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LDC1612: Inductance Sensing of a Spring while expanding or compressing.

Bhargav Mistry
Prodigy 10 points
Part Number: LDC1612
Other Parts Discussed in Thread: LDC1312, LDC3114, LDC1614

Hi,

I have an application to detect the change in Inductance value of a spring after its movement (expansion/compression).
Image is attached.

L = 3µH, C = 1nF

The spring has L = 3µH, Series resistance Rs = 3Ω.
If I use C = 1nF, which means; Resonant frequency Fr = 2.9MHz and Rp = 1K.
Resolution for change in Inductance of 0.01µH (10nH) is required.

  1. Would LDC1612 be able to detect this or do you recommend other ICs (LDC1312)?
  2. How to optimize resolution to detect change in Inductance with LDC1612, i.e. Increase C to 2.2nF ? Add additional inductance on 2.2µH in series with spring?
  • 0
    TI__Mastermind 18545 points

    Hello, 

    The Inductive Sensing Design Calculator Tool (Rev. G) has a tab for the spring calculation. You can use this to see the effective code difference that the LDC1612 will see. Changing the frequency (through L or C) will also the number of codes that you will see for the spring movement. Once you have the number of codes change for your given movement, you can determine the resolution of the application. I would also recommend reading the Optimizing L Measurement Resolution for the LDC161x and LDC1101 app note for further help optimizing the resolution. 

    The LDC1612 has more bits available than the LDC1312. The LDC3114 is also an option here. When it is used in raw data mode, it is very similar to the LDC1614. 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 10 points

    Thank you Justin,

    I've got it working LDC1612 and able to get the resolution needed.

    So the next question is to optimize Power consumption of the device.

    1. Is it possible to put LDC1612 in Sleep mode for 9ms then wake up and take sample for 5ms and again go to sleep?
    2. What is the minimum time needed to take a sample by LDC1612? 
    3. Do I need to do it manually or LDC1612 can handle it automatically?

    Best regards

  • 0 in reply to Bhargav Mistry
    TI__Mastermind 18545 points

    Hello, 

    We have the Power Reduction Techniques for the LDC131x/161x for Inductive Sensing app note describing how to use the LDC1612 by waking it up to take measurements. You will have to manually sleep and wake up the LDC1612. For built in low power, the LDC3114 that I mentioned is a better choice as it has a low power mode and variable sample rate included. 

    Best Regards, 

    Justin Beigel