6th 6 Months (Possibly not OPS) Flashcards
1
Q
One advantage of DC motors over AC motors is that a DC motor
A
offers better speed control
2
Q
In DC motors, eddy currents can cause
A
overheated brushes
3
Q
Which of the following cells has the shortest service life
A
Lead-acid
4
Q
In the electroplating process, the object to be plated is made the
A
cathode
5
Q
In arc welding, a “reversed polarity” exists when the electrode is _____ and the work is _____.
A
positive;negative
6
Q
If you double the distance between two magnetic poles, the magnetic force is
A
reduced to 25%
7
Q
A solenoid used for closing a valve or releasing a brake is usually made with a _____-shaped magnet.
A
C-T
8
Q
Mounting a solenoid from the end
A
improves its performance
9
Q
When a relay operates, its NC contacts
A
open and remain open
10
Q
The movable magnetic arm of a relay is called the
A
armature
11
Q
Which part of a DC generator makes electrical contact between the brushes and the coils of wire in the armature
A
Commutator
12
Q
In DC generators, the number of pulses during each rotation of the armature _____ with an increase in the number of ______.
A
increases;field poles
13
Q
Commutation in a DC generator keeps the current to the output terminals
A
in the same direction at all times
14
Q
A DC generator that supplies a nearly constant potential difference between terminals is called a ____ generator.
A
compound
15
Q
Eddy currents in a DC genrator cause ____ losses.
A
magnetic
16
Q
Commutation is the
A
reversal of current in a motor’s armature
17
Q
How much work do you accomplish if you carry a 50 lb object 10 ft horizontally?
A
0 ft-lb
18
Q
The field windings in a DC compound motor are connected so that _____ with the armature
A
one is in parallel and one is in series
19
Q
The armature current and the _____ determine the torque in a DC motor.
A
field strength
20
Q
The only kind of DC motor to run faster under a high load than under a low load is a ____ motor.
A
differential compound
21
Q
Which part of DC armature is made of copper bars that are insulated from each other?
A
Commutator
22
Q
A winding that doubles back on itself in a drum armature is called a ____ winding.
A
lap
23
Q
If the full-load current in a DC armature is 100A and the resistance between the brushes is 0.05 ohms the copper loss is
A
500W
24
Q
Which type of power loss varies with the speed of a DC armature and the volume of iron in the core?
A
Hysteresis loss
25
A bright spark produced while a DC machine is running indicates an _____ in the armature.
open circuit
26
A time-delay feature can be added to a magnetic overload relay in the form of an
oil dashpot
27
In a shunt relay, the size of the air gap between the coil and the armature determines the
voltage needed to operate the contactor
28
The current at which a series lockout relay will close can be changed by adjusting the
size of the air gap
29
The device that protects a relay by extinguishing the arc formed when contacts open is a
magnetic blowout coil
30
A disc brake is designed to be mounted on the _____ of a motor.
end bell
31
An adjustable-voltage motor controller varies the potential difference applied to the motor's
armature
32
Controllers are rated by duty as ___ or ____.
continuous;intermittent
33
Which overload relay is used only in AC circuits?
magnetic
34
Changes in ambient temperature will change the tripping characteristics of a thermal overload relay unless the relay is
temperature compensated
35
A DC motor that requires frequent starting, stopping, reversing, and changes speed usualy has a
drum-type controller
36
A rectifier changes
AC to DC
37
A pi filter network consists of ___ and ____.
two capacitors;one inductor
38
One advantage that a mercury-vapor diode has over a vacuum-tube diode is that the mercury-vapor diode
produces a higher power output
39
Most mercury-vapor rectifiers have a time-delay relay to
protect the diode
40
Semiconductor failures caused by high temperatures usually occur
in a fraction of a second
41
Another name for a silicon controlled rectifier is a
thyristor
42
The part of an SCR that either allows or prevents the flow of electricity is called the
gate
43
In an AC circuit, an SCR conducts during _____ of the cycle
either half but not both halves
44
An SCR in an AC circuit can be turned on earlier in the half-cycle in order to _____ the ____.
