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EEVBlog 121GW Multimeter Firmware Details
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chronos42:
Hi joeqsmith,

I can repeat this and get the same result every time.

Now with a 0.39 nF NP0.

DE EE 5000: 392.6pF @ 10kHz

121GW (Firmware 1.57) : 0.316nF.
The meter is about 80pF too low in the lowest range, capacitors lower than 81pF are shown as 0.000.

Unfortunately I don't know from which Firmware on the problem started, maybe I have lost a small part of the calibration. The other ranges are spot on as mentiond before.
Seems that I am the only one whith this problem?
chronos42:
Hi,

I did some more tests and found that this seems to be a problem only for my 121GW, it has nothing to do with the firmware.
My meter reads about 80pF too low in the lowest capacity range. It does this also with firmware 1.26 and the original calibration data, saved on the SD card.

Update:
After I have played with different firmware versions, I went back to 1.57, restored the original cal data again and made a new offset correction for all current ranges, because there was a large offset since firmware 1.5X.

And now the low capacity range works, it is only off for some pF.

WHAT???  :-//

This is really strange, I have no idea what happend, something in the calibration seems to be mixed up by some firmwareupdate in the past.
CDaniel:
It is not working reliable for small capacitors , sometimes a remanent value of 20-60 pF remain on display . Disapear only if I switch to resistance and back .
I assume this can be negative as well but you can't see it ( below 0 ) and substracts from real value , sometimes I can get -80pF lower reading like in your case .
chronos42:
Hi CDaniel,

thanks for the answer, so it seems I am not the only one with this issue.

Update:

I could repeat this behavior.
100pF capacitor:

I switched on the meter, it showed 0.100 nF, first time spot on!
Switching off and on again, now it showed 0.082nF.
Switched to Ohms an back to capactity: Now it showed 0.021nF, after switching off and on again sometimes 0.014nF, sometimes 0.021nF, but never again 0.100nF.

Does the 121GW only one time per day show the correct value in the pF range?... :-DD
CDaniel:
If I just put the fingers on buttons the value is changing by ~60pF ... so about what precision we are talking about ?  :-\
Measuring a precision capacitor the displayed value is drifting in time (10min) by at least 50pF .
This is again a problem with AC noise , like it was in resistance mode ( now resolved )

The behaviour can be somewhat different because everyone's lab is different , probably even the spot where it sits counts ...
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