We are using the TDC1011 AFE to interface to a 3MHz piezo sensor and the TOF we are getting is varying as much as 30uS when using a 3.5" container and as much as 60uS when using a 7.5" container.
All details of the test setup as well as TDC1011/TDC7200 register setting, scope screen shots, and output data are in the attached PDF.
If you need additional information/clarification please let me know.
Hello,
I have a few follow-up questions:
Have you been able to verify with a series of manual measurements and the resulting scope plots of COMPIN and STOP, that the measurement variance is seen in the TDC1011 receiver path? Do you see similar end results using averaging with the TDC7200?
You mention a TX voltage amplitude of 6.8V, is that the true voltage? The TDC1011 only supports up to 5V.
In the data you provided below for the 7.5" tank ToF, are these hexadecimal micro-seconds. If so the average ToF is about 70us off the expected time.
Regards,
Gabriel
Hi Gabriel,
Have you been able to verify with a series of manual measurements and the resulting scope plots of COMPIN and STOP, that the measurement variance is seen in the TDC1011 receiver path?
Yes what we see on the receiver path by using the scope (screen shots were part of the PDF) are the the same variance seen by the TDC1011, when we see 120uS START to STOP on the scope that is also what the TDC7200 reports after we do the calculations fond in section 8.4.2.2.1 of the datasheet.
Do you see similar end results using averaging with the TDC7200?
Yes we see the same results when we do our own averaging or median search as well as using the "Multi-Cycle Averaging Mode" in the TDC7200 set to average 4-measurement and using the calculation in section 8.4.4. The following are readings from the Multi-Cycle Averaging Mode and the data is in uS.
TOF 128
TOF 141
TOF 138
TOF 129
TOF 150
We have an external boost circuit that we can control from 2.9vdc to 11.7vdc. We use this external boost to drive the VDD of a Gate Driver FAN3111ESX (https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/FAN3111ESX/?qs=%2Fha2pyFaduiXsCcsFp16g8yI80aBsDmy%2FISOVa7Teva5Cwl2rloKAw%3D%3D). With the RX having the 300pF cap we are AC coupled to the TDC1011. The amplitude of TX was measured at the FAN311ESX without a sensor connected, with a sensor connected the actual RX amplitude into COMP_IN after the gain stages is 1.4v p-p and the RX signal before the 300pF cap is 5.060v p-p, see JPEGs
In the data you provided below for the 7.5" tank ToF, are these hexadecimal micro-seconds. If so the average ToF is about 70us off the expected time.
No the time is in actual uS, the "h" should not have been there, since these were sent I fixed that.
As an additional experiment we removed the ceramic plate that was below the container of water so that the container sat directly on rubber foam and it did not make any significant difference in readings, I was hoping that the "Acoustic Impedance" difference in the materials would have a different TOF response but it did not.
Thanks
Duane,
I see the transducer leads are quite long, twisting them may improve the signal quality and SNR. With a 1MHz transducer I see a signal similar to this replicating the example from the app note.
I'm not sure why the received pulse would vary like that.
If you send your register configuration file or register hex values I can try to replicate the issue with my test tank.
Regards,
Gabriel
