Effect of Temperature on Resistance A component whose function in a circuit is to provide a specified value of resistance is called a resistor The principal application of resistors are to limit current, divide voltage and in certain cases, generate heat. The following are the commonly used resistors in electrical and electronic circuits: • Carbon composition types • Film resistors • Wire-wound resistors • Cermet resistors Carbon composition type This type of resistors is made with a mixture of finely ground carbon, insulating filler and a resin binder. The ratio of carbon and insulating filler decides the resistive value. mixture is formed into a rod and lead connections are made. The entire resistor is then enclosed in a plastic case to prevent the entry of moisture and other harmful elements from outside. Carbon resistors are relatively in expensive to build. However they are highly sensitive to temperature. The car resistors are available in power ratings ranging 1/8 to 2W Film resistors In a film resistors, a resistive material is deposited uniformly onto a high grade ceramic rod. The resistive film may be carbon (carbon film resistor) or nickel chromium (metal film resistor). In these types of resistors, the desired resistance value is obtained by removing a part of the resistive material in a helical pattern along the rod. Metal film resistors have better characteristics as compared to carbon film resistors. Wire-wound resistors A wire wound resistor is constructed by winding a resistive wire of some alloy around an insulating rod. It is then enclosed in an insulating cover. Generally, nickel chromium alloy is used because of its very small temperatures coefficient of resistance Wire-wound resistors can safely operate at higher temperatures than carbon types. These resistors have high power ratings from 12 to 225W Cermet resistors A cermet resistor is made by depositing a thin film of metal such as nichrome or chromium cobalt or ceramic substrate. They are cermet which is a contraction for ceramic and metal . These resistors have very accurate values Effect of temperature on resistance Effect of temperature on resistance In temperature. Hence these materials have negative temperature co-efficient of resistance. Effect of temperature on resistance Temperature Co-efficient of resistance at a temperature of 100OC, it will have a life expectancy of only four years at a temperature of 110oC, of two years at a temperature of 120 oC and of only one year at 130oC