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Design of CT with ferrite core for reverse operation of CT

  1. Feb 20, 2017 #1
    I have to couple noise into data cable(cat5) in common mode. I have done this with a CT of 50A/1A, ferrite core. What I have done is, I connected the S1 and S2 of CT to probe of my signal generator and inserted the cable through the whole of CT(ring type). I got maximum of 380mV in the cable ends when only the signal from signal generator fed no data is transferring. But I have to couple atleast 1V to the cable. I want to know how can increase this, whether should I increase the turns on the ferrite core or any other method ? If I should increase the no of turns, how to calculate the no of turns and the wire specifications? (I used 200KHz, 10Vpp AC signal) ct_testing_0.png
  2. jcsd
  3. Feb 20, 2017 #2


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    The transformer will behave like a voltage transformer if there is no return path external to the transformer. The signal generator voltage will be reduced by the turns ratio of the transformer.

    If there is a separate conduction path, (such as a common ground), between the ends of the cable, the transformer will behave like a current transformer. As a CT, the voltage on the cable will be equal to the product of the induced current and the external return resistance. V = I * R

    You have not identified the complete circuit of the cable terminations so we cannot identify the transformer mode of operation.
  4. Feb 22, 2017 #3
    For my device to which I am connecting the wires, doesn't have a common ground line...
  5. Feb 23, 2017 #4


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    Then, as there is no alternative current path, the transformer is operating as a voltage transformer.
    The induced voltage in the cable will be 1/10 of the loaded signal generator voltage. 380 mV induced on the cable suggests signal generator voltage when driving the 10 turn winding will be about 3.8 V. You can check that with a multimeter.

    Without an external conduction path, what do you think you are testing ?
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