Andre Majorel wrote:

On 2008-10-03, Reinhard Zwirner wrote:
Andre Majorel schrieb:

...
What I don't get is how, after shorting the plugs with a 2-cm
long piece of wire, switching to "Velec" mode (270 k input
impedance), switching off all monitors and fluorescent lamps in
the vicinity and going outside, you *still* get 9 mV.

I have an old (~1980) 4.5 digit true rms DMM; given accuracy for
ACV: 0.25% rd. + 20D!

300 mV AC range, input shorted - display 000.12 (mV)
300 mV DC range, input shorted - display 000.00 (mV)

Your reading could be normal for this type of DMM. What says the
manual?

This is a 4000-point meter. For AC voltages, the spec is
"+/-1.5% reading +/-1 count".

I'm not sure what "reading" means in this context. If it means
"whatever number is on the display", 1.5% of 9 mV is 135 µV so
the actual voltage could be anywhere between 7.865 mV and 10.135 mV.


Just subtract that 9 mV from your readings when using that range.
Unless the thing can be NIST or similar certification for lab work, you
are going to have to put up with it.


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