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What three fundamental conditions must exist before a voltage can be produced by magnetism?
Conductor, magnetic field, relative motion between the field and the conductor.
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How is the voltage created with magnetism?
By a conductor, or conductors moving across a magnetic field so as to cut the lines of force, electrons within the conductor are impelled in one direction or another.
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What is the main application of voltage produced by friction?
Van De Graf Generators.
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Static electricity is produced by what method of EMF?
Friction.
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Heating a piece of copper metal on one end will have what effect on its electrons?
moves away from the hot end and move toward the cooler end.
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What commonly used instrument uses EMF produced by heat?
thermocouple.
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What type of materials are used to produce photoelectric voltage?
Silver oxide or copper oxide.
- A complete device that operates on the photoelectric principle is referred to as?
- A photoelectric cell.
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What method of EMF involves the altering of a substance's molecules?
Chemical action.
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Electricity is a combination of a force called voltage and the movement of invisible particles known as?
Current.
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What is OHMS law when expressed as an equation?
I=ER
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In a DC circuit power is equal to the product of what?
Voltage and the current, P = IE.
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A DC circuit that has two or more resistors, or loads and are connected directly to the same source of voltage are called?
Parallel circuits.
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How many basic formulas can be derived from OHMS law?
12.
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What type of DC circuits involve equal decreases in voltage and increases in voltage from the power source?
Series circuits.
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In a DC series circuit the total resistance is the sum of what?
The resistances of the individual parts of the circuit.
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The frequency of AC voltage is measured by?
Cycles per second (CPS).
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What formula determines AC voltage frequency?
f = P x rpm 120
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In AC voltage frequency formula what does the P indicate?
Number of poles.
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The amount of opposition to current flow in an AC inductive circuit is referred to as?
Inductive reactance.
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In accordance with OHMs Law for AC Circuits the effective current through a circuit is?
Directly proportional to the effective voltage and inversely proportional to the impedance.
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What is the equation used to express OHMs Law when dealing with AC circuits?
I=E Z
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In the equation I=E what does the I, E and Z stand for?
Z I=Current, E=EMF, Z=Impedance in OHMs.
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What is an ammeter?
A measuring device that is used to indicate current passing through a conductor.
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Ammeters must always be connected in what manner to the circuit being measured?
In series with the circuit.
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If an ammeter is connected in parallel, what detrimental effect will occur to the meter?
It would give an incorrect measurement and damage the ammeter due to excessive current flowing through the meter.
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How does an ammeter handle switchboard current?
By installation of a current transformer.
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What is produced in the secondary of a current transformer?
A fraction of the primary current.
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Ammeter sensitivity is defined as what?
The amount of current necessary to cause full scale deflection,
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How does an ammeter affect the circuit it is measuring?
It increases the resistance of the circuit and lowers circuit current.
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What can you do to minimize the effect of an ammeter on the circuit being measured?
By ensuring the resistance of the ammeter must be much smaller than the circuit load.
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What allows an ammeter to measure different ranges of current?
Shunt resistors.
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What type of shunt resistor is used for limited current below 50 amperes?
Internal shunt.
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Current ranges in excess of 50 amperes employ what type of shunt? -
External shunt.
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When conducting an initial measurement, the ammeter range adjustment should be placed in what position?
The highest range.
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When a final measurement is being taken using an ammeter, the ammeter scale should be read in what manner?
By reading the mid-scale portion.
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What type of voltmeter reads variable resistance?
portable voltmeter.
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What is the range of a switchboard voltmeter?
0-600 volts.
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Voltmeters installed with a fixed resistance can be found in what location?
Switchboards and control consoles.
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What is the principle operation of a voltmeter?
Measures the current that the voltage is able to force through a high resistance.
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How is a voltmeter always connected?
In parallel.
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What does the term loading effect mean when associated with a voltmeter?
Once connected the voltmeter adds a resistance in parallel with the circuit changing the total circuit resistance and loads the circuit.
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Voltmeter loading effect can be minimized by what action?
