2. Chapter 1 - Resistor Colour Code
Lesson Objectives
Upon completion of this topic, you should be able to:
Interpret the resistor colour code in terms of value and
tolerance.
2
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3. Chapter 1 - Resistor Colour Code
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.
IT2001PA Engineering Essentials (1/2)
4. Chapter 1 - Resistor Colour Code
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.
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5. Chapter 1 - Resistor Colour Code
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.
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6. Chapter 1 - Resistor Colour Code
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.
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8. Chapter 1 - Resistor Colour Code
Fixed Resistors
Carbon-composition 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.
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10. Chapter 1 - Resistor Colour Code
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.
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12. Chapter 1 - Resistor Colour Code
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.
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13. Chapter 1 - Resistor Colour Code
Fixed Resistors
Wire-wound resistors
low power rating
mid power rating high power rating
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14. Chapter 1 - Resistor Colour Code
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.
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15. Chapter 1 - Resistor Colour Code
Fixed Resistors
Film resistors (spiraling technique)
outer
insulating insulation
base coating
metal metal or carbon
end cap film scribe helix
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21. Chapter 1 - 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.
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22. Chapter 1 - Resistor Colour Code
Resistor Colour Code
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.
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23. Chapter 1 - Resistor Colour Code
Resistor Colour Code
Resistor reliability band
usually indicated by the fifth band.
indicates in percent of failures per 1000 hours of
use.
for military specification (mil. spec.).
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24. Chapter 1 - Resistor Colour Code
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
IT2001PA Engineering Essentials (1/2)
25. Chapter 1 - Resistor Colour Code
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
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26. Chapter 1 - Resistor Colour Code
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
IT2001PA Engineering Essentials (1/2)
27. Chapter 1 - Resistor Colour Code
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.
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28. Chapter 1 - Resistor Colour Code
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)
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29. Chapter 1 - Resistor Colour Code
Wattage Rating
Carbon-composition resistors
from 20mW to 1W.
Wire-wound resistors
less than 1W to several 100W.
Film resistors
up to 10W.
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30. Chapter 1 - Resistor Colour Code
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
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31. Chapter 1 - Resistor Colour Code
Resistance Factors
Temperature coefficient
indicatesthe change in resistance with
temperature
positive - proportional.
negative - inversely proportional.
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32. Chapter 1 - Resistor Colour Code
Applications
Limit/reduce current.
Divide voltage to produce a desired voltage
drop.
Generate heat in certain cases.
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