RE: Electrostatic Meters

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

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


I believe you are thinking of the electroscope which has two vanes that are
electrically connected. This means they will have     the same charge and
they will repel one another. They measure voltage and have extremely high
input impedance.  I show how to build a simple 15 KV electroscope in one of
my books.

A vacuum tube electrometer as described in one EE Handbook is "a direct
coupled amplifier having a specially designed grid circuit which draws
negligible grid current, and hence is capable of measuring accurately
extremely small currents". It does not have two vanes and does not depend
upon electrostatic forces.  Electrometers are also made using solid state
devices.

You are correct in that the electrostatic voltmeter does have two isolated
vanes, measures voltages, and works on the electrostatic attractive force
due to the opposite charges on the vanes.

John Couture

---------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, November 15, 2002 11:16 AM
To: tesla-at-pupman-dot-com
Subject: Re: Electrostatic Meters


Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<davep-at-quik-dot-com>


 >Sounds as if that meter has included the rectifier so it COULD measure
 >peak, and therefor would seem to need some sort of bleeder resistor
 >across it to set the time constant with which to measure the peak.
 >Diode and/or bleeder leakage would negate the main advantage of ES
 >meters - ultra high input resistance.  On the subject of ES meters I
 >looked at Bureau of Standards Circular No. 74, and found specific
 >references to the use of "electrometers" (same configuration, higher
 >sensitivity) to measure RF voltage.

          Same configuration as what?
          Classically:
                  electrometer refers to two vanes, charged
                  ALIKE, which repel each other.
                  Common class room version does not indicate,
                  but can be made to do so.

                  'electrostatic voltmeter' uses INSULATED
                  vanes, which attract....

          The later term is perhaps a bit confusing as BOTH use
          'electrostatic' effects.


 >     Either should work with a CW VTTC, where the RMS value is meaningful,
 >but wouldn't give a useful answer for the typical disruptive TC.

          RMS is always meaningful.  Its easier to understand on CW...


--
          best
          dwp

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          Vernor Vinge
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