Looking for a Recommendation for a Multimeter that can Measure the Peak Current of a Square Wave

Discussion in 'Test & Measurement Forum' started by Zohar, Apr 13, 2019.

  1. Zohar

    Thread Starter Member

    Nov 19, 2015
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    Hi

    If you try to do Current measurement on a square wave, in order to find the current in the "1" part of the wave,
    most multimeters will not give you that info, when you set them on Current measurement mode.
    You will probably get some effective value, instead of the value at the peak of the wave.

    Can anyone please recommend me a multimeter that can do it?

    For example,
    If you have an IR Remote Control for some device (TV, TV Box, Audio System, etc),
    and you want to know the current going thru the IR LED.. which receives a square wave.

    Thank you
     
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    The Fluke 87V has a peak MIN/MAX setting.

     
  3. Zohar

    Thread Starter Member

    Nov 19, 2015
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    1
    Thank you very much nsaspook.

    Fluke's Multimeters are quite expensive,
    maybe you know one that is not by Fluke, and should do it too?
     
  4. jpanhalt

    Expert

    Jan 18, 2008
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  5. danadak

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    Mar 10, 2018
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  6. Zohar

    Thread Starter Member

    Nov 19, 2015
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    Thank you both.

    If taking the example of an IR Remote Control, then we're talking about 38KHz..
    The USB Adapter will not be good since it's samples at 1ms intervals.
     
  7. danadak

    Distinguished Member

    Mar 10, 2018
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  8. danadak

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    Mar 10, 2018
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    Last edited: Apr 13, 2019
  9. Zohar

    Thread Starter Member

    Nov 19, 2015
    53
    1
    Thank you.

    BTW, in general, a Multimeter that has a Min/MAX feature should do the job?

    I should just set it to Current measurement, choose "Max",
    and then measure the current when a wave is passing, and then get the value of the "1"?
     
  10. crutschow

    Expert

    Mar 14, 2008
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    If it has the frequency response you need (as stated in its specifications), yes.
     
  11. KeepItSimpleStupid

    AAC Fanatic!

    Mar 4, 2014
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    Measurements like this are usually dependent on "crest factor".

    The current ranges on most multimeters are just resistors. This may be troublesome without an I-V converter.

    Frequency response is another issue.
     
  12. Zohar

    Thread Starter Member

    Nov 19, 2015
    53
    1
    I see.

    I have my eyes on Uni-T - UT139C.

    [​IMG]

    It looks like a nice Multuimeter, it has the Min-Max feature,
    and it's priced reasonably.. (even more than reasonably) - it's around 40$.

    Will it's Min-Max feature be relevant for a 38KHz wave?

    Here's its product page:
    http://www.uni-trend.com/html/product/General_Meters/Digital_Multimeters/UT139/UT139C.html

    Its manual is under the "Docs & Software" tab,
    I downloaded it but couldn't see any mentioning for a Frequency regarding Min-Max.

    Maybe you know how can I find this info - if this Multimeter is relevant for what I need?
     
  13. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    Zohar, I have never seen a multimeter designed to measure square waves. danadak has the solution....a pocket scope.
     
  14. wayneh

    Expert

    Sep 9, 2010
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    I'd just use the poor man's version: Measure the current with a cheap meter and multiply by two. You did say it's a square wave. I believe a cheap meter simply reads the time-averaged current. If you didn't really mean square wave and instead have some sort of PWM, that's different. You could set the PWM to 100% and measure the peak current directly.
     
  15. Zohar

    Thread Starter Member

    Nov 19, 2015
    53
    1
    It's an IR Transmission..
    o definitely not a square wave that we know its duty-cycle and can calculate anything about it.

    OK, I will use a scope..
     
  16. jpanhalt

    Expert

    Jan 18, 2008
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    Here are the footnotes to the AC Current measurement for that meter:
    upload_2019-4-14_18-33-47.png


    That is on pages 20-21 f the user's manual. I am not sure min/max has the same meaning as peak to peak for all meters. It can mean, the minimum and maximum voltages over a fairly long period, as is often needed in measuring temperature.
     
    Zohar likes this.
  17. Zohar

    Thread Starter Member

    Nov 19, 2015
    53
    1
    Thank you very much jpanhalt.

    OK in that case a Multimeter will not help :)

    Scope then.

    Thank you all
     
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