Author Topic: EEVblog 121GW Multimeter Issues  (Read 193753 times)

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Online CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #675 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 .
« Last Edit: September 10, 2018, 09:43:35 pm by CDaniel »
 
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Offline Brumby

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Re: EEVblog 121GW Multimeter Issues
« Reply #676 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".
 

Offline HKJ

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Re: EEVblog 121GW Multimeter Issues
« Reply #677 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.
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #678 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?

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.
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #679 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.
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #680 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
 

Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #681 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
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #682 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.
 

Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #683 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.
 

Offline Digital Corpus

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Re: EEVblog 121GW Multimeter Issues
« Reply #684 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.
 

Online CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #685 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  .
« Last Edit: September 14, 2018, 04:25:03 pm by CDaniel »
 

Online CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #686 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 ...
« Last Edit: September 21, 2018, 10:49:52 am by CDaniel »
 

Offline Seppy

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Re: EEVblog 121GW Multimeter Issues
« Reply #687 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.
 

Offline Seppy

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Re: EEVblog 121GW Multimeter Issues
« Reply #688 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.
 

Online CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #689 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 ) .
« Last Edit: September 24, 2018, 05:51:41 pm by CDaniel »
 

Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #690 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.
 
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #691 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?
I'm not an EE--what am I doing here?
 
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Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #692 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.
 

Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #693 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.
« Last Edit: September 24, 2018, 09:55:42 pm by bicycleguy »
 

Online CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #694 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.
« Last Edit: September 25, 2018, 12:03:16 am by CDaniel »
 
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Offline PeterL

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Re: EEVblog 121GW Multimeter Issues
« Reply #695 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
 

Offline dcac

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Re: EEVblog 121GW Multimeter Issues
« Reply #696 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.



 

Online CDaniel

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Re: EEVblog 121GW Multimeter Issues
« Reply #697 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 .
« Last Edit: September 25, 2018, 03:09:02 pm by CDaniel »
 

Offline DavidDLC

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Re: EEVblog 121GW Multimeter Issues
« Reply #698 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
« Last Edit: September 25, 2018, 04:52:46 pm by DavidDLC »
 

Offline Dr. Frank

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Re: EEVblog 121GW Multimeter Issues
« Reply #699 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.
« Last Edit: September 25, 2018, 10:19:26 pm by Dr. Frank »
 


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