Author Topic: EEVblog 121GW Multimeter Issues  (Read 58281 times)

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Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #600 on: August 17, 2018, 10:22:04 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.
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #601 on: August 17, 2018, 11:43:01 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.
« Last Edit: August 17, 2018, 11:55:33 pm by IanB »
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Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #602 on: Yesterday at 12:17:21 am »
We should be testing with the same firmware.   I set the sample rate to 0.    I then collected 450 samples (90seconds/0.2) with both firmware 1.0 and 1.26.   

While you measure roughly 0.01 ohm change, I see 0.07 when I use firmware 1.26.   With 1.0 installed it drops to 0.01 which is close to what you are seeing. 

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. 

What appears to be a higher frequency noise seen on the prototype does not concern me too much.  Different hardware.  UEI would need to chime in.  I see the 0.01 variance as a non-issue.  If I understand their spec, it seems well within it.
 
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #603 on: Yesterday at 12:26:39 am »
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.
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #604 on: Yesterday at 01:19:39 am »
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.
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #605 on: Yesterday at 01:31:22 am »
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.



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Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #606 on: Yesterday at 02:24:13 am »
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

 

 
« Last Edit: Yesterday at 02:34:44 am by joeqsmith »
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #607 on: Yesterday at 03:01:45 am »
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.
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Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #608 on: Yesterday at 03:34:34 am »
That Hycon part seem VERY sensitive to temperature.  As you can see from some of the data I have shown, if I cool it for a few minutes and power it back up the initial drift profile will stack right on top of run to run.  If I leave the meter on for about 10 minutes before I use it, it's pretty good.  It's not the room temperature or the test resistors that I have been using that are causing it and while it does appear the divider network has some effect, the majority seem to be from that one IC.    I had asked about the image for the BT so I could at least try and enable it on the proto.  No luck so far so I can't try to see if this has any effect. 

I am sure I can make the prototype move if I get it off the bench, rub my feet on the carpet and such.  I'm trying to give you a normal use case that you could possibly reproduce.   
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Online Dr. Frank

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Re: EEVblog 121GW Multimeter Issues
« Reply #609 on: Yesterday at 05:05:10 am »
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
 

Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #610 on: Yesterday at 05:55:14 am »
Dr. Frank, I am attempting to replicate a reported problem.  So when you ran your first test at 1.9Meg, I setup a 1.9M.  When Dave had posted his video showing the 0.5 ohm resistor, I assumed someone had posted an accuracy problem that he was attempting to replicate.  I asked him to provide some sort of link to the original post but sadly, no response.   I assumed it was maybe from the following:

1.- I also see intermediate values on the Ohm range.Ian reports a problem at low resistances.     

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.

So I ran mine at 0.5 as well assuming one of them had contacted Dave directly.  As mentioned, I was not too concerned with the drift or the accuracy.  For me, the problem was the noise I was seeing in 1.26 compared with 1.0 and I wanted to make sure this was not the cause of IanB's problem or what had been reported to Dave.   Just pushing the rope.   I have seen that initial short term drift all along.  At some point someone should dig into it beyond my quick soldering iron test.   

Could you try and replicate what IanB posted about touching the hold button?  I am curious if your meter with the new hardware is also unstable.
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #611 on: Yesterday at 06:53:45 am »
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.
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Online Dr. Frank

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Re: EEVblog 121GW Multimeter Issues
« Reply #612 on: Yesterday at 06:54:02 am »
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
« Last Edit: Yesterday at 06:56:41 am by Dr. Frank »
 

Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #613 on: Yesterday at 08:21:19 am »
The problem using the Rel could be the same problem IanB mentioned with the Hold button.

Besides the Gossen Ultra, I think the TPI 194 II also has a 0.001 Ohm resolution.   I think those are the only handhelds I have looked at that offer it.  The Gossen was by far the most stable and noise free but it comes with a price tag and added custom made shielding.  Hard to argue with the end results though. 
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #614 on: Yesterday at 10:22:13 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).


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Offline Brumby

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Re: EEVblog 121GW Multimeter Issues
« Reply #615 on: Yesterday at 11:00:58 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.
« Last Edit: Yesterday at 11:11:03 am by Brumby »
 

Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #616 on: Yesterday at 11:02:49 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.   
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #617 on: Yesterday at 03:50:00 pm »
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.
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Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #618 on: Yesterday at 06:43:25 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. 
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Online IanB

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Re: EEVblog 121GW Multimeter Issues
« Reply #619 on: Yesterday at 10:55:10 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.
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Online Dr. Frank

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Re: EEVblog 121GW Multimeter Issues
« Reply #620 on: Yesterday at 11:48:38 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
 

Offline joeqsmith

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Re: EEVblog 121GW Multimeter Issues
« Reply #621 on: Today at 12:07:00 am »
The reference current should have been 5mA, to get a stable reading as in 500 Ohm range.
I doubt they will be changing the hardware anytime soon. 
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