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LDC1612EVM: To use the LDC1612EVM evaluation board for non-invasive and contactless liquid conductivity monitoring

Yashwanth Ramesh
Prodigy 20 points

Part Number: LDC1612EVM

Tool/software:

My name is Yash, and I am a graduate student working on liquid conductivity measurements. I am currently using the LDC1612EVM evaluation board, which comes with coils connected to each of the two channels. To experiment with different inductance values and Q-factors, I also purchased the LDCCOILEVM evaluation board for testing alternative coil configurations relevant to my application.

In my experimental setup, I poured a salt solution into a glass container and situated the coil on the outer wall of the container. The coil was connected to the evaluation board, which was then connected with my computer and I tracked my measurements via the TI GUI for inductive/capacitive sensing. Now, when I increased the conductivity of the solution inside the container, the GUI consistently showed that the inductance of the coil increased as well.

I would like clarification on the following points:

  1. Cause: What possible physical mechanism causes the inductance to increase with increasing solution conductivity?

  2. Correctness: Is this response expected, or could it be an artifact / error of the measurement system?

  3. Application: Can this method serve as a reliable, non-invasive, contactless approach for liquid conductivity measurements?

Note: For experimental consistency, I ensured that the liquid volume inside the container remains constant across all conductivity levels.

Thank you for your time and guidance.

Best regards,
Yash

  • 0
    TI__Intellectual 1040 points

    Hello Yash,

    1. As the conductivity of your target increases, the inductance will increase as well.
    2. This should be repeatable but more testing may be needed. Try changing the amount of salt in the solution by a fixed amount and remeasuring the inductance. With some number of measurements you should be able to determine if there is a trend.
    3. To determine if this is valid method, you need to determine the noise floor of your system. You can find this by testing the system with no liquid (target). You would then take the standard deviation of the data collected and compare that value to the change in the output data when the liquid is present.

    Typically capacitive sensors (such as the FDC1004) are used for liquid level sensing, please refer to the app note here.

    I hope I was able to assist you with your problems. If you require any further assistance, please reply below.

    Thank you,

    Chase Girard

  • 0 in reply to Chase Girard
    Prodigy 20 points

    Hi Chase

    Thank you for your prompt reply. So you're saying that as the the conductivity of your target increases, the inductance of an LC tank coil connected to the the LDC1612EVM board will increase as well.

    But if you look at the tutorial video for the LDC1612EVM board, they show that the inductance reduces when they bring a metal target close to the coil (please refer to the image attached). This contradicts what I'm seeing and that's the reason why I posted this question. I didn't mention this previously, but the conductivity range of my salt solution is between 5-40 mS/cm. Compared to a solid metal piece's conductivity, is my conductivity range too low ? Is that why we see a different trend ?

    Or from an electrical engineering perspective do you think we can NOT put a conductive solution and a metal in the same category ? Like their properties are different ? Or do you think that doesn't matter ?

     

  • 0 in reply to Yashwanth Ramesh
    TI__Intellectual 1040 points

    Hi Yash,

    Yes you are correct, when placing metal by the sensor you are reducing the inductance. However with a liquid, there might be some capacitive effect the liquid is having on your circuit. By increasing the capacitance of your liquid, you might be increasing the capacitance of you LC tank circuit as well. When capacitance of you LC tank circuit increases, you sensor frequency decreases.

    As mentioned in my prior post, typically capacitive sensors (such as the FDC1004) are used for liquid level sensing, please refer to the app note here.

    I hope I was able to assist you with your problems. If you require any further assistance, please reply below.

    Thank you,

    Chase Girard