Film type resistors

Carbon, nichrome, or some mixture of ceramic and metal (cermet) can be applied to a cylindrical form as a film, or thin layer, in order to obtain a desired value of resistance. This type of resistor is called a carbon-film resistor or metal-film resistor. It looks like a carbon-composition type, but the construction technique is different (Fig. 6-7).

The cylindrical form is made of an insulating substance, such as porcelain. The film is deposited on this form by various methods, and the value tailored as desired. Metal-film units can be made to have nearly exact values. Film type resistors usually have low to medium-high resistance.

A major advantage of film type resistors is that they, like carbon-composition units, do not have much inductance or capacitance. A disadvantage, in some applications, is that they can’t handle as much power as the more massive carbon-composition units or as wirewound types.