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TDC1000: Long-time stability of ToF measurement accuray

Zou Yuehua
Prodigy 10 points
Part Number: TDC1000
Other Parts Discussed in Thread: TDC7200

Hi,

  I designed a ultrasonic ToF measurement PCBA by using the combination of TDC1000 and TDC7200. 10MHz MCLK, 2.5MHz Piezoelectric ultrasonic transducer were used, and run in ToF_MEAS_MODE 0. When run the accuracy evaluation on the test bench. I found its accuray would be around +/-0.5 ns, that's good for me, but it would drift as time goes by.

For example, the first STOP reached at 143.788269 us in the morning, while it would drift to 143.798355 us in the afternoon. As you see, there is about 10 ns drift, and it would even drift to 20 ns sometieme, that's not good for me. So, would you pls help me debug the issue, thanks very much.

  • 0
    TI__Mastermind 22120 points

    Hello Zou,

    Thank you for posting to the sensors forum! Temperature is a factor for ultrasonic measurements since the speed of sound in a medium is affected by the temperature. Was this factor taken into consideration for your measurements?

    On another note a 20ns second drift is a very small difference for level measurements are you attempting to use this device for flow measurements? The reason I am asking is because the TDC1000 is no longer recommended for flow measurements due to issues with its accuracy. We typically recommend customers to use the MSP430FR4063 series of microcontrollers since they have a higher accuracy for flow measurements. If you still plan on using this device some customers have mitigated the accuracy problem by taking multiple measurements and averaging the measurements.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 10 points

    Hello Isaac,

    Thank you for suggestions. Actually, I used the ultrasonic to measure the length change of a bolt in the wind power tower. The temperature maybe a factor, and I tried to measure the temperature by using the RTD interface of TDC7200, but failed. There was a problem when swithing the measurement process between ToF and TEMP mode, it seams that the result registers 0x10h ~ 0x1Ch of TDC7200 are not updated, the calculation results are same, and I didn't find the reason right now, maybe my FW has some problems?

  • 0 in reply to Zou Yuehua
    TI__Mastermind 22120 points

    Hello Zou,

    No worries glad to help out, and thanks for the feedback on the information on the usage of the sensor. If the measurement is done while being exposed to the elements this could definitely be the main source of error for your measurement. The temperature interface is on the TDC1000 not the TDC72000 so please make sure that you are writing the RTD configuration to the right device if not this could be the source of the problem.

    It could be an issue with your firmware but to rule that out you could always connect a scope to the START and STOP outputs of the TDC1000 and try to do a manual calculation of the temperature to ensure that the readings match what the TDC7200 is measuring.

    Do you know what the bolt you are trying to measure is made out of? Perhaps there is another technology that you might be able to use instead of ultrasonic.

    Best,

    Isaac  

  • 0 in reply to Isaac Lara
    Prodigy 10 points

    Hello Isaac,

    Thanks very much. Yes, the RTD interface is on the TDC1000. I wrote the configurations into the registers of TDC1000, and I got the START and STOP signals out from TDC1000 pins. Below listed the scope time of RTD measurement, and I think the TDC1000 is working correctly in this case, but the caculation of TDC7200 is wrong when used the same formula of ToF mode.

    PT1000
    tref/us td1/us 0.5tref/us td2/us trtd1/us total/us tclock/us
    202 142 100 188 184 816 0.1 8160
    Rref/k 1
    Rrtd1/k 1.097826
    Temp/℃ 25.1

    This is a steel bolt under test, what kind of another technology and TI solution could be used to do it better?

    Thanks again.

  • 0 in reply to Zou Yuehua
    TI__Mastermind 22120 points

    Hello Zou,

    Thanks for the info. These numbers you provided on the table seem to about right based on the information that you are providing here. Is the temperature not 25.1℃? I am trying to understand the issue here.

    For the steel bolt I was thinking that inductive technology might work really well for this type of application and you would be able to get a decent resolution. If you are able to share how you are measuring the length of bolt that might be helpful.

    Best,

    Isaac