A differential pressure switch responds to what?

• A. The difference between two pressures.
• B. The absolute pressure.
• C. The average of two pressures.
• D. The rate of pressure change.

Answer: (B)

A differential pressure switch responds to the difference between two pressures. It has two sensing ports connected to two points in the process, and the internal mechanism (often a diaphragm or bellows) responds when the pressure difference reaches a preset threshold, switching the electrical output on or off. This makes it ideal for monitoring things like filter condition or flow restriction, where the concern is how much pressure has built up across two points, not the absolute pressure at either point. The device does not measure absolute pressure, nor the average of the two pressures, and it isn’t inherently a rate‑of‑change device unless a specialized version includes that function.