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Measuring Peak Current with a Fluke 87 III

Discussion in 'Electronic Basics' started by FunFred, Jan 29, 2009.

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  1. FunFred

    FunFred Guest

    Just recently I was using a Fluke 87 III to measure the peak current
    in an AC circuit.

    It was pointed out that I should be using the 1ms sampling range with
    the Min/Max mode to catch it (it was on the default 100ms sampling).
    OK, I didn't know it was available but you learn...

    What confused me a little is that when you step through the readings
    (max, min average) in 100ms mode I got a good 12A etc reading for max,
    and a small negative value. I just ignored it as an irelivent

    Once the 1ms mode is used I now seem to have a valid Max(positive)
    reading and what apears to be a valid Min(Negative) reading.

    I have looked in the manuls and googled etc, I'm still can not find a
    statement as to what it means. Is it the Min reading in fact the max
    negative current?

    It would make sense to me.. it's just when you blow a fuse some times
    the Min value is larger than the Max value (ignoring the sign).

    So the question is, do I look at both the max and Min values, which
    ever is largest it the real maximum current?
  2. Shaun

    Shaun Guest

  3. Shaun

    Shaun Guest

  4. FunFred

    FunFred Guest

    Thanks Shaun.

    Whilst the notes explain similar information to what's in the manual
    with some history, it still does not say which is the highest reading

    for example

    meter is monitoring some AC current... an event occurs and the meter
    has recorded the following

    Max 2.86 Amps
    Min -3.08 Amps

    so in AC can you have -3.08 amps? (now i'm confused.)

    I'm sort of assuming that these are the outputs from two a/d stages.
    one for each polarity... every one says use the biggest but the manual
    does not say anything.

    I'm just concerned with the assumptions being made.


  5. Shaun

    Shaun Guest

    Well your right, it is kinda strange that the meter gives a negative number
    on AC range for MIN in MIN / MAX mode. I have the exact same model of meter
    you have but I haven't really played with that function.

    I'd suggest you ask your question on the Fluke Community Forum, here is the

    At the top of the page is "register" - go to that first so that you can post
    a question.

  6. FunFred

    FunFred Guest

    Hi Shaun et all

    I've got on to the forums, looked through them and searched etc...
    found some messages about min/max on resisitance and comparisons of
    various meters etc..

    I have asked for permission to post, but I'm still waiting..

    I wish I had the time to do a comparison...


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