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DMM problem in DC millivolts range
amir.razzaqi:
Hello guys
I have a Victor VC97 DMM than has an odd behavior in millivolts range. when the millivolts(DC) range selected and while the probes "OPEN ON THE AIR" then numbers showed on LCD start continuously increasing automatically. It sets to Zero when probes contact each other and measure millivolts correctly as well.
does this annoying behavior related to any problem?
Thanks for reading
EEEnthusiast:
This is prefectly Ok. This happens due to the noise pickup by the leads. Try to twist the red and black cables together and the problem will reduce. The best way to test the residual voltage is to short the two cables together and then measure the voltage. Remember that an open circuits is not the same as Zero voltage.
amir.razzaqi:
Thank you for reply
by the way twisting probes to each other did not change anything. how ever touching probes head by two hands change the numbers and speed of changing.
amir.razzaqi:
the video of this DMM:
https://www.youtube.com/shorts/Dy-N1WPPqag
2N2222A:
There is some very small leakage current that is causing the Voltage to slowly rise. In the higher ranges there is a resistor divider that guarantees an impedance of usually 10M ohms. In lowest mV range it may be connected to the ADC through a 1M ohm resistor with no other resistor to give it a stable impedance.
You can measure the impedance of your meter using another meter at the 20M ohm test range.
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