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LDC0851: about Sensing of deformed targets

Part Number: LDC0851

Thank you very much for your help.
I would like to connect a 90mm diameter sensor coil to the LDC0851EVM.
I would like to connect a 90mm diameter sensor coil to the LDC0851EVM and have it detect an object even if it is a target (mold) with a hole. 

The mold should be more than 300mm2 in size and have a 50-80mm hole in the center.

In the LDC target design section 3, there is a description of the case where the target is deformed, but please tell me how to design the sensor coil.
Please let me know how to design the sensor coil. If you have any examples like this one, please let me know.

Thank you very much for your cooperation.

Translated with www.DeepL.com/Translator (free version)

  • Hiroaki,

    If your mold/target is round and symmetrical, and the hole in the center is also round and symmetrical, I don't think there will be a problem because the eddy currents can flow in symmetrical closed loops, without a change in the eddy current density, as shown on the left in Section 3, Figure 3-1. You should be able to use the coil as designed by the Inductive Sensing Calculator Tool..
    One thing to try might be to adjust the coil windings so the ratio of Din and Dout as shown in the figure below match the ratio of the hole and the mold.
    This is shown in the tool as din, dout, and the coil fill ration, din/dout.
    If you can make din/dout match between the mold and the coil, it will tend to increase the coupling between them, and give better resolution.

    If the mold and/or the hole are not round, such as a square or rectangle, then the eddy current will need to flow around the corners.
    This will change the current density, create a mismatch between coil and the target and decreasing the inductance change and the resolution.
    You might be able to get around this by using a square or rectangular sensor, but our tool does not support this. One of our app notes, Sensor Design for Inductive Sensing Applications Using LDC shows a rectangular sensor in Figure 2-13, and makes the comment that the sensing range is dependent on the smaller axis length, rather than the length of the larger axis.

    I hope this helps. I

    f you have any related questions, please feel free to add them to this thread rather than creating a new thread.

    Regards,
    John

  • Mr. John.
    Assuming a mold with a hole in it, we punched a hole in aluminum foil.
    In the experiment, we confirmed that the object was detected even when the hole was placed in the center of the sensor coil.
    We confirmed that the object was detected even when the hole was placed at the approximate center of the sensor coil.

    Although the thickness of this aluminum target is not comparable to that of an actual mold, the ratio of the size of the hole to the target (DIN/DOUT) is assumed to be larger than the actual size.
    Is this correct?

    The prototype sensor coil described in the previous email was tested with a hole in it as well.
    I would appreciate it if you could tell me what I need to correct in the sensor design.
    I would appreciate it if you could tell me what I need to correct in the sensor design.

    Thank you very much.

    Hiroaki Yoshida

    Translated with www.DeepL.com/Translator (free version)

  • Hiroaki,

    I'm not sure I understand your first question.
    If the experiments show the behavior you are looking for, then the sensor should be okay, and should not need to be corrected.
    Are your experiments with aluminum foil giving you the results you want?
    Regards,
    John