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Trying to emulate Inductance with gyrator

  1. Feb 23, 2013 #1
    Hello All,

    I am working on a project where I am trying to replicate the behavior of a particular inductance module used on an automobile. It is a simple component that receives a signal from a control unit and the response is sent back via ground. The attached PNG file shows the setup, it is very simple. The signal is received at the positive terminal from a control unit and the response is read by the control unit at the negative terminal.

    http://imageshack.us/a/img17/2072/99268116.png [Broken]

    I have measured the response of this component using an oscilloscope and the files are attached below. I have read about convolution of signals and replicating a particular response based on it's response to a known signal but I am still somewhat confused on where to begin. One issue that I have is that I do not know what signal the module receives when it is being used in it's desired setting ( on a vehicle ) I believe that it receives a PWM signal from a control module but unfortunately I have not been able to measure the output signal from the vehicle.

    My ultimate goal is to produce a the same response using a gyrator circuit as opposed to the bulky inductance module. I have taken a module apart and it is just wound copper wire in a metal enclosure, my plan of attack at the moment is to model various circuits in LTSpice and try to produce a similar response. From what I can tell from the measurements that I made it looks like it is simply producing a steady voltage for the module to read...

    Response collected from the module on the bench...I wanted to read it's response using various input signals since I do not know the exact signal that it receives when plugged into the vehicle.

    http://imageshack.us/a/img841/1385/tek00015.png [Broken]

    http://imageshack.us/a/img43/1148/tek00010.png [Broken]

    http://imageshack.us/a/img109/5586/tek00000.png [Broken]

    http://imageshack.us/a/img96/3377/tek00001.png [Broken]

    Again I apologize if this seems trivial or a stupid question, I just wanted to know how other engineers would tackle this project, and and all comments welcome!
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Feb 24, 2013 #2
    You are getting exactly what you'd expect for the voltage step-response of an inductor or strictly an RL.

    The two issues you will see are:

    1. The response is inductor-like over a limited range of frequencies (strictly this is true of real inductors as well due to parasitics but an op-amp gyrator can have more limited frequency response range depending on the real life inductor you are emulating).

    2. The response will be limited to the range of inputs voltage/current levels the op amp can respond to. Related to 1. Outside this range the gyrator will look distinctly not-inductor-like.

    Gyrators tend to only emulate inductors well at low frequencies and low (small signal) levels. This is part of why you usually see them in active filter circuits and small signal amplifier broad banding (strictly not with op amps but with emitter inputs).
  4. Feb 25, 2013 #3
    Ok, thank you! So the next step would be to determing the input signal that it is receiving as I have honly been able to speculate thus far. Also, what would you consider to be a low frequency? Thank you for the help!
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