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Re: Calibrating E-field probes by simulation?

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 04:12 PM 4/4/2005, you wrote:
Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Steve,
           Needless to say, measurement of TC output voltage has
occupied my mind for many years. I do have a suggestion:

On 4 Apr 2005, at 8:48, Tesla list wrote:

> Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>
> Hi all,
> I was just thinking about ways of measuring the output voltage of a
> coil. E-field probes like Terry's planar antenna are a nice solution
> but the problem is how to calibrate them. It struck me that if you
> were to use a probe with an easily modelled geometry (a small toroid
> or sphere?) then the calibration could be done using a finite element
> modelling program like FANTC.
> Anyone have any thoughts on this?

Why not simply hook a known voltage source (e.g. a stiff 50Hz HV
transformer) to the sphere on top of a resonator in situ? Without
resonant effects to upset the output voltage calibration it should be
easy to physically measure both directly and by capacitive coupling.
In fact I see no reason why 5kHz or even 50kHz couldn't used as long
as the frequency is well below the self-resonant frequency of the
coil. I do like the idea of modelling but think that it _must_ be
verified by measurement no matter how solid the reasoning. I have
reason to suspect that unverified modelling is behind problems we
have found with hypotheses promoted by other researchers ;)


> Steve Conner

The problem is that you won't get the right electric field distribution along the secondary itself. What you really need is to cover the secondary with some sort of semiconductive layer (antistatic foam?). You'd want to duplicate the voltage distribution along the secondary. If the probe were in a suitable position (above the topload, looking down?) the deviation from a nice linear voltage change along the secondary (which is what the resistive approach will give you) should be small.