Kickstarter reminder on firmware (I already had 1.22) and manual updates. I tried to download the manual to see if it is newer than the 24 May version I have. The download was very slow (5+ minutes) so I just canceled.

Maybe the Kickstarter reminder caused a server overload? (Mostly joking about that).

In any case, if the manual version was listed I might not have needed to attempt the download.
 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 16, 2018, 12:30:34 am
Dave or David - It would be good to have a version or date for the manual on the 121gw page. Today I got the Kickstarter reminder on firmware (I already had 1.22) and manual updates. I tried to download the manual to see if it is newer than the 24 May version I have. The download was very slow (5+ minutes) so I just canceled.

Maybe the Kickstarter reminder caused a server overload? (Mostly joking about that).

In any case, if the manual version was listed I might not have needed to attempt the download.

Good idea, I'll add it now.

Edit : Added, your manual is out of date.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 16, 2018, 12:40:02 am
Got my meter today. Worked great first time I turned it on. Then I went to monkey with it later and found that the date and time wouldn't save no matter what I did. Anyways I kept messing with the settings and next thing I know nothing works. The light started turning on and off and it switched from AC/DC reading. I think it must be the mode button. This makes sense because when I turn it on it starts the cal process and displays "Cal.1" . I took it apart to try to take a look but nothing obvious is wrong. Tried updating the firmware, no luck.

Anybody else having these issues?

Where do I go to actually report this so I can get a replacement?

Edit: After looking at some pictures I took, it seems the pull-up resistor R3 is not populated. (I'm guess the X in the diagram means do not populate so thats fine) That means they're doing the pull-up on the STM32. Any chance this may be the cause of my issues? Issue is frustratingly intermittent. Firmware U-1.22

The solder mask, center left is damaged, this is a manufacturing defect, this unit needs to be replaced.
Please PM me your backer details, email address for correspondence and address (if it changed).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: wraper on July 16, 2018, 12:50:46 am
The solder mask, center left is damaged, this is a manufacturing defect, this unit needs to be replaced.
Please PM me your backer details, email address for correspondence and address (if it changed).
I don't see any solder resist damage  :-//. However C23 is soldered on footprint of larger size and looks like tombstoned. Although it might be just lighting.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChunkyPastaSauce on July 16, 2018, 01:05:06 am
The solder mask, center left is damaged, this is a manufacturing defect, this unit needs to be replaced.
Please PM me your backer details, email address for correspondence and address (if it changed).
I don't see any solder resist damage  :-//. However C23 is soldered on footprint of larger size and looks like tombstoned. Although it might be just lighting.

Circled areas:  https://imgur.com/a/dAZVSSC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: wraper on July 16, 2018, 01:05:55 am
The solder mask, center left is damaged, this is a manufacturing defect, this unit needs to be replaced.
Please PM me your backer details, email address for correspondence and address (if it changed).
I don't see any solder resist damage  :-//. However C23 is soldered on footprint of larger size and looks like tombstoned. Although it might be just lighting.

Circled areas:  https://imgur.com/a/dAZVSSC
That's light reflection, not damaged solder resist.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 16, 2018, 01:07:06 am
Hello.  I'm backer #1063.  I got my 121GW meter today and was super excited.  That is until I tried to turn it on, and nothing happened...  I've checked the factory installed batteries and they're fine.  Can any one help me either get this one fixed or tell me if there's a reset button I could try?

Thanks

Hello.  I'm backer #1063.  I got my 121GW meter today and was super excited.  That is until I tried to turn it on, and nothing happened...  I've checked the factory installed batteries and they're fine.  Can any one help me either get this one fixed or tell me if there's a reset button I could try?

Thanks

Hello, are you able to open up the meter and take photos similar to comeau? A replacement unit is on the table but it may be something simple, would be faster to fix it.
I would attempt to remove the plastic rotary switch and make sure that the contacts are seated correctly, a photo would be very helpful
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 16, 2018, 01:16:11 am
The solder mask, center left is damaged, this is a manufacturing defect, this unit needs to be replaced.
Please PM me your backer details, email address for correspondence and address (if it changed).
I don't see any solder resist damage  :-//. However C23 is soldered on footprint of larger size and looks like tombstoned. Although it might be just lighting.

Circled areas:  https://imgur.com/a/dAZVSSC
That's light reflection, not damaged solder resist.

I think we should reserve that judgment to comeau, he will have a definitive answer to that.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: comeau on July 16, 2018, 06:19:20 pm
I think we should reserve that judgment to comeau, he will have a definitive answer to that.

Can confirm solder mask appears intact, just the lighting. Sorry, it is difficult to get good lighting.

I don't see any solder resist damage  :-//. However C23 is soldered on footprint of larger size and looks like tombstoned. Although it might be just lighting.

C23 doesn't look pretty, but it appears to be in good contact.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on July 16, 2018, 09:59:11 pm
Dave or David - It would be good to have a version or date for the manual on the 121gw page. Today I got the Kickstarter reminder on firmware (I already had 1.22) and manual updates. I tried to download the manual to see if it is newer than the 24 May version I have. The download was very slow (5+ minutes) so I just canceled.

Maybe the Kickstarter reminder caused a server overload? (Mostly joking about that).

In any case, if the manual version was listed I might not have needed to attempt the download.
Good idea, I'll add it now.

Edit : Added, your manual is out of date.
FYI the July 9 Manual link provides a Manual with 25 June on the front page.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on July 17, 2018, 12:55:39 am
Haven't seen quite this issue posted.  Appears the auto range doesn't work when the meter's batterys are at ~5.2V and try to measure something around 6V.  It is supposed to work with the batteries as low as 4.2

https://youtu.be/CXcKBs3Twv8 (https://youtu.be/CXcKBs3Twv8)

Worked ok with the measured batteries in the meter.  Will try some more experiments with different voltages.
Edit: I probably switched range from AUTO DC to AUTO DC+AC.  See further posts next page.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 17, 2018, 01:12:13 am
Dave or David - It would be good to have a version or date for the manual on the 121gw page. Today I got the Kickstarter reminder on firmware (I already had 1.22) and manual updates. I tried to download the manual to see if it is newer than the 24 May version I have. The download was very slow (5+ minutes) so I just canceled.

Maybe the Kickstarter reminder caused a server overload? (Mostly joking about that).

In any case, if the manual version was listed I might not have needed to attempt the download.
Good idea, I'll add it now.

Edit : Added, your manual is out of date.
FYI the July 9 Manual link provides a Manual with 25 June on the front page.
Fixed, thanks
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on July 17, 2018, 01:31:25 am

That video link comes up unavailable.

I think I fixed it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: techy101 on July 17, 2018, 02:47:53 am
I see some people commented on this earlier, but mine showed up and I'm a little concerned about the viewing angles on the screen. I had to adjust the contrast up to the max value but it didn't help with the angle. Looking straight on, or sitting on the desk propped up on the tilting bale the display looks pretty hazy. This is accentuated if you're looking down at it. You really have to be looking at it from a very shallow angle, more or less looking up at the screen, to make it look crisp. In person it's much more pronounced than the pictures, but they were the best I could get and should get the point across. These pictures are with the backlight on, but there is no difference when it's off.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on July 17, 2018, 03:55:49 am
Haven't seen quite this issue posted.  Appears the auto range doesn't work when the meter's batterys are at ~5.2V and try to measure something around 6V.  It is supposed to work with the batteries as low as 4.2

https://youtu.be/CXcKBs3Twv8 (https://youtu.be/CXcKBs3Twv8)

Worked ok with the measured batteries in the meter.  Will try some more experiments with different voltages.
After further testing it appears this auto ranging issue only happens in DC+AC mode and is completely unrelated to meter battery voltage.  I tested in AUTO DC with meter battery voltage down to 4.0V and auto ranging and indicated voltage was the same as with 6.2V meter batteries.  The low battery indicator came on at exactly 4.2V as the manual says.

In AUTO DC+AC regardless of meter batteries at 4V or 6.2V auto ranging hunts indefinitely when measuring around 6V.

In conclusion I'm happy again.  I can safely use NiMH batteries and I almost never use AUTO DC+AC (TRUE RMS) for DC anyway.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on July 17, 2018, 06:44:07 am
But is it an issue or is it a limitation of the specific mode?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: jolshefsky on July 17, 2018, 09:22:56 pm
I got my meter the other day and I have to say it is quite amazingly feature-packed! I'm quite impressed overall and am pleased to have been able to help fund its creation.

Alas, I hate to jump right into issues, but, well that's what this post is about. I'm going to focus on user interface for a bit as I shouldn't be spending this much time explaining ...

The first thing I'd like to see is a proper bug database. I have done zero research on this (in other words, sorry if you already looked into it and it's not feasible), but I hope you'd all agree that a 14-page (and growing) list of bugs is not ideal. I was hoping to be able to search for what's already reported, being worked on, and if it's fixed (or won't ever be fixed).

I'd like to echo darik's comment about the red on the silkscreen labels around the dial being hard-to-read. I'll go further and talk about the whole appearance... The labels on the probe connections seem fine to me. The 8 top buttons need some rethinking in my opinion. RANGE/15V-▶|- and HOLD/AutoHOLD buttons access the alternate functions—written above—by extra presses but the RELΔ/▲/<1KHz 1ms PEAK/▼/BT buttons access their alternate-functions—written below—by press-and-hold.

If I were to vote, I'd say to keep "RANGE", "HOLD", "MODE", "MIN/MAX", and "SETUP" labels. I'd change "RELΔ" to "REL•⬆" as Δ is redundant—or "Δ/⬆" if you want to be all symbolic. I'd change "1ms PEAK" to "PEAK•⬇". In both cases, I'd move the alternate functions above the buttons. Change the "MEM" button to "log→SD" so I'm not thinking about a memory store on a calculator.

The setup functions are kind of a mess. Most need you to hold SETUP to confirm a setting which is okay, but then there's the unique ID selection where you push SETUP once to advance to the next digit, but the very similar date/time settings need a press-and-hold. (On a side note, my meter arrived set to the date 2073 ... I guess it's very advanced. I had to check the manual to realize that's the year.)

OK, I'll stop now ... this is getting way to involved and I've invested a solid 40 minutes already getting those arrow characters in there ...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on July 18, 2018, 07:17:11 am
I can maintain issues database, if needed. Just not sure how. In my opinion there are not that many issues, so a simple spreadsheet (google drive?) or even a post here would be suitable to do the job.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanJ on July 18, 2018, 12:33:03 pm
I see some people commented on this earlier, but mine showed up and I'm a little concerned about the viewing angles on the screen. I had to adjust the contrast up to the max value but it didn't help with the angle. Looking straight on, or sitting on the desk propped up on the tilting bale the display looks pretty hazy. This is accentuated if you're looking down at it. You really have to be looking at it from a very shallow angle, more or less looking up at the screen, to make it look crisp. In person it's much more pronounced than the pictures, but they were the best I could get and should get the point across. These pictures are with the backlight on, but there is no difference when it's off.

Hi,

Standing at my 94cm high workbench with the meter 40cm in from front edge the LCD is a little blurry. In effect I am looking at it very slightly tilted forward from the face on position......but to be fair my Fluke's are the same. For me, I might modify the tilting bale so the meter sits a little flatter.

I also think the transparent window should be slightly bigger or at the very least pull the segments (temp display etc) down a few mm in order the tops are not chopped off......but better the window is enlarged to allow more natural light onto the LCD and to minimize the shadows.

Other than slower than I would have likes auto-ranging in AUTO mode it's a great DMM for the price......and at the mo I'm trying to use it as my go-to meter.

Ian.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mmagin on July 18, 2018, 07:51:12 pm
WRT the ohms autoranging situation, the thing that kind of annoys me, and you can see it in Dave's video; https://www.youtube.com/watch?v=uUCQuIp_hzU&t=72s (https://www.youtube.com/watch?v=uUCQuIp_hzU&t=72s) is that it seems to always display a spurious value in the 5-50 Mohm range first, even though the resistance is much smaller, before blanking the display as it autoranges.  My Fluke 179 doesn't display a false reading like that while autoranging (haven't yet had a change to try out my various bench meters).
 
Nice meter otherwise though!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on July 19, 2018, 01:26:21 am
WRT the ohms autoranging situation, the thing that kind of annoys me, and you can see it in Dave's video; https://www.youtube.com/watch?v=uUCQuIp_hzU&t=72s (https://www.youtube.com/watch?v=uUCQuIp_hzU&t=72s) is that it seems to always display a spurious value in the 5-50 Mohm range first, even though the resistance is much smaller, before blanking the display as it autoranges.  My Fluke 179 doesn't display a false reading like that while autoranging (haven't yet had a change to try out my various bench meters).
 
Nice meter otherwise though!
Others have noted this above and yeah its something that should be fixed for a more 'polished' feel to the meter.
And as been remarked by others the red ink is not a good choice on the range switch etc. very hard for my aging eyes to see what is printed next to the white. Of course I will live with it but for future units it would be good idea to try alternate colors with better contrast say yellow or orange etc, as used by Keysight and Fluke. No issues visually for me quickly knowing whats printed on the meters I have from these manufacturers.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 20, 2018, 10:59:39 pm
Auto-range broken on V1.22

At work I'm measuring resistance and the auto-range cycles for ever. If I remember correctly there was an issue with this in the past and it was fixed with firmware change

In my case there is a capacitor that gets charged when measuring resistance. I did the same test with a Fluke in auto-range with no problem

Any comments ?

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 20, 2018, 11:14:45 pm
More issues with auto-range

I have a 27.8K resistor connected to the meter.

- When measuring the resistance in auto-range, the values displayed are all over the places, the range is changing and the decimal point is changin
- Then I record the values using the MEM function, when I read back the values they are correct 27.8K but...
- When MEM is showing the values, the decimal point moves, this decimal point is moved by the autorange getting crazy and running on the background probablly

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 20, 2018, 11:32:06 pm
Another issue with V1.22

When I measure the mains frequency, on the Frequency range, the temperature measurement goes crazy and after a while it stabilizes.

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on July 21, 2018, 09:45:55 am
Firmware V1.22: 10VDC on DC+AC confuses the autorange and it will not show a value, instead it ranges up/down all the time.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on July 21, 2018, 11:53:01 am
Firmware V1.22: mA range with burden voltage display on: Changing current from 5mA to 50mA (or 1mA to 10mA) will not change to 50mA range
Similar problem in uA and A.

Manual is not clear, the selection is: Hold SETUP, press arrow, hold SETUP, press SETUP
Changing range will clear the burden voltage setting.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on July 21, 2018, 03:13:54 pm
Firmware v1.22: Leaving 1ms peak capture will always change to auto range (min/max returns to previous setting)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on July 21, 2018, 03:33:36 pm
Firmware v1.22: High DC voltage can block for AC reading: 320VDC+120VAC -> Display shows below 1VAC sometimes.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: AdamHi on July 22, 2018, 10:56:07 pm
Inaccurate on DC mA measures in the Auto and 5 mA ranges when reading 1.00 mA DC.

Got my meter this week, updated to U 1.22. Batteries at 6.0 V. Burden voltage off.

I wanted to confirm the meter was at least close to spec using my DMMCheck Plus.

Everything ok, except having significant issues with the 1.00 mA DC standard. On Auto DC mA, i get readings ranging from 0.46mA, to nearly there at 0.953 (every time I change back to Auto, i get a completely different reading ). If i change range to 5mA range, I get the similar varying and inaccurate readings. When I change down to the 50 mA range (the one showing 3 places after decimal), it's fine at 0.998, and consistent every time.

It is consistently fine on the 1mA AC standard.  Voltage and resistance readings all fine. It's just the mA readings on Auto or 5 mA DC range.  I'm baffled.

Do I have a lemon  :scared:?

--adam

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 23, 2018, 12:43:01 am
Inaccurate on DC mA measures in the Auto and 5 mA ranges when reading 1.00 mA DC.

Got my meter this week, updated to U 1.22. Batteries at 6.0 V. Burden voltage off.

I wanted to confirm the meter was at least close to spec using my DMMCheck Plus.

Everything ok, except having significant issues with the 1.00 mA DC standard. On Auto DC mA, i get readings ranging from 0.46mA, to nearly there at 0.953 (every time I change back to Auto, i get a completely different reading ). If i change range to 5mA range, I get the similar varying and inaccurate readings. When I change down to the 50 mA range (the one showing 3 places after decimal), it's fine at 0.998, and consistent every time.

It is consistently fine on the 1mA AC standard.  Voltage and resistance readings all fine. It's just the mA readings on Auto or 5 mA DC range.  I'm baffled.

Do I have a lemon  :scared:?

--adam

Perhaps a lemon lets see.
1. Can you take a photo/s of your setup, with enough angles to fully describe the test setup?
2. Can you place a second meter in series with the measurement to confirm the current is what it claims at the moment it is tested?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: AdamHi on July 23, 2018, 05:44:25 am
. . . .
Everything ok, except having significant issues with the 1.00 mA DC standard. On Auto DC mA, i get readings ranging from 0.46mA, to nearly there at 0.953 (every time I change back to Auto, i get a completely different reading ). If i change range to 5mA range, I get the similar varying and inaccurate readings. When I change down to the 50 mA range (the one showing 3 places after decimal), it's fine at 0.998, and consistent every time.

It is consistently fine on the 1mA AC standard.  Voltage and resistance readings all fine. It's just the mA readings on Auto or 5 mA DC range.  I'm baffled.

Do I have a lemon  :scared:?

--adam

Perhaps a lemon lets see.
1. Can you take a photo/s of your setup, with enough angles to fully describe the test setup?
2. Can you place a second meter in series with the measurement to confirm the current is what it claims at the moment it is tested?
Here are several pictures:
1) Overview - Connections visible . From DMMCheck --> 121GW --> Amprobe AM-270
2) 0.84  , 
3) 0.94,   
4) 0.98  : mA readings all on either Auto or 5 mA DC range.
5) 50mA Range : on 50mA range - good read.
6) AC Range : (with 1mA AC standard) - good read.
7) DMMCheck : How the DMMCheck is set

Let me know if you need more detailed photos. I did notice during the photo shoot that on the problem range (5 mA DC), the meter was sensitive to lead movement - but the other meter stayed rock solid, and so did the 121GW on the 50 mA range. And it wasn't a faulty lead.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Frank_22 on July 23, 2018, 02:19:53 pm
Hello! Maybe somebody knows how this multimeter measures weak signals. We must measure a signal in a range 10-30 millivolts. Is it possible to do with this multimeter?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 23, 2018, 06:06:56 pm
Fw. 1.22

Based on what I have seen on my problem when measuring resistance with a capacitor on the circuit:

- Using manual range, it will take longer time to measure the resistance due the capacitor being charged
- Because it will take longer time to measure the resistance, now the auto-range will not work, because the auto-range was modified to make it to work faster.

But my Fluke will work fine on auto-range


This auto-range feature is giving some headaches

David
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 23, 2018, 08:58:56 pm
Dave on his videos complains and makes fun of products not working and gives them the tumbs down.

Well, now he needs to fix his 121GW that does not work properly.

My concerns with fw. 1.22

- When measure resistance with some capacitance the auto-range loops forever, Fluke does not do that
- When measuring frequency on mains, the temperature readings go crazy
- When shorting the leads, the buzzer is missed most of the times
- When reading the memory values, and the meter is on auto-range loop (wrong) the decimal point on the memory values shown moves

More to come ? Hopefully not

David



Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on July 23, 2018, 09:16:26 pm
Auto-Hold issues (FW 1.22), I notice there already are some reports on this, but anyway.

I can't get Auto-Hold to work properly in Resistance mode. Measuring resistance in it self works fine but using Auto-Hold I get totally wrong values. It seems to be related to Auto-range because selecting a manual range Auto-Hold seems to work (within that range), but in Auto-Range my 121GW will beep as if it captured the reading but the value it displays is totally wrong.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: tsman on July 23, 2018, 09:23:59 pm
The default contrast setting on mine (4) was way too low though, I have mine set at max (7) and do wish it would go a little higher.
Same with mine. The default 4 was far too low if viewed straight on. The max 7 is about 90% of the way there but 1 more notch would have made it perfect. There seems to be significant variation in the LCDs if some are okay with 4.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: techy101 on July 23, 2018, 09:25:40 pm
The default contrast setting on mine (4) was way too low though, I have mine set at max (7) and do wish it would go a little higher.
Same with mine. The default 4 was far too low if viewed straight on. The max 7 is about 90% of the way there but 1 more notch would have made it perfect. There seems to be significant variation in the LCDs if some are okay with 4.

Mine also has to be at full and I still have to have it nearly laying flat on the desk to see it. Straight on it's very dim and fuzzy.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on July 23, 2018, 09:28:17 pm
The default contrast setting on mine (4) was way too low though, I have mine set at max (7) and do wish it would go a little higher.
Same with mine. The default 4 was far too low if viewed straight on. The max 7 is about 90% of the way there but 1 more notch would have made it perfect. There seems to be significant variation in the LCDs if some are okay with 4.

I think there must be, I have mine set to 6 and it's pretty much black straight on. It's also at its darkest looking from maybe 15° below straight on, not way low like it seems to be for some people here.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 23, 2018, 10:17:19 pm
Voltage measurement DC + AC  Auto-range loops forever

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on July 23, 2018, 10:22:22 pm
Auto-Hold issues (FW 1.22), I notice there already are some reports on this, but anyway.

I can't get Auto-Hold to work properly in Resistance mode. Measuring resistance in it self works fine but using Auto-Hold I get totally wrong values. It seems to be related to Auto-range because selecting a manual range Auto-Hold seems to work (within that range), but in Auto-Range my 121GW will beep as if it captured the reading but the value it displays is totally wrong.

This I also observe. My impression is that it was working better until people complained it was too slow. In the attempts to speed it up it seems to have got broken. I would prefer if it went back to being slow and reliable.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on July 23, 2018, 10:39:51 pm
Auto-Hold issues (FW 1.22), I notice there already are some reports on this, but anyway.

I can't get Auto-Hold to work properly in Resistance mode. Measuring resistance in it self works fine but using Auto-Hold I get totally wrong values. It seems to be related to Auto-range because selecting a manual range Auto-Hold seems to work (within that range), but in Auto-Range my 121GW will beep as if it captured the reading but the value it displays is totally wrong.

This I also observe. My impression is that it was working better until people complained it was too slow. In the attempts to speed it up it seems to have got broken. I would prefer if it went back to being slow and reliable.

It would be interesting to know if it ever were working properly i.e. in the earliest firmware. It seems very bad if Auto-Hold was broken trying to speed the meter up, the meter isn't exactly 'fast' even with FW 1.22.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: tsman on July 24, 2018, 12:05:28 am
There is fluff and dirt under the LCD :o It is under the plastic shield so it doesn't look like it is possible to get in there easily to clean it. Turning on the backlight shows up the big speck of dirt. Can't unsee it now! :scared:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 24, 2018, 01:44:36 am
Voltage measurement DC + AC  Auto-range loops forever

David DLC

Regarding this issue and the resistance/capacitance issue do you have some specific values that you have found produce the auto ranging loop. I have experienced that loop before but cannot get it to happen under controlled conditions.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tsman on July 24, 2018, 01:59:14 am
A few times now, I've touched the screen with the meter off and a few random segments turned on briefly. Static electricity?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 24, 2018, 03:22:49 am
Voltage measurement DC + AC  Auto-range loops forever

David DLC

Regarding this issue and the resistance/capacitance issue do you have some specific values that you have found produce the auto ranging loop. I have experienced that loop before but cannot get it to happen under controlled conditions.

You can try these.  Looks like others are seeing it now as well.
https://youtu.be/RgzBC40gCoY?list=PLZSS2ajxhiQDBDdtQNjVnGxShaVQ3nUMY

Thanks joe! That seems to reproduce, has anyone been able to reproduce the resistance auto-ranging bug, it seems difficult to isolate.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Muttley Snickers on July 24, 2018, 05:08:02 am
You can try these.  Looks like others are seeing it now as well.
https://youtu.be/RgzBC40gCoY?list=PLZSS2ajxhiQDBDdtQNjVnGxShaVQ3nUMY

I haven't been following this meters progress nor read all of the associated threads and I don't know if this has been mentioned previously so please forgive me if it has. I am aware that the meter Joe Smith was testing in the video linked above was a pre-production model and that the current version may perform in an entirely different manner.

Anyway, at 2:59 in the video with approximately 20 volts applied and whilst manually cycling through the ranges the meter displayed 20.62 volts then 206.2 volts, the applied voltage was exactly the same but the decimal is in the wrong location, can somebody else please confirm what I saw and if it has been mentioned already then I will delete this post.

Edit: Added images below for reference.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 24, 2018, 06:12:42 am
I haven't been following this meters progress nor read all of the associated threads and I don't know if this has been mentioned previously so please forgive me if it has. I am aware that the meter Joe Smith was testing in the video linked above was a pre-production model and that the current version may perform in an entirely different manner.

Anyway, at 2:59 in the video with approximately 20 volts applied and whilst manually cycling through the ranges the meter displayed 20.62 volts then 206.2 volts, the applied voltage was exactly the same but the decimal is in the wrong location, can somebody else please confirm what I saw and if it has been mentioned already then I will delete this post.

I imagine they know it's a pre-production meter.   

I am not aware of a way to display the firmware version.  I have never attempted to update this one as there is no mention of a way to back it up.  It would be prior to 1.00 as there appears to be no support for exporting  the calibration data.  It does however give them one more data point if they suspect the firmware.

Newer versions of the firmware show the version when the multimeter boots.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 24, 2018, 09:47:22 am
Hi Seppy,

I have finally summarized the errors / gaps of the latest manual, 9th July,  see doc file.


During these investigations, I found a malfunction of the DC burden voltage item.
When I initially toggled to bd.on in any DC A range, the burden voltage display wouldn't appear, even not on the mobile via BT.
Only after I once engaged bd.on in AC A mode, it directly functioned there, and afterwards, also in DC A mode, permanently.
Seems to be a missing initialization flag in the 1-22 firmware.

Frank

PS: I'm still investigating on the spurious instability of the 5M and 50M ranges..
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on July 24, 2018, 01:42:12 pm
For the auto hold when measuring resistance,  I had tried various values from 10ohms to 10M and it seems to work as I would expect.

Thanks for checking, if I remember correctly your pre-production 121gw is about the same in Auto ranging speed as FW 1.22 so the speedup work might not be that related to Auto Hold not working anymore.

I've done some further testing on FW 1.22 and what's strange is that it seems to select the correct range as I can see Mohms, Kohms and decimal point changes but the value it displays is totally wrong.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 24, 2018, 04:59:38 pm
A few times now, I've touched the screen with the meter off and a few random segments turned on briefly. Static electricity?

My problem is with some resistances and a capacitor connected. It is not a simple RC and unfortunately I cannot share the schematics.

But it takes time for the capacitor to charge and then to get the resistance value, the circuit is slow.

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on July 24, 2018, 05:36:09 pm
Hi Seppy,

I have finally summarized the errors / gaps of the latest manual, 9th July,  see doc file.
...
Frank

Frank, thanks for the detailed look, everybody complains about poorly written manuals but nobody helps to fix. :-//
Glad you weren't my technical writing teacher back in the day.

Another minor quibble:  page 61 Multimeter ID  The ID entered appears to be appended to another mystery number in the log files.  Mine is 1708
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 24, 2018, 11:11:57 pm
Fw. 1.22

I think auto-range should not mess with the decimal point, just get the correct range (without moving the decimal point) and just show the final value.

There is an issue when the DMM is in the infinite auto-range loop and you read the memory values, the decimal point moves because the auto-range is handling it

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 25, 2018, 01:53:17 am
Hi Seppy,

I have finally summarized the errors / gaps of the latest manual, 9th July,  see doc file.


During these investigations, I found a malfunction of the DC burden voltage item.
When I initially toggled to bd.on in any DC A range, the burden voltage display wouldn't appear, even not on the mobile via BT.
Only after I once engaged bd.on in AC A mode, it directly functioned there, and afterwards, also in DC A mode, permanently.
Seems to be a missing initialization flag in the 1-22 firmware.

Frank

PS: I'm still investigating on the spurious instability of the 5M and 50M ranges..

Awesome, thanks for that, I have made suggested changes (well most of them).
I'll upload the new version soon, but we are expecting some new firmware so I'll release the new manual with that so the new firmware changes are in the up-to-date manual.

- I haven't added the period specifications yet, I want to make sure there wasn't a reason I didn't put it there in the first place
  (likely there was something ambiguous and in the rush I didn't note what it was).
- Haven't made RMS to pp change yet, and I won't until I figure out why it was RMS in the first place (although I agree it makes more sense to have pp).
- For frequency: I don't think offset is calibrated, only gain.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on July 25, 2018, 02:46:10 am
A few times now, I've touched the screen with the meter off and a few random segments turned on briefly. Static electricity?
I noticed that when I took off the protector. I put it back on and reduced it again to confirm and yes, the LCD does show to ‘illuminate’ certain elements with a discharge like that.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 25, 2018, 03:29:53 am

- For frequency: I don't think offset is calibrated, only gain.

Of course you're right.. I was completely confused, that Frequency even showed up in this list, and by the term 'Factory Calibrated'

Anyhow, as LowZ does not require any calibration at all, i.e. also no offset calibration, you simply might take both modes out this list.

And it's not clear from the table on page 69, whether capacitance needs any Offset alignment.

Thanks for all your effort,
Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: thals on July 25, 2018, 07:06:36 am
+1 for proper bug tracking system, it's not easy to look for already reported bugs in 14 16 pages of thread.

FW 1.22:
Resistance Measurement, Auto Range: If measuring a resistor while the meter is auto ranging (= disconnect probe tip shortly in resistance measurement), an intermittent wrong measurement (near 0 Ohm) is shown. This happens only in approx. 20% of the measurements.
E.g. (6R8 Resistor): Auto Range -> 0.0002 -> Auto Range -> 6.801

Very rarely (5%) it shows a measurement value with less digits, resets to zero and ranges again.
E.g. (6R8 Resistor): Auto Range -> 6.80 -> 0.00 -> Auto Range -> 6.801
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on July 25, 2018, 08:14:10 am
https://blog.github.com/2009-04-15-github-issue-tracker/ (https://blog.github.com/2009-04-15-github-issue-tracker/)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on July 25, 2018, 10:45:59 am
Who is addressing the bugs? The maker?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: npelov on July 25, 2018, 10:15:23 pm
Is there any indication thatmultimeter is in peak-detect mode? Manual doesn't sayanything about peak detect. In which modes/ranges it is available? Howdo I know if it's turned on or off?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: npelov on July 25, 2018, 10:30:08 pm
The braymen probes are nice but not perfect. So eone has tightened the banana addons to mine a bit too hard. When I tried to remove it one of them was rotating without unscrewing. Which means that there is no flat spot or anything preventing the metal pin from rotating and twisting the cable inside. That could lead to problems.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on July 26, 2018, 12:40:50 am

- For frequency: I don't think offset is calibrated, only gain.

Of course you're right.. I was completely confused, that Frequency even showed up in this list, and by the term 'Factory Calibrated'

Anyhow, as LowZ does not require any calibration at all, i.e. also no offset calibration, you simply might take both modes out this list.

And it's not clear from the table on page 69, whether capacitance needs any Offset alignment.

Thanks for all your effort,
Frank

Oh your right, I've removed LowZ, I've also removed capacitance until I can figure out what R1 is...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on July 26, 2018, 06:52:41 am
The spring for the battery terminal are to long. No need for it.

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on July 26, 2018, 08:25:39 am
The 50M \$\Omega\$ Range issue is also reported in a review:

https://www.eevblog.com/product/121gw/#tab-reviews (https://www.eevblog.com/product/121gw/#tab-reviews)

Quote
Kellee Crisafulli – July 21, 2018

2018-07-20, I was pleased to received my 121GW a couple days ago, first reaction is very cool 🙂
I plugged it into a Tektronix 515A meter calibrator to run a fast out of the box accuracy check.
Tested AC volts at 400hz, 1KHz, 50KHz, 1V to 100V, appeared to be within stated accuracy.
Tested DC volts 25uV to 100.0V and appeared to be within stated accuracy.
Test Ohms from 0 to 1MEG appeared to work OK.
10 Meg Ohms looks a bit “wonky” reading ~9.7 Mega Ohms +- 200K depending how I hold the cable, position of my hands, and if I blink or not (kidding). Other handhelds and my bench meter indicate very close to 10.00 Meg no matter which way I hold the cable.
As Dave might say “That’s a fine how do you do”, seriously something on the 10M scale appears to have a noise issue, not a show stopper but interesting…
That’s all the testing I have done so far.

https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1687298/#msg1687298 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1687298/#msg1687298)
Dr. Frank and IanB you are not alone.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Medo on July 27, 2018, 02:52:53 am
Any chance of detecting lower than 12V on Low Z mode in the future firmware upgrade?

Other multimeters I've tried this mode with (Agilent U1232A, Fluke 117, and Brymen BM235), work regardless of voltage. 121GW, if I use LowZ with under 10ish volts, just shows 0.00 (tested with alkaline and LiIon battery). At first I thought this was a mechanical failure but then I noticed here that other people have the same issue.

I find that measuring batteries with some load (i.e. in low Z mode) - especially 2032 and smaller ones - actually more realistically shows their state while measuring them with high impedance often results in normal 3V reading even for the ones dying.

PS: Tested with firmware 1.21
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on July 27, 2018, 06:59:56 am
AC+DC Mode while measuring 230VAC Mains do not shows anything to me: autorange goes in loop?

 :-//
Title: Re: EEVblog 121GW Multimeter Issues
Post by: npelov on July 27, 2018, 07:46:01 am
Is the 50MOhm range slowing down the resistance measurement? Maybe it should be removed from manual range and should only be accessible via manual ranging.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 27, 2018, 08:52:24 am
Hello,

I finally analysed the Ohm function.
The 500k and 5M ranges are especially unstable, sometimes giving an unreadable display.
But sometimes, also the 50 Ohm range is unstable on the last two digits, but may stabilize after some 'warmup'.

The 50M range sampling rate is a bit slower, and therefore delivers more stable readings, which makes sense for these high values.
Anyhow, it seems that in this range, there also exist some disturbance, which cause a virtually static shift of the reading (gain error).

I have digitized the probing current of the 121GW by means of my 34465A.
All currents from 470µA down to 20nA, were absolutely stable apart from some amplifier noise.

When I digitized the voltage across the D.U.T. resistor, I encountered a huge 50Hz signal, 100mVpp @ 700mV DC, which might be picked up by the mains environment (Germany = 50Hz). The 121GW seemed to be extremely sensitive to that 50Hz pickup, although its A/D should suppress the mains frequencies of either 50Hz, or 60Hz.

I have the suspicion, that the sampling rate especially in Ohms mode is not selected correctly, for 60Hz only, so that this would be stable in U.S. or other countries with 60Hz mains frequency, but unstable here in Europe.

Do other owners here in EU see that same effect? 

How can I check inside the guts of the 121GW, which mains frequencies are suppressed?

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on July 27, 2018, 08:59:34 am
Interesting,

Can you repeat the experiment with the R DUT in a closed box and by using coax BNC cables to the 121GW, surely you have some of those adapters:

(https://showmecables-static.scdn3.secure.raxcdn.com/media/catalog/product/cache/c687aa7517cf01e65c009f6943c2b1e9/b/n/bnc-female-to-dual-banana-plug-adapter-988bnc-1.jpg)

Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on July 27, 2018, 09:28:19 am
In my setup it is stable reading 100kOhm and 10Mohm, but jumps up to 1% up/down on 1Mohm:

(http://lygte-info.dk/pic/DMM-Other/EEVBlog%20121GW/DSC_0495.jpg)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on July 27, 2018, 10:37:13 am
AC+DC Mode while measuring 230VAC Mains do not shows anything to me: autorange goes in loop?

 :-//

True. But if you allow AC+DC to settle to zero and then measure, it works.

Do you know if in AC+DC mode it can display the AC or DC component in the second display?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 27, 2018, 11:00:31 am
Interesting,

Can you repeat the experiment with the R DUT in a closed box and by using coax BNC cables to the 121GW, surely you have some of those adapters:


I could, but I won't, for logical reasons.

It is crystal clear for me, that the 121GW is susceptible to 50Hz, as the variation is smaller (but well visible), when short cables are attached, but it goes wild, when I additionally connect longer cables towards the 34465A, and latter records that high 50Hz hum.


I also encounter the same behavior, and same magnitude, like HKJ, i.e 100k and 10M relatively stable, but 1M is jumping on the 1% scale.. my BM869 in comparison is rock solid in all these ranges.

Perhaps others might also confirm that finding...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on July 27, 2018, 11:44:23 am
Got it, yes it's logical. The 50-60Hz will always be present picked up by the cables in a normal DMM curstomer user case.
With BNC we could reduce the problem but it's not the solution.

I looked up the frontend:
http://www.hycontek.com/wp-content/uploads/DS-HY3131_EN.pdf (http://www.hycontek.com/wp-content/uploads/DS-HY3131_EN.pdf)

It's not very easy to understand, I suppose you should play with the pre-filter to get rid of the 50Hz noise and generate a clean AD1FP and a AD1FN signals.
Between FTP and FTN there is a 27nF C21.

It's getting compicated.

Maybe a simple aluminum foil around the 121GW case? Meh... nevermind.

Do we have the BM869 schematics? A simple frontend comparison could help...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 27, 2018, 11:52:27 am
I don't remember the pre-production meter being all that unstable. 




Don't you have 60Hz mains, by chance?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on July 27, 2018, 12:06:20 pm
Could you please remind me how 50/60Hz filtering works? I thought there are only three ways of get rid of ripple: 1) synchronize measurements to mains frequency 2) set integration time (or whatever) equal to one period of sine. 3) low-pass filter, but it may make DMM unresponsive and slow to settle.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on July 27, 2018, 12:37:06 pm
Could you please remind me how 50/60Hz filtering works? I thought there are only three ways of get rid of ripple: 1) synchronize measurements to mains frequency 2) set integration time (or whatever) equal to one period of sine. 3) low-pass filter, but it may make DMM unresponsive and slow to settle.

1) Impossible on a battery device with no main input.
2) With 300ms integration time, you get 5@60Hz or 6@50Hz cycle. This could be a winner.
3) as you said, no.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on July 27, 2018, 01:40:19 pm
1) Impossible on a battery device with no main input.

It should be possible to sense it remotely, shouldn't it? Although, would eat internal space and increase power consumption...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on July 27, 2018, 02:09:39 pm
Any chance of detecting lower than 12V on Low Z mode in the future firmware upgrade?

I recall asking this a long time back and they said maybe not, I don't recall the reason.
Will have to ask again.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on July 27, 2018, 02:10:54 pm
Hello,

I finally analysed the Ohm function.
The 500k and 5M ranges are especially unstable, sometimes giving an unreadable display.
But sometimes, also the 50 Ohm range is unstable on the last two digits, but may stabilize after some 'warmup'.

The 50M range sampling rate is a bit slower, and therefore delivers more stable readings, which makes sense for these high values.
Anyhow, it seems that in this range, there also exist some disturbance, which cause a virtually static shift of the reading (gain error).

I have digitized the probing current of the 121GW by means of my 34465A.
All currents from 470µA down to 20nA, were absolutely stable apart from some amplifier noise.

When I digitized the voltage across the D.U.T. resistor, I encountered a huge 50Hz signal, 100mVpp @ 700mV DC, which might be picked up by the mains environment (Germany = 50Hz). The 121GW seemed to be extremely sensitive to that 50Hz pickup, although its A/D should suppress the mains frequencies of either 50Hz, or 60Hz.

I have the suspicion, that the sampling rate especially in Ohms mode is not selected correctly, for 60Hz only, so that this would be stable in U.S. or other countries with 60Hz mains frequency, but unstable here in Europe.

Do other owners here in EU see that same effect? 

How can I check inside the guts of the 121GW, which mains frequencies are suppressed?

Frank

I don't recall seeing that here (we use 50Hz too).
We'll have to do more testing to see if it can be replicated.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on July 27, 2018, 02:20:48 pm
The manual states:

(https://i.imgur.com/my6B5QC.png)

But this is not the case. It will remember the last mode.

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on July 27, 2018, 02:52:38 pm
Hello,

I finally analysed the Ohm function.
The 500k and 5M ranges are especially unstable, sometimes giving an unreadable display.
But sometimes, also the 50 Ohm range is unstable on the last two digits, but may stabilize after some 'warmup'.

The 50M range sampling rate is a bit slower, and therefore delivers more stable readings, which makes sense for these high values.
Anyhow, it seems that in this range, there also exist some disturbance, which cause a virtually static shift of the reading (gain error).

I have digitized the probing current of the 121GW by means of my 34465A.
All currents from 470µA down to 20nA, were absolutely stable apart from some amplifier noise.

When I digitized the voltage across the D.U.T. resistor, I encountered a huge 50Hz signal, 100mVpp @ 700mV DC, which might be picked up by the mains environment (Germany = 50Hz). The 121GW seemed to be extremely sensitive to that 50Hz pickup, although its A/D should suppress the mains frequencies of either 50Hz, or 60Hz.

I have the suspicion, that the sampling rate especially in Ohms mode is not selected correctly, for 60Hz only, so that this would be stable in U.S. or other countries with 60Hz mains frequency, but unstable here in Europe.

Do other owners here in EU see that same effect? 

How can I check inside the guts of the 121GW, which mains frequencies are suppressed?

Frank

I don't recall seeing that here (we use 50Hz too).
We'll have to do more testing to see if it can be replicated.

I've noticed this behavior too, I'm in Sweden, 50Hz mains.

I compared with my U1252B which has 15 fps update rate. I put it next to the 121gw using equal length test leads laying in more or less the same path on the table measuring same valued 1% metal film resistors.

10M - seemed equally stable on both meters, although very very slow update rate on 121gw about 1-2 fps.

1M - U1252 was only flickering on 1 count - but 121gw was very unstable, recorded min = 0.9674, max = 1.0261 over about 10 sec time.

100K - seemed nice and stable on both meters.

51K - 121gw was unstable again, not nearly as much though as 1M and the reading was more like slowly crawling up and down, recorded min = 50.566, max 50.667.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 27, 2018, 04:24:54 pm
As an example, here's one log of 1000 samples, 5M range, 1.9000 MOhm from the 5450A, short cables, 'noise' is 0.4%RMS or 1.3% PP.
That's not usable at all.