By ensuring the voltmeter has a high resistance compared with the circuit being measured.
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How is voltmeter sensitivity expressed?
In ohms per volt.
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Voltmeter sensitivity is determined by what?
- Divide 1 by the amount of current needed to cause full-scale deflection of the meter movement or 1
- full-scale current
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How is the full-scale voltage reading calculated using a voltmeter?
Full-scale current x resistance.
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Electrostatic voltmeters are used to measure what?
High voltage.
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The series-type ohmmeter's pointer deflection is controlled by what?
The amount of battery current passing through the moving coil.
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How is the series-type ohmmeter calibrated prior to use?
By placing the test leads in a shorted position.
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How are the test leads of a series-type ohmmeter connected?
In series with the circuit being measured.
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What is easiest way to tell the difference between a series-type ohmmeter and a shunt ohmmeter?
By the scale on the meter.
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What are the two primary elements of a megger?
A hand-driven dc generator and a instrument portion.
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What element of a megger supplies high voltage for making the measurement?
The hand-driven dc generator.
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What protects the megger from excessive test voltage?
A friction clutch.
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The mirror installed on a multimeter serves what function?
To eliminate parallax error.
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Switchboard and portable ammeters and milliammeters for use on direct-current are of what design?
Permanent magnet moving-coil type.
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What are two types of alternating-current ammeters?
Moving-iron and electrodynamometer type.
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What type of AC ammeter operates on the movement of a magnetic field of a fixed coil or coil-system carrying the current to be measured?
Moving-iron type.
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How many coils are present in an electrodynamometer type ammeter?
Two.
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Switchboard and portable ammeters for use primarily on alternating current are usually of what type?
Moving-iron type.
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What type of ammeter uses a magnetic field around a current-carrying conductor to cause a deflection of an indicating element?
Split-Core Ammeter.
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What type of speed sensor is used to measure main reduction gear speed?
A tachometer.
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A device that senses speed by using a toothed gear that cuts a magnetic field of the pickup is known as?
A magnetic speed pickup.
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What type of speed sensor outputs a square wave ac voltage?
Magnetic.
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What is the difference between an electronic digital multimeter amd a multimeter?
Display is digital and it has a higher input impedance.
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What is used to measure electrical power?
A wattmeter.
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The amount of power produced by a generator is measured in what?
Kilowatts.
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A kilowatt meter is connected to what two transformers?
A current and potential transformer.
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What does a kilowatt meter measure?
Measures line current and voltage.
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Why is a kilowatt meter vital to balancing electrical loads?
Allows the operator to monitor the electrical load while paralleling generators.
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Loss of the kW on an operating generator will cause what?
Failure of the effected generator.
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What does a frequency meter measure?
Cycles per second or hertz(Hz).
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What is the range of a frequency meter?
55 to 65 Hz.
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What converts the input frequency to an equivalent output frequency within the frequency meter?
A transducer.
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What are two types of frequency meters?
Vibrating reed and moving-disk type.
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A hook-on type voltmeter uses what type of transformer?
A split-core type.
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What measuring instrument can be connected to the conductor without disconnecting it?
A hook-type voltmeter.
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A frequency meter that is used as an in-circuit meter is usually known as what?
A vibrating reed type.
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Frequency meters employed as an out-of-circuit meter are known as what type?
Moving-disk type.
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What are in-circuit meters used to measure?
Monitors the operation of electrical devices.
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Out-of-circuit meters are designed to give the operator what advantage?
More versatile by allowing the operator to monitor more than one piece of equipment.
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What is a rectifier?
A device that changes ac current to a form of dc current.
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The term "Damping" means what when associated with meter movement?
Smoothing out the oscillation of the pointer.
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What device is used before a 3-phase generator is connected to the bus bar?
A synchroscope.
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A synchroscope is designed to ensure you have proper phase sequence between the generator and bus bar and what other permissives prior to loading a generator?
Generator and bus-bar voltage must be the same, generator and bus-bar frequency must be same, generator frequency must be constant, generator and bus-bar voltage must be in phase.
