Ammeter design

Discussion in 'The Projects Forum' started by akifnadeem, Oct 27, 2010.

  1. akifnadeem

    Thread Starter Member

    Apr 9, 2010
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    In the case of an ammeter, the shunt in parallel with the ammeter (which
    also may be measuring the voltage drop across a resistor) is necessary
    because in an ammeter the current is typically too large, and several
    amps may "blow" the internal circuitry. Therefore it is more important
    to have a shunt resistor(s) in parallel with the meter to "siphon off"
    the large share of the electric current.

    so how does a ammeter measure the full circuit current,if it is letting the minimum current passing through its deflection part,while rest of current is passing in the shunt resistor?
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. akifnadeem

    Thread Starter Member

    Apr 9, 2010
    15
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    thnax....but thats not the way to reply?
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
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    Try to think of the Ammeter as "measuring the voltage drop across the shunt resistor which is carrying the full current of the circuit".

    Then it is a matter of ohms law to label the meter's face correctly.
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    That's easy.

    The ammeter needle will deflect to a certain degree when current is flowing.

    One just pass the current say 10Amp through the meter(with shunt) and then mark the position of the needle to be 10A.

    This doesn't means 10A is actually flowing in the shunt(it is a bit less as some go through the meter coil) but 10A is flowing via the meter & the shunt combination.
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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  7. Blackbull

    Well-Known Member

    Jul 26, 2008
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    If the meter requires 1mA for full scale deflection, shunting 9.999 mA around the meter and 1mA driving the meter to full scale will represent a current of 10A. Any reduction in current will be shown proportionately on the meter scale. The resistance of the shunt is determined by the internal resistance of the meter divided by the shunts multiplication factor. In the above case this would be 9.999. A digital meter will measure the mV drop across the shunt.
     
  8. Blackbull

    Well-Known Member

    Jul 26, 2008
    70
    6
    Should read 9.999A
     
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