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LDC0851: Proximity sensing with distance bigger than coil diameter

Sai Loo
Expert 4370 points
Part Number: LDC0851
Other Parts Discussed in Thread: LDC1612, LDC1614

Hi team,

I have a customer using inductive sensing for proximity switch and interested in our LDC0851.

They need to sense up to 40mm distance, but the max coil diameter is < 40mm (range from 8mm to 40mm). They are testing with our EVM and get < 8mm distance.

In our datasheet, it is recommended that the sensing distance is up to 40% of the coil diameter. Could we increase this to beyond 100% of the coil diameter? Will using multi-layer coil help? And any guide for designing multi-layer coil (they prefer discrete coil than using the PCB).

Is it very critical for the reference coil to be identical to the sensing coil? what is the best positioning for the reference coil and sensing coil?

assuming the reference coil and the sensing coil is identical, what will be the tolerance change with temperature (from -40C to 100C). They need to achieve +/-10% tolerance with all variable (including the tolerance of the coil).

  • 0
    TI__Genius 13335 points
    Hello,
    The LDC0851 is not designed to sense distances greater than the coil diameter for proximity applications. This is because when using the Threshold Adjust mode, the first setting (ADJ=1) requires a change in frequency of 2% to switch the device output. As a metal target moves closer to the coil, a frequency change of 2% occurs when the metal approaches around 40% of the coil diameter. The relationship between frequency change and metal proximity (relative to coil diameter) is the same for all of the LDC devices.
    If you need to sense a longer distance, this means you need to detect frequency changes smaller than 2% which can be done with our higher resolution devices such as the LDC1612 or LDC1614. Refer to figure 65 of the LDC1614 datasheet for data measurements that show up to 200% coil diameter sensitivity. Note that longer ranges will require a higher value of RCOUNT which slows down the measurement, so there will be a tradeoff between sampling speed and resolution. Additional collateral exists on the LDC161x resolution in the following application note: www.ti.com/.../snoa944
    Regards,
    Luke