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35 Cards in this Set
- Front
- Back
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What are three reasons circuit control is needed?
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To remove power from a malfunctioning device; to remove power from a device you wish to work
on and restore power when the work is completed; to turn devices on and off as the device is needed; to select the function or circuit desired within a device. |
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What are the three types of circuit control devices?
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Switches, solenoids, and relays.
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What is the difference between a manual and an automatic switch?
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A manual switch must be turned on or off by a person. An automatic switch turns a circuit on or
off without the action of a person (by using mechanical or electrical devices). |
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What is one example of a manual switch?
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A light switch, an ignition switch, television channel selector, etc.
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What is one example of an automatic switch?
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A thermostat, an automobile distributor, a limit switch, etc.
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Why are multicontact switches used?
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Multicontact switches make possible the control of more than one circuit or the selection of one of
several possible circuits with a single switch. |
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What classification of a switch is used when you describe it as a rocker switch?
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The type of actuator.
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In describing a switch by the number of positions of the actuator, what are the two possible
configurations for a single-pole, double-throw switch? |
Two-position and three-position.
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What type of switch should be used to control a circuit that requires a temporary actuation
signal? |
A momentary switch.
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What type of switch is used if it is necessary to guard against a circuit being accidentally turned
on or off? |
A locked-position switch.
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What is the common name used for an accurate snap-acting switch?
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A microswitch.
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What is the current rating of a switch?
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The maximum current a 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 installed.
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What two types of meters can be used to check a switch?
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An ohmmeter and a voltmeter.
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If a switch must be checked with power applied, what type of meter is used?
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A voltmeter.
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What should you check when performing preventive maintenance on a switch?
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The switch operation for smooth and correct operation, the terminals for corrosion, and the
physical condition of the switch. |
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What is the operating principle of a solenoid?
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The magnetic field created in a coil of wire and core will attract a soft iron plunger when current
flows through the coil. |
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What is one example of the use of a solenoid?
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A starter motor and solenoid.
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What is the operating principle of a relay?
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The magnetic field created in a coil of wire will attract aft armature causing a movement in sets of
contacts. |
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How does a relay differ from a solenoid?
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The solenoid provides a mechanical movement of a plunger (a moveable core) while the core of a
relay is fixed. |
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What are the two classifications of relays?
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Control relays and power relays (contactors).
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How can you determine if a relay is operating (changing from one position to the other)?
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By observing the movement of the contacts if the relay is open or sealed with a transparent cover.
If the relay has an opaque cover, you can "feel" the operation of the relay by placing your finger on the cover. |
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What items should be checked on a relay that is not operating properly?
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The coil should be checked for opens, shorts, or a short to ground; terminal leads should be
checked for charred or burned insulation; the contact surfaces should be checked for film, carbon, arcing, and contact spacing. |
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What is used to clean the contacts of a relay?
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A burnishing tool.
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What tool is used to set contact clearances on a relay?
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A point bender
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The part of a switch that is acted upon to cause the switch to change contact connections;
e.g., toggle, pushbutton, and rocker. |
ACTUATOR
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A meter used to measure current.
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AMMETER
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A meter used to measure small values of current by electromagnetic or electrodynamic means.
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GALVANOMETER
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The cylindrical metallic ends of a cartridge fuse.
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FERRULES
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meter that measures very large values of resistance; usually used to check for insulation breakdown in wires.
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MEGOHMMETER
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A meter used to measure resistance.
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OHMMETER
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A device used to convert ac to pulsating dc.
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RECTIFIER
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An electromagnetic device with one or more sets of contacts which changes position by the magnetic attraction of a coil to an armature.
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RELAY
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The resistance of a magnetic path to the flow of magnetic lines of force through it
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RELUCTANCE
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A meter used to measure electrical power.
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WATTMETER
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