What type of flow meter requires particles in the fluid to reflect signals back to the flow sensor?

• A. Ultrasonic
• B. Magnetic
• C. Mass
• D. Turbine

Answer: (A)

Ultrasonic flow meters that use the Doppler principle depend on particles or gas bubbles in the fluid reflecting the ultrasonic signal back to the sensor. When the ultrasound hits a moving particle, the reflected wave experiences a frequency shift (the Doppler effect). Measuring this shift lets the meter determine the velocity of the reflecting targets along the beam, and with the flow path geometry, infer the flow rate. That reflective behavior is what makes this type specifically suited to fluids that contain particles or bubbles.

The other methods operate on different principles. Magnetic flow meters rely on the fluid’s conductivity and measure voltage generated by a magnetic field, not reflections. Turbine meters use a physical rotor spun by the flow to gauge rate, and mass flow meters (like Coriolis or thermal) determine mass flow through inertial or thermal effects rather than reflected signals from particles.