Measurements using field probe

From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Thursday, July 02, 1998 2:01 PM
To:  Tesla List
Subject:  Re: Measurements using field probe

  Terry, All -

  Your experiments on measuring the voltage on the TC secondary terminal are
interesting and instructive. I thought you would be interested in tests I
did several years ago to check the voltage on the Morris and Lee 250 KV Van
De Graaff generator. I got 241 KV which was close enough.  This is similar
but not exactly what you are doing.

  The VDG generator charges a terminal with DC not AC like a Tesla coil. A
charged object in space can be detected in two ways, either by the potential
it produces or by the force it produces. These tests require two different
methods and two different equations. The potential varies directly as the
distance and the force varies as the square of the distance.

  To detect the potential of the charged VDG terminal I used a 2 inch dia
brass door knob connected to an electrostatic voltmeter. The setup and
calculations are simple but electrostatic units are used which are not
familiar to most coilers. The equation is:

      Stat Volts = Stat Coulombs/cm

  This equation has the advantage that it combines the three important
parameters, that is, volts, coulombs, and distance. This equation tells us
that the charged object (statcoulombs) produces a potential (statvolts) at a
certain distance (CM). The electrostatic  potential varies directly as the
distance and can easily be found for any distance from the object with the
electrostatic voltmeter. Note that this test is not the same as the radio
field strength meter test.

  The details on using electrostatic units can be found in electrical
engineering handbooks and physics texts.

  John Couture