"Those extra digits on your meter may be meaningless."
They may be meaningless or they could be very useful. Finding a peak or null,
or looking for any small amplitude change, does not require absolute accuracy
but high resolution can be useful.
"A freebie Harbor Freight digital voltmeter appears to have a helluva lot
better accuracy than reality."
What is important is knowing what you want to measure and how useful your
instrument is for making that measurement. For example I have an LP 100A ,
spectrum analyzer, and a digital storage scope but the multimeter I usually
use is a freebie from Harbor Freight. I have quite a few of these and
measurements are remarkably consistent between meters. The only one I found to
be bad had a very interesting anomaly. The display acted as a photo cell and
skewed the readings if used in direct sunlight! Indoors it was as good (or
bad) as all the others.
A mistake many seem to make is to assume that something that is calibrated is
therefore accurate. Typically a calibrated instrument is only as good as the
manufacturer's specification. A 20% instrument is still a 20% instrument even
if it has a current calibration certificate. What calibration does is weed out
the instruments that no longer meet the manufacture's specification and brings
them back to that specification level.
It used to wind me up that at work I was required to use a DVM with a current
calibration certificate to check whether a signal was in asserted or non
asserted state. Any instruments that were not in calibration were routinely
rounded up by the metrology lab police. Few instruments suddenly change their
properties on the day the calibration certificate expires.
Andy k3wyc
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