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37 Cards in this Set
- Front
- Back
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WHAT ARE THE THREE TYPES OF CIRCUIT CONTROL DEVICES?
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Switch, solenoids, and relays
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How are multi-contact switches classified?
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By the number of poles and the number of poles
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What does the number of throws in a switch indicate?
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The number of different circuits that can be controlled by each pole.
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How can switches be classified?
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single break or double break
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What is a rotary switch?
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A midcontact switch part of the schematic with the contacts arranged in a full or partial circle.
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What is a snap-acting switch?
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A switch in which the movement of the switch mechanism (contact) is relatively independent of the activating mechanism movement. (i.e. the actual switching of the circuit is at a fixed speed no matter how fast or slow the switch is moved)
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What is a microswitch?
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Also called an accurate snap acting switch, is a snap acting switch in which the operating point is pre-set and very accurately known.
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What is the operating point of a micro switch?
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The point at which the plunger causes the switch to switch.
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In a microswitch what does C, NO, and NC stand for?
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C=common
NO=normally open NC=normally closed |
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How are switches rated?
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According to their electrical characteristics (i.e. contact size, contact material, and contact spacing)
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What is the current rating of a switch?
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The maximum current the switch is designed to carry
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What is the voltage rating of a switch?
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The maximum voltage allowable in the circuit in which the switch is used
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What can happen if more voltage is applied to a switch than it is rated?
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The voltage can jump to the open contact in the switch
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What are the two tools that can be used to check a switch?
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Ohmmeter and a voltmeter
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WHat is a solenoid?
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A control device that uses electromagnetism to convert electrical energy into mechanical motion
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How is the electromagnet in a solenoid formed?
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By a conductor wound in a series of loops in the shape of a spiral with a soft iron core and a moveable plunger inserted within it
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How is a magnetic field produced in a solenoid?
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When current flows through the conductor
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What is the first step for troubleshooting a solenoid?
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Visually inspect the connections for poor soldering, loose connections, or broken wires
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What is the second step in troubleshooting a solenoid?
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Check the energizing voltage with a voltmeter.
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What can happen if the voltage is too low in a solenoid?
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Less current flowing through the coil and a weak magnetic field resulting in slow or poor operation, chattering, or no operation
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What can happen if the voltage is too hot in a solenoid?
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Overheating or arching
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What is the third step in troubleshooting a solenoid?
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Checking for shorts, opens, and proper resistance with an ohmmeter
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What is the fourth step in troubleshooting a solenoid?
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Check to see if it is shorted to ground
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What is the difference between a relay and a solenoid?
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A relay does not have a moveable core (plunger) while a solenoid does
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How are relays classified?
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According to their use as power relays or control relays
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What are power relays called?
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contactors
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What kind of wires are used to connect the control switch to the relay coil?
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light weight control wire
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What are control relays used for?
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In the control of low power circuits or other relays
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What is a clapper relay?
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A relay with multiple sets of contacts
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What is a thermal time delay relay used for?
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To produce a delayed action when energized
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How are relays described?
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By the method of packaging; open, semisealed, and sealed
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What kind of coil is used in a relay?
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single coil
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What is a common cause of relay failure?
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An open coil
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What problem may form when current flows in one direction through a relay?
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Cone and crater
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What is a crater?
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It is formed by the transfer of metal from one contact to the other
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What is the only tool used to clean a ball shaped contact?
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A burnishing tool
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What tool is used to straighten a bent contact in a relay?
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A point bender
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