[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: Watt meters



Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com> 

 >My question is -
 >will this read true watts with a reactive (i.e. Tesla coil) load?

It SHOULD. These wattmeters basically multiply the instantaneous voltage and
current together, then average it, which is the formula for true watts.
BUT... All wattmeters will start to misread once the current or voltage
waveforms get distorted enough. The "crest factor" is a measure of how much
distortion the wattmeter can take before it messes up.

AFAIK, analog wattmeters are like a regular moving coil voltmeter, but
instead of having a permanent magnet, they have a second coil with the line
current flowing through it. This type should cope well with distorted
waveforms.

Some of the more modern ones have an electronic circuit but they should
still read true watts. They may be more useful since they often have a red
light that comes on to say you are exceeding the crest factor and the
reading will be garbage.

Steve C.