Frank

PS: I've verified, that the correct XTAL of 4.9152MHz is assembled, and also re-soldered these bad junctions J1 / J2 (wrecking my soldering tip by the lead-free stuff) - no change at all.
UEI manufacturing also burnt the edge of one coil a bit..   :palm:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on July 27, 2018, 06:29:29 pm
Assuming you feel the meter is sensitive to something going on with the mains...

My meter appears to be quite sensitive to electrostatic fields. For example if I move my fingers near some of the buttons like Hold or Rel when in certain ranges (e.g. some resistance ranges) the display reading jumps around a lot.

I also find a similar effect with the test leads. Moving my hand near the test leads or moving the test leads around will also cause the reading to be unstable.

I previously mentioned that trying to measure a 10 M resistance is unsuccessful. Either the meter locks on the wrong reading, or when it does settle it reads ~9.6 M rather than 10 M.

Similarly, the lowest ohm range has a 0.000 resolution, but I cannot successfully make use of those digits. The reading is very unstable and will not settle reliably or repeatably.

I would have to say right now that the resistance ranges are compromised and not easy to trust.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on July 27, 2018, 06:29:43 pm
Are those issues firmware addressable?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: MadModder on July 27, 2018, 06:59:10 pm
Firmware 1.22
I logged my mains voltage for 1 hour plus a few minutes. (MEM button) Logging interval 1 second.
I stopped the logging when the display said 4049 data points.

Issue 1: When reviewing the data on the instrument, it only steps from 1 to 60 and then back to 1 (maybe it should be like that, I don't remember), and the decimal point is in the wrong place. It says 2350.4V for example, not 235.04V.
Issue 2: When loading the data off of the SD-card, the data is only 3990 lines. Not 4049. They're all consecutive. And the decimal point is in the right place.
Issue 3: This is really weird. Look at the attached diagrams. I find the regularity in the right half highly unlikely. Exactly 60 second periods. I must log for longer to see what that looks like.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on July 27, 2018, 07:07:11 pm
Firmware 1.22
I logged my mains voltage for 1 hour plus a few minutes. (MEM button) Logging interval 1 second.
I stopped the logging when the display said 4049 data points.

Issue 1: When reviewing the data on the instrument, it only steps from 1 to 60 and then back to 1 (maybe it should be like that, I don't remember), and the decimal point is in the wrong place. It says 2350.4V for example, not 235.04V.
Issue 2: When loading the data off of the SD-card, the data is only 3990 lines. Not 4049. They're all consecutive. And the decimal point is in the right place.
Issue 3: This is really weird. Look at the attached diagrams. I find the regularity in the right half highly unlikely. Exactly 60 second periods. I must log for longer to see what that looks like.

I reported something similar, I mentioned that it may be that the reading on the background is handling the decimal point, when you are looking at your stored data.

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: MadModder on July 27, 2018, 07:23:04 pm
Yes, I think you're right on that point. The decimal point moves around all over if selecting ohms range and pressing MEM before the auto sense has settled. :D
Title: Re: EEVblog 121GW Multimeter Issues
Post by: fubar.gr on July 27, 2018, 10:39:08 pm
Don't know if it is mentioned already, but I got mine today and I noticed some segments on the screen turning on as I peeled off the protective film.

It is quite reproducible, you can see the video here:

https://twitter.com/FubarGR/status/1022971753340039169

Has anyone else noticed that?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Muttley Snickers on July 27, 2018, 10:51:13 pm
The preproduction meter is also sensitive to the proximity of my hand, similar to that Gossen I looked at but not to that extent.

I commented a while back in another thread about the Keysight U1282A multimeter also acting in a similar manner with the readings dramatically fluctuating if the users hand was moving in close proximity to the meter.

It was mentioned elsewhere that these meters use the same chipset so perhaps it could be an inherent problem regardless of the filtering or front end configuration, I don't have a 121GW to compare against but perhaps somebody else does.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: mattselectronics on July 28, 2018, 12:41:22 am
Hello,
I have an issue with the power measurement.
The meter is still reading too high voltage values when it is in the VA range.
If I switch it to the voltage range, everything is as expected.
My Firmware Version is 1.22
Look at this Video at 5:40:
https://youtu.be/QpeivpCtZSk
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on July 28, 2018, 02:56:55 am
As an example, here's one log of 1000 samples, 5M range, 1.9000 MOhm from the 5450A, short cables, 'noise' is 0.4%RMS or 1.3% PP.
That's not usable at all.

Frank

PS: I've verified, that the correct XTAL of 4.9152MHz is assembled, and also re-soldered these bad junctions J1 / J2 (wrecking my soldering tip by the lead-free stuff) - no change at all.
UEI manufacturing also burnt the edge of one coil a bit..   :palm:

I attempted to repeat your test the best I could.  I am using a few Caddock TK series resistors to make up roughly 1.9M.   The two plots shown are my HP34401A (white) compared with the pre-production 121GW (red).   I have also included the CSV file off the meter (renamed to .txt to allow uploading).  The recording interval is 1 second for both meters.

Looking at the schematic, nothing pops out other than you should have a better reference.  A bit odd you don't see the problem in every range. 

Added your data set for completeness.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: exe on July 28, 2018, 08:53:37 am
Don't know if it is mentioned already, but I got mine today and I noticed some segments on the screen turning on as I peeled off the protective film.

I'm no expert, but this looks pretty normal to me. Static electricity powers up segments, I'd consider this normal. Probably, all LCDs are susceptible to some extent.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on July 28, 2018, 11:22:19 am
Yes it is normal.

Nothing to worry about at all.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 28, 2018, 11:37:07 am

I attempted to repeat your test the best I could.  I am using a few Caddock TK series resistors to make up roughly 1.9M.   The two plots shown are my HP34401A (white) compared with the pre-production 121GW (red).   I have also included the CSV file off the meter (renamed to .txt to allow uploading).  The recording interval is 1 second for both meters.

Looking at the schematic, nothing pops out other than you should have a better reference.  A bit odd you don't see the problem in every range. 

Added your data set for completeness.

Hello Joe,
thanks for your tests.. the measurement of the 1.9M inside the 5450A by a 34465A, or a 3458A at NPLC 10 is as stable to the last digit, as yours with the 34401A, but w/o drift.
I could replicate that instability with other very stable 1M resistors and short, drilled cables also, but sometimes, I also get stable readings.. very strange.

So I wonder, what you mean by 'you should have a better reference', do you mean the 121GW internal reference resistors?

I doubt that these are the root cause for this instability problem.. because the Ohm mode is usually realized by a ratio measurement, so I suppose, that it's caused by the AD1.
And yes, this instability is visible part time in other ranges also, surprisingly in the 50 range, although that's driven by a high 470µA current.

Maybe you still have an old firmware running. In the latest 1-22, the counter register for the sampling frequency might be set improperly. Otherwise, 50 and 60Hz should be suppressed by 120dB @ 5Sa/sec, but 75dB only, when using a faster sampling rate... that could also be the case, as the sampling seems much too fast.
 
Maybe something inside the Ohm circuit is oscillating, or super sensitive, depending on the hardware version..

 I did not fully understand the schematics, either, and also the HY3131 datasheet is really crap., still  searching for an Application Note.

Anyhow, I really think, that this problem could be solved by software.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on July 28, 2018, 03:50:33 pm

I attempted to repeat your test the best I could.  I am using a few Caddock TK series resistors to make up roughly 1.9M.   The two plots shown are my HP34401A (white) compared with the pre-production 121GW (red).   I have also included the CSV file off the meter (renamed to .txt to allow uploading).  The recording interval is 1 second for both meters.

Looking at the schematic, nothing pops out other than you should have a better reference.  A bit odd you don't see the problem in every range. 

Added your data set for completeness.

Hello Joe,
thanks for your tests.. the measurement of the 1.9M inside the 5450A by a 34465A, or a 3458A at NPLC 10 is as stable to the last digit, as yours with the 34401A, but w/o drift.
I could replicate that instability with other very stable 1M resistors and short, drilled cables also, but sometimes, I also get stable readings.. very strange.

So I wonder, what you mean by 'you should have a better reference', do you mean the 121GW internal reference resistors?

I doubt that these are the root cause for this instability problem.. because the Ohm mode is usually realized by a ratio measurement, so I suppose, that it's caused by the AD1.
And yes, this instability is visible part time in other ranges also, surprisingly in the 50 range, although that's driven by a high 470µA current.

Maybe you still have an old firmware running. In the latest 1-22, the counter register for the sampling frequency might be set improperly. Otherwise, 50 and 60Hz should be suppressed by 120dB @ 5Sa/sec, but 75dB only, when using a faster sampling rate... that could also be the case, as the sampling seems much too fast.
 
Maybe something inside the Ohm circuit is oscillating, or super sensitive, depending on the hardware version..

 I did not fully understand the schematics, either, and also the HY3131 datasheet is really crap., still  searching for an Application Note.

Anyhow, I really think, that this problem could be solved by software.

Frank

I was just comparing the two versions of the schematics and noting what I saw.  ZD1 and circuit surrounding it was changed.   U14 is no longer populated.   D14 clamp was also changed.  There could be other changes.  These are just what I noticed.   

As mentioned in a previous post, the firmware is pre 1.0.  Also, I had responded to your original post previously where I tried a few quick tests at 50 and 60Hz. 

The parts I used for this test were not temperature controlled.  No towels were used.  I didn't let the HP warm up for very long and the room temperature changes.   Its stable enough to show your 121GW doesn't behave like the pre-production unit I have.  Maybe down the road after you get this first problem sorted out we can look at drift.   

If there was an easy way to backup the firmware on this meter using the tools I have, I would attempt to load the same version of firmware you are running.  At least split the problem in half.   I am not even sure if Dave would have the images for this old firmware available.   That may be an option as well.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on July 28, 2018, 06:29:48 pm
I wrote Dave about the obtaining the older image for this meter.  If he provides it, I will try to repeat the noise test with the same version of firmware. 

In the meantime, I had let the original setup stabilize and changed the value of the small resistor to bring it in a little tighter.   I used some epoxy mixed with heatsink compound and glued a section of copper to the resistor network and made a case from Pyropel wrapped in alumimum foil to keep the air off it.   Still not temperature controlled.   I let the HP warmup  for 2 hours and ran another sweep.   I had left the 121 on for about 10 minutes this time before I started to collect the data. 

The HP (red) still has a bit of drift but again, I am not using any sort of temperature control.   I would have expected the pre-production 121GW to read a lower resistance, not higher (blue).   But from what I saw, the meter was fairly sensitive to temperature which I assume is why they changed the reference. 

It looks like if I subtract off the pre-production meter's drift, we are down to maybe a count of noise.  After a half hour, it was getting pretty stable.    I have attached the raw data CSV file. 

***************  Other Data *****************

Sadly, I never purchased the interface cable for my Brymen but I thought I would show how a few other meters  compare with the pre-production 121GW.   The UNI-T UT61E had really bad temperature drift and I had compensated it (plus it has several other mods).  The UT181A was the most stable meter I had tested.   For these two meters, I did not allow any warmup time.   

The CEM DT9939 (top yellow) has a pretty bad drift problem as well so I let it warm up for 10 minutes. 

And just for the fun of it I tried the Gossen MetraHit Ultra (dark blue).   This meter has Netic in the back along with an aluminum shield in the face that I added to help tame it.   

***************  And still more data  *****************

I repeated your test at 500K.  I tried both ranges.   I didn't have a clean way to put together a 19M but I do have some low tempco 20M 2ppm parts.     

As was mentioned, the 121GW production as well as the pre-production meters are sensitive to static fields.  Looking at the 20M data,  the first spike is me walking away from the meter.   The second two spiked are me walking out and back into the office.  The last spike is walking up to the meter to turn off the logging. 

It would be interesting to see you repeat your test once the noise problem is sorted out.  I remember the pre-production meter not being all that stable with temperature.  They didn't change the reference for the fun of it. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on July 29, 2018, 11:58:58 am
Is this the place to report issues or is there a more official place?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on July 29, 2018, 02:51:56 pm
Here is good.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: eV1Te on July 29, 2018, 04:00:34 pm
I received my meter today and I am quite pleased with most aspects of it. However the SD card logging seems broken. I have the original firmware 1.22 that came installed.

I can start the logging by holding MEM, and stop it by holding MEM again, however the saved CSV file do not contain any time stamps, so it is impossible to know when the measurements were taken.

Also looking at the display of the number of points stored during the logging, I can see that the time between each save/point is not constant, sometime it saves several points quickly, sometimes it takes longer time between points. Hence it is not possible to calculate the time for each point based solely on the "Point No."

If there is a fix for this issue that I have simply missed, please let me know.

Edit:
I noticed more things with the logging function that seems poorly optimized.
1. The function/mode that you are currently logging is printed on every row in the CSV, this is a huge waste of memory space since it could easily just be printed once at the top of the file. Switching functions during logging stops the logging, so it is not possible to have several functions in one CSV in any way.
2. I can not get it to log the values in the secondary display. For example I connect a thermocouple that is not Type K and I measure mV and have the meters internal temperature in the secondary display. I intend to process the data in post and calculate the real temperature based on the mV and the internal temperature, this is because the meter only supports type K thermocouples natively. But no matter what I do and press I can not get it to log the internal temperature.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: MadModder on July 29, 2018, 07:19:29 pm
Both date and time is on the first row in the file, then it says what interval is used. So it is not impossible, just somehwat cumbersome. Add another column, copy the time from the top row, then next row is the one above+(interval in seconds)*(1/86400). If using excel or the like. Otherwise I suppose a script could be used...
But it would be very easy codewise to implement the timestamp into the log file, so we don't have to mess around like that.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 30, 2018, 11:18:59 am
..  I updated the pre-production meter to 1.02 then saved the calibration data.  I then proceeded up upgrade the meter to 1.22.   

I remember reading something early on about the firmware may have required the meters to be realigned.   This appears to be the case but it should be good enough to see if running the latest firmware will cause the noise problem.   

...

*********** Update *************

...

One last note,  it does appear that at least with a 0.5 ohm resistor, with the 1.22 firmware installed, the readings are VERY unstable.  The meter will display 0.5 and noise for the other two places.  After downgrading, the meter again changes a couple of counts at most.   So it does appear that the noise people are seeing could very well be due to the firmware.   The other thing I noticed is the display update rate for the low values is much faster with the 1.22 firmware.


Joe, thank you very much, once again.

So you could at least confirm that the 50 Ohm range is noisy / unstable with FW 1-22, and that the sample rate is too fast.

I did it the other way round, downgraded to 1-05, but the readings in 5M range were as unstable as with 1-22.
I did not check the 50 Ohm range, though.

Then on my bench in the basement, I arranged the 121GW, the cables and a small resistor box with a 1M Ohm PWW, T.C. 1 resistor inside, so that the reading was stable to +/- 2 counts at most. Moving the whole setting 20 cm to the left or to the right, or changing the angle of the cables from perpendicular to horizontal on the bench, created again that heavy noise disturbance.

In that 'quiet' configuration, when I approach the cables with a mains transformer (inside a table lamp @ 50Hz, no SMPSU), the reading again will go wild.
That's the final proof for me, that 50Hz pickup really creates these misreadings, i.e. also the gain shift in the 50M range.

I will try to make a setup to quantitatively measure the mains suppression at 50Hz and at 60Hz, probably by a coil around the measuring cable, and inducing controlled levels of 50 and 60Hz signals from an oscillator.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: axel15 on July 30, 2018, 01:23:23 pm
121GW just arrived to Scandinavia. One detail paid my attention: I barely can read red labels. Too dark tone compared to the background.

Axel.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: eV1Te on July 30, 2018, 06:28:01 pm
Both date and time is on the first row in the file, then it says what interval is used. So it is not impossible, just somehwat cumbersome. Add another column, copy the time from the top row, then next row is the one above+(interval in seconds)*(1/86400). If using excel or the like. Otherwise I suppose a script could be used...
But it would be very easy codewise to implement the timestamp into the log file, so we don't have to mess around like that.

The default setting is to sample and save points as fast as the ADC allows, hence the interval is not fixed but depends on the mode, range, etc. It is therefore impossible to calculate the time for each point using the default setting.

However it is true that if you change the settings and limit yourself to a slower sampling speed, i.e. not using the full potential of the meter, it does seem like the timing is consistent so that can assume a fixed number of seconds between each point. I tried it over 4 minutes using a stopwatch and I could not detect any drift or dropped points by eye at least. Hence I guess this is the recommended method for now.

In order to allow for faster sampling I guess you need the actual time in a column (seconds since start is probably easiest), as it would make analysis much easier without having to process the time manually every time. Also as a separate improvement I would remove the "mode" from being printed on every row, either print it once in the header or only print it when it changes (if you intend to include mode switching during logging in the future). This would save approx 10-30 % in space depending on the mode used.

I also noticed that the meter does not autorange during logging (it goes into manual ranging when starting the logging process). This is definitely a feature that I would like to see in future updates.

Edit:
More issues I noticed today:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on July 30, 2018, 10:45:02 pm
One detail paid my attention: I barely can read red labels. Too dark tone compared to the background.

This is the reason I changed the colour of the red markings on my recent crap meter refacing project to something more orange.  Pure red on grey or black does not have the greatest contrast.

(https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=482912;image)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: MadModder on July 31, 2018, 03:54:02 pm
The default setting is to sample and save points as fast as the ADC allows, hence the interval is not fixed but depends on the mode, range, etc. It is therefore impossible to calculate the time for each point using the default setting.

However it is true that if you change the settings and limit yourself to a slower sampling speed, i.e. not using the full potential of the meter, it does seem like the timing is consistent so that can assume a fixed number of seconds between each point. I tried it over 4 minutes using a stopwatch and I could not detect any drift or dropped points by eye at least. Hence I guess this is the recommended method for now.

In order to allow for faster sampling I guess you need the actual time in a column (seconds since start is probably easiest), as it would make analysis much easier without having to process the time manually every time. Also as a separate improvement I would remove the "mode" from being printed on every row, either print it once in the header or only print it when it changes (if you intend to include mode switching during logging in the future). This would save approx 10-30 % in space depending on the mode used.

I also noticed that the meter does not autorange during logging (it goes into manual ranging when starting the logging process). This is definitely a feature that I would like to see in future updates.

Edit:
More issues I noticed today:
  • The claimed "update rate" is 5 samples/s nominal, however my display only updates 1-2 times/s, hence the meter feels slow and unresponsive, is this an error in the manual or is the meter supposed to be faster?
  • When manually selecting the 10 A current range, the display tells you that you are in the 1000 A range. Perhaps there is no 10 indicator in the LCD and this is intended, if that is the case please update the manual.
  • There is a 1000 V range, however the manual specifies maximum 600 V for the input protection. Perhaps this is the same issue as above? Please update the manual.
  • There are no range indicators in the display for Frequency, Period, Capacitance. Perhaps indicators is lacking in the LCD? In that case I suggest to always show leading zeros in these modes when in a manual range. For example the 100 nF range, write 07.6 nF, instead of just 7.6 nF in order to indicate the amount of headroom available.

Yes, you're absolutely right about the "free flow" logging. Didn't think about that. That is in this format impossible to use for example in a diagram with a time axis. Or to just reference if one wants to point at a specific time when searching for irregularities. In some cases I would even go so far to say useless.

I can not find any numbered range indicators on the display other than 500 and 1000. (max contrast and backlight helps). 500 is three segments. But the 1000 I believe is only one big segment?  :-//
 :-+ for leading zeroes instead.

And there's a lot in the manual saying things are set in a way as default, when it's not. For example it says logging delay is 1 sample/s, when it is 0. It describes things as if the beep is on by default. It is off.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on July 31, 2018, 06:28:22 pm
I've tested the 50/60Hz mains suppression of the Ohm ranges.
At first, there's a log of this 'quiet' arrangement, about +/- 5 counts noise, although the direct reading is more like +/- 1 count.

Then I coupled a noise signal via a ferrite core into one of the Ohms cables.

That creates now +/- 100 counts of noise readings, but there is no difference between 50 or 60Hz.
I alternated between 50 and 60Hz each 50 samples.

So I conclude, that for Ohm mode, there is no proper mains suppression programmed into the HY3131.

I have read about delta-sigma converters, and these do not have a natural mains suppression like dual / multiple slope converters.
Due to the architecture, they need a digital filter, which has to be programmed to the 48...62 Hz frequency range to notch these by about 120dB, as given by the datasheet.

Obviously, that fails at Ohm mode, as DCV suppresses 50..60Hz AC signals down to the last digit.

I have no problem at all with the MEM function, all logs were done correctly, no failure happened up to now.

But I have measured the logging interval at ln 0 to be 4 Sa/sec, or 250ms, but not 5 Sa/sec, as implied in the manual.
That's important to know, if one makes timed logging of data.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Woodsy on August 01, 2018, 12:51:21 am
Arrived this morning. Flabbergasted. Cant use it, NO PROBES and no zippy-up case thing...

Package contained:
No bullshit packaging box.
One piece of cardboard with a serial number.
Bubble wrap sleeve containing - 121GW MM with blue case - Batteries already installed.
Bubble wrap sleeve containing - One thermocouple.

Newsletter said: "The 121GW is finally in stock for all those who have constantly been asking.
AND they are on special AND come with a free carry case for this first offer!"

Website says "NOTE: The meter may come with either Brymen (gold) probes or UEI (nickel) probes depending upon availability at the time. Both are high quality silicone rubber probes."

Oh, and the phone number on the "Certificate of Conformity".. The number you have dialed is not in service.

WTF?!

EDIT: For complete transparency there was also a sachet of silica gel and a piece of protective plastic on the LCD.

EDIT2: Package appeared to be sealed when I opened it.

EDIT3: (https://i.imgur.com/o10RuId.jpg)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 01, 2018, 01:45:47 am
Arrived this morning. Flabbergasted. Cant use it, NO PROBES and no zippy-up case thing...

Sorry about that, I screwed up.
I used meters from a box that I thought were fully packed with the cases and probes  :palm:
This was only Oz orders.
Everyone will be shipped probes and a case.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on August 01, 2018, 08:35:36 am
What other DMM use the HY3131?

Uni-T UT171A... then?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 01, 2018, 08:40:30 am
Can someone clarify the DC+AC mode? Should the meter show on the secondary display the AC or  DC component? Are the segments in red circle for that purpose?\


(https://i.imgur.com/kqwqGUJs.png) (https://i.imgur.com/kqwqGUJ.png)

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on August 01, 2018, 08:44:18 am
Can someone clarify the DC+AC mode? Should the meter show on the secondary display the AC or  DC component? Are the segments in red circle for that purpose?\

AC+DC mode means the meter measured the AC and the DC part of the voltage and then sums them together before showing them.
The meter cannot show both AC and DC at the same time.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 01, 2018, 09:03:38 am
What other DMM use the HY3131?

Keysight U1282A
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on August 01, 2018, 11:10:13 am
What other DMM use the HY3131?

Keysight U1282A

Has anyone noticed similar stability issues with resistance measurements in U1282A?.

It seems odd if only Keysight could get the hy3131 working reasonably well - and UEI can’t.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 01, 2018, 01:31:09 pm
What the AC DC sgments next to the secondary display are for? Many manuals explain all the segments of the screen. It would be nice touch.

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on August 01, 2018, 02:36:00 pm
AC+DC mode means the meter measured the AC and the DC part of the voltage and then sums them together before showing them.
That's not true.   To avoid having Dave remove this post as a non-issue, the manual should be updated to show it as a feature and the proper equation should be added as well.

That I leave out the actual formula to use for summing do not make it wrong.



What the AC DC sgments next to the secondary display are for? Many manuals explain all the segments of the screen. It would be nice touch.

Hopefully for a software update sometime in the future (Many meters have displays with unused segments).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: axel15 on August 01, 2018, 03:28:44 pm
Brumby: Yep. That color looks better.
I can't read red labels on my workbench at all. Agilent orange is fine to read tho.
I would not expect such an issue because they're supposed to be number of protos and testers thru the dev process.

A.
Title: EEVblog 121GW Multimeter Issues - Manual Erratum (1-22)
Post by: Dr. Frank on August 02, 2018, 09:01:06 am
Hello seppy,

here's a last erratum:

Page 70:

5. “IAP” will appear on the screen, then press <SETUP> to begin the firm-ware upgrade.

=> remove whole paragraph '6.' and renumber '7.' to 6.

explanation: After switching on with HOLD and MEM pressed, the 121GW will directly start in the IAP / upgrade mode, so only one press of SETUP is required to start the update process.

Frank
Title: Millivolt (mV) measuring issue when using EEVBlog uCurrent
Post by: vyruz on August 02, 2018, 10:22:56 am
Hi everyone,

I received my 121GW 2 weeks ago and am really happy with it, great job Dave!
It wasn't until this week that I had time to play with it. I decided to test the meter's ultra-low current measuring capabilities, something for which I've relied on my trusty EEVBlog uCurrent gold until now.
Good news: The 121GW can measure mA and uA very well, no need for my uCurrent anymore :)

But that's not what this post is about.
While comparing measurements of my uCurrent I hooked the uCurrent up to the 121GW, and set the 121GW to the mV measuring setting, and noticed something strange.
While the V setting seems to do fine, the mV setting is giving weird measurements. I couldn't identify another means of generating a reliable sub-10mV source right away, so I only tested with the uCurrent.
I made a video of the whole process since I'm not ruling out at all that I botched something which resulted in this behavior :):
https://www.youtube.com/watch?v=6OoFH99jLOU (https://www.youtube.com/watch?v=6OoFH99jLOU)
I had my bench PSU set to 10V and applied this across a 1.8k resistor. This should give ~5.5mA current, which I also did measure when I had to the 121GW set to V, but when I set it to mV, the results were way off, it was showing ~0.260 mV while I was expecting ~5.550. To my surprise, when dropping the voltage on my bench PSU to 5V (expecting to measure ~2.7mA or ~2.7mV on the uCurrent), the voltage on the 121GW went UP to ~2.000 mV ?!?

Something else which I forgot to record on the video, but perhaps someone else can try:
using the uCurrent, I was measuring an ESP module running at 70mA, with the 121GW set to V the measurement from the uCurrent was 0.0070V, which is correct.
But when I switched the 121GW to mV, the measurement was reading ~7.000mV, so there seems to be a decimal point issue here.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: eV1Te on August 02, 2018, 11:51:19 am
But I have measured the logging interval at ln 0 to be 4 Sa/sec, or 250ms, but not 5 Sa/sec, as implied in the manual.
That's important to know, if one makes timed logging of data.

That is interesting, did you check if it was exactly 4 Sa/s in all ranges/modes or does it vary? I believe I read somewhere that it is "as fast as the ADC can sample" and that the speed depends on several factors.
When I look at the display I can see that the sampling numbers do not increment smoothly, perhaps this is only an issue with the update rate of the LCD?

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 02, 2018, 01:14:33 pm
But I have measured the logging interval at ln 0 to be 4 Sa/sec, or 250ms, but not 5 Sa/sec, as implied in the manual.
That's important to know, if one makes timed logging of data.

That is interesting, did you check if it was exactly 4 Sa/s in all ranges/modes or does it vary? I believe I read somewhere that it is "as fast as the ADC can sample" and that the speed depends on several factors.
When I look at the display I can see that the sampling numbers do not increment smoothly, perhaps this is only an issue with the update rate of the LCD?

I did not check all modes, but the Ohm modes and also DCV is 4Sa/s only.
I timed that by a stop watch, measuring 100 samples.

Also, if you use the BT logging, the rate is 0.5sec/sample only, which is exactly 1/2 of that rate of 250msec.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 03, 2018, 11:28:08 am


Did you by chance try any of the older ones to see if your meter was stable?   I suspect the pre-production meter will require realignment before I can use it again.  If not, I will try 1.02 (assuming it uses the same tables) and report back.   

It's possible that when the meter is in the calibration mode that they use different routines to sample the data.  Maybe the notch is correct in this mode.  Otherwise, I wonder what their process was to align them.  Maybe they update the firmware again after alignment and that's why they did not catch this. 


Hello Joe,
no I went back to 1-05 only, because I feared exactly these incompatibilities , which you describe, i.e. regarding calibration.. as I have a series device, I won't take any further risk.

The calibration process works differently.. there is a countdown of maybe 5 sec for each constant, so at least the sampling time is much longer.

What I also found out, that external hum noise might create a shift, which gives a constant, but not permanent different reading.

That is visible on the 50M range of the 121GW, which might explain the part time out-of-calibration reading.
I also have seen that effect on my BM869, but that were a few counts of shift only, not several %.

I think, that this a common rectification effect, probably on protection semiconductors.

Frank
Title: EEVblog 121GW Multimeter Issues - 5MOhm range
Post by: Dr. Frank on August 04, 2018, 04:48:28 pm
I had an even closer look at the noise suppression of 5M and 50M range.

It's possible to greatly suppress this 50Hz noise on the 5M range by a parallel 100nF MKP capacitor, even with a strong magnetic 50Hz field of a transformer inside a lamp, see picture:
The 'normal' noise can be suppressed so far, that you get an absolute stable reading, only a few counts fluctuation..

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=490499;image)


The 50MOhm range, though, is absolutely stable, it even shows no static shift by the noise, because the 100nF capacitor makes no difference.

In contrast, my BM869 shows not that kind of noise as in the experiment above, but in both 5M and 50M ranges, a static upwards shift is observed, when the 50Hz magnetic field influences the cables.
This shift can be completely suppressed by adding the 100nF capacitor.


In the schematic  of the 121GW, there are range reference resistors R13 (1.11M) and R29 (10M) and a 27nF capacitor, C30, tied together on one side, and towards the network MUX on the other side.

I assume, that at first, the 50Hz noise filter is not correctly programmed, at least in the 5M range.
Then I assume, that this filtering capacitor C30 is switched on, parallel to the 10M reference resistor, so that even this static shift effect is suppressed.
In the 5M range, I suppose, this C30 is not switched on, in parallel to the 1.11M resistor.

In the lower ranges, either the noise filter, and/or this suppression capacitor might be correctly configured.

The 50 Ohm range is unstable on the last digit, due to another reason, as the 100nF does not change that behavior.

So I propose to UEI, to check the digital filtering, and also propose to switch on the 27nF capacitor in the 5M range, if that is really the method used on the 50M range.

Frank
Title: EEVblog 121GW Multimeter Issues - Erratum calibration 50MOhm
Post by: Dr. Frank on August 05, 2018, 04:09:06 pm
Seppy, again a last final erratum:

Page 69, line 7, Resistor:

Replace text for GAIN:

R0~R6: 50000

(Remove 2nd line for R6)

explanation: The gain of the 50 MOhm range also has to be adjusted at full scale, i.e. a 50.000 MOhm standard is needed, instead of 40MOhm.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 05, 2018, 05:07:02 pm
So I dug into the firmware and it's interesting. For the 5MΩ range, v1.02 configures an oversampling ratio of 4096 but v1.22 has it configured as 1024. That's the only difference in the chipset configuration. Presumably, they did this to help with autorange speed. You are also correct about C30; 50MΩ (which BTW has an oversampling ratio of 8192 on v1.02 and 16384 on v1.22) has it switched in, but 5MΩ does not. Try changing the byte at 0x1F732 in the v1.22 firmware from 0 to 8 to kick it in on 5MΩ too and see how much that improves things. The byte at 0x17F2A controls oversampling at 5MΩ, changing it from 0x10-0x17 changes the ratio from 256 to 32768 (i.e. 2^(n-8)).

Edit: you can use your favorite hex editor to make these modifications. There is no checksum required. Byte 0x0 is the beginning of the file.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 05, 2018, 05:15:30 pm
So I dug into the firmware and it's interesting. For the 5MΩ range, v1.02 configures an oversampling ratio of 4096 but v1.22 has it configured as 1024. That's the only difference in the chipset configuration. Presumably, they did this to help with autorange speed. You are also correct about C30; 50MΩ (which BTW has an oversampling ratio of 8192 on v1.02 and 16384 on v1.22) has it switched in, but 5MΩ does not. Try changing the byte at 0x1F732 in the v1.22 firmware from 0 to 8 to kick it in on 5MΩ too and see how much that improves things. The byte at 0x17F2A controls oversampling at 5MΩ, changing it from 0x10-0x17 changes the ratio from 256 to 32768 (i.e. 2^(n-8)).

Is it possible to tweak the bin file with a HEX editor, and w/o any checksum alignment?

THX Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 05, 2018, 05:26:45 pm
So I dug into the firmware and it's interesting. For the 5MΩ range, v1.02 configures an oversampling ratio of 4096 but v1.22 has it configured as 1024. That's the only difference in the chipset configuration. Presumably, they did this to help with autorange speed. You are also correct about C30; 50MΩ (which BTW has an oversampling ratio of 8192 on v1.02 and 16384 on v1.22) has it switched in, but 5MΩ does not. Try changing the byte at 0x1F732 in the v1.22 firmware from 0 to 8 to kick it in on 5MΩ too and see how much that improves things. The byte at 0x17F2A controls oversampling at 5MΩ, changing it from 0x10-0x17 changes the ratio from 256 to 32768 (i.e. 2^(n-8)).

Is it possible to tweak the bin file with a HEX editor, and w/o any checksum alignment?

THX Frank

Exactly, just change those two with your favorite hex editor. I clarified in the post itself.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 05, 2018, 05:43:28 pm
Could you also please check version 1.0 as well while I dig out a Hex editor...
I'm sorry but I don't have that binary so I can't look. Please PM me a link or attach it.

If you are good with a hex editor, here is (https://github.com/tpwrules/121gw-re/blob/master/tables/hy_regtbl.h#L144) what v1.02's looks like so you can find them in the binary. You can crossreference them with the HY3131 datasheet (https://github.com/tpwrules/121gw-re/blob/master/pdfs/DS-HY3131_EN%20-%20HY3131%20multimeter%20chipset.pdf); each entry is the values for R20-R33, one per range. R2A bits 0-3 are the switches for C30 (bit 3 is the switch to the input); lowest 3 bits of R22 are the oversample ratio.

Edit: yes, that byte is 0x12 to select 1024x oversampling. Valid values are 0x10-0x17 to select oversampling degree; I guess you thought I meant "change 0x10 to 0x17".
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 05, 2018, 06:45:48 pm
I can't find anything obviously different in the ohms measurement logic between v1.00 and v1.02. The chip registers are the same and the software averaging is the same. The only difference I can find is that v1.00 log processing happens in a different place and not as frequently (part of it executes whether logging is enabled or not). Maybe the CPU is less busy and thus contaminating the measurement less. If you like, you can try and patch the 4 bytes in v1.02 at 0x1B672 with 0x00 0x80 0xAF 0xF3 (to disable that bit) but I don't really believe it will help. Maybe I'm missing something.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 05, 2018, 07:37:52 pm
I compared the section in 1.00 you pointed out as well as it is indeed the same as 1.02.  When I run the two versions they appear different.

I have uploaded the modified 1.22 changing just the two bytes to start.   Just looking at how it behaved, it did not appear to make much if any difference in the 5M range.   Let me collect some data and we can compare the results.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 05, 2018, 09:59:32 pm
The card is a pain for logging.  I have left the meter apart since starting this little side project.  I don't have long enough finger nails to reach the card and my fingers are too large.  So needle nose pliers.  Not wanting to crush the card, I tend to be very careful when pulling it out.  Today, I dropped it into the meter and it falls behind the cover.   :palm:   I understand they are not wanting to download the contents of the card using BT like I can with the CEM or Gossen meters.  So logging really will require the B/T to work.   

TPW, it appears that you are at least on the right track.   The first set of data shows the unmodified 1.22 (yellow) dominating all the other data sets.   

The second set is showing the unmodified turned off.   The modified version of 1.22 is purple.   It doesn't appear to be as stable as 1.0, the unknown version or the old December firmware but it's not as noisy as 1.02 was.  From my test setup, I can't explain why the older versions do not have these spikes and appear to have less noise.   Beyond the firmware, about the only environmental change is temperature. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 06, 2018, 02:10:34 am
To be honest I wonder if it's just how the software is structured. In firmwares v1.02 and above, the logging engine captures the current value on the screen every 100ms. In v1.00 and below, the logging engine captures the value on screen whenever it changes. This period I don't know, but it is not a nice round number of milliseconds. In both cases, this captured value is written to SD when the logging interval elapses (every 200ms, 1s, 2s, etc). This might explain the noise in the last count being different between the two, especially on the fastest logging setting.

I've attached v1.00 patched with v1.02's logging method. See if using it gives you the same kind of noise as v1.02.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 06, 2018, 02:21:31 am
I had attempted to patch the 1.02 as you suggested with the 4 bytes.  I ran it but sadly when I went to retrieve the data, the file was not created.  Anytime this has happened, the MEM is displayed and the counter is being updated.  I press MEM, stop the logging and turn off the meter to pull the card, but there is no file.  Maybe it's doing some house keeping on the card and I am not giving it enough time before turning off the meter.   

Anyway, I have restarted this test.   Once this is done, I will try the 1.0 version you patched as well.  After I have all of the data, I will post a new set of plots.

Again, thank you for taking the time to help dig into this.   Seems early when I saw you post, you did not yet have a meter.  Is this still the case? 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 06, 2018, 02:31:31 am
I had attempted to patch the 1.02 as you suggested with the 4 bytes.  I ran it but sadly when I went to retrieve the data, the file was not created.  Anytime this has happened, the MEM is displayed and the counter is being updated.  I press MEM, stop the logging and turn off the meter to pull the card, but there is no file.  Maybe it's doing some house keeping on the card and I am not giving it enough time before turning off the meter.

Anyway, I have restarted this test.   Once this is done, I will try the 1.0 version you patched as well.  After I have all of the data, I will post a new set of plots.

Yes, that 4 byte patch deliberately breaks SD logging to test if it's interfering with the measurement. I thought you were using Bluetooth to get data out, but I now see your meter can't use Bluetooth. In that case, the patch is worthless. Try the v1.00 patch instead, it has complete logging functionality that's like in v1.02.

Again, thank you for taking the time to help dig into this.   Seems early when I saw you post, you did not yet have a meter.  Is this still the case?

Yes, I have a preproduction unit Dave generously donated and a Kickstarter US unit I purchased. I just don't have the test equipment you have. I will though once I get back to school, but then I'll have less time for fooling with the meter.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 06, 2018, 05:45:08 am
I have noticed, that in FW 1-22 at least, the display content (in 5MOhm range) is different than the data written to the SD card; there is a small offset, and the written data might be more noisy.

In 50MOhm range, the sampling rate on the display is much slower, but at ln 0, data is still written at 4 Sa/sec, obviously producing multiple data logs on one A/D cycle.

BT logging is always slower than SD card logging, 1/2 of the speed.

That I do call: no reliable data logging.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 06, 2018, 02:13:48 pm
I spent some time running a few sweeps.  The patch you provided acts very strange.   It appears to log and actually creates the files.  I am testing in the 5Meg range with the same 1.9Meg resistor I have been.  While logging the meter displays 1.9Meg.   I have attached the two files.  At least it appears to be repeatable.

Heh, teaches me to be hand assembling at 10PM. I confused some registers so I think memory got a little corrupted.

However, I did discover something more interesting. In v1.00, the log engine captures the value on the main screen as soon as it updates. In v1.02, the log engine captures the value _for the bargraph_ every 100ms. The value for the bargraph is the value from the ADC after it has been scaled according to the calibration, but before software averaging (8x), smoothing (rolling average of past 10 numbers), and nonlinearity correction (on 5MΩ and 50MΩ). So this noisier value, with a small offset due to nonlinearity, is exactly what you're getting in the log. It's perfectly suitable to scale down to the 25 bargraph segments, but why they're writing it to the log is beyond me. I've attached v1.02 modified to use the screen value. And actually tested it this time...

Regarding sample and logging timing, it's not "as fast as the ADC goes". The ADC speed can be calculated, but it might be different for every mode and range; someone would have to sit down and work it out. The bargraph is updated as soon as the ADC has a new measurement and the screen is updated at a fixed divisor of the ADC speed, to account for averaging. However, the ADC and screen speed is completely unrelated to the logging speed. With an interval greater than 0, the captured value (as described above) is written at the start of the appropriate calendar second (as measured by the RTC). When the interval is 0, the captured value is written every 200ms, but the 5th value in each calendar second will be skipped due to a bug. The net result is four samples per second, but the periods are 3x 200ms and 1x 400ms, instead of 4x 250ms. You can actually see this if you watch the sample number carefully, it will pause every four numbers.

On the other hand, the bluetooth engine simply captures and immediately transmits everything every 250ms. Maybe the bluetooth hardware or the app drops every other packet, resulting in 500ms update speed.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Caelarius on August 06, 2018, 02:31:56 pm
I encountered a bug with the logging: After logging temperatures for a long time (21 hrs) I got a file where a number of data points keeps repeating itself.

- Firmware 1.22
- Temperature logging
- Logging interval 145 seconds
- Total logpoints: 520, pretty much 21 hours of logging with that interval
- The logging was started and stopped normally through the mem-button

The first 180 points are normal. The next 60 points, however, keep repeating themselves. So logpoint 181 has got the same value as logpoint 241, 301, etcetera. See the attached file for a graph. The logged csv is available at: https://www.dropbox.com/s/1zq2uf1xgz10y9w/18073002.CSV?dl=0 (https://www.dropbox.com/s/1zq2uf1xgz10y9w/18073002.CSV?dl=0)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 06, 2018, 03:13:08 pm
I encountered a bug with the logging: After logging temperatures for a long time (21 hrs) I got a file where a number of data points keeps repeating itself.

- Firmware 1.22
- Temperature logging
- Logging interval 145 seconds
- Total logpoints: 520, pretty much 21 hours of logging with that interval
- The logging was started and stopped normally through the mem-button

The first 180 points are normal. The next 60 points, however, keep repeating themselves. So logpoint 181 has got the same value as logpoint 241, 301, etcetera. See the attached file for a graph. The logged csv is available at: https://www.dropbox.com/s/1zq2uf1xgz10y9w/18073002.CSV?dl=0 (https://www.dropbox.com/s/1zq2uf1xgz10y9w/18073002.CSV?dl=0)

So the logging engine logs points to EEPROM. Every 60 points, it reads all the points from EEPROM and flushes them to SD card. If you power off the meter completely and restart logging, are the points still stuck there? You may have gotten a bad EEPROM for some reason. I can't think of anything else except a bad EEPROM or cosmic rays which would cause this. Maybe it got write protected somehow, but the built in write protection circuitry should have crashed the processor.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 06, 2018, 04:53:52 pm
Firmware 1.22
I logged my mains voltage for 1 hour plus a few minutes. (MEM button) Logging interval 1 second.
I stopped the logging when the display said 4049 data points.

