Certified Control Systems Technician (CCST) program

The correct answer is C, “ultrasonic flowmeter.” Ultrasonic meters measure the velocity of a fluid flowing through a pipe in one of two ways, either via a difference in transit time from source to receiver or by Doppler technology. Doppler technology measures the difference in sound wave frequency reflected off gas bubbles or particles in the flow stream.

Oval gear flowmeters are positive displacement devices that displace a known volume of material per revolution. Turbine meters measure the fluid velocity based on the number of revolutions per minute. The most used mass flowmeters measure flow by changes in angular vibration due to the Coriolis effect.

Reference: Goettsche, L. D. (Editor), Maintenance of Instruments and Systems, Second Edition, ISA, 2005.