• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 30 subscribers
  • Views 332 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LDC1314: LDC1314: Metal target only changes LC circuit *amplitude*, not frequency.

Marcel Hensen
Prodigy 10 points
Part Number: LDC1314

Hi, I am using a LDC1314 to detect the presence of a piece of metal.

My coil is a 3-layer PCB coil with seven windings and a ferrite core, measuring 26µH with metal target missing, 36µH when metal target is present.

No matter what parallel capacitor i use, at every sensor frequency, moving the metal target only ever changes the *amplitude* of my sensor freqwuncy, not the frequency itself.

What would be typical things to check when encountering this behavior?

  • 0
    TI__Mastermind 40295 points

    Marcel,

    The presence of the metal target should decrease the sensor inductance, not increase it.
    This effect is due to the eddy currents in the target opposing the sensor's magnetic field, thereby decreasing the sensor's inductance.

    What is your measured versus target sensor frequency?
    Can you provide some additional info on the sensor coil?
    Can you measure the coil's impedance versus frequency with a vector network analyzer? This could help us figure out if the coil's self-resonant frequency is affecting your sensor frequency.

    Just so you know, tomorrow is the July 4th holiday in the US and replies may be delayed.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 10 points

    Hi John, thanks for your reply.

    In this case, the metal target acts as a magnetic core in the coil, and raises its AL-value when present, thus increasing the inductance.

    PM me your contact details and I can provide some pictures of our test board and the requested measurements. I'm absent for the rest of the week, so please allow for a few days response time.

    Best regards, Marcel

  • 0 in reply to Marcel Hensen
    TI__Mastermind 40295 points

    Marcel,

    I will reach out to you via the E2E PM feature. Please accept the friendship request and we can go from there.

    Regards,
    John