Transcript Resistors - DINFOS Blackboard

Resistors
Overview
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Resistors and Resistance
Resistor Types
Resistor Characteristics
Resistor Faults
Resistors and Resistance
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A Resistor is an electronic component used as a
limiting device to adjust and set voltage and
current levels in an electronic circuit.
Just as the Hoover
Dam controls water
flow, a resistor
controls the amount of
current flow in a
circuit.
Resistor and Resistance
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Resistors are the most common
component in an electrical circuit.
Resistors provide an opposition to
current flow.
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The larger the resistance, the less
current is able to flow.
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The letter reference designator is “R”.
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The unit of measure for resistance is
OHMS; represented by the Greek letter
Omega.
Resistors Types
There are two types of resistors: Fixed and Variable
Fixed
Fixed resistors have a
specific value.
Variable
Variable resistors are those
whose value can be adjusted.
Resistor Types
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There are three categories of fixed resistors: general purpose, power, and
precision.
● General purpose
– General purpose resistors are the most common and are
used to limit current flow in all parts of a circuit. They are
cheaply made; most are carbon. They are identified by
color bands.
● Power
– Power resistors are used in circuits with higher currents
and higher voltages. They are wire wound, and have their
value printed on their bodies.
Resistor Types
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There are three categories of fixed resistors: General purpose, power, and
precision.
● Precision
– Precision resistors have a .01 percent tolerance. They are
composed of metal film, and are used where accuracy is a must,
such as in medical or test equipment. The value of the precision
resistor is in printed code on the body of the component.
Resistor Types
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There are two types of variable resistors:
Potentiometers
Rheostats
REMEMBER: Variable resistors are those whose value can be adjusted.
Resistor Types
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Potentiometers- Have a carbon composition, and are used
when circuit current is low. They are used for such things as
volume control and light dimmers.
Resistor Types
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Rheostats are wire wound, and are used when circuit
current is high. Rheostats are used as temperature
controls for soldering irons and electric griddles.
Resistors Characteristics
Three Resistor Characteristics:
● Power rating
– The flow of current through a resistor generates heat. In fact, one of the
resistor’s jobs is to dissipate heat. If more heat is generated than the
resistor can dissipate, the resistor will burn up. A larger resistor has more
surface area for the heat to escape. The larger the resistor, the higher the
power rating. Power rating is measured in Watts.
Resistors Characteristics
Three Resistor Characteristics:
● Ohmic Value
– All fixed resistors have a fixed ohmic value. This value is determined by
the manufacturer. All carbon film and carbon composition resistors have
color bands. By reading these color bands, you can identify the ohmic
value of the resistor. Below is the RESISTOR COLOR CODE:
Resistors Characteristics
Three Resistor Characteristics:
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Ohmic Value
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RESISTOR COLOR CODE:
0
1
2
3
Read bands from left to right:
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The 1st Color is the 1st significant digit
● Example: violet=7
The 2nd Color is 2nd significant digit
● Example: green=5
The 3rd Color is the multiplier
● Example: orange= x 103 (# of zeros)
The 4th Color is Tolerance
● Example: gold= 5% (see next slide)
4
5
6
7
8
9
Resistors Characteristics
Three Resistor Characteristics:
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Tolerance
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Tolerance is the amount that the ohmic value can vary from the actual
ohmic value. The tolerance rating of general purpose resistors aren't
exact (usually between 5 and 20 percent allowance for accuracy).
5%
10%
20% (default)
Resistor Faults
● Open
– An open is a break in the current path in a circuit. Just like a
drawbridge 'opens' a roadway, an open resistor prevents current
from getting through. If you were to measure the output of an open,
you would see the applied voltage of the circuit along with infinite
resistance.
● Short
– Technically a resistor can short, but only for a split second; then it
opens! A short is the opposite of an open. Instead of the applied
voltage and infinite resistance, you would measure zero voltage
and zero resistance. In other words, maximum current would flow
through. If this happened to a resistor, the heat from the increased
current would quickly surpass the power rating of the resistor,
destroying it.
Resistor Faults
● Changed Value
■ Changed values can cause errors, fluctuations, drifts, or even
catastrophic outages. The voltage, current and resistance in an
electrical circuit must be accounted for between all components. If
calculated values versus measured values are different, you could
have a changed value.
Summary
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Virtually every piece of electronic equipment contains resistors.
Competently troubleshooting them will allow you to isolate
outages much faster than pure guesswork.
Resistance
is Futile!
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A resistor is an electronic device used to limit circuit current.
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Resistors are either fixed or variable.
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There are three general categories of fixed resistors: general
purpose, power and precision.
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There are two types of variable resistors: potentiometers and
rheostats.
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The most widely used resistor is made of carbon, and has color
bands on the body to indicate their ohmic value.
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The three common faults in electronic components are opens,
shorts and changed values.
Resistors