Type of resistors

Type of resistors | Construction and characteristics of various types of resistors | functions and applications of the resistors in electrical and electronic circuits

These are the most common passive component used in electrical and electronic circuits.

A resistor is manufactured with a specific value of ohms (resistance). The purpose of using a resistor in circuit is either to limit the current to a specific value or to provide a desired voltage drop (IR).

The power rating of resistors may be from fractional watts to hundreds of Watts.

There are five types of resistors

1) Wire-wound resistors

2) Carbon composition resistors

3) Metal film resistors

4) Carbon film resistors

5) Special resistors

1) Wire-wound resistors

Wire-wound resistors are manufactured by using resistance wire (nickel-chrome alloy called Nichrome) wrapped around an insulating core, such as ceramic porcelain, Bakelite pressed paper etc.

Fig 1, shows this type of resistor.

The bare wire used in the unit is generally enclosed in insulating material.

Wire wound resistors are used for high current application.

They are available in wattage ratings from one watt to 100 watts or more.

The resistance can be less than 1 ohm and go up to few thousand ohms.

Fig 1

One type of wire-wound resistor is called as fusible resistor enclosed in a porcelain case. This resistor is designed to open the circuit when the current through it exceeds certain limit.

2) Carbon composition resistors

Fig 2

These are made of fine carbon or graphite mixed with powdered insulating material as a binder in the proportion needed for the desired resistance value.

Carbon-resistance elements are fixed with metal caps with leads of tinned copper wire for soldering the connection into a circuit.

Fig 2 shows the construction of carbon composition resistor.

Carbon resistor are available in values of 1 ohm to 22 mega ohms and of different power ratings, generally 0.1, 0.125, 0.25, 0.5, 1.0 and 2 watts.

3) Metal film resistors

Metal film resistors

Metal film resistors are manufactured by two processes.

Thick film resistors are pasted with metal compound and powdered glass which are spread on the ceramic base and then backed.

Thin film resistors are processed by depositing a metal vapor on a ceramic base.

Metal film resistors are available from 1 ohm to 10 MΩ, up to 1W. Metal film resistors can work from 120°C to 175°C.

4) Carbon film resistors

Carbon film resistors

In this type, a thin layer of carbon film is deposited on the ceramic base/tube.

A spiral groove is cut over the surface to increase the length of the foil by a specialized process.

Carbon film resistors are available from 1 ohm to 10 meg ohm and up to 1 W and can work from 85°C to 155°C.

All the above four types of resistors are coated with synthetic resin to protect them against mechanical damages and climatic influences, It is therefore, difficult to distinguish them from each other externally.

Specification of resistors :

Resistors are specified normally with the four important parameters

1) Type of resistor

2) Nominal value of the resistors in ohm (or) kilo ohm (or) mega ohm.

3) Tolerance limit for the resistance value in percentage.

4) Loading capacity of the components in wattage.

For Example :

100 ± 10% , 1W, where as nominal value of resistance is 100Ω.

The actual value of resistance may be between 90Ω to 110 Ω, and the loading capacity is maximum 1 watt.

The resistors can also be classified with respect to their function as

1) Fixed resistors
2) Variable resistors

1) Fixed resistors :

The fixed resistors is one in which the is nominal value of resistance is fixed. These resistors are provided with pair of leads. (type 1 to 4)

2) Variable resistors

Variable resistors are those whose values can be changed.

Variable resistors includes those components in which the resistance value can be set at the different levels with the help of sliding contacts.

These are known as potentio meter resistors or simply as a potentio meters.

carbon track variable resistors

wire wound variable resistor

About Admin MC3

This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.