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LDC1614: How close can two coils be before they influence each other

Part Number: LDC1614

If I have two coils which are 0.6" square, how close do they have to be before they start to inter with each other ?

This is assuming the conversion of the inductance starts at the same time for both coils and that their inductance is the same.

Cheers

  • Hello Stephen,

    The distance at which the coils interfer with each other depends on a few parameters - the physical size of the sensors, how close they are in frequency to each other, and the sensor Q.

    The LDC161x devices short the inactive channels which greatly reduces the interference - this functionality is more effective when the LDC161x is closer to the sensor. We have placed coils adjacent to each other at <0.2mm with robust operation. Offsetting the sensor caps is also helpful.

    Regards,

    ChrisO
  • Chris

    Thanks for the reply. These will be two separate LDC161x so the option to short the coil while the other one is sampling is not possible.

    By offsetting caps you mean choosing different capacitor values to change the Q of the circuit ?

    If for discussion we assume two identical coils being driven at the same frequency, the same Q etc how close would they have to be to interfere assuming they are in proximity to a steel plate?

     

  • Hi Stephen,

    The primary change from the different sensor cap is that the sensor frequency shifts; there may be a modest change in Q as a result. For example, one sensor may have 330pF and the other 400pF.

    A pair of sensors with the same resonant frequency and a higher Q (>30) will couple at a farther distance than a sensor with a lower Q, but the higher Q sensors will couple less if they have different resonant frequencies.

    I don't have a good answer for the proximity at which there will be interference - the desired measurement resolution also determines this. Usually I will mitigate by changing the sensor capacitor to offset the frequency if an issue is found.

    Finally, you may be able to align the sampling across multiple devices moderately well if you are using an external oscillator (and you should with the LDC161x) - configure the parts with the same sampling rate (settle counts, dividers, and RCOUNTS) and distribute the same clock to all the LDCs. You should be able to synchronize the sampling so that adjacent channels are not being sampled simultaneously. You will need to monitor the INTB of all devices and periodically put the devices into standby mode and then resume them to resynchronize them (depending on the sample rate, you may need to do this every few seconds).

    To make this technique more effective, add some additional time on the settle count if possible.

    Regards,

    ChrisO