The platinum resistance thermometers known as RTD operates on the principal of change in electrical resistance of platinum wire as function of temperature and it normally operates between the range of -200^o to +500^oc

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THERMOCOUPLE'S

A thermocouple is fundamentally a pair of electrical conductors of dissimilar metals so joined as to produce a thermal emf when the junctions ae held at different temparatures. The two junctions are termed as "Hot" and "Cold" junction. The cold junction is terminated on the temparature measuring instrument.
There are various types of thermocouples. The most commonly used along with its range are given below.

Element & Type			Range
Copper/Constantan	(Simplex/Duplex)	'T'	100^oC - 400^oC
Iron/Constantan	(Simplex/Duplex)	'J'	100^oC - 800^oC
Chromel/Alumel	(Simplex/Duplex)	'K'	100^oC - 1100^oC
Platinum 13% Rhodium/Platinum	(Simplex/Duplex)	'R'	200^oC - 1600^oC