What is pirani gauges?

Pirani gauges are commonly used as vacuum gauges to measure low pressures in the range of 10⁻³ Torr to 10⁻⁹ Torr. They work on the principle of thermal conductivity where a heated wire is exposed to the vacuum and the rate of cooling is measured to determine the pressure.

Pirani gauges are typically made up of a filament which is heated by passing a current through it. Heat is lost from the filament due to convection and conduction to the surrounding gas, which is related to the gas pressure. The rate of heat loss is proportional to the pressure, and this is used to determine the vacuum level.

The output of the gauge can be read directly or fed into a controller for automated pressure monitoring. Pirani gauges are relatively inexpensive, easy to use, and provide reliable measurements. However, they have limitations at higher pressures due to the dependence of thermal conductivity on pressure. They are mainly used for vacuum monitoring in various industries such as semiconductor manufacturing, vacuum coating, and research.