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Decay time constant

  1. Dec 16, 2013 #1
    What is the decay time constant of the waveform? How to determine it from this oscilloscope?
    The waveforms are in the pictures below:
     

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  2. jcsd
  3. Dec 16, 2013 #2

    rude man

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    Look at the 100 ns/div. oscillograph (the orhers are useless).

    How long would you estimate it takes the bottom trace to get to 63% of its way to the top?

    (This would be just an estimate since there may be nonlinearities involved, or two or more time constants. But a pretty good estimate anyway).
     
  4. Dec 16, 2013 #3
    Thanks for replying but could you explain this method, please?
     
  5. Dec 16, 2013 #4

    rude man

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    Your trace begins at the bottom and ends at the top. How much time along the time axis to reach 63% of the distance from the bottom to the top? Use the 100 ns/div. trace.
     
  6. Dec 17, 2013 #5
    Should 8~10ns be correct?
     
  7. Dec 17, 2013 #6

    rude man

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    Yes.
    To get a better estimate you should have run 10 ns/division instead of just 100 ns.
     
  8. Dec 17, 2013 #7
    Actually, 100ns is the sweep time.
     
  9. Dec 17, 2013 #8

    rude man

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    Actually, I know.

    You should have chosen 10 ns/div. sweep time
     
  10. Dec 17, 2013 #9
    Well, I just followed the procedure in the textbook. It says to set the sweep time to 2.5mircrosec, 250nsec and finally 100nsec.
    I tried calculated the decay time and taking the best point that I could and I got 9.2ns. Is this ok? By the way, thanks for helping me out.
     
    Last edited: Dec 17, 2013
  11. Dec 17, 2013 #10

    rude man

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    Maybe your oscilloscope didn't have a 10 ns.etting.

    Anyway, I think your number is fine.
     
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