[Amps] Non-inductive resistors

[R.Measures]

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