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Frequency of Target and Its Effect on LDC1000 Parameters

Sami Lakka
Intellectual 315 points
Other Parts Discussed in Thread: LDC1000EVM

In our application the frequency of the target varies considerably (between 20 Hz to 200 Hz or more). I have noticed that in order to see the vibrations in the higher frequency range, setting the LDC to 0x15 instead of 0x17, provides better measurement. How does the target frequency generally affect the LDC1000 parameters.

  • 0
    TI__Expert 6550 points

    Hello Sami,

    Unfortunately, we dont have reference designs where target frequency is considered. Generally, LDC technology outputs the change in inductance and resistance values while a conductive target is brought near the LC tank. As I understand, as your target vibrates it moves closer to the coil?
     
    Best Regards,
    Natallia Holubeva

  • 0
    TI__Prodigy 500 points

    Sami,

    can you explain what you mean by the frequency of the target? I assume you mean the frequency that is measured by the LDC? Which register is being set when you say "... setting the LDC to 0x15 instead of 0x17...).

    I assume you are using a coil. What is the free-air inductance, and what is its diameter and number of turns? What is the cap value that you are using? How close is the target when you observe these values?

     

    Jim

  • 0 in reply to Jim Catt
    Intellectual 315 points

    Hi

    By frequency of the target I mean that my target (a small metal plate) is vibrating. This vibration frequency changes between 20Hz to over 200Hz. 

    I am using the LDC1000EVM coil. From FAQ: The LDC1000 EVM is a 2-layer PCB with 23 turns per layer, 14mm outer diameter, 5mm inner diameter, 4mil (0.1mm) trace width, 4 mil (0.1mm) trace spacing. The top layer is clockwise inward; the bottom layer is clockwise outward (as seen from top). The EVM is manufactured with 1oz copper thickness (1.37mil or 34.8um)

    LDC register is at address 0x04.

    The target distance varies between about 6 to 10mm.

  • 0 in reply to Sami Lakka
    TI__Expert 6550 points
    Hello Sami,

    The rule of a thum is that you can detect your target with the max range 1/2 of coil diameter. As you mentioned, the target distance varies between 6 and 10 mm. Using a larger coil should improve your detection range.

    Best Regards,
    Natallia Holubeva
  • 0 in reply to Natallia Holubeva1
    Intellectual 315 points
    The EVM coil has a hole in the center. If this hole is removed and instead the whole diameter is filled with turns, will the depth resolution improve?
  • 0 in reply to Sami Lakka
    TI__Expert 6550 points

    Sami,

    It will increase the electoromagnetic field. However, this increase is useful when the taget is next to the coil. At a maximum distance between the coil and the target, the coupling of the inner turns will not be noticable.

    Best Regards,

    Natallia Holubeva