Temperature Measurement and Heating Procedures

Thermometers. Conventional mercury thermometers are used to measure temperatures not exceeding 300 °C. Special thick-walled glass thermometers make it possible to determine temperatures up to 500 °C. 

Thermocouples (Thermoelements). High temperatures are usually measured with thermocouples connected to millivoltmeters having 

A thermocouple consists of two wires of dissimilar metals or alloys insulated from each other by placing them in a two-channel porcelain tube. The wires are welded together at one end (the hot or measuring junction of the thermocouple) 

To measure temperatures not exceeding 800 °C, one should use thermocouples made from copper and constantan (the latter is an alloy of 45-60% copper, 40-55% nickel, and 0-1.4% manganese it usually also contains about 0.1% carbon), Alumel (an alloy of 95% nickel, 2 % aluminium, 2% manganese, and 1% silicon), and Chromel (90% nickel and 10% chromium), or iron and constantan. Platinum-platinum/rhodium thermocouples are generally used for measuring high temperatures (up to 1600 °C). 

For accurate temperature measurements, the reference ends of a thermocouple are maintained at a constant temperature, for example at that of melting ice or the vapour of boiling water. The temperature of a heated body (tube, ceramics, furnace) can be determined 

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