The working principle of vacuum gauges depends on the type:
Pirani Gauge: A filament is heated electrically, and the loss of heat due to the surrounding gas is measured. The rate of heat loss correlates to the pressure. Ionization Gauge: Gas molecules are ionized by electrons from a heated filament. The resulting ions are collected, and the current produced is proportional to the pressure. Capacitance Manometer: A diaphragm deflects under pressure, changing the capacitance between the diaphragm and a fixed electrode. This change is measured to determine the pressure.
