Fixed resistor

Fixed resistors are the most frequently used resistors in the electronic circuits. These resistors have the fixed resistance value. Hence, it is not possible to vary the resistance of the Fixed Resistor.

Resistance definition

The process of restricting the flow of electric current to certain level is called resistance. The device or component used to restrict the flow of electric current to certain level is called resistor.

The device, which only restricts the flow of electric current to certain level but does not vary or control the flow of electric current is called fixed resistor.

Fixed resistor definition

Fixed resistors are the resistors whose resistance does not change with the change in voltage or temperature. Fixed resistors are available in various shapes and sizes.

An ideal fixed resistor provides a constant resistance under all environments. However, the resistance of the practical resistors varies slightly with increase in temperature.

The most frequently used resistance values of the fixed resistors include 100KΩ, 10kΩ, 100Ω, 10Ω.

The cost of fixed resistors is high when compared to the cost of variable resistors, because each time to change the resistance we need to buy a new fixed resistor. In case of variable resistors, we use a single resistor for different resistance values. The resistance of the fixed resistor is measured by using the ammeter.

Symbol of fixed resistor

The IEC (International Electro-technical Commission) standard and American standard fixed resistor symbol is shown in the below figure.

A fixed resistor consists of two terminals. This two terminals are used to connect with the other components in the electronic circuit.

Types of fixed resistors

The different Types of Fixed Resistors include:

• Wire wound resistor

The wire wound resistor is a type of passive component, which is made by winding the metal wire around a metal core. The metal wire acts as the resistive element to the electric current. Hence, the metal wire restricts the electric current to certain level. The metal core acts as the non-conductive material. Hence, it does not allow electric current through it.

A manganin or nichrome is generally used as the metal wires because they provide high resistance to the electric current.

• Carbon composition resistor

The carbon composition resistor is a type of passive component, which restricts the flow of electric current to certain level.

The carbon composition resistors are made from a cylindrical resistive element with embedded metal end caps. The cylindrical resistive element of the carbon composition resistor is made from the mixture of carbon powder and ceramic. The carbon powder acts as the good conductor of electric current.

The carbon composition resistors are the most frequently used resistors in the 1960’s and earlier. However, now a days these resistors are rarely used because of its high cost and low stability.

• Carbon film resistor

Carbon film resistors are the most widely used resistors in the electronic circuits. The carbon film resistors are made by placing the carbon film on a ceramic substrate. The carbon film acts as the resistive element to the electric current and the ceramic substrate acts as the insulating material to the electric current.

The metallic end caps are fitted at both ends of the resistive element. The leads made of copper are joined at two ends of these end caps. The carbon film resistors produce less noise than carbon composition resistor.

• Metal film resistor

The metal film resistor is a type of passive component in which metal film is used to restrict the flow of electric current to certain level. The construction of metal film resistor is almost similar to the carbon film resistor. The only difference is the material used for constructing the film. In carbon film resistors, the film is constructed by using carbon whereas in metal film resistors the film is constructed by using nickel chromium or tin and antimony.

Metal film resistors have low TCR (Temperature Co-efficient of Resistance). The rate at which the resistance of the material changes with increase in temperature is called TCR.

• Metal oxide film resistor

The metal oxide film resistor is a type of passive component in which metal oxide film is used as the resistive element to restrict the flow of electric current to certain level.

The construction of metal oxide film resistor is almost similar to the metal film resistor. The only difference is the material used for constructing the film. In metal film resistor, the film is constructed by using the metals such as nickel chromium whereas in metal oxide film resistors, the film is constructed by using the metal oxide such as tin oxide.

The cost of metal oxide film resistor is low compared to the carbon composition resistor. These resistors operate at high temperatures.

• Metal glaze resistor

The metal glaze resistor is a type of passive component in which glass powder and metal particles mixture is used to restrict the flow of electric current to certain level.

Metal glaze resistors have low TCR (Temperature Co-efficient of Resistance). The rate at which the resistance of the material changes with increase in temperature is called TCR.

• Foil resistor

Foil resistors are the most accurate and stable components used to restrict the flow of electric current to certain level. Foil resistors produce low noise compared to the other types of resistors. These resistors are also called high precision resistors. Foil resistors have low TCR (Temperature Co-efficient of Resistance.