increase;power to the load
45
Increasing the effective current and power level from an SCR controller to a DC motor requires
narrower intervals between pulses
46
A sudden drop in the potential difference between terminals usually indicates an _____ circuit in the field winding of a DC _____.
open;generator
47
Before installing a new field coil in a machine you should
determine the polarity of the new coil
48
If silver relay contacts become slightly roughened or pitted, you should
do nothing
49
To ensure proper communication in a reversible motor, you should set the brushes _____ degrees from electrical neutral.
0
50
A blackened, scratched, or dirty commutator should be cleaned with a
a high-quality cleaning stone
51
In Boolean algebra, all logic functions can be expressed by equations based on three operations:
and, or, not
52
For an AND gate, the output is TRUE if input A is ___ and input B is ____.
TRUE;TRUE
53
A solid-state logic switch must be able to
indicate which state is at its input
54
The AND function in positive logic is equivalent to the ___ function in negative logic.
OR
55
If CMOS logic is used in a circuit with TTL logic, the input is usually
5V
56
An application requires an R-S flip-flop that will trigger when S goes HIGH and reset when R goes HIGH. The required flip-flop can be made up of _____ gates.
two NOR
57
The advantage of using an R-S flip-flop with a mechanical switch is that the flip-flop ______ the output when the switch changes
makes changes in
58
The output of a clocked flip-flop will change only when the clock pulse is
present
59
If you need to use a sine wave to control the frequency of a logic clock, you can use a _______ to produce sharp clock pulses.
Schmitt trigger
60
What is the hexadecimal equivalent of the binary numeral 11100?
1C
61
The problem with ripple counters is that
propagation delay is cumulative
62
A device commonly used for converting parallel data to serial data is the
multiplexer
63
A half-adder can be made of an ____ gate and an ____ gate.
AND;Exclusive OR
64
Large memories are typically accessed by
matrix addressing
65
Unlike a RAM, a ROM
stores data that do not change
66
An output interface contains a _____ that produces a ____ signal in response to the output of the logic system.
transistor;high voltage
67
A programmable logic array consists of many ______ that can be connected in various ways by _____.
logic gates;fusible links
68
One of the problems with micrporcessors is that they must perform logic operations _____ and perform them ____.
one-by-one;in sequence
69
Seven binary digits in the ASCII code can repesent a certain number of alphanumeric characters. How many characters can be represented by a code that uses one more digit?
Twice as many
70
Parallel data transfer is _____ than serial transfer, but serial transfer is____.
faster;simpler
71
Intermittent problems in solid-state equipment are often caused by
faults in software
72
Your first step in troubleshooting a solid-state system should be to
gather information
73
One of the best ways to speed up trouble-shooting logic circuits is to
follow a troubleshooting tree
74
A good general practice for localizing trouble in logic systems includes
performing the easy tests first
75
The best instrument for viewing many logic levels at once is the
logic analyzer
76
A programmable logic controller is a device that
responds to status changes in a system
77
Programmable controllers are well suited for control applications that require
decisions in a real-time environment
78
The time it takes a programmable cntroller to run through its program and return to the beginning is called _____ time.
scan
79
The logical decisions of a programmable controller are made in the
processor
80
The memory used for PLC firmware is usually
nonvolatile
81
The binary system is based on the number __. The hexadecimal system commonly used with PLCs is based on the number __.
2;16
82
The code most often used to represent alphanumerics is
ASCII
83
The Boolean NOT function acts as an
inverter
84
Ladder logic differs from most other computer languages in that it is
drawn graphically
85
In ladder logic, the output instruction that looks like a coil is called
output energize
86
The final step of a PLC scan involves
writing the output image
87
The first step in constructing a PLC program is
analyzing the process to be controlled
88
Although an output generally appears on only one rung of a ladder logic program, it may be energized by several sets of conditions that appear as
branches
89
In Boolean programming, all logic is some combination of which operation?
