Re: HV Meter

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

Original poster: "Nicholas Field by way of Terry Fritz <twftesla-at-qwest-dot-net>" <nick.field-at-hvfx.co.uk>

Electrostatic meters will read pretty true rms on ac and dc whatever the
waveform or frequency.  They are also very tolerant of overvoltage events
(up to a point) and generally wonderful things.  You may have to de-rate the
meter by 1/(sqrt.2) to keep the peak voltage below 4kV, although many of the
one's I've used are built well enough to take the overvoltage from reading
AC.

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: Saturday, November 09, 2002 3:33 AM
Subject: Re: HV Meter


 > Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<evp-at-pacbell-dot-net>
 >
 > Tesla list wrote:
 >  >
 >  > Original poster: "Mccauley, Daniel H by way of Terry Fritz
 > <twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
 >  >
 >  > The meter is labelled as being electrostatic:
 >  > 1) Am I correct in assuming that this means that it's DC only?
 >  > 2) If (1), would an MO diode and capacitor make adequate rectification
for
 >  > it?
 >  >
 >  > Yes, any typical rectifier configuration should work as long as your
 >  > components are rated as such.
 >  >
 >  > 3) Would I be reading peak or RMS with such a half-wave arrangement?
 >  >
 >  > Neither.  I believe half-rectified with large filter capacitor will
read :
 >  >
 >  > Vout = Vpeak / 3.14
 >  >
 >  > For full wave rectification with large filter capacitor will read :
 >  >
 >  > Vout = (Vpeak * 2) / 3.14
 >  >
 >  > As you can see, it can be very difficult to implement an analog circuit
 >  > capable of getting
 >  > true RMS measurements.
 >  >
 >  > Basically you need to take the absolute value of the signal, square
that
 >  > signal, and simulatenously integrate
 >  > that signal over one period.
 >  >
 >  > Of course, you could always use just a single diode and capacitor and
make a
 >  > peak detector.  The output voltage
 >  > of this type of circuit would be the peak voltage - forward diode
voltage
 >  > drop (plus any ripple on there)
 >  >
 >  > Dan
 >
 > 1. The DC value of a rectified sine wave is about Vrms * 1.4 (square
 > root of 2).  If there is no load on the circuit it doesn't matter
 > whether a half-wave or full-wave rectifier is used.
 >
 > 2. The force-balance electrostatic voltmeters I have used respond to AC
 > as well as DC; since it's a panel meter I suspect that is what you
 > have.  I don't know whether they read average or rms voltage in ac
 > measurements, but wouldn't be surprised if it were the latter.
 >
 > 3. In looking on the web I find that there are other gadgets called
 > electrostatic voltmeters which uses principles other than the classic
 > force balance (field mills, for example) and suspect they have peculiar
 > responses to AC.
 >
 > Ed
 >