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Syncing 2 phases

  1. May 21, 2014 #1
    Hi all,

    Doing some energy monitoring of some various equipment using ct clamps and an diy arduino based energy monitor. I have limited number of arduino inputs available so have been experimenting to boost the capacity of the monitor without using multi arduino. I have found no problem joining 2 or 3 clamps into one input if they are of the same phase but what would i need to do to sync the tiny voltage between clamps so that i could put all of my lights, which are split between the 3 phases into one input using 3 clamps.

    I know the answer if there is one would be to use capacitors but it would be great if any1 could tell the values or configuration and what i would use to measure to make sure i've done it right it'd be much appreciated.

    Thanks

    Samuel
     
  2. jcsd
  3. May 21, 2014 #2

    NascentOxygen

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    Hi Powerpoucher. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    The clamps are sensing the amplitude of the current?

    You have 3 clamps, and would like to produce a signal equal in amplitude to the sum of the three individual signal amplitudes? Do you want this sum to be a single-phase AC signal, or a DC level? What is your line frequency?

    In any case, I think it would have to be an op-amp circuit.
     
    Last edited by a moderator: May 6, 2017
  4. May 21, 2014 #3
    You are exacty correct and thank you for putting it in a more coherent form than I did. The line frequency is 50htz and it will need to be a single phase AC signal.

    And thanks for the welcome :)
     
    Last edited by a moderator: May 6, 2017
  5. May 21, 2014 #4

    berkeman

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    I agree with NO -- use an opamp circuit that does peak detect on each phase, and add those 3 voltages before digitizing with your Arduino.
     
  6. May 22, 2014 #5

    jim hardy

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    You didn't say what does the current wave look like. Phase shifting by capacitors will affect harmonic content of non-sine wave load currents

    If this is more than just a hobby application , it might be worth using RMS to DC converters for the phase currents.
    Electric company probably hands you a pretty decent sinewave voltage.

    http://www.analog.com/static/imported-files/data_sheets/AD737.pdf

    around eight bucks at Digikey

    application notes here
    http://www.analog.com/en/special-linear-functions/rms-to-dc-converters/ad737/products/product.html

    Linear Technology has similar products
     
  7. May 23, 2014 #6

    NascentOxygen

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    Using the fairly simple arrangement I had in mind, it will not produce accurate results when the load predominantly comprises lights with dimmers and speed-controlled ceiling fans. These cause distortions in the current waveform, rendering it non-sinusoidal.

    Are you likely to have such loads? (Jim, that true RMS processor sounds handy.)

    I'm also interested to know why you prefer the sensor to give you a sinusoidal signal, in preference to a DC level.
     
    Last edited: May 23, 2014
  8. May 23, 2014 #7
    If your are looking at different phases and the output of the sensors is AC ( representative V or I ) this really will not work. As an example - if the phases are 180 out of phase - and they both have 100A - the sum will be 0 Amps....
    If the output of the sensors is DC Voltage representing the current, then the DC voltages can be summed - possibly in series, depending on the output circuit in the sensor ( YOu may be able to rectify the signal yourself - creat DC ands then sum)- -- Summing with an op amp will work, but you still need to get the V input to the ADC input on the Arduino to 3.3 or 5 V MAX ( basic v divider will work)

    However looking at all of this- you are introducing a lot of error...- so each step is not ideal and you are getting further and further from the truth. If you really want to measure energy / power - perhaps a power measuring IC - or try to convert each signal into power first... still I a sure more work than you are asking about.
     
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