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AC DPM's -- are the all DPM'$?

Discussion in 'Electronic Components' started by David Lesher, Jun 8, 2010.

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  1. David Lesher

    David Lesher Guest

    I've been seeking some inexpensive AC digital panel meters; but
    thus far, there's as hard to find as a popular BP executive.

    Marel sells some that are $100 each, gulp.

    Or is there a $6.95 AC-DC addon I can use on my pile of old DC
    Analog Devices units?
  2. JW

    JW Guest

  3. David Lesher

    David Lesher Guest

    Thanks. Those will do fine, but I guess I'll need separate
    wallwart power supplies for each one. That, or isolation
    transformers which will cost far more.

    [Unless you have a spare 8-channel isolated power supply.]
  4. David Lesher

    David Lesher Guest

    Not the issue. My point is, each one needs a separate supply. If I could
    find very low current 277v primary xfmrs [I'm monitoring a 480 Y system];
    then I could use one common supply. But such would be $$$ in quantity.
  5. David Lesher

    David Lesher Guest

    I've not found same at good prices.
    Not sure where to find an xfmr with 6-8 identical windings...

    I am thinking this would work. Find some old small B+
    transformers. Use them to isolate and step down the 277V. Than
    an appropriate resistor or two per meter, and a lower range on
    the DPM would give me good data.
  6. ehsjr

    ehsjr Guest

    Why do you need 8 separate supplies? You should be able
    to run 8 (or N) of those DPMs from the same power supply
    using the isolated ground configuration.

  7. David Lesher

    David Lesher Guest

    I'm less sure of that. I will be measuring 3 legs of 277VAC with them.
    Less then good isolation could get....noisy...
  8. ehsjr

    ehsjr Guest

    Ok, I can't address how sure or unsure you are, but I can provide
    some general information that may assist.

    To understand their isolated ground, google on "virtual ground".
    It should yield a _very_ high impedance (for practical purposes
    you can consider it op amp input impedance) between the DPM's DC
    supply and the input (the signal that is being measured) ground.

    Also, this datasheet may help:

    I guess, for you to be absolutely sure, you'd have to try it.
    I have not done it with these DPM's myself.

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