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TDC1000: Seeking advice on building a fluid identification device.

Divraj Singh
Prodigy 20 points
Part Number: TDC1000
Other Parts Discussed in Thread: TIDA-00322, TUSS4470, , TDC7200

Hello everyone,

I am interested in building a fluid identification device that measures the time of flight (ToF) through a liquid and determines the liquid present based on its density. I have looked into the TDC1000 and specifically the TIDA-00322 reference design's test report to see if it's suitable for my application.

However, I am looking for a product that can measure the speed of sound more accurately and precisely, with an accuracy of around +/- 2 m/s at the speed of 1600 - 1000 m/s, through a fixed distance of no more than 10cm (from transducer to acoustic-reflective surface). Based on the test report of the TIDA-00322, it seems that it cannot meet my requirements.

I have a few questions:

1. Does Texas Instruments offer a more accurate and precise solution for my needs?

2. If I change the size of the transducer, will it affect the results provided by the TDC1000?

3. Is it possible to purchase the TIDA-00322 instead of building it from scratch?

Thank you in advance for any advice and guidance you can offer.

Best regards,

  • 0
    TI__Mastermind 23045 points

    Hello Divraj,

    Thanks for posting to the sensing forum! Let me help address your questions.

    1. Does Texas Instruments offer a more accurate and precise solution for my needs?

    • The main contributor to your accuracy on this application will be your timer. The difference of +/-2 m/s can mean different timing requirements at 1600 m/s vs 1000 m/s hence why this is accuracy is typically referred to in terms of time. You will need to ensure that your timer must be very stable to have very little variation to tell the difference between +/- 2 m/s. At max speed for your application this difference could be as small as 40ns. Another device that I would recommend for this application would be the TUSS4470. This is an analog output device but it contains a programmable digital output on a specific threshold. It can be used similar to the TDC1000 but it does not generate a START pulse like the TDC1000 it would have to be setup in your timer system via another method.

    2. If I change the size of the transducer, will it affect the results provided by the TDC1000?

    • Changes in the transducer can definitely change the behavior of the system. Size wouldn't be my biggest concern but other items like frequency would be items that could impact your system behavior more significantly.

    3. Is it possible to purchase the TIDA-00322 instead of building it from scratch?

    • Unfortunately we don't sell most of our reference designs, but realistically I don't think you would require the use of this board to do any testing. TIDA-00322 is mainly geared to make measurements in large automotive tanks where the distance can be pretty large so the transducer must be driven at a higher voltage. In your case the distance is no more than 10cm so you should be able to test your application using the TDC1000-C2000EVM which is orderable on TI.com.

    I hope this helps let me know if there are any other questions!

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 20 points

    Hey Issac, pretty new to using ultrasonic sensors, can the TUSS4470 provide the received signal to detect the phase change between the transmitted and received signals?

  • 0 in reply to Divraj Singh
    TI__Mastermind 23045 points

    Hello Divraj,

    No worries, I can help clear up any confusion if there are any.

    Not sure what you mean by the phase change of the received signal, TUSS4470 does provide the analog data of what is received by the sensor but the info that you get is the envelop of the signal which is filtered and amplified. Are you trying to identify if there is a frequency shift from when you transmit vs when you receive?

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 20 points

    Hey Isaac,

    The phase shift as seen in the image below. The red line is my sent signal through the liquid and blue is the received from the other side.

    Ill then calculate the angle change.

  • 0 in reply to Divraj Singh
    TI__Mastermind 23045 points

    Hello Divraj,

    This is not possible to do with TUSS4470. The return echo is significantly different from what is transmitted by the transducer. Note that the signal that is used to excite the transducer will be mechanically vibrate the transducer in order to generate the pulse. The pulse then travels to the target then back and then signal received is heavily attenuated and must go through some filters to eliminate noise. The phase would be extremely hard to calculate since the signal produced by the transducer is essentially unknown and the signal at return is so small that once amplified and filtered there are additional phase changes due to the filtering the device received.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 20 points

    Hey Issac, What if we used two different transducers (one for receiving and one for transmitting)

  • 0 in reply to Divraj Singh
    TI__Mastermind 23045 points

    Hey Divraj,

    You can use two transducers with the TUSS4470 EVM. The input to the transducer during the excitation period will only be a square wave.

    While the received echo might be two small to detect without any additional gain or filtering the VOUT pin of the TUSS4470 looks like the following:

    The initial peak near 0 is the transducer excitation while the second peak at about 14ms is the return echo. If you use two transducers the initial peak near 0 will be reduced significantly because the RX transducer is not directly saturated. If you were to probe the RX data directly you might load the transducer eliminating your signal and it could be hard to see the data. If you are able to see the data then you should see actual waves.

    I am still trying to understand what the advantage of obtaining the phase angle in your system would be. Are you trying to obtain the ToF using this method somehow?

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 20 points

    My idea was to use the phase shift to measure the speed of sound in liquid more accurately for the range that im working with (less than 10cm). Are you suggesting to use the TUSS4470 for ToF? Wondering how I can be sure it will provide the right resolution (+- 2m/s)? Is there a way I can calculate this with what is provided in the datasheet?

    From your intial reply is it just the case of finding a crystal oscillator with very stable frequency? (i.e. very low +-ppm)

  • 0 in reply to Divraj Singh
    TI__Mastermind 23045 points

    Hello Divraj,

    It may be possible to use the phase angle but I honestly have not seen anyone attempt this method of measurement before. Perhaps because there could be some challenges or limitations to this method. 

    The TUSS4470 can be used for ToF at 10cm. Typically we see TDC1000 being used for the specifications you listed since the range is very small (10cm) and this is a liquid based application which is what we recommend TDC1000 for but TUSS4470 could be a suitable device as well. I would usually recommend TUSS4470 if the range were bigger since it has a better dynamic range and ability to generate large pulses.

    The resolution of the sensor is based on the frequency and and this is typically in meters so you need to have a frequency high enough to obtain the resolution you require a 1MHz transducer or higher should be suitable. I think what you are looking for is accuracy and above I established you need an accuracy of ~+/- 40ns to stay within your +/- 2 m/s requirement. The comment on the clock is mainly based on the TDC1000 or if using the digital output pin on the TUSS4470.

    Now the accuracy of your measurement is not really something we can specify on the datasheet because it depends on other external factors. Since the TDC1000 does not provide users with the ToF but instead just provides that signals to calculate it, you must ensure that you have the proper tools to obtain the ToF. This means your timer needs to be able to provide a timer clock with very good the accuracy required by your system. So if its an MCU or an external timer like TDC7200. As mentioned earlier the biggest difference your system can tolerate is 40ns, if it cant time better than 40ns then your system will not be able to make the measurements you require then your accuracy will always be below.  Other factors to consider would be the temperature, as this can have an effect on the speed of sound in a medium. Since the speed of sound can vary at different temperature having the temperature factored into your calculations will provide better stability to your calculations and obtain a more accurate ToF.

    Here is a document that may help you learn about fluid identification using ultrasonic sensors: https://www.ti.com/lit/an/snaa265/snaa265.pd

    Best,

    Isaac