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TDC7200: In the application of TDC7200 measuring wind speed, if it is placed in a low temperature of -20℃, there will be no feedback of TOF measurement data after 1 minute.

KONG XIANGXU
Expert 1996 points
Part Number: TDC7200
Other Parts Discussed in Thread: TDC1011

Tool/software:

Hi TI，

       In the application of TDC7200 +TDC1011 measuring wind speed,The anemometer was placed in a low temperature of -30℃. After 1 minute, the TOF (measurement mode 1，Chapter 8.4.2.1) measurement data had no feedback, but when using measurement mode 2（chapter 8.4.2.2）, the TOF data returned to normal. Why is this? The propagation path distance of 200k ultrasonic waves is 8cm。In addition, it failed after cold and hot shock, but when changing its mode 1 to mode 2, the function returned to normal.

  • 0
    TI__Mastermind 23045 points

    Hello Xiangxu,

    Thank you for posting to the sensors forum and for the information. The TDC7200 uses two different clocks for these modes. So mode 1 uses the internal ring oscillator for the entire measurement while for mode 2 the external clock is used as the source for counting while the internal ring oscillator is only used to count the fractional parts in between the clock cycles. Whenever you collected the data at -30C with the device in mode 2 were you also getting the fractional data from the ring oscillator in this mode or were you only getting the clock cycle data from the external clock?

    My thought is that perhaps the internal ring oscillator may be shutting down hence why you dont get any data in mode 1 since it entirely depends on this while it only partly is needed for mode 2.

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Expert 1996 points

    Isaac, thanks for your reply. In mode 2, the fractional data is also obtained from the ring oscillator, but its accuracy cannot be determined, or how to confirm that the internal ring oscillator has stopped working? The chip specification supports an operating temperature range of -40°C to 85°C. In addition, when using mode 1, the 8cm travel time far exceeds its recommended measurement range of 12ns to 500ns.Will this also affect its data collection?

  • 0 in reply to KONG XIANGXU
    TI__Mastermind 23045 points

    Hello Xiangxu,

    So just to confirm, when you are using mode 2 at -30C are you getting any of the fractional information from the ring oscillator? 

    If you are not getting any fractional data then this would determine that there is an issue with the ring oscillator portion of the device. Do you mind sharing your register configuration so that I can try the settings you are using? I haven't come across this issue before so I would need to look further into debugging it. But you are right mode 1 should be functional at -30C.

    Can you explain how you are exposing the device to -30C?

    The standard deviation of the measurements starts to go up in mode 1 once the measurements exceed the 800ns that's why the recommendation to not make measurements above 500ns exists. Below is a figure from the datasheet that shows this behavior. The standard deviation for your measurements could be much worse than this if taking such a large measurement.

    Best,

    Isaac