What type of meter measures water velocity by sending sound pulses and measuring travel time?

• A. Positive displacement meter
• B. Orifice meter
• C. Sonic velocity meter
• D. Electromagnetic meter

Answer: (C)

Understanding how flow is measured with sound helps here: a sonic velocity meter uses ultrasonic pulses sent through the water to determine how fast the liquid is moving. Two transducers around the pipe send a pulse in the downstream direction and one in the upstream direction. Because the water is moving, the pulse traveling with the current arrives sooner downstream and later upstream. The difference in those travel times is used to calculate the flow velocity, and then the flow rate is obtained from that velocity and the pipe’s cross-sectional area. This approach is distinct from meters that rely on moving parts or pressure differences, such as positive displacement, orifice, or electromagnetic meters. That combination of sending sound and measuring travel time is the hallmark of a sonic (transit-time) velocity meter.