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Duty Cycle test on DMM?

Discussion in 'Electronic Basics' started by Lumpy, Aug 3, 2005.

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  1. Lumpy

    Lumpy Guest

    My DMM has a scale to measure
    Duty Cycle %.

    Exactly what is that measuring?



    I suppose there is more than one way to say it. To me Duty Cycle is the
    percentage of time the circuit is on vs. off in one period of the cycle.

    Usually a term used when talking of square waves. Lets say the period is
    one second for the entire cycle and the circuit is on for .5 sec. Then this
    is a 50% duty cycle. Now say it is on for .25 sec. and off for. 75sec.
    This is a 25% duty cycle...
  3. John Fields

    John Fields Guest

    Sorry, but that's wrong. duty cycle is the ratio of ON time of a
    periodic waveform to the period of one complete cycle of the
    waveform, expressed as a percentage.

    for instance, for:

    _____ _____
    SIG_____| |____________________| |_____

    5-->| |<--- ton
    20-->| |<-- tcy

    100 ton 100 * 5
    D = --------- % = --------- = 25% (1)
    tcy 20

    If it was, as you said,

    "the percentage of time the circuit is on vs. off in one period of
    the cycle", then we'd be looking at:

    _____ _____
    SIG_____| |____________________| |_____

    5-->| |<--- ton
    15->| |<-- toff

    100 ton 100 * 5
    D = --------- % = --------- = 33.3% (2)
    toff 15

    Which is wrong.
  4. Lumpy

    Lumpy Guest

    Ok. What, in practical terms, might someone
    want to measure to know the duty cycle % ?

  5. chuck

    chuck Guest

    What field are you in?

    Auto mechanics often need to measure the duty cycle of fuel injectors.


    Well, hello John!

    I do see your point, the "vs. off" should be removed from the first
    definition. Hopefully the second paragraph clarified my point.

    To the OP, Duty cycle adjustments are made in many electronic applications.
    In my experience I have had to tweak duty cycle when performing servo and
    timing circuit alignments. A common application might be your VCR.
    However, I have never done this with a DMM. Typically an O'scope is used
    but I suppose there are applications where one can use a DMM.
  7. Lumpy

    Lumpy Guest

    I'm a musician.

  8. Well in that case, old analog synthesizers counted on variable duty
    cycle in order to get the right "tone", but they were only vaguely
    calibrated when it came to most functions. Actually, calibration is
    the wrong word, it's more like a scale so you could reset the controls
    at a later time. Most likely you'd be listening, and you had the
    right duty cycle when it sounded like you wanted ( in other words,
    you weren't concerned with how much duty cycle a violing had, but
    you'd adjust duty cycle until you had the same level of harmonic
    content out of the oscillator, based on a mental comparison with
    a real violin). I suppose if you actually needes something specific,
    you'd pull out an oscilliscope and look at the waveform.

  9. Lumpy

    Lumpy Guest

    [what's a duty cycle measurement for]

    Thanks! That's an analogy that I can understand.

    I played an Arp 2 voice analog synth in the 70's.
    My understanding (my guess) was that as we altered
    the shape of the waveform, we made the wave look
    more sawtooth or squarewave, less sine.

    If that's a correct understanding, then how does
    duty cycle relate to those saw or square waves?

    Or in the specific case of this DMM of mine,
    does the ability to measure duty cycles mean that
    I could measure and then repeat the settings on
    the hypothetical analog synth?

    Thanks everybody for the education.



    On second thought, if I read your notation correctly, I don't think you can
    substitute "divided by" for "vs.". You can say Ali vs. Frazier and it
    means, opposed by (my meaning was, "as opposed to") you can't say Ali
    divided by Frazier. That would not make sense.

    To re phrase, Percentage of time the circuit is on as opposed to off in one

    At any rate, probably still more word than needed and not very eloquently
    put, hence the second paragraph.

    New topic

    Do you have an understanding of Quantum Entanglement?
  11. John Fields

    John Fields Guest

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