Ultrasonic Flow and Heat 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 (see also animation on the right)!

The 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 time difference is then 33ns.  The needed resolution is 165ps - for the TDC-GP2 with its 65 ps single shot resolution this is no problem!

Also have a look at our application note AN002 (PDF, 114KB, Feb 1999)

And see all the advantages of the TDC-GP2  in this application:

• High resolution: TDC-GP2 has 65 ps resolution in single shot. An integrated phase shift unit allows to improve the resolution by averaging
• High bandwidth: TDC-GP2 can measure up to 4 ms Time-of-Flight
• Integrated fire pulse generator for up to 15 pulses with programmable phase and frequency
• Industrial operating range: from -40°C to 125°C
• Battery applications: Discover the TDC-GP2 - it's perfect for this! The total current of the measuring unit can be decreased down to 3 to 5 µA.
• Supply voltage range: 1.8V to 5.5V
• Temperature measurement: The intergrated temperature measurement unit allows to measure the cold and hot water temperature with 0.002 °C resolution at 50 times less current than A/D converter solutions
• Small size: Single-chip solution in the small QFN32-package (5x5 mm²)