Author Topic: EEVblog 121GW Multimeter Issues  (Read 400367 times)

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Offline bicycleguy

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Re: EEVblog 121GW Multimeter Issues
« Reply #1250 on: October 16, 2020, 04:13:47 pm »
I was able to reproduce the issue as well.  I ran some quick tests with a 66332A at around 2.5V, 4V, 5V, 12V.  I did not notice the issue at 2.5V?


2.5V volts? We got issues with current reading, not voltage. It only shows up in VA mode - both on display without data logging and with data logging. The current reads and data logs correctly in current (A) mode.
I think that J-R is pointing out that the current reading problem in VA mode also depends on the Voltage your around, even a  constant voltage.  Haven't spent the time to look at it enough but it also may have something to do with what range (voltage & current) you are on.  Definitely another small but irritating bug.
 

Offline BU508A

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Re: EEVblog 121GW Multimeter Issues
« Reply #1251 on: October 16, 2020, 08:00:22 pm »
Hello,

I think, I was able to reproduce the issue.

My setup:

PSU Rohde & Schwarz NGB 32/10
- voltage set to 0V at the beginning
- CC limit set to max (10A)

Load: 2.2 Ohm 50W resistor

DMMs used (left to right):
- EEVBlog BM235, measuring the voltage
- Agilent 1252B, measuring the current
- EEVBlog 121GW (Firmware 2.04), set to VA mode

I have increased  voltage output until the current was around 2.6 Ampere.
Because of the self-heating of the resistor the current begins to drop. During this time I  took the pictures below.
One can see, that the current measured by the 121GW in VA mode is clearly higher than the current measured by the 1252B. When the current drops below 2.49 Ampere the current shown by the 121GW is agreeing with the 1252B.







« Last Edit: October 16, 2020, 08:04:43 pm by BU508A »
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Offline Kal

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Re: EEVblog 121GW Multimeter Issues
« Reply #1252 on: October 17, 2020, 12:32:51 am »

Code: [Select]
1361,2020/10/15,12:02:37,DCVA,0022.32,VA,DCV,008.401,V,DCA,002.657,A,,
1362,2020/10/15,12:02:38,DCVA,0021.00,VA,DCV,008.401,V,DCA,002.500,A,,

I was testing the 12V 35W halogen bulb, using my Agilent E3642A power supply, using 0-8V/5A output.

I was varying the output voltage on the PSU in few mV increments. The PSU would show change from something like 2.500A to 2.503A, or even less. The display of the multimeter will then jump from 20.99W or 21.00W to about 22.0W, or 22.3W.

The 2.657A figure is absolutely wrong


This puts into question months of my data gathering on one of my project.

That's exactly the same problem indeed. So as second and third datapoint (from user BU508A measurements) we can assume that at least in the range 7.3V - 12.7V the same current offset problem appears when current >= 2501mA.
As for your data gathering, the result are likely wrong and need correction. I'm quite sure this offset is fixed (I just added conditional 157mA substraction for every Excel row over 2500mA). So not all is lost. But if your project had wide ranges of resistances/voltages then the current offset problem might be intermittent, needs further testing.

Someone with variable digital load could do full sweep with constant current at for example 2550mA (to be surely in the problem range) and see if current display offset is indeed constant.
Also would be interesting if this offset remains at bigger currents, I did not go over about 3A, or for the matter at any bigger and lower ranges really.

Maybe you followed the instructions in the manual?  If so, that would give some poor results. 

Thanks for this link, it is not this problem but that is another thing I did not think about, did measure the voltage at battery terminals with other multimeter and values were in sync and that was enough for the time. Turns out in my case the total voltage was thats what needed as measuring total battery capacity - so burden voltage must be included in logs.
It's good example to always think about what exactly is the target you need to measure and always be aware and doublecheck with other multimeters. Some projects will need the Com/Amp lead swap and others not.
 

