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Original question:

TDC1000-Q1: Received signal very poor or not there at all

PGA460PSM-EVM: Using a 40Khz Transducer for Liquid Level Sensing

Sahaj Walia
Prodigy 120 points
Part Number: PGA460PSM-EVM
Other Parts Discussed in Thread: TDC1000, , TUSS4440, PGA460, TDC1000-C2000EVM, TUSS4470

Tool/software:

Good Afternoon,

I was looking for some guidance on if this is the best approach. I am currently doing some testing where I am trying to take water level readings up to the distance of 10ft in a tube. I have mounting the transducers at the bottom of the tank with the top of the transducer actually in the water.

I was originally using the TDC1000 with a 1Mhz sensor and found that the distance was only reading up until 14 inches. I then tried to increase the excitation voltage up to 20V but only saw up to 30 inches which is still short of my goal.

After some digging online I read that using a lower frequency transducer would be best as it can travel a larger distance in water with attenuating. Now my question is, if I use the following transducer from steminc: Piezo Ultrasonic Air Transducer 40 Khz 10mm would this work with the TDC1000 or should I order the PGA460PSM-EVM and take readings with that? Or is there a better method using off the shelf items that I can use to achieve my goal?

Regards,

Sahaj

  • 0
    TI__Mastermind 21110 points

    Hello Sahaj,

    Thanks for posting to the sensors forum! That is correct a lower frequency transducer will carry more energy allowing the signal to travel farther than lower frequency signals, the main issue is that the lower frequency transducers will not offer as much resolution for the measurement since the resolution is a function of the frequency. When the transducer is directly water coupled the medium of transmission is much faster than in air so this is why the resolution becomes more important.

    I think you may need to find a good balance between the distance you are trying to achieve and the resolution needed by your system. If you can sacrifice quite a bit of resolution then it may certainly be good to use something like a 40kHz transducer. But if you need some resolution then perhaps using something like 100kHz or 200kHz will get your to your target resolution and still achieve the large distance you are looking at.

    As far as what EVM you should try, the TDC1000 is not recommended for usage below 500kHz so this may not works for you. As far as what other devices I may recommend, it might be worth it to looking into the BOOSTXL-PGA460EVM or the BOOSTXL-TUSS4440EVM. The reason I don't recommend the PSM-EVM is that the PGA460 is a very feature heavy device so having access to the GUI is very important, and this requires the larger version of the EVM. The TUSS4440 is a much simpler device that can work similar to the TDC1000 essentially generating a STOP signal based on a threshold. It can support various frequencies and it is transformer driven so it can support driving much larger voltages.

    Let me know if there are other questions I can help out with!

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 120 points

    Hello Isaac,

    Thank you for your response. I've purchased the DEV Boards to experiment with the lower frequency transducers. I do have one final question: I ordered the transducer from this link (https://www.steminc.com/PZT/fr/air-transducer-300-khz) and connected it to the TDC1000-C2000EVM. However, I only observed a single TOF reading. My intention was to immerse the sensor in water to obtain TOF readings, but the value remained constant and did not change. I assumed that since the transducer was already encapsulated, I wouldn't need to glue it to anything or use any dampening material. Could you advise on the correct method for mounting this sensor if I intend to submerge it in water for level readings?

    Note: The calculated TOF reading should be 100uS and I was getting around 50us regardless if the transducer was submerged

  • 0 in reply to Sahaj Walia
    TI__Mastermind 21110 points

    Hello Sahaj, 

    For the TDC1000 you have to change the clock division to make sure you are emitting at the 300kHz that this transducers resonating frequency. There are a couple of other nuances with the TDC1000EVM such as reconfiguring the external filters and configuring the listening window to the appropriate time. Since this frequency is lower than the 1MHz transducer the blind zone is much larger hence why you might be getting a consistent ToF reading of 50us, so check the listening window to make sure that the decay period has elapsed. The TDC1000 is configured to work with a 1MHz transducer so this might also be contributing to the issue.

    Typically the transducer is mounted outside of the tank and not submerged in the water, but we have dealt with a couple of instances there. You might need to check with the manufacturer to see if this transducer is fine with being submerged inside of water. Other than that there weren't any other concerns with the way that the transducer was mounted. 

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 120 points

    Thank you for you response, I received the boards and am using the 40Khz transducer that came with the development board for the TUSS4470, the GUI is a bit complicated and the guide is not very clear on what configuration to use. Do you have recommended settings for the transducer provided

  • 0 in reply to Sahaj Walia
    TI__Mastermind 21110 points

    Hello Sahaj,

    For the longer distance you may require TUSS4440, this device was recommended over the TUSS4470 due to the fact that the TUSS4440 is transformer driven and can reach a larger drive voltage if necessary. The TUSS4470 is a direct driven architecture which may not have enough voltage range to reach the 10ft requirement. 

    The frequency has to match the transducer frequency, record length depends on the distance you are trying to measure, number of pulses will also depend on the distance you are trying to measure.

    Make sure VDRV_HI_Z is not in high Z. Aside form that the BPF will reconfigure itself after changing the frequency and the rest of the configurations are somewhat system dependent.

    Let me know if this helps.

    Best,

    Isaac