Week 1 Flashcards
1
Q
Phase
A
Each winding of an alternator, motor, or of a branch circuit forming part of a load.
2
Q
True or False: An overcurrent is excess current resulting from either a short circuit or an overload.
A
True
3
Q
True or False: An overload is a current that is several hundred times the normal current and it is NOT confined
to normal circuit paths.
A
False
4
Q
True or False: A short circuit current is a current that is one to six times the normal current.
A
True
5
Q
True or False: The voltage rating of a fuse is marked on the fuse.
A
True
6
Q
True or False: The interrupting rating is the maximum value of voltage that a fuse can safely interrupt without
restrike.
A
True
7
Q
True or False: A fuse is said to be current limiting if it limits the current to 1 amp above its continuous current rating.
A
False
8
Q
True or False: Fuses operate from increased ambient temperature.
A
False
9
Q
Basic Electrical Theory
A
Simply put, electricity is nothing more than the flow of electrons through a conductor.
10
Q
How much is one coulomb?
A
6.28 x 10^18
11
Q
True or False: The fundamental characteristic of an electric charge is its ability to exert a force.
A
True
12
Q
True or False: The ability of a charge to do work is called its potential.
A
True
13
Q
What is electromotive force (emf)?
A
The sum of the differences of potential of all the charges in the electrostatic field
14
Q
Potential difference is
called ___________.
A
voltage
15
Q
Current
A
Movement or the flow of electrons. To produce current, the electrons must be moved by a potential difference
16
Q
Symbol for Current
A
I
17
Q
The basic unit in which current is
measured is the ______.
A
ampere (A)
18
Q
True or False: One ampere of current is defined as the movement of 3 coulombs (6.28 x 10^18 electrons) past any point of a conductor during one second of time.
A
False. It’s measured in ONE coulomb.
19
Q
Electron flow theory
A
The direction of electron flow is from a point of negative potential to a point of positive potential.
20
Q
Static electricity
A
Static electricity is dealing with electrons at rest
21
Q
What is needed to have a complete circuit?
A
- source of electromotive force (emf)
- complete path from one side of the emf
source to the other side of the emf source for current flow
22
Q
Resistance
A
Resistance is the opposition to current flow
23
Q
What is resistor?
A
A resistor is a device whose resistance to current flow is a known or specified value.
24
Q
What is resistance measured in?
A
measured in ohms (Ω) and is represented by the symbol R in equations
25
What are some uses uses for resistors?
To establish the proper value of circuit voltage, to
limit current, and to provide a load.
26
Ohm's Law
The current in a circuit is DIRECTLY proportional to the applied voltage and INVERSELY proportional to the circuit resistance.
27
What is for the formula for ohm's law?
V = I x R
28
What is I?
Current, measured in amps
29
What is V?
Voltage, measured in volts.
30
What is R?
Resistance, measured in ohms
31
What is the prefix for 1 x 10^6?
Mega, M, 1,000,000
32
What is the prefix for 1 x 10^3?
Kilo, K, 1,000
33
What is the prefix for 1 x 100
Unity
34
What is the prefix for 1 x 10^-3?
Milli, m, .001
35
What is the prefix for 1 x 10^-6
Micro, (µ), .000,001
36
True or False: The principle of rounding off a number is to write the closest approximation, with the last significant
digit in a specified position, or with a specified number of significant digits.
True
37
Alpha
Area, angles, coefficients
38
Zeta
Coefficients, coordinates, impedance
39
Theta
Symbol Θ
Phase angle, temperature
40
Kappa
Dielectric constant, susceptibility
41
Mu
µ, Permeability, micro, amplification
42
Omega
Ohms, angular velocity
43
Series circuit
In this circuit there is only one current path
44
True or False: For series circuit, the battery is the voltage source and is usually referred to as the applied or total voltage of the circuit.
True
45
What is constant in a series circuit?
Current
46
What is Kirchhoff's Voltage Law in a series circuit?
The sum of the voltage drops around a circuit
loop must be equal to the applied voltage.
VT = VR1 + VR2 + VR3....
47
True or False:
Rule for Series Circuits: Total resistance for any series resistive circuit is the sum of the individual resistances.
True
RT = R1 + R2 + R3
48
What is power?
Power is the rate of doing work, and the unit of electrical power is the watt.
49
What is the formula for power?
P = I x E
50
By substituting Ohm's Law into the expression P = V x I we can get:
P= V^2 / R
Or
P= I^2 * R
51
True or false:
Power for electric motors is sometimes rated in ohms but more usually in Horsepower
(hp).
False. It's rated in watts or kilowatts.
52
1 hp = _____
746 watts
53
True or false:
Power is different, however, because it is the time rate of doing work.
True
54
What is pushbutton?
A pushbutton station is a device that can provide control of a motor with the pressing of the appropriate
pushbutton. With pushbutton stations a motor can be controlled from any one of several locations while
only using one magnetic starter.
55
Pushbuttons are classified as what 2 things according to their current handling capabilities?
Standard-duty or heavy-duty
56
Standard Duty Pushbuttons
Most systems use standard duty pushbutton stations to control A-C or D-C starters. General-purpose
pushbutton stations are designed for operating flexibility and ease of wiring.
57
Heavy Duty Pushbuttons
They have approximately twice the current rating of the standard-duty station.
Pushbuttons are available with flush, extended, or mushroom
heads. They may have either momentary or maintained contacts
58
What is the highest heavy duty pushbuttons rated for in AC?
6 Amps, 120 Volts
59
What is the highest heavy duty pushbuttons rated for in DC?
1.1 Amps, 120 Volts
60
What is the standard-duty units have contacts rated for pilot duty in AC?
3.0 Amperes, 120 volts
61
When are oil tight pushbutton control stations used?