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When conducting maintenance on group-D enclosures, what is the maximum plane joint gap clearance?
.010 inch.
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What tool is used to determine gap clearances?
Thickness gauge.
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Shafts and motors that are centered by radial bearings have a max radial gap clearance of what?
.016 inch.
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What must be done with equipment that exceeds designed gap clearance?
Equipment must be replaced.
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What will happen to the test instrument if your connection is across a line?
A dead short circuit will occur and immediate destruction of the test instrument.
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What type of voltage tester is designed for shipboard use?
A multi-voltage, multi-frequency with polarity indication.
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Polarity indicators provide identification of DC polarity above how many volts?
90 volts.
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Voltmeters for direct current use only are of what design?
Permanent magnet moving-coil type.
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Switchboard and portable voltmeters are of what design?
Moving-iron type.
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A precision portable voltmeter that is used for both AC and DC current is of what design?
Electrodynamometer.
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How is the range of a voltmeter effectively doubled?
By use of a multiplier.
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When conducting tests, how is electrical power measured on a DC circuit?
By measuring the current through the voltage across the load with an ammeter and voltmeter, power is the product of the two.
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When conducting testing, how is electrical power measured on an AC circuit?
By measuring the current through the load, the voltage across the load, and the power factor of the load, using an ammeter, voltmeter and power factor meter.
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Wattmeters are usually of what design?
Electrodynamometer type.
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What is the power in a three-wire three-phase system usually measured with?
A three-phase wattmeter.
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What is the difference in construction between a varmeter and a wattmeter?
The varmeter is constructed so that the current through the potential coil is shifted in phase with respect to the line voltage.
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What type of power does a varmeter measure?
Reactive power.
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The pointer deflection of a wattmeter indicates what?
Power or the product of current, voltage and power factor.
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What is the proper way to connect a wattmeter to a source to be measured?
One that places the two coils at approximately the same potential.
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Define the term power factor?
The ratio of useful power to the square root of the sum of the squares of useful power and reactive power.
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Power factor meters depend for their operation on the interaction between what?
A pulsating single-phase magnetic-field produced by a single coil and a rotating magnetic field.
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Before connecting a polyphase generator to bus bars already connected to one or more generators, what conditions must be met?
Phase sequence must be the same for generator and bus bar, generator and bus bar voltage and frequency must be the same, generator frequency must be constant and the generator bus bar voltage must be in phase.
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The sequence in which the currents in A, B and C phases of a three-phase system reach their maximum values is measured by what device?
A phase-sequence indicator.
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A phase sequence indicator uses how many neon lamps as a visual display to indicate phase sequence?
Three.
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What type of portable measuring device permits a visual presentation of some varying electrical quantity, such as voltage or current or any other quantity which can be expressed in terms of voltage?
An oscilloscope.
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Oscilloscopes used aboard naval vessels are designed to operate at what voltage and frequency?
120 Volt, 60 Hz.
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When using an oscilloscope, what action can be taken to prolong tube life?
By adjusting the intensity and focus controls for minimum readable brilliance and to produce the smallest practical spot or narrow line.
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A standard magneto is capable of giving a ring through a resistance of how many Ohms?
50,000 Ohms.
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When measuring resistance with a DC ammeter or voltmeter, how is the resistance in Ohms determined?
The resistance in Ohms is equal to the volts divided by the amperes.
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What is the function of a resistance box?
It is used to measure an unknown resistance or check the accuracy of an ohmmeter or insulation resistance tester.
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What method of measuring resistance is used with a decadence test set?
Wheatstone bridge method.
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Name three types of insulation resistance indicator instruments?
An Ohmmeter, Megohmmeter and Meggers.
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What is the range of a Navy-type GC insulation resistance indicator?
0 -100 Megohms.
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What is the energy source of the Navy-type GC insulation resistance indicator?
A 500 volt Direct Current energy source.
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What is the two digit designation given to a pocket size insulation resistance indicator?
PC.
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