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I Applied physics of current probe / generator clamps

  1. Aug 31, 2016 #1
    Im studying Maxwell's equations in a part time degree and I starting thinking in job about a particular task we perform...

    The situation

    In work we have a power cable and attach two items to it. One current-clamp-loop-generator (ferrite core wound N turns with wire) and one current-loop-clamp-probe are placed anywhere on the wire but so they are spaced 50cm apart. Picture the power cable running through two circular loops (clamps)

    The current generator clamp is connected to a transient voltage generator and we trigger a high frequency voltage to it, the current clamp probe is attached to a Oscilloscope to measure the induced current on the power cable that is situated 50cm away from the current generator clamp.

    So my thinking is the following....

    1. The high frequency transient voltage from the transient voltage generator induces an alternating current along the wires which are wrapped around the ferrite core of the current-generator-clamp. The Alternating current then produces an alternating magnetic field.

    2. By using the right hand rule and curling my fingers around the loop of the clamp the alternating magnetic field points along the central axis of the loop parallel or anti parallel to the power cable.

    3. The alternating magnetic field changes the flux running parallel or anti parallel to the wire (inside it) and thus produces a voltage that will drive an induced current.

    4. That induced current flows down the power cable from the position of the current clamp generator to the current clamp probe. The alternating current produces an alternating magnetic field with a flux that changes inside the current clamp probe, this induces voltages and drives a current that is measured on the oscilloscope.

    Can someone please assist with my explanation and in the quote place a 1,2,3 or 4 to represent one of the laws of maxwell equations that applies at that situation. I've been struggling all day to get the equations to fit my explanation...
  2. jcsd
  3. Aug 31, 2016 #2


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    Staff: Mentor

    It's probably just better to think of them as transformers. When you run the power conductor through the core once, that forms a 1-turn primary or secondary on the core (including the return path for the conductor). Then you can just use your traditional transformer equations for an N:1 transformer to figure out how it works. :smile:
  4. Aug 31, 2016 #3
    I am not clear what you mean here. Would you be able to explain this differently please?
  5. Aug 31, 2016 #4


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    Staff: Mentor

    Sure. Have a look at this wikipedia page that explains how current transformers work (N:1 transformers):


    The primary in this case is the single turn of the conductor through the CT core, with the N-turn Secondary connected to a measuring circuit.

    The drive circuit you describe would work in a similar way, but with the waveform generator connected to the N-turn Primary side of a CT to drive the waveform into the single turn Secondary.
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