Re: Calibration

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Matthew,

At 07:44 PM 4/20/2003 +0930, you wrote:
>Hi All
>
>I have a couple of electrostatic voltmeters, the latest being a 5kV model 
>built back in 1944 - beautiful instrument in a wooden case.  I also have a 
>3.5kV insulation tester.  All ex-armed forces stuff and in nice condition.
>
>However, I have no idea as to how accurate these are and would like to 
>calibrate them.

I am not sure things like this go out of calibration...  It is sort of like 
calibrating brass weights every year...  Unless something is obviously 
damaged, there is nothing to go wrong...


>The only "modern" instrument that I have is the "Coilers' Pal", a Wavetek 
>27XP digital multimeter.  Although it's limited to a measly 750V on the AC 
>range, I have some seriously meaty HV resistors with which I can do a 
>"divide by four".

Probably you mean mean "XT" If it says "XP" it has a many big software 
problems :o))  That should work fine.  At <5kV and 60Hz, such a setup 
should be very accurate.  Be extra careful to get everything hooked up 
right the "first time" ;-))


>Just how accurate would the Wavetek be, if I were to use it to calibrate 
>the other instruments?  My guess is that, for my purposes, more than adequate.

Measure the values of the resistors first and use there "actual" values in 
your divider calculations.  Then the accuracy of your measurement will 
approach that of your meter.


>Has anyone done any comparisons between the Wavetek and "the really nice 
>machine at work" (whatever that might be)?

They are 0.5% meters but probably far more important is that they are NOT 
"true RMS".  So if an AC sine wave is distorted, the voltage reading will 
be technically off some.  I would actually trust you older voltmeters more 
than the 27XT if the readings are different.  You would probably need a 
fancy digital scope and high voltage probes to really figure out where any 
difference lies.  I worry a bit since I don't know if you insulation tester 
is going to put out a nice sine wave.  However, chances are very good all 
the meters will agree very well with each other.

Cheers,

         Terry


>Cheers
>
>M
>
>--
>Matthew Smith
>IT Consultant - KBC, South Australia
>KBC Web Site    http://www.kbc-dot-net.au
>PGP Public Key  http://gpg.mss.cx
>