Steam pressure thermometer

Vapor pressure thermometers are thermometers that are based on the change in the vapor pressure of liquids with temperature (see also the Clausius-Clapeyron equation ). They use the effect that the vapor pressure in the measuring range changes more with temperature than would be the case with a pure gas.

Your advantage over z. B. bimetal thermometers or direct reading liquid thermometers is that the measurement location can be far away from the display location.

Vapor pressure thermometers consist of a hermetically sealed vessel that contains a liquid suitable for the measuring range. The vessel is connected to a pressure measuring device (e.g. pressure cell ) via a pipeline , which actuates a pointer or a switch .

Vapor pressure thermometers are used on heat pumps , refrigeration machines , freezers, older washing machines, but especially in low-temperature technology ( cryotechnology ). For example, at very low temperatures, the temperature of liquid helium can be accurately determined by measuring the vapor pressure above the helium liquid. This means that a temperature measurement in the range of approximately 0.65… 5  K is possible.