Re: Vortex gap loss measurements

["Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Tesla list wrote:

> Original poster: "Malcolm Watts" <M.J.Watts-at-massey.ac.nz>

> The linear decrement of a ringing RLC circuit which has a gap
> in series with it was discovered by Stone circa 1914. The
> Corums mention it in their literature but unfortunately never
> went on to use the information in their modelling. The linear
> decrement is entirely due to the gap characteristics. An RLC
> circuit by itself produces only a logarithmic decrement. This
> clearly shows that modelling the gap as a resistancwe does not
> work. You cannot apply the classic time constant equations to
> this situation. The gap is dissipative but that is where the
> similarities with resistance end. I analysed this and wrote a
> note on it several years ago. It is important to note
> (ultimate pedantry) that you *cannot* ascribe a value for Q to
> the primary if the primary includes a gap. You can compare
> various primaries with each other by comparing the ringdown
> slope (gentler is obviously better).

Note that unless the primary losses are very high, you can
approximate exp(-a*t) as 1-a*t with great precision for the
time used for complete energy transfer to the secondary (the
intial value and the first derivative fot t=0 are identical). 
The transfer takes just a few cycles, and modeling the gap as a linear
resistor during this time, if the main difference is that the decay 
is linear and not exponential, doesn't make significant difference.
("a" would be Rgap/(2*Lprimary) if you consider only the primary
circuit. Considering the secondary, there are two time constants
in the system, a compliated function of the element values and
losses in the entire circuit.)

Antonio Carlos M. de Queiroz