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Electrical > Process Control I5 > Flashcards

Process Control I5 Flashcards

(96 cards)

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1
Q

What is a process variable

A

The variable being controlled.

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2
Q

What does a sensor do?

A

Measures and senses process variable to indicate its value.

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3
Q

What is the purpose of a sensor

A

Provide feedback to the controller

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4
Q

What is a set point

A

Provides info to controller about desired value of process

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5
Q

What is the error signal

A

Difference between setpoint and feedback signal

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6
Q

What is the controller?

A

Controls actuator. Consists of comparator and output. Compares set point to feedback and Generates error signal

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7
Q

What are the components of a controlling device

A

Comparator and amplifier

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8
Q

What is a comparator

A

Measures difference between set point and feedback signal. And whether it is higher or lower.

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9
Q

What are the two types of controlling devices

A

Open loop control system

Closed loop control system

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10
Q

How many process variables are controlled in open loop

A

One

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11
Q

What 2 things are needed in an open loop system to keep the process variable constant

A

Indicator

Operator

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12
Q

How is a closed loop system different from open loop

A

Control of process variable is automatic

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13
Q

Give an example of a process variable, sensor, controlling device and actuator

A

PV: room temp
S: thermometer
CD: heater switch
A: heater

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14
Q

What is the function of an actuator

A

Uses the error signal to alter the process variable

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15
Q

What does the actuator use to bring the process variable closer to the desired value

A

Error signal

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16
Q

What component is needed in open loop but not closed loop

A

Monitor/Indicator

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17
Q

What is the difference between discontinuous and continuous control

A

Discontinuous: full power is on or off
Continuous: power is controlled from low to high

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18
Q

What type of sensor converts energy from one form to another

A

Transducer

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19
Q

What type of signal provides continuous variable output

A

Analogue

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20
Q

How many counts in 12 but resolution

A

0- 4095

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21
Q

How many counts in 8 but resolution

A

0-255

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22
Q

What type of signal is discontinuous, either on or off

A

Digital

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23
Q

What are the 3 types of motion sensors

A

Linear, angular, rotary

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24
Q

What are the three main types of linear motion sensor

A

Resistance, inductance, capacitance

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25
What is a sensor called if the resistance changes
Potentiometer
26
What is a sensor called of the inductance changes
Inductor
27
What is a sensor called of the capacitance changes
Capacitor
28
Why will a linear motion potentiometer wear out over time
The slider wipes mechanically along the resistance element
29
What moves in a LVDT
The core
30
What sensor uses the principle of a differential transformer
LVDT | Linear variable differential transformer
31
Which sensor is good for 300 degrees
Angular motion potentiometer
32
What is linear motion
Straight line
33
What is angular motion
Rotary movement of a shaft in degrees CW or CCW
34
What type of sensor allows >360 degree movement
Angular variable inductor
35
What is the difference between a linear and angular capacitor
Distance between plates changes in linear. Area of contact of plates changes in angular
36
What type of sensor allows 180 degrees of movement
Angular variable capacitor
37
What sensor allows 45 degrees of movement
Rotary variable differential transformer
38
What does rotary motion measure
The speed of rotation of a shaft and it’s direction
39
How does a tachogenerator work
Induced voltage is proportional to the speed of rotation
40
How does an bonded wire strain gauge work
As wire is compressed the length is reduced, the cma is increased and the resistance decreases
41
What formula is used with a sensor of force
R=kL/CMA
42
What are the 3 types of fluid pressure sensors
Bourdon tube, bellows, diaphragm
43
Which fluid pressure sensor is used for low pressure
Diaphragm
44
What is a piezoelectric pressure transducer used for
Sensing vibrations
45
What are the 3 types of fluid flow sensors
Orifice plates, magnetic flow tubes, coriolis type (gyroscope)
46
How does an orifice plate work?
Fluid flows through a hole of fixed size and pressure drops across the restriction
47
How does a magnetic flow meter work
Non magnetic pipe placed in a magnetic field. Conductive liquid cuts the magnetic field and induced a voltage.
48
What are the 3 types of liquid level sensors?
Float, capacitive, moose balls
49
What are the 2 characteristics of a thermistor output
Non Linear, negative temp coefficient
50
Where are thermistors commonly used
Motor windings
51
2 characteristic of RTD output
Linear, positive temp coefficient
52
Two characteristics of thermocouples
Non linear, negative temp coefficient
53
Why is a thermocouple considered an active device
As contact between dissimilar metals heats up a voltage is generated
54
What is a fluid temp sensor made with
Bourdon tube
55
What temp sensor is used for very high temps
Radiation pyrometer
56
How does a radiation pyrometer work
Radiation caused by heat is focused on a thermopile and generates a voltage
57
What are the three basic types of light sensors
Photo emission, photo conduction, photo voltaic
58
Describe photo emission
Electrons liberated when light energy falls on it
59
What is photo conduction
Resistance is reduced with light
60
Photo voltaic
Voltage generated when light falls on it
61
Give an example of photo emission
Photo tube
62
Give an example of photo conduction
Light Dependent Resistor
63
What is a photo voltaic cell
PN junction with light collecting surface that generates a voltage with light intensity
64
What is a photo diode
A reverse biased PN junction
65
Which has higher current output, photo transistor or photo diode
Transistor
66
Why is a photo transistor higher current output
Because of the gain effect
67
What is another name for a comparator
Summing junction
68
What is negative feedback
Error signal is difference between set point and feedback signal
69
What is positive feedback
Error signal is sum of set point and feedback signals
70
What eventually happens with positive feedback
System goes out of control or runs away
71
What are the four modes of control
On-off Proportional Proportional + integral Proportional + integral+ derivative
72
Why is on-off popular
Simplicity
73
What is a problem with on-off control
Can lead to large overshoots
74
When is proportional control best used
Temperature or level
75
Which type of control sees the gain set just below the point of overshoot
Proportional
76
What is the most common form of drive speed control
P + I
77
Why is it good to add integral control
Increase speed of response
78
What happens to the output from PI control
Process value overshoots the set point and oscillates
79
Why is PID control used
To reduce magnitude of overshoot Improve controller process stability
80
Which type of control is most sensitive to feedback noise
PID
81
What is another name for an actuator with mechanical output
Servomechanism
82
How does a solenoid provide motion
Linear motion in lush or pull with a spring to return plunger
83
What are the four types of electrical actuators
Solenoid Motor Clutch Brake
84
Which electrical actuators use DC fields only
Clutches and brakes
85
What are servo motors used for
Precise operations like antenna direction
86
What high torque motor is used for precise operations
Servo motors
87
What does a stepper motor turn digital pulses into
Angular position or speed of rotation
88
Which is more precise, a stepper motor with more or less windings
More
89
Which stepper motor works on the principle that fields align and travel through the path of least resistance
Variable reluctance SM
90
Which stepper motor operates on the principle that Like poles repel and unlike attract
Permanent magnet SM
91
What are the two modes for a permanent magnet SM
Full step and half step energization
92
What type of stepper motor is most commonly used
Four step
93
What 3 things are used to construct an encoder
Rotating disk LED Photo sensor
94
What is usually required to measure frequency with an encoder
High speed counter card
95
How does a resolver measure speed
Using transformer principle
96
Which is more accurate, encoder or resolver
Resolver

Electrical (3 decks)

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