Issue 1: When reviewing the data on the instrument, it only steps from 1 to 60 and then back to 1 (maybe it should be like that, I don't remember), and the decimal point is in the wrong place. It says 2350.4V for example, not 235.04V.
Issue 2: When loading the data off of the SD-card, the data is only 3990 lines. Not 4049. They're all consecutive. And the decimal point is in the right place.
Issue 3: This is really weird. Look at the attached diagrams. I find the regularity in the right half highly unlikely. Exactly 60 second periods. I must log for longer to see what that looks like.

This seems to be the same issue as Caelarius. Regarding Issue 1, only the last 60 points are available. As mentioned in the previous post, the meter buffers 60 points in EEPROM before writing them to SD card. Only the contents of EEPROM is viewable on-instrument. Regarding the 3990 points, perhaps you didn't give it time to finish flushing? You have to hold the MEM button to turn off logging and wait a few seconds to ensure every sample is saved. Did it tell you the MIN and MAX at the end? It might be a symptom of Issue 3, because I would expect that number to be a multiple of 60. Can you upload the .csv the meter produced?

Issue 3 is the tough one for me. It's stopped writing new points to EEPROM and so whatever was there last is getting saved to SD over and over. Is this behavior present with v1.02? Is the data still stuck in EEPROM? What happens if you start logging fresh? Based on my understanding of the firmware, I don't get what would cause it to stop saving points but continue writing them to the card. The only thing I can think of is that the EEPROM is becoming write protected due to abuse. It's not really designed to stream 18bytes/sec for an hour. They do try every EEPROM write at most 10 times (but don't ever check if the correct value was written!), perhaps to cover up some issues. Maybe I'll have to try and replicate it while the meter is attached to a debugger...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Caelarius on August 06, 2018, 06:40:57 pm
So the logging engine logs points to EEPROM. Every 60 points, it reads all the points from EEPROM and flushes them to SD card. If you power off the meter completely and restart logging, are the points still stuck there? You may have gotten a bad EEPROM for some reason. I can't think of anything else except a bad EEPROM or cosmic rays which would cause this. Maybe it got write protected somehow, but the built in write protection circuitry should have crashed the processor.

I just started a new log, I'll have a look tomorrow morning how it looks. Where did you see that the meter logs 60 points to EEPROM before flushing? I couldn't find any reference to that. I'm still cautiously optimistic that this is a software bug rather then a hardware error. Maybe this problem occurs universally with the above parameters and is being caused by the long interval, or the date ticking over to the next day during the measurement, or a combination or maybe something completely else. :-//
I'll also do some logging with a short interval, see where that leaves me.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 06, 2018, 07:08:23 pm
So the logging engine logs points to EEPROM. Every 60 points, it reads all the points from EEPROM and flushes them to SD card. If you power off the meter completely and restart logging, are the points still stuck there? You may have gotten a bad EEPROM for some reason. I can't think of anything else except a bad EEPROM or cosmic rays which would cause this. Maybe it got write protected somehow, but the built in write protection circuitry should have crashed the processor.

I just started a new log, I'll have a look tomorrow morning how it looks. Where did you see that the meter logs 60 points to EEPROM before flushing? I couldn't find any reference to that. I'm still cautiously optimistic that this is a software bug rather then a hardware error. Maybe this problem occurs universally with the above parameters and is being caused by the long interval, or the date ticking over to the next day during the measurement, or a combination or maybe something completely else. :-//
I'll also do some logging with a short interval, see where that leaves me.

I've done a complete reverse engineering (https://github.com/tpwrules/121gw-re) of the v1.02 firmware, which is how I know basically all the information I've posted in this thread. I pored over my disassembly for anything that could explain this bug but I don't see anything. The fact that it's writing bogus data but at a consistent interval is really weird. As you can see, someone else reported something similar. It's 100% a fixable software issue, except for maybe cosmic rays or damage to the EEPROM. Could you reprogram your meter with the v1.02 firmware and see if the issue is still there? I understand it a little more than v1.22. If you can't reproduce the issue, then I can look at what's changed between the versions for clues. Is there any chance whatsoever you own an ARM SWD CMSIS-DAP programmer?

There is a way to test if the EEPROM became write protected. Set up your experiment, start logging, wait however long, then hold the MEM button to turn off logging. Without turning off the meter, turn the dial to your favorite selection and note what mode is shown on the screen. Now, press the MODE key to change modes, and note what mode is now shown. Wait a few seconds, turn the dial to another selection, and then back to your favorite. If the mode shown is the one before you pressed the MODE key, the EEPROM is going into write protection somehow.
Title: Re: Millivolt (mV) measuring issue when using EEVBlog uCurrent
Post by: vyruz on August 06, 2018, 09:31:44 pm
Haven't seen a reply to this and it's being buried under other issues people are posting. Can anyone confirm the behavior I've demonstrated in the video?
Hi everyone,

I received my 121GW 2 weeks ago and am really happy with it, great job Dave!
It wasn't until this week that I had time to play with it. I decided to test the meter's ultra-low current measuring capabilities, something for which I've relied on my trusty EEVBlog uCurrent gold until now.
Good news: The 121GW can measure mA and uA very well, no need for my uCurrent anymore :)

But that's not what this post is about.
While comparing measurements of my uCurrent I hooked the uCurrent up to the 121GW, and set the 121GW to the mV measuring setting, and noticed something strange.
While the V setting seems to do fine, the mV setting is giving weird measurements. I couldn't identify another means of generating a reliable sub-10mV source right away, so I only tested with the uCurrent.
I made a video of the whole process since I'm not ruling out at all that I botched something which resulted in this behavior :):
https://www.youtube.com/watch?v=6OoFH99jLOU (https://www.youtube.com/watch?v=6OoFH99jLOU)
I had my bench PSU set to 10V and applied this across a 1.8k resistor. This should give ~5.5mA current, which I also did measure when I had to the 121GW set to V, but when I set it to mV, the results were way off, it was showing ~0.260 mV while I was expecting ~5.550. To my surprise, when dropping the voltage on my bench PSU to 5V (expecting to measure ~2.7mA or ~2.7mV on the uCurrent), the voltage on the 121GW went UP to ~2.000 mV ?!?

Something else which I forgot to record on the video, but perhaps someone else can try:
using the uCurrent, I was measuring an ESP module running at 70mA, with the 121GW set to V the measurement from the uCurrent was 0.0070V, which is correct.
But when I switched the 121GW to mV, the measurement was reading ~7.000mV, so there seems to be a decimal point issue here.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 06, 2018, 11:18:05 pm
TPW,  did you happen to archive the original firmware from the prototype meter? 

Unfortunately, no. I'm not even sure my prototype meter came with prototype firmware, I think it was just v1.01. I honestly can't remember.

The attached video is showing how the patched 1.02 compares with the original firmware's auto-ranging speed.   If you have an older version, if may be worth understanding why there is such a dramatic difference. 

Since I don't have the original firmware, I instead compared v1.02's behavior with v1.22's. As for every problem which faced the firmware engineers, they implemented a function, some timers, a handful of globals, and some conditions which together comprise a poorly programmed and even more poorly thought out "fix".

Here's the behavior in v1.22. It's the same code as v1.02, except the "mode/range change delay" in ohms is now 0, i.e. the meter will perform an autorange on the next sample. This figure was 1 or 2 in v1.02, depending on range. To replace that, there is now an "autorange lock" function called right before the autorange change happens. Rule A: If not in ohms mode, the change is allowed. Rule B: If in ohms mode and changing to a lower range, deny changes for 1 second, then allow all changes. Rule C: If in ohms mode and changing to a higher range, deny the change, then allow one to happen in 1 sample. This leads to some bizarre behavior. If changing from a lower to a higher range, the meter will switch ranges quickly as expected. However, if changing from a higher to a lower range, Rule B above will force the meter to range down as quickly as possible, until either it's at the lowest range or a new ADC measurement arrives. Then it will use each sample to decide to range up, and eventually end up at the desired range. This behavior can easily be demonstrated by starting with open leads and connecting the meter to something like a 100k resistor.

This behavior to me is completely crazy. I don't quite understand the code behind the rules or what purpose they serve, but they are clearly there. I have no idea why they designed it like this. My fix was extremely simple: If the autorange triggered a range change, set the mode/range change delay to 0 in all cases. Maybe that oscillated sometimes, or maybe their method gets 0.001% more accuracy out of the ADC. But based on the above, there's no way to tell why the prototype firmware behaved like it did, and I'm not entirely sure I want to know.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 06, 2018, 11:40:40 pm
This behavior to me is completely crazy. I don't quite understand the code behind the rules or what purpose they serve, but they are clearly there. I have no idea why they designed it like this.

What's worse, is the behavior appears and acts completely crazy. So much so, that I don't think I would be prepared to use my 121GW for resistance measurement. That function for me is effectively absent from the meter.

Resistance measurement should either be "slow and sure", or not at all.

I don't care a fig if the autoranging is slower than other meters as long as it actually works.

(Having re-read my post, I should clarify. It would of course be great if the auto-ranging for resistance were "fast and sure", but if it is a choice between "fast and unreliable" or "slow and sure", then I want slow and sure. Messing up the functionality in order to win some hypothetical speed race with other meters is not a good way to proceed.)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 07, 2018, 01:02:21 am
I am not suggesting that the original firmware was bug free by any means.  It makes me wonder if they (UEI) can't produce firmware for the meter, what's the future plans.  It's painfully obvious they are unable to test the code they release.   If you are going to charge a premium for it, it should at least perform as well as other meters in that price class and I don't see that happening today.

I'm about to start my own open source firmware project for all the bugs and idiosyncrasies I have pointed out. I have lots of very unkind words regarding the firmware design and implementation, which I will not repeat here because I don't believe them to be useful. Instead, I will aim to correct them in my own code and perhaps lead by example.

However! I am starting open source firmware only because I want to. I think it's unfair for me (and whoever will contribute in the future) to have to provide all of the features that are promised, and perhaps to influence future UEI meters. I think it's even more unfair for owners of the meter to have to rely on the free time of some bored college kid (and the free time of future contributors) to make their ~$400 instrument usable.

The other great loss of an open source firmware is that UEI has presumably acres of expensive testing, characterization, and calibration equipment they can use to make the meter the best it can be (whether they use it is another matter). An open source firmware would have to rely on the generous effort of people like joeqsmith and others in this thread who have access to similar equipment in order to make the guarantees that make the equipment worth its price. Will this be practical? I guess we will soon see.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tsman on August 07, 2018, 03:17:47 am
The card is a pain for logging.  I have left the meter apart since starting this little side project.  I don't have long enough finger nails to reach the card and my fingers are too large.  So needle nose pliers.
A small piece of tape on the card as a pull tab makes it so much easier to extract the card.

It makes me wonder if they (UEI) can't produce firmware for the meter, what's the future plans.  It's painfully obvious they are unable to test the code they release.
I wondering if it is because it is a STM32 inside and they're having issues with development + testing. The 121GW development video mentions that it originally a PIC with a choice of a MSP430 as well but UEI changed it for a STM32 later on.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Andrew McNamara on August 07, 2018, 06:17:14 am
The other great loss of an open source firmware is that UEI has presumably acres of expensive testing, characterization, and calibration equipment they can use to make the meter the best it can be (whether they use it is another matter). An open source firmware would have to rely on the generous effort of people like joeqsmith and others in this thread who have access to similar equipment in order to make the guarantees that make the equipment worth its price. Will this be practical? I guess we will soon see.

UEI are seriously missing a trick here - Open Sourcing their code would make this meter into a unique platform, and the extra eyeballs would quickly solve these niggling firmware issues. They're likely worried about clones, but I doubt keeping the source secret will slow the cloners down much - they need to have more confidence in the value of their offering.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanJ on August 07, 2018, 06:32:43 am
The other great loss of an open source firmware is that UEI has presumably acres of expensive testing, characterization, and calibration equipment they can use to make the meter the best it can be (whether they use it is another matter). An open source firmware would have to rely on the generous effort of people like joeqsmith and others in this thread who have access to similar equipment in order to make the guarantees that make the equipment worth its price. Will this be practical? I guess we will soon see.

UEI are seriously missing a trick here - Open Sourcing their code would make this meter into a unique platform, and the extra eyeballs would quickly solve these niggling firmware issues. They're likely worried about clones, but I doubt keeping the source secret will slow the cloners down much - they need to have more confidence in the value of their offering.

My opinion is that it's probably less about clones and more that UEI probably have quite a lot of routines and generic blocks of code in the meter that they use or want to use in forthcoming products and don't want to give those ideas away...…...I couldn't blame them for that. I think the fully open source idea would only have happened if it had been designed that way from the start......but then price point and timing would have been affected.

Ian.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Andrew McNamara on August 07, 2018, 07:01:38 am
My opinion is that it's probably less about clones and more that UEI probably have quite a lot of routines and generic blocks of code in the meter that they use or want to use in forthcoming products and don't want to give those ideas away...…...I couldn't blame them for that. I think the fully open source idea would only have happened if it had been designed that way from the start......but then price point and timing would have been affected.

Maybe, although tpw_rules's analysis suggests coding is not their strength...  :(

My feeling is the UEI could benefit enormously from an Open Source code base for this meter - if they are unable to release their code for whatever reason, an alternative would be for them to actively participate in the development of an Open Source alternative code base, and to seriously consider using this as the shipping code when it's ready. At the very least, stating that they support the effort would win them some points.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 07, 2018, 07:24:02 am
I wondering if it is because it is a STM32 inside and they're having issues with development + testing. The 121GW development video mentions that it originally a PIC with a choice of a MSP430 as well but UEI changed it for a STM32 later on.

I doubt that it should be that. Software engineering is a generic skill, just like hardware engineering. Apparently many weaknesses in the code relate to structure and organization, which would point to poor design skills.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nugglix on August 07, 2018, 07:37:01 am
I doubt that it should be that. Software engineering is a generic skill, just like hardware engineering. Apparently many weaknesses in the code relate to structure and organization, which would point to poor design skills.

See  https://en.wikipedia.org/wiki/Conway%27s_law
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on August 07, 2018, 03:09:12 pm
Here's the behavior in v1.22. It's the same code as v1.02, except the "mode/range change delay" in ohms is now 0, i.e. the meter will perform an autorange on the next sample. This figure was 1 or 2 in v1.02, depending on range. To replace that, there is now an "autorange lock" function called right before the autorange change happens. Rule A: If not in ohms mode, the change is allowed. Rule B: If in ohms mode and changing to a lower range, deny changes for 1 second, then allow all changes. Rule C: If in ohms mode and changing to a higher range, deny the change, then allow one to happen in 1 sample. This leads to some bizarre behavior. If changing from a lower to a higher range, the meter will switch ranges quickly as expected. However, if changing from a higher to a lower range, Rule B above will force the meter to range down as quickly as possible, until either it's at the lowest range or a new ADC measurement arrives. Then it will use each sample to decide to range up, and eventually end up at the desired range. This behavior can easily be demonstrated by starting with open leads and connecting the meter to something like a 100k resistor.

Hot off the presses is the v1.25 release, which claims to fix this behavior, and in fact does. They've reinstated the mode/range change delay, but kept all the autorange lock stuff. There seems to be a lot more code related to the HOLD feature when in ohms mode and 50M range, maybe that fixes the "loop"? It's so difficult to understand.

They also tried to fix the noisy 5M range, not by changing the hardware configuration like this thread tried, but by cranking up the smoothing way past reasonable. As I mentioned before, the displayed value was the rolling average over the last 10 (I misunderstood and wrote 20) readings, and the averaging would reset if there was a delta of more than 20 counts. Now, it's the last 50, and the averaging resets with a delta of 300.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Caelarius on August 07, 2018, 05:04:22 pm
I've done a complete reverse engineering (https://github.com/tpwrules/121gw-re) of the v1.02 firmware, which is how I know basically all the information I've posted in this thread.
how.

Ah, that was you? Awesome work that! I read the post at that time, but forgotten who did that in the meantime  :)

I pored over my disassembly for anything that could explain this bug but I don't see anything. The fact that it's writing bogus data but at a consistent interval is really weird. As you can see, someone else reported something similar. It's 100% a fixable software issue, except for maybe cosmic rays or damage to the EEPROM. Could you reprogram your meter with the v1.02 firmware and see if the issue is still there? I understand it a little more than v1.22. If you can't reproduce the issue, then I can look at what's changed between the versions for clues. Is there any chance whatsoever you own an ARM SWD CMSIS-DAP programmer?

There is a way to test if the EEPROM became write protected. Set up your experiment, start logging, wait however long, then hold the MEM button to turn off logging. Without turning off the meter, turn the dial to your favorite selection and note what mode is shown on the screen. Now, press the MODE key to change modes, and note what mode is now shown. Wait a few seconds, turn the dial to another selection, and then back to your favorite. If the mode shown is the one before you pressed the MODE key, the EEPROM is going into write protection somehow.

I'll give that a go later. I needed my meter for different purposes today, so haven't had the chance to go through some reproducing scenario's like I mentioned before. It's currently logging again. After that, I'll give firmware 1.25 and 1.02 a go to see how they behave. I'll try to scrounge up some time for that in the upcoming days.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 07, 2018, 05:10:16 pm
Hot off the presses is the v1.25 release, which claims to fix this behavior, and in fact does.
I am not too surprised to hear this. 

I noticed I have cracked the SD card connector.  I am surprised none of the pins nave broke yet as many times as I have cycled the card in and out.   I always saw this as a mechanically weak point and thought they would do something to try and make it more robust in the final design but it appears to still be the same. 

Something to be aware of.  It's not Fluke tough and needs to be treated like a princess.     
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 07, 2018, 05:47:30 pm
Yep, FW 1-25 fixed several oddities of the Ohm mode.

The 5 MOhm is far more stable, and  it is not that susceptible to 50Hz mains influence any more.
Could do even better, if a capacitor is paralleled.
But I would call that a Fix.

Also, auto-ranging seems to work fine now, no false intermediate readings any more, and auto ranging speed seems to be the same as before.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on August 07, 2018, 06:44:28 pm
Also, auto-ranging seems to work fine now, no false intermediate readings any more, and auto ranging speed seems to be the same as before.

With 1.25 I am still consistently picking up a false intermediate reading in the 50 MOhm range when I short the probes, pretty much exactly as it did with 1.22.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 07, 2018, 07:09:00 pm
Plots comparing the various versions of firmware.   Again, this is the same resistor, same location on the bench, same batteries. 

For 1.25, tried the tape eraser test.   I zoomed into the data and turned off everything except version 1.0, 1.22 and 1.25.   

I also added the autorange speed test to the previous video. 

https://youtu.be/q4h4ieNCN0I
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 07, 2018, 08:03:26 pm
Same data zoomed in a little further with thicker lines to show a better contrast between the data sets. 

It's strange that on every release the noise seems to get worse.  I can go back to an old version and it will calm back down so it does not appear to be anything with the test setup.   It appears to be very reproducible but perhaps something else is going on. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 07, 2018, 09:45:04 pm
Just for transparency sake and to provide you with some data on repeatability after running the sweep using the new 1.25 firmware I reinstalled  TPW_rules's modified version of 1.02.  Picture showing the test setup. Basically meter sitting on the bench with the CADDOCK TK resistor installed.   Nothing fancy.   This time, I did however at 2450 data points swept around the meter with the tape eraser like I did with 1.25.

The plots show the two data sets using the 1.02 firmware.  One from yesterday and the other just now.  The office temperature again is not constant.   The meter appears almost immune to the tape eraser.   

I included the latest firmware in blue for a reference.  I have to conclude that the firmware is worse than ever in regards to the noise level and sensitivity to the tape eraser.   If anyone feels that the test is invalid for some reason or has some suggestion for a better way to test it, let me know.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on August 08, 2018, 04:38:38 am
Fw 1.25

1.- I also see intermediate values on the Ohm range.

2.- When looking at the mem values, the background measurements still handles the decimal point, very easy to reproduce:
- Record some values
- Set the meter to ohm
- View the recorded data
- Immediately short the probes

You will see the problem.


3.- The temperature measurement still goes crazy for some time while measuring the mains frequency


More coming

David DLC

Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 08, 2018, 07:56:36 am
The also doesn;t default to the "white mode" when turned off.

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 08, 2018, 09:52:13 am
DavidDLC and joeqsmith,

concerning the noise, are you referring to data logged to SD card?

The reading on the display is now stable, compared to 1-22, and as far I could determine.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 08, 2018, 04:23:44 pm
DavidDLC and joeqsmith,

concerning the noise, are you referring to data logged to SD card?

The reading on the display is now stable, compared to 1-22, and as far I could determine.

Frank
In my case, I am always referring to the data collected on the SD card.  I have no desire to watch the LCD for 40 minutes and try to manually pick out any sort of trend.   

Again, keep in mind this is not the same hardware you are testing.  I have damaged the meter three times and have changed some of the hardware in an attempt to make it more robust.  I have also completely realigned the meter.   Maybe there is some other difference.   

I would expect with your setup you should easily replicate anything I show.   If you are seeing something different there must be something we have not accounted for.   

I did make a short video for you.   I start out with the modified 1.02 firmware.  I just let it run for a few minutes.  You can see the drift as the meter warms up.   Again, I assume this is caused by the Hycon chip they chose.    I always found it strange they used that part after Dave's review of the Keysight meter.    Anyway,  I then reprogrammed the latest firmware and let the meter run for 15 minutes or so to stabilize.   I then captured some video while it continued to run for several more minutes.   

One point of interest is that I understood  the kickstart to have roughly 2000 participants and that the vast majority have been delivered.  I assume very few people have firmware 1.0 installed.   Your recent post where you used the 1.9M was really brought my attention to this potential problem.  It does not seem to be common.  So, it's possible that people are just trusting the meter is fine.   Perhaps they really have no need for a higher class meter and bought it for other reasons.    Another possibility is they are not seeing the problem.   If it's the later, then why.   Also,  why would your meter all of a sudden behave different from mine.    Mine seems to reproduce based on the firmware but then again, as many tests as I have ran, we still don't have a lot of data showing how repeatable my results are.  We may just be chasing our tails right now.  It may be a case where we just have to wait for a next generation of the meter (assuming they go ahead with it) and I can have a look at the latest hardware. 

******************
Pulled the video for now.  I have ran a much larger test and put together a video explaining some of the data I have collected and will include this short clip as part of it.   

****  Updated with additional testing and description ****
https://youtu.be/RWqP0gM_Qf0
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 08, 2018, 06:11:12 pm
One point of interest is that I understood  the kickstart to have roughly 2000 participants and that the vast majority have been delivered.  I assume very few people have firmware 1.0 installed.   Your recent post where you used the 1.9M was really brought my attention to this potential problem.  It does not seem to be common.  So, it's possible that people are just trusting the meter is fine.

I bought the meter out of curiosity, and because it might have some useful features.

I have not had time to give it a comprehensive evaluation, but I have decided for now that I don't trust any of the resistance ranges.

So I for one don't think the meter is "fine". So far, it passes as a curiosity, but not as a working tool. For a working tool I trust my Brymen meters.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on August 08, 2018, 06:56:28 pm
One point of interest is that I understood  the kickstart to have roughly 2000 participants and that the vast majority have been delivered.  I assume very few people have firmware 1.0 installed.   Your recent post where you used the 1.9M was really brought my attention to this potential problem.  It does not seem to be common.  So, it's possible that people are just trusting the meter is fine.

I bought the meter out of curiosity, and because it might have some useful features.

I have not had time to give it a comprehensive evaluation, but I have decided for now that I don't trust any of the resistance ranges.

So I for one don't think the meter is "fine". So far, it passes as a curiosity, but not as a working tool. For a working tool I trust my Brymen meters.

I think most people haven't had the time and inclination to do this kind of evaluation, so who knows how common it is.

I got mine for the low burden and as a curiosity. I personally would have been shocked if it didn't have some problems, I'm a software engineer, I know what version 1.0 is like. I just hope the hardware design is sound enough that the roughest edges can be taken off with firmware updates.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 09, 2018, 06:03:06 am
In my case, I am always referring to the data collected on the SD card.  I have no desire to watch the LCD for 40 minutes and try to manually pick out any sort of trend.   

OK, and I was referring to the stability on the display, where you need a couple of seconds only to see, that it's now stable to the last digit
The SD card logging, though, contains completely other data, 50 times more noisy, and a different average value, see graph.
That's not usable, analysis from disassembling by tpw_rules explains the whole story.

Again, keep in mind this is not the same hardware you are testing.  I have damaged the meter three times and have changed some of the hardware in an attempt to make it more robust.  I have also completely realigned the meter.   Maybe there is some other difference.   

I would expect with your setup you should easily replicate anything I show.   If you are seeing something different there must be something we have not accounted for.   

Well, I don't think, that this makes a qualitative difference, as I in fact see the same behavior.

I did make a short video for you.   I start out with the modified 1.02 firmware.  I just let it run for a few minutes.  You can see the drift as the meter warms up.   Again, I assume this is caused by the Hycon chip they chose.    I always found it strange they used that part after Dave's review of the Keysight meter.    Anyway,  I then reprogrammed the latest firmware and let the meter run for 15 minutes or so to stabilize.   I then captured some video while it continued to run for several more minutes.   

Thanks a lot! Very instructive, and confirms that for recent firmware 1-25, the logged data is noisy, in contrast to the displayed data.

One point of interest is that I understood  the kickstart to have roughly 2000 participants and that the vast majority have been delivered.  I assume very few people have firmware 1.0 installed.   Your recent post where you used the 1.9M was really brought my attention to this potential problem.  It does not seem to be common.  So, it's possible that people are just trusting the meter is fine.   Perhaps they really have no need for a higher class meter and bought it for other reasons.    Another possibility is they are not seeing the problem.   If it's the later, then why.   

Well, only few people of this Kickstarter project have the means to check the 121GW in depth, and even less might go into detail, and just trust the manufacturer, with Dave as the initiator in the background.

Nevertheless, it's very positive, that several members of  the eevblog community take their time to make a deep analysis of the faults and traps of this eevblog DMM, and especially for me it's a great pleasure to cooperate with you and tpw_rules on this special problem.

Btw.: I signed up for this 121GW, because I wanted to have THE 'Dave-O-Meter', which is simply iconic.
Initially, I did not expect this instrument to be perfect.
So I also expected to have some fun in detecting errors in the instrument, and in the documentation.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on August 09, 2018, 10:40:42 am
I've contacted Hycontek about the HY3131 Configuration Application Notes (APD-DMM003) that's mentioned on their site, and they've kindly emailed it to me.

Maybe it has some useful information for 121gw-re project. I noticed it's not yet included in the pdfs folder so I thought I post it here (had to zip it as it was >1MB):




Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 09, 2018, 11:36:35 am
I wondering if it is because it is a STM32 inside and they're having issues with development + testing. The 121GW development video mentions that it originally a PIC with a choice of a MSP430 as well but UEI changed it for a STM32 later on.

Correct. It was changed from a PIC to an STM32 at their request. I chose the final STM part used, but IIRC they said they hadn't done STM dev before that. We don't have visibility on their development environment and how they use it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 09, 2018, 12:01:45 pm
I noticed I have cracked the SD card connector.  I am surprised none of the pins nave broke yet as many times as I have cycled the card in and out.   I always saw this as a mechanically weak point and thought they would do something to try and make it more robust in the final design but it appears to still be the same. 

The SD card was added after the case tooling was done. We did not want to scrap it all and do it again.
The meter was never designed to be a heavy use and convenient data logger (the SD card was always going to be under the cover for safety compliance reasons).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 09, 2018, 01:26:04 pm
Maybe the newer firmware enables more hardware options and it causes the noise.

What is the name of the software you are using to plot the logs?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: floobydust on August 09, 2018, 07:27:20 pm
On another product, I have seen the ohms constant-current source be noisy or even oscillate.
Try adding small capacitance across the resistor-under-test to see if it's a hardware issue. Firmware can average small oscillations and AC hum to a point.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: AdamHi on August 10, 2018, 09:49:14 pm
5 mA DC range FAILS again - can anybody replicate?

So i got a replacement 121GW after the problem i had with my first unit (see my posts
 https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1692650/#msg1692650 (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1692650/#msg1692650)
and
https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1693298/#msg1693298) (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1693298/#msg1693298))

I repeated the same tests with a 1 mA DC source, and got essentially the same results, here are photos showing the poor measurement on the 5 mA DC range, but the perfect measurement on the 50 mA range, on my Amprobe AM270 meter, and also using the uCurrent Gold.

Summary: On the 5mA DC current range, the 121GW reads off, and is quite significantly affected by touching the leads. None of these effects are seen on the 50mA range, on the Amprobe meter, nor when using the uCurrent.

Can anybody replicate these findings? Figure out a way to mitigate this problem? Should I consider the 5mA DC current range to be an "extreme" measurement and i'm just expecting too much? I wouldn't think so in a meter in this price range, considering the Amprobe is a significantly lower price class instrument. I kind of think Dave would be giving a Thumbs Down  :-- on this performance if he was reviewing it.

Thanks.

--adam
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on August 11, 2018, 12:44:48 am
If I compare my U1252A and 121gw - measuring about 1mA in series with each other and using uA range on U1252A to get the same resolution - I can make 121gw go +/- 30 counts depending on where I touch the cables. The U1252A only flicker on 1 count.

FW ver. 1.25

Title: Re: EEVblog 121GW Multimeter Issues
Post by: AdamHi on August 11, 2018, 03:07:45 am
Thanks for checking in Joe.
I assume you checked your test setup before concluding the 121GW was defecting and returning it.   

I was asked to perform the two DMM's in series set-up as shown in second post, and again here, before the meter defected back to KaneUSA. I showed that 121GW was way off and bounced around, while other meter, connected in series, was rock solid. 121GW was also rock solid on the next range up (50mA). And in this most recent post showed that uCurrent also gives rock solid output given the same 1mA source.

BTW - New meter is running FW 1.25

Quote
What's the output of your test signal look like?  How did you check it?

Connected the same 1mA source to uCurrent (1mV/uA), and put the voltage output of that to scope. Wasn't sure of exact proper method, was a bit kludgy looking (10x scope probe clipped to one output, ground to other), DC coupled; see other parameters in screen grabs below at 50us, 5ms, and 100ms per division.

With the sensitivity to touching the probes that i have seen on both 121GW's, but not on my Amprobe or uCurrent, as has
. . . . I can make 121gw go +/- 30 counts depending on where I touch the cables. The U1252A only flicker on 1 count.
it seems that the 121GW is excessively sensitive to either stray capacitance, or EM pickup, pushing it out of spec.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 11, 2018, 07:36:47 am
5 mA DC range FAILS again - can anybody replicate?

So i got a replacement 121GW after the problem i had with my first unit (see my posts
 https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1692650/#msg1692650 (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1692650/#msg1692650)
and
https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1693298/#msg1693298) (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1693298/#msg1693298))

I repeated the same tests with a 1 mA DC source, and got essentially the same results, here are photos showing the poor measurement on the 5 mA DC range, but the perfect measurement on the 50 mA range, on my Amprobe AM270 meter, and also using the uCurrent Gold.

Summary: On the 5mA DC current range, the 121GW reads off, and is quite significantly affected by touching the leads. None of these effects are seen on the 50mA range, on the Amprobe meter, nor when using the uCurrent.

Can anybody replicate these findings? Figure out a way to mitigate this problem? Should I consider the 5mA DC current range to be an "extreme" measurement and i'm just expecting too much? I wouldn't think so in a meter in this price range, considering the Amprobe is a significantly lower price class instrument. I kind of think Dave would be giving a Thumbs Down  :-- on this performance if he was reviewing it.

Thanks.

--adam

I have never seen this issue. Many people have measured all current range and they are spot on. Every unit is fully calibrated before shipping. You must be using it in some environment or under some condition that is causing some sort of interference issue. We will need to be able to replicate this before being able to comment further.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 11, 2018, 07:59:24 am
v1.26 is now on the website for download. We have not tried it yet, but UEi have said that it now logs the displayed data instead of the bargraph data. There should now be no noise on the logged data as per previous versions. Please try it and report.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 11, 2018, 08:31:57 am
This is the only change?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 11, 2018, 09:46:08 am
This is the only change?

Yes, I believe so.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on August 11, 2018, 10:12:17 am
v1.26 is now on the website for download. We have not tried it yet, but UEi have said that it now logs the displayed data instead of the bargraph data. There should now be no noise on the logged data as per previous versions. Please try it and report.
Dave sorry to report that the new V1.26 will not load!
Tried numerous times and then copied V1.25 back onto the SD card and it loaded fine.
Maybe something wrong with the file image you have placed on your site to download?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: knapik on August 11, 2018, 10:34:54 am
v1.26 is now on the website for download. We have not tried it yet, but UEi have said that it now logs the displayed data instead of the bargraph data. There should now be no noise on the logged data as per previous versions. Please try it and report.
Dave sorry to report that the new V1.26 will not load!
Tried numerous times and then copied V1.25 back onto the SD card and it loaded fine.
Maybe something wrong with the file image you have placed on your site to download?

Seems as if I am facing a similar issue.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: knapik on August 11, 2018, 10:38:15 am
I guess it also helps to have the microSD card plugged in :-[
It worked fine for me after a small technical issue.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 11, 2018, 10:52:52 am
No problem for me. Did you rename the file to EEVBlog.bin?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on August 11, 2018, 11:03:32 am
Damn I didn't drop off the version number from the bin file!
I'll try again.
Yep that was my dumb mistake, you would think after the numerous firmware upgrades I would have remembered to do that  :palm:
Title: EEVblog 121GW Multimeter Issues - FW 1-26 datalogging
Post by: Dr. Frank on August 11, 2018, 12:41:16 pm
Yes, it works now, logged data are derived from display, which was 4.4993M +/- a few counts in average
Great job & support by UEI.


THX - Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 11, 2018, 12:47:07 pm
I think so, did not yet test 1.0

Here's the same log with with 1-00. sample rate is also 4Sa./s
Obviously, data were also fetched from the display, seems to be more noisy, again, as in the beginning and the end, it reacts very sensitively to my hand movement.
This initial drift / relaxation seems to exist, also.

PS: These different average values might be caused by the temperature rise / change here in my bureau.
Back on FW 1-26, reading is now also at 4.5023M, and logging looks very similar to 1-00.
These 5 / 50M ranges are very sensitive to hand movement, but that's quite normal @ 200nA and 20nA, but not to 50Hz mains influence, obviously.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on August 11, 2018, 03:05:08 pm
5 mA DC range FAILS again - can anybody replicate?
I just tried with firmware 1.25 and the 121GW of course and a Brymen 235, Fluke 27II and 2 other DMMs in series. As source I used my DMMCheck Plus vom voltagestandard.com as you did and I think I used the same green 4mm banana cable and the clips from Franky ;-). I could not reproduce the problem you have. So it may have something to do with your configuration I think. How about the 9V battery of your DMMCheck Plus, maybe it's somewhat flat even if the Amprobe shows the correct value?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on August 11, 2018, 03:28:51 pm
In my test I used a AD587 5V source + 5.1K metal film resistor as a current source.

I'm not really suggesting that the 121gw is 'faulty' for being much more sensitive to EM fields than i.e. U1252A - but I think its an important fact to know about. Also I think the 121gw would be much easier to use if it wasn't that EM sensitive.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: fubar.gr on August 11, 2018, 09:38:43 pm
I have this weird problem that started after I used the multimeter to log my socket voltage (230V AC, 50Hz) for a full day.

Now in VAC mode, the autoranging continuously hunts. If I manually select the range, it shows weird and very low values. It seems to get the frequency right though. It also shows the correct value in 1ms peak mode.

Is my meter farked?

EDIT: Tried installing latest (1.26) firmware. Nothing changed.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 11, 2018, 09:43:56 pm
5 mA DC range FAILS again - can anybody replicate?

So i got a replacement 121GW after the problem i had with my first unit (see my posts


I repeated the same tests with a 1 mA DC source, and got essentially the same results, here are photos showing the poor measurement on the 5 mA DC range, but the perfect measurement on the 50 mA range, on my Amprobe AM270 meter, and also using the uCurrent Gold.

Summary: On the 5mA DC current range, the 121GW reads off, and is quite significantly affected by touching the leads. None of these effects are seen on the 50mA range, on the Amprobe meter, nor when using the uCurrent.

Can anybody replicate these findings? Figure out a way to mitigate this problem? Should I consider the 5mA DC current range to be an "extreme" measurement and i'm just expecting too much? I wouldn't think so in a meter in this price range, considering the Amprobe is a significantly lower price class instrument. I kind of think Dave would be giving a Thumbs Down  :-- on this performance if he was reviewing it.

Thanks.

--adam

I tested the 5mA DC range of the 121GW, with a precision DC current source, and a 34465A in series.

The 121GW is rock solid, even testing with a strong magnetic 50Hz disturbance by transformer did not show any deviation  to the last digit.

I also tested the ac rejection, when I applied a sine wave ac current.
The 121GW in its 5mAdc range shows about +/- 50 counts in very random manner, when I apply 100µAac, the 34465A suppresses this signal about ten times better.
At 10µAac, the 121GW reads about zero.

That means, if you see variations, there must be a strong ac current present in your setup....

Think about it, it's extremely improbable, that two new instrument would be both defective, if nobody else can reconstruct this sensitivity against external noise.

You have set up the  experiment both times in the same manner, if I understood you correctly, so you might also have replicated the probably erroneous setup.
It would have been better to modify your setup, before concluding that the 121GW is defective.

I have one idea, what could be your problem:
The DMMCheck PLUS has a small ac/dc switch, which type I assume to be unreliable.
So it could output the 1mA ac current, even  if it's set to dc current.

The ac current seems to be a pulsed square wave dc current only, i.e. a 2mA switched unipolar signal, in contrast to the ac voltage, which is a 'true bipolar' square wave.

So the 121GW would see a relatively strong 100Hz ac current, which is not averaged as well as other dual / multiple slope instruments.. and the other DMM could average that to 1mA, as this might be the correct average, but also the rms value (I have to confirm that by the correct math).

So please check with both instruments, whether this supposed dc current gives a reading on the ac current ranges.

There could also be some other failures, like oscillations of the DMMcheck, too high compliance voltage (500mV max!), disturbance from the other DMM, cable or plugs error (the 121GW has segmented current jacks!).

So from remote, it's really difficult to make a correct guess, but for me it's very improbable, that the 121GWs are the culprit.

Frank 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 11, 2018, 09:46:35 pm
I have this weird problem that started after I used the multimeter to log my socket voltage (230V AC, 50Hz) for a full day.

Now in VAC mode, the autoranging continuously hunts. If I manually select the range, it shows weird and very low values. It seems to get the frequency right though. It also shows the correct value in 1ms peak mode.

Is my meter farked?

EDIT: Tried installing latest (1.26) firmware. Nothing changed.

Did you use the LoZ mode for this test, as you explicitly stated, to be 'NOW in VAC mode' ??

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: fubar.gr on August 11, 2018, 10:10:52 pm
I have this weird problem that started after I used the multimeter to log my socket voltage (230V AC, 50Hz) for a full day.

Now in VAC mode, the autoranging continuously hunts. If I manually select the range, it shows weird and very low values. It seems to get the frequency right though. It also shows the correct value in 1ms peak mode.

Is my meter farked?

EDIT: Tried installing latest (1.26) firmware. Nothing changed.

Did you use the LoZ mode for this test, as you explicitly stated, to be 'NOW in VAC mode' ??

Frank

No, normal VAC mode. By the way, here's the logged data: http://fubar.gr/wp-content/uploads/2018/08/18080600.csv (http://fubar.gr/wp-content/uploads/2018/08/18080600.csv)

No weird values, it was still logging correctly up until the moment I stopped it.

EDIT: By the way, now that you mentioned it, the Low-Z mode doesn't seem to work correctly. When switched on shows 0.0 for a brief time and then OFL and the meter starts to beep.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DrGeoff on August 12, 2018, 12:11:11 am
Do I want to even ask why you were trying to log the AC line..  Nah.   Many people believe the meters don't need to survive a transient, just keep the operator safe.  Sounds like you are still fine.

Nothing wrong with that. I had to log the AC line for several weeks to help identify a problem with the line voltage being way too high (260VAC instead of 230-240VAC) which caused failures of several things (SMPS included). Ausgrid then performed checks and dropped the taps on the pole transformer so it's down to around 245VAC now. Really handy having the meter on hand to easily do this logging,
Title: Re: EEVblog 121GW Multimeter Issues
Post by: fubar.gr on August 12, 2018, 08:50:22 pm
In Fubar.gr's case I wonder if they damaged their meter.  The 121GW has a pretty weak front end compared with some of the other meters I have looked at.  Maybe they will chime in again with more details about the other modes.

I will test extensively in a couple of days and maybe upload a video.

Right now I have the meter at home and no way to do a meaningful test, apart from batteries and whatever else I have lying around the house. I am getting mixed results in all voltage and resistance modes, but I can't tell for sure right now.

But the Lo-Z mode seems completely dead.

How long can the Lo-Z mode withstand a 230 V AC that is not a phantom voltage, ie directly from the wall socket?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: malagas_on_fire on August 12, 2018, 09:49:19 pm
What about all of the other modes?  No mention of them.   

Do I want to even ask why you were trying to log the AC line..  Nah.   Many people believe the meters don't need to survive a transient, just keep the operator safe.  Sounds like you are still fine.

For logging AC line in university projects we used the Fluke 43B which is designed for that kind of stuff, plus report the quality of the energy.:

https://www.testequity.com/products/1076/ (https://www.testequity.com/products/1076/)

It is now outdated and a similar device is more apropriaded for this task and i believe it was rated CATIII 600. It is still used in class and projects after many years
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Medo on August 12, 2018, 10:34:11 pm
Is there a possibility to get a setup option to turn off secondary function memory?

While multimeter remembering its secondary function (e.g. temperature) and using it next time it's turned on seemed like a nice idea, I find it actually quite cumbersome in real life. It works fine when I am actively using it. However, the next day when I measure something else I find myself reaching for Mode button and cursing. :)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 13, 2018, 02:59:17 am
Trying to recreate the 1mA DC current noise problem, couldn't do it, so  :-//

https://www.youtube.com/watch?v=D00OAUr_haw (https://www.youtube.com/watch?v=D00OAUr_haw)

Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 13, 2018, 04:01:13 am
I had tried it as well towards the end of that last video.  I asked them about trying it with a battery/resistor to at least eliminate their current source.   No word if they did anything more with it.    You don't by chance have one of those meter calibrator things do you?

