Re: KV meter

["Mike Harrison" <mike-at-whitewing.co.uk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

On Sun, 08 Oct 2000 11:55:14 -0600, you wrote:

>Original poster: "David Euans" <davidwe-at-telocity-dot-com> 
>
>I am trying to build a 50 KV high voltage meter for directly measuring
>the voltage from my various high voltage transformers.  I have tried
>using a 100 microamp full scale DC meter with one 250 (32 KV) megohm
>resistor on each leg and an 80 KV diode string (four 20 KV units)
>directly off of one side of a 9 KV neon sign transformer in series with
>one of the 250 megohm resistors, but I get faulty readings each time.
>Using Ohm's law, 500 megohms should yield 18 microamps at 9 KV, but I am
>only getting about 5 microamps of output.  I have tried several
>different diodes, but get similar results regardless.  The NST is
>working properly.  Am I missing something here?   The diodes seem to be
>dropping too much voltage.  If anyone knows how to properly set up a
>voltage divider circuit for measuring AC with a DC meter, I would love
>to hear it.  To illustrate, my circuit is as follows:

At these voltages, capacitance effects will probably be significant.
Instead of a HV rectifier, you could probably use a low-voltage
bridge-rec across the meter, or a shunt-diode arrangement. 

(use fixed-pitch font)
        D1
---R---|>|---R----
      |    |
      |    -
      |    V D2
      |    -
      \(M)/
 

D2 compensates for the forward voltage-drop of D1