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EEVBlog 121GW Multimeter Firmware Details

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Lion_Tamer:
I had a dig through my parts bin and found a 27pF ceramic capacitor to try drift testing with tonight - so far I have only tried V1.57

Using a peak LCR meter the cap measured at 22.5pF

This time I also turned on logging (Results below). The maximum value that I obtained was 21pF with a minimum of 0.15pF in a non temperature controlled environment (probably only changed by a couple of degrees).

After the drift test I tried turning the meter off then back to capacitance mode several times, initially the read value would drop by a couple of pF before suddenly dropping to zero after which it did not seem to matter what I did with the meter it would not read any pF value for about 30 minutes.

Jem

lowimpedance:
 I would say that behaviour is consistent with my meter. Could you also cycle through the modes on that switch position, (from capacitance  through ohms etc and back to capacitance), when starting with 21 pF.
What reading do you get after the mode cycle ?.

Terry01:
Hi Joe can I ask a very beginner question? Do you use the 2 x BNC to 4mm connectors to give a more stable reading of the cap under test and eliminate the capacitance that would be in the leads if you used them? Sorry for the dumb question but I would like to learn these things.  ???

Terry01:

--- Quote from: joeqsmith on November 27, 2018, 02:17:44 pm ---
--- Quote from: Terry01 on November 27, 2018, 12:30:04 pm ---Hi Joe can I ask a very beginner question? Do you use the 2 x BNC to 4mm connectors to give a more stable reading of the cap under test and eliminate the capacitance that would be in the leads if you used them? Sorry for the dumb question but I would like to learn these things.  ???

--- End quote ---
I started out with an old VTVM and later a Radio Shack analog meter.   

The leads can interact with themselves and their surrounding environment.   Looking at extreme values of anything makes the setup more critical.  In short, I would say stability is a good word.

--- End quote ---

Cool...thanks for the explanation.  :)

chronos42:
Good to see that I am finally not the only one with this odd problem...

And to joeqsmith: You had every reason to ask, i did not belive it too after I saw this behaviour the first time.

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