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ECT > Week 1 > Flashcards

Week 1 Flashcards

1
Q

Phase

A

Each winding of an alternator, motor, or of a branch circuit forming part of a load.

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2
Q

True or False: An overcurrent is excess current resulting from either a short circuit or an overload.

A

True

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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

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4
Q

True or False: A short circuit current is a current that is one to six times the normal current.

A

True

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5
Q

True or False: The voltage rating of a fuse is marked on the fuse.

A

True

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6
Q

True or False: The interrupting rating is the maximum value of voltage that a fuse can safely interrupt without
restrike.

A

True

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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

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8
Q

True or False: Fuses operate from increased ambient temperature.

A

False

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9
Q

Basic Electrical Theory

A

Simply put, electricity is nothing more than the flow of electrons through a conductor.

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10
Q

How much is one coulomb?

A

6.28 x 10^18

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11
Q

True or False: The fundamental characteristic of an electric charge is its ability to exert a force.

A

True

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12
Q

True or False: The ability of a charge to do work is called its potential.

A

True

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13
Q

What is electromotive force (emf)?

A

The sum of the differences of potential of all the charges in the electrostatic field

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14
Q

Potential difference is
called ___________.

A

voltage

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15
Q

Current

A

Movement or the flow of electrons. To produce current, the electrons must be moved by a potential difference

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16
Q

Symbol for Current

A

I

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17
Q

The basic unit in which current is
measured is the ______.

A

ampere (A)

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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.

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19
Q

Electron flow theory

A

The direction of electron flow is from a point of negative potential to a point of positive potential.

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20
Q

Static electricity

A

Static electricity is dealing with electrons at rest

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21
Q

What is needed to have a complete circuit?

A
  1. source of electromotive force (emf)
  2. complete path from one side of the emf
    source to the other side of the emf source for current flow
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22
Q

Resistance

A

Resistance is the opposition to current flow

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23
Q

What is resistor?

A

A resistor is a device whose resistance to current flow is a known or specified value.

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24
Q

What is resistance measured in?

A

measured in ohms (Ω) and is represented by the symbol R in equations

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25
Q

What are some uses uses for resistors?

A

To establish the proper value of circuit voltage, to
limit current, and to provide a load.

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26
Q

Ohm’s Law

A

The current in a circuit is DIRECTLY proportional to the applied voltage and INVERSELY proportional to the circuit resistance.

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27
Q

What is for the formula for ohm’s law?

A

V = I x R

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28
Q

What is I?

A

Current, measured in amps

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29
Q

What is V?

A

Voltage, measured in volts.

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30
Q

What is R?

A

Resistance, measured in ohms

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31
Q

What is the prefix for 1 x 10^6?

A

Mega, M, 1,000,000

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32
Q

What is the prefix for 1 x 10^3?

A

Kilo, K, 1,000

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33
Q

What is the prefix for 1 x 100

A

Unity

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34
Q

What is the prefix for 1 x 10^-3?

A

Milli, m, .001

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35
Q

What is the prefix for 1 x 10^-6

A

Micro, (µ), .000,001

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36
Q

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.

A

True

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37
Q

Alpha

A

Area, angles, coefficients

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38
Q

Zeta

A

Coefficients, coordinates, impedance

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39
Q

Theta

A

Symbol Θ

Phase angle, temperature

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40
Q

Kappa

A

Dielectric constant, susceptibility

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41
Q

Mu

A

µ, Permeability, micro, amplification

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42
Q

Omega

A

Ohms, angular velocity

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43
Q

Series circuit

A

In this circuit there is only one current path

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44
Q

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.

A

True

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45
Q

What is constant in a series circuit?

A

Current

46
Q

What is Kirchhoff’s Voltage Law in a series circuit?

A

The sum of the voltage drops around a circuit
loop must be equal to the applied voltage.

VT = VR1 + VR2 + VR3….

47
Q

True or False:

Rule for Series Circuits: Total resistance for any series resistive circuit is the sum of the individual resistances.

A

True

RT = R1 + R2 + R3

48
Q

What is power?

A

Power is the rate of doing work, and the unit of electrical power is the watt.

49
Q

What is the formula for power?

A

P = I x E

50
Q

By substituting Ohm’s Law into the expression P = V x I we can get:

A

P= V^2 / R

Or

P= I^2 * R

51
Q

True or false:
Power for electric motors is sometimes rated in ohms but more usually in Horsepower
(hp).

A

False. It’s rated in watts or kilowatts.

52
Q

1 hp = _____

A

746 watts

53
Q

True or false:

Power is different, however, because it is the time rate of doing work.

A

True

54
Q

What is pushbutton?

A

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
Q

Pushbuttons are classified as what 2 things according to their current handling capabilities?

A

Standard-duty or heavy-duty

56
Q

Standard Duty Pushbuttons

A

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
Q

Heavy Duty Pushbuttons

A

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
Q

What is the highest heavy duty pushbuttons rated for in AC?