Offline J-R

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Re: EEVblog 121GW Multimeter Issues
« Reply #1253 on: October 17, 2020, 02:18:03 am »
I was able to reproduce the issue as well.  I ran some quick tests with a 66332A at around 2.5V, 4V, 5V, 12V.  I did not notice the issue at 2.5V?


2.5V volts? We got issues with current reading, not voltage. It only shows up in VA mode - both on display without data logging and with data logging. The current reads and data logs correctly in current (A) mode.
I think that J-R is pointing out that the current reading problem in VA mode also depends on the Voltage your around, even a  constant voltage.  Haven't spent the time to look at it enough but it also may have something to do with what range (voltage & current) you are on.  Definitely another small but irritating bug.

Yes, that was my initial thought as well, is it range related?  My very first quick and dirty test was just with the 121GW and a PSU in series, without even the voltage being measured and the VA mode current reading was accurate.  So I used the 66332A as a synthetic load to run some further quick tests.

Thinking back to the 4V and 5V tests, I neglected to ensure the 121GW switched to the lower range.  I will run more tests and report back.  Although I suspect someone with some better equipment could have a full analysis for us shortly?

Could be a calibration issue, I'm noticing the R0 and R1 ranges for the VA calibration in the manual.  I suppose I will have to attempt a re-calibration as part of the tests now...
« Last Edit: October 17, 2020, 02:26:41 am by J-R »
 

Offline J-R

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Re: EEVblog 121GW Multimeter Issues
« Reply #1254 on: October 17, 2020, 06:51:51 am »
OK, confirmed, the amperage readings are correct until the range flip at approximately 5.5V at which point the fixed offset is observed until OFL is displayed at ~55V.

The problem exists at voltages below 5.5V if you manually select that range.

The amperage offset was observed up through 10A.  It seems quite constant.

I attempted the offset calibration but just get OFF-E after the countdown.  Probably there is actually no offset calibration?

Seems like it should be an easy firmware fix.
« Last Edit: October 17, 2020, 06:55:20 am by J-R »
 

Online joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #1255 on: October 17, 2020, 08:36:34 pm »
I haven't played with the VA mode since making the very first videos with the prototype.   I wouldn't be too surprised if there was a bug.  It looks like the calibration is at 25000mVA so it makes sense this is where we would see the problem. 

In DCA mode, I swept from 0-5A and saw nothing odd. Then tried DCV and swept from 0-15V and again, didn't see anything unexpected.  Not surprised as they use a different cal.   

My software didn't support VA, so I added the ability to plot all three graphs.  I am using the wireless interface.  This meter was purchased as a control and has not been exposed to anything outside of normal use when making the review.  It is an older version of the hardware running firmware 2.02.   Used a fixed resistor for a load.   

At 2.5A, there is a large step in the current while the voltage remains stable.   I allowed the voltage to continue to sweep and it appears to be a constant offset.   I tried a few different resistance values and it seems to happen at the same current.     

I have also included the data collected from all three sweeps.  This is just ASCII format.   
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Offline movax

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Re: EEVblog 121GW Multimeter Issues
« Reply #1256 on: October 18, 2020, 02:24:14 pm »
I can confirm that the offset is range dependent. 121GW set in mVA, and auto ranging (default). I retested at 3.84V, and the offset was 15mA-16mA.  At 8.4V it was 157mA offset. Below 2.500A there is no offset (<3mA, which is within spec).

[attachimg=1][attachimg=2][attachimg=3]
« Last Edit: October 18, 2020, 02:37:07 pm by movax »
 

Offline Jonathon_Doran

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Re: EEVblog 121GW Multimeter Issues
« Reply #1257 on: October 28, 2020, 08:45:39 pm »
I just got my 121GW and want to verify the ground on mains.  I'm probably doing something wrong, but am lost at this point.  When I put the meter on volts, set the mode to AC, and connect to hot and ground  (not neutral) I get 15V.  This is US, so I expect 120VAC.

