Re: Inductance meter?

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

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

I used to work with switched mode power supplies. One way of measuring an 
inductor was to put a square wave voltage across it, and look at the ramp 
rate of the current through it, which would be a triangle wave. Then by 
Faraday's Law (or is it Lenz's Law- I can never remember) L=V/(di/dt)

You could extend this concept to mutual inductance by putting a square wave 
voltage across one winding and looking at the current in the other winding 
(which you would short via a current shunt). What you would be measuring 
here is the leakage inductance between the two windings. I believe you can 
calculate the mutual inductance between two windings if you know the 
inductances of both, and the leakage inductance between them. I don't know 
the equation for this, maybe Antonio or someone could help us out?

Of course, you could use a sine wave drive and measure the RMS current with 
a multimeter like "normal" people do :) but the square wave drive can help 
you visualise/measure the saturation behaviour which is very important in 
SMPS work. Plus it's easier to generate high-current high-frequency square 
waves than sine waves, and multimeters often don't read HF AC too accurately.

Steve C.


>Original poster: "Jolyon Vater Cox by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
>
>Is it possible get useful measure of  self- and mutual inductance in 
>Henries or microhenries by (a) ramping a current with predetermined slew 
>rate through a coil, or (b) by  breaking a fixed current flowing through 
>the inductor  in a fixed time, by virtue of the voltage induced in the 
>current-carrying inductor, or a separate coil inductively coupled to it?
>
>Could the ping tester be amended to allow such measurents?
>
>Jolyon
>
>
>