What is the purpose of a differential pressure transmitter in flow measurement?

• A. To monitor ambient temperature around the pipe
• B. To measure the pressure difference across a restriction and convert it to a signal proportional to flow after calibration
• C. To provide a direct reading of flow velocity
• D. To measure pipe vibration

Answer: (B)

The key idea is that a differential pressure transmitter measures the pressure drop across a flow restriction and turns that pressure difference into a signal that represents flow after calibration. When fluid passes through a restriction like an orifice, the velocity rises and the static pressure drops between upstream and downstream taps. This pressure difference is related to how much fluid is flowing. The transmitter senses that differential pressure, amplifies it, and converts it into an electrical signal (for example, a 4-20 mA loop). Because the relationship between differential pressure and flow depends on the specific geometry and fluid properties, it must be calibrated so the signal accurately reflects the actual flow rate. This is why the purpose is to convert the measured pressure difference into a calibrated signal proportional to flow. It isn’t about monitoring ambient temperature, providing a direct reading of flow velocity, or measuring pipe vibration.