Not the ebay ones.
I have an Ian Johnston one, an MV106, and a couple of old school Keithley's. I can try them all and see what happens. But IIRC I've done that before without issue.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 13, 2018, 06:37:31 am
When in mA range without any probes connected the meter shows about 80 uA. When Inserting the probes goes to 800 nA and with the probes shorted it goes to 1.5 uA.

Something similar happens when in uA range. It is present only in DC mode. In AC everything is 0.000

Is it normal? Is it an effect of the opamp used for the low burden voltage?

 (https://i.imgur.com/PO2BvWZs.jpg) (https://i.imgur.com/PO2BvWZ.jpg)  (https://i.imgur.com/cwrVGzDs.jpg) (https://i.imgur.com/cwrVGzD.jpg)  (https://i.imgur.com/ZLVVEIhs.jpg) (https://i.imgur.com/ZLVVEIh.jpg)

(https://i.imgur.com/kV2xMhbs.jpg) (https://i.imgur.com/kV2xMhb.jpg)  (https://i.imgur.com/oIJF5d4s.jpg) (https://i.imgur.com/oIJF5d4.jpg)  (https://i.imgur.com/jUBnRw9s.jpg) (https://i.imgur.com/jUBnRw9.jpg)


Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: PA0PBZ on August 13, 2018, 01:37:53 pm
Looking at their pictures, I thought I could pick up the same source but they are out of stock.
http://shop.voltagestandard.com/product.sc;jsessionid=DAEB70EDBC48F53DD528284FB53FCF35.p3plqscsfapp003?productId=5&categoryId=1 (http://shop.voltagestandard.com/product.sc;jsessionid=DAEB70EDBC48F53DD528284FB53FCF35.p3plqscsfapp003?productId=5&categoryId=1)

I have one of those, I can hook it up to a scope tonight if you are interested?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: PA0PBZ on August 13, 2018, 02:15:56 pm
If you have a 121, it may be worth it.  They claim 500mV compliance but that would be with a good battery.  Looks like it has a microcontroller for some reason.   Maybe try it with the source running off your bench supply and dial it down.  Maybe it goes unstable before it drops out. 

I don't have a 121 (yet), but I can certainly torture the DMMCheck with awkward supply voltages and loads. If I find something interesting I will report here.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 13, 2018, 03:41:03 pm
Does anyone else have this offset when in DC mA range, even with the leads shorted?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 13, 2018, 05:00:54 pm
When in mA range without any probes connected the meter shows about 80 uA. When Inserting the probes goes to 800 nA and with the probes shorted it goes to 1.5 uA.

Something similar happens when in uA range. It is present only in DC mode. In AC everything is 0.000

Is it normal? Is it an effect of the opamp used for the low burden voltage?


Alexander.

Hello Alexander,
I think, everything is fine with your instrument.

At first, your pictures are not very good, display nearly unreadable, maybe you finally could remove that protection foil...

2nd, be aware, that both the current jacks have a segmented plug detector inside.. so that the instrument can detect, if and where's a plug inserted, and to beep if the jack used does not fit the selected range, and also to do some internal range switching.
If you don't plug anything in these jacks, that is a non-defined state. Maybe there's a small current flowing from the detection circuit.
Anyhow I also see some counts offset in that state.. so forget about that.

3rd, for the 50µA range at least, maybe you have a look in the manual, page 16, footnote 4, about offsets due to x10 amplification, that might also apply to other ranges.
Simply use REL to zero these effects.

4th, whenever you connect two cables, especially holding them with your warm fingers, you'll create a thermo - couple, which not only creates a thermo voltage, but also creates a current (Peltier element / Seebeck effect).
That also depends on the quality of your cables, and the finish of the tips.
You're using these cheap clamps, so that's no wonder. That should not happen (or give a small effect only) with the gold plated brymen tips.
Remember, that you're down to 1nA in these ranges, and 1µA also can easily be generated by this effect.
Try different cables, and if you don't touch that junction with your fingers, probably these currents vanish when it adopts room temperature again.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 13, 2018, 05:12:18 pm
Originally they were testing w/ 1.22 but I have no idea after that what was loaded.  I installed 1.22 in the prototype and it seems just as stable.    So I setup the Brymen BM869s next to the 121GW prototype and had some fun with the tape eraser.   

It would seem that there are a few things that the OP could have going on. 

*****

Combined it all into one video and added another test

At least, you should have set the BM869 to the same resolution, in 5000µA range, also.
Probably, the last digit would also have been affected by your tape eraser.. and as I already tested with ac currents, something in the setup of the OP creates strong disturbances, probably an alternating current from the DMMCheck.

Btw.: Where's the OP? No feedback so far?

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bratster on August 13, 2018, 05:36:44 pm
If you have a 121, it may be worth it.  They claim 500mV compliance but that would be with a good battery.  Looks like it has a microcontroller for some reason.   Maybe try it with the source running off your bench supply and dial it down.  Maybe it goes unstable before it drops out. 

Looking at the manual for the AM270, looks like in the 5000uA range its spec'ed at 150uV per uA.  Maybe just stick a 150 ohm resistor in series with the 121 to simulate it.
I have a dmm check plus  and a 121gw.

What firmware and test setup would you like to see?

I may be able to try it today.

Sent from my Fi Moto x4 using Tapatalk

Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 13, 2018, 06:35:21 pm
Hello Alexander,
I think, everything is fine with your instrument.

At first, your pictures are not very good, display nearly unreadable, maybe you finally could remove that protection foil...

2nd, be aware, that both the current jacks have a segmented plug detector inside.. so that the instrument can detect, if and where's a plug inserted, and to beep if the jack used does not fit the selected range, and also to do some internal range switching.
If you don't plug anything in these jacks, that is a non-defined state. Maybe there's a small current flowing from the detection circuit.
Anyhow I also see some counts offset in that state.. so forget about that.

3rd, for the 50µA range at least, maybe you have a look in the manual, page 16, footnote 4, about offsets due to x10 amplification, that might also apply to other ranges.
Simply use REL to zero these effects.

4th, whenever you connect two cables, especially holding them with your warm fingers, you'll create a thermo - couple, which not only creates a thermo voltage, but also creates a current (Peltier element / Seebeck effect).
That also depends on the quality of your cables, and the finish of the tips.
You're using these cheap clamps, so that's no wonder. That should not happen (or give a small effect only) with the gold plated brymen tips.
Remember, that you're down to 1nA in these ranges, and 1µA also can easily be generated by this effect.
Try different cables, and if you don't touch that junction with your fingers, probably these currents vanish when it adopts room temperature again.

Frank
[/quote]

Thanks you for the reply. I could understand it for 50 uA range and I mentioned it in my original post. But in 500 mA range also? And why only DC mode?

This offset current is always there. Regadless If I connect probes or not. I tested with many probes. With golden ones, even with a thick wire soldered directly in banana plugs.

And the most important is that the meter measures high in relation the the other meters I own. How much higher? 100 uA. Exactly the offset I see. If I rel the offset, it measures exactly like the others.

(https://i.imgur.com/Bwt9sZVs.jpg) (https://i.imgur.com/Bwt9sZV.jpg)  (https://i.imgur.com/x7IOe1Es.jpg) (https://i.imgur.com/x7IOe1E.jpg)

What the rest of you see if you sort COM and 500 mA input?

I am just trying to figure it out. To understand it.

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on August 13, 2018, 06:54:20 pm
Did you play with the calibration function of the 121GW?

I did a quick check with the DMMCheck Plus and low supply voltage. I tested with my 121GW and a Brymen 235 and a Fluke 28II in series to the 121GW with the 1 mAdc setting. The 121GW measurements are identical to the other DMMs when battery voltage of the DMMCheck Plus is reduced. At about 7,15V the output of the DMMCheck Plus begins to be bad (current drops). I didn't look what the output of the DMMCheck Plus  is like with the oscilloscope but could if interesting.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 13, 2018, 07:27:26 pm

Thanks you for the reply. I could understand it for 50 uA range and I mentioned it in my original post. But in 500 mA range also? And why only DC mode?

This offset current is always there. Regadless If I connect probes or not. I tested with many probes. With golden ones, even with a thick wire soldered directly in banana plugs.

And the most important is that the meter measures high in relation the the other meters I own. How much higher? 100 uA. Exactly the offset I see. If I rel the offset, it measures exactly like the others.

What the rest of you see if you sort COM and 500 mA input?

I am just trying to figure it out. To understand it.

Alexander.

Well, the 500 mA and upper ranges all read zero on my 121GW.

Anyhow, what you see, is probably no offset current, it must be the offset from the amplifiers, acc. to my 3rd explanation.

Remember, that this DMM is specially designed for low burden, so it contains either one or two x10 amplifiers on certain ranges, also on these higher DCI ranges.
The specification is not complete, as this footnote 4) FOR SURE applies to other ranges also, than only the 50µA.
And there's no table, which shunt / amplification combination is used for the different ranges.

So I can't judge, if this 10 count offset is too much, and what equivalent in µV that would be, or if your 121GW has another problem, like some leakage on the PCB.

You might want to open your DMM and inspect its PCB, or may also measure the voltage directly across the shunts, and the output of the 1st amplifier stage, that's the special Chopper which Dave has chosen.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 13, 2018, 08:14:42 pm
Did you play with the calibration function of the 121GW?

No.

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 13, 2018, 08:48:29 pm
Ok, here we go:

The DCI ranges vs. shunts are configured as follows:

500mA, 5A, 10A: 10mOhm (10A jack only)
5mA, 50mA: 1.01 Ohm
50µA, 500µA: 101.01 Ohm

If you calculate the equivalent voltage on each range for one count on the last digit, you'll recognize, that this equals 100nV for the 50µA, 5mA and 500mA ranges, and 1µV for the 500µA, 50mA and 5A ones.

So these 10 counts (or 100µA) you see on the 500mA range, is equivalent to an offset of 1µV only, and that is quite normal even for a chopper amplifier (MAX4238), but also for these many internal junctions you have on the PCB, including the range switch.

Simply zero that offset, and you're done.

This footnote 4) applies to all these 3 sensitive ranges.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 13, 2018, 09:08:17 pm
Thanks you very much! <3 <3 <3

 It's just I had never seen it in any other of my DMMs. 

If it was yours, would you perform a zero offset calibration?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 13, 2018, 10:32:59 pm
Well, probably yes.
I already re- calibrated 3 of the Ohm ranges, because it was done improperly (not optimal) @ UEI...
It might depend on the environmental temperature, if this offset can be persistently be calibrated, may be it vanishes, when summer temperatures go back to normal.

I'm not sure, if a zero calibration only is possible,  because both cal constants for a particular range are stored after gain adjustment only.
Therefore you might need a calibrated constant current source.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 14, 2018, 06:12:51 am
Well, probably yes.
I already re- calibrated 3 of the Ohm ranges, because it was done improperly (not optimal) @ UEI...
It might depend on the environmental temperature, if this offset can be persistently be calibrated, may be it vanishes, when summer temperatures go back to normal.

I'm not sure, if a zero calibration only is possible,  because both cal constants for a particular range are stored after gain adjustment only.
Therefore you might need a calibrated constant current source.

Frank

If I read the manual correctly it is possible to make only a zero calibration.

(https://i.imgur.com/1aDL2nGs.png) (https://i.imgur.com/1aDL2nG.png)

Since I have backed up the calibration data, is it safe to play around with calibration?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on August 14, 2018, 06:30:08 am
Well, probably yes.
I already re- calibrated 3 of the Ohm ranges, because it was done improperly (not optimal) @ UEI...
It might depend on the environmental temperature, if this offset can be persistently be calibrated, may be it vanishes, when summer temperatures go back to normal.

I'm not sure, if a zero calibration only is possible,  because both cal constants for a particular range are stored after gain adjustment only.
Therefore you might need a calibrated constant current source.

Frank

If I read the manual correctly it is possible to make only a zero calibration.

(https://i.imgur.com/1aDL2nGs.png) (https://i.imgur.com/1aDL2nG.png)

Since I have backed up the calibration data, is it safe to play around with calibration?

Alexander.

It is not safe to play around with calibration data.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 14, 2018, 06:57:55 am
Well, probably yes.
I already re- calibrated 3 of the Ohm ranges, because it was done improperly (not optimal) @ UEI...
It might depend on the environmental temperature, if this offset can be persistently be calibrated, may be it vanishes, when summer temperatures go back to normal.

I'm not sure, if a zero calibration only is possible,  because both cal constants for a particular range are stored after gain adjustment only.
Therefore you might need a calibrated constant current source.

Frank

If I read the manual correctly it is possible to make only a zero calibration.

(https://i.imgur.com/1aDL2nGs.png) (https://i.imgur.com/1aDL2nG.png)

Since I have backed up the calibration data, is it safe to play around with calibration?

Alexander.

It is not safe to play around with calibration data.

OK!

Have you noticed any 121GW meters with the display offset I describe? Should I leave it alone? :D :D :D

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 14, 2018, 08:34:39 am
Hi,
according to the manual you can make a backup of the cal data. Before playing with the calibration make a backup. In case you have messed up the calibration just restore the data. That is a very good feature from this meter.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ChrisG on August 14, 2018, 08:52:43 am
hi Dr Frank, what did you use to calibrate the ohms ranges? e.g. Vishay 0.01% low ppm resistors?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 14, 2018, 09:15:22 am
hi Dr Frank, what did you use to calibrate the ohms ranges? e.g. Vishay 0.01% low ppm resistors?

I used a massive copper short for zero (there's a thread about short construction), and a burster resistor box, and my 3458A, to have exactly 50.000 Ohm or 500.00 Ohm at the end of the cables.

For 50MOhm, I used a series circuit of several 10M thin film resistors, to trim that to exactly 50.000M, measured again by my 3458A.

That's all a bit tricky, so I plan to build an Impedance Synthesizer box for the next time.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 14, 2018, 02:42:55 pm
Comparing the 121 prototype with some of my lower end meters.  I thought I would use the Kasuntest ZT-102 and UNI-T UT61E as both of these meters were specifically modified for making this measurement.    It's becoming apparent that the 121GW prototype is unique in how sensitive it is.  I would be interesting in knowing how the hardware from the kickstart behaves.     

https://youtu.be/_u_34E5ZUOI
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on August 14, 2018, 03:29:05 pm
I only did a quick test. But let me see... shit no tape eraser around  :D.

What I did was DMMCheck Plus with 1mAdc and the 121GW with my Fluke 28II in series. Then I used a strong neodymium magnet and the 121GW reacts on it (not as much as to the electrical field of your tape eraser but noticeable) and the Fluke 28II does not. I did not do any further or deep testing and did not check other DMMs.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 14, 2018, 05:01:22 pm
Hi,
today I also made a test with a DC current calibrator with 1mA DC and a tool / head degausser. There is a clear fluctuation in the display, the same like in Joe`s video. So the 121GW is indeed still very sensitive for alternate magnetic fields, even with the latest hardware revision. (I bought my 121GW today directly by Welectron, the company is very close to my home.)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on August 14, 2018, 07:30:49 pm
So with better shielding like you made for the Gossen this should be addressable?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 16, 2018, 06:18:04 am
I repeated the same tests with a 1 mA DC source, and got essentially the same results, here are photos showing the poor measurement on the 5 mA DC range, but the perfect measurement on the 50 mA range, on my Amprobe AM270 meter, and also using the uCurrent Gold.

Summary: On the 5mA DC current range, the 121GW reads off, and is quite significantly affected by touching the leads. None of these effects are seen on the 50mA range, on the Amprobe meter, nor when using the uCurrent.

Can anybody replicate these findings?

I just did a quick test on my meter with firmware 1.26, using the 1 mA current source on a DMM Check device.

The BM869s indicated a stable 1000.2 µA in the 5000 µA range.

The 121GW indicated a stable 1.0012 mA in the 5 mA range, with some wavering of ±1 in the last digit.

I did not detect any influence of touching the test leads or waving my hands near the meter.

My guess would be that maybe you have a problem with your test setup or measurement procedure?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Towger on August 16, 2018, 08:07:20 am
My guess would be that maybe you have a problem with your test setup or measurement procedure?

Or some meters/batches are more susceptible to the problem than others. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on August 16, 2018, 09:23:29 am
Remember that Joe has a prototype that he highly modified. So everything and nothing is possible.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 16, 2018, 03:22:36 pm
Hey IanB, please try downgrading to 1.0 and see if your low resistance range becomes stable. 

I ran the same test using the UNI-T UT181A.  This meter has a 10mohm res, so you loose a digit.  Even with that handicap, the 181A still appears slightly tighter than the 121 prototype with the 1.26 firmware installed.     

Just to verify, you are measuring a 0.5 ohm resistor, not a 0.5 meg resistor as suggested by the axis label?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 16, 2018, 05:14:56 pm
0.5 ohms.  You are the one who brought it up, so what ever values you were trying to measure will be fine.  Just do a before and after comparison and report the results.  If the noise you were seeing is reduced, I think we have our answer.

Maybe I'll give it a try after work tonight.

However, the problems I was seeing seemed to be related to static fields, caused by proximity of my hands to the meter or test leads.

The only way I think firmware can fix that is by having lots of software filtering. So it might be a choice between "slow and steady" or "fast and erratic".
Title: Re: EEVblog 121GW Multimeter Issues
Post by: M4x on August 16, 2018, 05:15:53 pm
Joe should get a "regular" 121GW ;-)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on August 16, 2018, 08:13:16 pm
If/when they release it and we start seeing positive reviews,  I will be more than happy to put it through it's paces.   Seeing its a bit of a novelty, I may give it some special treatment like the Gossen and take it on a road trip.  That's big investment on my part so I want to make sure its stable first.

What do you mean release it? Dave sells it in his shop (It is out of stock) and and welectron sell it in his (And it is in stock).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 17, 2018, 10:09:20 am
Hey IanB, please try downgrading to 1.0 and see if your low resistance range becomes stable.

Here are the results of a test on a 0.5 ohm resistor sampled on a human time scale. On looking at this data I think sampling over a much longer period might also be interesting, but I don't think this is a common use case for a handheld meter. Normally you would want to apply the probes, take a reading in a few seconds, and move on to the next measurement. For such a use case I don't know if the v1.00 firmware has significant advantages over the v1.26 firmware. Even though v1.00 appears to have stronger high frequency filtering, the overall measurement uncertainty doesn't seem to be any different.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=499673;image)

Edit: Fixed incorrect firmware versions
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 17, 2018, 01:43:01 pm
Where did you find firmware version 1.7?  What is the sample rate you are using?   Are you collecting to the SD card or using BT?   

I would like to try and repeat your 90 second test.

I'm sorry, that was a brain fart resulting from working at 3am when I couldn't sleep. It was v1.00 vs v1.26 of course. I'll fix my post.

I am collecting using the SD card at the maximum sample rate (0 seconds in the setup menu). There is no time stamp included with the data values, so I am assuming 0.2 sec per sample as per the manual. It seems about right.

I tried to use Bluetooth, but the v1.00 firmware doesn't appear to work with the app. The maximum sample rate with BT is also limited to 0.5 sec.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 17, 2018, 02:26:39 pm
Can you do related test for me on your hardware?

While measuring the 0.5 ohm resistance, can you repeatedly reach out and lightly touch the Hold button with your finger and then pull it away again? Don't press the button, just touch it. Repeat the touch/withdraw cycle a few times. What happens to the reading when you do that? On my meter I can make the reading vary between about 0.2 ohms and 0.9 ohms.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 17, 2018, 03:19:39 pm
So the question now is if that 0.01 you are seeing is good enough.  It sounds like you are expecting much better results.  For some reason, I was thinking your meter had a lot more variance when you first posted about it.  IMO, on a 2 wire handheld, I wouldn't have expected it to be much better than this.   In the second attachment, I compare it with the data I collected at 1 second intervals with the other meters.  The yellow is the UNI-T UT181A.   0.01ohm res and 4 counts, its a pretty big swing.

Yes, I'm expecting much better results than I'm seeing. In my next post I'll show some other results to support my contention.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 17, 2018, 03:31:22 pm
Here's an interesting data set. I used the 121GW in two ways. On the green plot I used the 121GW to measure mV drop across the resistor when subjected to a 1 mA constant current source. On the blue plot I used the 121GW to measure the resistance directly after using the Rel button to null out the leads. Since I can't physically touch the Rel button without disturbing the reading I activated it remotely using the Bluetooth app. I also collected the data using Bluetooth since (a) it is too much trouble to reach in and retrieve the SD card and (b) when I tried to press the Mem button to start logging it appeared to disable the Rel mode.

Observations:

1. The mV reading is mostly stable to ±1 count. This for me is the ideal situation.

2. The resistance reading climbed dramatically over the test interval and was not stable. I was surprised by this so I repeated the test again, with the same outcome. The reading started around 0.5 and climbed to over 0.53.

3. At about 100 s on the green trace there are some glitches with sharp spikes in the reading followed by a decay. I did not move or touch any part of the experiment at this time, so I attribute the glitches to some environmental influence beyond my control.


(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=499727;image)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 17, 2018, 04:24:13 pm
Look at the drift in my post #583.   Once the meter has had a chance to warmup it does alright. 

I would expect the voltage would be better with that new reference in there.  That was one of the things they changed in the kickstart hardware from the prototype I have.   Dr Frank had made a few comments about the poor choice in components used in the divider network.  The short term drift as I have mentioned a few times now, I believe is the Hycon device.  Maybe UEI could chime in on this.   

I'm not expecting any equipment to come up from a cold start and instantly provide optimum results and I'm not too concerned with the drift yet.  I will leave that to Dr Frank. 

Can you do related test for me on your hardware?

While measuring the 0.5 ohm resistance, can you repeatedly reach out and lightly touch the Hold button with your finger and then pull it away again? Don't press the button, just touch it. Repeat the touch/withdraw cycle a few times. What happens to the reading when you do that? On my meter I can make the reading vary between about 0.2 ohms and 0.9 ohms.

When I tested the Gossen, I had it in a screen room, me grounded with a shorting bar or a 50 ohm terminator installed in the meter.  That meter was really bad.  The worst I have ever seen.    The 121 proto is no where near that bad but it's sort of a subjective test.   Are you rolling around on carpeted floor with your chair building up a charge?  I really have no idea what you are doing other than touching the button.  :-//

The best thing I can do is try and show you the prototype 121 with some sort of controlled test.   I will use the 1.0 firmware as with the prototype, it seems to at least give the same noise levels as your hardware.  You do not specifically mention logging but only measuring so I will not enable logging.  The BT radio on this meter does not appear to be enabled so consider that off.  The meter is located on a grounded static mat.  The 0.5 ohm resistor is directly inserted into the meter without test leads.  I will have a wrist strap on.  For me, this would be the normal way I would be using a meter anyway.   I have no other tests running.  There's no high voltage supplies turned on.  Should be a fairly stable environment right now.   

Watch for yourself and let me know if this differs from what you are seeing and how you are conducting your test.

********
Also, I should add that while this is a prototype and I have damaged the meter and rebuilt it three times now and I have changed the design to harden it, I have NOT added any shielding to this meter.  I've changed out one IC and added a couple of TVSs.  I have a few jumpers on the board to route the return paths for the TVSs.  More people would need to run the test with the kickstart hardware but it seems like many may have left them in their original boxes hoping to retire when they sell them in 50 years on eBay.   :-DD

https://youtu.be/ikROglTyclM 

 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 17, 2018, 05:01:45 pm
OK, for you it appears that touching the Hold button has no effect. But it always does for me, and at least one other person has reported the same phenomenon. I will have to look more closely and try to eliminate any environmental factors that may be at play.

Regarding the drift, I didn't see such drift when I did the previous 90 second test with the SD card. So I was surprised to see it today. I didn't like it, so I discarded the data. Then I ran the mV test that gave the flat line, and after that I came back to the resistance test with the same outcome. I think the meter was warmed up by the time I did the last test. One difference is that BT was on when I saw the drift and was off before.

All that is left is to try to eliminate causes and see if I can narrow anything down.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 17, 2018, 07:05:10 pm
Why do you (Ian, Joe and Dave) perform these tests on the low end of the range?

If you do it @ around 50 Ohm, this drift might behave much different.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 17, 2018, 08:53:45 pm
Why do you (Ian, Joe and Dave) perform these tests on the low end of the range?

I think that if the meter has a feature, then that feature should have a use and should be usable.

For example, milliohm resolution might be useful when troubleshooting possible bad or high resistance connections in wiring, or bad traces on a PCB, or similar things.

If the stability is so poor that the information you are looking for is concealed by noise and drift, then what is the point of designing it into the meter?

I think if a feature is there it is fair game to test it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 17, 2018, 08:54:02 pm
I did not understand Daves video @ 0.5 Ohm, neither. He also did not respond to my question about his experiment.
You can see an increased jitter at 50 Ohm, compared to the upper ranges, but for sure you're not in the residual mOhm specification, but instead in the % specification..so everything is fine..

What I have seen, and not understood, why it's quite tricky to make a REL (zero) setting.. even if the residual reading is quite stable, that will jitter around, and give some +/- 10 mOhm offsets after pressing REL by your hand.. Ian used the mobile app, which would be better.. can't understand that behavior at all.

And that really sucks, because a 1 mOhm resolution is really great for some applications, compared to other DMMs, but it has to be stable, and the zero has to work smoothly.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 18, 2018, 12:22:13 am
Here is a quick illustration of the problem I observe with the Hold button. The resistor under test is connected to a grounded lead and I am also holding a grounded lead during the test, so both meter and I should be at equal potential. I don't know the cause of the effect, but it seems very specifically tied to the Hold button. Touching the Rel button has much less effect, but actually pressing the Rel button does disturb the reading (not shown in this video).

https://youtu.be/p2zuhvFwmIs
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on August 18, 2018, 01:00:58 am
The resistor under test is connected to a grounded lead and I am also holding a grounded lead during the test, so both meter and I should be at equal potential.

My immediate reaction was one of a possible ground loop.  I would be interested to see what effects are observed with a different lay of the test leads.

My second thoughts were of the exact same movement of your hand in every test.  I would have liked to have seen what happens when approached from different directions - and also what happens if you just 'hover' above the button (3" or so) between attempts rather than move your whole hand out of shot and back in.  While simply repeating the same movement does demonstrate the issue, testing other movements may help characterise the forces at play.


It's an interesting phenomenon, though - and if it is a susceptibility in special circumstances that don't exist in most situations, then it's worth knowing about for that odd occasion.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on August 18, 2018, 01:02:49 am
You have the radio on, which I did not and I'm on a grounded mat.  I would start by turning off the radio.  Would be funny if the BT was the cause.   
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 18, 2018, 05:50:00 am
I just wanted to show what the effect looks like so you can see what I have been describing. I don't have an anti-static mat, however in this test the whole meter was tied to ground at the COM terminal. BT was on simply to show the response more clearly.

To be clear, this effect happens with BT on or off, with the meter in different rooms and orientations, when I touch the Hold button from any direction, with different lengths and orientations of test leads, and with various different ranges (for example temperature). The test setup in the video was in no way unique or special.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 18, 2018, 12:55:10 pm
I would have no idea what this "ground" is you describe.  What I see are a bunch of antennas.  Are you using 1.0?  It's very possible for what you are showing in this video that it would make a difference as it appears the filter has a lower cutoff.   

Personally, I would not have all this added wire, BT off, twisted the test leads, rev 1.0.   Then again, you can see what I am doing to make this same measurement.

Ground is what in England I would call "earth". It is the protective safety ground in my house, the third wire in power outlets. Since you suggested that static charge might be a cause I was trying to eliminate it by earthing all parts of the apparatus including myself.

Please do not be distracted by the long test leads. The effect is observed whether test leads are plugged in or not. I do not have your lab facilities with anti-static mats,  banana-to-coax adapters, shielded coax, fabricated widgets with shielding or any of that stuff. If all of that is a prerequisite for using a DMM then few people going to be able to use a DMM.

Also I am using the latest firmware as published. I do not see any point an backtracking to v1.0 as that is now long superseded and has problems of its own.

Finally, I will say again, this effect happens merely by touching the Hold button. The meter can be in any location, in any orientation, with or without test leads plugged in (for example it happens measuring temperature with a thermocouple).

If I had to guess at a cause, I would say the meter is somehow responding to capacitance between my finger and the button (or whatever is behind the button).

I have observed a similar problem when pressing the Rel button. Upon releasing the button the reading jumps, rendering the Rel action useless as it locks in the "jumped" value rather than the original value. I have tried to avoid this jumping of the reading by using a conductive or non-conductive push stick instead of my finger. However neither eliminated the problem, it still jumped even when using a plastic pen to push the button.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 18, 2018, 01:48:38 pm
Ground, Earth, Static Field... whatever.

I propose simply to calculate the equivalent voltage on the last digit in 50mOhm range, that is about 0.4 mA times 1mOhm = 400nV.

That's simply extremely sensitive, so shielding is also difficult in a handheld DMM.

The reference current should have been 5mA, to get a stable reading as in 500 Ohm range.

Instead both ranges are derived from the same 1k reference resistor, but the 50 Ohm range uses an amplified AD range, which is the culprit
Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 19, 2018, 09:20:54 am
Don't know if this is an Android software error or the meters sends wrong data, but when the scale overflows the bar graph stays near zero. Momenteraly it will gow to max but returns and stays close to zero.

The photo is out of focus cause it was taken with a 10+ years old phone.

(https://i.imgur.com/wJduI0Xs.jpg) (https://i.imgur.com/wJduI0X.jpg)  (https://i.imgur.com/ATvAf4Is.png) (https://i.imgur.com/ATvAf4I.png)

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: evava on August 19, 2018, 10:45:31 am
Ground, Earth, Static Field... whatever.

I propose simply to calculate the equivalent voltage on the last digit in 50mOhm range, that is about 0.4 mA times 1mOhm = 400nV.

That's simply extremely sensitive, so shielding is also difficult in a handheld DMM.

The reference current should have been 5mA, to get a stable reading as in 500 Ohm range.

Exactly, e.g. Fluke 289 on 50.000 ohms range uses current about 6mA.
(but, Fluke 289 has other problem on this range, namely extreme slowness)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 20, 2018, 04:34:31 am
0.5 ohms.  You are the one who brought it up, so what ever values you were trying to measure will be fine.  Just do a before and after comparison and report the results.  If the noise you were seeing is reduced, I think we have our answer.

Maybe I'll give it a try after work tonight.

However, the problems I was seeing seemed to be related to static fields, caused by proximity of my hands to the meter or test leads.

The only way I think firmware can fix that is by having lots of software filtering. So it might be a choice between "slow and steady" or "fast and erratic".
  There are more clever ways to do noise filtering than just a LPF, the plots I'm seeing with V1.26 are glitchy, not just noisy, if I had the data I'd run an fft or find the spectral density to have a more meaningful data about the required filter for the job, or what filtering they are using, if it is a linear one it should show up quite nicely in the spectral density plot. If you just want a slow filter you could run the averaging on the meter to get a stable value, to find if you can repeat the measurement you could run a few and see if you will trust the first the next time.
  What I'm saying is with some smart filtering, non linear, with some hysteresis, averaging till a step bigger than X or a faster average goes further than X, etc. you could ignore those glitches but get a faster reading if the value is actually changing. Nice thing about having the fast data logged is that you can make your own filter afterwards, that could be nice to keep but show a filtered data on the display so it's easier to read than having 2 digits jumping around in a 3 digit reading (0.5Ω)

  I do have the meter, it came with V1.18 which doesn't seem to apear anywhere, let me say auto hold was really really bad, I upgraded it to V1.26 after a very short play around, as I found many many things wrong with that version. It came from US, I could look the SN but I haven't seen anybody with that FW version. Now I could get some data by myself but stabilizing temp to get a decent resistance measurement won't happen tonight while the cold cold wind is getting under the doors. I should set up a parallel of 1% MF resistors to get a low value, close to the 500mΩ you are using. While I'm at it I could set up something to short the leads as I run the measurement and look at the step response of the filter, opening could also do in manual range, as in auto range will start to jump around like crazy. I don't know what should I use as a switch to make it low resistance, fast and not bouncy, a mosfet maybe.

  Having an open source of the firmware would be so so great, ideally the original one but Dave already said that wasn't going to happen apparently as UEI wouldn't want to release some of their proprietary code. Playing around with filters, some functionality and possibly introducing new measurement math functions, not only statistics but also some automation in the measurement if you want to measure a parameter that means something else in a non linear way would be sooo great. Maybe someone could come around with an open source firmware at some point, I would totally get involved in the process.

  If I had to report, one thing I think it's missing is the ability to look at other logs than the last one, which is the only that shows, also the possibility to tag logs, a few characters makes a great difference in that respect. There might be some easter eggs in the firmware to be found, as we are in V1.26 and the user manual is only V1.07

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ELzekio on August 21, 2018, 02:16:19 pm
The issue about the movement on low ohms measurements should be pretty easy to replicate for anyone.

When I test a less than .5 ohm resistor and just lightly touch the hold button, I can easily make the reading jump around excessively. As soon as you pull the finger away, it will settle back down to the proper value.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ggchab on August 21, 2018, 03:35:35 pm
Same on mine. But also with range, mode, min/max and rel buttons.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 21, 2018, 04:02:15 pm
Same on mine. But also with range, mode, min/max and rel buttons.

Well, apparently you have to use the meter in a sterile environment, inside a Faraday cage, with no mains wiring nearby, on a static-dissipative mat, wearing an anti-static wrist band; otherwise you are not following proper procedures...  ;D
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 21, 2018, 05:16:32 pm
  Here is my shot at the low resistance noise... I also have the noise when I touch any button but that's not what I'm addressing here.

  I grabbed a 2.2Ω 1% metal film resistor, BT connection, run some measurements of it and a short circuit using standard leads, to connect the resistor to the leads I screwed with the banana inserts pressing the resistor leads, for the short I did the same thing over the resistors leads but at the same lead of the resistor. I took a really crappy picture of the setup so wouldn't be so useful for you but I hope you get the idea. The DMM internal temp was around 17ºC.

  After a short warmup where I saw no more shifting of the readings and noise got noticeable lower I run a few logs via BT in different settings (short, short with delta, 2.2Ω with the delta of the short, 2.2Ω and 2.2Ω delta) From this last one I will show the data I obtained and some processing I'm proposing.

  From 380 samples via bluetooth, at about 0,5s each, I see 5 glitches of a few samples, if I were to guess this is product of some kind of calibration messing the readings. What I did was running a crude fft (I didn't correct for the mirroring or put freq reference) and plot (same thing, no freq or time ref, but with 380 samples at 0.5s you can see divide the x axis by roughly 100 to get a rough freq idea and divide by 2 to get the time. Of course the FFT data after half the plot is just a reflection of the first half. I added a moving average to the FFT plot to make things easier to read, if not it was just a mess of dots.

  Then I made some filtering, to impact on those 5 glitches, to do so I used the average of the measurement, and if the difference of the sample is more than 8 counts away from the average I ignore it, and the next two samples, to put something to fill the signal I used the last 3 samples before the glitch. I know this is not a usable filter for real time measurements as it's not a causal system, but I think that's not to hard to come by just taking the last few samples, detecting an actual change would be a tad slower as is usual with filters but 3 samples should be enough, bigger changes than the amplitude of the glitches could ignore the filter all together so it only acts in variations smaller than the glitches. In my measurements all the points fall within 5 counts to the average and the glitches go over 15 counts to about 30 counts, that difference should be enough to detect them within a few samples and not affect speed of measurement in any other case than fast variations between 10 counts and 40 counts, even just detecting inter sample variations of that amplitude and ignore that and the next two samples would do, just freeze the screen for that time.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=503210;image)

  The LF noise isn't reduced too much up to 0.2Hz by the filter but the HF noise up to 2Hz is reduced roughly 10dB, the messy display would go over completely with jumping digits other than the last one which in this measurements is expected to be. As there is a LPF key and display segment already in the meter it could be cool to be able to slow down the measurement even further to make the reading more stable, wouldn't be 1kHz but rather 0.1Hz or something but would be nice to have for almost every range so you can get a stable reading without needing to run an average each time, reset it and all that, even more as pressing the average button messes the readings.

  I hope something is implemented in order to correct this, as it was good in V1.0 of the FW doesn't make sense to have it wrong 27 versions later. For an extra FW feature I would add such LPF as moving average or something like that which would give only ±2 or 3 counts in this scenario changing slow rather than ±5 counts changing fast. For the issue with the buttons delaying the function could be a walk around, so if you press delta it does to the next few readings (or the ones before) rather than the actual one, same thing for hold, min max should start checking a few samples after the button press. Also, I'd like the delta function to take the avg value while the avg is active instead of the instantaneous reading.

  Just to clarify, here we are talking of reading noise rather than precession but is useful to detect those small changes in the short term and be able to read from the screen rather than needing go post process the data to get an actual reading.

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 22, 2018, 01:53:34 am
You forgot firmware 1.0 as well.  Had you given me a detailed procedure, I would have tried to follow it. So I documented what I did for you.  I'm not sure why that bothers you.  A more productive approach maybe to ask if I can repeat the test some other way.  You would just need to describe it.

You really don't have to be very detailed or precise. If you merely move your finger near any of the buttons, especially the hold button, the display reading jumps around as attested to by ELzekio, ggchab and others previously.

The fact that you didn't reproduce it suggests your pre-production sample differs in some significant way from later production meters. The effect is not subtle. It jumps right out at you. If you were going to see it, you would have seen it by now without needing to look for it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 22, 2018, 02:00:16 am
So I documented what I did for you.  I'm not sure why that bothers you.

It doesn't bother me at all. I am happy that you tried to reproduce it. It is curious that you didn't observe any effect, which suggests there is something different about that particular hardware compared to later revisions.

The reason for my comment was your suggestion that rugged and portable meters, that are inherently designed for field use, should have to be used under carefully controlled laboratory conditions to avoid malfunctions in their behavior. That doesn't seem quite realistic.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 22, 2018, 02:31:02 am
Joe, about the buttons, I see that too, just trying to press a button (delta, min/max, hold and maybe mem are the more problematic as you want the meter to capture the readings and it does so right after) makes the reading jump like 100 counts or something. I see it even worse when taking the fingers out of the button after a slight touch. I haven't tried V1.0 so I don't know if that is still present there.

First, thanks for taking the time to help look into this.   I assume the data is normalized and that's why the "signal" is shown near zero rather than 2.2ohms.    At least you are seeing what appears to be the same spikes. It sounds like you may have tried rolling the firmware back to 1.0 as well.   

I'm with Dr. Frank on this one.
  I didn't went back to V1.0, I should tonight and try something similar, will be back soon with the results.

  I used the rel function once the 2.2Ω resistor was in place, that's why the readings are close to zero (centered at 2.2mΩ as the average of the signal suggests rather than 2.2Ω, which suggest the rel function works really nice, just 0.1% from long average) but for the FFT I did substracted those 2.2mΩ to avoid the spike at zero which would mess the scale of the plot, cheating with that instead of fixing the axes range as I used different samples with the same program, just posted that one which was pretty representative of the test, being longer and having quite a few spikes. During the test I didn't came even close to the meter, I sit in the couch looking at the phone and controlled the whole experiment from there (except of course swapping the resistors, but not at all while datalogging)

  Now for homework I will take it back to V1.0 and check what happens, I will try making a causal filter for the spikes and lastly use a switch to short the leads during the logging (maybe over a higher resistor) to check what filtering is shown on the signal. For now I should test a mechanical switch and if I see some problems come up with a remote solution so I don't affect the measurement with that either.

JS

PS, I'm running some logs right now, the display didn't jumped as much as I saw it do yesterday, I don't know what changed, all my setup is more relaxed than yesterday... probes wires all around the PC and noise doesn't look that bad, I will need to check for those few glitches if they are there.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on August 22, 2018, 03:26:14 am
So I documented what I did for you.  I'm not sure why that bothers you.

It doesn't bother me at all. I am happy that you tried to reproduce it. It is curious that you didn't observe any effect, which suggests there is something different about that particular hardware compared to later revisions.

The reason for my comment was your suggestion that rugged and portable meters, that are inherently designed for field use, should have to be used under carefully controlled laboratory conditions to avoid malfunctions in their behavior. That doesn't seem quite realistic.
While documenting the details of a test gives you and other members an opportunity to try and replicate the results, the real purpose is to provides the designers with enough detail that they can replicate it.  If they can replicate a problem, there is a good chance they will be able to solve it.

I want to emphasise this point ... very strongly.

The testing regime is just that ... TESTING.  If some are finding an anomaly that others are not, then there is likely to be some rather subtle difference in the testing process that accentuates it or hides it.  In fact, this is not "likely" - it is almost a certainty.

It is only by fully describing the TESTING environment and setup can any subtle influences be properly investigated - and with electronics, an extra couple of feet of wire can have a different effect when left dangling or is rolled up, when it's laying on a grounded chassis or next to a powered transformer.

Full and proper testing protocols are a hassle, especially if you're not used to them.  They require a discipline that some may consider over the top - but such attention to detail is absolutely essential.

Nobody is saying you have to use the equipment this way!!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 22, 2018, 03:30:08 am
We know how 1.0 implements the filter is a fair bit different.  The fact I keep going back to it as a baseline should tell you how unstable the code base is.    You have no desire to try and run it to see if it has any effect on what you are seeing and I have no problem with you ignoring that.   I just find it odd that you take the time to suggest there is something different but fail to look at the most obvious change.   

My test case doesn't suggest how it behaves under different conditions.  As I have said, this is how I normally work on electronics.  If you would like to see how the prototype works in a different environment that you would consider less controlled, you only need ask and to define what that environment should be.

It does not seem to me that changing the firmware would affect something that looks like a hardware behavior. However, just to make sure I put the firmware back to v1.00 and the effect is indeed observed just the same.

If you would like to try to reproduce what I am seeing, I am doing the following:
1. Put the meter on a sensitive range where it is measuring DC mV (e.g. measuring a low resistance like 0.5 ohms, or measuring temperature, or actually measuring a few mV)
2. No special precautions taken (meter on a normal bench, no wrist strap, 60 Hz mains in the environment)
3. Place finger on the Hold button. On approach the display may dip. On taking the finger away the display may jump. A stronger effect is observed if the finger is rested on the Hold button for three seconds or so before pulling it away. Try slow and fast movements with different intervals between actions.

