TDC1000-C2000EVM: I have some questions about the TDC1000. Can you help me to solve them, thank you !

Hello Songjiang,

Thanks once again for posting on the sensing forum, I am glad you were able to source the transducer for your EVM! There could be a couple of various reasons as to why the ToF is showing a set value. Can you provide your EVM register configuration. Also is it possible for you to probe the TX/RX waveform and STOP test points on your EVM. My thought is that perhaps the device keeps detecting the burst transmission as and triggering a STOP pulse during this time.

Keep in mind that the transducer is also 1MHz, higher frequency signals get attenuated very quickly in the air. If you are attempting to do air coupled measurements this is definitely not the best device to use and would make a different recommendation based on your needs. Looking forward to your response!

Best,

Isaac

Hello Mr. Lara,

Thanks for your reply! This time I want to use the TDC1000 to measure the liquid level by TOF, and I use a cubic container with some water in it, like the picture below, I add some alcohol in the container but the TOF is still a set value. There is the configuration of the EVM. Since I can't find a oscilloscope to get the waveform, could you help to find weather there is some parameter false? Thanks!

Songjiang Hou

Hello Songjiang,

Thanks for the info. Do you know what the speed of sound of the ultrasonic signal in alcohol? and what is the distance you are trying to measure in your tank?

This should tell us how to program the listening window for the TDC1000. If the listening window is too quick then the device can trigger on the initial pulse and if the listening window is not placed at the appropriate time then we could miss the echo entirely. Hence why I am asking for the other parameters above and we can calculate where our listening period should fall.

Also the transducer need to be glued directly to the water tank to make sure that all the energy couples directly through the tank. You can read this guide here: https://www.ti.com/lit/an/snaa266a/snaa266a.pdf?ts=1654616977798&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTDC1000

Best,

Isaac

Hello Mr. Lara,

Thanks for your reply! I try to find the listening window on the EVM-User-Interface, but I can't find it and how to configure it. I know what the listening window mean, but from the technology files I couldn't find the way about how to set the listening window.

This time, the phenomenon is like last time, thought I change the transducer to the official recommended, the TOF is always a fixed value. For the link you gave me, what I think is that the TOF would change though the transducer is not glued in the water tank. I press the transducer close to the tank or my hand, but the TOF still fixed, and when I make the transducer attached to the tank filled with air and filled with water respectively, the TOF almost has no change. Could you help me and please let me know if my thought correct?

Thanks!

Songjiang Hou

Hello Songjiang,

No worries always glad to help. The EVM user interface does not refer to it as the listening window but the device datasheet does refer to it as this. What constitutes as the echo listening window is the time period set by by the TIMING_REG (highlighted in red below). 

This establishes when the device will begin to listen to echoes, if the device is configured incorrectly then it will attempt to listen to echoes while the transducer is still transmitting the pulses causing an inaccurate ToF, or it could be listening too late which means it would completely miss the echo and no time of flight would be captured since the device would timeout.

My theory is that your device is configured to measure to early so you are still capturing the device emitting the signal but this is hard to prove since you cannot measure the STOP pulse and the initial pulses with a scope. So that lead me to the question of the expected speed of sound in your tank along with the dimensions of your tank. With that we should hopefully be able to calculate a better listening window.

Assuming a speed of sound of water ~1480m/s and using your constant result of 38us we obtain a distance of .02812 meters which is very small hence why I believe that your triggering on the transducer bursting the pulses. Distance =  (ToF*speed of sound)/2

I have had users try to use their hand to press the transducer into place and test it out that way and did not yield good results. You need good mechanical adhesion to the tank or else a lot of the signal will be reflected off of the tank instead of coupling through the tank and traveling through the water.

I hope this helps!

Best,

Isaac

Hello Mr. Lara,

Thanks for your reply, I will buy glue to connect the transducer with the tank to try again. By your help I know maybe it's caused by the attenuation from air.

I will try to connect them to get the echo.

Thanks for your help!

Songjiang Hou