Author Topic: Weird behaviour of BK Precision 2709B in capacitance measure mode  (Read 1701 times)

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Offline SchorschTopic starter

  • Newbie
  • Posts: 3
  • Country: ch
I recently got my first decent DMM after watching the 100$ shootout video and decided on the 2709B. It works perfectly fine but seems to have a quirk.

I tried the capacitance mode with 8 identical 1mF 50V electrolytic capacitors and the display would first say O.L. then jump to about 0.8mF and after another second drop down to 40?F. Then it goes to O.L. again and back to 0.8mF and it keeps repeating that cycle.

I tested all 8 capacitors with the included probes and some extech probes and behaviour was the same. But only some of the time. It seemed that sometimes the orientation of the meter affected the stability of the measurment. So naturally I assumed the meter was busted and promply ordered a replacement from Amazon only to find that the new one behaves the same way.
From that I excluded the meter, the caps and the probes as cause of the issue and fiddled around with my physical setup and found the following:
Whenever there was some distance between the cables of the probes the measurment becomes unstable and when taped or wound together the measurment is rock solid.
I figure the capacitance of the cables themselves must have something to do with it but the capacitance of only the leads varies between 30pF and 50pF depending on distance.

Now that I know the cause of the problem I can avoid it, nonetheless it seems odd. Is this a common occurence? And what may cause it?

 


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