For everyone who has reported this problem it is very obvious. You don't have to look very hard to see it. It is not subtle!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on August 22, 2018, 03:47:00 am
Well, the first thing I would suggest is that we get the serial numbers of those meters that are out there -  and whether they exhibit the problem or not.  I would further suggest only meters with a specified firmware version be included.  If there is a change between "problem seen" and "no problem seen" at a point in the serial number range, then the question could be asked if UEI changed something in the hardware at that point.


However, if the problem seems to NOT follow such a pattern, then it will be something else.  But what?  Could it be related to temperature? Humidity? Barometric pressure? Urban/Rural location? The list goes on and on .... and on ... and this list is only to identify some commonality so that we can zero in on the real, underlying problem.

Saying something is obvious and just pointing at may be quite valid from your perspective, but it isn't helping find a solution.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 22, 2018, 03:51:22 am
One problem is that hundreds of meters have been shipped, but very few people are commenting in this thread or reporting their experiences with their meters. As Joe said, it is almost as if everyone has just put them on a shelf in their boxes for posterity.

So trying to find a pattern is very difficult with such a small sample size.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on August 22, 2018, 04:07:41 am
That is true - and it does make things much more difficult.

My thought is that many of the ones sitting on the shelf are awaiting a stable release of the firmware that everyone is pretty happy with - and then they will get pressed into service.  I also think there will be a lot of meters just opened up and are being used in the belief they are "good enough" for the people who are aware of these discussions and those who blindly believe that it's a brand new product and therefore must be A-OK.  Unfortunately, this takes a lot of meters out of the testing pool.

I hope we can at least characterise the circumstances for the behaviour (as was done with a certain meter from the Keysight stable not so long ago).  Fixing it would be great.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bratster on August 22, 2018, 04:23:12 am
I have one of the kickstarter meters and would be happy to check some things out on it. But only be able to get to it on a weekend.



Sent from my Fi Moto x4 using Tapatalk

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on August 22, 2018, 05:17:07 am
That would be great.  I don't think a few days' delay will be a problem at all.  Any additional information you can contribute will be welcome, I'm sure.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 22, 2018, 05:40:22 am
Quote from: joeqsmith on Today at 12:58:22 pm (https://www.eevblog.com/forum/index.php?topic=101807.msg1764368#msg1764368)
JS, sounds good.  I didn't even consider the rel function.  Makes sense.   I can tell you that the prototype with the later firmware is not near as stable beyond just the noise.  I've posted a few times how it is sensitive to the proximity of my hand.  If you look at some of that early data I took I even mentioned that the spikes were from me walking by the meter.  1.0 does seem to help tame it on the proto.  Look forward to seeing your results.

I do see the jumping with V1.00 while touching the buttons as well, 100 counts or so and all over the place, not the single sided glitches of a few samples.

Well, I did my homework... The meter connected to a resistor (22Ω and 2.2Ω in different experiments) and parallel with the resistor a toggle switch. Everything up and running switch open, press the mem button to start recording (yes, this time no BT) wait for about 200 samples in the fastest speed (40s or so) toggle the switch to close it, wait for 100 samples, toggle the switch open again, wait for another 100 samples and stop recording. All that done with both resistors and both versions (1.00 and 1.26)

  Now, what did I saw, let's start by looking at the switching moments... 10 samples are plenty to observe the switching, so we are looking at a 2s interval. Here I normalized the resistances and placed the 22Ω and 2.2Ω together, the observer eye will detect which is which.
  FW V1.00 looks consistently slower, taking 4 samples to settle to within the noise floor, strangely only one signal looks 5 samples, so we call it 4.25 samples for version 1.00.
  FW V1.26 looks consistently faster, taking one or two samples to settle within the noise floor, so we call it 1.5 samples, which is about 3 times faster than V1.00.
  Is interesting to look at the shapes of the different pulses, going down all show slower, and for V1.00 a step in mid air lasting up to 4 samples in exactly the same value (stop for a coffe maybe). V1.26 settles in just one sample going up, while going down stops for a single sample in a place where it doesn't seems to be a single pole filter, but also doesn't seem to be just toggling the switch during the sampling time, too similar shape for both traces, I wouldn't call consistency 2 samples but something to look for if I was trying to replicate the filter.
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=503570;image)

  Enough with the step response, let's go to the noise observations, I took the first 200 samples of each measurement for this, from the start to a few samples before the switching, this time I did normalized the resistance to just look at the noise around zero. Looking at the 2.2Ω resistor plot, for V1.26 there are no glitches in those 40s, just within 5 counts of the mean, I guess I just got lucky, they were around 30s to 90s apart, while the V1.00, after a high start of 4 counts over, stays within 2 counts from the mean for the rest of the time. In the frequency plot shows a faster response from V1.26 as in the step plots, with higher noise all over the spectrum.
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=503576;image)

  Now the 22Ω plots, all other just as before. Hey! We have glitches :scared:  So noise went up to the roof for all the spectrum and now we cant even see clearly the V1.00 noise while glitches go like 30 counts away from the mean. The first one was just at the start, could be due to the button problem but I don't think so, I'm observing such behavior mainly with the hold, not the mem button. Also, the reading just shift around and doesn't stabilize just one or two samples after, slower process all together, but it could very well be. Second glitch I don't think I went even close to the meter, as it was way before toggling the switch. Due to those glitches the noise goes up all the way up to 5Hz to about 4 times than without the glitches, and 10 times higher than the V1.00 figures.
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=503582;image)

  To wind up, I don't think the glitches are external perturbations, as I said I was quite a few meters away in yesterday experiments and it was in the middle of the room with just one incandescent bulb on, main source of noise would be the BT or the cellphone on my hand. If I had to guess the thing is doing some kind of calibration, auto zero or something at a pseudorandom intervals and just showing up whatever value it reads instead of ignoring the samples affected by the cal procedure.
  The noise levels and frequency response of V1.00 are similar to what I was expecting, falling within 2 or 3 counts, I was getting that with a moving average of about 15 samples. The staircase response tells me it's not doing just that or other type of linear filter but some other processing about that, I kind of like that a bit more but if I could I wouldn't switch completely to that, I would still prefer for the data logging to have the faster response but ignoring the glitches. For me the best choice would be to have the choice at the time of the measurement (and not having to change firmwares to do so) and make use of the buttons that are not being used, could be the 1ms but the LPF symbol makes more sense, to add a LPF even if it's not 1kHz but 0.1Hz. Also, using a linear filter to deal with the spikes doesn't seem right to me, they are clearly not random noise and getting them into the averaging isn't the way to go, just masking the problem but introducing even more error than leaving it there, hard to catch with the eye and can be suppressed while processing the logged data.
  If I were to design a filter for an application like this, just for the display, I would make it varying with time, a very fast, almost non existent as it detects a fast change in the signal and slower as it just detects the noise of the system, let's say (in time constants) single sample for a change over 200 counts, 4 samples for a change over 20 counts and 20 samples for a change under 20 counts. For the data logging I would always prefer faster, noisier samples, the V1.00 clearly shows slugginess in the data, as has many consecutive samples in the same reading. Good for display, bad for logging (IMO) the problem with the BT logging is that you are logging the display value. A walk around of all this would be to write a BT app to do the trick, and look at whatever kind of reading I want from the phone, just leave my noise alone so I have something to work with...


  Hope all this helps, I'd be happy to run any test with this, just bare in mind I don't have a higher resolution meters if that's what's required, can't do long term stability, calibration checks, etc, but for this kind of feedback I'm available. I just got my meter two weeks ago, that's why I'm just jumping in here now...

Regards
JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 22, 2018, 06:00:06 am
One problem is that hundreds of meters have been shipped, but very few people are commenting in this thread or reporting their experiences with their meters. As Joe said, it is almost as if everyone has just put them on a shelf in their boxes for posterity.

No, people are using them, I get a ton of feedback this is the case, and they are simply not running into any issues in their use.
Yes there are some outstanding issues, but in the scheme of a multimeter that has dozens of different functions and ranges, only a few of those are affected. Most people will not see any issues in daily use.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 22, 2018, 06:02:32 am
UEi have reported back on the Mohm range drift issue, and the problem is the 1N4007 diodes D7 and D8, they are going to be replaced by a single TVS in future builds.
I don't have any further details, but I presume there is some sort of temperature/voltage dependency related issue with those diodes that can manifest itself under certain circumstances.
They are sending me an updated meter with the new part fitted for testing.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 22, 2018, 07:07:40 am
I'm loving the meter, haven't come across it too much to use it as I just got it but I'm totally happy with this, looking for the switch press on the low ohms I came across the noise issue with the low ohms and saw people working on it and wanted to help...
UEi have reported back on the Mohm range drift issue, and the problem is the 1N4007 diodes D7 and D8, they are going to be replaced by a single TVS in future builds.
I don't have any further details, but I presume there is some sort of temperature/voltage dependency related issue with those diodes that can manifest itself under certain circumstances.
I haven't tested that yet on my DMM, nice to know they found something about it.

I run a 15 minutes log using V1.26 and had a play around with the filtering, this time using causal systems. To address the glitches It just took me comparing 2 samples, the new and the last, and if they were more than 9 counts away ignore it and the next two samples filling it with the last samples of the filtering I was making using 0.95 and 0.05 as coefficients. Samples taken are in black, after ignoring glitches in red, filtered in blue.

I don't know about the drift, likely warmup, I placed the thing inside a cabinet but looks like not long enough, reads starts to settle at the end.

One problem I'm having is not being able to log the second function, is there a way to do so? Not with BT nor to the SD.

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on August 22, 2018, 07:12:43 am
UEi have reported back on the Mohm range drift issue, and the problem is the 1N4007 diodes D7 and D8, they are going to be replaced by a single TVS in future builds.
I don't have any further details, but I presume there is some sort of temperature/voltage dependency related issue with those diodes that can manifest itself under certain circumstances.
They are sending me an updated meter with the new part fitted for testing.

Please make a video on that, I am interested on details.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 22, 2018, 07:17:31 am
UEi have reported back on the Mohm range drift issue, and the problem is the 1N4007 diodes D7 and D8, they are going to be replaced by a single TVS in future builds.
I don't have any further details, but I presume there is some sort of temperature/voltage dependency related issue with those diodes that can manifest itself under certain circumstances.
They are sending me an updated meter with the new part fitted for testing.

Will this improve be user addressable?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 22, 2018, 08:23:29 am
UEi have reported back on the Mohm range drift issue, and the problem is the 1N4007 diodes D7 and D8, they are going to be replaced by a single TVS in future builds.
I don't have any further details, but I presume there is some sort of temperature/voltage dependency related issue with those diodes that can manifest itself under certain circumstances.
They are sending me an updated meter with the new part fitted for testing.

I assumed a temperature dependent leakage current in Ohm mode, due to protection diodes:
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1728887/#msg1728887 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1728887/#msg1728887)

but only now I know where these are located!

It's clear, that 1N4007 has high leakage currents on reverse voltages, not suitable for such a circuit. These create non-linearity over voltage, and the strong temperature dependence of this leakage current creates that huge 0.64%/K gain change in 50MOhm range.

Edit: I'd replace these 1N4007 by reversed npn transistors, as these usually have very low leakage current, as already being used similarly  in the 121GW, i.e. Q1, Q2 (n.a.), Q3, Q5. n-JFETs. Used as diodes, these have low leakage, but also high breakdown voltage (which the E-B diode of npns don't have), as 15V may be present there.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: M4x on August 22, 2018, 11:49:43 am
I have one of the kickstarter meters and would be happy to check some things out on it. But only be able to get to it on a weekend.



Sent from my Fi Moto x4 using Tapatalk
+1.

I've one of the first available meters ordered directly from Dave. I've standard components, a linear laboratory power supply, a Gossen Metrahit One Plus, different test leads and a Logic analyzer from Saleae (can record analog signals) at hand.

Just tell me what you would like to see.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on August 22, 2018, 12:29:19 pm
I'd replace these 1N4007 by reversed npn transistors, as these usually have very low leakage current, as already being used similarly  in the 121GW, i.e. Q1, Q2 (n.a.), Q3, Q5. n-JFETs. Used as diodes, these have low leakage, but also high breakdown voltage (which the E-B diode of npns don't have), as 15V may be present there.

Cool idea, and then recal the meter isn't it? Keep us posted.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on August 22, 2018, 05:05:49 pm
One problem is that hundreds of meters have been shipped, but very few people are commenting in this thread or reporting their experiences with their meters. As Joe said, it is almost as if everyone has just put them on a shelf in their boxes for posterity.

So trying to find a pattern is very difficult with such a small sample size.
I take a little offense to that thought.

Most people have no time to look at every little problem, most of which, like this, are in the noise.  Thank you for looking at this problem though, but don't expect everyone to care about it.  I have used the meter nearly everyday since its arrival and found and posted a few issues I've had.  If I was measuring sub 3ohm resistances I would be more concerned, but I'm not.  I also think that maybe a different instrument might be better suited for that task.

I also have to comment that if the software was truly open source (or hacked to be) as I thought when I purchased the meter I might be more inclined to get into the discussion.

Edit: I think I new going in the software wasn't open source, but assumed it would be revealed shortly.  It's getting there: https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-firmware-details/msg1407514/#msg1407514 (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-firmware-details/msg1407514/#msg1407514)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 22, 2018, 05:20:43 pm


...
As for logging, if the spikes were real I would want to see them but they are not.   I don't see a problem like this with even the cheapest logging meters I have when sampling at the same rates.    I really can't think of a time where I have needed a handheld meter to record faster than a second.  In most cases, even that is fast.   If I am need to see faster changing signals, I am using something else to collect the data.  For me, what ever I collect, I want the data to be accurate first and foremost.   If the meter is not the right tool for the job because of it's speed, I will use another tool.
  I think that slower samples in 121gw are single samples stored every once in a while but from the set of fast samples, not filtered to get better, more stable readings, so the spikes would still br there but you wouldn't have way to know that is a spike without the samples around it.
I saw 13 spikes in 15 minutes at 5Sa/s, with the spikes taking at least 3 samples, thats 1% of the samples corrupted.
So if you were to sample once every minute  you would catch a spike every two hours but you probably wouldn't be able to tell thats a spike.

If Im logging Im going to the pc and can filter myself, so I rather use the raw data than a unknown filter. For the display I want a steady reading, so if it can log something to the SD and show other to the display would be fine, but BT logs the display, so would make the app a bit worse. Also, when logging slow I do like to be filtered, as I don't have that much data around each point. The apikes I don't want them anywere, the signal might be changing fast and would be harder to filter. It might be something in the chipset that flags this samples.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 22, 2018, 06:30:23 pm
I saw 13 spikes in 15 minutes at 5Sa/s, with the spikes taking at least 3 samples, thats 1% of the samples corrupted.

I saw a spike when measuring DC mV directly (the green trace below just after 100 s). At the time I thought it might have been some external influence. It didn't occur to me that the meter itself might have introduced the artifact. That's interesting.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=499727;image)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 22, 2018, 10:41:37 pm
I saw 13 spikes in 15 minutes at 5Sa/s, with the spikes taking at least 3 samples, thats 1% of the samples corrupted.

I saw a spike when measuring DC mV directly (the green trace below just after 100 s). At the time I thought it might have been some external influence. It didn't occur to me that the meter itself might have introduced the artifact. That's interesting.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=499727;image)
Thanks! I should check the mV range then, it could help to narrow the cause, IE if it's present there we know for sure the problem is not on the resistor current source but on the ADC side...

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 23, 2018, 02:44:55 am
Hand proximity tests using various configurations with firmware 1.0. 

https://youtu.be/s7QVwFXmxgQ

  You are seeing something similar to what I did, I haven't tested with any ESD protection as I don't even have grounding here, I have a stick half way into earth (need a bigger hammer for the other half) as I'm moving and haven't settled yet.
  I found something interesting that might have to do with this, if I snap the right side of the rubber protector the reading jumps, the left side doesn't do that...

  I will run some logging in mV range now, to look for correlations between the noise I see in the ohms range and there, as usual, the logs without perturbations, no touching buttons.

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 23, 2018, 07:34:10 am
New measurements tonight, this is getting serious...

  I ran some short captures in the mV range, 200 samples or so, I saw a few glitches but interestingly right at samples 61, 121 and 181 at V1.26, even more intresting, in V1.00 there are smaller glitches one or two samples later. With the open leads, right at the start is easy to see the error introduced by me taking the finger out of the meter after pressing mem, in both versions, V1.00 smaller and slower as expected.
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=504488;image)

  Now at the freq plots, V1.26 shows a flat noise response in both tests, while V1.00 shows a low pass response.
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=504494;image)

  If we compare the two versions, doing V1.00/V1.26 we see a similar frequency behavior with the leads open or closed.
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=504500;image)

  Then I decided to make a longer sample, to see if I can catch the pole, left it running for about 11 minutes and cropped some samples at each end, so we can see the response down to a few mHz, for this I think I over did it leaving long leads open far away and ended with some strange noise with a clear frequency at around 1Hz, and the overall noise of the V1.26 was much higher so the ref plot doesn't start at 0dB. Also, I tweaked a freq plot a bit as I don't really know the sampling rate, but with the long test I estimated a slower sampling rate than the 200ms specified in the manual, that's why the response looks a bit shifted.
  Even at a few mHz the response doesn't flattens out, going down by 10dB/dec up to a few 100mHz where it steeps down even further and returns back up, I guess due to the measurement being so noisy. I don't have a more controlled LF noise source to generate for this measurements but should be easy enough for the next test using a zener and a divider to work in the mV range, I guess I'd need to run it even longer to catch the pole. Also, with a more controlled noise source I'd like to run some intercorrelation calculations between the samples to put a number in the glitches being the same between both versions.
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=504506;image)

  To finish up, the glitches and button press sensitivity is present in both versions, V1.00 clearly has some filtering going on, checking the schematic and datasheet of the HY3131 there are many analog selectable LPF available at the chipset, first C21 with the internal resistors and then C16 to C26 and likely some of the surrounding resistors, plus a configurable digital comb filter after the ADC, to then go the the µC where they could be doing more processing of the signal... We need an open source code right now!!!

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 23, 2018, 08:11:33 am
Thanks for this update.  Good to hear they are working on it.  What ever their reason for this change, it could have an added advantage if they pick the parts right.  U9 is the first thing to get damaged in my testing.  I am using a TVS rather than the 4007s to protect it and swapped the HEF4053 for a CD4053.  It held up pretty good after that.

Yes, that is what future meters will have. The TVS is the same as used in the other protection path.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 23, 2018, 08:14:27 am
I also have to comment that if the software was truly open source (or hacked to be) as I thought when I purchased the meter I might be more inclined to get into the discussion.

Sorry anyone thought the meter would be open source firmware, that was never promised.
The schematic is available, the PC software is fully open source, and the protocols are open.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 23, 2018, 08:32:29 am
Is any of these problem a show stopper? I believe not for the vast majority of users. If you need a feature pact meter the 121GW is great. I would say it's still away from a meter that you can trust all the digits though.

The bugs like not defaulting to the default scale is more "serious" imho.

Maybe after all the hardware changes someone could purchase only a bare populated pcb to replace the old revision!  :scared: :scared: :scared:

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 23, 2018, 08:53:19 am
Show stopper not at all, but I have two reasons to have this quality time with my meter, first getting to know it's strengths and limitations, take the most out of it, know when it's suitable or not. Then if I can help polish it a little bit firther great, I don't think this is a project without any more effort into it, I still see tweaks being made, I wish I had my meter much earlier and have a pinch into helping for any upgrade, but I'm not demanding anything, just putting some more processed info and MHO into this.

I always understood that the firmware wasn't going to be open source, I'm not demanding that the UEI original firmware gets releases. The display lib already is public, the schematic is public, the datasheets are available, all it's left is getting to wright some code and some people is already doing so. I'm not great at that, not my highest strenght, there are better people with that around here, at least to start building up something more complete but I would totally jump in to help in the signal processing for instance. I'd probably start mocking around with the app sooner, where some of that can be done and still useful to add functionality in the phone display that's not on the main display already.

Thanks Dave for all the info about this meter, there is no other brand new one around that has this much info available...

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 23, 2018, 11:21:23 am
The bugs like not defaulting to the default scale is more "serious" imho.

What bug is that?  :-//
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 23, 2018, 11:47:08 am
The bugs like not defaulting to the default scale is more "serious" imho.

What bug is that?  :-//

Select a position. E.g. V DC. Press Mode to change it in AC. Turn off the meter and on. Select again V. It remembers the AC mode selected.

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 23, 2018, 11:54:49 am
Select a position. E.g. V DC. Press Mode to change it in AC. Turn off the meter and on. Select again V. It remembers the AC mode selected.

That's a feature. Some like it, some don't. The Brymen does exactly the same thing.
I can't see how this can possibly be a "serious" issue?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 23, 2018, 12:00:04 pm
One scenario is that you try to measure a high DC or AC voltage and the meter is in the other mode. It will show 0...

Could it be implemented as a user option?

The manual clearly states that the DC is the default mode.

(https://i.imgur.com/4trToZh.png)

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 23, 2018, 12:03:03 pm
One scenario is that you try to measure a high DC or AC voltage and the meter is in the other mode. It will show 0...

It's a multimeter, it does multiple things, you should check your range before measurement.
Look, many people love this feature.
Yes, maybe it can be an option, but that's way down our list of issues to address.
We'll fix the manual.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on August 23, 2018, 12:05:47 pm
We'll fix the manual.

Bug solved! :D :D :D

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 23, 2018, 03:04:03 pm
Hi,

I think I found another design issue in the meter circuit.
I wanted to find out whether the meter can be used with lithium batteries instead of standard cells or not.
Problem with lithium cells ist the higher voltage. 4 lithium cells have up to 7.7V when they come out of the package. After a short time the voltage goes back to approximate 6.6V and stays a long time at this value.
Problem or not?
I could not find any hint to this question, so I started to explore the schematics.
First it looked good, all internal voltages came from low drop regulators.
+4V, VDD(3.3V) analog supplies and VDD_P  (3.3V) for the 15V booster and the CPU.
So, no problem at all, none of the voltages can go to high.
But wait, what is that?
The voltage reference, ZD1, a ADR3412 reference regulator is connected directly to B+ via R94, a 0 ohm resistor. B+ is the battery voltage. And this is a problem in my opinion. According to the datasheet the input voltage range of the ADR3412 is 2.3V..5.5V, the absolute maximum is 6V.
That means even with alkaline batteries the voltage is above the input range and with new alkaline batteries also above the absolute maximum. With lithium cells it is way off from the allowed input voltage.
Populate R12 instead of R94 will supply the reference with +4V, so no problems in this configuration. But R94 is populated, not only in the schematics. I have checked this in my meter and actually R94 is populated. I will remove R94 and place it in the R12 position.I cannot understand why the reference is connected to B+, that makes no sense for me. Is this really a design flaw or did I overlook something?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 23, 2018, 04:20:56 pm
Hi,

I think I found another design issue in the meter circuit.
I wanted to find out whether the meter can be used with lithium batteries instead of standard cells or not.
Problem with lithium cells ist the higher voltage. 4 lithium cells have up to 7.7V when they come out of the package. After a short time the voltage goes back to approximate 7 V and stays a long time at this value.
Problem or not?
I could not find any hint to this question, so I started to explore the schematics.
First it looked good, all internal voltages came from low drop regulators.
+4V, VDD(3.3V) analog supplies and VDD_P  (3.3V) for the 15V booster and the CPU.
So, no problem at all, none of the voltages can go to high.
But wait, what is that?
The voltage reference, ZD1, a ADR3412 reference regulator is connected directly to B+ via R94, a 0 ohm resistor. B+ is the battery voltage. And this is a problem in my opinion. According to the datasheet the input voltage range of the ADR3412 is 2.3V..5.5V, the absolute maximum is 6V.
That means even with alkaline batteries the voltage is above the input range and with new alkaline batteries also above the absolute maximum. With lithium cells it is way off from the allowed input voltage.
Populate R12 instead of R94 will supply the reference with +4V, so no problems in this configuration. But R94 is populated, not only in the schematics. I have checked this in my meter and actually R94 is populated. I will remove R94 and place it in the R12 position.I cannot understand why the reference is connected to B+, that makes no sense for me. Is this really a design flaw or did I overlook something?
I think a lower rail would be even better, as the voltage at 4V reg would change with batteries running low, and to avoid the up to 50ppm/V line regulation coef, typ is lower but gets worse when it's warm. Using a 3.3V rail would make sense but a quiet one would be needed, as a LDO running there will stay there even with the batteries at 0.9V or 0.8V each.

The footprint is not there, so the 4V would still be much more stable than the batteries so... And the meter should stay within cal at 4V so you could do the swap and still kind of trust factory calibration, but meh...

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on August 23, 2018, 04:22:52 pm
I also have to comment that if the software was truly open source (or hacked to be) as I thought when I purchased the meter I might be more inclined to get into the discussion.

Sorry anyone thought the meter would be open source firmware, that was never promised.
The schematic is available, the PC software is fully open source, and the protocols are open.

Sorry for my comment, I've edited it.  I first thought it was open source firmware, but by the time I ordered I knew what I was getting and don't regret the purchase .. love it and look forward to improving it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on August 24, 2018, 12:26:34 am
We'll fix the manual.

Bug solved! :D :D :D

Alexander.

Updated manual.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 24, 2018, 12:50:12 am
I had a glitch today, V1.26 in the 50Ω manual range, leads open showed OFL as expected, with shorted leads, 22Ω or even 1kΩ resistor connected showed 0.000Ω (not GΩ, MΩ or kΩ, I looked at the screen like 10 times to be sure)

Happened just once and I've not been able to reproduce it yet.

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 24, 2018, 12:52:29 am
Hi,

I think I found another design issue in the meter circuit.
I wanted to find out whether the meter can be used with lithium batteries instead of standard cells or not.
Problem with lithium cells ist the higher voltage. 4 lithium cells have up to 7.7V when they come out of the package. After a short time the voltage goes back to approximate 6.6V and stays a long time at this value.
Problem or not?
I could not find any hint to this question, so I started to explore the schematics.
First it looked good, all internal voltages came from low drop regulators.
+4V, VDD(3.3V) analog supplies and VDD_P  (3.3V) for the 15V booster and the CPU.
So, no problem at all, none of the voltages can go to high.
But wait, what is that?
The voltage reference, ZD1, a ADR3412 reference regulator is connected directly to B+ via R94, a 0 ohm resistor. B+ is the battery voltage. And this is a problem in my opinion. According to the datasheet the input voltage range of the ADR3412 is 2.3V..5.5V, the absolute maximum is 6V.
That means even with alkaline batteries the voltage is above the input range and with new alkaline batteries also above the absolute maximum. With lithium cells it is way off from the allowed input voltage.
Populate R12 instead of R94 will supply the reference with +4V, so no problems in this configuration. But R94 is populated, not only in the schematics. I have checked this in my meter and actually R94 is populated. I will remove R94 and place it in the R12 position.I cannot understand why the reference is connected to B+, that makes no sense for me. Is this really a design flaw or did I overlook something?

The voltage reference is connected to AGND, not AVSS which is the battery negative. The full battery voltage is not across the reference, as AGND is a referenced voltage rail lifted above ground.
If you actually measure the voltage across the reference I think you'll find it's fine.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ELzekio on August 24, 2018, 02:08:31 am


Will instructions be provided for replacing the 4007 diodes with the TVS for current 121gw owners in the future?

Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on August 24, 2018, 05:19:24 am


Will instructions be provided for replacing the 4007 diodes with the TVS for current 121gw owners in the future?
Good question, which you could also add and a suitable supplier for 1 of TVS components.
There is also a resistor that Dr. Frank has identified that may need replacing to enable a higher current for stability reasons. Its probably a bit early for Dave to do a video on a 121GW hack/modification/repair just yet as more hardware may need changing.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 24, 2018, 06:44:20 am
There is also a resistor that Dr. Frank has identified that may need replacing to enable a higher current for stability reasons.

Sorry, I have not been following ever post, link to post?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 24, 2018, 07:28:57 am
The 50 Mohm range uses 20nA reference current by its internal R9 = 10MOhm reference resistor, which causes a susceptibility to leakage currents (I will demonstrate that later). Maybe it's possible to increase the Vref (by firmware) from about 0.2V to 2V, to get 200nA test current, but probably that's not possible due to supply/reference voltage  limitation, as in total >4V would be required. See HY3131 Configuration document, page 31.
 
The 50 Ohm configuration also follows  the HY3131 document, see page 33, so R26 = 1k is used also for 50 Ohm, giving 470µA test current only, and a sensitivity of 470nV on the last digit, causing the noise trouble. The analog multiplex bus of the HY3131 is completely occupied, so it's not possible to add another 100 Ohm reference resistor for 5mA test current.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on August 24, 2018, 07:30:06 am
Ground, Earth, Static Field... whatever.

I propose simply to calculate the equivalent voltage on the last digit in 50mOhm range, that is about 0.4 mA times 1mOhm = 400nV.

That's simply extremely sensitive, so shielding is also difficult in a handheld DMM.

The reference current should have been 5mA, to get a stable reading as in 500 Ohm range.

Instead both ranges are derived from the same 1k reference resistor, but the 50 Ohm range uses an amplified AD range, which is the culprit
Frank

This is the post I'm referring to!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 24, 2018, 07:43:35 am

The 50 Mohm range uses 20nA reference current by its internal R9 = 10MOhm reference resistor, which causes a susceptibility to leakage currents (I will demonstrate that later). Maybe it's possible to increase the Vref (by firmware) from about 0.2V to 2V, to get 200nA test current, but probably that's not possible due to supply/reference voltage  limitation, as in total >4V would be required. See HY3131 Confirguration document, page 31.
 
The 50 Ohm configuration also follows  the HY3131 document, see page 33, so R26 = 1k is used also for 50 Ohm, giving 470µA test current only, and a sensitivity of 470nV on the last digit, causing the noise trouble. The analog multiplex bus of the HY3131 is completely occupied, so it's not possible to add another 100 Ohm reference resistor for 5mA test current.

Frank

  There is the 15V generator for the diode test, with that and a ratiometric measurement with the 10M reference something could be worked out. I have to take a second look at the datasheet to see what else could be done in FW.

For the 500Ω range I should take another look as well, isn't there any other resistor that can be paralleled to the existing one? Or again using the 15V zener source to do measurement against the 1k reference. I haven't looked enough to this, I will take a look at the datasheet and come back tomorrow.

JS

PS: two more ideas, there is the 100Ω resistor I the μA range, the resistor might need to be connected to that input for measuring small resistors but who cares our connected by u11 but I guess that last wouldn't work. The second once, couldn't we spare C30 to get the extra resistor there.
Title: EEVblog 121GW Multimeter Issues - 50MOhm temperature dependence
Post by: Dr. Frank on August 24, 2018, 08:51:00 am
Following Daves hint, I removed the over voltage protection diodes D7 and D8.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=505322;image)

By means of an Impedance Synthesizer circuit, I measured different resistors from 5MOhm to 50MOhm.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=505328;image)

The gain calibration of the 121GW is now -6% low, that means, that the nominal test current of about 20nA is decreased by that amount also, that is -1.2nA.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=505334;image)

These 1.2nA were leaked by D7, or by the difference in leakage currents between D7 and D8.
At 6V reverse voltage, I have determined leakage currents of about 500..800pA for the one diode, but about 3nA for the other, so this difference causes this effect, at least.

Without the diodes, I re-calibrated the 50MOhm and 5MOhm ranges, and measured the change of reading over a 3°C temperature change.

(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=505340;image)

It's now -0.04% only, giving a virtual T.C. of about -133ppm/°C, instead of +6400ppm/°C, as with the diodes assembled.

That clearly indicates that the diodes were the root cause for the bad temperature behavior and out-of-spec of the 50MOhm range.

The replacement of the 1N4007s by a TVS (SM6T22CA) probably is much better for ESD / overvoltage protection, as these TVS react much faster than ordinary power diodes.
A TVS can't be used in that application, though, because they have leakage currents of up to 200nA @ 25°C, which is 10 times the reference current of the 50M range.
In other words, a TVS in place of D8 would simply short both the 5MOhm and 50MOhm ranges.

So a solution with two JFETs would be the correct measure, although I doubt that they'd withstand Joes ultra-violent HV pulse testing  8)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 24, 2018, 01:45:07 pm

The voltage reference is connected to AGND, not AVSS which is the battery negative. The full battery voltage is not across the reference, as AGND is a referenced voltage rail lifted above ground.
If you actually measure the voltage across the reference I think you'll find it's fine.

Doh... :palm:

i was sure I made some mistake.
I have mixed up AVSS with AGND, sorry.
I must subract 1.8V from B+ of course.

So it is clear that the 121GW can be used with lithium batteries.
In case that the lithium cells are brandnew the voltage at the reference chip is above the operation voltage for a short time, but never above the absolute maximum voltage.

Thanks for clarifying.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 24, 2018, 01:48:29 pm
The 50 Ohm configuration also follows  the HY3131 document, see page 33, so R26 = 1k is used also for 50 Ohm, giving 470µA test current only, and a sensitivity of 470nV on the last digit, causing the noise trouble. The analog multiplex bus of the HY3131 is completely occupied, so it's not possible to add another 100 Ohm reference resistor for 5mA test current.

I can get stable voltage readings when I independently apply a 1 mA source current and have 1 µV sensitivity on the last digit. This is the same order of magnitude as 470 µA. So I think there is more to the noise than just the magnitude of the test current.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on August 24, 2018, 09:12:49 pm

The voltage reference is connected to AGND, not AVSS which is the battery negative. The full battery voltage is not across the reference, as AGND is a referenced voltage rail lifted above ground.
If you actually measure the voltage across the reference I think you'll find it's fine.

Doh... :palm:

i was sure I made some mistake.
I have mixed up AVSS with AGND, sorry.
I must subract 1.8V from B+ of course.

So it is clear that the 121GW can be used with lithium batteries.
In case that the lithium cells are brandnew the voltage at the reference chip is above the operation voltage for a short time, but never above the absolute maximum voltage.

Thanks for clarifying.

Beware that the AGND voltage seems to change depending on measurement mode. It's i.e. 1.09V in Ohms mode and 0.38V in Diode mode - and that seems to put more voltage over the ADR3412 than it perhaps was designed for - all depending on how fresh the batteries are.

Or am I also missing something? I measured the voltage between the batteries (-) which = VSS and the COM terminal which = AGND.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on August 25, 2018, 02:52:21 am
Is there a specific reason why the thermocouple update rate is 1 Hz? Its as such in 1.22, 1.25, and 1.26. I realize the time constants for thermocouples is usually fairly high, but I have probes with TC's less than a second that I was hoping to not need to spin a custom solution for.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 25, 2018, 03:53:29 am
The replacement of the 1N4007s by a TVS (SM6T22CA) probably is much better for ESD / overvoltage protection, as these TVS react much faster than ordinary power diodes.
A TVS can't be used in that application, though, because they have leakage currents of up to 200nA @ 25C

That's not correct.
Not only is the 200nA a maximum figure (not typical), it's at the rated voltage.
It drops drastically with lower voltage.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 25, 2018, 07:10:40 am

The voltage reference is connected to AGND, not AVSS which is the battery negative. The full battery voltage is not across the reference, as AGND is a referenced voltage rail lifted above ground.
If you actually measure the voltage across the reference I think you'll find it's fine.

Doh... :palm:

i was sure I made some mistake.
I have mixed up AVSS with AGND, sorry.
I must subract 1.8V from B+ of course.

So it is clear that the 121GW can be used with lithium batteries.
In case that the lithium cells are brandnew the voltage at the reference chip is above the operation voltage for a short time, but never above the absolute maximum voltage.

Thanks for clarifying.

Beware that the AGND voltage seems to change depending on measurement mode. It's i.e. 1.09V in Ohms mode and 0.38V in Diode mode - and that seems to put more voltage over the ADR3412 than it perhaps was designed for - all depending on how fresh the batteries are.

Or am I also missing something? I measured the voltage between the batteries (-) which = VSS and the COM terminal which = AGND.

I was not aware that the virtual ground is changing with the measurement mode. With 0.38V in Diode mode my doubts would be true, event though I made a mistake with AGND. That needs further investigations. But I think like you, we maybe overlook something. i cannot believe that UEI has overlooked such a problem.

Update:
Meanwhile I made the same measurement, the voltage between com terminal and - battery. It is -1.8V as expected in all modes, except Diode test. In 15V Diode test mode there are indeed only 0.38V. I assume because of the high 15V level they had to shift the virtual gnd level in Diode mode, prevent the adc to overrange.
And now the problem is back again, with lithium batteries the voltage at the reference element is over 6 V in 15V Diode test mode.

Update 2:

Actually there is no problem.
With alkaline batteries the voltage at the reference chip will never exceed 6 V, even in the 15V Diode mode. According to the manual there are only alkaline batteries mentioned.

This meter cannot be used with lithium batteries. In the 15V Diode test mode is a high risk to damage it.

So: Do not use the meter with lithium batteries!

That is the point we have overlooked.
It should be a warning in the manual.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on August 25, 2018, 09:27:55 am
The replacement of the 1N4007s by a TVS (SM6T22CA) probably is much better for ESD / overvoltage protection, as these TVS react much faster than ordinary power diodes.
A TVS can't be used in that application, though, because they have leakage currents of up to 200nA @ 25C

That's not correct.
Not only is the 200nA a maximum figure (not typical), it's at the rated voltage.
It drops drastically with lower voltage.

Hello Dave,
you're right, that these 200nA are a maximum value at Vrm ~ 18.8V, but the term I have used: 'up to' is an equivalent expression to 'maximum', I think.

There is no specification or diagram of the behavior of this leakage current at lower voltages, so your statement that this current drops 'drastically' has to to be quantified / measured on an appropriate  TVS, probably with Vr = 18V, Vrm ~15V.

As these are sort of zener diodes, I expect the leakage current being much higher at 1..6V than  these 1N4007, several 10nA maybe, therefore still being unsuitable for this application.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 27, 2018, 05:49:47 pm
Hi,
I noticed that the meter is locked in an auto-ranging loop in the DC+AC mode in some conditions (Ver. 1.26).

For example: Generate this signal with a function generator:
6.4Vss, sinus, 800Hz together with a DC offset of +6.6V.

With this values a stable auto-ranging loop occures.
No other of my meters (Agilent U1252B, Brymen BM869S, Gossen Metrahit Energy) has this problem.

In manual mode the 121GW shows the correct value, the reading is very close to the other meters.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: emece67 on August 28, 2018, 12:08:59 am
Hi,
I noticed that the meter is locked in a auto-ranging loop in the DC+AC mode in some conditions (Ver. 1.26).

For example: Genrate this signal with a function generator:
6.4Vss, sinus, 800Hz together with a DC offset of +6.6V.

I've seen this very same auto-ranging loop in AC+DC simply measuring the mains 50 Hz, 230 V.

Regards.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bratster on August 28, 2018, 01:21:27 am

The voltage reference is connected to AGND, not AVSS which is the battery negative. The full battery voltage is not across the reference, as AGND is a referenced voltage rail lifted above ground.
If you actually measure the voltage across the reference I think you'll find it's fine.

Doh... :palm:

i was sure I made some mistake.
I have mixed up AVSS with AGND, sorry.
I must subract 1.8V from B+ of course.

So it is clear that the 121GW can be used with lithium batteries.
In case that the lithium cells are brandnew the voltage at the reference chip is above the operation voltage for a short time, but never above the absolute maximum voltage.

Thanks for clarifying.

Beware that the AGND voltage seems to change depending on measurement mode. It's i.e. 1.09V in Ohms mode and 0.38V in Diode mode - and that seems to put more voltage over the ADR3412 than it perhaps was designed for - all depending on how fresh the batteries are.

Or am I also missing something? I measured the voltage between the batteries (-) which = VSS and the COM terminal which = AGND.

I was not aware that the virtual ground is changing with the measurement mode. With 0.38V in Diode mode my doubts would be true, event though I made a mistake with AGND. That needs further investigations. But I think like you, we maybe overlook something. i cannot believe that UEI has overlooked such a problem.

Update:
Meanwhile I made the same measurement, the voltage between com terminal and - battery. It is -1.8V as expected in all modes, except Diode test. In 15V Diode test mode there are indeed only 0.38V. I assume because of the high 15V level they had to shift the virtual gnd level in Diode mode, prevent the adc to overrange.
And now the problem is back again, with lithium batteries the voltage at the reference element is over 6 V in 15V Diode test mode.

Update 2:

Actually there is no problem.
With alkaline batteries the voltage at the reference chip will never exceed 6 V, even in the 15V Diode mode. According to the manual there are only alkaline batteries mentioned.

This meter cannot be used with lithium batteries. In the 15V Diode test mode is a high risk to damage it.

So: Do not use the meter with lithium batteries!

That is the point we have overlooked.
It should be a warning in the manual.
Can Dave maybe weigh in on this? It would be nice to know if there is a legitimate cause for concern using lithium batteries in this or not.

Seems like this would be a fairly serious issue...

Sent from my Fi Moto x4 using Tapatalk

Title: Re: EEVblog 121GW Multimeter Issues
Post by: gdewitte on August 28, 2018, 01:39:02 am
I agree that an input from Dave would help. Specifically, can one use Lithium or LSD NiMH batteries? Maybe pros and cons of each? I've had enough things ruined or compromised by leaking alkaline batteries and don't want to sacrifice my 121GW.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Mr.B on August 28, 2018, 01:46:56 am
I put Lithium in mine the first day I got it - wanting to avoid any potential leakage problems with the usual chemistries.
Now I am worried about the Lithiums...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Bratster on August 28, 2018, 02:06:01 am
I put Lithium in mine the first day I got it - wanting to avoid any potential leakage problems with the usual chemistries.
Now I am worried about the Lithiums...
Same as me...

Sent from my Fi Moto x4 using Tapatalk

Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 28, 2018, 03:30:26 am
Hi,
I noticed that the meter is locked in a auto-ranging loop in the DC+AC mode in some conditions (Ver. 1.26).

For example: Genrate this signal with a function generator:
6.4Vss, sinus, 800Hz together with a DC offset of +6.6V.

I've seen this very same auto-ranging loop in AC+DC simply measuring the mains 50 Hz, 230 V.

Regards.
I've seen it too, unable to repeat as I turned off and on again and was good.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on August 28, 2018, 02:31:56 pm
can one use Lithium or LSD NiMH batteries?

