RE: 37XR inductance range

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Carl Litton" <Carl_Litton@xxxxxxxxxx>

Mike,

Most inductance meters are not capable of 
accurately measuring the inductance of an iron 
frame inductor.  The small (~5V) current they 
produce is not enough to fully magnetize the core 
and the reading will be low.  These meters appear 
to be fine for air core inductors.

Another list member, Finn Hammer, recently 
pointed this out to me.  The correct way to 
measure an iron core inductor is indirectly by 
observing the actual current flow.  A Variac is 
connected across the inductor with an ammeter in 
series with the circuit and the voltage slowly 
increased to a value sufficient to fully 
magnetize the core.  The current reading on the 
ammeter plus the voltage from the Variac is then 
used to calculate the inductance, using 
L=V/ùI  (on 60 Hz circuits = Voltage divided by 
377 times the current in Amps gives the inductance in Henries).

The core magnetization issue is probably at the 
root of your measurement inconsistencies.

Hope this helps.

Carl Litton
Memphis HV Group



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Friday, January 06, 2006 11:07 AM
To: tesla@xxxxxxxxxx
Subject: 37XR inductance range

Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>

I recently purchased the Meterman 37XR per the list members favorable
use. I was just measuring the inductance of my variable ballast, and
a few hig power isolation xfmr I have laying around. One measured 365
mh. When I changed ranges to henrys, it dramatically changed to
0.260H ! Does anyone else notice this vast discrepincy? Can I trust the meter?