Because it is difficult to produce films of uniform thickness, it is not possible to control their resistance values accurately as in the case of wire wound resistors. The high resistance values are due to the thinness of the film. They consist of a thin metal coating deposited on cylindrical insulating support. They are also referred to as thin-film resistors. Very often, they are made in a small square with leads to fit into a printed circuit board. The main purpose is to have more precise resistance values and greater stability with heat. They consist of a thin carbon coating fired on to a solid ceramic substrate. They are cheaper than composition resistors. They consist of a high-grade ceramic rod or core (called the substrate) on which is deposited a thin resistive film of carbon. Carbon resistors with a power rating of 1 W or less are most common in electronic equipment. Where power dissipation is 2 W or less, such resistors are preferred because they are smaller and cost less. Such resistors are available in power ratings of 1/10,1/8,1/4,1/2,1,2 watt and in resistance values ranging from 1 Ω to 20 MΩ. The two ends of the carbon resistance element are joined to metal caps with leads of tinned wire for soldering its connections into a circuit. Often, the resistance element is a simple rod of press carbon granules which is usually enclosed in a plastic case for insulation and mechanical strength. They are made of finely divided carbon mixed with a powered insulating material in suitable proportion. (b): Precise and stable resistance values are required for meter shunts and multipliers Carbon composition Resistors (a): Large power dissipation is necessary These can be of either a fixed value or variable type. Such resistors are generally available in power ratings from 5 W to several hundred watts and resistance values from 1 Ω to 100 k. The wire is bare but the entire assembly is covered or coated with a ceramic material or special vitreous enamel. The length of the wire used and its resistivity determines the resistance of the unit. They are constructed from a long fine wire(usually nickel-chromium wire) wound on a ceramic core. Resistors are mainly of two types and can be either of the fixed or variable value.Īnother type is called a metal thin film resistor. Types of resistors and their applications Resistors can be connected in the circuit in either direction because they have no ‘polarity’. The two main characteristics of a resister are its resistance and power rating. to establish proper values of circuit voltage due to IR drops.