Final answer:
Pneumatic humidistats operate by measuring changes in air pressure caused by changes in humidity. They contain sensing elements that detect these pressure changes and convert them into an electrical signal. Common sensing elements used in humidistats include diaphragms, capacitive sensors, and resistive sensors.
Step-by-step explanation:
Pneumatic humidistats operate by measuring changes in air pressure caused by changes in humidity. They contain sensing elements that detect these pressure changes and convert them into an electrical signal, which can then be used to control humidity levels. One common sensing element used in humidistats is a diaphragm or bellows that expands or contracts in response to changes in pressure.
Other sensing elements used in humidistats include capacitive and resistive sensors. Capacitive sensors measure changes in electrical capacitance caused by changes in humidity, while resistive sensors measure changes in electrical resistance. These sensors are commonly used in electronic humidistats.