A

6 Amps, 120 Volts

59
Q

What is the highest heavy duty pushbuttons rated for in DC?

A

1.1 Amps, 120 Volts

60
Q

What is the standard-duty units have contacts rated for pilot duty in AC?

A

3.0 Amperes, 120 volts

61
Q

When are oil tight pushbutton control stations used?

A

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
Q

What pushbutton stations usually use mushroom heads?

A

E-stops

63
Q

Limit Switches

A

Limit switches are devices used for interlocking a mechanical motion or position with an electrical circuit

64
Q

Actuators

A

An actuator is the external linkage that detects the mechanical movement of the machine

65
Q

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.

A

True

66
Q

True or false:
Control stop devices start machines for normal operations.

A

False.
Control stop devices STOPS machines for normal operations.

67
Q

Kirchhoff’s Current Law in parallel circuit

A

The sum of the currents entering a junction must equal the sum of currents leaving the junction.

68
Q

What is constant in parallel circuit?

A

Voltage

69
Q

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.

A

True

70
Q

True or false:
When two resistors are connected in parallel, the electrons can move more easily

A

True

71
Q

Name the 3 types of proximity switches.

A

inductive, capactive and ultrasonic

72
Q

True or False: The current in a circuit is DIRECTLY proportional to the applied voltage and INVERSELY proportional to the circuit resistance.

A

True

73
Q

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.

A

True

74
Q

Hysteresis

A

The difference between the On and Off points

75
Q

Why is hysteresis needed?

A

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
Q

Capacitive proximity sensors

A

designed to operate by generating an electrostatic field and detecting changes in this field caused when a target approaches the sensing face.

77
Q

What does a capacitive proximity sensor consist of?

A
  1. probe
  2. oscillator
  3. signal rectifier
  4. filter circuit
  5. output circuit
78
Q

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.

A

True

79
Q

Unshielded capacitive sensors

A

Unshielded capacitive sensors are also more suitable than shielded types for use with plastic sensor wells, an accessory designed for liquid level applications

80
Q

True or False: unshielded capacitive proximity sensors have longer sensing distances than shielded versions.

A

True

81
Q

Photoelectric sensors

A

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
Q

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

A

True

83
Q

What are the four basic components to any photoelectric sensor?

A
  1. Light source
  2. Light detector
  3. Lenses
  4. Output switching device
84
Q

Define light emitting diode (LED)

A

a solid-state semiconductor that emits light when current is applied

85
Q

True or False: A photo-detector is the component used to detect the light source.

A

True

86
Q

What do lenses do?

A

They help focus the light

87
Q

What are the three basic types of Photoelectric Sensing Modes?

A
  1. Transmitted beam
  2. Retro-reflective
  3. Diffuse
88
Q

On-Delay Timers

A

When the coil for the timer is energized the contacts do not close immediately. The contacts delay changing state.

89
Q

Off-Delay Timers

A

When the coil for the timer is energized the contacts immediately change state. Once power is removed the contacts delay changing states.

90
Q

Describe the light operate mode output

A

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
Q

Describe a dark operate output

A

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
Q

Transmitted Beam

A

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
Q

True or False: Transmitted beam sensors provide the longest sensing distances and the highest level of operating margin.

A

True

94
Q

Retro-reflective

A

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
Q

Is the retro-reflective is the most popular sensing mode?

A

Yes

96
Q

Misalignment of a reflector or reflective tape of up to _____ degrees will typically not significantly reduce the margin of the sensing system

A

15 degrees

97
Q

Diffuse Sensing (standard diffuse)

A

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
Q

What are the 2 modes of Ultrasonic Proximity Sensors?

A

opposed and diffuse (echo)

99
Q

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.

A

True

100
Q

True or false: A contactor belongs to both the control circuit and the power circuit

A

True

101
Q

Which circuit is a relay in?

A

The control circuit

102
Q

What is the function of a relay?

A

It is used to remember machine events such as the momentary closure of a limit switch contact.

103
Q

Impedance

A

the total opposition to current flow.

104
Q

The main feature of a contactor that distinguishes it from a manual starter is the use of an _________.

A

electromagnet

105
Q

Electromagnet consists of what 3 things?

A
  1. coil
  2. stationary core
  3. moveable core
106
Q

What does a coil produce in an electromagnet?

A

The coil produces magnetic flux as the result of current flow.

107
Q

What are the 2 basic types of overload relays?

A
  1. Thermal type (Bimetallic or Eutectic Alloy)
  2. Electronic Current monitoring type
108
Q

True or False:
Adjusting dial must be set to read the full load current of the motor (FLC).

A

True

109
Q

When only two of the three phases are active, this is called “________”.

A

single-phasing

110
Q

True or false: When a motor is singlephasing it will not operate properly.

A

True

111
Q
A

ECT (3 decks)

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