Re: Pythagorean Idea for Inductance Meter?

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

This is kind of how some of the older impedance bridges work.  These days,
they digitize everything and use a microprocessor to do the math.  You can
get a more than powerful enough micro and display to do this sort of thing
for around $50...(it doesn't need to be a ball of fire, speed wise..)
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, November 10, 2002 11:58 AM
Subject: Pythagorean Idea for Inductance Meter?


 > Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 >
 >
 > For the purpose of measuring the inductance of the windings used in TCs ,
 > is it possible (and economical) to design a meter for true inductance
using
 > Pythagorean principles -based on fact that the AC voltage across a coil
 > with no resistance is proportional to the AC current alone?
 >
 > I envisage using two opamps (wired as squarers) to register voltages
across
 > L the test inductor and a reference resistor R connected in series across
 > an AC supply
 >
 > the squares of the two voltages would be subtracted in a difference amp
 >
 > then square-rooted (by an opamp with a squarer in the feedback loop) to
 > give the voltage component due to inductance alone; the latter would be
 > displayed on a meter as a measure of the inductance.
 >
 > Is this method as simple as it sounds or more complicated in practice?
Does
 > anyone have a schematic for such a circuit?
 >
 >