Re: Electrostatic Meters - AC not possible

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Nick, Dan, Bert, and all,

Hmm... this is getting very interesting!  A true electrostatic (ES) 
voltmeter measures the attractive force between two parallel plate 
electrodes. And, as Bert Pool indicated, the mean value of the attractive 
force between plates will be proportional to the DC voltage squared OR to 
the AC RMS voltage squared (it is a "square law" type of meter):

    F = k*e*A*(V^2)/2*(S^2)
where:
    k = relative permittivity of the insulating medium
    e = vacuum permittivity
    A = Area of an electrode plate
    S = Gap space between plates
    V = Volts (DC or Vrms)

ES voltmeters will normally measure either DC or AC RMS voltages with equal 
ease. This is covered in Bill Sarjeant's excellent "High Power Electronics" 
book (as previously mentioned by Bert Pool) but also in Kuffel and Zaengl's 
"High Voltage Engineering", Alston's "High Voltage Technology", Meek and 
Craggs, "High Voltage Laboratory Technique", and numerous other 
HV/measurement references. Unlike rectifier and peak AC meters, a typical 
ES voltmeter can accurately measure AC RMS voltages without waveform errors 
(after allowing for the capacitive loading introduced by the meter on the 
voltage source), making them ideal for AC RMS, DC, or any combination of 
superimposed AC RMS on DC below the peak rating of the meter.

The real question is why didn't Dan's ES voltmeter register the 4000 volt 
AC source if it was constructed in the fashion of a classic ES voltmeter? 
Apparently Sensitive Research must use a measurement approach that's 
significantly different than a typical ES voltmeter. BTW, a Sensitive 
Research (EIS) Model ESH ES Voltmeter (similar in appearance perhaps to the 
model Dan used) IS rated for up to 100 KVAC (or 150 KVDC):
http://www.elecins-dot-com/%21EIS3A.HTM

Very interesting... :^)

Best regards,

-- Bert--
-- 
Bert Hickman
Stoneridge Engineering
"Electromagically" (TM) Shrunken Coins!
http://www.teslamania-dot-com


Tesla list wrote:
>Original poster: "Nicholas Field by way of Terry Fritz 
><twftesla-at-qwest-dot-net>" <nick.field-at-hvfx.co.uk>
>Hi Dan,
>I have an Ernest Turner electrostatic voltmeter here which reads 20kVAC just
>fine. I believe there are several types of electrostatic meters, maybe one
>of the Bert's can enlighten us.
>Safe Coiling,
>Nick
>_______________
>Nick Field, HVFX
>www.hvfx.co.uk
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Tuesday, November 12, 2002 2:20 PM
>Subject: Electrostatic Meters - AC not possible
>
>  > Original poster: "Mccauley, Daniel H by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
>  >
>  >
>  >
>  > To prove that AC measurements using a electrostatic meter is NOT possible,
>I
>  > went into our lab today and tried measuring 4000VAC (60Hz) using both an
>EIS
>  > electrostatic meter and a Sensitive Research type electrostatic meter.
>  >
>  > For each test, the negative terminal of the electrostatic meter was
>grounded
>  > and connected to the return for the 4000VAC
>  > source.  A true RMS multimeter with a high voltage probe was used to
>verify
>  > any readings.
>  >
>  > In each instance, the multimeter read the nominal 4000VAC rms, but the
>each
>  > electrostatic meter read ZERO volts.
>  >
>  > To verify the electrostatic meters were working i switched the source to
>  > output 4000VDC and voila, the electrostatic meters both read 4000V on the
>  > nuggin' !
>  >
>  > Dan
>  >
>