Re: Van de Graaff (Toroid Design)
The physics theory is correct, however, in a small generator one can not
acheive theorectical values mainly due to imperfect terminals and corona
points on the lower pulleys, belt tracking, etc. A "k" fudge factor
(a.k.a. empirical) enters into the equation to adjust to measured values.
We have measured between 24.5 and 32.5 values for most of our machines with
28 uA per sq. inch the average value for design work.
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Van de Graaff (Toroid Design)
> Date: Wednesday, January 06, 1999 9:17 PM
> Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
> Tesla List wrote:
> > Other info for designers is, in theory, 50 uA of terminal to ground
> > is produced with every sq. inch of belt passing over the pulley,
> > in actual practice 28 uA per sq. inch is a much more reliable design
> The correct figure (and units) is 2.65 nC/cm^2, or 17.n nC/in^2,
> or 26.5 uC/m^2, for a flat belt transporting charge at one side.
> This value comes from the surface charge density that produces
> a field of 30 kV/cm: D=e0*E=8.85e-12*3e6=26.5 microcoulombs/square
> Antonio Carlos M. de Queiroz