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Problems in Measuring 200mV in audio range (AC)
Problems in Measuring 200mV in audio range (AC)
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Old 17th June 2002, 12:45 PM   #1
r_s_dhar is offline r_s_dhar
diyAudio Member
Join Date: Jun 2002
Location: Mangalore, Karnataka State, India
Default Problems in Measuring 200mV in audio range (AC)

I sat down the other day to do some Thiele-Small tests and discovered that my multimeter would not settle down to zero in the 200mV range. At first I put it down to an instrument fault.

I later discovered that I was using the multimeter very near the computer and that my DMM registers 4-24mV neary any power source!

Is it a general phenomenon or is there anything wrong with my DMM?

Please respond.
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Old 17th June 2002, 01:07 PM   #2
leroy is offline leroy
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Join Date: Oct 2001
Prevent large (pickup) loops in your measuring cables, that means: run the two wires as close to each other as possible. If you do so, and short the wires your DMM should be displaying between zero and a few mV (never trust the last digit).
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Old 17th June 2002, 06:01 PM   #3
mrfeedback is offline mrfeedback  Australia
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Join Date: Feb 2002
Location: Perth, Australia.
Default Cheap Meter Hunting

Hello r_s_dhar,
Modern DMM's have very high impedence input, and are therefore prone to EM noise pickup.
Minimising the loop area of your meter leads will help to reduce this, and loading (50Kohm) the meter inputs will reduce noise pick up.
Cheap meters will hunt even with the inputs shorted, and good meters such as Fluke are much more immune.

Regards, Eric.
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