TDC -Ultrasonic Flow & Heat Meter
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 below)!
TIME OF FLIGHT
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 measure 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!