Chapter1 - Resistors color coding

12-Jul-12

Lecturer Name [email protected] Contact Number

IT2001PA Engineering Essentials (1/2)

Chapter 1 - Resistor Colour Code


IT2001PA Engineering Essentials (1/2) 2

Lesson Objectives

Upon completion of this topic, you should be able to: Interpret the resistor colour code in terms of value and

tolerance.

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Specific Objectives

Students should be able to :

Identify the symbol of resistors. Identify the various types of resistors :

Carbon composition and carbon film wire wound Wire wound Printed and integrated circuit

Describe their characteristics. State their functions.




Specific Objectives

Students should be able to :

Compute resistance according to colour code bands provided.

Identify the wattage rating of a given resistor. State the 4 factors that affect the resistance of a

resistor. State the applications.




Resistors

Components that are specifically designed to have a certain amount of resistance. 2 main categories

fixed resistors

resistance value are set during manufacturing and cannot be changed.

variable resistors

resistance values can be changed easily with a manual or an automatic adjustment.




Fixed Resistors

Carbon-composition resistors constructed by molding mixtures of powdered

carbon and insulating materials into cylindrical shape.

an outer sheath of insulating material affords mechanical and electrical protection.

copper connecting wires are provided at each end.




Fixed Resistors

Carbon-composition resistors

colour bands resistance material insulation coating

leads




Fixed Resistors


small in size and inexpensive but less accurate and less rugged, the most common type used in electronics.

generally used in low current circuits with relatively low power ratings.

values available from 20mW to 1W.




Fixed Resistors





Fixed Resistors

Wire-wound resistors consists of a length of nickel wire wound on a

ceramic tube and covered with porcelain. low-resistance connecting wires are provided and

the resistance value is usually printed on the side of the component.




Fixed Resistors

Wire-wound resistors connectors

wire wound on ceramic tube

insulation coating




Fixed Resistors

Wire-wound resistors

large in size but more accurate and more rugged.

often used in high current circuits with relatively high power ratings.

values available from less than 1W to several 100W.




Fixed Resistors

Wire-wound resistors

low power rating

mid power rating high power rating




Fixed Resistors

Film resistors similar to wire-wound resistor. wire replace by a resistive material and is

deposited evenly onto a high-grade ceramic rod. the resistive film may be carbon (carbon film) or

nickel chromium (metal film). small in size having performance in-between

carbon-composition and wire-wound resistors.




Fixed Resistors

Film resistors (spiraling technique)

insulating base

outer insulation

coating

metal end cap

metal or carbon film scribe helix




Fixed Resistors

Film resistors (resistor network)

insulation coating

resistive element

termination




Fixed Resistors

Film resistors

common integrated circuit resistive network




Variable Resistors

Manual potentiometer - voltage. rheostat - current.

Automatic thermistor - temperature. photoconductive cell - light intensity.

Examples are the volume controls on our TV receivers and radios.




Variable Resistors

Carbon-composite Wire-wound Film




Resistor Colour Code




Resistor Colour Code Normal resistors colour coded with 4 bands

start from the end that does not begin with a gold or silver band (banded end).

first band is the first digit of the resistance value. second band is the second digit. third band is the multiplier. fourth band indicates the tolerance.





Precision resistors colour coded with 5 bands

first band is the first digit of the resistance value. second band is the second digit. third band is the third digit. fourth band is the multiplier. fifth band indicates the tolerance.





Resistor reliability band

usually indicated by the fifth band. indicates in percent of failures per 1000 hours of

use. for military specification (mil. spec.).




Example 1 yellow = 4

R = 46 x 103 Ω = 46 000 Ω = 46 kΩ + 10%

yellow blue

orange silver

tolerance = 10% of 46 000 Ω = 4 600 Ω

R = (46 000 Ω - 4 600 Ω) to (46 000 Ω + 4 600 Ω) = 41 400 Ω to 50 600 Ω = 41.4 kΩ to 50.6 kΩ

blue = 6 orange = 103

silver = 10%




Example 2 green = 5

R = 523 x 104 Ω = 5 230 000 Ω = 5.23 MΩ + 1%

green red

orange yellow

brown

tolerance = 1% of 5.23 MΩ = 0.523 MΩ

R = (5.23 MΩ - 0.523 MΩ) to (5.23 MΩ + 0.523 MΩ) = 4.707 MΩ to 5.753 MΩ

red = 2 orange = 3 yellow = 104

brown = 1%




Example 3 purple = 7

R = 76 x 10-2 Ω = 76 ÷ 100 Ω = 0.76 Ω = 760 mΩ + 5%

purple blue

silver gold

tolerance = 5% of 760 mΩ = 38 mΩ

R = (760 mΩ - 38 mΩ) to (760 mΩ + 38 mΩ) = 722 mΩ to 798 mΩ

blue = 6 silver = 10-2

gold = 10%




Wattage Rating

The maximum amount of power that a resistor can dissipate without being damaged by excessive heat buildup. Not related to the ohmic value (resistance). Determined mainly by the physical size and

shape of the resistor.




circumference (c)

Wattage Rating

The larger the surface area of a resistor, the more power it can dissipate.

surface area of a cylindrically = (l x c) shaped resistor

length (l)




Wattage Rating

Carbon-composition resistors from 20mW to 1W.

Wire-wound resistors less than 1W to several 100W.

Film resistors up to 10W.




Resistance Factors Resistance of resistor is affected by 4 factors

ρ l A R =

environmental temperature (temperature coefficient).

manufacturer diameter (cross-sectional area, A). length (l) type of material (resistively, ρ).




Resistance Factors

Temperature coefficient

indicates the change in resistance with temperature positive - proportional. negative - inversely proportional.




Applications

Limit/reduce current. Divide voltage to produce a desired voltage

drop. Generate heat in certain cases.




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Chapter1 - Resistors color coding

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