Author Topic: EEVblog 121GW Multimeter Issues  (Read 194266 times)

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Offline EEVblog

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Re: EEVblog 121GW Multimeter Issues
« Reply #475 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.
 

Offline EEVblog

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Re: EEVblog 121GW Multimeter Issues
« Reply #476 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).
 

Offline firewalker

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Re: EEVblog 121GW Multimeter Issues
« Reply #477 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.
« Last Edit: August 09, 2018, 01:27:37 pm by firewalker »
Become a realist, stay a dreamer.

 

Offline floobydust

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Re: EEVblog 121GW Multimeter Issues
« Reply #478 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.
 

Offline AdamHi

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Re: EEVblog 121GW Multimeter Issues
« Reply #479 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
and
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
 

Offline dcac

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Re: EEVblog 121GW Multimeter Issues
« Reply #480 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

 

Offline AdamHi

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Re: EEVblog 121GW Multimeter Issues
« Reply #481 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.
 

Offline EEVblog

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Re: EEVblog 121GW Multimeter Issues
« Reply #482 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
and
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.
« Last Edit: August 11, 2018, 07:38:22 am by EEVblog »
 

Offline EEVblog

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Re: EEVblog 121GW Multimeter Issues
« Reply #483 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.
 
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Offline firewalker

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Re: EEVblog 121GW Multimeter Issues
« Reply #484 on: August 11, 2018, 08:31:57 am »
This is the only change?

Alexander.
Become a realist, stay a dreamer.

 

Offline EEVblog

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Re: EEVblog 121GW Multimeter Issues
« Reply #485 on: August 11, 2018, 09:46:08 am »
This is the only change?

Yes, I believe so.
 

Offline 1anX

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Re: EEVblog 121GW Multimeter Issues
« Reply #486 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?
 

Offline knapik

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Re: EEVblog 121GW Multimeter Issues
« Reply #487 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.
 

Offline knapik

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Re: EEVblog 121GW Multimeter Issues
« Reply #488 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.
 

Offline firewalker

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Re: EEVblog 121GW Multimeter Issues
« Reply #489 on: August 11, 2018, 10:52:52 am »
No problem for me. Did you rename the file to EEVBlog.bin?

Alexander.
Become a realist, stay a dreamer.

 
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Offline 1anX

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Re: EEVblog 121GW Multimeter Issues
« Reply #490 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:
« Last Edit: August 11, 2018, 11:09:00 am by 1anX »
 
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Offline Dr. Frank

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EEVblog 121GW Multimeter Issues - FW 1-26 datalogging
« Reply #491 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
« Last Edit: August 11, 2018, 12:46:20 pm by Dr. Frank »
 

Offline Dr. Frank

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Re: EEVblog 121GW Multimeter Issues
« Reply #492 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.
« Last Edit: August 11, 2018, 01:29:43 pm by Dr. Frank »
 

Offline Candid

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Re: EEVblog 121GW Multimeter Issues
« Reply #493 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?
« Last Edit: August 11, 2018, 03:29:47 pm by Candid »
 
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Offline dcac

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Re: EEVblog 121GW Multimeter Issues
« Reply #494 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.

 

Offline fubar.gr

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Re: EEVblog 121GW Multimeter Issues
« Reply #495 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.

Offline Dr. Frank

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Re: EEVblog 121GW Multimeter Issues
« Reply #496 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 
 

Offline Dr. Frank

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Re: EEVblog 121GW Multimeter Issues
« Reply #497 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
 

Offline fubar.gr

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Re: EEVblog 121GW Multimeter Issues
« Reply #498 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

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.
« Last Edit: August 11, 2018, 10:13:52 pm by fubar.gr »
 

Offline DrGeoff

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Re: EEVblog 121GW Multimeter Issues
« Reply #499 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,
Was it really supposed to do that?
 
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