I agree with Bill. The use of your meter as a Voltmeter has several
benefits. First, it is EASY to use standard resistors for the shunt.
Second, it is EASY to calibrate. Third, it is inexpensive. Forth, it'll
save your bacon if you have a BIG BANG! It is much easier to protect a
meter that is isolated from the primary current path by series
resistance than one that is connected directly to a low resistance shunt.
My favorite method of using a 1 mA meter is to series the meter with a
fixed 470 Ohm resistor and then a 1K Ohm trimpot. Place your protection
diodes from the directly connected side of the meter to the junction of
the fixed resistor and the trimpot. A 1 mA meter gives you a 1000 Ohm
per volt meter so if you choose a standard value resistor to put in
series with your load so as to provide 1 volt across it at your maximum
current, your meter circuit trimpot will be about mid scale on calibration.
73, Tony W4ZT
Bill Turner wrote:
> ORIGINAL MESSAGE:
>
> At 08:52 PM 2/3/2006, w2cqm@juno.com wrote:
>> Hopefully, someone can suggest an easy technique to wire meter shunts in
>> fractional parts of an ohm.
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> An alternative method is to put a low value R in series with the
> current and then connect the meter across the R as if it were a
> voltmeter, with the appropriate resistor in series with the meter. If
> you use a potentiometer as the voltmeter resistor you can calibrate
> it exactly very easily.
>
> You may already know this but some others might find it useful.
>
> 73, Bill W6WRT
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