In article ,
Ian Stirling writes:
Andrew Gabriel wrote:
I bought one of the current Maplin ones, and I think that might
not be too bad. I'm having trouble getting my proper true power
meter back from someone I've lent it to (my boss;-), so I haven't
been able to do a real check on the Maplin one.

What's the name, I've forgotten the name of mine, IIRC began with
a b, and was german.

Yes, that's the crap one which is way off -- I think the model was
PM230. The one Maplin stock now is a different make and I can't
remember what it is (nothing well known though, but it is Asian
not German).

I bought one of the older ones Maplin stocked a few years ago,
and that's hopeless on non-resistive loads (out by a factor of
3 on SMPSU's -- too high, which is a puzzling way for it to be
in error).

If it does not sample fast enough, then it may well overestimate
current consumption.

Yes, I guess if the spike width at the voltage peaks is small
compared with the sampling rate (hello Mr Nyquist;-) and the
sampling is somehow always catching it (prehaps due to synching
with the voltage waveform), then that would account for it.

--
Andrew Gabriel