Used wherever there is presence of oil, coolant, and other non-corrosive industrial liquids. These control stations may be the surface mounted, flush mounted or pendant
types. These stations have an enclosure that is sealed with a neoprene gasket
62
What pushbutton stations usually use mushroom heads?
E-stops
63
Limit Switches
Limit switches are devices used for interlocking a mechanical motion or position with an electrical circuit
64
Actuators
An actuator is the external linkage that detects the mechanical movement of the machine
65
True or false:
One technique is a limit switch used as a control stop device to prevent moving parts of machines from over-running the normal mechanical limits of the machine.
True
66
True or false:
Control stop devices start machines for normal operations.
False.
Control stop devices STOPS machines for normal operations.
67
Kirchhoff's Current Law in parallel circuit
The sum of the currents entering a junction must equal the sum of currents leaving the junction.
68
What is constant in parallel circuit?
Voltage
69
True or false:
The voltage across one branch of a parallel circuit is equal to the voltage across any other parallel branch of the circuit.
True
70
True or false:
When two resistors are connected in parallel, the electrons can move more easily
True
71
Name the 3 types of proximity switches.
inductive, capactive and ultrasonic
72
True or False: The current in a circuit is DIRECTLY proportional to the applied voltage and INVERSELY proportional to the circuit resistance.
True
73
True or False: Inductive proximity sensors are designed to operate by generating an electromagnetic field and detecting the eddy current losses generated when ferrous and nonferrous metal target objects enter the field.
True
74
Hysteresis
The difference between the On and Off points
75
Why is hysteresis needed?
Hysteresis is needed to help prevent chattering (turning on and off rapidly) when the sensor is subjected to shock and vibration or when the target is stationary at the nominal sensing distance.
76
Capacitive proximity sensors
designed to operate by generating an electrostatic field and detecting changes in this field caused when a target approaches the sensing face.
77
What does a capacitive proximity sensor consist of?
1. probe
2. oscillator
3. signal rectifier
4. filter circuit
5. output circuit
78
True or False: Shielded capacitive proximity sensors are best suited for sensing low dielectric constant (difficult to sense) materials due to their highly concentrated electrostatic fields.
True
79
Unshielded capacitive sensors
Unshielded capacitive sensors are also more suitable than shielded types for use with plastic sensor wells, an accessory designed for liquid level applications
80
True or False: unshielded capacitive proximity sensors have longer sensing distances than shielded versions.
True
81
Photoelectric sensors
Photoelectric sensors operate by sensing a change in the amount of light that is either reflected or blocked by an object to be detected (target).
82
True or False: photoelectric sensor can be thought of as a “limit switch-like” device, where the mechanical actuator or lever arm function is replaced by a beam of light
True
83
What are the four basic components to any photoelectric sensor?
1. Light source
2. Light detector
3. Lenses
4. Output switching device
84
Define light emitting diode (LED)
a solid-state semiconductor that emits light when current is applied
85
True or False: A photo-detector is the component used to detect the light source.
True
86
What do lenses do?
They help focus the light
87
What are the three basic types of Photoelectric Sensing Modes?
1. Transmitted beam
2. Retro-reflective
3. Diffuse
88
On-Delay Timers
When the coil for the timer is energized the contacts do not close immediately. The contacts delay changing state.
89
Off-Delay Timers
When the coil for the timer is energized the contacts immediately change state. Once power is removed the contacts delay changing states.
90
Describe the light operate mode output
A light operate mode output is ON (energized, logic level one) when the receiver can “see” sufficient light from the light source.
(Light mode will be true when it makes contact with the light. It has the to see the light.)
91
Describe a dark operate output
A dark operate output is ON (energized, logic level one) when the receiver cannot “see” the light from the light source.
(Dark mode: when object is blocking the light. It sees the dark.)
92
Transmitted Beam
In this mode the light source and receiver are contained in separate housings. These two units are positioned opposite each other so that the light from the light source shines directly on the receiver.
93
True or False: Transmitted beam sensors provide the longest sensing distances and the highest level of operating margin.
True
94
Retro-reflective
A retro-reflective sensor contains both the light source and receiver, in one package. The light beam emitted by the light source is reflected by a special reflective object and detected by the receiver. The target is detected when it breaks this light beam.
95
Is the retro-reflective is the most popular sensing mode?
Yes
96
Misalignment of a reflector or reflective tape of up to _____ degrees will typically not significantly reduce the margin of the sensing system
15 degrees
97
Diffuse Sensing (standard diffuse)
when light strikes the surface of an object, it is diffused/dispersed from the surface at all angles and is then detected by the sensor.
98
What are the 2 modes of Ultrasonic Proximity Sensors?
opposed and diffuse (echo)
99
True or false: Ultrasonic sensors have an inherent blind zone located at the sensing face. The blind zone depends on the frequency of the transducer.
True
100
True or false: A contactor belongs to both the control circuit and the power circuit
True
101
Which circuit is a relay in?
The control circuit
102
What is the function of a relay?
It is used to remember machine events such as the momentary closure of a limit switch contact.
103
Impedance
the total opposition to current flow.
104
The main feature of a contactor that distinguishes it from a manual starter is the use of an _________.
electromagnet
105
Electromagnet consists of what 3 things?
1. coil
2. stationary core
3. moveable core
106
What does a coil produce in an electromagnet?
The coil produces magnetic flux as the result of current flow.
107
What are the 2 basic types of overload relays?
1. Thermal type (Bimetallic or Eutectic Alloy)
2. Electronic Current monitoring type
108
True or False:
Adjusting dial must be set to read the full load current of the motor (FLC).
True
109
When only two of the three phases are active, this is called “________”.
single-phasing
110
True or false: When a motor is singlephasing it will not operate properly.
True
111
