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Department of Technical EducationAndhra Pradesh

Name : N. Ranga Prasad.

Designation : Lecturer in ECE.

Institute : GMR Polytechnic Gajwel.

Year / Semester : 1 st year.(EC -105)

Subject : Electronics Components and Devices.

Topic : Resistors.

Duration : 50 min.

Sub Topic : Common faults in resistors.

Teaching Aids : PPT.

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OBJECTIVES

Upon completion of this topic you will be able to understand

The common faults in resistors.

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RECAP

In previous class we discussed about:

.thermistors

.sensistor

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Common faults in Resistors

• Resistors are reliable components and their rate of failure is very low.

• Still faults do occur .

• Some common faults which will occur in resistor are :

• Open Resistor : A resistor may become open by excessive current through resistor.

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Faults in Resistors Cont’d…

1) Mechanical stress in carbon resistor and corrosion in metal resistor may also result in open resistors.

2) Increase in the Value of Resistance : The Value of carbon resistors may increase due to lack of proper environmental conditions.

For Example increase in temperature increases the resistance value of carbon resistors.

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Faults in resistors cont’…

3) Short Circuited Resistor :

Generally a resistor does not become short circuited .But a meter a may show short due to some component ( capacitor ,Transistor etc ) that is connected across the resistor may get shorted.

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Faults in Resistors cont’d

4) Noise in Resistors:

Random motion of electrons in a resistor results in nose called JOHNSON Noise or WHITE Noise .some noise is normal depending on the value of resistance and temperature. However bad contacts of end-connectors may cause noise higher than normal

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Faults of Resistor Cont’d

5) Intermittent Contact :

Particles of Dust ,grease or abrasive matter between the wiper and resistance material (track) may result in intermittent contact and may increase noise signal and may cause intermittent faults.

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Faults of Resistor Cont’d

6) Dry or Cold solder Joint : 6) Dry or Cold solder Joint :

The Dry or Cold Solder joint may behave as high The Dry or Cold Solder joint may behave as high resistance leads .resistance leads .

A Resistor cannot be repaired and hence if the faults is in A Resistor cannot be repaired and hence if the faults is in the resistor itself, it should be replaced with a good one of the resistor itself, it should be replaced with a good one of the same specifications.the same specifications.

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Summary

We have already discussed about common faults in a resistor.

• Open resistor.

• Short circuited resistor.

• Change in the value of resistor.

• Noise in resistors.

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Quiz 1

RESISTORS can be repaired. (a)yes (b)no (c)sometimes

(d)none of the above

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Quiz 2 Resistors do not get affected due

to excess current flow.

(a)yes (b)no (c)sometimes

(d)none of the above

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Frequently asked questions

• Explain the different types of faults that may occur in Resistors.

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Assignment questions

1. Write short notes on common faults in resistors