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TDC1000-TDC7200EVM: Problems regarding readings/measurements in both air and liquid

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Replies: 5

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Hello! I received the TDC1000-THDC7200EVM test board just recently, and I have not been able to get it to work as intended. Furthermore, I'm using an oscilloscope to inspect the problems.

I followed the datasheet/user guide and attempted to use the provided piezo (SMD15T21R111WL), for a simple test application in air (short distance measurements). Simply, to retrieve back signals. Sadly, I was unable to receive any sensible data on the GUI (graph) or on the oscilloscope.

The setup: Piezo aimed towards the surface.

The result was as following (Orange signal = START, Purple single = COMP_IN, Blue signal = STOP)

Problem:

No matter how far the piezo's distance is towards the surface, or the angle towards the surface it would still give me the same result, no changes occur. The signal only changed when any object touched the piezo. 

What I have tried:

1. Loaded default configuration for the piezo

2. Tried it with two piezos, same type: SMD15T21R111WL, one is set as RX and the other TX. Same problem, the signal does not change if I move the transducers away from each other. 

3. Changed configurations and tried it with a liquid application, but same result.. Signal stays the same as before, does not change.

My current setup configuration:

I'd appreciate any help!

Kind regards,

Hamza Mubasier.

  • Hamzra,

    I see that you have received the STOP & thereby should be able to find the TOF.
    Please refer the document: www.ti.com/.../snaa266a.pdf on how to attach the transducer to get accurate results.

    ---------------------------------

    Bharat Aravamudhan

    Sensor Signal Conditioning Applications

  • In reply to Bharat Aravamudhan:

    Thanks for replying ,

    Indeed, I have received the STOP signal, but the readings from the oscilloscope/the graph (GUI) do not change. So, therefore the TOF measurements are the same at all times.

    Take for example the piezo aimed towards the surface above (short distance measurement in air). Here's the scenario:

    1. If I move the piezo away from the surface, the stop signal should go more to the right, but it stays the same. So, TOF stays the same.

    2. If I move the piezo towards the surface, the stop signal should go more to the left, but it stays the same. So, TOF stays the same.

    3. The readings' only change if the piezo touches another object.

    The readings are the same at all times, what may I be doing wrong here?

    If you need more clarification or pictures please ask.

    Awaiting your reply,

    Hamza.

  • In reply to Hamza Mubasier:

    Hamza,

    the piezo that comes with the EVM pack is 1Mhz transducer and it is typically suitable to measure ultrasounds throud liquid rather that in air. You will need to use transducers of say 40khz till 300khz for accurate ToF through air. In case you plan to use this EVM to measure the liquid level/concentration do use this EVM with the provided transducer, however please attach the transducer as shown in the app note above.

    ---------------------------------

    Bharat Aravamudhan

    Sensor Signal Conditioning Applications

  • In reply to Bharat Aravamudhan:

     I'm fully aware that 40kHz-300kHz is intended for air application, whilst 1 MHz is intended for liquid applications. 

    I won't be using it for air application, that was only a test to see if everything is operational. I'll be using it for a liquid application with two transducers (1Mhz) with a distance of approximately 15-20mm. 

    The app note shows how to mount the transducer with glue and such. But before I do that, I wanted to make sure that it fully works, so I tried to tape two transducers on both sides with a distance of approximately (15-20mm). The stop signal is there, but when I de-mounted the transducer it was still the same, no change in the signal. Even if the transducers were not aiming at each other, I'd still get a stop signal.

    Shouldn't the stop signal change by distance? Why does it stay the same?.

  • In reply to Hamza Mubasier:

    Hamza,

    Please refresh the GUI and see if you still see the STOP pulses. If you still see the stop pulses without really transmitted from the transducer then it could be a case wherein the transducer is picking up noise and that is producing a STOP pulse.
    Try to either increase or decrease the threshold that could help to get over the noise issue.

    ---------------------------------

    Bharat Aravamudhan

    Sensor Signal Conditioning Applications

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