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Re: TC Electrostatics
Tesla List wrote:
>
> >From rwall-at-ix-dot-netcom-dot-com Sat Dec 7 00:02:49 1996
> Date: Thu, 5 Dec 1996 19:59:15 -0800
> From: Richard Wayne Wall <rwall-at-ix-dot-netcom-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: TC Electrostatics
>
> 12/5/96
>
> A Weston thermo-galvanometer was placed in series with the base of the
> TC helix and earth ground. TC Imax is at the base. The meter is a RF
> meter and the scale is 0-100 and represents I^2. The meter pegs about
> 0.25" on both sides of the 0 and 100. The meter is rated at R = 5.2
> ohms at I = 115 mA. This was a $2 hamfest buy, but a real nice meter.
> I first fired the coil at low power with 8 and 5 Amp RF thermometers
> and got no reading. Eventually I settled on the above meter. I can
> adjust TC firing by adjusting neon primary voltage. I fired the TC at
> 57 vac. Various caps and diodes were place in shunt across the meter.
> The findings are tabulated. (The square root of I is not taken.)
>
> Input 57 Volts
>
> meter only Shunt Cap -->| to grnd |<-- to grnd Blocking diodes
>
> +91 ma +4 ma +5-10 ma irreg +40 ma +91 ma
>
> There is no grossly observed increase or decrease in TC spark output.
>
> RF thermal meters are very interesting. They essentially convert all
> current, including DC up to very high RF range, resistively into heat.
> They perform a perfect resistive integration of any wave form to rms
> energy in the form of heat. This heat drives a thermocouple and hence
> the meter. The devices are very compact and usually have a very linear
> scale and fairly good response time. These meters measure + & - DC and
> all AC currents as a positive deflection.
>
> All measurements were all performed by shunting the meter. Back to
> back blocking diodes were exactly the same as the meter in series with
> the TC base. Shunt diodes positive to grnd conducted more current
> (less current through meter) than diodes negative to grnd. This
> difference in base current direction may be related to electrostatic
> emission from the top terminal.
>
> Placing a thermometer in series with the base of a TC does not appear
> to affect its performance. It automatically integrates total RF
> current in the TC base. The meter is sensitive to TC current changes
> and a "rough" running coil makes current measurements a bit irregular.
> As the coil is tuned an runs smoother the meter reflects higher current
> and measures very smoothly. This is a good instrument for experimental
> measurements and tuning a TC.
>
> I am currently conducting base "series experiments" using the same
> components. I am also putting a larger current thermometer in series
> with the primary circuit, using a current shunt of course.
>
> RWW
Richard,
This is similar to the old "hot wire" ammeters of the turn of the century
used for determining antenna current. All these gave an time averaged
current. They are indeed, very usful for tuning a system for max base
current. Peak currents, of course, are always on the order of tens or
hundreds of amps in big systems.
The key to using such thermal instruments is to keep the inducatnce of
the measuring circuit to near zero while having a slightly elevated ohmic
resistance.
Richard Hull, TCBOR