[sdiy] How much DMM accuracy do you need?

[David Ingebretsen]

One must not confuse precision with accuracy. The meter might read 5.1234
volts, great precision, but if the voltage is really 6.4321 volts, not
accurate. 

Also, the relative accuracy can be important, too. Nonlinearities, loading
due to input impedance, etc. can affect the absolute and relative
accuracies. If you are tuning a VCO, the relative accuracy is probably much
more important than the absolute accuracy.

Most (all?) higher end meters offer a model at modest higher cost that is
traceable to NIST. That sort of traceability is probably critical only for
forensic, government contracts, and some commercial applications.

In the DIY stuff we do here, how often have you seen a test point voltage to
any higher precision that 1 decimal point or an accuracy greater than about
0.5 volts? The inexpensive Radio Shack meter is fine.

The only time I think 4 decimal point precision and sub-milivolt accuracy is
needed is in tuning a VCO etc. by instrument. For guys like me who are
musically challenged (I know, a weird hobby for one with little musical
talent/skill) it's the best (maybe only) way to tune. For this, you need a
high count meter that will give you sub-milivolt precision and accuracy in
the +/- 5.0000 volt range.

As I said before, I love my Extech MM570 meter. 50,000 count, gets to
sub-milivolt accuracy/precision, rugged, and not too hard on the pocketbook.



David

David M. Ingebretsen M.S., M.E.
Collision Forensics & Engineering, Inc.
2469 East Fort Union Blvd. STE 114
Salt Lake City, UT 84121
www.CFandE.com

801 733-5458 Office
801 842-5451 Cell

dingebre at CFandE.com
dingebre at 3dphysics.net