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Old 3rd February 2009, 03:58 AM   #1
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Default Testing Resistors for inductance ?

How would I test a resistor to determine it's inductance ?

I have some wirewound types, that I think are non inductively wound, but I'm not sure.

=R=
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Old 3rd February 2009, 04:01 AM   #2
PH104 is offline PH104  United States
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just came across this gizmo........

http://www.electronics-diy.com/lc_meter.php
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Old 7th February 2009, 05:29 AM   #3
Cliff45 is offline Cliff45  United States
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FWIW, I would think that trying to measure the actual inductance of a wirewound resistor very accurately would be a rather difficult endeavor indeed. Even the ones that are not expressed to be the "non-inductive" types often have inductance down in the single-digit nH range when well-constructed. Maybe someone else has a better opinion on this, though....

I do like the looks of that little DIY tester in the link given by ph101 above, but I think they could have used quite a better connector for the device under test, IMO!

Here's an interesting quote from the Stackpole Electronics website-

Quote:
Wirewound technology has long been known as a leading technology for power resistor needs though it is inherently inductive. By using a non-inductively wound version this greatly reduces the inductance of any given resistor size and value combination; however, it does not completely eliminate the inductance. A non-inductively wound wirewound has one winding in one direction and one in the other direction; known as Ayrton-Perry winding, and a byproduct of this design is that it creates two resistors in parallel in each device. Because of this, non-inductive wirewounds have an upper resistance range limit of half the value possible with a standard winding.
Now I have a new term to use someday, "the Ayrton-Perry winding"

HTH-
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Old 7th February 2009, 05:38 AM   #4
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If you have a network analyzer it's rather easy -- you plot output vs frequency for a given load and le voila...but you generally need a network analyzer which goes out to a few megahertz.

Inductance in a source or emitter resistor isn't a bad thing, to quote the orange-suited non-recidivist criminal of Greenwich CT.
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Old 8th February 2009, 04:59 PM   #5
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The old GR 1608 LCR bridge had three little knobs at the bottom for balancing the Q of resistors. From that it's easy to calculate inductance. Or, a vector impedance meter will do the job nicely. The old HP units are easily available, but the probes come very dear. To set up something simple on the test bench, maybe just make a divider between a known low inductance resistor, say a film type, and the DUT. Drive it with a signal generator and look at the junction with a scope. As the frequency rises, you'll see an error in the divider ratio. Calculate from that. Since we're talking small values of inductance here, stray L or C will be a big factor so the layout and ground plane will be important.
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Old 8th February 2009, 05:08 PM   #6
HK26147 is offline HK26147  United States
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redrabbit:
The Woofer Tester 2's will measure impedance and phase continuously from 1 to 20 kHz.
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Old 9th February 2009, 02:54 PM   #7
infinia is offline infinia  United States
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Difficult to measure ie mid VHF band. Sometimes if you examine the part closely you can see both winding of a non inductive type. If not.... it's cheaper/time wise to buy a known source.
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Old 9th February 2009, 04:34 PM   #8
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Quote:
Originally posted by HK26147
redrabbit:
The Woofer Tester 2's will measure impedance and phase continuously from 1 to 20 kHz.

Make sure you have the most recent software update for the WT-2.

Conrad --- you guys defrosted up there?
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