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High frequency from AC tig welder affects digital ammeter?

  1. Jul 15, 2010 #1
    I need a solution to the question, Which clamp-around-the-cable ammeter (digital or analog) can be trusted in measurement of current draw by a high-frequency AC tig welder? High-frequency AC is a requirement of welding aluminum, and an electrician measured 150+ amps at full power welding aluminum. A serviceman brought in to find the problem told us, after checking the machine, that high frequency creates error in digital ammeters and his analog meter indicated 105 amps in a duplicate situation. We might have left it at that but are being told (by an engineer) that the digital reading was correct and we have to take the welder offline. Help!
  2. jcsd
  3. Jul 15, 2010 #2
    This has nothing to do with analog and digital. Both can be constructed to show the correct current. Did you check the specifications of your meter.

    If the serviceman is from the welder's company I would tend to trust him.
  4. Jul 16, 2010 #3
    The power supplied to the welder can be measured for a limiting result, which I hope will satisfy the engineer.
  5. Jul 16, 2010 #4
    The Wiki Current_clamp page has some interesting info.

    If you are running AC for Al, with a high-freq starter signal, I'd bet the high-freq is not a sine wave and might confuse the clamp meter a bit. It could also induce more signal due to being coupled better than good-ole-60hz. But it should only run at startup and not affect a continuous reading. It's possible that your welding AC is not a sine wave as well, so you would have to adjust the reading to the waveform. In fact a square wave might give you 1.4 the reading you'd expect from a sine.

    If your other reading was made with an in-line meter calibrated for real RMS, I would trust it a bit more.

    However I don't follow why the equipment should be taken out of service. Is it welding correctly as set, or can't you "dial it down"? Is it fully automated and not current limiting as it should?
  6. Jul 18, 2010 #5
    There's so much noise around one of these machines, you may have to fall back on a very fundamental measurement.
    First, I'd attempt to get through the applications help people at the equipment manufacturer. Behind the thin line of question answer's is a group that have had to address this issue.

    If that doesn't work, I'd try wiring in a current shunt with a non-electronic meter.
  7. Jul 19, 2010 #6
    Thank you for the answers. High frequency does remain past the start because of stabilization ([URL="[URL]http://www.lincolnelectric.com/knowledge/articles/content/alum2.asp"] and I believe due to the difference in exhibited measurements it is a digital meter issue. Sure we can dial it down, the test was done at maximum power in an attempt to register a spike or overload on a recording ammeter at the building entrance. While we may not have a definitive answer to the question, the ammeter did not see it out there. Indications seem to be that the digital meter was incorrect; but the engineer is not accepting it. Sense and politics are often at odds. Thank you all for your input and help.
    Last edited by a moderator: Apr 25, 2017
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