Re: Amp Meter
From: Roger Johansson (no-email_at_home.se)
Date: 02/18/05
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Date: 18 Feb 2005 21:37:55 GMT
Rich Grise <richgrise@example.net> wrote:
> I've also seen a circuit where a microammeter is turned into a
> voltmeter - in this case, 10.4K gives 1.5V full-scale. A shunt resistor
> that drops 1.5V at 60A would be .025 ohm, which is much more manageable
> of a value than 0.0083 ohm, and the calibration isn't anywhere near as
> persnickety.
>
In this case you are wasting a major part of the signal. That is not a
good idea, seen from an engineering point of view.
We want a shunt which gives as low voltage drop as possible. Your
idea would make the voltage drop many times bigger, from 50mV to 1500mV.
The 0.0083 Ohm shunt is easy to construct from heavy gauge copper wire.
Or a thinner wire laid double, in quadruple, etc..
Adjustment can be made by moving the probe measuring point a little, or
by connecting an adjustment pot in parallell with the shunt. A wirewound
pot will be suitable for this.
-- Roger J.
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