AC milliameter

I have recently purchased 2 AC milliameters 0 to 500milliamps, I want to
use these meters to read ac current in the range of 0 to 30 amps, can a
shunt resistor be used as in DC meters, I havent actually received the
meters yet so I dont know the value of the meter movements

Thanks Joe L

 

Can't see any reason why not ??

 

I...purchased 2 [500milliamp] AC milliameters

....or a non-invasive solution: current transformers.

 

The internal resistance of your meter is going to be
way low, and so calibrating a shunt will be a real PITA.
One thing that can help is to put a resistor in series
with the ammeter, turning it into sort of a voltmeter -
they used to use 1mA meters and call them a "1000 ohms
per volt" meter, a 50 uA movement gives you "20K ohms
per volt", I think for a 500 mA meter, a 2 ohm series
resistor would give you a "2 ohms per volt" meter. Since
the meter movement resistance is probably practically
negligible, just use 2 ohms then for your shunt calc.
(and still 500 mA FS, but you'd be losing 2 volts from
the circuit).

To actually measure the internal resistance of a meter,
you need two pots. Start with one in series with the
meter and a supply, and adjust to full scale. Put the
other pot in parallel with the meter (without changing
R1) and adjust for exactly half-scale. The pot is now
equal to the meter's internal resistance.

Have Fun!
Rich