Integrated circuits, such as LM3911N, are available, combining athermotransistor temperature-sensitive element with an operationalamplifier. When the connections to the chip are so made that the amplifier isconnected as a comparator, the output will switch as the temperature traversesthe set point and so directly give an on/off temperature controller.Such temperature sensors have the advantages of being cheap and giving areasonably linear response. However, they have the disadvantage of a limitedtemperature range.• Another commonly used temperature sensor is the thermocouple.• The thermocouple consists essentially of two dissimilar wires, A and B, forming ajunction. When the junction is heated so that it is at a higher temperature than theother junctions in the circuit, which remain at a constant cold temperature, anelectromotive force (EMF) is produced that is related to the hot junction temperature.