One part of the filament heating is transferred to the surrounding gas molecules, which calculates the loss of produced heat of heat transferring to the gas molecules lead to measuring the pressure inside the chamber.
Pirani gauge is one of the most common thermal conductivity gauges, which is used at it of platinum, nickel or tungsten filament. Pirani gauge is designed and built based on the dependence of the heated wire resistance to its temperature. These gauges are applied to measuring pressure about 10-2 MPa.