12-Jul-12
Lecturer Name [email protected] Contact Number
IT2001PA Engineering Essentials (1/2)
Chapter 1 - Resistor Colour Code
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.
Chapter 1 - Resistor Colour Code
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Carbon-composition resistors
colour bands resistance material insulation coating
leads
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Carbon-composition 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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Carbon-composition resistors
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Wire-wound resistors connectors
wire wound on ceramic tube
insulation coating
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Wire-wound resistors
low power rating
mid power rating high power rating
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Film resistors (spiraling technique)
insulating base
outer insulation
coating
metal end cap
metal or carbon film scribe helix
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Film resistors (resistor network)
insulation coating
resistive element
termination
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Fixed Resistors
Film resistors
common integrated circuit resistive network
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2) 19
Variable Resistors
Carbon-composite Wire-wound Film
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Resistor Colour Code
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.).
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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%
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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%
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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%
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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)
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Wattage Rating
Carbon-composition resistors from 20mW to 1W.
Wire-wound resistors less than 1W to several 100W.
Film resistors up to 10W.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
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).
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Resistance Factors
Temperature coefficient
indicates the change in resistance with temperature positive - proportional. negative - inversely proportional.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2)
Applications
Limit/reduce current. Divide voltage to produce a desired voltage
drop. Generate heat in certain cases.
Chapter 1 - Resistor Colour Code
IT2001PA Engineering Essentials (1/2) 33
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