Chapter 14 – Temperature Measurement

Publisher Summary This chapter examines ten different physical principles used commonly as the basis for temperature-measuring devices. It is clearly impractical to connect a voltage-measuring instrument at the open end of the thermocouple to measure its output in such close proximity to the environment whose temperature is being measured, and therefore extension leads up to several meters long are normally connected between the thermocouple and the measuring instrument. The measuring system is completed by connecting the extension leads to the voltage-measuring instrument. Unfortunately, the use of extension leads of the same basic materials as the thermocouple but manufactured to a lower specification is still prohibitively expensive in the case of noble metal thermocouples. Thermocouples are delicate devices that must be treated carefully if their specified operating characteristics are to be maintained. One major source of error is induced strain in the hot junction. Thermocouples are manufactured by connecting together two wires of different materials, where each material is produced so as to conform precisely with some defined composition specification.