AND, NOT, OR
90
According to the stack rule, what happens each time a LOAD instruction is used?
The logic is pushed down one level
91
In most PLC applications, each push button contact is wired to an
input terminal on an input module
92
The function of a float switch is to indicate
liquid level
93
Which output device is sometimes used as a repeater, using a signal to control several different loads?
relay
94
If an I/O module supplies current, it is considered a ____ module.
sourcing
95
To be useful to a PLC , analog signals must be ___ by an input module.
digitized
96
Working with accurate, thorough specifications ensures that
all efforts move toward a common target
97
When sizing a programmable controller system, you must consider I/O, memory, and
scan time
98
The most important elements in a PLC documentation package are the
hardware drawings and program listing
99
The first step in developinga PLC system to meet given specifications is
sizing the system
100
Before turning a newly designed and installed system over to production, use the output disable function and indicating lights to check for correct
input wiring
101
The most important tool a maintenance technician can possess is a
documentation package
102
Information concerning the parts replacements, adjustments, and other system changes can be found in the
maintenance log
103
When control components fail, the problem is most often related to
dirt
104
As a good general rule, you should replace the battery in a programmabe controller
annually
105
Once you understand how a PLC system works, the next step in troubleshooting is to
gather information
106
The process of relating software addresses to the physical locations of remote I/O points is called _____ the system.
configuring
107
Moving numbers from one register to another involves the use of a _________ instruction.
data-handling
108
The speed at which a LAN processes a piece of information is called
throughput
109
A LAN application in which information stored in different drops is collected at a central location is known as
data acquisition
110
Which of the following transmission media has the highest data rate
fiber optic cable
111
Raising the temperature of a semiconductor material _____ its _______.
increases;conductivity
112
Boron acts as an ______ when added to silicon, making a _____-type semiconductor material.
acceptor;p
113
When a junction diode conducts, electrons move _____ the junction and holes move ______ the junction.
toward;toward
114
As the voltage across a forward-biased junction diode increases beyond the barrier potential, the current
increases rapidly
115
Light shining on a photoconductive cell increases the cell's
current-carrying capacity
116
Among the environmental problems of semiconductors, _____ is almost always caused by human contact.
ESD
117
Most semiconductors can be damaged by an accidentally applied potential difference as low as _____ volts.
100
118
You can neutralize a positively charged nonconductive material by
exposing it to negative ions
119
Soldering irons used with semiconductor devices should be in the range of ____ watts.
25-30
120
The simplest way to protect semiconductor devices against RFI is to
provide enough distance
121
Printed circuit boards provide several advantages over direct wiring including
better reliability
122
Printed circuit boards having several layers are generally _____ than single- layer circuit boards
More complex in function
123
Unlike conventional PCB methods, SMT alows
High-speed automated assembly
124
The advantage of edge connectors over pin connectors for mounting PCBs include
smaller size
125
If you must attempt to repair a PCB that has a conformal coating, you should
remove the coating from the repair site only
126
The base in an npn bipolar junction transistor is made of ______ -type material lightly doped with _____ material.
p;acceptor
127
In order for an npn transistor to function as an amplifier without distortion, it must operate in the ______ region.
active
128
The most common transistor connection is the common-_____, because it provides ______ gain in voltage and current.
emitter;high
129
If a transistor operates as a switch, it is ON when it operates in the _____ region and OFF when it operates in the _____ region.
saturation;cutoff
130
CMOS ICs consume ____ amounts of power, making them desirable for ___ circuits.
small;complex
131
Compared to plastic IC packages, ceramic packages cost ___ and withstand high humidity and high temperatures ____.
more;better
132
The color band or dot on a DO semiconductor package indicates then
n-type region
133
In removing a flatpack that is glued to a PCB, you should avoid ____ because you might damage the ____.
prying;PCB
134
A transistor has a maximum Pd rating of 200 mW at 25 degrees C and a derating factor of 2 mW degree C. What is the maximum Pd at 30 degrees C?
