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On the measurement of watts (fwd)
---------- Forwarded message ----------
Date: Fri, 28 Feb 97 09:48:20 EST
From: pierson-at-gone.ENET.dec-dot-com
To: mail11:;;;;-at-us4rmc.pko.dec-dot-com-at-us4rmc.pko.dec-dot-com-at-digital-dot-com;;; (-at-teslatech)
Subject: On the measurement of watts
!> (1) Measure power input (watts, not V.A.)
!Maybe a dumb question: How do *YOU* measure watts?
Several Ways.
1) assuming the usual ac lf type input, "four wire wattmeters"
are standard devices. The have two coils, one for voltage,
one for current and measure both, simultaneously. Not cheap,
but thats one way.
2) arguably more common, esp if one has friends at the power co
are wattHOUR meters, as on your house. A used one, duly wired up,
would yield watthours, divide out the hours and there you are.
3)read watthour meter on the house with and without coil (or whatever)
operating, subtract out the 'house load' and proceed as in 2.
[nb: The meters above read TRUE WATTS, not VA. The placement of
coils internally is such as to measure IN PHASE product.]
4) various electronic 'true power' meters with a variety of
internal multipliers for getting the inphase component of E and
I and displaying it.
5) A digitizing scope, can, in general, be set up to do the math in
real time.
6) I bet there are others...
IMO, it would be real interesting and instructive to do E, I and P with a
coil just below breakout, and same coild sparking heavily.
regards
dwp