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Using TDC1000 and TDC7200

Gert Mema
Intellectual 305 points
Other Parts Discussed in Thread: TDC1000, TDC7200

Hello,

I want to do a distance measurement using the TDC1000, TDC7200 and an ultrasonic sensor. The measurement range is between 65 mm and 375 mm.

Is it possible to achieve a resolution of 10 µm or less with this setup? 

I only saw the reference design from TIDA00322, which doesn´t use the TDC7200.

I would appreciate your help.

Kind Regards

  • 0
    TI__Genius 16890 points
    Hello Gert,

    The following applications reports (snaa270.pdf, snaa266a.pdf, and sniu021a) that can be downloaded from ti.com show how to do distance measurement using an ultrasonic sensor.

    The minimum time that the TDC7200 can measure between the start and stop pulse is 12ns. Using a speed of sound in water of 1483m/s gives a minimum distance that it can measure of 17um. This is an ideal number and it would probably be larger in a real application. The setup will not be able to do sub 10um measurements.

    Mike
  • 0 in reply to Michael Stout
    Intellectual 305 points

    Hello Mike,

    Thank you for your reply.

    The transmission medium is air, so the speed of sound is about 340 m/s. This means that the the TDC7200 should be able to measure a distance of 4 µm. 

    The TDC7200 has two measurement modes. Mode 1 for short distance and Mode 2 for long distance. Is the accuracy of the TDC suitable for my measurement range assuming that the measurement mode is Mode 2?

    Thank you in advance.

    Kind regards,

    Gert

  • 0 in reply to Gert Mema
    TI__Genius 16890 points

    HI Gert,

    When it is in mode 2 the minimum measurement time is 2xtclock.  If you are using a 16MHz clock, that would be340m/s x 125ns = 42.5um, so it wouldn't be able to measure down to 4us.


    Mike

  • 0 in reply to Michael Stout
    Intellectual 305 points

    Dear Mike,

    Thank you for your help.

    Isn´t it possible to apply a clock of 100 MHz to achieve a higher resolution? Do you see any problems using a 100 MHz clock?

    Kind regards

    Gert

  • 0 in reply to Gert Mema
    TI__Mastermind 21685 points
    Gert,

    To clarify, TDC7200 is basically a stop watch that measures the time period between its START and STOP input pulses. It's not the TDC200 minimum measurement period or its clock frequency that limits resolution. Instead measurement resolution is determined by the ultrasonic transducer resonant freq and Csound of the material as TDC1000 generates START/STOP signals corresponding to the transducer TX pulses (at resonant freq) and received echo signal.

    Here's a quick table that shows the relationship between transducer freq, Csound of the material (assuming measurement from top), and resolution:
    Freq(Hz) Cmedium(m/s) Distance resolution (mm)
    40,000 343 4.2875
    60,000 343 2.858333333
    100,000 343 1.715
    200,000 343 0.8575
    400,000 343 0.42875
    500,000 343 0.343
    For Water (with 1MHz transducer at the bottom)
    1000,000 1480 0.74
    The formula used above is: Cmedium / 2 x Freq of the transducer

    Thanks,
    Vishy