pressure. The thermocouple was first used as a vacuum gauge by Voege in 1906. The mathematical model for the thermocouple as a vacuum gauge is quite complicated, as explained in detail by Van Atta, but can be simplified to: where P is the gas pressure, B is a constant that depends on the thermocouple temperature, the gas composition and the vacuum-chamber geometry, V0 is the thermocouple voltage at zero pressure (absolute), and V is the voltage indicated by the thermocouple. The alternative is the Pirani gauge, which operates in a similar way, over approximately the same pressure range, but is only a 2-terminal device, sensing the change in resistance with temperature of a thin electrically heated wire, rather than using a thermocouple. See also Heat flux sensor Bolometer Giuseppe Domenico Botto Thermistor Thermoelectric power List of sensors International Temperature Scale of 1990 Bimetal (mechanical) References External links Thermocouple Operating Principle – University Of Cambridge Thermocouple Drift – University Of Cambridge Two Ways to Measure Temperature Using Thermocouples Thermocouple data tables: Text tables: NIST ITS-90 Thermocouple Database (B,E,J,K,N,R,S,T) PDF tables: J K T E N R S B Python package thermocouples_reference containing characteristic curves of many thermocouple types. R package Temperature Measurement with Thermocouples, RTD and IC Sensors. Data table: Thermocouple wire sizes Temperature control Thermometers Sensors Thermoelectricity Bimetal