• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 30 subscribers
  • Views 229 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LDC1101: Best setting for high resolution for short distance sensing

Eric
Prodigy 140 points
Part Number: LDC1101

Hello,

I have an application where my sensing range is very small. I am sensing a shaft and I need to sense small changes in shaft displacement. (0.01mm iterations) with a desired sensing range of about 0.5mm. As you can tell, this is a short range, high precision application.

I'm aware that the LDC1101 has 2 different sensing modes: Rp + L measurement mode and high resolution L mode. For my application where I want to get the best accuracy, what mode would be best to pick? What are the advantages and disadvantages of each.

Finally, in Rp + L measurement mode, is there a difference in accuracy whether I read Rp or L? Do I need an external clock signal to measure L? If so, how would I set this up?

Thank you!

Eric

  • 0
    TI__Mastermind 34125 points

    Eric,

    I believe your best approach will be to measure L, and disable the Rp measurement.
    Disabling Rp measurement disables the sensor modulation used by the LDC1101 to measure RP and can reduce L
    measurement noise. Section 9.1.11 of he device data sheet has more details.

    Section 9.1.13 has some clock recommendations:

    "Use a clean, low jitter, 40-60% duty cycle clock input with an amplitude swing within the range of VDD and GND;
    proper clock impedance control, and series or parallel termination is recommended. The rise and fall time should
    be less than 5 ns. Do not use a spread-spectrum or modulated clock.
    For optimum L measurement performance, it is recommended to use the highest reference frequency (16 MHz).
    LHR conversions do not start until a clock is provided on CLKIN."

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 140 points

    Hello John, 

    Thank you for your reply, I'm a bit new to this. I just had a few more questions. 

    Would I have to source my clock from a clock IC? Does the external clock signal need to be fed into the LDC1101 simultaneously as I perform the inductance readings through my SPI transmission?  If that's the case, wouldn't that mean that I'd need a continuously generated clock signal?

    Would a clock signal sourced from the ePWM modules be appropriate? I was thinking of setting up a 50% duty cycle PWM on one of my MCU pins (I am using the F28379D launchpad). However, I've noticed that at higher frequencies, the MCU draws a lot more current from my power supply.

    What are your thoughts? 

    Best wishes,

    Eric

  • 0 in reply to Eric
    TI__Mastermind 34125 points

    Eric,

    Any clocking source should be okay as long as it conforms to the conditions in section 9.1.13 of the data sheet.
    The LDC1101 won't perform LHR conversions until the clock is active on CLKIN, so the clock is needed as long as you need conversions to happen.

    I am not familiar with the ePWM module. If it meets the criteria of 9.1.13 it should be okay. Please be sure there are no time-varying signals (e.g. modulation) embedded on your clocking signal is you use this approach.

    Regards,
    John