Which meters are NOT recommended for clean liquids?

• A. Doppler Ultrasonic
• B. Ultrasonic Transit-Time
• C. Magnetic Flowmeter
• D. Turbine Flow Meter

Answer: (A)

Doppler ultrasonic flow measurement relies on the ultrasound waves being reflected by particles or gas bubbles in the liquid. In clean liquids there are very few scattering centers, so there aren’t enough echoes to produce a reliable Doppler shift. That makes this method inaccurate for pure or very clean liquids, which is why it’s not recommended in those cases.

Other meters handle clean liquids well. Transit-time ultrasonic meters send pulses along and against the flow and compare travel times; this approach doesn’t depend on reflections from particles, so it works reliably with clean liquids. Magnetic flowmeters measure flow from the voltage generated as conductive liquid moves through a magnetic field, which suits clean, conductive liquids like water. Turbine flow meters use a rotor whose rotation rate corresponds to flow; with clean, low-viscosity liquids and minimal particulates, they provide accurate readings.