Types Of Resistors

TYPES OF RESISTORS

This type of resistor is made up of finely divided Carbon or graphite mixed on the powdered insulating material as a binder, in proportion to the desired "R' value. The msistive element is enclosed in a plastic case for insulation and mechanical strength.

 

Carbon resistors are available in resistanee values of in to 20 Mn. Power rating generally available is 1/4,1/2 and 2 W.

 

FAILURE IN RESISTORS

Generally resistors are very reliable and have a very low failure rate. But failures oeeur due to passage of time, heat, applied voltage, humidity, and meehanieal stress.

 

Carbon Composition Type Resistor

 

These types of resistors have poor stability and poor temperature eoeffieient. The possible failures and their eauses are:

a) OPEN CIRCUIT

1. Burning of resistor center due to exeess heat.
2. Fraeturing of resistor due to meehanieal stress.

a) HIGH VALUE

1. Heat, voltage or moisture can cause movement of carbon or binder.
2. Separation of carbon particles due to swelling caused by absorption of water.

 

 

Wire Wound Resistors

In this a speeial type of wire called resistance wire is wrapped around an insulating core. The length of the wire and specific resistivity determines resistance of the unit. The types of resistance wire include Tungsten and Manganin. The insulated core is commonly porcelain or cement.

 

These are used for generally high current applications with law resistance and appreciable power. The resistance are available in wattage rating from 5 W to 100 W. The resistance can be less than 1 ohm and upto several thousand ohms.

 

 

Film type resistors:

There are two kinds of film type resistor. The earbon film type has thin eoating around an insulator; the metal film resistor has spiral winding around a eeramie substrate. The advantage of metal film resistor over earbon type resistor is its more precise value of resistanee.

 

Metal Film Resistors

These resistors exhibit law temperature eoeffieient and good stability. The metal resistors are available in power ratings of 250 mw to 2W.The possible failures are:

a) OPEN CIRCUIT

1. Scratching of film.
2. High voltage or temperature eausing disintegration.
3. Open eireuit failure oeeurs in higher value of resistors due to thin resistanee spiral.

 

a) HIGH NOISE

1. Bad contact of end connectors due to poor assembly on the circuit

 

 

Chip resistors:

These have carbon coating filled into a solid ceramic substrate. The purpose is to have more precise resistance volume and greater stability with temperature.

 

 

Fusible resistor

 

This is wire wound resistor type. It burns open easily when power rating is exceeded. It serves dual purpose of a fuse and also a resistor to limit the current.

for more information corbon film resistors Click Here

Keywords : Resistance, Resistors, Series, Parallel, Power, Ohm, Ohmmeter, Circuit, Basic Electronic Parts, Ampere, Voltages, Henry, Farad