AC RMS current measurement, converting to DC for Arduino

Discussion in 'Test & Measurement Forum' started by ebeowulf17, Jan 11, 2018 at 5:52 PM.

  1. crutschow

    Expert

    Mar 14, 2008
    17,243
    4,750
    That will give you Fourier waveform harmonics up to 500Hz, which probably is sufficient for your requirements.
    You likely want to average the readings over several complete cycles to give a stable and more accurate value.
     
    ebeowulf17 likes this.
  2. Danko

    Member

    Nov 22, 2017
    151
    28
    Maybe you will like Closed loop Hall Effect Sensor for AC , DC , & Complex Currents.
    It gives you information about current in voltage mode.
    http://www.tamuracorp.com/uploads/currentsensor/ClosedlloopPDF.pdf
    EDIT: LA 55-P $24.86 SENSOR CURRENT HALL 50A AC/DC
    https://www.digikey.com.mx/product-detail/en/lem-usa-inc/LA-55-P/398-1010-ND/409823
     
    Last edited: Jan 13, 2018 at 10:43 PM
  3. ebeowulf17

    Thread Starter Well-Known Member

    Aug 12, 2014
    1,477
    239
    Thanks for the idea, and the link. I think my main challenge is just deciding on the best conditioning circuitry and/or code choices. Regardless of transformer or sensor type, I've still got to eliminate negative voltages and get them scaled to suit my needs.
     
  4. Danko

    Member

    Nov 22, 2017
    151
    28
    EDIT: R3/R1=1+R7/R6
    Bridge.png
     
    Last edited: Jan 14, 2018 at 1:47 AM
  5. ebeowulf17

    Thread Starter Well-Known Member

    Aug 12, 2014
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    I found that one of the Arduino sketches that I might want to add current sensing to is already pretty heavily bogged down, only completing 30 cycles of the main loop per second (I think a lot of the speed issues are related to serial and LCD character display outputs, and plan to do some testing soon to get a better understanding of this.) This realization got me more interested in an analog answer, so I breadboarded my original idea.

    It seems to be working pretty well so far - I don't see any obvious distortions in the waveform from the bridge rectifier, the peak voltages come through the same, and the RC averaging filter seems to work reasonably well. The DC output of the filter read 558mV for a signal that appears to be a little over 900mV peak on the oscilloscope, so the average is just a little lower than I expected, but of course this isn't a perfect sine wave either.

    The pics below show the current transformer waveform for just using a burden resistor vs running through a bridge rectifier, then a burden resistor. The second shot also includes the output of the RC averaging filter.
    IMG_4208.JPG
    IMG_4209.JPG
     
  6. ebeowulf17

    Thread Starter Well-Known Member

    Aug 12, 2014
    1,477
    239
    This looks solid, but it would require a dual power supply, right? I'd like something that can run on a single 5V supply.
     
  7. RamaD

    Senior Member

    Dec 4, 2009
    288
    39
    I would prefer a power meter ic, around $1 in digikey, that can give you Vrms, Irms, real & reactive power and of course, the power factor, again true RMS. Calibration is one issue to be solved though apart from some code. ATM90E26, for example.
     
  8. ebeowulf17

    Thread Starter Well-Known Member

    Aug 12, 2014
    1,477
    239
    Wow, that's a pretty impressive chip!

    All of the projects I currently have in mind will be one-off, hand made jobs, and I'm no good with surface mount soldering, so no help at the moment. I'll definitely keep those in mind if I need power monitoring for any bigger projects in the future.

    Thanks!
     
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