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LR Circuit data logging

  1. Sep 7, 2011 #1
    Heya Everyone

    I decided to do some experiment with an LR circuit. I have an inductor in series with a resistor connected to a function generator. I will set the frequency to the resonant frequency of the circuit. Now, I will change the inductance of the inductor by bringing in a conductor close to the circuit. I would connect the voltage across the inductor to an oscilloscope to see the change in voltage.

    What I am really interested in is to see how the frequency of the circuit changes as I bring the conductor close to the circuit. As the curcuit resonante at fundametal frequency- I expect to see a stright horizontal line in the frequency vs time graph. As the resonant frequency changes , I would expect some peaks in the graph. I understand the physics behind the circuit but totally lost on how to collect , save and then graph the frequency of the circuit. What equipment would I need ?

    I believe some oscilloscope come with USB interface to a PC. I will probably buy that - still doesn't solve the problem of data logging. Can I somehow use the frequency data to obtain the inductance? Would be cool if I am able to do so

    Thanks in advance :)
  2. jcsd
  3. Sep 8, 2011 #2


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    Science Advisor

    An LR circuit by itself will not resonate anywhere. The reactance of the coil will increase with frequency and with the inductance of the coil. XL = 2 * pi * F * L

    So, if the reactance increases at a steady frequency, then more of the input voltage will appear across the inductor and less across the series resistor.

    Real inductors do have some capacitance and the coil will probably resonate at some frequency, but you can't use this because you won't know the capacitance. It is usually quite small and the resonance frequency is quite high, depending on the coil.

    If you have access to a multimeter that can measure inductance, you could just use that.

    Or, you could place a capacitor across the coil, or in series with it, and then you will get resonance effects.
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