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LDC1612 coil pattern for motor

PAN-M
Mastermind 8375 points
Other Parts Discussed in Thread: LDC1101, TIDA-00508

Hi

We're going to try experiment to measure a revolution and location of a motor by LDC.
The pattern is drawn in a board of diameter 42mm.
A coil uses 2 of φ13 of LDC Reference Coils (snou136).
Do you have a best design pattern?
For example, is 13mm best in the part indicated by a red arrow?

coil_pattern.pdf

How much are the maximum of number of rotations and the resolution of angle?
(ex. 10000PRM/1°)

Regards,
PAN-M

  • 0
    Expert 1070 points
    Hi, PAN-M,
    I would like to share my humble experience about this item. You should design your target shape in accordance with recomendations from tidu953.pdf document. There is a d1:d2:d3 = 1:1.1:1.2 rule for sizing and also very important is to be sure that centers of coils be placed on a circle that is simmetrical to target shape: the target shape is formed of two spirals one of wich is increasing and the other decreasing there diameter with the angle. And the center line (circle) between them is the circle on which centers of coils should be placed. Otherwise you'll get wrong-shaped sin and cos waves.
    Best wishes,
    Igor Gorbounov
  • 0 in reply to Igor Gorbounov
    Mastermind 8375 points
    Thank you for reply Igor.
    I know TIDA-00508I and have it.
    However, we make revolve a disk at high speed and moreever try to know the location.
    The coil is 1mm distance from a board.
    I'd like to know whether it is able to gauge a little decrease pattern of the 13mm by a coil of 13mm.
    (Is 12mm better for performance?)
    PAN-M
  • 0 in reply to PAN-M
    TI__Genius 14270 points

    Hello Pan,

    Using a slightly larger sensor is recommended if you are going to have a 1mm gap between the sensor and target. With a 2 channel solution, it is very important to control the Z height of the target disk with respect to the sensor array.

    For higher speed operation, using 2 LDC1101 devices may be a better choice, as multiple LDC1101 devices can have synchronized sampling by gating the sample clock applied on the CLKIN pin.

    Regards,

    ChrisO

  • 0 in reply to Chris Oberhauser66
    Mastermind 8375 points

    Hi Chris

    The details of our target(angle, rotation speed, coil width, gap) aren't decided.
    But, when we don't have data, customer don't know whether LDCxxxx can be used by the motor application.

    Our concern is;
    When 13mm coil and 13mm(max) pattern is use,  how many mm of difference can detect?
    The pattern width of the 13mm is edge of a coil of 13mm.
    For example, can we measure the difference in the 0.01mm? (12.99 < 1300)
    If we can't measure, should maximum width be made 12mm? (13mm coil)
    About the data rate, we are thinking by attached file calculation that influence between the rotation and the angle.
    I think I2C is bery slow for this application but LDC1101 x2 are very expensive.

    LDC_4_motor.xlsx

    Thanks and Regards,
    PAN-M

  • 0 in reply to PAN-M
    TI__Genius 14270 points
    Hi Pan,

    The lateral/rotational measurement resolution of the LDC is a function of the distance, target composition, and sample rate.

    If you bring the target closer to the sensor, the measurement resolution increases.

    With a lower sample rate, the LDC will have a higher effective resolution.

    TIDA-00508 recommends the thickest target dimension be ~80% of the sensor size.

    Also, ensure that you are using a sensor frequency which works with the target thickness. TIDA-00508 uses a 1oz (35um) thick target; at the nominal sensor frequency of ~6.9MHz, the target will give ~75% of the maximum possible response. However, if the sensor frequency was only 1Mhz, then the response would be only around 42%.

    As for the 2x LDC1101, if the target is rotating above the maximum speed of TIDA-00508 (~200RPM), then the accuracy will be reduced. Using two synchronized LDC1101s will provide better angular measurement capability.

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Mastermind 8375 points
    Chris
    Thank you for support.
    I will make a board by your information.
    Thanks and Regards,
    PAN-M