Chapter1 - Resistors color coding

IT2001PA
Engineering Essentials (1/2)

Chapter 1 - Resistor Colour Code

Lecturer Name
lecturer_email@ite.edu.sg
12-Jul-12
Contact Number


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

2
IT2001PA Engineering Essentials (1/2)


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

 resistancevalues 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.
 anouter sheath of insulating material affords
mechanical and electrical protection.
 copper connecting wires are provided at each end.



Fixed 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.
 generallyused in low current circuits with relatively
low power ratings.
 values available from 20mW to 1W.



Fixed Resistors



Fixed Resistors
 Wire-wound resistors
 consistsof 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
connectors

wire wound on insulation
ceramic tube coating



Fixed 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

low power rating

mid power rating high power rating



Fixed Resistors
 Film resistors
 similar to wire-wound resistor.
 wirereplace 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).
 smallin size having performance in-between
carbon-composition and wire-wound resistors.



Fixed Resistors
 Film resistors (spiraling technique)
outer
insulating insulation
base coating

metal metal or carbon
end cap film scribe helix


Fixed Resistors
 Film resistors (resistor network)
insulation
coating
resistive
element

termination



Fixed Resistors
 Film resistors

common resistive network integrated circuit



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

19


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 blue
yellow = 4
blue = 6
orange = 103
orange silver silver = 10%

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



Example 2
green red brown green = 5
red = 2
orange = 3
yellow = 104
orange yellow brown = 1%
 R = 523 x 104 Ω = 5 230 000 Ω = 5.23 MΩ + 1%
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



Example 3
purple blue
purple = 7
blue = 6
silver = 10-2
silver gold gold = 10%

 R = 76 x 10-2 Ω = 76 ÷ 100 Ω = 0.76 Ω = 760 mΩ + 5%
tolerance = 5% of 760 mΩ = 38 mΩ
R = (760 mΩ - 38 mΩ) to (760 mΩ + 38 mΩ)
= 722 mΩ to 798 mΩ



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.



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) circumference (c)



Wattage Rating
 from 20mW to 1W.
 less than 1W to several 100W.
 Film resistors
 up to 10W.



Resistance Factors
 Resistance of resistor is affected by 4 factors
 environmental
 temperature (temperature coefficient).
 manufacturer
 diameter (cross-sectional area, A).
 length (l)
 type of material (resistively, ρ).

ρl
R =
A



Resistance Factors
 Temperature coefficient

 indicatesthe 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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