Re: High frequency impedance of a neon sign transformer

Malcolm Watts wrote:
Hi all,
        I did some measurements on a 12kV 60mA unit last night. The
impedances I measured were somewhat higher than others I've read about
here :     f         1/2sec     full sec
         300kHz      11.5k       14.5k
         100kHz      29.8k       >50k
         10kHz       >50k
Measuring the full winding presented some difficulties as there are
several radio station antennas in the vicinity (the most powerful
is about 50kW. Grounding the case and measuring 1/2 the winding el-
iminated the fuzzies on the scope.
    Anyhow, that was a nice bit of work Ed. I should have done this
ages ago :(
Hi Malcolm,
Very interesting, I wonder why we differ by about a factor of 7 in
impedance for the 300kHz measuremt. Still, it's a lot lower than
one would get from a pure 60H inductor! (and gets lower as the 
frequency increases)

I was also thinking that the small signal impedance probes the
differential permeability for low frequencies. The upshot being
that the measurements might be different by some (small?) amount
everytime the thing is energized by the mains circuit - thus 
leaving the core on some random part of the B-H curve. This shouldn't
affect the 300kHz impedances, however.

-Ed Harris