EEVblog 121GW Multimeter Issues

[malagas_on_fire]

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/

It is now outdated and a similar device is more apropriaded for this task and i believe it was rated CATIII 600.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

[Medo]

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.

[EEVblog]

Trying to recreate the 1mA DC current noise problem, couldn't do it, so 

[EEVblog]

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.

[firewalker]

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.

[PA0PBZ]

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

I have one of those, I can hook it up to a scope tonight if you are interested?

[PA0PBZ]

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.

[firewalker]

Does anyone else have this offset when in DC mA range, even with the leads shorted?

Alexander.

[Dr. Frank]

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

[Dr. Frank]

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

[Bratster]

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

[firewalker]

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.

 

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.

[Candid]

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.

[Dr. Frank]

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

[firewalker]

Did you play with the calibration function of the 121GW?

No.

Alexander.

[Dr. Frank]

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

[firewalker]

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.

[Dr. Frank]

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

[firewalker]

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.



Since I have backed up the calibration data, is it safe to play around with calibration?

Alexander.

[Seppy]

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.



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.

[firewalker]

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.



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?

Alexander.

[chronos42]

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.

[ChrisG]

hi Dr Frank, what did you use to calibrate the ohms ranges? e.g. Vishay 0.01% low ppm resistors?

[Dr. Frank]

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

[joeqsmith]

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