190 mW
135
The best operating point (Q point) for a transistor is near the
center of the active region
136
Power supplies can receive ____ as an input and can deliver _____ as an output.
ac or dc;ac or dc
137
One possible functionof a power conditioner added to a power supply is to _____ the _____.
regulate;frequency
138
An oscillator driven inverter
produces a sine-wave output
139
A voltage regulator changes its _____ in response to changes in the _____.
resistance;power drawn
140
Low voltage can be as lethal as high voltage because the damage is done by the
current passing through your body
141
The essential parts of an electrochemical cell are the _____ and the _____.
electrolyte;electrodes of different metals
142
Among carbon-zinc cells, the ____ cell works better than the Laclanche cell for continuous use, but not as well for intermittent use. However, the ____ cell has the longest shelf-life and service life.
high-energy;alkaline
143
A 12-volt automotive (lead-acid) battery is overchargin if the voltage between the terminals is moree than ____ volts while the engine is running.
15.0
144
To protect yourself while working with cells and batteries, you should always be aware that the
battery may produce explosive gases
145
The best way to provide electricity at remote mirowave relay stations is to install _____ cells.
photoelectric
146
The maximum forward current in most diodes causes a forward voltage drop of ____ V.
1.00
147
If necessary, you can temporarily connect two diodes in parallel to provide the necessary ____ in a circuit. Diodes can be connected in series to produce the necessary _____.
current;voltage
148
A forward-biased SCR ____ current until a trigger pulse passes from the ___ to the cathode.
blocks;gate
149
The peak-to-peak voltage across the secondary of a transformer is 50 volts (from -25 V to +25 V). If a half-wave rectifier is connected to this secondary, the range of its output will be ____, less that the diode drop. A full wave rectifier (not a bridge rectifier) connected to this secondary wil produce an output in the range ____ less than the diode drop.
0 to +25 V;0 to 12.5 V
150
In a voltage multiplier, the output of the _____ is the input to the _____. Their outputs combine to produce the higher voltage.
diodes;capacitors
151
The power supply to an audio circuit delivers to an output that oscillates between +48 and +52 V at 60 Hz. What is the percent ripple in the audio circuit's power input?
2.8
152
In a power supply, the function of a capacitor is to ____ energy.
store and release
153
An advantage of an LC filter in a power supply is its _____. A disadvantage is its ____.
low ripple;high cost
154
A bleeder resistor connected between the terminals of a power supply should have ____ resistance. Its purpose is to _______.
high;discharge the capacitors
155
The purpose of using external bypass filters in addition to the filters in a power supply is to
prevent interference among circuits on a PCB
156
A shunt voltage regulator maintains a constant voltage across the load by varying the _____ a path parallel to the load.
current in
157
In a series regulator, the control circuit must keep the transistor _____ in order to maintain a constant voltage across the load.
forward biased
158
One of the most common types of IC voltage regulators has three terminals and is available in the most common preset voltages, ranging from ___ to ___ V.
5;24
159
A switching voltage regulator operates by switching rapidly between
full OFF and full ON
160
In a circuit regulator, _____ triac is the equivalent of ____ SCRs.
one;two
161
In troubleshooting power supplies, you are likely to need an
oscilloscope
162
One of the three major steps in troubleshooting power supplies is the _____ test.
section
163
As part of the major step in troubleshooting power supplies you should perform an
output
164
When you perform a power-on test on a power supply, you should try to start it at the ____ voltage and then ____, unless a problem appears.
lowest possible;increase it
165
If you test a diode with an ohmmeter, you know the diode is good if the resistance is ______ in one direction and _____ in the other direction.
high;low
