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LDC1612: Code differences after 24 hours

jz1354
Prodigy 30 points
Part Number: LDC1612
Other Parts Discussed in Thread: LDCCOILEVM,

Hello,

 

I am utilizing a LDC1612 with a F28379D launchpad to measure lateral movement on coil B from the LDCCOILEVM. Yesterday, I was able to create a 1mm resolution scale used from LDC data from 0mm to 59mm. To create this scale, I divided DATA0 by 1000 and mapped mm points along the coil with a ruler. With this data collected, I was able to create a linear equation that was included in the code. I power cycled the system a few times to see if the scale was usable, and in fact it was. After 24 hours however, I noticed that the scale does not work. Yesterday’s 0mm data point was 7403, and today’s 0mm data point is 7484, leading to a offset of 81. I included this offset in the code today, however the scale is not as reliable. I was wondering what could lead to this variation in data. The hardware system/ target has not changed. The only change in software is the subtraction of the offset.  Below are the system parameters:

 

Coil B from LDCCOILEVM with 820pF capacitor connected to LDC1612 portion of LDC1612EVM.

100mm x 25 mm meta target.

Launchpad is utilizing a 400k i2c clock.

Register values for LDC1612:

RCOUNT0: 0xFFFF

RCOUNT1: 0x0009

SETTLECOUNT0: 0x0012

SETTLECOUNT1: 0x0001

CLOCKDIV1/2: 0x1001

ERRORCONFIG: 0x0001

DRIVECURRENT0/1: 0xF000

MUXCONFIG: 0x820C

DEVICECONFIG: 0x1E01

Thank you.

  • 0
    TI__Mastermind 18545 points

    Hello, 

    The our LDC devices are best at determining a change in the inductance rather than an accurate measurement of it. Part of this is because changes in the environment, like temperature, can cause deviation in the data similar to what you describe. One way to deal with this is to have a secondary sensor connected to use a reference to track changes in the environment. If you use a coil that is identical to your sensor coil, you can directly remove any change on your reference from your sensor coil. 

    Best Regards, 
    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 30 points

    Hello Justin,

    Thank you for reaching out. I will try the reference coil out.