RE: Magnetic quenching.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Ed -

I have tried several techniques to find the wattage of the TC without using
a wattmeter but with little success. I would be interested in hearing of
anything you may have tried that looked promising.

Years ago I saw an article describing a method that electric utility lineman
used to measure the power factor on a distribution line. The test required
only a voltmeter and power capacitor. If you had the power factor and you
knew the current (clip-on ammeter) you could easily find the wattage.

John Couture

------------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Sunday, March 14, 2004 11:41 AM
To: tesla-at-pupman-dot-com
Subject: Re: Magnetic quenching.


Original poster: Ed Phillips <evp-at-pacbell-dot-net>

"With an AC voltmeter, a series resistor and a series capacitor or
inductor,
you can measure true power, apparent power, vars, watts, power factor
etc.
It's called the "three meter technique" when measuring RF impedances.
Requires a bit of math, but these days, that's no big deal.  You want a
capacitor or inductor that has a reactance that's not too huge compared
to
the load, but also not so small that there's a lot of measurement error.
(X=1/(377 * C) (in 60 Hz lands).... Say you're looking at 1 kW loads on
120V
(i.e about 0.1 ohm).. you want a reactance that's probably in the area
of
0.01 ohm.  That would be a HUGE capacitor (1/3 Farad!), so, an inductor
is
probably a better bet.  (X=377*L)  1mH=.377 ohm, 10 uH = .0038 ohm,
which is
in the right ball park."

	OK except for the numbers. Try ~10 ohms instead of 0.1 ohm.  I thought
the "three voltmeter method" was long forgotten, and never heard of its
use for RF.  Actually, all it takes is a resistor and the load to be
measured - the reactance isn't needed. I worked out the arithmetic and
posted it here a while back.  The arithmetic is simple, and a graphical
construction works fine too.

	All this applies to LINEAR impedances.  I suspect that the results with
a TC load might be quite misleading, whereas a true electrodynamic
wattmeter is quite accurate.

Ed