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Ultrasonic Flow Meters

The market for ultrasonic flowmeters is one of the fastest growing in flow Measurement. More and more users treasure the advantages of non-contacting measurement - as the one based on ultrasonics. The base for this method is an accurate but low current time measurement. The explanation of the mechanism will show you why:

schematicsThe Time-of-Flight (also Transit-time) method uses the change in sonic velocity with and against the direction of flow. It is: v = d*(t2-t1)/(2*t1*t2) = ca. c2/(2d*cosb)*(t2-t1) That means: high resolution demands high precision time-measurement - especially for small flow velocities. Take an example: we want to meassure a flow of 0,5m/s in water (c=1480m/s at 20°C) with a resolution of0.5%. The distance between the two ultrasonic transducers may be 10cm at an angel of 45°. The final timedifference is then 33ns.

The needed resolution is 165ps - for the TDC-GP1 this is no Problem!

ALso have a look at our application note AN002 (114KB Feb 1999)

And see all the advantages of the TDC in this application:

  • Small size: Single Chip-solution in the small TQFP44-package
  • You need a broad dynamic range up to 24 Bit. That's no challenge for our TDC. The GP1 allows measurements up to 100ms with the high resolution of 110ps - this equals a dynamic range of 30Bit!!
  • Highest resolution: by averaging - the TDC-GP1 is well suited for this - the standard deviation can be reduced down to several picoseconds
  • Industrial operating range: from -45°C to 85°C even +100°C is possible.
  • Battery applications: for handheld devices a low current consumption is essential. Discover the TDC-GP1 - it's perfect for this! When you work in measuring range 2 with only one measurement plus calibration per second, the current consumption will be only 3uA for a 5V supply (Remarkable: nearly the comlete 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!)
  • Supply voltage range: 2,7V ....5,5V
  • Temperaturemeasurement: The velocity of sound depends on the temperature. Therefore it's essential to permanently control the temperature of the fluid. As a temperature measurement can be reduced easily to a time measurement, we have allready implemented the necessary functions to the GP1. The RLC-unit allows a reolution of 1°C in the standard configuration. This value can be easily decreased by the use of some external components