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Accuracy Claim on test instrument

Accuracy Claim on test instrument

Accuracy Claim on test instrument

(OP)
I have a new digital ohmmeter that claims an accuracy of 2%+-2digits on the 20ohm scale (19.9). The resolution is 0.01ohms.
Does this mean that a reading of say 0.4ohms could be 0.18 or 0.62 resulting in a deviation from the measurand of circa 55%?

Regards,

Lyledunn

RE: Accuracy Claim on test instrument

I would say it could range from 0.4*1.02=0.41 + 2 digits = 0.43 on the top end to 0.4*.98=.39 - two digits = 0.37.  So 0.4 ohms could show up on the meter as anything from 0.37 to 0.43.

RE: Accuracy Claim on test instrument

That would depend on whether the specification is 2% of FS or 2% of reading.

TTFN



RE: Accuracy Claim on test instrument

Well, if it was 2% of full scale, a resistance of 0.4 ohms could read anywhere from 0 to 0.82 ohms.  I would hope that it would be 2% of reading, but who knows?

RE: Accuracy Claim on test instrument

(OP)
Yes, thanks David, as pointed out by IRstuff there is ambiguity in the claim. My little knowledge of error theory recalled that accuracy is referenced to f.s.d. However, I read an article in a trade mag that alluded to the almost proposterous margin of error in some instruments designed for field work. I have of course asked company to clarify.

Regards,

Lyledunn

RE: Accuracy Claim on test instrument

Just as a general comment, 0.4 ohm should NOT be attempted on a standard ohmmeter.  The probe contact resistance is a sizable portion of 0.4 ohm.  You should and must use a micro-ohm meter or a Kelvin connection for measurements that low.

TTFN



RE: Accuracy Claim on test instrument

IRstuff you can use a standard meter with acceptable accuracy if you ZERO it on one side of the unknown.  That works very well.

RE: Accuracy Claim on test instrument

True, if you've got a zero function winky smile.  And, if you remember to set it back to zero every time you use it.  None of my DMMs have that particular feature.

TTFN



RE: Accuracy Claim on test instrument

You should get a meter made this century.  You know... the kind without a needle.

laughtears





Actually I have to teach my daughter about magnetic fields verses current and wish I had a needle based meter Now....

RE: Accuracy Claim on test instrument

I'll assume that you missed the "DMM" winky smile

TTFN



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