In differential pressure flow measurement, select the component that creates the flow-resisting pressure drop.

• A. The transmitter electronics
• B. A bypass line
• C. A valve regulator
• D. A restriction such as an orifice or venturi

Answer: (D)

The key idea is that differential pressure flow measurement relies on a known flow resistance that creates a measurable pressure difference. A restriction device—such as an orifice plate or a venturi—narrows the pipe area, causing the liquid or gas to speed up and lose static pressure as energy converts to kinetic energy. This creates a predictable pressure drop between the upstream and downstream sides. The differential pressure transmitter then reads that drop and translates it into a flow rate using a calibration relationship (for many systems, roughly proportional to the square of the flow rate for incompressible fluids).

The other items don’t establish the fixed, calibrated pressure drop needed for flow measurement: transmitter electronics merely sense the pressure, a bypass line provides an alternate path that bypasses the main restriction and thus doesn’t generate the needed differential, and a valve regulator is used for controlling pressure rather than producing a measurement-friendly, fixed drop.