A pyrometer; a temperature-measuring device used extensively in refining. The thermocouple is based upon the principle that a small electric current will flow through two dissimilar wires properly welded together at the ends, when one junction is at a higher temperature than the other. The welded ends are known as the "hot junction" which is placed where the temperature is to be measured. The two free ends are carried through leads to the electromotive force detector, known as the "cold junction." When the hot junction is heated, the millivolts can be measured on a temperature scale.
