[AMPS] measuring meter shunt resistance

[Ian White, G3SEK]

Lane Zeitler wrote:
>
>Gents,
>Is there a simple way to accurately measure the low resistance of a current
>meter shunt? I am trying to get my plate current and grid current meters
>calibrated and I need to verify the values of the shunt R but the Ip shunt
>is less than .3 ohms and the Ig shunt is less than 1.6 ohms. My Fluke 77BN
>is of no real help at these low values.
>

Try thinking about it a different way - what you really need is to know
is that when (say) 1.0A is passing through the plate meter shunt, the
plate meter reads 1.0A. Thinking about it that way gives a much easier
solution.

With the amp dead, cold and disconnected, use an external power supply
to force exactly 1.0A through the relevant part of the circuit, with the
Fluke in series reading the current. Adjust the shunt until the meter
reads 1.0A too (don't forget to zero it accurately first).

A power supply with an adjustable current limit is best for this, but
you can use a variable-voltage supply and a fixed resistor, or a fixed-
voltage supply and a variable resistor.


73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm