Which of the following are considered pressure sensing devices?

• A. A helical sensor, bourdon tube and bellows sensor
• B. A thermometer, hygrometer, and barometer
• C. A microphone, speaker, and subwoofer
• D. A gyroscope, accelerometer, and magnetometer

Answer: (A)

Pressure sensing devices respond directly to fluid pressure and convert that pressure into a readable signal or motion. A bourdon tube is a curved tube that tends to straighten as pressure rises, which moves a gauge needle or activates a sensor. A bellows expands and contracts with pressure changes, translating that change into a mechanical or electrical signal. A helical (spiral) sensor operates on a similar principle, using deformation of a spiral element to produce a measurable response to pressure. Together, these elements are classic examples of sensing pressure in a piping system, which is why they are considered pressure sensing devices.

The other options mix devices that measure unrelated quantities or operate on different principles—temperature and humidity (and barometers that measure pressure) are not all pressure sensors, acoustic devices like microphones and speakers respond to sound pressure rather than process pressure, and inertial or magnetic sensors measure motion or magnetic fields rather than pressure.