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LDC1614: Does anyone try to use higher resistance material (e.g., 20 Ohm per m) instead of copper to make a sensing coil for inductive sensing?

Jun Gong
Prodigy 110 points
Part Number: LDC1614


I tried to use conductive thread (e.g., 20 Ohm per m) to make a sensing coil for inductive sensing. I spotted some weird things:

1) sensor value fluctuates larger than using the common copper coil 

2) when metal approaching the sensor, the inductance increases instead of decreasing 

Any thoughts on what if the sensing coils are made of higher resistance material instead of copper?

Thanks!

  • 0
    TI__Genius 11015 points
    Hi,

    We have received your question & we will respond to you soon.
  • 0
    TI__Mastermind 23810 points
    Jun,

    We haven't tried sensors like that. Here are a few thoughts about possible effects:
    1. Lower Rp, double check that the amplitude of the INx signals are in the correct range:
    www.ti.com/.../snoa950

    2. Additional capacitive parasitics, this could effect the excitation frequency

    3. Worse matching sensor to sensor. PCB based coils have excellent matching.

    I'm unsure why the inductance increases instead of decreases. There can be interesting effects if you are using magnetic material.
  • 0 in reply to Bharat Aravamudhan
    TI__Expert 6625 points
    Hi Jun,
    What conductive material are you using? The general rule of thumb is to use the most conductive material as possible. Based on that fact, silver would be ideally the best option but it is also expensive. Copper is a good option considering the cost and other properties. The more conductive the material, the stronger the eddy's current will be on the target which leads to a bigger delta in the inductance that the LDC can detect. When the metal is approaching the sensor the eddy's current would be stronger which will oppose the sensor's magnetic field resulting in a lower inductance. How did you measure the inductance increase? Finally, higher resistance is directly proportional to higher resistivity which increases the skin depth. Your goal is to minimize the skin depth as much as possible, because your target needs to be at least 3x the skin depth to have at least 95% of current to flow through the conductor. Please refer to our sensor design and target design app notes for more information on this:
    1. Sensor Design: www.ti.com/.../snoa930a.pdf
    2. Target Design: www.ti.com/.../snoa957a.pdf

    Best Regards,
    Bala Ravi

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