DC voltages and resistance look spot on.

I have a nice Fluke somewhere, but during the move it is lost.

Any thoughts/suggestions?
 

Offline Brumby

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Re: EEVblog 121GW Multimeter Issues
« Reply #1258 on: October 28, 2020, 09:45:03 pm »
What do you get when you measure between hot and neutral?
 

Offline Jonathon_Doran

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Re: EEVblog 121GW Multimeter Issues
« Reply #1259 on: October 28, 2020, 10:34:43 pm »
Got 123V
 

Offline BU508A

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Re: EEVblog 121GW Multimeter Issues
« Reply #1260 on: October 28, 2020, 10:38:25 pm »
Got 123V

And you are sure, that this is a proper ground? Have you measured between neutral and PE (ground) in Low Z mode?
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Offline Brumby

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Re: EEVblog 121GW Multimeter Issues
« Reply #1261 on: October 28, 2020, 10:44:23 pm »
Have you measured between neutral and PE (ground) in Low Z mode?
That's going to show zero, whether the ground is good or bad - unless it is connected to a real source of voltage with a low-ish impedance.
 

Offline Jonathon_Doran

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Re: EEVblog 121GW Multimeter Issues
« Reply #1262 on: October 28, 2020, 10:44:47 pm »
Sorry, I confused hot/neutral.  I don't work on mains.  The little socket is hot.  123V from hot-ground and hot-neutral. 

PS:  Checking to see if I can ground my ESD mat to this outlet...
« Last Edit: October 28, 2020, 10:47:19 pm by Jonathon_Doran »
 

Offline Brumby

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Re: EEVblog 121GW Multimeter Issues
« Reply #1263 on: October 28, 2020, 10:47:00 pm »
OK - that's better.

So the 15V is Ground-Neutral?
 

Offline Jonathon_Doran

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Re: EEVblog 121GW Multimeter Issues
« Reply #1264 on: October 28, 2020, 10:48:15 pm »
I believe so.  I'll go back and try it again in a bit. 
 

Offline BU508A

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Re: EEVblog 121GW Multimeter Issues
« Reply #1265 on: October 28, 2020, 11:06:15 pm »
If you have 15V between neutral and ground, then there is a lot going on (assumed, that you have set your meter to Low-Z mode, otherwise you are going to catch ghost voltages).

Please check, if you are using the Low-Z mode of the meter.
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Offline Jonathon_Doran

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Re: EEVblog 121GW Multimeter Issues
« Reply #1266 on: October 29, 2020, 01:09:14 am »
No I was not using low Z.  I really don't know what most of these features are.  I just looked in the manual under Voltage.
 

Offline Jonathon_Doran

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Re: EEVblog 121GW Multimeter Issues
« Reply #1267 on: October 29, 2020, 01:06:14 pm »
Using  low-Z the voltage disappeared.  I read up on ghost voltage.  Yep, that was what I saw.
Thanks for your assistance.
 
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Offline BrianG61UK

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Re: EEVblog 121GW Multimeter Issues
« Reply #1268 on: November 04, 2020, 11:28:16 pm »
Using  low-Z the voltage disappeared.  I read up on ghost voltage.  Yep, that was what I saw.
Thanks for your assistance.
Surely that means your ground is a high impedance, which means it's not ground at all and could be dangerous if you use it to ground something that needs a ground for safety reasons.
 

Online AVGresponding

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Re: EEVblog 121GW Multimeter Issues
« Reply #1269 on: November 05, 2020, 05:54:53 am »
Using  low-Z the voltage disappeared.  I read up on ghost voltage.  Yep, that was what I saw.
Thanks for your assistance.
Surely that means your ground is a high impedance, which means it's not ground at all and could be dangerous if you use it to ground something that needs a ground for safety reasons.

It could be induced voltage from a parallel running cable, however I'd recommend it's investigated by a qualified electrician using an installation tester.
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