AC Ammeter HELP PLEASE!!!!!

Discussion in 'Homework Help' started by Knightas4, Apr 15, 2011.

  1. Knightas4

    Thread Starter New Member

    Mar 21, 2011
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    0
    Hi, i am working on my senior project. I am building an AC ammeter. My design as of right now is a DC voltmeter with a .1 ohm shunt which allows it to read correct DC current. I have already proved this works correctly. My problem now is rectifying an AC signal to DC and have the correct current read on the meter. I have tried using a low resistance power resistor as a shunt on the AC side then in parallel to the shunt is a full wave bridge rectifier. As of now i have not been successful. I would like any suggestions on how to fix this problem or ways to read the AC current correctly.
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    What is the voltage developed across the 0.1Ω shunt? What is the minimum voltage required by your rectifier? If the shunt develops only a small voltage, this may be insufficient to allow the rectifier to function.

    You might consider simply increasing the increasing the shunt resistance to obtain a bigger voltage to drive the rectifier, but this would considerably increase the power loss (burden) and the response would still tend to be non-linear and temperature dependent, especially at lower currents.

    Alternatively, if you can get a rectifier rated for the full load current, this could be inserted before the shunt so that the shunt is passing DC.

    Finally, a current transformer can be used to derive a divided down current with a relatively large driving voltage capability. This can be rectified and fed to an ammeter (or a shunt to give a voltage to drive a voltmeter). Don't ever leave the output open-circuit though, as the output voltage can get dangerously large.
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
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