Relay Circuit Assignment - Job #9
Here are the tasks to complete for this assignment. You may want to print
this page. Check off each task when done. Then move on to the next task.
Definitions Before You Begin
Be sure you have an understanding of these terms before beginning this exercise.
You may need to use a dictionary, a code book, a theory book, or even ask other
electricians you may know for help. This is part of the learning activity. Begin
now.
terminology
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definition
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control relay
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CR contacts
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F run mode
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F jog mode
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R run mode
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R jog mode
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Read this
As background, here are some details which will help you understand this
assignment. If you encounter words, terms, phrases or abbreviations which you do
not understand, then stop. Research the meaning before going on. This is very
important to your learning activity. The essence of any technical education
activity is comprehensive understanding of all topics which are encountered.
Background Information
There is a wonderful source book for details about relays. Take about ten
minutes to look over some of these links. You may want to save this link for
future use. Source
The following reference material is reprinted, with permission, from the Engineer's
Relay Handbook, 5th edition, published by the National
Association of Relay Manufacturers (NARM). For information on the association or
how to obtain the complete handbook, contact:
National Association of Relay Manufacturers (NARM)
2500 Wilson Boulevard
Arlington, VA 22201
(703) 907-8025
Fax: (703) 875-8908
Email: narm@ecaus.org
National Association
of Relay Manufacturers (NARM)
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Electromechanical
relays are devices that complete or interrupt a circuit by
physically moving electrical contacts into contact with each
other. A relay involves two circuits: the energizing
circuit and the contact circuit. The coil is on the energizing
side and the relay contacts are on the contact side. When a
relay coil is energized, current flow through the coil creates a
magnetic field. Whether in a DC unit, where the polarity is
fixed, or in an AC unit where the polarity changes 120 times per
second, the basic function remains the same: the magnetic coil
attracts a ferrous plate, which is part of the armature. One end
of the armature is attached to the metal frame that is formed so
that the armature can pivot, while the other end opens and
closes the contacts. Relay contacts are designed, built and
specified for the type of application for the relay. No single
voltage and current rating applies to a given set of contacts
under all circumstances. Contact the relay manufacturer for
guidance if your requirements are unusual or the specifications
seem incomplete.
Relay-type choices available for electromechanical
relays include general-purpose relay, machine control or
heavy-duty relay, reed
relay, and aerospace or MIL-Spec relay.
General-purpose relays operate with AC or DC current, at common
voltages and they can control currents ranging from 2A to 30A.
A heavy-duty relay is used to control starters and other
industrial components. Reed
relays are capable of switching industrial components such
as solenoids, contactors and starter motors. An aerospace
or MIL-spec relay meets appropriate military specifications or
is intended for aerospace applications. Mounting choices
for electromechanical
relays include PC board, socket or plug-in style, bracket or
flange mount, and DIN rail.
Pole and throw specifications are important to consider when
searching for electromechanical
relays. Pole choices include single pole (SP), double
pole (DP), triple pole (TP), four pole (4P), and greater than
four poles. Throw choices are single throw or double
throw. Single throw (ST) relays have a pair of contacts
open in one position and closed in the other. Double throw
(DT) relays have three contacts. The common one is in contact
with the second, but not with the third, in one position of the
relay, and reverses this connection in the other relay position.
Important contact specifications to consider when searching for electromechanical
relays include the number of normally open contacts, the
number of normally closed contacts, and the number of changeover
contacts. Contact ratings to consider include maximum
switching current, maximum AC switching voltage, maximum DC
switching voltage, maximum AC switching power, maximum DC
switching power. Important coil ratings to consider
include AC coil voltage, DC coil voltage, coil resistance, coil
nominal AC power, and coil nominal DC power. Important
performance specifications to consider for electromechanical
relays include make time (operate time) and break time
(release time). Common features for electromechanical
relays include convertible contacts, poly-phase relay, time
delay, intrinsically safe, visual indicators, sealed relay,
push-to-test button, current sensitive, voltage sensitive,
expandable deck, and latching controls. An important
operating parameter to consider is the operating temperature.
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Go to the Diagram of this Job
Click HERE to go to the diagram, lecture, and picture for this exercise. Follow
the instructions found there. Then return to this page with your back button.
Connect the Components
Use the material list on the diagrams page to have ready all the components you
will need to complete this exercise. Connect all required components based on
the diagram.
Check your Connections
With the diagram as a guide, verify that all the connections have been made
properly.
Apply Power To Test
Wear safety glasses when testing this circuit. Locate the overcurrent protective
device for the circuit you will use. If possible, connect to a GFCI protected
circuit for the added safety. Be sure you have a full understanding of this
circuit before applying power. Then when you test the circuit, there should be
no problem with it working properly. Make corrections to the wiring as needed so
the circuit works properly. Memorize these connections.
Sketch the diagram from Memory
A sure way to determine if you have internalized this circuit is to draw a
sketch of the diagram from memory. You may choose to use a straight edge. But
that is not necessary. When you have completed the sketch, check it against the
diagram which is given for accuracy. Electricians must have the ability to
remember circuit connections without reference. Here is your chance to
demonstrate what you have learned. If you are unable to sketch the ladder
diagram from memory, refer back to the given ladder diagram. Then try again.
Repeat this activity until you feel confident that you can sketch this specific
diagram without reference.
Reconnect From Memory
Now on to the real test. Reconnect this diagramed circuit from memory. This will
ultimately tell you if you understand this circuit or not.
Review Before Answering Questions
Go back to review definitions, the diagram, the picture, your notes, your sketch
and any other details which will help you as you move on to the questions about
this diagram.
Answer the Questions
When you are satisfied that you can draw a sketch of the diagram, and wire it
all from memory, it is time to go on to answer questions about the diagram.
Click HERE to go to the questions.
Check Your Answers
When you have completed the questions, go on to check your answers. If you have
any which are different than the given answers, try to determine the reason. Go
back to the diagram. Research the question. Ask other electricians you may know.
But do all it takes to understand the correct answer to each question.
Click HERE to go to the answers.
Go On
When you can answer all questions without error, and strongly feel you
understand all answers, it is time to go on to the next assignment.
Click HERE to go on to the next assignment page.
If you would like to research any of these topics further, enter the search
term in this Google Search Box:
Use these Relay Circuit links to go to where you left off in
your online activities.
Job
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Assignment
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Diagram
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Lecture
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Picture
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Questions
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Answers
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