Looks like the problem is when the batteries voltage goes above 6V. Full Lithium batteries are at 1,7V and they stay above 1,5V until they are done:

http://data.energizer.com/pdfs/l92.pdf (http://data.energizer.com/pdfs/l92.pdf)

So it's 1,7x4=6,8V

LSD NiMH are more relaxed:

https://www.kronium.cz/uploads/BK-3MCCE.pdf (https://www.kronium.cz/uploads/BK-3MCCE.pdf)

they start at 1,5V and they drop to 1,2V.

So LSD NiMH are just fine, Lithium are dangerous, see posts above.

PS: In my future projects the MAX AA Battery Voltage MUST be 1,8V 2V (EDIT: see post below) to be safe.

Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 28, 2018, 03:51:58 pm
can one use Lithium or LSD NiMH batteries?

Looks like the problem is when the batteries voltage goes above 6V. Full Lithium batteries are at 1,7V and they stay above 1,5V until they are done:

http://data.energizer.com/pdfs/l92.pdf (http://data.energizer.com/pdfs/l92.pdf)

So it's 1,7x4=6,8V

LSD NiMH are more relaxed:

https://www.kronium.cz/uploads/BK-3MCCE.pdf (https://www.kronium.cz/uploads/BK-3MCCE.pdf)

they start at 1,5V and they drop to 1,2V.

So LSD NiMH are just fine, Lithium are dangerous, see posts above.

PS: In my future projects the MAX AA Battery Voltage MUST be 1,8V to be safe.
Actually 6.38V and above is the critical value.
My 121GW showed 7.7V (!!) with brandnew lithium cells. That value settled down to 6.7V after some time. Still too much for the reference chip.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: zucca on August 28, 2018, 04:10:41 pm
My 121GW showed 7.7V (!!) with brandnew lithium cells...

wow, so in the future Vmax of a AA must be considered 2V.

Okay, idiots will always win:

(https://www.jablotron.com/runtime/cache/ftpclientdata/10905/img679/10905_maxi.png)

 :horse:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 28, 2018, 05:49:48 pm
Use a bateroo!

If designed for four 1.5V to 2V cells two 3.7 cells could do but you need to change the arrangement (or put one backwards |O), but Li could go over 4V when fully charged, so we need to provide a way to work with batteries between 0.8V to 4.2V, bit streetchy without a switching regulator...

About leaking batteries, just replace them every a year or two, that's all it takes, even ig they are not fully depleated, and use them till they die in the mouse, tv remote or torch.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on August 28, 2018, 05:54:02 pm
About leaking batteries, just replace them every a year or two, that's all it takes, even ig they are not fully depleated, and use them till they die in the mouse, tv remote or torch.

That's not all it takes, unfortunately. I've had batteries well under a year old that weren't depleted pop on me. I think they aren't building them as heat resistant as they used to. I have become pathological about checking on my alkalines now because they seem to pop on me all the times these days and they never used to do that.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 28, 2018, 06:51:31 pm
About leaking batteries, just replace them every a year or two, that's all it takes, even ig they are not fully depleated, and use them till they die in the mouse, tv remote or torch.

That's not all it takes, unfortunately. I've had batteries well under a year old that weren't depleted pop on me. I think they aren't building them as heat resistant as they used to. I have become pathological about checking on my alkalines now because they seem to pop on me all the times these days and they never used to do that.
I don't know if you canmake a claim, they aren't supposed to leak so easily, after expiration day or really abused. Alkalines can take a fair share of abuse, not as sensitive as lipo where a short will most likely make them explode, or being too empty, or too full, or too warm, or too cold, or you get my point...

You should swap brands or something, I don't see blown batteries that often, a calculator I got from a friend, parched a few traces in the keyboard and got away with it and, a tv remote or two, where the things last for ever, and some really old stuff forgotten with the batteries on. I don't use cheap batteries either, I mostly gpt them from a friend's music shop who buys mostly for personal use, replace or fit in products, so I get them for cheap or free, but still you won't loose your salary over different brands.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on August 28, 2018, 06:56:40 pm
About leaking batteries, just replace them every a year or two, that's all it takes, even ig they are not fully depleated, and use them till they die in the mouse, tv remote or torch.

That's not all it takes, unfortunately. I've had batteries well under a year old that weren't depleted pop on me. I think they aren't building them as heat resistant as they used to. I have become pathological about checking on my alkalines now because they seem to pop on me all the times these days and they never used to do that.
I don't know if you canmake a claim, they aren't supposed to leak so easily, after expiration day or really abused. Alkalines can take a fair share of abuse, not as sensitive as lipo where a short will most likely make them explode, or being too empty, or too full, or too warm, or too cold, or you get my point...

You should swap brands or something, I don't see blown batteries that often, a calculator I got from a friend, parched a few traces in the keyboard and got away with it and, a tv remote or two, where the things last for ever, and some really old stuff forgotten with the batteries on. I don't use cheap batteries either, I mostly gpt them from a friend's music shop who buys mostly for personal use, replace or fit in products, so I get them for cheap or free, but still you won't loose your salary over different brands.

JS

You think I haven't tried different brands? I've tried everything. It just doesn't matter unless I'm checking once a month or more a popped AAA or AA always sneaks up on me. AAAs are the worst. I recently had two Energizer AAA go in a laser pointer that were only 6 months old and they were still reading 1.2V and working fine. My understanding is there's a sealed plastic membrane of some kind inside them that pops. And it seems like that membrane is more delicate than it used to be. I wish I knew what causes it, but it's not age or being deep discharged.

Up until 2010 or so this NEVER happened to me with alkalines, now it happens all the time. Something has changed.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 28, 2018, 07:26:59 pm
About leaking batteries, just replace them every a year or two, that's all it takes, even ig they are not fully depleated, and use them till they die in the mouse, tv remote or torch.

That's not all it takes, unfortunately. I've had batteries well under a year old that weren't depleted pop on me. I think they aren't building them as heat resistant as they used to. I have become pathological about checking on my alkalines now because they seem to pop on me all the times these days and they never used to do that.
I don't know if you canmake a claim, they aren't supposed to leak so easily, after expiration day or really abused. Alkalines can take a fair share of abuse, not as sensitive as lipo where a short will most likely make them explode, or being too empty, or too full, or too warm, or too cold, or you get my point...

You should swap brands or something, I don't see blown batteries that often, a calculator I got from a friend, parched a few traces in the keyboard and got away with it and, a tv remote or two, where the things last for ever, and some really old stuff forgotten with the batteries on. I don't use cheap batteries either, I mostly gpt them from a friend's music shop who buys mostly for personal use, replace or fit in products, so I get them for cheap or free, but still you won't loose your salary over different brands.

JS

You think I haven't tried different brands? I've tried everything. It just doesn't matter unless I'm checking once a month or more a popped AAA or AA always sneaks up on me. AAAs are the worst. I recently had two Energizer AAA go in a laser pointer that were only 6 months old and they were still reading 1.2V and working fine. My understanding is there's a sealed plastic membrane of some kind inside them that pops. And it seems like that membrane is more delicate than it used to be. I wish I knew what causes it, but it's not age or being deep discharged.

Up until 2010 or so this NEVER happened to me with alkalines, now it happens all the time. Something has changed.
Have you contacted energizer?  Use them all the time, one of the few brands I use, and never seen one leaking, what enviroment do you usually have? Where I live 40°C is not unussual, humidity well over 90% most nights.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: gdewitte on August 28, 2018, 07:37:17 pm
The fine print on most of the packages for alkaline batteries requires that you contact the manufacturer, that you are responsible for shipping any damaged items back to them for replacement, and the replacement will be an "equivalent" device. I've had some "new" AA alkalines leak when they were in one of those handy battery storage carriers (e.g., Powerpax Storacell).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 28, 2018, 10:51:29 pm
I wish I knew what causes it, but it's not age or being deep discharged.

Up until 2010 or so this NEVER happened to me with alkalines, now it happens all the time. Something has changed.

I think what has changed is "High Power" or "Super Extra Power" or "Ultra Performance".

The marketing people have been pushing for more buzzwords on the packaging. To increase the performance of the batteries the chemical formulation has been made more and more active. This means the chemicals inside the battery can react and produce hydrogen even when the battery is not being used. The hydrogen increases the pressure inside the cell until it is too much, when the gas pressure breaks the seal and pushes the electrolyte out of the casing.

The best solution is to avoid all the expensive, high performance brands and buy the cheap dollar store brands instead. The cheaper cells use the older, less active formulations and don't have the same leaking tendency.

I have been buying Sunbeam branded batteries for a while at 4/1$ and I haven't seen one leak yet.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on August 29, 2018, 01:25:57 am
Have you contacted energizer?  Use them all the time, one of the few brands I use, and never seen one leaking, what enviroment do you usually have? Where I live 40°C is not unussual, humidity well over 90% most nights.

My apartment only has windows in the west and the evening sun can really cook the place. I'm pretty sure at least once it was caused by the thing sitting in a spot where a sunbeam was on it for a while. But I think batteries should be able to survive sitting in direct sunlight.

I think what has changed is "High Power" or "Super Extra Power" or "Ultra Performance".
...
The best solution is to avoid all the expensive, high performance brands and buy the cheap dollar store brands instead. The cheaper cells use the older, less active formulations and don't have the same leaking tendency.

That's a very good theory. I tried buying premium batteries and that sure didn't work. I never once had an alkaline leak on me until well after 2000. I'd be happy to go back to an old design.


Looks like that's what I'll be doing in my 121GW. It would be nice to know officially if lithiums are a bad choice and to see that added to the manual.


Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 29, 2018, 05:24:09 am
Looks like the ultra performance batteries didn't reach our sudamerican market, one nice thing of living that far south...

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on August 29, 2018, 07:10:34 am
Looks like that's what I'll be doing in my 121GW. It would be nice to know officially if lithiums are a bad choice and to see that added to the manual.

Confirmed. Fresh Lithium cells produce an overvoltage on the reference on both diode and ohms ranges. Don't use fresh Lithiums and these ranges.
The manual will be updated, and a possible future fix allowing this investigated.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tomp on August 29, 2018, 04:37:09 pm
Possible an issue with the range switch:
 - disconnect any leads
 - turn beep off in setup
 - rotate range switch to resistance/continuity/...
 - press "Mode" and switch it to continuity (the meter remembers the mode)
 - rotate the range switch to "mVA/VA" while applying a small pressure to it (when you are very careful and do not apply any pressure, it does not do that)
 - the meter will beep during the switching
 - you can even find a position of the range switch where the meter reads 0 ohms and beeps continuously
My meter is a Kickstarter one - Johnny B. Goode, delivered by Welectron.
Video showing the problem:
https://vimeo.com/287278487
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Scottjd on August 29, 2018, 05:21:00 pm
Possible an issue with the range switch:
 - disconnect any leads
 - turn beep off in setup
 - rotate range switch to resistance/continuity/...
 - press "Mode" and switch it to continuity (the meter remembers the mode)
 - rotate the range switch to "mVA/VA" while applying a small pressure to it (when you are very careful and do not apply any pressure, it does not do that)
 - the meter will beep during the switching
 - you can even find a position of the range switch where the meter reads 0 ohms and beeps continuously
My meter is a Kickstarter one - Johnny B. Goode, delivered by Welectron.
Video showing the problem:

I think this is because of the jack detection for current ranges and because you have it in continuity mode. I think pressing down is spreading the switch wipers giveing the meter less time to recognize the mode change as the wipers are spread out more between the traces on the PCB.
It’s still beeping even with beep off because the current jack detection and continuity will still beep with beep off in the settings.
I may be wrong, but I think this is just giving the meter a few less milliseconds to figure out the mode changed by spreading the wipers from the pressure.
It’s only an issue if both modes make contact at the same time. But it can also be argued this is only an issue if you have current applied to the meter and you really should not be changing modes with an active DUT powered up and plugged into the meter.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tomp on August 29, 2018, 05:55:05 pm
I think this is because of the jack detection for current ranges and because you have it in continuity mode.
It is probably not the jack detection thing. It seems that there is a position of the range switch between "ohm" and "mVA/VA", where the meter is still switched do "ohm", however it reads short. In principle, I do not mind that, other meters do similar things, however the 121GW switch does not have the best indent, it is very easy to accidentally leave it in an intermediate position. However, the fact that the meter beeps when switching ranges even when it should not is quite annoying. Even if I do not apply any pressure on the switch and I try to switch as fast as possible, it beeps in 10 % of cases.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on August 30, 2018, 12:06:42 am
That'd be consistent with minor tolerances of the trances for the switch and being between modes. The added pressure flattened the contact wider with a slightly larger than normal contact area causing it to just barely switch part of one position and the next at the same time. Could also be a result of solder mask tolerances. This could literally be an edge case.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: ButterToast1134 on August 30, 2018, 08:51:15 pm
Is anyone having bluetooth connectivity problems?

My meter does not want to connect to through bluetooth.
My buddy's meter he can connect to it using his Android and I can connect to his using my Iphone.
My meter however will not show up on either phone.
When holding the bluetooth button it says its active but can't see it with any phone or devices.
Any one have any suggestions?

Oh if it matters my SN is EEVBLog 001563

Thanks

I said my a lot.

MINE! MINE! MINE!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 30, 2018, 08:57:25 pm
My meter connects fine to my Apple devices. However, I had lots of trouble with Windows 10. It connected one day and not the next. I had to reboot to fix it.

What firmware do you have on the meter? You might wish to update to the latest v1.26 if you have not done so already.

Also, make sure you are using the right app. There is an obsolete app floating around somewhere that is no good. You need to make sure you get Dave's current 121GW app.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 30, 2018, 10:11:06 pm
First activate bluetooth on the phone, close everithing, activate bluetooth on the meter, once activated open the app, if it doesnt show press refresh. I uave build 9 on android and works fine.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: ButterToast1134 on August 30, 2018, 11:22:00 pm
Well as I said my buddys 121GW will connect to my phone.

My meter does not show up on his phone or my phone.

His meter connects flawlessly.

I have build 1.7 App even though his connects to mine.
Just did a firmware update today so I am running the 1.26 on the meter still doesnt work.

This leads me to believe there is a problem with the bluetooth module on the meter.

No devices can see it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 31, 2018, 01:02:50 am
Bummer!

  I've heard of some BT modules without the proper FW, there are no terminals installed in the BT module but I believe there are pads to connect there. If that's the case you could probably take the dumps from the thing in your friends and take it to yours, I haven't seen those online, I've seen them from the STM firmware. If you do you could send them to Thomas, who's getting a lot of info for reverse engineering the meter, he has a lot of info in it.

https://github.com/tpwrules

  Of course you could talk to Dave and hear what he has to say, but he will most likely encourage you to "take it apart!!" and try to fix it yourself if you believe you can. I don't think there's a warranty void if removed sticker, it might have one if not removed!

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on August 31, 2018, 02:50:55 am
This leads me to believe there is a problem with the bluetooth module on the meter.

No devices can see it.

You probably need to contact Dave for a replacement meter, unfortunately. They probably would like you to send the meter back to them so they can investigate what is wrong.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 31, 2018, 03:12:49 pm
First activate bluetooth on the phone, close everithing, activate bluetooth on the meter, once activated open the app, if it doesnt show press refresh. I uave build 9 on android and works fine.

JS

That does not work for me. When I first tried the bluetooth function that drove me nuts.
The App seems to have a problem either with my Nokia 8 or Android 8.1.

What I did:
Activate bluetooth at the phone and let it seach for a new device.
Activate bluetooth at the 121GW, the meter is detected by the phone and will connected to the meter.
Until this point everything is ok, the phone is connected to the meter.

Start the Android app and nothing happens...mostly only an empty screen, that`s all, the app does not see the meter. Sometimes it worked for some reason, mostly it does not.
 
I found this solution:
Connect the meter to the phone as described.
Open the app.
In case that nothing happens: Switch off the bluetooth function at the meter and switch it on again immediately.
Than the app shows the meter ID.
Confirm the meter ID and the app connects and works without any problem from now on.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on August 31, 2018, 03:24:53 pm
Hi,
I noticed that the meter is locked in a auto-ranging loop in the DC+AC mode in some conditions (Ver. 1.26).

For example: Genrate this signal with a function generator:
6.4Vss, sinus, 800Hz together with a DC offset of +6.6V.

I've seen this very same auto-ranging loop in AC+DC simply measuring the mains 50 Hz, 230 V.

Regards.
I've seen it too, unable to repeat as I turned off and on again and was good.

JS

It is easy to repeat:
Set the meter to AC and connect it to the 230V mains.
Then change from AC to DC+AC and the auto-ranging loop occures.

This should be fixed in the next firmware.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 31, 2018, 04:21:11 pm
It happend to me in a very differemt situation, measuring a DC IIRC, the meter was already set to AC+DC, I switched it on and connected the source. But as I said, I couldn't repeat it.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on August 31, 2018, 04:30:29 pm
Maybe your meter got in sync with your phone, and being already linked is bringing problems for you. You could try connect them both via th bluetooth menu in the phone and then making it forget the connection.

JS

Title: EEVblog 121GW Multimeter Issues - 50MOhm protection
Post by: Dr. Frank on September 01, 2018, 07:23:56 am
I have now replaced D7, D8 by two BF256B, n-JFETs. They show leakage currents of the Gate vs. Drain/Source reversed diode of < 20pA @ up to 20V, and as expected no zener effect, as they are specified up to 30V D-G and S-G voltage. The B-E diode of a BC547 transistor also had very low leakage in the pA range, but started to zener at about 6..7V, as expected.
 
(https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/?action=dlattach;attach=512150;image)


The assembly was a bit tricky, because there is only 5mm clearance above the PCB, and I had to bend flat the metal shield of the battery case a bit.

After assembling these FETs, I observed big deviations in the 50M and 5M Ohm ranges, so I cleaned this area on the PCB, around the U9 multiplexer.

After drying, the Ohm ranges were again spot on.
Additionally, I observed that concerning the leakage effect in the 50 mV dc range of about 170pA:
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1728887/#msg1728887 (https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1728887/#msg1728887)

the 50mV range now shows a few µV only, when left open, so leakage should be <1pA.

Therefore I assume, that I also removed the leakage path on pin 14 of U9.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on September 01, 2018, 09:11:19 am
Hi Frank,

the maximum forward gate current of the the BF256 is 10mA. So I assume this is not joeqsmith compatible...

BTW: A MMBF5457 would better fit mechanically.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 02, 2018, 07:10:32 am
A "normal" test for average user should be at least mains voltage in resistance mode ... then is a fix .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: vk3zgw on September 02, 2018, 07:38:17 am
Lost my posting for some reason, site bombed me out!

Just picked up my meter. v1.17

Tried to update to 1.26 and nothing happened. Followed the instructions as per page 70 of the latest manual. The meter just sat there showing 'down'. File on SD card is there and changed to EEVBlog.bin.

Tried to download 1.17, same result.

Any suggestions?
Thanks
Geoff
Title: Re: EEVblog 121GW Multimeter Issues
Post by: EEVblog on September 02, 2018, 09:16:29 am
Lost my posting for some reason, site bombed me out!
Just picked up my meter. v1.17
Tried to update to 1.26 and nothing happened. Followed the instructions as per page 70 of the latest manual. The meter just sat there showing 'down'. File on SD card is there and changed to EEVBlog.bin.
Tried to download 1.17, same result.
Any suggestions?

Strange, first report of someone having issue with this.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on September 02, 2018, 10:45:38 am
Lost my posting for some reason, site bombed me out!

Just picked up my meter. v1.17

Tried to update to 1.26 and nothing happened. Followed the instructions as per page 70 of the latest manual. The meter just sat there showing 'down'. File on SD card is there and changed to EEVBlog.bin.

Tried to download 1.17, same result.

Any suggestions?
Thanks
Geoff

Does the meter write to the card if you start logging?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: vk3zgw on September 02, 2018, 12:21:18 pm
Haven't tried to write from the meter. I'll give it a go in the morning.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: tpw_rules on September 02, 2018, 02:38:23 pm
The 50 Mohm range uses 20nA reference current by its internal R9 = 10MOhm reference resistor, which causes a susceptibility to leakage currents (I will demonstrate that later). Maybe it's possible to increase the Vref (by firmware) from about 0.2V to 2V, to get 200nA test current, but probably that's not possible due to supply/reference voltage  limitation, as in total >4V would be required. See HY3131 Configuration document, page 31.
 
The 50 Ohm configuration also follows  the HY3131 document, see page 33, so R26 = 1k is used also for 50 Ohm, giving 470µA test current only, and a sensitivity of 470nV on the last digit, causing the noise trouble. The analog multiplex bus of the HY3131 is completely occupied, so it's not possible to add another 100 Ohm reference resistor for 5mA test current.

Frank

Can you remind me which Configuration Document you're referring to?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on September 02, 2018, 03:08:01 pm


Can you remind me which Configuration Document you're referring to?

Somebody recently posted the HY3131 configuration document, you have to look for it.

Frank
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on September 02, 2018, 03:40:05 pm


Can you remind me which Configuration Document you're referring to?

Somebody recently posted the HY3131 configuration document, you have to look for it.

Frank

https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1733579/#msg1733579 (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1733579/#msg1733579)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: vk3zgw on September 02, 2018, 11:24:39 pm
Lost my posting for some reason, site bombed me out!

Just picked up my meter. v1.17

Tried to update to 1.26 and nothing happened. Followed the instructions as per page 70 of the latest manual. The meter just sat there showing 'down'. File on SD card is there and changed to EEVBlog.bin.

Tried to download 1.17, same result.

Any suggestions?
Thanks
Geoff

Does the meter write to the card if you start logging?

Alexander.

Hi Alexander,

Data logged this morning ok. Viewed Excel file and all the data was there. Tried again to update with 1.26 and same result as meter stays showing "douun", bar graph remains at zero. Waited 10 mins, no change.

Geoff.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on September 02, 2018, 11:32:07 pm
Tried again to update with 1.26 and same result as meter stays showing "douun", bar graph remains at zero. Waited 10 mins, no change.

And if you press the "SETUP" button while the meter is showing "douun", still nothing happens?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on September 03, 2018, 12:09:54 am
What is the actual filename of the firmware file you put on the microSD card?

It is supposed to be EEVblog.bin as per the note on https://www.eevblog.com/product/121gw/ (https://www.eevblog.com/product/121gw/)  (click on the firmware link)

FIRMWARE

Note: When upgrading a multimeter the “.bin” file must be renamed “EEVBlog.bin”:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: vk3zgw on September 03, 2018, 05:39:06 am
Brumby, you will see from my first post that I have changed the file name as required.


IanB, yep, just sits there.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on September 03, 2018, 05:43:23 am
Brumby, you will see from my first post that I have changed the file name as required.
Have you tried with other versions other than 1.26?

Check upper/lower cases in the bin file, I think they need to match. Also BIN or bin? My meter takes the .CSV on upper cases which is a pain!

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: vk3zgw on September 03, 2018, 06:54:55 am
This is how the file change instruction in the manual has it. I think we might have heard by now if others were having this trouble. Appears its just me :-\

“EEVBlog.bin”

Tried another version, same thing. I can read/write to the SD card from the PC, and read from the meter but can't write to the meter.

Geoff
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on September 03, 2018, 07:08:29 am
This is how the file change instruction in the manual has it. I think we might have heard by now if others were having this trouble. Appears its just me :-\

“EEVBlog.bin”

Tried another version, same thing. I can read/write to the SD card from the PC, and read from the meter but can't write to the meter.

Geoff
Yes, appears it's just you. If you want to fix it yourself the bootloader is in the reverse engineering docs so you can write it with a st-link. Before doing so try writing your cal data to the sd file and decode it with the phyton routing that's there as well, to checl it makes sense. Then take what's in the stm with the st-link, save it and then write the new bootloader to it, then try installing the new firmware with the SD again. Looks like it's that or shipping it back for a fix at Dave's HQ.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on September 03, 2018, 07:36:55 am
Brumby, you will see from my first post that I have changed the file name as required.

Oooof.  Sorry.   :palm:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: vk3zgw on September 03, 2018, 07:45:08 am
Thanks JS but I'll wait and see what Dave comes back with as I registered the issue on the web site's "Report an Issue".

Geoff
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on September 03, 2018, 08:00:08 am
Thanks JS but I'll wait and see what Dave comes back with as I registered the issue on the web site's "Report an Issue".

Geoff
That's fine, I think he's aware of your case, he answered your first post on this IIRC... I'm just saying something that might solve your issue, and what reaources there are to do so, in case he gives you green light to poke with it.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: vk3zgw on September 04, 2018, 10:13:09 am
Thanks JS but I'll wait and see what Dave comes back with as I registered the issue on the web site's "Report an Issue".

Geoff

OK...so my bad!! This is the text from the web site;

Note: When upgrading a multimeter the “.bin” file must be renamed “EEVBlog.bin”:

So being a literal being, that's exactly what I did already knowing it was a bin file, I assumed the program looked at the "name" wanting to see a .bin. So I had in effect EEVBlog.bin.bin. The penny dropped when I saw Dave's email from EEVBlog with a included file to try. Now I have v1.26.

Sorry all for the distraction. I'll now email Dave and apologies  :palm:

Geoff
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on September 04, 2018, 01:16:23 pm
I think I can withdraw my apology..........

Brumby, you will see from my first post that I have changed the file name as required.

Oooof.  Sorry.   :palm:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on September 04, 2018, 09:11:10 pm
So being a literal being, that's exactly what I did already knowing it was a bin file, I assumed the program looked at the "name" wanting to see a .bin. So I had in effect EEVBlog.bin.bin. The penny dropped when I saw Dave's email from EEVBlog with a included file to try. Now I have v1.26.

Sorry all for the distraction. I'll now email Dave and apologies  :palm:

Geoff

Dont worry be happy! I did something similar but got pointed in the right direction by all the good people who read the 121GW threads.
Guaranty we wont make that mistake ever again  :)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on September 05, 2018, 01:38:26 am
Thanks JS but I'll wait and see what Dave comes back with as I registered the issue on the web site's "Report an Issue".

Geoff

OK...so my bad!! This is the text from the web site;

Note: When upgrading a multimeter the “.bin” file must be renamed “EEVBlog.bin”:

So being a literal being, that's exactly what I did already knowing it was a bin file, I assumed the program looked at the "name" wanting to see a .bin. So I had in effect EEVBlog.bin.bin. The penny dropped when I saw Dave's email from EEVBlog with a included file to try. Now I have v1.26.

Sorry all for the distraction. I'll now email Dave and apologies  :palm:

Geoff

*David's email (me)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on September 08, 2018, 09:07:56 pm
Hi, new one, I've seen some comments on this but now I'm aeeing it on my meter. On the low ohms range sometimes it just measures zero when you short the leads, or a low resistance path, sometimes as expected I need to zero out the leads and it's left with a few counts and sometimes it is left with a few tens of counts left.

Turning it off and on again changes this, in which of the states it is at.

Have you seen this? Do you know something about that?

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 09, 2018, 09:14:57 pm
On this 600V meter, the latest version of the manual August 30, 2018, still confusingly specifies AC and DC VA as 500VA without mentioning its limited to 50V for whatever reason :(
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on September 10, 2018, 08:42:25 am
On this 600V meter, the latest version of the manual August 30, 2018, still confusingly specifies AC and DC VA as 500VA without mentioning its limited to 50V for whatever reason :(
I don't understand that limitation, everything is in the meter to measure higher voltages and that's all that should be required. I guess I'm missing something but measuring VA directly on mains would be nice.

JS
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 10, 2018, 09:41:11 pm
Agree with that , this could be usefull sometime for DC ( ex. power supply ) and AC ( mains , power amplifiers ) . 10A x 500V .  For minuscule VA ranges i can't think of any practical usage ... I remember reading somewhere that David said that is not enough "room " in the micro for all ranges and in this case some lower ranges must disappear .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on September 11, 2018, 07:10:01 am
I would have thought higher VA on mains would be better served with one of those mains power monitor products like the "Kill-a-Watt".
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on September 11, 2018, 04:53:45 pm
I've seen a few people change out the shunt in the Kill-a-Watt to use it for lower current devices.  I assumed a meter like the 121GW would fit nicely as they have the scaling built-in already.  I never understood the reason why they limited it to 50V.  The prototype was limited as well.

A VA meter is not very useful on mains, usual you want W.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on September 11, 2018, 11:36:56 pm
We have a beefy micro in the 121GW, maybe some fancy smoothing such as Savitzky–Golay filtering (http://"https://en.wikipedia.org/wiki/Savitzky%E2%80%93Golay_filter")?

I noticed that the update rate for the mV range is the same as temperature/thermocouple. Is there is a specific limitation that necessitates the lower update rate?

My UT171C is faster than the 121GW with the same stability. I know Uni-T catches flack for not being fully up to snuff on some of the lower end models and I'd like to compare functionality between the two meters, but I feel the bias against Uni-T will make these comparisons useless by virtue of opinion only.

Call it an obsessive compulsive tendency, but the meter would show a lot more "polish" if the boot up/power-on sequence *didn't* flash the LCD backlight.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on September 12, 2018, 12:08:53 am
Both date and time is on the first row in the file, then it says what interval is used. So it is not impossible, just somehwat cumbersome. Add another column, copy the time from the top row, then next row is the one above+(interval in seconds)*(1/86400). If using excel or the like. Otherwise I suppose a script could be used...
But it would be very easy codewise to implement the timestamp into the log file, so we don't have to mess around like that.

The default setting is to sample and save points as fast as the ADC allows, hence the interval is not fixed but depends on the mode, range, etc. It is therefore impossible to calculate the time for each point using the default setting.

However it is true that if you change the settings and limit yourself to a slower sampling speed, i.e. not using the full potential of the meter, it does seem like the timing is consistent so that can assume a fixed number of seconds between each point. I tried it over 4 minutes using a stopwatch and I could not detect any drift or dropped points by eye at least. Hence I guess this is the recommended method for now.

In order to allow for faster sampling I guess you need the actual time in a column (seconds since start is probably easiest), as it would make analysis much easier without having to process the time manually every time. Also as a separate improvement I would remove the "mode" from being printed on every row, either print it once in the header or only print it when it changes (if you intend to include mode switching during logging in the future). This would save approx 10-30 % in space depending on the mode used.

I also noticed that the meter does not autorange during logging (it goes into manual ranging when starting the logging process). This is definitely a feature that I would like to see in future updates.

Edit:
More issues I noticed today:
  • The claimed "update rate" is 5 samples/s nominal, however my display only updates 1-2 times/s, hence the meter feels slow and unresponsive, is this an error in the manual or is the meter supposed to be faster?
  • When manually selecting the 10 A current range, the display tells you that you are in the 1000 A range. Perhaps there is no 10 indicator in the LCD and this is intended, if that is the case please update the manual.
  • There is a 1000 V range, however the manual specifies maximum 600 V for the input protection. Perhaps this is the same issue as above? Please update the manual.
  • There are no range indicators in the display for Frequency, Period, Capacitance. Perhaps indicators is lacking in the LCD? In that case I suggest to always show leading zeros in these modes when in a manual range. For example the 100 nF range, write 07.6 nF, instead of just 7.6 nF in order to indicate the amount of headroom available.
Additionally, all log files are dated 2006.09.02 (yyyy.mm.dd format used) @ 21:30:00. Yes, a timestamp is in the actual file, but that doesn't help things if you go searching through the files for one at a specific time. Timestamps for the actual sample should be trivial to do since there is a hardware RTC in the DMM. A solution some other logging packages takes is to either log the absolute time or even using a relative time in thousandths of a second. I've well enough versed in Excel to add fractional second timestamps if I have at least 1 second resolution added in, but when you are using the fastest ADC output, and given that there is no "end" timestamp in the log file, it is not possible to determine the duration of a logged session.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on September 12, 2018, 01:29:30 am
New bug, also logging related. Anyone with a freezer could verify this for me. Regardless of sample rate, negative Celsius temperature values are logged as 7.1-7.6 °C regardless of their value. Lost a couple days worth of logging as a result. This is on firmware 1.26
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 12, 2018, 04:12:49 am
New bug, also logging related. Anyone with a freezer could verify this for me. Regardless of sample rate, negative Celsius temperature values are logged as 7.1-7.6 °C regardless of their value. Lost a couple days worth of logging as a result. This is on firmware 1.26
Just tried and no problem with 1.26
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on September 12, 2018, 08:30:25 am
Thanks for this check. I looked at the data again, applied a little formatting, and all data up until record 12120 is real. From 12121 on, it is a repetition of the previous 60 records. If I log data once per second, I'll hit this same bug at 202 minutes and 1 second, if the bug is with the counter. I'll be asleep by then so I'll have it log once every two seconds to see if it'll reproduce as such.

The original, but zipped, CSV file is attached and a trimmed Excel file are attached.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 12, 2018, 04:36:42 pm
The test done yesterday was for just a few minutes at 1 per second.  Previously, July 18th, in Fahrenheit, I had 23690 records at 10 second intervals with no problems with whatever version was the latest at the time.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Digital Corpus on September 12, 2018, 11:11:13 pm
Didn't happen after 19K records. Trying again to see if it is time-based so I'll report back in a few days.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 14, 2018, 03:12:52 pm
Probably it is known by now , just in case , DC+AC is autoranging endlenssly if DC voltage is greater than 5V . I used just an adjustable power supply . Latest firmware .


In AC mode , last measured frequency on secondary display stay there for about 15sec , way too long , even with shorted leads ...  Could be very misleading if you measure some small voltage around 0.15Vac , at the threshold of frequency sensitivity  .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 21, 2018, 10:46:47 am
As other people mentioned , it is very susceptible to mains noise through probes , especially in resistance mode ... I wonder what can be done , maybe changing some switching resistors around HY3131 to increase the measuring current ? 

Also , when using LowZ voltage input , the heat dissipated inside by the 2 thermistors makes resistance mode to be inaccurate for many minutes ...
as nearby thermistors that are in measurement path are heating too ...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on September 24, 2018, 04:29:29 am
Probably it is known by now , just in case , DC+AC is autoranging endlenssly if DC voltage is greater than 5V . I used just an adjustable power supply . Latest firmware .


In AC mode , last measured frequency on secondary display stay there for about 15sec , way too long , even with shorted leads ...  Could be very misleading if you measure some small voltage around 0.15Vac , at the threshold of frequency sensitivity  .

This issue should be resolved in latest firmware 1.51.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on September 24, 2018, 04:30:19 am
Both date and time is on the first row in the file, then it says what interval is used. So it is not impossible, just somehwat cumbersome. Add another column, copy the time from the top row, then next row is the one above+(interval in seconds)*(1/86400). If using excel or the like. Otherwise I suppose a script could be used...
But it would be very easy codewise to implement the timestamp into the log file, so we don't have to mess around like that.

The default setting is to sample and save points as fast as the ADC allows, hence the interval is not fixed but depends on the mode, range, etc. It is therefore impossible to calculate the time for each point using the default setting.

However it is true that if you change the settings and limit yourself to a slower sampling speed, i.e. not using the full potential of the meter, it does seem like the timing is consistent so that can assume a fixed number of seconds between each point. I tried it over 4 minutes using a stopwatch and I could not detect any drift or dropped points by eye at least. Hence I guess this is the recommended method for now.

In order to allow for faster sampling I guess you need the actual time in a column (seconds since start is probably easiest), as it would make analysis much easier without having to process the time manually every time. Also as a separate improvement I would remove the "mode" from being printed on every row, either print it once in the header or only print it when it changes (if you intend to include mode switching during logging in the future). This would save approx 10-30 % in space depending on the mode used.

I also noticed that the meter does not autorange during logging (it goes into manual ranging when starting the logging process). This is definitely a feature that I would like to see in future updates.

Edit:
More issues I noticed today:
  • The claimed "update rate" is 5 samples/s nominal, however my display only updates 1-2 times/s, hence the meter feels slow and unresponsive, is this an error in the manual or is the meter supposed to be faster?
  • When manually selecting the 10 A current range, the display tells you that you are in the 1000 A range. Perhaps there is no 10 indicator in the LCD and this is intended, if that is the case please update the manual.
  • There is a 1000 V range, however the manual specifies maximum 600 V for the input protection. Perhaps this is the same issue as above? Please update the manual.
  • There are no range indicators in the display for Frequency, Period, Capacitance. Perhaps indicators is lacking in the LCD? In that case I suggest to always show leading zeros in these modes when in a manual range. For example the 100 nF range, write 07.6 nF, instead of just 7.6 nF in order to indicate the amount of headroom available.
Additionally, all log files are dated 2006.09.02 (yyyy.mm.dd format used) @ 21:30:00. Yes, a timestamp is in the actual file, but that doesn't help things if you go searching through the files for one at a specific time. Timestamps for the actual sample should be trivial to do since there is a hardware RTC in the DMM. A solution some other logging packages takes is to either log the absolute time or even using a relative time in thousandths of a second. I've well enough versed in Excel to add fractional second timestamps if I have at least 1 second resolution added in, but when you are using the fastest ADC output, and given that there is no "end" timestamp in the log file, it is not possible to determine the duration of a logged session.

The timestamps meta information issue should be resolved in the latest firmware.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 24, 2018, 05:07:41 pm
Thx for update , is much better now  :D , the only big issue left that I can see is the resistance mode instability when mains noise is present .
https://streamable.com/e4kfa

If you really work with a multimeter is certain that you will touch the probes and  tips all the time . For now is picking the "hum" like a bad shielded audio amplifier  :P
I will investigate if the capacitor C21 27nF in the schematic is switched across input to form a low pass filter , as it should be when measuring a DC voltage ( resistance is just a DC voltage ) .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 24, 2018, 05:19:04 pm
Slight regression in Ver 1.51     In AUTO DC, AUTO AC or AUTO DC+AC:

After hitting the range button the range button will no longer cycle back to AUTO.  You must hit the mode button to get back to AUTO xx, but it will be the next mode.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on September 24, 2018, 05:21:49 pm
After hitting the range button the range button will no longer cycle back to AUTO.  You must hit the mode button to get back to AUTO xx, but it will be the next mode.

To get back to AUTO, shouldn't you press and hold the range button?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 24, 2018, 05:28:50 pm
To get back to AUTO, shouldn't you press and hold the range button?

Thanks IanB,  that seems to work.  Need to add this to the manual.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 24, 2018, 06:13:47 pm
...
I also noticed that the meter does not autorange during logging (it goes into manual ranging when starting the logging process). This is definitely a feature that I would like to see in future updates.
...
...
...


In version 1.51, the log file auto ranges even while the display shows OFL.  This seems like a bug.

This shows a log with auto.  Since I started near zero auto was in 5V then obviously moved to 50V while the display showed OFL, then went back to 5V at 19 seconds, and the display resumed.
Code: [Select]
No. Func. Value Unit
1 DCV -0.0362 V
2 DCV -0.0362 V
3 DCV -0.0359 V
4 DCV 2.634 V
5 DCV 4.8042 V
6 DCV 7.4089 V
7 DCV 7.4623 V
8 DCV 9.9954 V
9 DCV 13.7631 V
10 DCV 13.7631 V
11 DCV 13.7631 V
12 DCV 13.7631 V
13 DCV 13.7631 V
14 DCV 13.7631 V
15 DCV 13.7631 V
16 DCV 13.7631 V
17 DCV 9.194 V
18 DCV 4.539 V
19 DCV 0.7786 V
20 DCV -0.0204 V
21 DCV -0.0356 V
22 DCV -0.0359 V
23 DCV -0.036 V
24 DCV -0.0374 V
25 DCV -0.036 V
26 DCV -0.0382 V

Also if in any manual range and voltage exceeds it during a log, the range auto will take over and then it will drop back to the selected manual.  This seems to be as would be desired.

Edit:  Fixed quote indentation in post, added version # and more test info.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 24, 2018, 09:11:32 pm
I removed C21 27nF , the input LPF capacitor , and for measuring resistance seems to be no change , exactly the same instability ... so it is not used by firmware in my opinion . Or if it is used the effect is very weak .
In this case DC ranges become unstable  , picking up the noise , as should be expected without it . For measuring DC that filter is useful , no doubt .

I added a 47nF capacitor ( first value I found ) from PB0 to AGND ( ADC input is PB0 - PB3 connected to AGND with 10Kohm  ) and now there is first some charging effect ( big capacitor and low measurement current) but then the resistance value is pretty stable and you can move the probes around , touch them and the tips . No worries  ;D . More or less like other multimeters .

In the HY3131 configuration document for measuring resistance it is clearly shown that this capacitor must be used , the red one between FTP and FTN pins . I'm not sure what that selectable resistors 100K , 10K and 0 (short) do , are in series with this capacitor or not ... if they are in series than 100K + 27nF may not be such a good filter for cutting down strong AC 50Hz induced noise ... than 10K or the capacitor directly connected at input could be selected.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: PeterL on September 25, 2018, 07:21:21 am
I don't think that's autoranging. To me it looks like looks like the meter works as a 50k count meter on the display, and as a 100k count meter in the logfile. Only at these higher counts the meter loses accuracy. I noticed the same on firmware 1.22
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dcac on September 25, 2018, 01:37:44 pm
I removed C21 27nF , the input LPF capacitor , and for measuring resistance seems to be no change , exactly the same instability ... so it is not used by firmware in my opinion . Or if it is used the effect is very weak .
In this case DC ranges become unstable  , picking up the noise , as should be expected without it . For measuring DC that filter is useful , no doubt .

I added a 47nF capacitor ( first value I found ) from PB0 to AGND ( ADC input is PB0 - PB3 connected to AGND with 10Kohm  ) and now there is first some charging effect ( big capacitor and low measurement current) but then the resistance value is pretty stable and you can move the probes around , touch them and the tips . No worries  ;D . More or less like other multimeters .

In the HY3131 configuration document for measuring resistance it is clearly shown that this capacitor must be used , the red one between FTP and FTN pins . I'm not sure what that selectable resistors 100K , 10K and 0 (short) do , are in series with this capacitor or not ... if they are in series than 100K + 27nF may not be such a good filter for cutting down strong AC 50Hz induced noise ... than 10K or the capacitor directly connected at input could be selected.

In the “hy_regtbl.h” file from the disassembled 1.02 firmware you can see the hy3131 setup table for ohms mode and it seems the low pass filter is only enabled for the 500k range. It would be interesting to know why that is - possibly they want to avoid the rather long settling times - you can i.e. notice this if you manually select 500k range and short the probes - notice how much slower the reading takes to reach absolute zero compared with the other ranges - that behavior I believe is caused by the discharge of the 27nF cap through the 100k series resistor in the low pass filter.

When the filter is disabled the 27nF cap is completely bypassed - so changing its size should not have any effect.



Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 25, 2018, 02:16:42 pm
Maybe they had some kind of reason for doing that , but I doubt it , since the schematic and everything else looks identical with the datasheet , anyway to have  readings affected by noise is much worse , any multimeter I know can do better .

I didn't modify C21 value , I added one 47nF across inputs , of course for testing only  since the filter must be disabled when measuring capacitors and frequency .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on September 25, 2018, 04:49:40 pm
After installing version 1.51:

- The mA range shows 0.30 mA with no leads connected, went back to 1.26 and it shows 0, programmed 1.51 again and then press Rel when 0.3 mA  was showing and now it shows 0 mA ?????


- The uA range shows 0.021 uA with no leads connected, went back to 1.26 and it shows 0, same as the mA range, after pressing Rel no it shows 0.

In both cases even when turning the unit off and on now shows 0

David DLC


Never mind, after turning it off for a while, it when back to show 0.3 and 0.021

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on September 25, 2018, 05:11:13 pm
After installing version 1.51:

- The mA range shows 0.30 mA with no leads connected, went back to 1.26 and it shows 0, programmed 1.51 again and then press Rel when 0.3 mA  was showing and now it shows 0 mA ?????


- The uA range shows 0.021 uA with no leads connected, went back to 1.26 and it shows 0, same as the mA range, after pressing Rel no it shows 0.

In both cases even when turning the unit off and on now shows 0

David DLC


Never mind, after turning it off for a while, it when back to show 0.3 and 0.021

David DLC

Yes, I confirm these values of 0.022µA and 0.32mA @ FW 1.51.
With FW 1.26, it's 0.046µA and 0.06mA, though.

Maybe there's a systematic bug inside these modes.
Change was 'Amp range sensitivity improved'.. probably that causes this offset.

Frank

[Adder]: It makes no difference, whether probes are inserted, or not.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on September 25, 2018, 05:39:49 pm
There has to be a sanity check every time a new firmware is released.

A huge checklist testing mainly every possible scenario.

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on September 25, 2018, 05:57:18 pm
Ok , but when I insert the probes those values go to almost zero , this wasn't happening before in my case even with shorted leads. Maybe has something to do with input warning circuit leaking some DC back if you look at schematic ... and was corrected by adding some offsets in firmware .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on September 25, 2018, 06:11:02 pm
I recall when I connect and short the leads, still showing 0.3.

On any case, you should not have to do anything for the meter to show 0.

Do not accept or justify anything that is not good quality

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on September 26, 2018, 05:41:56 pm
I wonder if this could have any connection with the spikes I have observed?

The difference is that the spikes I have seen are very frequent, and they are visible on the meter's LCD display. They also happen whether or not the BT interface is enabled.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Lion_Tamer on September 27, 2018, 08:48:55 pm
I have been looking at the packet protocol document but as it seems to be missing a fair bit of information (It may be me not be reading it correctly) I decided to start making my own but as I don't have a blue tooth adapter on the PC I have been probing the UART interface to the BLE112 inside the meter with my logic analyser and have noticed a couple of quirks.

1. The Year value of the packet never changes no matter what is set on the meter.
2. The Month value of the packet never changes no matter what is set on the meter.
3. While decoding the Main LCD Range packet (7) I noticed that on AC and DC micro Watts the 2500.0uVA range appears to be repeated - this shows on both the meter display and the UART packet.

I am using V1.51 on my meter.

Jem
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on September 28, 2018, 12:08:54 am
I have been looking at the packet protocol document but as it seems to be missing a fair bit of information (It may be me not be reading it correctly) I decided to start making my own but as I don't have a blue tooth adapter on the PC I have been probing the UART interface to the BLE112 inside the meter with my logic analyser and have noticed a couple of quirks.

1. The Year value of the packet never changes no matter what is set on the meter.
2. The Month value of the packet never changes no matter what is set on the meter.
3. While decoding the Main LCD Range packet (7) I noticed that on AC and DC micro Watts the 2500.0uVA range appears to be repeated - this shows on both the meter display and the UART packet.

I am using V1.51 on my meter.

Jem

Have a look at the code example for the packet in the packet document, it might assist in your understanding of the packet.
The document currently doesn't have outgoing packets.

1.
Are you referring to the serial number as the date?

2.
^

3.
Edit, I had wrong branch before:
You can look at the source for the packet processing in the app here:
https://gitlab.com/Sepps/app-121gw/blob/PrivatePostRelease/121GW.Core/Controls/Multimeter/Packet121GW.cs

Older branches used different reject criteria for the packets, this one checks length and checksum only.
Please also ensure you have the latest firmware as the packet document V2 refers to the latest versions of the firmware only.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on September 28, 2018, 01:21:18 am
It was posted earlier about the battery springs.  At that time, I saw no problem but now, updating to 1.51, had an almost scary moment.  I did the update with the battery cover off. All went well but then the battery cover was not quite all the way on, as I reinstalled it.   I removed it again and noticed that one of the batteries had partly popped out, but the spring was still contacting.  Had the battery fully dislodged during the update, that might have been a bad thing.

So - I think it's best to replace the battery cover fully before starting the update.  That's the safest thing.

I also suggest that this caution be added to the manual under firmware update.  "Replace Battery cover before update to prevent interruption if battery pops out".
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on September 28, 2018, 01:34:32 am
I think that when the upload of an EEVBlog.bin file is complete, it should be deleted.  This would free up that space for meter logging functions.  I can't think of a reason why to keep it there once the upload is done.  A user would not have to go back into the meter to delete the file, assuming they are OCD about that.  Then - as I prior recommended, the battery door can be screwed down before an upload is started.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: JS on September 28, 2018, 01:58:22 am
I think that when the upload of an EEVBlog.bin file is complete, it should be deleted.  This would free up that space for meter logging functions.  I can't think of a reason why to keep it there once the upload is done.  A user would not have to go back into the meter to delete the file, assuming they are OCD about that.  Then - as I prior recommended, the battery door can be screwed down before an upload is started.
Seriously? How much does the bin file weights? How much time for logging it is? And compare that with the 8GB the SD has... If you record that much data will need to be in many separate batches as the batteries won't last that long, then you have the problem with the naming and k owong which is which...

I save a few bins so I just need to rename if I want to change it, I've been going back and forth a few times from V1.26 to V1.00. For me it would be much cooler being able to select the fw versions from many in the SD without needing to remove it and change the name. Note that some versions are noisier while others are faster, among other differences between them, like features and bug corrections.

JS

Title: Re: EEVblog 121GW Multimeter Issues
Post by: darik on September 28, 2018, 09:06:15 pm
What ever is causing the communications to slow down appears to be the 121GW's main firmware.

Do you know it's not something going on in the Bluetooth protocol? It's probably doing it's own error checking and 2.4 GHz band is crowded with interference. It could be getting backed up with retransmissions or something. It's wireless, it cannot be trusted.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 29, 2018, 03:16:32 am
...
Your having so much fun with the new 121GW !!    and so persistent :-+

I was going to try something but maybe you want to.  I think your getting close in your tests.

1. Hook up a SPI interface to the SD card pins and time the intervals of writing to the card.
2. While doing 1 put a signal generators output at a DC + slowly swept frequency in to the meter to make the pauses show while it hunts.
3. After doing this you can test how it relates to the bluetooth.


Have fun ;)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: firewalker on September 29, 2018, 03:46:10 pm
Probably answered before. But... are those Matlab programs available for download yet?

Alexander.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on September 29, 2018, 04:33:21 pm
...
As a side note, I had changed the meter to Eneloop NiMH and had never charged it. The battery indicator never came on.  Even after all of this testing.   Finally it gave up last night.  ...

I think the 4.2V at which the meter assumes your going to replace the batterys is great for replacement but to low for NIMH if you want them to last.  Numerous references suggest 1.1V minimum cell voltage.  However, here's a typical quote, this one from Wikipedia:

 "Complete discharge of multi-cell packs can cause reverse polarity in one or more cells, which can permanently damage them. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one completely discharges before the others due to small differences in capacity among the cells. When this happens, the good cells start to drive the discharged cell into reverse polarity (i.e. positive anode/negative cathode)."

I use 5.0V on the bat display and still get plenty of life.  I have only re-charged the 2 to 3 year old batteries once since acquiring the meter and many days of logging.  At the current firmware revision rate, that's about one charge every 3 revisions. ^-^
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 03, 2018, 01:48:53 am
It appears by the time version 10.0 rolled out, they had converted to a 19 byte, binary format.  It's very similar to what we have today.   They were still running at 250ms.   It looks like the firmware, even with only 30% of the amount of data that had been sent, it was already starting to lag.   

Firmware Version -  Format, #Bytes in packet, Packet Rate, Timing Stable or does it lag

1.00 - ASCII, 56 Bytes, 250ms, Stable
1.05 - ASCII, 56 Bytes, 250ms, Stable
1.07 - ASCII, 56 Bytes, 250ms, Stable
1.10 - Binary, 19 Bytes, 250ms, Lags

Corrected version numbers

Do you have some details about the test you performed, I'm writing a bug report but not really sure specifically what you've done. By lag do you mean the time between logging and the actual signal or the the sample rate is slower than expected slightly?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 03, 2018, 03:21:34 am
It appears by the time version 10.0 rolled out, they had converted to a 19 byte, binary format.  It's very similar to what we have today.   They were still running at 250ms.   It looks like the firmware, even with only 30% of the amount of data that had been sent, it was already starting to lag.   

Firmware Version -  Format, #Bytes in packet, Packet Rate, Timing Stable or does it lag

1.00 - ASCII, 56 Bytes, 250ms, Stable
1.05 - ASCII, 56 Bytes, 250ms, Stable
1.07 - ASCII, 56 Bytes, 250ms, Stable
1.10 - Binary, 19 Bytes, 250ms, Lags

Corrected version numbers

Do you have some details about the test you performed, I'm writing a bug report but not really sure specifically what you've done. By lag do you mean the time between logging and the actual signal or the the sample rate is slower than expected slightly?

Forget the RF link for now.  Just monitor the serial lines from the meter's MCU.  You will find that the rate that the packets are sent will vary depending on the input signal.  Depending on the version of firmware you install, the time between packets will be 500ms or 250ms.  I have shown where this time can be seconds.   This does not appear to be a problem with the older firmware.   It appears the problem showed up in version 1.10 when the packet sized was reduced and the binary format was introduced. 

I suspect the packet rate was slowed down even further after 1.10 in an attempt to resolve the lag between packets.  However, in 1.00, they were sending almost 3X more data at the 250ms rate and not lagging. 

I would think they could write the newer binary formatted, smaller packet like 1.51 uses at the same rate they write to the SD card and not lag.

I'll look into this for you, I think we will be able to work it out.
Just so I don't have to redo your test (will be faster), do you have examples of the sampled UART data that show this (a screen shot or photo of the logic analyzer)? Something that shows the jitter between samples.

If you don't see this before 4pm I'll do the test myself but I figured I'd ask.
Title: EEVblog 121GW Multimeter Issues
Post by: Dr. Frank on October 03, 2018, 04:31:05 pm

Yes, I confirm these values of 0.022µA and 0.32mA @ FW 1.51.
With FW 1.26, it's 0.046µA and 0.06mA, though.

Maybe there's a systematic bug inside these modes.
Change was 'Amp range sensitivity improved'.. probably that causes this offset.

Frank

[Adder]: It makes no difference, whether probes are inserted, or not.

Loading the new FW 1.51 simply affected the zero calibration of the DCI ranges:

               1.26          1.51
50µA      -0.055       0.017
500µA     0.14        -0.07
5mA      -0.0015      0.0027
50mA     0.001       -0.020
500mA  -0.12         0.25
5A        -0.0001     -0.0021
10A       0.000       -0.001

I have re-calibrated only the zero offset of ranges 50µA .. 5A, so now all ranges have a few counts offset.
That did not influence the gain calibration, as far as I could tell.

Frank

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 04, 2018, 12:34:46 am
I'll look into this for you, I think we will be able to work it out.
Just so I don't have to redo your test (will be faster), do you have examples of the sampled UART data that show this (a screen shot or photo of the logic analyzer)? Something that shows the jitter between samples.

If you don't see this before 4pm I'll do the test myself but I figured I'd ask.

There are several posted on this thread.  If you look at this picture for example, there are two different programs shown.  The one in the upper left is using a FTDI TTL to USB adapter to sniff the serial line from the MCU.   In this case, I am counting the number of times the the time between packets is longer than 800ms.   The main program is looking at the data across the RF link.  The yellow trace is also the number of times the packet spacing has exceeded 800ms.  Note how the two track.  Als note that the blue trace, showing the CRC failure rate is not effected.   

It you would rather see the actual time, TEST2E is showing just that using different modes and signals applied.  Again, in the 5V range with nothing attached to the meter, so the readout is basically all zeros, the packet spacing is very repeatable.   

You could use a LA but I was wanting to capture more metrics.   Actually, you could add some checks to your Windows application and check it on the RF receiver side like I was originally doing.   Should be easy enough to replicate. 


****

On TEST2E, the vertical axis is time in ms.

Alright I was able to reproduce this a fix will come some time soon.
But that is at the discretion of UEi.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on October 04, 2018, 05:21:03 pm
Did you noticed that in diode mode when shorting probes the beeping sound is very slow responding ? I must hold the short for about 0,5sec  :P 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on October 04, 2018, 06:13:00 pm
Hi,

I have tried to calibrate out the high offset in the current  mode in firmware 1.51, but that seems impossible because of a lack of information or a hardware issue. (Or I am simply to stupid)

I first tried to calibrate the offset in the µA range.

No cable plugged in the mAµA binding post : -0.028µA
Cable plugged in: 0.015 µA. I assume that has to do with the cable sensor.
Cable plugged in and shorted to COM: 0.030µA

In the A/mA Range: No Cable plugged in: 0.23mA offset.
In this case the meter uses the A 500mA binding post. This connector seems not critical and is the only range that can be calibrated out without problems.
Cable plugged in the mAµA binding post: 0.0025mA
Shorted to COM: 0.0006 mA after a long settling time.
Any hints how to proceed best?
No cable plugged in?
With cable plugged in?
With cable plugged in and shorted to COM?  :scared:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: OldEE on October 05, 2018, 01:45:02 am
I'm wondering how many of you are seeing the offset on DC current ranges?

For example my 10 day old 121GW, on the 500mA range, has about a 0.2 mA positive offset.  Like Dr. Frank I'm likely going to do the offset calibration.  My concern is that the offset varies over time.  I've seen it as low as 0.07 mA and as high as 0.28 mA on the 500 mA range. 

The offsets were about the same for the as shipped 1.22 firmware and the 1.51 firmware so no issue there or on DCV or any AC modes.  As of now the offsets for the 5, 50, 500 mA ranges are 0.0016, -0.0019, 0.19 and the 5 A and 10 A ranges are -0.0018 A and -0.001 respectively.

Below is about 5 hours of logging at 10 per hour on the 500 mA range.  You can see the randomness.  The room temperature varied about 1.5C over the 5 hours.  The first reading is anomalous (is that a bug?).  No leads were connected per the calibration table except for one open lead in the mA/uA jack to activate the 5 and 50 mA range.

START,2018/10/03,22:53:01,
ID,170800000,
INTERVAL,300,sec,
,MAIN,,,SUB-1,,,SUB-2,,,Remark,
No. ,Func. ,Value,Unit,Func. ,Value,Unit,Func. ,Value,Unit,
1,DCA,-0003.51,mA,,,,,,,,
2,DCA,0000.24,mA,,,,,,,,
3,DCA,0000.19,mA,,,,,,,,
4,DCA,0000.16,mA,,,,,,,,
5,DCA,0000.22,mA,,,,,,,,
6,DCA,0000.18,mA,,,,,,,,
7,DCA,0000.17,mA,,,,,,,,
8,DCA,0000.17,mA,,,,,,,,
9,DCA,0000.19,mA,,,,,,,,
10,DCA,0000.16,mA,,,,,,,,
11,DCA,0000.20,mA,,,,,,,,
12,DCA,0000.16,mA,,,,,,,,
13,DCA,0000.18,mA,,,,,,,,
14,DCA,0000.18,mA,,,,,,,,
15,DCA,0000.18,mA,,,,,,,,
16,DCA,0000.19,mA,,,,,,,,
17,DCA,0000.19,mA,,,,,,,,
18,DCA,0000.20,mA,,,,,,,,
19,DCA,0000.24,mA,,,,,,,,
20,DCA,0000.22,mA,,,,,,,,
21,DCA,0000.14,mA,,,,,,,,
22,DCA,0000.19,mA,,,,,,,,
23,DCA,0000.19,mA,,,,,,,,
24,DCA,0000.26,mA,,,,,,,,
25,DCA,0000.13,mA,,,,,,,,
26,DCA,0000.22,mA,,,,,,,,
27,DCA,0000.26,mA,,,,,,,,
28,DCA,0000.15,mA,,,,,,,,
29,DCA,0000.23,mA,,,,,,,,
30,DCA,0000.22,mA,,,,,,,,
31,DCA,0000.19,mA,,,,,,,,
32,DCA,0000.22,mA,,,,,,,,
33,DCA,0000.22,mA,,,,,,,,
34,DCA,0000.18,mA,,,,,,,,
35,DCA,0000.25,mA,,,,,,,,
36,DCA,0000.21,mA,,,,,,,,
37,DCA,0000.23,mA,,,,,,,,
38,DCA,0000.25,mA,,,,,,,,
39,DCA,0000.15,mA,,,,,,,,
40,DCA,0000.20,mA,,,,,,,,
41,DCA,0000.15,mA,,,,,,,,
42,DCA,0000.14,mA,,,,,,,,
43,DCA,0000.26,mA,,,,,,,,
44,DCA,0000.22,mA,,,,,,,,
45,DCA,0000.21,mA,,,,,,,,
46,DCA,0000.23,mA,,,,,,,,
47,DCA,0000.20,mA,,,,,,,,
48,DCA,0000.17,mA,,,,,,,,
49,DCA,0000.18,mA,,,,,,,,
50,DCA,0000.28,mA,,,,,,,,
51,DCA,0000.26,mA,,,,,,,,
52,DCA,0000.20,mA,,,,,,,,
53,DCA,0000.23,mA,,,,,,,,
54,DCA,0000.26,mA,,,,,,,,
55,DCA,0000.24,mA,,,,,,,,
56,DCA,0000.22,mA,,,,,,,,
57,DCA,0000.21,mA,,,,,,,,
58,DCA,0000.21,mA,,,,,,,,
MAX,50,DCA,0000.28,mA,
MIN,1,DCA,-0003.51,mA,
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 05, 2018, 02:59:11 am
Very nice.  Thanks for taking the time to dig into it. 

I am playing around with a UNI-T meter using BLE as well.  There is still a lot of work to do on it but there are some things that UNI-T does that UEI could leverage.  One major difference is how the display data is sent.  The 121GW has the data, sign bit, scaling...  The UNI-T sends the data as a float.  IMO this is much easier on the PC side of things. 

They also embed a checksum and like the 121GW, it seems to be required but the error rate is much lower for what ever reason.    They can update at 10Hz rather than 2Hz and are sending 55 Bytes.  If anything, I would expect the CRC error rate to be higher on the UNI-T. 

https://www.eevblog.com/forum/projects/uni-t-ut-d07a-bluetooth/ (https://www.eevblog.com/forum/projects/uni-t-ut-d07a-bluetooth/)

Hello Joe,

Does this resolve sampling rate the issue for you?
Not an official released version yet. I figured you'd appreciate the update asap.

https://www.eevblog.com/wp-content/uploads/2017/11/EEVBlog1_52.zip (https://www.eevblog.com/wp-content/uploads/2017/11/EEVBlog1_52.zip)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on October 05, 2018, 08:51:21 am
Hi,

I tried out how to calibrate the DC current offset  and made a short instruction how to proceed.


1: Backup your calibration data! (See page 66 in the manual)
2: Copy the backup from the SD card also to your PC, because one wrong keypress and you overwrite your CAL backup inadvertently at the SD card.
3: Remove all leads from the meter.
4: Switch off the meter.
5: Hold MODE and turn on the meter.
6: Release MODE and press REL immediately
7: Set the meter to A mA , press SETUP and wait
8: Press RANGE, press SETUP and wait
9: Plug in a lead in binding post mAµA
10: Press SETUP and wait
11: Press RANGE, press SETUP and wait
12:  Switch to µA, cable is still plugged in the mAµA binding post
13: Press SETUP and wait
14: Press RANGE, press SETUP and wait
15: Press MEM until CAL dissapears for short time, then switch off the meter.

In case that somthing went wrong restore your saved CAL data.

I found that the offset is not really stable, after some time it is again 4..5 digits off. But still much better than before the calibration.

Update: Add some more steps.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on October 06, 2018, 11:41:49 am
Current mode uses an electronic switch and the x10 operational amplifier on some ranges , it is not like DC volts circuit . If you don't measure anything , is somewhat normal to have some drifting over time because of induced noise which is not constant , the same if you move the probes and the multimeter .
This test should be done with a precision current source , measuring some real currents.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on October 06, 2018, 01:28:37 pm
Every mode uses electronic switches and operational amplifiers, so that is not the reason for the offset behavior in the ampere mode. I suspect that the reason is mostly a problem with thermo voltages in the junctions of the shunt resistors that are amplified also.
The low burden voltage has the advantage that it has a low voltage drop. But the disadvantage is a higher and unstable offset. That may be the reason that no other provider offers a low burden voltage multimeter. The disadvantages seems greater for them than the lower burden voltage.

I did tests with a precision current source and the offsets were still there. And yes, mostly the meter is within its specs, but these specs are at a low level with 0.75% + 15 counts. It is much better after recalibrating the offsets in the ampere mode. (Tested with a Knick JS 3010 voltage/current calibrator)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 10, 2018, 02:19:49 am
I was a little confused about what I was seeing when I was attempting to write a Labview app for the 121.  Looking deeper into the BLE interface, if you fire up Wireshark you will find that the 121 sends a single packet for the start byte.  It's a bit odd as the entire data structure could fit into a single packet but the 121 will send two.     I suspect this may have been a carry over from the earlier structure.   

It's too bad that the BLE112's serial interface was not routed to the MCU so you could field upgrade it with the firmware.   It looks like you are stuck with what you have unless there is a newer release of the meter at some point.

Indeed, we discovered this too. It is indeed a carry over from when the structure was much larger.
What version of the firmware are you using?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 10, 2018, 03:04:52 am
I am back to 1.26 with the BLE112 image that was uploaded.   

Did you try to see if you could still replicate the lag with the beta firmware like I showed?


In your image you have a note that says, "see page 66 of API" what do you mean?
I haven't yet, the plan was for tomorrow morning, I'm doing a few tests at once.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: eV1Te on October 10, 2018, 06:08:43 pm
I am seeing very large offset voltages (up to several mV) in mV range after having measured larger voltages some minutes earlier. Offset voltage recovers slowly over the course of some 30 minutes, until it is a few uV. But in that time one can not measure temperature or low voltages to any degree of accuracy.

The way I noticed this is that I measured normal 50 Hz 230 V in the Volt range, then switcher over to Freq. mode to measure the frequency. However while doing so you need to cross over the mV range, which will cause a large overvoltage. But as far as I am aware the meter should be able to handle it?! However it seems it does not handle it very well, it causes a temporary (some 30 min) offset in the mV range on the order of several mV!

The same issue would occur if one want to measure Volt and then go to VA and measure VA without disconnecting the probes while crossing the mV range.

I am not sure if this issue has been reported earlier or not. If you need more info/testing let me know.

I am guessing this is hardware related, perhaps some internal capacitance in some IC that gets charged too high and causes incorrect biasing of some stage until it dissipates?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on October 10, 2018, 07:44:53 pm
Ok , the meter is able to swallow that overvoltage and survive , but don't expect to be very happy . It's a mistake to switch like that ... and should be a very rare occurrence not something normal as you seem to suggest . Frequency range is for low voltage ( signal ) too , the same as you would use a stand alone frequency meter ...  For AC high voltages frequency you have the secondary display
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 11, 2018, 01:26:49 am
It's loaded and running now.  I am using the mVDC mode.   I am only looking at the data rate from the MCU to the BLE112.   

I can already tell you that the problem appears to still be there but it may be improved.   Try it on your setup and see if you have similar results.

I cannot reproduce this, I did this on an oscilloscope, I watched the scope for an hour, no jitter.
Is it possible your USART to USB has a buffer or windows is buffering and it is causing the remaining jitter?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 11, 2018, 02:33:52 am
Sorry, time to head out. 

Consider the following when attempting to replicate my tests:

* The lag can be longer than one second. 
* The lag is aligned on the packet boundary. Or in other words, you need to measure the time between packets and look for missing events.
* When using a separate program to measure the time between packets with the RF interface, it will track the times seen on the serial line going to the BLE112.
* If I run older versions of the firmware prior to 1.10, even though the data rate is doubled, it is stable.

If you scope can measure the time between packets, this is what you want.  A simple thing you could do is just add the timing metric to your application software and trend the data as I have done.

All of the above was considered. I used wires directly soldered to the USART which I then triggered to the start of a packet with some hold off, then measured period between starts of packets.
I might leave it searching for min/max for a day or two.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: eV1Te on October 11, 2018, 05:55:18 pm
Ok , the meter is able to swallow that overvoltage and survive , but don't expect to be very happy . It's a mistake to switch like that ... and should be a very rare occurrence not something normal as you seem to suggest . Frequency range is for low voltage ( signal ) too , the same as you would use a stand alone frequency meter ...  For AC high voltages frequency you have the secondary display

I did not know that the frequency range was only for low volt signals. The manual only says that the input in frequency mode needs to be more than 2.5 V and that it has overvoltage protection up to 600 volt. Does anyone know what voltage range it is designed for?
I have so far used the frequency mode instead of the dual display since it has better resolution.

Even if it is not normal to put 230 VAC on the mV or Ohm/C ranges etc, I know Dave has in the past complained when other meters could not handle such a case. Hence I assumed this meter would not have an issue with it since it is certified by Dave  ;)

By the way I found a different serious bug regarding logging, where all measurements become corrupted/incorrect, will try to replicate it now... Will post it later if can figure out when and why it happens.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on October 11, 2018, 09:34:55 pm
The protection ESD supressor diode is SM6T22CA , so around 22V will start conducting current like 2 zeners in anti-paralel ... and the thermistor in series will start to heat up. For AC sine wave the voltage should be max 15Vrms .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 11, 2018, 11:26:46 pm
It should happen in minutes, assuming the input signal is varying enough to cause the display to change.   One other thing to consider is that the failure rate is low, less than 1%.   It's not something you would want to watch for. 

If you like, I can see if I can capture the events with scope.  I assume your scope was decoding and storing the packets and there was nothing wrong with the data.   If the MCU were corrupting the packet, I would have no way of knowing with my current setup but I certainly could detect a problem like this with the scope.

Do you mean varying enough to cause an autorange, if yes I did not do that, I'll need to.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on October 12, 2018, 01:37:59 am
It should happen in minutes, assuming the input signal is varying enough to cause the display to change.   One other thing to consider is that the failure rate is low, less than 1%.   It's not something you would want to watch for. 

If you like, I can see if I can capture the events with scope.  I assume your scope was decoding and storing the packets and there was nothing wrong with the data.   If the MCU were corrupting the packet, I would have no way of knowing with my current setup but I certainly could detect a problem like this with the scope.

Do you mean varying enough to cause an autorange, if yes I did not do that, I'll need to.

I believe I will have an answer for you shortly.   Let me start by apologizing for sending  you, UEI developer's and possibly others, on a wild goose chase on the communications lagging problem I am seeing.    Let me explain where I am at with it.

I changed my test setup to use a scope to monitor the serial communications between the microcontroller and the BLE112.   I set the scope to decode the packets  and then changed my PC software that I use to monitoring the serial bus (using the FTDI controller) so when a lag fault was detected, it sends a trigger signal to the scope.   

138 shows the trigger pulse in red.  Note that the packets before it are not missing.  At first I though maybe a framing error, clock mismatch, etc,  but ...

140 shows the decoding of the first packet prior to the fault.  Everything looks good.   I tried this a few more times and everything seems fine.

So I started looking at my software and realized I had made a mistake in how I architected the packet parsing.   I have not looked into why the pre 1.10 versions worked with my BLE software but suspect that it is linked to the short message.   The parsing is done differently for the UT181A which is why that software does not have a problem.

Of course, I used this same parsing routine for both the 121GW BLE software as well as the serial sniffer.   This is why the two programs tracked the lag as well.   

I have corrected the parser and have been running the serial sniffer using firmware 1.26 and have not seen a single miss.    The BLE software will need to be corrected and then I can repeat all of my testing but I am pretty confident that this is all on my end. 

Again, I am very sorry for not digging into this before bringing it up.   I will let you know in a day or so if I saw any problems. 

|O |O |O |O

No worries I appreciate what you have done. After the firmware change it was a planned test anyway so its good to have more data.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on October 14, 2018, 07:53:29 am
Hi,
I also assume that there is something wrong with the 121 GW bluetooth. I have trouble to connect the 121GW with my mobile (Nokia 8 with Android 8.1). The 121GW app cannot find the 121GW. I first must switch off and on the bluetooth function in the 121GW to connect with the meter. No other of my  bluetooth devices behaves like that.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on October 14, 2018, 05:53:41 pm
Hi,

no, there is no other bluetooth device active at the same time. Possibly this is a problem with either the Nokia 8 or Android 8.1, I don't know. But the fact that the 121GW is the only (so far) device that has trouble to connect reliable with my phone tells me, that this could point to a problem in the 121GW bluetooth system. Once the 121GW has connected the app shows all data without any problems, but same as your meter it has a very short range until the phone lost the connection. The app can't recover the connection automatically, I have to switch off and on the bluetooth again to restore the connection. For me bluetooth is usable, but not really good.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on October 14, 2018, 06:09:17 pm
I wonder in your case if you have another device in range that is opening an connection to the meter.  I don't own a cell phone so I can't test  to see if there is a difference with their other applications.   Is anyone else having problems connecting?

I previously had some trouble connecting to Windows 10. I did not reach a conclusion about the causes of that and have not done any investigations since, but I did observe that if the meter was connected to one device it could not connect to a second. In the end I got the connection to Windows 10 reestablished by rebooting the computer. Switching the meter on and off didn't seem to help.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on October 14, 2018, 07:24:47 pm
Hi,

I have used Rev. 1.26. for my tests.

Today I had a strange experience.

Now I am using 1.51 and I tried it again today. Now it connected without any problems several times. Between my tests the 121GW firmware has changed and the mobile also got an update recently, maybe this has solved the problem. :-//

No, don't think so.
Meanwhile I belive you were right, there is very likely a disturbance from other bt devices. Not in my home, but from my neighbours. Because today  the bt receiving range also is much higher than at my last tests. And my direct neightbours are not at home....hmmmm

Now it workes as intended except of one exception. After closing the app and restart it, the app did not see the meter again, I have to switch off and on bluetooth at the meter for reconnecting, like before. But that is not a problem for me.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on October 14, 2018, 08:04:35 pm
I am fortunate that the neighbors are far enough away that they don't cause a problem.   It will be interesting to see when they return if it stops working again.   My CEM meter uses 900MHz with a simple FSK modulation.  I've been amazed at how far that meter will transmit. 

Maybe IanB's problem is similar.

I'm not sure about neighbors with Bluetooth. For example, if I turn on my phone when I am in Fry's I see dozens of BT devices available to connect from all around me. My phone is inundated. If I turn on my phone when I am at home I see no BT devices ever, except the devices I own that I have turned on. Granted there could be long range interference, but the problem I had with Windows 10 seemed more like a Windows 10 problem. My Apple devices have never had any issues connecting.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Antonov225 on November 01, 2018, 09:25:12 am
Hello EEVBlog!
I feel honored to now be a part of this awesome community. What makes me very sad is that my first post has to be a negative one.

I purchased my 121GW meter on July 26th 2018, during a small batch at official EEVBlog store, after being informed about its availability by the newsletter. Soon I discovered how big mistake I have made.

After receiving the meter and unboxing it, few things immediately stood out. The meter was scratched in many places (especially the knob and in the area around lead sockets) - see attachment. Scratches on two flat sides of the knob clearly came from someone's else fingernails. Part of the knob you grab by your fingers was noticably shinier than other areas. Batteries have also already been put inside the meter - From what I've seen on unboxing videos, these should be included seperately in the pouch.  Conclusion is simple - I recieved a used meter. I thought - "Ok, fine. This is not that bad. I can use this meter nevertheless." And I could - for a month. After that strange things started to happen.

Before making the purchase I did some research online (mainly this forum) and discovered that at some point a common problem with 121GW meters was the knob itself. Apparently there was a recall done at some point regarding the contact issues (knob replacement and addition of a shim). This took place months earlier. Common sense suggested that my meter should have already been free of this issue. This couldn't be farther from the truth.

After a month of very, very light use the meter is basically unusable. The knob wipers stopped making a good contact with the PCB (i think) and the meter reboots constantly while switching modes. Resistance mode cannot be turned on at all. The meter just turns off when I select it. The issue is present for every single knob position.
I made a short video where the issue is clearly visible:

https://www.youtube.com/watch?v=DIlfYcioE4w (https://www.youtube.com/watch?v=DIlfYcioE4w)

As you can see, this is clearly not a 121GW revision with a fixed knob. I must have received an older, flawed version. This is absolutely unforgivable for a meter this expensive (and every other for that matter). What I find the most frustrating is that the recall was done some time before I bought my meter from the EEVBlog store. At that point I should expect this issue to be already resolved but in the end I recieved a meter with this exact defect still present.

I've sent Dave an email describing these issues on 5th October. He replied a week later and promised to send me a new meter. I was really happy about that. So why am I even writing this post, you may ask? Well, because the new meter has never been shipped and Dave has not replied to any of my emails since then :palm:. I've been trying many times to contact him through at least 3 EEVBlog email adresses and sending him PMs on the forum, asking why the new meter hasn't been shipped. Three weeks have passed and I have not recieved any reply. I have no idea why.

I can only hope that this post will grab Dave's attention and that my meter will get replaced eventually. Do you know if there is any other way to contact Dave or to fix the meter? I just want to be able to use the product i paid for.

Thank you for your help in advance,
A VERY frustrated customer.



Title: Re: EEVblog 121GW Multimeter Issues
Post by: problemchild on November 01, 2018, 12:49:05 pm
I'm sorry to hear this, I really can not comment on the technical problems regarding the meter as I've not played with mine yet as it as only just arrived (yes nearly a month now but you get it!!). Any way I had a similar problem regarding comunications after cleaning up a percieved problem with my address I then asked for confirmation that it was all Ok and the Meter would be sent. After a few weeks I sent another letter to both Daves and then again acouple after and finally yet another a couple of weeks after. At that point I got a reply from Suse the Logistics Lady and my meter arrived all they way from Australia in about 4 days!!

I think that I'm far from been alone in this matter and I also think that Dave isnt been malicious just over worked but we cut him slack since we are not only expecting a quality meter but also hoping to support Dave in a practical manner. That said we dont expect to be ignored for weeks on end, if it wasnt Dave we probably would of made more complaints and probably this would of been picked up by trading standards or by another fancing to make a name by doing to Dave what he's done to others rightly or not!

Dave I hope the Logistics lady is here to stay for a while and keeps it all in order otherwise there will be a queue of replies here I'm sure!
John A
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on November 07, 2018, 01:13:08 am
As noted in Firmware thread, the latest FW at the store is listed as 1.52 shows on the meter as 1.53.

As usual, change log is lagging.  Haven't noticed a difference from 1.51 which disappeared.  What does it all mean  |O
Title: Re: EEVblog 121GW Multimeter Issues
Post by: alex-sh on November 12, 2018, 01:45:27 am
Firmware version 1.51
I cannot check capacitance any more - a little dot is blinking and no values coming up on the screen.
Tried several caps.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on November 12, 2018, 05:08:20 am
Have you tried 1.52 (1.53) ?.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: link87 on November 13, 2018, 06:23:46 pm
Quote
As usual, change log is lagging

Is the ChangeLog available somewhere other than the manual? Seems like it ought to be included in the firmware ZIP or at least as a link beside the download link for it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Candid on November 13, 2018, 06:32:38 pm
This would be way to easy  ::)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: alex-sh on November 18, 2018, 01:13:42 pm
Quote
As usual, change log is lagging

Is the ChangeLog available somewhere other than the manual? Seems like it ought to be included in the firmware ZIP or at least as a link beside the download link for it.

Thanks for heads up. Yes, in 1.53 the bug with capacitance has been corrected. However, the manual is not updated.
Anyone knows what has been done in 1,53?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: rattnallen on November 21, 2018, 02:18:14 pm
Firmware version 1.57 at https://www.eevblog.com/product/121gw/ (https://www.eevblog.com/product/121gw/)
The manual is still not updated ...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on November 22, 2018, 10:16:00 pm
It is very good that now we have improved capacitance mode .

But I can't understand how a team of profesional coders make a software and not check the basics - now in manual mode is not showing "overrange" , the display just freeze or show 0.000 .

Autoranging an 100uF capacitor is going into 10.00mF range so you see only 2 digits , 97uF for exemple .
10nF , 100nF , 1uF , 10uF seems to be fine ...

Other issues not corrected yet ...
In resistance mode , the autorange hysteresis is way too big , switch in upper range at 55000 counts but down at 40000 counts . So , as the resistance ranges switch from high to low resistance , a 470ohm resistor is showing 0.4700 in 5K range not at full resolution in 500ohm range as should be .

In voltage mode hysteresis is too big also .
This cause problems when measuring something in between , loss of resolution when measuring variable or adjustable voltages .
For a 50.000 counts multimeter I think it is normal to switch at 55.000 counts up and probably at 51.000 down , to have 50.000 counts all the time . And 5V is the most used voltage in electronics ... this value should never be in hysteresis


Edit
Interesting , when measuring capacitors in manual range is showing overrange if the capacitor is not too big , so in 10nF range is showing overrange for 100nF but just freeze for 10uF ...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on November 23, 2018, 02:26:51 am
Edit
Interesting , when measuring capacitors in manual range is showing overrange if the capacitor is not too big , so in 10nF range is showing overrange for 100nF but just freeze for 10uF ...

Confirmed

Sheesh, two EEVBlog engineers and an instrument manufacturer like UEI, you would think they would have a test procedure worked out for firmware revisions by now!

If Dave was reviewing this meter and its updates on EEVBlog it would rate the dreaded FAIL conclusion.

If Dave is looking to bring out a version 2 of this meter, the thing needing change the most would be their testing procedures because at the moment its not professional.

My verdict is that the 121GW has potential, but is hampered by the driving force behind it, namely Dave being more interested in releasing regular blogs than fixing the meters problems.

I own one of these meters and am looking forward to the good faith shown by supporting the kickstarter being returned by proper quality checks and testing. Its so close, but still so far from being a great meter!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on November 23, 2018, 07:16:09 am
Now there are some warning beeps when auto power off timer is about to expire , this is a nice thing .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: dr.diesel on November 27, 2018, 06:32:59 pm
I suspect this has already been noted, and perhaps a hardware limitation, but manual range is lost after APO and back on again.

As of v1.57
Title: Re: EEVblog 121GW Multimeter Issues
Post by: n3mmr on November 30, 2018, 02:11:43 pm
A minor issue with the manual: it doesn't talk you thru the idiot startup phase you have with  any new piece of gear.
Make sure meter is off.
Open it
Batteries in
Reattach the back
Turn the rotary switch to V
Display will show "U- FWversion", like "U- 1.54" for FW v 1.54.
.....

A minor tech issue with the meter:
I would have liked an AC DC mode where main display shows V DC and secondary display shows V AC.

Kudos for the meter being useful, albeit not too accurate, up to at least 40kHz for sub-1V voltage.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nonentity on December 03, 2018, 08:01:48 pm
Nanofarad values of capacitance yield readings of zero with nanofarad manual ranging.  Occasionally an incorrect low value for a capacitance is displayed which then very slowly increases over a ~30 minute period up to the correct value.
Also the Logging/Bluetooth value for the nonofarad capacitance is 10 times what it should be.

Using 121GW meter recently purchased from Welectron with V1.57 firmware.
iPhone bluetooth app version: build 1.78
Problem is reproduced by:
1.) Attach 0.14 nf cap                            [edited 4 Dec 2018]
2.) Turn on meter, select capacitance
3.) Set mode to capacitance - the correct value usually displays.
4.) Cycle through mode selection and ranges once or twice.
5.) The capacitance shows zero in both nonfarad ranges or an incorrect slowly increasing value toward the correct value.

Slowcap1 shows the initial Log file.
Slowcap2 shows Log file after about 20 minutes.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: lowimpedance on December 03, 2018, 10:26:15 pm
There was some discussion that had started in relation to this over in the firmware detail thread, that discussion morphed somewhat but to preserve that detail it stayed in that thread.
If there is a way for the 'moderators' to move the relevant posts here that would be better than diluting the other threads intent.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nonentity on December 04, 2018, 12:07:47 am
I agree.  This is the issues thread.  The other thread is for something else.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on December 04, 2018, 03:04:28 am
Nanofarad values of capacitance yield readings of zero with nanofarad manual ranging.  Occasionally an incorrect low value for a capacitance is displayed which then very slowly increases over a ~30 minute period up to the correct value.
Also the Logging/Bluetooth value for the nonofarad capacitance is 10 times what it should be.

Using 121GW meter recently purchased from Welectron with V1.57 firmware.
iPhone bluetooth app version: build 1.78
Problem is reproduced by:
1.) Attach .014NF cap
2.) Turn on meter, select capacitance
3.) Set mode to capacitance the correct value usually displays.
4.) Cycle through mode selection and ranges once or twice.
5.) The capacitance shows zero in both nonfarad ranges or an incorrect slowly increasing value toward the correct value.

Slowcap1 shows the initial Log file.
Slowcap2 shows Log file after about 20 minutes.

The resolution of the capacitance is 0.01 nF, unless I've misunderstood you might be using it for values out of the meters range.

Regarding the app, an update hasn't yet been released to add support for the additional capacitance ranges (there is a note on the 121GW firmware page)
"NOTE: This version has a change that will not function correctly with the app in capacitance range. An update to the app will be released soon."
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on December 04, 2018, 03:38:16 am
Hello EEVBlog!
I feel honored to now be a part of this awesome community. What makes me very sad is that my first post has to be a negative one.

I purchased my 121GW meter on July 26th 2018, during a small batch at official EEVBlog store, after being informed about its availability by the newsletter. Soon I discovered how big mistake I have made.

