What operation is performed by a pneumatic differential pressure transmitter on its high and low pressure sides?

• A. It subtracts them
• B. It adds them
• C. It multiplies them
• D. It divides them

Answer: (A)

A pneumatic differential pressure transmitter measures the difference between two pressures. The high-pressure side and the low-pressure side act on opposite faces of the sensing element (like a diaphragm), and the resulting net force is proportional to the difference between the two pressures. The transmitter then converts that differential pressure into a pneumatic output signal. In other words, it subtracts the low-side pressure from the high-side pressure to produce a signal that reflects how far apart the two pressures are.