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From: is813cs@pyr.gatech.EDU (Cris Simpson)
Newsgroups: sci.electronics
Subject: Re: Inductance Measurement (Big V)
Message-ID: <9465@pyr.gatech.EDU>
Date: 26 Oct 89 15:44:55 GMT
References: <9450@pyr.gatech.EDU> <3467@kitty.UUCP>
Reply-To: is813cs@pyr.UUCP (Cris Simpson)
Distribution: usa
Organization: VA Rehab R&D | Ga Inst of Technology
Lines: 56




>>From: jk3k+@andrew.cmu.edu (Joe Keane)

>>As long as the magnetic field in the inductor is weak, inductance
>>shouldn't change much with voltage.  You may be OK just using the value
>>from a lower voltage.

The field will not be weak, we will be looking at saturation effects.
Also the resistance is high, 30 Ohms.  (These are motor windings.)



>>What i'd do is to put the inductor in series with a small resistor, the
>>value depending on what frequency you're using.  Hook them up to a
>>sinusoidal source at the voltage and frequency you're interested in. 
>>Then look at the voltages across both on a scope, making sure you don't
>>ground something that isn't.  Given the ratio and phase angle between
>>the two voltages, you can figure out both the inductance and resistance
>>of your inductor at the given voltage and frequency.  I assume of course
>>that the capacitance is negligible.

From above, you see why this is difficult.  We don't have any frequency
generators that can push 4A through 30 Ohms.  (At up to 20khz.)




In article <3467@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
>
>	Are you referring to superimposed DC voltage, open-circuit AC
>execitation voltage, a common mode voltage, or what?  Inductors don't
>generally care about voltage, but they sure do care about *current*
>(both AC and DC), however.  Also, other considerations in selecting an
>inductance bridge are: (1) do you want to measure Q, (2) do you want
>to measure R; and (3) at what *frequency* do you want to measure?
>
>	I haven't seen any Wayne-Kerr apparatus in years.  Come to
>think of it, I haven't seen any Freed Transformer Co. inductance
>bridges in a good many years, either.
>

From above, AC excitation.   We borrowed a Wayne-Kerr, it was very nice,
with a video screen, 20A bias unit, etc.  Unfortunately, only 5v.

Any ideas now?

Thanks, cris


-- 
||   Gee, do you think it'd help if I plugged in both ends of this cable?   ||
Cris Simpson              Computer Engineer               VA Rehab R&D Center
                        GATech      Atlanta,GA
  is813cs@pyr.gatech.edu           ...!{Almost Anywhere}!gatech!gitpyr!is813cs