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  • Differential sensor

    Greetings to all!
    Has anyone tried to make a similar sensor (coil)?
    Click image for larger version

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    Looking at the Bigfoot coil, I became interested in this design, but I did not like that in such a sensor, the target is determined only in one half of the PX coil.
    In the proposed design, the target detection zone should be in the "middle" part of the sensor. And this is quite an optimal option.
    With my new Stalker IB metal detector, I have already tried an Omega type sensor. I really liked him. I did it on 18 kHz. Now a similar sensor is being manufactured for 12kHz.
    I had the experience of building a Super DD sensor, but it can only be used for uncluttered places. He does not see very deeply, but he determines well the coins that are "on the edge".
    And now I want to gain experience in the manufacture of a differential sensor. Therefore, I would like to ask everyone for advice:
    1. What dimensions are needed for such a sensor. For a bigfoot, I saw, you need dimensions of 480mm x 65 mm.
    2. The TX coil will be with a consistent resonance. And what kind of RH coil to make: with parallel resonance or without resonance?
    2.1 The metal detector circuit allows you to embed an H-bridge to control the TX coil. The signal power can be regulated by the bridge supply voltage. Does it make sense to use such a bridge?

  • #2
    1. You can make it any size you want.
    2. I would start without resonance. RX coils like this can do funny things when you try to resonate them.
    2.1. Yes, especially if you want to make a variable frequency design. But with an H-bridge drive you don't want to resonate the TX coil.

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    • #3
      Thank you for the answer.
      For TX, as I understand it, it does not matter the resonance or the bridge.
      And is there a requirement for the ratio of the proportions of the RH coil?

      For Omega, for example, I have seen quite specific diameter ratios on this forum.​

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      • #4
        Yes, the positions of the "twists" in the RX coil are critical to achieving a null. You will need to determine this experimentally.

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        • #5
          Cast. I assumed as much. And what do you say about such a differential sensor? The blue coil is TH, the two red coils are RH. The inclusion of the PX coils is done in such a way that in the "common zone" the currents are directed in one direction. Click image for larger version

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          • #6
            It'll probably work, but when the TX is smaller than the RX you can get some strange target responses. I don't know what you mean by "PX" coils.

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            • #7
              I apologize. By the РХ=RХ coil, I mean the receiving coil (RX).

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