Test capacitor with an oscilloscope?

Discussion in 'Homework Help' started by GregJ7, Jul 15, 2015.

  1. GregJ7

    Thread Starter New Member

    Jun 7, 2014
    18
    2
    I'm trying to figure out how to use a simple oscilloscope to show me a curve so I can determine if a capacitor is working as it should or not (and then calculate its Farad rating). First I want to make sure I have set the non-oscilloscope portion up correctly. My goal was to use a switch that discharges the cap in one position and applies power to the cap in another position, which in theory will trigger the oscilloscope when the voltage becomes non-zero. Can anyone verify that my schematic will do that? Does the voltage on the hot ("+") end of the cap rise as the cap charges and then stay constant when it is fully charged?

    TestCapSch.jpg
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,226
    You need a resistor in series with the Charge line so that you can see the charge curve on the oscilloscope and calculate the capacitance from the RC time-constant (in one time-constant it charges to 0.636 of the input voltage).
    Note that you may need some small resistance in the Discharge line to keep the peak discharge current to a safe level for the switch you are using.

    Yes the voltage rises exponentially to the supply voltage and stays there.
     
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