After receiving the meter and unboxing it, few things immediately stood out. The meter was scratched in many places (especially the knob and in the area around lead sockets) - see attachment. Scratches on two flat sides of the knob clearly came from someone's else fingernails. Part of the knob you grab by your fingers was noticably shinier than other areas. Batteries have also already been put inside the meter - From what I've seen on unboxing videos, these should be included seperately in the pouch.  Conclusion is simple - I recieved a used meter. I thought - "Ok, fine. This is not that bad. I can use this meter nevertheless." And I could - for a month. After that strange things started to happen.

Before making the purchase I did some research online (mainly this forum) and discovered that at some point a common problem with 121GW meters was the knob itself. Apparently there was a recall done at some point regarding the contact issues (knob replacement and addition of a shim). This took place months earlier. Common sense suggested that my meter should have already been free of this issue. This couldn't be farther from the truth.

After a month of very, very light use the meter is basically unusable. The knob wipers stopped making a good contact with the PCB (i think) and the meter reboots constantly while switching modes. Resistance mode cannot be turned on at all. The meter just turns off when I select it. The issue is present for every single knob position.
I made a short video where the issue is clearly visible:

https://www.youtube.com/watch?v=DIlfYcioE4w (https://www.youtube.com/watch?v=DIlfYcioE4w)

As you can see, this is clearly not a 121GW revision with a fixed knob. I must have received an older, flawed version. This is absolutely unforgivable for a meter this expensive (and every other for that matter). What I find the most frustrating is that the recall was done some time before I bought my meter from the EEVBlog store. At that point I should expect this issue to be already resolved but in the end I recieved a meter with this exact defect still present.

I've sent Dave an email describing these issues on 5th October. He replied a week later and promised to send me a new meter. I was really happy about that. So why am I even writing this post, you may ask? Well, because the new meter has never been shipped and Dave has not replied to any of my emails since then :palm:. I've been trying many times to contact him through at least 3 EEVBlog email adresses and sending him PMs on the forum, asking why the new meter hasn't been shipped. Three weeks have passed and I have not recieved any reply. I have no idea why.

I can only hope that this post will grab Dave's attention and that my meter will get replaced eventually. Do you know if there is any other way to contact Dave or to fix the meter? I just want to be able to use the product i paid for.

Thank you for your help in advance,
A VERY frustrated customer.

Hello, not sure if this has been dealt with. Are you able to check whether a shim is installed internally in your meter.
It should be there. The shim resolved that issue earlier on, but it is possible your unit is missing this part...
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Antonov225 on December 04, 2018, 05:47:57 pm
Hi, This issue has been resolved. I have already received a replacement meter from Dave. Thank you.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: nonentity on December 04, 2018, 10:46:40 pm
Quote
The resolution of the capacitance is 0.01 nF, unless I've misunderstood you might be using it for values out of the meters range.


My apologies, my message and post had the wrong capacitance value.  The capacitance used was 0.14 nano-farad.   Please see the corrected EEVblog 121GW Multimeter Issues Reply #869
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on December 05, 2018, 06:38:15 pm
I just installed firmware version 1.57, and it still shows a fixed current value of about 34 mA with nothing connected.

I had to go back to 1.26.

Does anybody know about this issue ?

David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on December 05, 2018, 09:24:23 pm
I just installed firmware version 1.57, and it still shows a fixed current value of about 34 mA with nothing connected.

I had to go back to 1.26.

Does anybody know about this issue ?

David DLC

look at #819 in this thread, maybe that helps.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Seppy on December 06, 2018, 12:28:13 am
Quote
The resolution of the capacitance is 0.01 nF, unless I've misunderstood you might be using it for values out of the meters range.


My apologies, my message and post had the wrong capacitance value.  The capacitance used was 0.14 nano-farad.   Please see the corrected EEVblog 121GW Multimeter Issues Reply #869

Right, the app just hasn't been updated thats a planned update (needed because multimeter added some capacitance ranges).
After a while I have been able to reproduce the issue, we will look into this.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: joeqsmith on December 15, 2018, 05:12:18 pm
Seems like YOU are the one polluting it.  Have anything technical to add?

I'll be very clear again.
This thread is for REPORTS of bugs and issues and CONFIRMATIONS of those bugs and issues.
DO NOT discuss them here, PLEASE!


I did not realize you were censoring posts in this area.   I resubmitted the post you removed twice because I literally thought I had forgotten to press the send key, not because I was trying to be a dick about it.   

I've had a go at cleaning up this area as well to save you the time.  Looks like about three pages were my posts so it does add up.   
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on December 16, 2018, 10:17:47 am
Hi,

I want point out the capatitance measure issue for low values again.
It was first discussed in the Firmware tread and also here.
This is a serious bug and makes the capacitance measurement unreliable for low values.
I still assume this is a firmware issue but I am unsure whether the developers are aware of this issue or not.

With a 100pF capacitor the meter has this behaviour:

First it shows the correct value.
After cycling through the modes it shows 21pF instead of 100pF and comes back very slowly to 100pF.

I had measured the waveform across the capacitor with a scope and found that it did not change in amplitude and time after cycling through the modes, so there seems no hardware related issue like wrong setups for the Hycon chip. Maybe a bug in the averange filter for the low capatitance mode? After cycling throug the modes it seems that the filter has a very long settling time for some reason. This issue should be investigated from UEI.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on December 16, 2018, 11:11:32 am
Hi,

beside of the unacceptable slow autorange in ohms mode there is another issue in this mode.

After shorting the leads and pushing the rel button the meter zeros out the low ohm range and compensates the lead resistor as expected. But it also disables simultaneous the autorange function.
Why? That makes no sense, no other of my meters does this.
Re-enabling the auto mode deletes the resistor compensation  :palm:.
That should be changed.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: IanB on December 16, 2018, 04:32:09 pm
After shorting the leads and pushing the rel button the meter zeros out the low ohm range and compensates the lead resistor as expected. But it also disables simultaneous the autorange function.
Why? That makes no sense, no other of my meters does this.
Re-enabling the auto mode deletes the resistor compensation  :palm:.

As far as I know this is typical behaviour in DMMs. The Rel function is specific to the range you are in. If a meter autoranges to a different range the Rel function is cancelled.

It appears the 121GW is locking in the Rel'd range rather than autoranging away and undoing the Rel setting. This seems to me like a reasonable and valid design choice.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on December 16, 2018, 05:00:35 pm
When people characterize something as "unacceptable" - in this case auto range, why not state what you are comparing it too and how you have used that other "acceptable" device.  Price, other functions? All really acceptable?  Why didn't you buy that one?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on December 16, 2018, 05:23:37 pm
GeoffreyF , 121GW is very slow in comparison with cheap or expensive multimeters , so stop being a fanboy troll . This firmware program should be scrapped completely and start from scratch with speed efficiency in mind . With a PIC family microcontroller a long time ago many , many users could have done a better firmware .

To add something , autorange hysteresis is 55000 counts up and 40000 counts down .Unreasonable huge . So , when you measure a 470ohm resistor from infinite resistance ( autoranging down ) , it will autorange in the 5K range and you will see 0,4700K .

But if you short the leads first and wait for 0 ohm reading ,  then measure fast ( now autorange is going up in ranges )  that 470ohm resistor , it will autorange correctly in 500ohm range as 470.00ohm .

Title: Re: EEVblog 121GW Multimeter Issues
Post by: Marco1971 on December 16, 2018, 05:43:52 pm
Hi,

beside of the unacceptable slow autorange in ohms mode there is another issue in this mode.

After shorting the leads and pushing the rel button the meter zeros out the low ohm range and compensates the lead resistor as expected. But it also disables simultaneous the autorange function.
Why? That makes no sense, no other of my meters does this.
Re-enabling the auto mode deletes the resistor compensation  :palm:.
That should be changed.

Hi, my Fluke 89IV/189 and 287 (with firmware 1.16) all do it in the same way with automatically switching to MANUAL ranging.

Regards from Italy.

Marco1971
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on December 16, 2018, 06:14:35 pm
GeoffreyF , 121GW is very slow in comparison with cheap or expensive multimeters , so stop being a fanboy troll . This firmware program should be scrapped completely and start from scratch with speed efficiency in mind . With a PIC family microcontroller a long time ago many , many users could have done a better firmware .

So you can't make any real point and you call me a fan boy troll?  You discredited yourself completely.   Did I say I was a "fan"?  No.  I own one. I own others.   Troll?  I am not one of these people who never gets tired of repeating the same point again and again, completely unproductively.   As for "Scrapped completely" (as opposed to correcting bugs).  It is equally obvious you never really worked on production code. 

This is an Engineering blog - that means numbers, facts, comparisons - not rude school boy remarks. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: HKJ on December 16, 2018, 06:28:07 pm
A few meters do not disable auto range when doing min/max or REL, one of them is Hioki DT4282
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on December 16, 2018, 07:12:25 pm
GeoffreyF , 121GW is very slow in comparison with cheap or expensive multimeters , so stop being a fanboy troll . This firmware program should be scrapped completely and start from scratch with speed efficiency in mind . With a PIC family microcontroller a long time ago many , many users could have done a better firmware .

So you can't make any real point and you call me a fan boy troll?  You discredited yourself completely.   Did I say I was a "fan"?  No.  I own one. I own others.   Troll?  I am not one of these people who never gets tired of repeating the same point again and again, completely unproductively.   As for "Scrapped completely" (as opposed to correcting bugs).  It is equally obvious you never really worked on production code. 

This is an Engineering blog - that means numbers, facts, comparisons - not rude school boy remarks.

Yes , sure I'm discredited not you for implying that 121GW slowness has something to do with price ... Fanboys allways find excuses for any issues .
I don't think this firmware could be "corrected" that much . This is a core feature when designing a software to work efficiently . Not 3 lines of code that they couldn't change in 1 year or more ...
But I don't care how is done
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Simon on December 16, 2018, 07:23:11 pm
GeoffreyF , 121GW is very slow in comparison with cheap or expensive multimeters , so stop being a fanboy troll . This firmware program should be scrapped completely and start from scratch with speed efficiency in mind . With a PIC family microcontroller a long time ago many , many users could have done a better firmware .

To add something , autorange hysteresis is 55000 counts up and 40000 counts down .Unreasonable huge . So , when you measure a 470ohm resistor from infinite resistance ( autoranging down ) , it will autorange in the 5K range and you will see 0,4700K .

But if you short the leads first and wait for 0 ohm reading ,  then measure fast ( now autorange is going up in ranges )  that 470ohm resistor , it will autorange correctly in 500ohm range as 470.00ohm .



The 121GW is cheaper than the venerable Fluke 179, far more functional and nearly twice as accurate with one more digit. stop bleating.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on December 16, 2018, 08:16:28 pm


Hi, my Fluke 89IV/189 and 287 (with firmware 1.16) all do it in the same way with automatically switching to MANUAL ranging.

Regards from Italy.

Marco1971

Hi,

yes, some Fluke meters do it the same way and i also don't like that. But my Agilent U1252B, Brymen 869S and the Gossen Metrahit Energy does not. These meters ignore the low ohm offset correction in higher ranges, but they don't switch off the auto mode. This is the better way in my opinion.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on December 16, 2018, 09:05:54 pm
GeoffreyF , 121GW is very slow in comparison with cheap or expensive multimeters , so stop being a fanboy troll . This firmware program should be scrapped completely and start from scratch with speed efficiency in mind . With a PIC family microcontroller a long time ago many , many users could have done a better firmware .

So you can't make any real point and you call me a fan boy troll?  You discredited yourself completely.   Did I say I was a "fan"?  No.  I own one. I own others.   Troll?  I am not one of these people who never gets tired of repeating the same point again and again, completely unproductively.   As for "Scrapped completely" (as opposed to correcting bugs).  It is equally obvious you never really worked on production code. 

This is an Engineering blog - that means numbers, facts, comparisons - not rude school boy remarks.

Yes , sure I'm discredited not you for implying that 121GW slowness has something to do with price ... Fanboys allways find excuses for any issues .
I don't think this firmware could be "corrected" that much . This is a core feature when designing a software to work efficiently . Not 3 lines of code that they couldn't change in 1 year or more ...
But I don't care how is done

It's about Electronics - NOT YOU.   You keep repeating yourself.  Adding nothing.  Who found excuses?  This is an engineering forum.   Act like you are in one.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on December 17, 2018, 12:12:17 am
I think if the 121GW ever gets to the point where everybody is happy (I'll set the bar at 95%), Dave could double the price.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on December 17, 2018, 02:25:18 am
This may have been reported before, but I came across this video that shows the meter's strange behavior in Auto Hold. My meter is a kickstarter unit and was shipped to me with the switch shim installed. It is running V1.57 firmware and I have tested it on the same precision voltage source, (ebay) as shown in the video it performs exactly the same.

The meter seems overly sensitive and the readings jump around especially when removing the probe from the voltage source. Also has the problems shown with not always working when auto hold selected. Its just flaky behavior that keeps me guessing if I can rely on the readings and necessitates taking numerous readings to be sure it is as shown on the display. Anyone else found this behavior with their meter?

https://www.youtube.com/watch?v=l7hBJh_NMOo (https://www.youtube.com/watch?v=l7hBJh_NMOo)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 17, 2018, 11:00:27 am
So pleased I haven't bothered trying to keep up with this thread since about page two or whenever I gave up in disgust initially. 10 months later and what a bunch repetitive whining :bullshit: from some armchair manufacturing and importing gods who know exactly how to fix all the problems by sooky keyboard power alone.

Apart from dropping a shim in mine, upgrading the firmware and learning to live within the much over discussed auto range time mine has proven faultless, accurate , reliable and still well within spec. It lives in my on site bag and gets hauled all over the place dropped into a bag of tools and generally treated as a workhorse.

If you want the perfect meter grow some balls and go get one made, show the world and make your fortune seems how it is so easy and you know all the fixes.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Simon on December 17, 2018, 11:40:44 am
I had mine calibrated by work to use as a new reference in place of my fluke 179 (0.05% versus 0.09%), the results came back more bang on than the fluke by comparison. I am more than happy. 5 digits, astounding low voltage measurements that allow even lower current measurements. Why buy a bench meter when i have this.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on December 17, 2018, 01:26:56 pm
Faster Settling time can be achieved by sacrificing accuracy.  Ultimately what the user is waiting for is a more accurate result.  Often I don't wait. The values I see are all within nominal and so I move on to another part of the circuit in my quest to find out why it is not working.  Often one expects a range of values in a particular circuit area.  By setting a range, settling time improves.  You are giving the meter a hint where to start averaging.  I suppose if someone is going through a big bag of parts trying to pick the perfect capacitor, long settling time would be frustrating.  Here I would also say that in building a circuit, a good engineer often designs for a range of possible values and not always an exact one.

Instruments have a job to do.  Ultimately that job is for the engineer or tech to do their job efficiently in time and money.  Not every instrument, even of the same type, is perfect for every situation.  Some are more rugged, some are less expensive - perhaps even approaching disposable. All have something they are not best at.  Some are more accurate or easier to use in some conditions.  The 121GW is a great meter for a lot of things, for the price it costs.  It's not the meter to end all meters. None of them are.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: 1anX on December 17, 2018, 08:22:58 pm
There is one other issue with my meter that occurs from time to time and that is with the Rel button operation. I have had the Rel button refuse to function when pressed and it requires turning the meter off and on to reset the function back into operation.

Anyone else experienced this when using Rel?

Note: All those above comments about the whining on this thread should be removed and re-posted to the Discussion thread!

This thread is for reporting on issues that are effecting the meter, so may appear as whining to the thin skinned crowd of proud owners. Reporting issues may seem negative, but without this feedback the meter will never reach its potential.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: newbrain on December 17, 2018, 09:16:34 pm
This may have been reported before, but I came across this video that shows the meter's strange behavior in Auto Hold. My meter is a kickstarter unit and was shipped to me with the switch shim installed. It is running V1.57 firmware and I have tested it on the same precision voltage source, (ebay) as shown in the video it performs exactly the same.

The meter seems overly sensitive and the readings jump around especially when removing the probe from the voltage source. Also has the problems shown with not always working when auto hold selected. Its just flaky behavior that keeps me guessing if I can rely on the readings and necessitates taking numerous readings to be sure it is as shown on the display. Anyone else found this behavior with their meter?
Actually I tried following the video, but this person (apart from the confusion between uV, hundreds of uV and mV) has, for my tastes, a terrible way of exposing his thoughts.
I had serious problems in understanding what he was trying to convey in 20 minutes that could not have been said in 3.

That said, I tried my 121GW, (Johnny B. Goode kickstarter, FW 1.57, arrived pre-shimmed) with my PSU and:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 17, 2018, 09:46:26 pm
There is one other issue with my meter that occurs from time to time and that is with the Rel button operation. I have had the Rel button refuse to function when pressed and it requires turning the meter off and on to reset the function back into operation.

Anyone else experienced this when using Rel?

Note: All those above comments about the whining on this thread should be removed and re-posted to the Discussion thread!

This thread is for reporting on issues that are effecting the meter, so may appear as whining to the thin skinned crowd of proud owners. Reporting issues may seem negative, but without this feedback the meter will never reach its potential.

In the past few pages you have tried to tell the owner of the contract made meter how it should be built by the manufacturer and to what standards and with what parts, consumer protection and warranty requirements under Australian law. All you have demonstrated is you know nothing much about any of those things. And now you want my comment shifted because reasons...... :-DD

Trawling the minutia of details for the 1000'th time and the backlots of youtube and repeating it twisting it to suit calling others trolls is not reporting faults at all it's called shit stirring in this country!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 17, 2018, 10:59:04 pm
In case you think my comments on your 'issues' unfair you had made nearly 40 posts prior to getting a meter including this gem where you had prejudged it 'poorly executed' without having ever touched it and taken a cheap shot at Dave for good measure.

A one sentence summary would be that the 121GW meter was a good idea poorly implemented!

Hindsight is a wonderful thing, but maybe if Dave ponied up and backed his own idea and design instead of a freebie UEi deal, it may have actually been developed and tested before being released to backers to buy?

The potential for getting a useful meter, (I'm Johnny Be Goode backer) is still high, but the way it has been handled with bugs and switch problems has certainly knocked the gloss of acquiring this meter for me!

Since then nearly 50 more posts with the bulk of them negative to the meter or other contributors in the couple of threads. 'Dog with a Bone' would be understating your content because even they loose interest in a bone after gnawing on it for a long while. Go buy some more test gear and broaden your negativity base!
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on December 17, 2018, 11:04:20 pm
This thread is for reporting on issues that are effecting the meter, so may appear as whining to the thin skinned crowd of proud owners. Reporting issues may seem negative, but without this feedback the meter will never reach its potential.

However, you never really reported an issue.  This is an engineering blog.  A real issue has a context in actual engineering work for which this instrument is made. Lack of objectivity, lack of repeatable cases, lack of numerical characterization are the opposite of engineering and issues.  Calling folks "Thin Skinned" is a subjective attempt at skipping actual raising of issues!  Do you actually think that will gain you respect for your redundant repetition?  Quite the opposite.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: DavidDLC on December 20, 2018, 06:24:23 pm
I think if the 121GW ever gets to the point where everybody is happy (I'll set the bar at 95%), Dave could double the price.

Really ? How can you be suggesting that.


David DLC
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Brumby on December 20, 2018, 10:50:53 pm
It was tongue-in-cheek ... a reflection on the impossible task of making everybody happy.  (I'm sure a few people worked that out.)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on December 20, 2018, 10:56:53 pm
I think some folks don't understand that it's an instrument, a tool, a bunch of functions that presumably you needed and that's why you bought it.  If happiness is a goal -go fix, debug or develop something.  Better yet, send your client the bill.  If the 121GW played a role in that then it's worth it.

Some folks just don't know where to stick their probes.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 20, 2018, 11:49:56 pm
In my dozen+ meters none are perfect for all tasks and all of them have quirks be they mechanical, firmware, electronic or in software interfaces. Am I unhappy I got any of them well no they each fill a function in what I do with them (a couple are just because I could ;) ). The very few that didn't or became redundant I have given them away to friends who didn't have a meter at all.

In the case of the 121GW I would most likely be over Brumby's 95% satisfaction point because I know of this meters few weaknesses but for day to day accuracy form factor, toughness and reliable function it is fit for purpose and performs better than specified. Am I a fanboy well NO I am just a fairly happy user of the product along with the other meters I own.

Doesn't mean the other 5% are not important either but some issues of the currently released meters can not be improved beyond firmware and minor hardware adjustments such as we have already seen take place. So while those issues vary from the 'end of the world' to a small minority to 'annoying quirk' to some to 'oh well I will just live with it' because nothing can be done by me the meter still works and does its job well.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on December 23, 2018, 09:41:14 am
Autorange slowness in all modes ( voltage , resistance , capacitance ... ) makes it pretty useless for any professional use ... This is not a small bug like others .
Could be enough for beginners ( first meter ) ,  occasional users , fanboys and people who bought it like a toy because they have too many meters . No offence .
 
Reporting issues is not whining because we can't afford or own something "expensive" like a Fluke  |O   

Just try to work on something when you have to wait about 1sec ( an eternity compared with other multimeters )  to switch the ranges up and down , maybe with some fast changing voltage . Annoying is not enough to describe the feeling ... when you have fast meters to compare . Could have 1000 extra features , if the simple ones are not implemented right.

Of course I hope they will resolve all the issues , it is for their own good , this meter can become a Fluke "killer" if they want . 





Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 23, 2018, 10:23:32 am
Autorange slowness in all modes ( voltage , resistance , capacitance ... ) makes it pretty useless for any professional use ... This is not a small bug like others .
Could be enough for beginners ( first meter ) ,  occasional users , fanboys and people who bought it like a toy because they have too many meters . No offence .
 
Reporting issues is not whining because we can't afford or own something "expensive" like a Fluke  |O   

Just try to work on something when you have to wait about 1sec ( an eternity compared with other multimeters )  to switch the ranges up and down , maybe with some fast changing voltage . Annoying is not enough to describe the feeling ... when you have fast meters to compare . Could have 1000 extra features , if the simple ones are not implemented right.

Of course I hope they will resolve all the issues , it is for their own good , this meter can become a Fluke "killer" if they want .

I am offended when you or others decide anyone who is fairly happy with the meter is a 'fanboy'. This meter is my primary professional onsite meter and fulfills that role very accurately and consistently it is certainly not a toy! Clearly we have very different ideas of what is needed and your ideas make you no more a hateboy than I am a fanboy. I have from day one talked about the few issues I had found if you head back to January in these threads you will find that. Grow UP and drop the tags.

Clearly you have missed the point that the multimeter chipset in use is one of the limiting factors with the Auto Range speed and that won't magically change by bringing it up once again  :palm:  there is clear limits as to what can be done in firmware.

Circuit redesign including possibly different chipsets is not an 'issue' and I very much doubt it would be done in public by the masses as it just won't work. Dave has mentioned this in videos before over another project. If you want to re engineer it go do it sell a mod board, rewrite the firmware for the 'new' light speed chipset, make sure it wont go bang.... We await your design if you go down that path.

Repeatably 'reporting' again the same issues is whining in my book so I guess we will just have to differ. The Auto range was known in January so repeating it AGAIN in what must be for the multiple hundredth time in your post is  :horse: Or are you hoping to reach the 1% of the members here who aren't already aware of it?

Perhaps you should broaden your scope too instead of the 90% of your posts you have made about this meter you might discover something better until you find that 'better meter' too has flaws or short comings including Flukes. :palm:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on December 23, 2018, 10:52:01 am
What chipsets ? How do you know it is hardware ? HY3131 is faster in other multimeters , and if a 32MHz 32bit ARM micro is not fast enough for a multimeter than what "rocket" should be used ?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 23, 2018, 11:04:13 am
Best left for Dave to answer as I am not privy to the firmware or feel I have a need to even see it. But a quick check revealed from the changelog

1.04 Resistance auto-ranging speed improved.
1.05 Further improved auto-ranging speed.

There may be more after that but I can't be bothered looking even after a couple of goes at it you would think the firmware had been tweaked within as close as it could be. And mentioning it AGAIN won't add anything else to what Dave or UEI already know. If you have a new code then start a thread and show it to us.

Unless you know of a secret electronic ingredient Firmware and Hardware are the two I know about so that leaves one being Hardware. And so again you miss the point of 'reporting' issues the alternative is to redesign the board and or change chipsets neither of these are 'issues' so start a redesign thread and I will enjoy reading it  :popcorn:
Title: Re: EEVblog 121GW Multimeter Issues
Post by: CDaniel on December 23, 2018, 11:23:35 am
They did something in resistance mode autorange which was the slowest , but not enough . So there is hope that further improvement is possible with some skill , will and money .
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on December 23, 2018, 11:31:14 am
What chipsets ? How do you know it is hardware ? HY3131 is faster in other multimeters , and if a 32MHz 32bit ARM micro is not fast enough for a multimeter than what "rocket" should be used ?

That is the point! The 121GW has the most powerful processor in its class but is as slow as a 20 Euro multimeter with autoranging.
Yes, it is a "Dave meter", it has some unique features. But meanwhile I am tired to read the fanboy gossip again and again from some members.
The 121GW is all in all a meter like all others on the market. Its downsides and quirks has to be mentioned in the same way like for all  other meters too, like Dave do it whith other brands. There is nothing wrong with pointing out the quirks of the 121GW, only fanboys have a problem with this.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 23, 2018, 11:47:15 am

 There is nothing wrong with pointing out the quirks of the 121GW, only fanboys have a problem with this.

When it was known 11 months ago repeating it yet AGAIN serves what purpose apart from you knowing you are 'keeping up the fight'? Bring a solution to it instead of repeating what is known.

As you clearly don't know what a fanboy is and as English may not be your first language here is a link https://www.urbandictionary.com/define.php?term=Fanboy (https://www.urbandictionary.com/define.php?term=Fanboy) I would welcome you to point out where I have not been 'objective' about the 121GW or fall into other parts of the general definition? Trying to use it as a put down to those with a more reasonable and balanced view is what I would expect in the schoolyard not an engineering forum.

Clearly I am a Fanboy Jan 10th https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1396270/#msg1396270 (https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1396270/#msg1396270)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on December 23, 2018, 12:13:50 pm
Hi,

You are a very good examble how not to discuss technical issues....

And by the way: The 121GW is not my design, neither the hardware nor the firmware. So I (and others) only can point out some issues, but not solve it.
But we also can solve it this way: Close the three 121GW related subjects, no discussion, no problems. Better now?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 23, 2018, 12:31:14 pm
So repeated pointing out some issues again and again and again is discussing 'technical issues' :-DD

You have not offered any 'solutions' (very different to discussions) as far as I can see to any of the life ending issues you clearly have with the meter but show me if you have I would be interested to read these technical remedies you have offered?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: chronos42 on December 23, 2018, 12:46:28 pm
Hi,

Where did I repeat pointing out the same issue again and again?
What did you not understand in this sentence: "The 121GW is not my design, neither the hardware nor the firmware. So I (and others) only can point out some issues, but not solve it."
Title: Re: EEVblog 121GW Multimeter Issues
Post by: beanflying on December 23, 2018, 01:04:25 pm
Hi,

beside of the unacceptable slow autorange in ohms mode there is another issue in this mode.

......

That is the point! The 121GW has the most powerful processor in its class but is as slow as a 20 Euro multimeter with autoranging.
...

Only twice in the last week but as this is your issue to keep flogging go ahead I guess the Aliens on the dark side of the moon may not have heard you yet ::)

Taking a quick look at a few of your posts in this thread you purchased your meter in August knowing full well of the auto range speed and yet you keep raising it as life ending? Why did you buy it if you were going to be so effected by it?

You seem to have played with several things broken them and fixed them and had more problems than any one else at a rate of several problems per post. It is a strange thing but those of us who are happy and have left our meters relatively alone have far less issues. Is there a tip there for others?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on December 23, 2018, 02:48:31 pm

You are a very good examble how not to discuss technical issues....

Rather than claiming someone else is as an "examble" - show what you are as an example to emulate.  You didn't.  If you believe you have a good point, make it with clear methods and actual numbers.  Reference the specifications you believe it doesn't meet or reference a use case that this meter doesn't meet and another does.   If nobody cares about your issue - don't repeat it.  People will still not care and you will appear tedious and annoying.

Be an example yourself.  The rest of us can decide which exemplar is the one we wish to emulate. 
Title: Re: EEVblog 121GW Multimeter Issues
Post by: AlanS on December 31, 2018, 06:35:14 am
Has anyone seen an error message 5d.E03? It appears to be an data logging error code.

It occurs when I start data logging to an internal SD Card. After pressing MEM to start the logging, it starts and then fails with the above message. I have used data logging to the card multiple times and this error only occurred today. I am using the current firmware - and couldn't find any reference to this message on the forum.

BTW - where do we find out what the other error codes are?

Good product for my purposes.
Title: Re: EEVblog 121GW Multimeter Issues: Activate Bluetooth on Meter??
Post by: barjammar on January 09, 2019, 04:33:32 am
Hi, I may have missed it but is there an instruction on how to use the Bluetooth “activate Bluetooth on the meter” as I can’t see the meter on my iPhone or in the app.
Many Thanks.
Barry
Title: Re: EEVblog 121GW Multimeter Issues: Activate Bluetooth on Meter??
Post by: GeoffreyF on January 09, 2019, 12:13:04 pm
Hi, I may have missed it but is there an instruction on how to use the Bluetooth “activate Bluetooth on the meter” as I can’t see the meter on my iPhone or in the app.
Many Thanks.
Barry

Yes, it is in the manual.  Page 53 as follows:

To enable Bluetooth communications, hold the “1ms PEAK” button until BT is displayed on the LCD.
Ensure that Bluetooth is enabled on the host device before running the application on the remote computing device.
The multimeter will continue to functional as normal in Bluetooth mode, but the display data will be transmitted via the Bluetooth connection.
To disable Bluetooth mode press and hold the 1ms Peak button until BT is not displayed.
 
Title: Re: EEVblog 121GW Multimeter Issues: Activate Bluetooth on Meter??
Post by: Seppy on January 23, 2019, 03:44:38 am
Hi, I may have missed it but is there an instruction on how to use the Bluetooth “activate Bluetooth on the meter” as I can’t see the meter on my iPhone or in the app.
Many Thanks.
Barry

With the iPhone it should be nearly instant, android and windows are much slower at detecting devices.
You don't need to pair the 121GW with the iPhone and it will not connect if it (the 121GW) is already paired to another device. Paired devices take precedence until they are unpaired.
BLE doesn't have much power, if your near other high power devices you might experience issues.
Title: Re: EEVblog 121GW Multimeter Issues: Activate Bluetooth on Meter??
Post by: 1anX on January 23, 2019, 07:54:55 pm
With the iPhone it should be nearly instant, android and windows are much slower at detecting devices.
You don't need to pair the 121GW with the iPhone and it will not connect if it (the 121GW) is already paired to another device. Paired devices take precedence until they are unpaired.
BLE doesn't have much power, if your near other high power devices you might
"You might" what Seppy? Seems to have been accidentally edited out mid sentance?
Title: Re: EEVblog 121GW Multimeter Issues
Post by: WattSekunde on February 11, 2019, 12:37:03 am
Manual 2019-01-29 vs. 121GW 1.57 in VA mode?

The Manual (p.20) shows 3 µVA ranges and 6 mVA/VA ranges in AC or DC. But I can select 4 ranges at the µVA position of the rotary switch and 4 ranges at the mVA/VA position. I don't get it.

Rotary Switch in position µVA input. MODE = AC or DC.
I see this decimal point positions. (RANGE) pressed between each step:
1. AUTO
2. ##0.00
3. ###0.0
4. ###0.0 ?
5. ####0
back to step 2
(Hold RANGE to go back to AUTO range)

Rotary Switch in position mVA/VA input. MODE = AC or DC.
I see this decimal point positions. (RANGE) pressed between each step:
1. AUTO
2. #0.000
3. ##0.00
4. ##0.00 ?
5. ###0.0
back to step 2
(Hold RANGE to go back to AUTO range)

Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on February 11, 2019, 02:59:25 pm
Manual 2019-01-29 vs. 121GW 1.57 in VA mode?

The Manual (p.20) shows 3 µVA ranges and 6 mVA/VA ranges in AC or DC. But I can select 4 ranges at the µVA position of the rotary switch and 4 ranges at the mVA/VA position. I don't get it.

Rotary Switch in position µVA input. MODE = AC or DC.
I see this decimal point positions. (RANGE) pressed between each step:
1. AUTO
2. ##0.00
3. ###0.0
4. ###0.0 ?
5. ####0
back to step 2
(Hold RANGE to go back to AUTO range)

Rotary Switch in position mVA/VA input. MODE = AC or DC.
I see this decimal point positions. (RANGE) pressed between each step:
1. AUTO
2. #0.000
3. ##0.00
4. ##0.00 ?
5. ###0.0
back to step 2
(Hold RANGE to go back to AUTO range)

Now actually measure something.  Your post is about manual selection, NOT ranging.   If you used your 121GW you would get  it.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on February 11, 2019, 05:55:26 pm
Manual 2019-01-29 vs. 121GW 1.57 in VA mode?

The Manual (p.20) shows 3 µVA ranges and 6 mVA/VA ranges in AC or DC. But I can select 4 ranges at the µVA position of the rotary switch and 4 ranges at the mVA/VA position. I don't get it.

Rotary Switch in position µVA input. MODE = AC or DC.
I see this decimal point positions. (RANGE) pressed between each step:
1. AUTO
2. ##0.00
3. ###0.0
4. ###0.0 ?
5. ####0
back to step 2
(Hold RANGE to go back to AUTO range)

Rotary Switch in position mVA/VA input. MODE = AC or DC.
I see this decimal point positions. (RANGE) pressed between each step:
1. AUTO
2. #0.000
3. ##0.00
4. ##0.00 ?
5. ###0.0
back to step 2
(Hold RANGE to go back to AUTO range)

version 1.58 works similarly.  The VA measurements are fairly confusing and the manual furthers the issue with ambiguity.

Only the designers (or someone who wants to spend a little time experimenting) can fully explain.  Here's some observations:

1. For each VA range there is a current reading with its range and resolution multiplied by a voltage reading with its range and resolution.  The exact selections for each are not given in the manual.  You may get some idea by the number of digits and units in the current and voltage readings that alternately flash on the secondary display.  But you don't know for sure if that means anything.
2. The math of resolution and range carry over is not defined.
3. Even which range is selected is not known as you indicated as the only indication is the # of digits and the uVA or mVa or VA symbol.

Most of this detail doesn't matter for the casual user and critical measurements should be made with separate voltage and current readings.

However, I think the manual should say a little more.


Title: Re: EEVblog 121GW Multimeter Issues
Post by: WattSekunde on February 11, 2019, 10:39:30 pm
OK, let's say it's a manual issue but I can't check the multimeter against hidden information. The manual could have been created more carefully. I like the very clear Gossen manuals most.


BTW: I read nearly this whole thread and someone said there are not enough "active tester" reporting possible bugs. Until the VA strangeness I stumbled upon these days the 121GW worked fine to my needs. I like the very nice iOS App, too! But I also like a critical community who drives a product forward. Maybe with HW and SW hacks. That's the biggest difference between the 121GW and all other meters on the market. Let's take it apart...  :-/O  ;)
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on February 12, 2019, 01:33:38 am
OK, let's say it's a manual issue but I can't check the multimeter against hidden information. The manual could have been created more carefully. I like the very clear Gossen manuals most.

But you can use it.  You will see the ranges.  Even in your report on pushing the range button, you noticed two ranges that were the same.  No they aren't. They just look that way at zero.   The purpose of the range button is to give the meter a hint as to where to start.  That doesn't mean that's the only place.  USE IT!  It's really there.  Try to measure something and if its to a limited number of decimal places, check the spec. It's in spec.  You are simply confusing the ranges and accuracy with the use of the range function!   Actually use it on a project.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Alex Rodriguez on February 26, 2019, 02:45:17 pm
The 121GW bluetooth is not working. I have the iPhone XS MAX firmware iOS 12.1.4 - I turn ON the 121GW bluetooth, and search for it on my phone, not joy. The iPhone never finds it, as a result the application is not working.  I installed the latest 1.58 121GW beta firmware, still no joy.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: GeoffreyF on February 26, 2019, 04:10:22 pm
It works for me on Android.   When the meter is first turned on, bluetooth is off.  Did you turn it on, as discussed in the manual?  It would be helpful if you wrote the steps you used to use bluetooth.   Generally speaking - the bluetooth feature works.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: Alex Rodriguez on February 27, 2019, 04:39:31 am
It works for me on Android.   When the meter is first turned on, bluetooth is off.  Did you turn it on, as discussed in the manual?  It would be helpful if you wrote the steps you used to use bluetooth.   Generally speaking - the bluetooth feature works.

Yes, I turned bluetooth  ON, I followed page 53 instructions. I pressed the "1ms PEAK," and I see the "BT" on the screen, but the iPhone does not see the meter at all.  So the application is blank.
Title: Re: EEVblog 121GW Multimeter Issues
Post by: bicycleguy on February 27, 2019, 05:51:21 am
Alex
The bluetooth has been very reliable on a iPhone and iPad.  All I can suggest is that you try to remove the 121GW from the background tasks to get a fresh start.  So quit the app, double click to see the background apps and swipe up to stop it.  Then try opening it again.  I don't thing you have to restart bt on the 121gw.

good luck
Title: Re: EEVblog 121GW Multimeter Issues
Post by: imaradiostar on March 01, 2019, 04:48:33 am
I'm a new forum member and I searched, so please help me understand if my post breaks rules!

My other (high count) meters are a Fluke 8060a and 8050a, and a Keithley 2015THD. All are capable of displaying dBv in one way or another. On the 8060a I have to use relative mode, but once given a reference voltage, it plays nicely and is very accurate. Arguably, it tracks the 6.5 digit meter better than the 121GW.

I can't seem to get the 121GW to play nicely. It'll display dBm (a useless metric in 2019 for all but the most select circumstances, I would argue) but I can't take advantage of relative mode in reference to the dB display. As a result, I'm unable to directly display measurements in dBv or relative measurements, such as the gain of an amplifier.

I can always get out a calculator and 20*log(acv2/acv1), but the whole point of a fancy meter is to NOT have to do that!

Can anyone address this for me? It seems dBv should be available, and on the MAIN display.

thanks!

Jamie
Title: Re: EEVblog 121GW Multimeter Issues
Post by: newbrain on March 01, 2019, 07:57:30 am
It'll display dBm (a useless metric in 2019 for all but the most select circumstances, I would argue)
I'd beg to differ. It does not make much difference if the the display is in dBm or dBV or any other dBxxx. A reference level is needed in any case.

I can always get out a calculator and 20*log(acv2/acv1), but the whole point of a fancy meter is to NOT have to do that!
And, in fact, you don't need to do that. Just measure the dBm value at the input, and subtract it from the dBm at the ouput...though I agree that being able to use Rel would be nice (I stand by your words on this, I'm away from home at the moment).
Title: Re: EEVblog 121GW Multimeter Issues
Post by: imaradiostar on March 02, 2019, 02:52:20 am
It'll display dBm (a useless metric in 2019 for all but the most select circumstances, I would argue)
I'd beg to differ. It does not make much difference if the the display is in dBm or dBV or any other dBxxx. A reference level is needed in any case.

I suppose it comes down to your intended purpose. I still think that dBv makes the most sense. If a meter has a sufficiently high impedance, it's "invisible" to any circuit under test, so an external termination of any given value could be connected. I live in an HP/Agilent dominated analog world where dBv is by far the most common comparison point. If I'm reporting amplifier gain or frequency response, it's always a dBv thing. I'm sure other labs/work environments are different, of course. I used to work in pro audio and I can see why they like dBu/dBm with a 600 ohm reference.

My lab does RF and audio frequency work. I mostly work in audio, so dBv seems to be the most useful, as it is referenced to a voltage and not a given impedance.

I guess my opinion is unfair to those that prefer dBm. I am hoping for more dialogue about what is possible with the hardware. If the meter has an internal dc reference and is programmable, perhaps it could be programmed to have multiple reference impedances/voltages, like the Fluke 8050a did in 1980. In any case, the ability to at least use relative measurement mode means that someone could measure the gain of a circuit and provide their own reference impedance/voltage/terminator.

If dB made it to the primary display rather than just the secondary field, it could be manipulated withe the relative measurement function, as has been done in other meters.

Jamie
Title: Re: EEVblog 121GW Multimeter Issues
Post by: newbrain on March 02, 2019, 10:27:39 am
Emphasis added by me:
If a meter has a sufficiently high impedance, it's "invisible" to any circuit under test, so an external termination of any given value could be connected. I live in an HP/Agilent dominated analog world where dBv is by far the most common comparison point. If I'm reporting amplifier gain or frequency response, it's always a dBv thing.
The meter impedance remains around 10 M \$\Omega\$ when in dBm mode, it does not use a 600 \$\Omega\$ load: it is, in fact, measuring dBu not dBm.
To report gain, one just uses dB: it's a pure (power) ratio, no m, u or V. A subtraction in dBx is all that is needed (easier to do in my mind than logs and ratios).
The value in dBV is a also simple subtraction away:
dBV ~= dBu - 2.22
I'm sure you don't need the calculation spelled out, that's one of the advantages of using a logarithmic measure!

So to wrap it up, there are for sure improvement points:
At the same time, I still don't see any major advantage in one dBx over the others (I would have been just as happy with dBV, really...).

1: The internal DC reference and its programmability have nothing to do with it. The displayed dBm value is just a fixed calculation on the measured AC value.
Storing the dBm reference value along the AC value (or recalculating it from the latter) and doing a subtraction is all that it takes.
2: e.g. Measure (and display) 1.00V / 2.218 dBm, hit Rel, then measure 2.00V: display is now 1.00V / 6 dBm
Title: Re: EEVblog 121GW Multimeter Issues
Post by: imaradiostar on March 04, 2019, 05:27:39 am
You're right, the LCD should say dBu. That's why in my post above I said dBm/dBu (saying 600 ohm reference added confusion), because obvious the meter has no internal termination. dBu makes sense, and I can do the -2.2 as easily as the next person. Or I can use a Fluke 8050a and not bother. For that matter, when I'm doing low-noise EIN and gain testing, I usually use a Fluke 8920a anyway.

Most folks don't care. I get that. I am not complaining, but I am to some extent responsible for purchasing stuff like this for our lab. For less than the cost of a Fluke this met