Which statement about the DP Flow Meter is correct?

• A. It measures temperature difference to infer flow.
• B. It measures the pressure drop across a constriction, which increases with flow.
• C. It uses ultrasonic pulses to calculate velocity.
• D. It requires the fluid to be magnetic.

Answer: (B)

A differential pressure flow meter works by measuring the pressure difference across a restriction in the flow path. When fluid passes through a constriction such as an orifice plate, venturi, or flow nozzle, the velocity increases and the pressure drops between the upstream and downstream points. As the actual flow rate rises, this pressure drop becomes larger, and the meter translates that deltaP into a flow rate using calibration for the specific geometry and fluid properties. This method relies on Bernoulli’s principle and continuity, and it’s common for liquids where a controlled pressure loss is acceptable; it does require the pipeline to have a deliberate restriction and introduces a pressure loss elsewhere in the system. Since temperature-difference methods rely on heating elements to infer flow, ultrasonic meters determine velocity from sound waves, and magnetic meters need a conductive fluid and measure induced voltage, they do not describe how a differential pressure flow meter operates.