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Ultrasonic Thickness Measurement

Non-destructive testing and material inspection methods like the ultrasonic methods are well established in production quality control. The checking of the thickness of metal layers, pipe walls or synthetic foils are good examples. The different times of flight for reflected ultrasonic pulses is interpreted as material thickness - once again a precise time measurement is the key (see animation on the right)!

 

The velocity of sound in aluminium is 5100 m/s (at 20 °C). An ultrasonic pulse is reflected on both, the entry wall and the back wall. Take as an example a layer of 1 mm aluminium . The difference in travel time for the two reflected pulses is 2*d/c = 3,9 µs. For a needed resolution of 0.1% this means a resolution of time of 390 ps - no problem for the TDC! A TDC can measure even a layer of 10 cm aluminium with the same absolute resolution!

 

See all the advantages of the TDC in this application:

  • Small size: Single-chip solution in the small QFN/TQFP-package
  • You need a broad dynamic range? That's no challenge for our TDC. The TDC-GP1 e.g. allows measurements up to 100 ms with the high resolution of 110 ps - this equals a dynamic range of 30Bit!!
  • Highest resolution: by averaging - the TDC is well suited for this - the standard deviation can be reduced down to several picoseconds
  • Industrial operating range: from -40 °C to 120 °C
  • Battery applications: for handheld devices low current consumption is essential. Discover the TDC - it is perfect for this! When you work in measuring range 2 with only one measurement plus calibration per second, the current consumption will be only 3 uA for a 5V supply (Remarkable: nearly the complete consumption is delivered to the calibration clock. If the active period of this clock can be fitted well, the current consumption can be reduced to nA!)
  • Temperature measurement: The velocity of sound depends on the temperature. Therefore it's essential to permanently check the temperature of the fluid. As a temperature measurement can be reduced easily to a time measurement, we have already implemented the necessary functions into the TDC. The temperature-unit allows a resolution of 0.002 °C

Animation of Measurement Principle