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AC milliameter

Discussion in 'Electronic Basics' started by Joe Lees, Apr 1, 2004.

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  1. Joe Lees

    Joe Lees Guest

    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
  2. Can't see any reason why not ??
  3. JeffM

    JeffM Guest

    I...purchased 2 [500milliamp] AC milliameters
    ....or a non-invasive solution: current transformers.
  4. Rich Grise

    Rich Grise Guest

    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!
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