EEVblog 121GW Multimeter Issues

[tsman]

There is fluff and dirt under the LCD It is under the plastic shield so it doesn't look like it is possible to get in there easily to clean it. Turning on the backlight shows up the big speck of dirt. Can't unsee it now!

[Seppy]

Voltage measurement DC + AC  Auto-range loops forever

David DLC

Regarding this issue and the resistance/capacitance issue do you have some specific values that you have found produce the auto ranging loop. I have experienced that loop before but cannot get it to happen under controlled conditions.

[tsman]

A few times now, I've touched the screen with the meter off and a few random segments turned on briefly. Static electricity?

[Seppy]

Voltage measurement DC + AC  Auto-range loops forever

David DLC

Regarding this issue and the resistance/capacitance issue do you have some specific values that you have found produce the auto ranging loop. I have experienced that loop before but cannot get it to happen under controlled conditions.

You can try these.  Looks like others are seeing it now as well.
https://youtu.be/RgzBC40gCoY?list=PLZSS2ajxhiQDBDdtQNjVnGxShaVQ3nUMY

Thanks joe! That seems to reproduce, has anyone been able to reproduce the resistance auto-ranging bug, it seems difficult to isolate.

[Muttley Snickers]

You can try these.  Looks like others are seeing it now as well.
https://youtu.be/RgzBC40gCoY?list=PLZSS2ajxhiQDBDdtQNjVnGxShaVQ3nUMY

I haven't been following this meters progress nor read all of the associated threads and I don't know if this has been mentioned previously so please forgive me if it has. I am aware that the meter Joe Smith was testing in the video linked above was a pre-production model and that the current version may perform in an entirely different manner.

Anyway, at 2:59 in the video with approximately 20 volts applied and whilst manually cycling through the ranges the meter displayed 20.62 volts then 206.2 volts, the applied voltage was exactly the same but the decimal is in the wrong location, can somebody else please confirm what I saw and if it has been mentioned already then I will delete this post.

Edit: Added images below for reference.

[Seppy]

I haven't been following this meters progress nor read all of the associated threads and I don't know if this has been mentioned previously so please forgive me if it has. I am aware that the meter Joe Smith was testing in the video linked above was a pre-production model and that the current version may perform in an entirely different manner.

Anyway, at 2:59 in the video with approximately 20 volts applied and whilst manually cycling through the ranges the meter displayed 20.62 volts then 206.2 volts, the applied voltage was exactly the same but the decimal is in the wrong location, can somebody else please confirm what I saw and if it has been mentioned already then I will delete this post.

I imagine they know it's a pre-production meter.   

I am not aware of a way to display the firmware version.  I have never attempted to update this one as there is no mention of a way to back it up.  It would be prior to 1.00 as there appears to be no support for exporting  the calibration data.  It does however give them one more data point if they suspect the firmware.

Newer versions of the firmware show the version when the multimeter boots.

[Dr. Frank]

Hi Seppy,

I have finally summarized the errors / gaps of the latest manual, 9th July,  see doc file.


During these investigations, I found a malfunction of the DC burden voltage item.
When I initially toggled to bd.on in any DC A range, the burden voltage display wouldn't appear, even not on the mobile via BT.
Only after I once engaged bd.on in AC A mode, it directly functioned there, and afterwards, also in DC A mode, permanently.
Seems to be a missing initialization flag in the 1-22 firmware.

Frank

PS: I'm still investigating on the spurious instability of the 5M and 50M ranges..

[dcac]

For the auto hold when measuring resistance,  I had tried various values from 10ohms to 10M and it seems to work as I would expect.

Thanks for checking, if I remember correctly your pre-production 121gw is about the same in Auto ranging speed as FW 1.22 so the speedup work might not be that related to Auto Hold not working anymore.

I've done some further testing on FW 1.22 and what's strange is that it seems to select the correct range as I can see Mohms, Kohms and decimal point changes but the value it displays is totally wrong.

[DavidDLC]

A few times now, I've touched the screen with the meter off and a few random segments turned on briefly. Static electricity?

My problem is with some resistances and a capacitor connected. It is not a simple RC and unfortunately I cannot share the schematics.

But it takes time for the capacitor to charge and then to get the resistance value, the circuit is slow.

David DLC

[bicycleguy]

Hi Seppy,

I have finally summarized the errors / gaps of the latest manual, 9th July,  see doc file.
...
Frank

Frank, thanks for the detailed look, everybody complains about poorly written manuals but nobody helps to fix.
Glad you weren't my technical writing teacher back in the day.

Another minor quibble:  page 61 Multimeter ID  The ID entered appears to be appended to another mystery number in the log files.  Mine is 1708

[DavidDLC]

Fw. 1.22

I think auto-range should not mess with the decimal point, just get the correct range (without moving the decimal point) and just show the final value.

There is an issue when the DMM is in the infinite auto-range loop and you read the memory values, the decimal point moves because the auto-range is handling it

David DLC

[Seppy]

Hi Seppy,

I have finally summarized the errors / gaps of the latest manual, 9th July,  see doc file.


During these investigations, I found a malfunction of the DC burden voltage item.
When I initially toggled to bd.on in any DC A range, the burden voltage display wouldn't appear, even not on the mobile via BT.
Only after I once engaged bd.on in AC A mode, it directly functioned there, and afterwards, also in DC A mode, permanently.
Seems to be a missing initialization flag in the 1-22 firmware.

