Thermocouple gauges are widely used on systems operating in the 1X10-3 Torr to atmosphere range to indicate the pressure in such applications as vacuum drying, impregnation, etc. 
 
Thermocouple gauges are widely used on systems operating in the 1X10-3 Torr to atmosphere range to indicate the pressure in such applications as vacuum drying, impregnation, etc. 
 
These gauges are also frequently used to check mechanical pump performance during system pump-down and to monitor mechanical pump pressure during the vacuum cycle. When used in combination with other gauges, such as hot filament ionization types, the thermocouple gauge indicates whether the pressure has been reduced into the safe operation range, thus protecting against inadvertent filament damage. 
 
Thermocouple gauges are sensitive to gas composition. The variation in gauge readings caused by a change in gas composition is useful in locating gross leaks in a vacuum system. Freon, acetone, or other hydrogen-rich gases can be sprayed over portions of a vacuum system and leaks will be indicated by a sudden increase in the meter reading.