Re: [TCML] NST Measurements

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Voltage is misleading. We should call out "input current" and not input 
voltage. From zero current up to a level that begins to increase 
permeability is not all that high with NST's or MOT's. This is important 
for turns ratio measurements. Even with the 15/30 I measured, the low 
10V range measured the winding ratio correctly at 125 matching the rated 
Vout/Iout, but go to 20V, and the change in core permeability begins to 
alter the "expected" value (and gets worse as current increases).

This is why I mentioned previously to look at turns ratio at a "low" 
voltage (so that the current is low). If you try to use a higher voltage 
to look at turns ratio (say on an unidentified transformer), it wouldn't 
be too difficult to cause a high enough current that would alter the 
"real" turns ratio and thus affect inductance calculations forward.

Turns ratio should be measured (IMHO) when flux density has not yet 
scared the permeability of the core. A very low voltage is best for this 
value since this value determines inductance ratio.

Regards,
Bart

Ed Phillips wrote:
> Correct.  Common mistake.  Answer is "look at the B-H curve" for core 
> material.  Permeability is constant with flux density starting from 
> zero primary voltage up to some level at which it increases with 
> increasing flux, eventually decreasing as saturation is approached.
> Ed
>
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