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Peak detector

Discussion in 'Electronic Design' started by scada, Mar 21, 2006.

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  1. scada

    scada Guest

    I need to measure the peak of two waveforms occurring simultaneously. The
    peaks will only be somewhere around 50 µs, the entire pw 20-40 ms. Of course
    the best solution is to monitor it with a storage scope, however the
    personnel involved have not the training. Any ideas?
     
  2. Tom Bruhns

    Tom Bruhns Guest

    50 usec is a very long time in terms of response of modern electronic
    circuits. It should be possible to capture the peak using either
    analog or digital techniques. How accurately do you wish to capture
    it, and what amplitude is it? (What is the range of possible
    amplitudes, including the peak and the value at other times?)

    A digital method: let a very simple microprocessor (or even a logic
    circuit) monitor the output of an ADC that's taking reading at an
    appropriate rate, say 100k/second, and hold the maximum value in a
    register. If a new ADC reading is higher than the value in the
    register, replace the register contents with the new reading. This
    could easily be equipped with a digital readout and a reset button, or
    it could respond to an external electronic reset line and provide its
    register value to a computer...lots of flexibility.

    An analog method: there are many op amp peak detector circuits around.
    I'd look on the TI and Analog Devices and National Semiconductor
    websites for ideas, or look in op amp databooks. I particularly
    remember some good ones in the Burr-Brown data books (now part of TI).
    You can read out the value with an ADC or digital voltmeter; beware
    that the design has low droop rate. It should be possible with modern
    parts to get a value held to 1% accuracy for more than 10,000 times as
    long as it takes to acquire the peak value. The peak is held on a
    capacitor, and the ability to hold a value a long time is set by having
    a high ratio between leakage currents that affect the capacitor voltage
    and the current available to charge the cap to the peak value to be
    held. It's capturing the held value quickly enough to avoid droop
    problems in the analog circuit that make the digital solution
    particularly attractive. (Analog methods are probably more appropriate
    for capturing very short peaks.)

    Obviously, you can make two such circuits to monitor the two inputs.
    And you can arrange gating to enable each, either digital or analog,
    only for a "window" of time around when you need the result.

    Cheers,
    Tom
     
  3. scada

    scada Guest

    Thanks Tom. I forgot to mention, these are single pulses. I also thought of
    using an AD on a pic chip. If I have to go that far, I will add memory and
    display the waves on a laptop using my favorite graph program (Dplot). Then
    I could instruct the operator to save the files, and I could evaluate them
    at a latter date. I was hoping to avoid all that however. I was looking for
    a simple one chip solution just to capture peak amplitude, do some math and
    give a go - no go indication. I can assume the waves to be similar if the
    gain difference is where it should be. I found Analog devices makes the
    PKD01, I don't know if it can detect a single pulse - I will read the
    datasheet latter.
     
  4. Joerg

    Joerg Guest

    scada wrote:

    Study the trigger capabilities of your scope. Many modern ones offer an
    amazing plethora of possibilities. Runt pulse qualifiers, length or
    shape qualifiers, you name it.

    What I sometimes do is built a simple circuit that resembles a little
    bit of a matched filter to the event I am looking for, run the signal
    also through a FET probe and a stack of HP lab amps and the trigger on
    whatever comes out of the filter.

    Regards, Joerg
     
  5. Ken Smith

    Ken Smith Guest

    Thanks Tom. I forgot to mention, these are single pulses. I also thought of
    using an AD on a pic chip. If I have to go that far, I will add memory and
    display the waves on a laptop using my favorite graph program (Dplot). Then
    I could instruct the operator to save the files, and I could evaluate them
    at a latter date. I was hoping to avoid all that however. I was looking for
    a simple one chip solution just to capture peak amplitude, do some math and
    give a go - no go indication. I can assume the waves to be similar if the
    gain difference is where it should be. I found Analog devices makes the
    PKD01, I don't know if it can detect a single pulse - I will read the
    datasheet latter.[/QUOTE]

    Is the go-no-go output all you need? or do you also want the actual height
    of the peak?

    If you just want go-no-go, a comparitor and a latch would do.

    Since LM339s come 4 to the pack and they make lots of latches per package,
    you could make a "2 bit" flash converter to drive a string of 4 LEDs to
    give, "horrid", "bad", "good" and "wow" indications.
     
  6. Joerg

    Joerg Guest

    Hello Ken,

    On the other side of the pond that would be "rather frightening", "not
    quite on par", "splendid" and "smashing".

    Regards, Joerg
     
  7. Genome

    Genome Guest

    I FUCKING WOULDN'T FUCKING LIKE TO FUCKING STATE THE FUCKING OBVIOUS BUT YOU
    FUCKING MIGHT LIKE TO FUCKING TRAIN THE PERSONNEL INVOLVED.

    dna
     
  8. scada

    scada Guest

    Let me begin with, training has nothing to do with the technical question I
    asked! Training can't be done do to reasons I will not get into, mainly
    because it is irrelevant to my question! If you have no constructive
    solution, I suggest you mind your own Fucking Business Ass Hole!
     
  9. Jim Thompson

    Jim Thompson Guest

    Poor baby! Can't cope with being drubbed by the great and wonderful
    Genome ;-)

    ...Jim Thompson
     
  10. Genome

    Genome Guest

    OK, so correct me if I am wrong here.....

    For your own reasons you are not either capable or prepared to train someone
    how to do the job you want them to do with the equipment you have available.

    And Yet

    You come along here and ask someone else to tell (teach or train) you how to
    do the job in a simpler way.......

    And then I'm the Ass Hole because you have a problem.

    Of course, you are correct. I was just looking for some form of
    reaffirmation.

    DNA
     
  11. John Fields

    John Fields Guest

    ---
    If training were irrelevant, then there was really no point in your
    bringing up the storage scope solution in the first place, other
    than to demean the personnel who don't know how to run the scope,
    since it's really a non-solution.

    Or to pose as one who is knowledgeable about storage scopes but is
    being kept from using one for a solution by the winds of fate.

    As far as whose business what is, as soon as you put anything on
    this newsgroup it becomes _all_ of our business, and if you want to
    get nasty you're in for a _very_ rude awakening.
     
  12. scada

    scada Guest

    The issue of using a scope is a union one, nothing to do with the ability of
    my personnel. I only mentioned it because I knew someone would suggest using
    a scope, and I ruled that scenario out from the beginning!
    available.

    It's a simple person who assumes and jumps to his own conclusions!
     
  13. ROTFLMAO. You need to find a new company to work for...
     
  14. YD

    YD Guest

    Now you really have to come up with the sordid details! What is it
    you're trying to accomplish? What kind of union tells you not to use a
    DSO and not tell the personnel involved how not to use it? Are they
    allowed to use computers? Abacuses? If you can't work around the
    obstacle just barrel over it.

    - YD.
     
  15. Fred Bloggs

    Fred Bloggs Guest


    Hmmm- a third possibility would be an analog-digital hybrid with a
    run-of-the-mill el-cheapo analog classic pre-conditioning the input for
    a quasi digital job similar to circuit shown here:
    http://www.elecdesign.com/Files/29/3473/Figure_01.gif .
    Infinite hold times with 0% error and easily adapted to provide an
    output comparison of two channels.
     
  16. scada

    scada Guest

    I like that! I will give it a try. Thanks...
     
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