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TDC1000-TDC7200EVM: Measuring liquid levels in liquid tanks - coupling material and extending the timing register

Glenn Glashagen
Prodigy 40 points

Part Number: TDC1000-TDC7200EVM

Hello,

I just started to measure fluid levels in a metal tank using the TDC 1000 board by mounting the ultrasonic sensor at the bottom of the tank just as in "How to perform liquid level sensing through the bottom of a metal tank".

However I'd like to avoid gluing the sensor to the tank. I sometimes get signal using all sorts of coupling media but it seems to me that the coupling media between the tank and the sensor is really important and that it also highly depends on the sensor and frequency. Do you have any experience on the crucial factors like maybe thickness, consistency of the coupling media or the frequency that is used best?

Moreover I'm struggling with the timing register on the evaluation board. I need a maximum time of 3.4 ms to detect the highest liquid level. Is there  a way to to slow down the clock of the timing register or at least i´hinder the board from cutting the signal after 1ms?

All the best,

Glenn

  • 0
    TI__Mastermind 31655 points
    Hi Glenn,

    Aside from the basic recommendations listed in the transducer mounting application note, our expertise is a bit limited as far as ideal materials for transducer coupling go. I recommend that you contact the transducer manufacturer for better results.

    With the evaluation board and a 1Mhz transducer you can achieve longer measurement periods by using the CPU clock on the MSP430 instead of the onboard crystal oscillator. The goal is to increase T0 (the input clock period after the CLOCKIN_DIV is adjusted which controls the blanking times and overall measurement length) while keeping T1 (the TX output period after TX_FREQ_DIV) to 1us or 1Mhz frequency.

    You can set the MSP430 clock to 2Mhz. On the setup page choose CPU_CLK, and click CPU_CLKEN. Make sure to change the jumper JP5 on the EVM to CPU. Next change the TX_FREQ_DIV to Divide by 2. Change the CLOCKIN_DIV to Divide by 2 for the maximum T0 period. This will increase the maximum TIMEOUT time to about 1ms, and you can adjust the TIMING_REG and AUTOZERO_PERIOD to add up to a 2.4ms or greater time to have a full measurement length of 3.4ms or more.

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 40 points
    Hi Scott,

    thanks a lot for your answer! Unfortunately I had to wait until today to continue on the project.

    I did just as you said and was able to extend the timing register by a maximum of about 8ms which is more than enough.
    But somehow I could not see the signal of the reflection anymore even though I divided the frequency by two so that I had 1 MHz again.
    (As I'm writing this it comes to my mind that the autozero period might have extended much further also so that the signal vanished but could it have another reason as well?)
    Other than that I still get this step like behavior on the oscilloscope after 2ms (which I contributed to the point where it stops measuring) rather than the time which i set in the timing register which should be far more that 2ms.
    Could you think of a reason for that?

    All the best,
    Glenn