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TDC1000-TDC7200EVM: How to perform liquid level sensing through the bottom of a metal tank

Part Number: TDC1000-TDC7200EVM

Hi,

I have a TDC1000-TDC7200EVM development kit to provide a MVP.

My main goal is measure liquid level through the bottom of a metal tank.

The first test with a plastic cup was nice! I'm able to detect a great range of the liquid level. Follows the image:

After these first test, I changed the plastic cup to a metal bottle, 7 cm of diameter and 20 cm of height. I set the TDC1000 register like the suggestion of a "good start" from Matthew Minasi in this thread: https://e2e.ti.com/support/sensor/ultrasonic/f/991/t/467713

My transducer was installed like Matthew Minasi thread.

I don't know why I'm not able to get the same result. I debugged the signal with my oscilloscope and the TDC1000 can't even generate the STOP signal.

The image below is the START and COMP_IN signal.

Can anyone help me to find what am I doing wrong?

Thank you very much!