How does a differential pressure transmitter measure flow?

• A. Temperature
• B. Vibration
• C. Measures the pressure difference at two points where a fluid flows through two different orifice plates
• D. Chemical composition

Answer: (C)

The main idea is that flow is inferred from the pressure difference created when a fluid is forced through a restriction. A differential pressure transmitter uses two pressure taps placed on opposite sides of a flow element (such as an orifice plate, venturi, or flow nozzle). It measures the static pressure upstream and downstream, and the resulting pressure difference (ΔP) is proportional to the flow rate. As the fluid speeds up through the restriction, its pressure drops; the greater the flow, the larger the pressure difference. The transmitter converts this ΔP into an electrical signal that represents the flow.

Other options aren’t related to how a DP transmitter measures flow: temperature, vibration, or chemical composition aren’t determined from the pressure drop across a flow element.