[BC] HV probes

[Cowboy]

On Friday 20 February 2009 10:03 pm, Tom wrote:
 >  Hmm
 >
 >  I always wondered about that - you'd have to match - or at least know
 >  what the conversion would be - to use any given probe with any given
 >  meter.....

  Yes, and no.

 >  Yeah, if the probe's designed for a specific meter, the calibration
 >  would match, but would be different for a different meter; not
 >  necessarily a 100x, 1000x, or whatever.  Might be something like 
538.2x.....

  If you're trying to use a probe designed for a particular movement, yes.

 >  Thomas G. Osenkowsky wrote:
 >  > A Fluke model 80K 40 kV HV probe consists of
 >  snip
 >  > Not all HV probes are the same! Each one is
 >  > designed for use with a particular model of meter

  It's a simple voltage divider.
  99 M reresistor in series with a 1 M, total 100 M, gives 10% of the
  original voltage across the 1 M. If you try to measure it with a 5 K
  meter, you'll read real low, because that 1 M isn't 1M anymore.
  It's 1M in parallel with 5K.
  On the other hand, if you put a 100 M resistor in series with a 1 K
  resistor, and bridge that 1 K with the typical 20 M input DVM, it'll
  read well within tolerance of the parts.

  One can use any movement handy, IF one knows the resistances
  of the various components, and know how to use a calculator, or
  a pencil.
  ;)

-- 
Cowboy