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Finding the component values of a RLC circuit

  1. Feb 25, 2015 #1
    What methods could I utilise to find the individual values of the components - resistor, inductor and capacitor - of a series RLC circuit using an oscilloscope, signal generator and 10 ohm resistor. Where each component can be isolated in order to find the voltage etc.

    I've already found the value of the resistor component by connecting it in series with the 10 ohm resistor, finding the voltage difference using the oscilloscope and then using the following equation:

    Vout / Vin = R2 / (R1 + R2)

    However I'm not sure how to find the other components, thanks for all the help in advance.
     
  2. jcsd
  3. Feb 25, 2015 #2

    Svein

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    Science Advisor

    Just use the same equation with R1 replaced by Z1 (which may be jωL or 1/jωC).
     
  4. Feb 25, 2015 #3
    Let's assume that your signal generator can generate both sine waves and square waves and supports a low impedance output. You already have the resistor value.
    Now connect only the LC part of the circuit across the signal generator outputs, and give a very low frequency square wave as an output. Try to observe the waveform at the node between the inductor and the capacitor. You should see some ripples on the edge of every square wave. That is the characteristic frequency of the LC combination. Now, the only thing you need to do is to measure the inductor or the capacitor frequency separately. Use the resistor that you have in series with the one of the inductor or the capacitor. Now, to measure the inductance, you have to put the scope in XY mode. X should show the voltage across the resistor + inductor series combination. Y should show the voltage across inductor only. If you sweep across frequencies, you will get an unskewed ellipse/circle at some particular frequency. This is the 3dB frequency for the inductor. You can derive the values of the inductor and capacitor from the 2 frequencies.
     
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