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pcb coil

sadiq khan
Prodigy 10 points

i have to design a metal detector search coil on PCB. . . 

is there any limitation to design a primary and secondary search coil of diameter 9 in and 500 turns on PCB . . 

  • 0
    TI__Expert 4890 points

    Hi,

    You can refer to this:

    Q2. What is the min/max inductance or min/max coil diameter which the LDC1000 can drive?

    A2: There is no a single-number answer to this question. The LDC1000 is limited by the equivalent parallel resistance, Rp, as opposed to solely inductance. Rp = L/Rs/C, where Rs is the equivalent series resistance and C is the cap value. The LDC1000 can measure anywhere from 800 to 4MΩ Rp. 

    Coil design governs both L and Rs, and for different coil designs the ratio of L/Rs varies. The smaller the capacitor, the higher Rp will become, which makes smaller coil designs possible. The resonance frequency of the LC tank, however, is limited from 5kHz to 5MHz, which limits the minimum size of the capacitor.

  • 0
    TI__Genius 9300 points

    The highest risk with such a coil is self-capacitance, that can potentially bring the self-resonant frequency too low, potentially outside of the LDC1000 range.

    Low resonant frequency also means that detection of thin object will be problematic

    To mitigate the risk, one can make fewer turns, removing half or more of the inner windings. Then inductance will still be sufficient for oscillations while self-capacitance greatly reduced.