Frank

PS: I'm still investigating on the spurious instability of the 5M and 50M ranges..

Awesome, thanks for that, I have made suggested changes (well most of them).
I'll upload the new version soon, but we are expecting some new firmware so I'll release the new manual with that so the new firmware changes are in the up-to-date manual.

- I haven't added the period specifications yet, I want to make sure there wasn't a reason I didn't put it there in the first place
  (likely there was something ambiguous and in the rush I didn't note what it was).
- Haven't made RMS to pp change yet, and I won't until I figure out why it was RMS in the first place (although I agree it makes more sense to have pp).
- For frequency: I don't think offset is calibrated, only gain.

[Digital Corpus]

A few times now, I've touched the screen with the meter off and a few random segments turned on briefly. Static electricity?

I noticed that when I took off the protector. I put it back on and reduced it again to confirm and yes, the LCD does show to ‘illuminate’ certain elements with a discharge like that.

[Dr. Frank]

- For frequency: I don't think offset is calibrated, only gain.

Of course you're right.. I was completely confused, that Frequency even showed up in this list, and by the term 'Factory Calibrated'

Anyhow, as LowZ does not require any calibration at all, i.e. also no offset calibration, you simply might take both modes out this list.

And it's not clear from the table on page 69, whether capacitance needs any Offset alignment.

Thanks for all your effort,
Frank

[thals]

+1 for proper bug tracking system, it's not easy to look for already reported bugs in 14 16 pages of thread.

FW 1.22:
Resistance Measurement, Auto Range: If measuring a resistor while the meter is auto ranging (= disconnect probe tip shortly in resistance measurement), an intermittent wrong measurement (near 0 Ohm) is shown. This happens only in approx. 20% of the measurements.
E.g. (6R8 Resistor): Auto Range -> 0.0002 -> Auto Range -> 6.801

Very rarely (5%) it shows a measurement value with less digits, resets to zero and ranges again.
E.g. (6R8 Resistor): Auto Range -> 6.80 -> 0.00 -> Auto Range -> 6.801

[Zucca]

https://blog.github.com/2009-04-15-github-issue-tracker/

[firewalker]

Who is addressing the bugs? The maker?

Alexander.

[npelov]

Is there any indication thatmultimeter is in peak-detect mode? Manual doesn't sayanything about peak detect. In which modes/ranges it is available? Howdo I know if it's turned on or off?

[npelov]

The braymen probes are nice but not perfect. So eone has tightened the banana addons to mine a bit too hard. When I tried to remove it one of them was rotating without unscrewing. Which means that there is no flat spot or anything preventing the metal pin from rotating and twisting the cable inside. That could lead to problems.

[Seppy]

- For frequency: I don't think offset is calibrated, only gain.

Of course you're right.. I was completely confused, that Frequency even showed up in this list, and by the term 'Factory Calibrated'

Anyhow, as LowZ does not require any calibration at all, i.e. also no offset calibration, you simply might take both modes out this list.

And it's not clear from the table on page 69, whether capacitance needs any Offset alignment.

Thanks for all your effort,
Frank

Oh your right, I've removed LowZ, I've also removed capacitance until I can figure out what R1 is...

[firewalker]

The spring for the battery terminal are to long. No need for it.

Alexander.

[Zucca]

The 50M Range issue is also reported in a review:

https://www.eevblog.com/product/121gw/#tab-reviews

Kellee Crisafulli – July 21, 2018

2018-07-20, I was pleased to received my 121GW a couple days ago, first reaction is very cool 🙂
I plugged it into a Tektronix 515A meter calibrator to run a fast out of the box accuracy check.
Tested AC volts at 400hz, 1KHz, 50KHz, 1V to 100V, appeared to be within stated accuracy.
Tested DC volts 25uV to 100.0V and appeared to be within stated accuracy.
Test Ohms from 0 to 1MEG appeared to work OK.
10 Meg Ohms looks a bit “wonky” reading ~9.7 Mega Ohms +- 200K depending how I hold the cable, position of my hands, and if I blink or not (kidding). Other handhelds and my bench meter indicate very close to 10.00 Meg no matter which way I hold the cable.
As Dave might say “That’s a fine how do you do”, seriously something on the 10M scale appears to have a noise issue, not a show stopper but interesting…
That’s all the testing I have done so far.

https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1687298/#msg1687298
Dr. Frank and IanB you are not alone.

[Medo]

Any chance of detecting lower than 12V on Low Z mode in the future firmware upgrade?

Other multimeters I've tried this mode with (Agilent U1232A, Fluke 117, and Brymen BM235), work regardless of voltage. 121GW, if I use LowZ with under 10ish volts, just shows 0.00 (tested with alkaline and LiIon battery). At first I thought this was a mechanical failure but then I noticed here that other people have the same issue.

I find that measuring batteries with some load (i.e. in low Z mode) - especially 2032 and smaller ones - actually more realistically shows their state while measuring them with high impedance often results in normal 3V reading even for the ones dying.

PS: Tested with firmware 1.21

[Zucca]

AC+DC Mode while measuring 230VAC Mains do not shows anything to me: autorange goes in loop?

 

[npelov]

Is the 50MOhm range slowing down the resistance measurement? Maybe it should be removed from manual range and should only be accessible via manual ranging.