Thermocouples are a precision method to measure temperature
by generating a small voltage using the Seebeck effect. They are
especially useful at very high and very low temperatures.

Although special temp displays are normally used that must be very
carefully matched to the characteristics of the chosen thermocouple,
an ordinary digital voltmeter and table lookup can sometimes be 
substituted instead. As can computer or embedded processing.

You can click here for a Thermocouple Tutorial.

Related items are also found on our Sensors Bargains page.