Measuring rms value of the mains

Discussion in 'General Electronics Chat' started by rich1608, Feb 2, 2015.

  1. rich1608

    Thread Starter New Member

    May 30, 2011
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    Is there a way to accurately measure the true rms value of the mains? I have a generator test box with a moving-iron volt meter which I want to calibrate. The frequency meter is easy - just use the mains but I can't think of an obvious way to calibrate the volt meter. Thanks. test (Large).jpg
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Are you asking about making a ballistic average meter read True Root Mean Square, which requires integration and other computation, or are you just asking how to put a scaling resistor and/or trimpot in series with the meter?
     
  3. rich1608

    Thread Starter New Member

    May 30, 2011
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    I simply want to know how to adjust the meter via the black screw on the front so it gives an accurate reading of the mains rms value. I could compare it to a DMM but how accurate are they?
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    The black screw on the front of the meter is for adjusting the zero setting.
    With no power to the meter, adjust to show zero on the meter.
    After that the meter should read correctly if it has been properly calibrated at the factory.
     
  5. rich1608

    Thread Starter New Member

    May 30, 2011
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    Thanks - I've adjusted it to zero then compared it to the reading of two DMMs and it seems spot on.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Nice to hear.
     
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