A thermocouple is a sensor used to measure temperature in a number of processes. Thermocouples consist of two wire legs made from dissimilar metals which are fixed together at one end, creating a junction. When this junction experiences a change in temperature a voltage is created, this voltage can then be measured and referenced back to the temperature. This is also known as the "Seebeck Effect".
Type K -nickel-chromium vs. nickel-aluminium
Type J -iron vs. copper-nickel
Type E -nickel-chromium vs. copper-nickel
Type T -copper vs. copper nickel
Type R -platinum vs. platinum, 13% rhodium
Type S -platinum vs. platinum, 10% rhodium
Type N -nickel-chrome-silicium vs. nickel-silicium