Electronics > Metrology

DMM behaviour

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donescamillo:
Hello,
I just bought an AstroAI digital multimeter (M6KOR model) about 30 pounds form amazon UK.
I set it on measuring resistance and connect the test leads to a 9V battery.
When the test leads match the battery polarity it measures 0.L, when they don't it measures 0 Ohms.
Is that the right behaviour?
I thought in both cases should be 0.L or some indication of error.
Thank you

Kleinstein:
The resistance measurement is not meant to measure a voltage source. The 9 V are more than the meter normally gets there. So it is normal to get the OL indication.
For the reverse direction it would be the wrong polarity. So one may expect a negative overflow, at lieast internally. It looks like the meter decides that a negative resistance is not right and shows 0 instead.
Also showing overflow would make more sense though.

donescamillo:
Thank you for your timely reply.
I thought so too, multimeter should treat voltage on RESISTANCE selection as an error and be consistent and show something 0.L.

tggzzz:

--- Quote from: donescamillo on February 29, 2024, 08:22:10 am ---Thank you for your timely reply.
I thought so too, multimeter should treat voltage on RESISTANCE selection as an error and be consistent and show something 0.L.

--- End quote ---

Meters measure resistance by forcing a known current through the device, and measuring the resulting voltage.

Your meter is indicating that the voltage is too high to measure, i.e. an overload "O.L.".

Decent meters won't be damaged by such overloads.

donescamillo:
I absolutely understand this, I used to work in the field long ago.
My point was that a good multi-meter would somehow indicate an error when set for resistance and sensing voltage or at least be consistent no matter how you connect to a voltage source.
I have some recalls that previous multi-meters I used would indicate 0.L no matter how I connect to a voltage source.
This one thinks it is measuring voltage disregarding that RESISTANCE is selected by the rotatory switch.
Oh, well, next one will be a FLUKE, if the better half allows it.

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