On Sun, 25 Jun 2006 13:40:03 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:


The type of rectifier doesn't make a great deal of difference, although
full wave probably has the edge on accuracy. Don't put a capacitor after
it, just let the meter do the averaging, then do the sums: power = v
squared / R.

I'd be wary of this unless I knew the details of the meter. I've seen some
that can give odd results when asked to give a dc level in the presence of
much ac. e.g. One I recall seemed to only sample the input at a low rate,
so became confused as the level flutuations 'beat' with its sampling rate.

Slainte,

Jim

I reckoned that the chosen method (and prologue) indicated no great
ambition for accuracy, more a wish to get some sort of idea. Now
damping the meter movement with a big cap is fine and it will take the
ballistics out of the equation, but it will now certainly be a peak
reading meter that doesn't correspond to apparent loudness in any but
the vaguest way.

Also, I assumed that this is a real meter with a needle, not a
sampling DMM - otherwise why the question about rectifiers? It could
simply have been used on a AC range. Mine will read Watts or dBWatts
by setting an appropriate impedance in a menu.

d

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Pearce Consulting
http://www.pearce.uk.com