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Re: [Amps] Non-inductive resistors

To: craxd <craxd1@ezwv.com>
Subject: Re: [Amps] Non-inductive resistors
From: R.Measures <r@somis.org>
Date: Sun, 26 Sep 2004 01:50:38 -0700
List-post: <mailto:amps@contesting.com>

On Sep 25, 2004, at 8:41 PM, craxd wrote:


Since the discussion came up about dummyloads, and I remembered about how non-inductive resistors were wound, I couldn't think of the winding type name in the last post. The type of winding used is the "Ayrton-Perry" winding. It takes two lengths of nichrome wire which seriesd will equal 50 ohms or 25 ohms each. They are wound bifilar on a form. On one end, they are connected together and the other end has the two leads. This throws the two windings 180 degrees out of phase and cancels the inductance. This would be the same as hooking up two transformer windings out of phase and killing the inductance.

Will -- This technique is okay for LF terminations, but not MF and HF.
- Also, there is no such thing as a conductor that does not have inductance.


This is exactly what is needed in the case of a non-inductive resistor. The windings would need to be spaced so they didn't contact each other along the length. The Alloy 87 I read about with 7/8 ohms per foot would be somewhat ideal for this. Something like two lengths 28-1/2 feet would equal 25 ohms each. It don't take much to wind up 28-1/2 feet of wire around a form. Every 3.8 turns around a 1" diameter form is 1 foot. Thats only 108-1/2 turns which don't take up too much space. I wouldn't see any problem experimenting with this is that alloy wire is affordable and large enough to do whats wanted.

Will Matney

Richard L. Measures, AG6K, 805.386.3734. www.somis.org


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