In a flow measurement context, which property does the signal from a magnetic flowmeter correlate to?

• A. density
• B. velocity
• C. temperature
• D. velocity

Answer: (D)

Magnetic flowmeters generate a signal that is proportional to the velocity of the conductive liquid as it moves through a magnetic field. This uses Faraday’s law: a moving conductor in a magnetic field produces a voltage between electrodes. The stronger the fluid’s velocity, the larger the induced voltage. Therefore the primary signal corresponds to flow velocity (and, with area known, can be converted to volumetric flow). It does not directly measure density or temperature.