Compare magnetic flow meters and turbine flow meters in terms of principle of operation and typical applications.

• A. Turbine meters rely on magnetic induction principles.
• B. Magnetic meters measure flow of conductive liquids via Faraday's law; turbine meters use a rotating turbine whose speed is proportional to flow.
• C. Magnetic meters measure flow of conductive liquids; turbine meters measure viscosity.
• D. Both measure density and require temperature compensation.

Answer: (B)

Magnetic flow meters and turbine flow meters operate on different principles, which drives their best-use scenarios. Magnetic flow meters rely on Faraday’s law of electromagnetic induction: a conductive liquid moving through a magnetic field generates a voltage across electrodes on the pipe wall, and the measured voltage is proportional to the flow velocity. Because there are no moving parts, they are robust for conductive liquids like water, wastewater, slurries, and many chemicals, with little or no pressure drop. They won’t measure non-conductive fluids such as oils or hydrocarbons, since no signal is induced in those liquids.

Turbine flow meters, on the other hand, use a small turbine that spins as fluid flows through the meter. The rotational speed (or the pulses generated by the rotor) is proportional to the flow rate. They provide high accuracy for clean, low-viscosity liquids such as water, fuels, and some chemicals, but moving parts mean wear and potential clogging from particulates; they require straight piping to ensure a stable flow profile and they introduce a small pressure drop.

So the best description: magnetic meters measure flow of conductive liquids via Faraday’s law, while turbine meters measure flow by the speed of a rotating turbine.