Final answer:
Bellows pressure sensors are devices that use the mechanical movement of collapsible tubes to measure pressure changes. The movement of the bellows is linked to a pointer on a calibrated scale to indicate pressure, and these sensors are used in applications like HVAC systems, industrial processes, and scientific measurements. They can measure both gauge and absolute pressure, with gauge pressure being relative to atmospheric pressure and absolute pressure including the atmospheric pressure in its measurement.
Step-by-step explanation:
Bellows as Pressure Sensors
A pressure sensor such as a bellow gauge is designed to measure the pressure of a gas or liquid. Bellows are flexible, accordion-like devices that expand and contract with changes in pressure. The construction of a bellows pressure sensor includes a set of nested, collapsible tubes that form an airtight chamber. When pressure is applied, the bellows move, and this movement is mechanically linked to a pointer on a calibrated scale, which indicates the pressure being measured.
The operation of bellows is based on the principle that a change in pressure causes them to either compress or expand. This mechanical motion is transduced into a readable gauge indication, typically through a lever system that amplifies the movement of the bellows. For higher pressure sensitivity, the bellows may also be counterbalanced with springs.
Applications for bellows include HVAC systems to measure duct pressures, in industrial processes to monitor system pressures, and in scientific equipment where precise pressure measurement is critical. They are chosen for their durability, resistance to temperature fluctuations, and ability to measure both gauge and absolute pressure.
Gauge and Absolute Pressure
Gauge pressure is the pressure that is measured relative to the atmospheric pressure, whereas absolute pressure is the sum of gauge pressure and the atmospheric pressure. Aneroid gauges, which sometimes use bellows, measure absolute pressure when calibrated to a vacuum and gauge pressure when calibrated to atmospheric conditions.