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LVL 4 ELEC > I5 > Flashcards

I5 Flashcards

1
Q

Process variable

A

The variable that is controlled

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2
Q

Sensor

A

Measures and senses the process variable, provides feedback to controller

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3
Q

Actuator / Controlled device

A

Alters the process variable

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4
Q

Set Point

A

Provides information to the controller about desired value of process variable

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5
Q

Error (signal)

A

The difference between the set point signal and the feedback signal
Command signal

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6
Q

Controlling device / controller

A

Controls the actuator, compares feedback signal to set point signal to generate an error signal

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7
Q

Open Loop control system

A

Controlled manually

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8
Q

Open-loop system operator

A

A person that monitors the process variable and operates the controlling device as needed.

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9
Q

The process variable has no effect on the operation of the controlling device.
This means the system (is/is not) self correcting, is (open/closed)-loop.

A

Not self correcting, Open-loop.

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10
Q

Closed-loop control system

A

Controlled automatically

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11
Q

Closed-loop system is also called

A

Closed-loop feedback control system

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12
Q

Why is a closed loop system called a closed-loop feedback control system?

A

Because an automatic system requires feedback from the process variable

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13
Q

Discontinuous control system

A

full power is applied or removed to modify the process variable

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14
Q

Continuous control system

A

power supplied to the process variable is controlled from very low to full power

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15
Q

3 examples of process variables

A

Motor speed
Fluid pressure
Liquid level
Room temperature
Liquid flow

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16
Q

What is the function of a sensor?

A

To measure the process variable and provide feedback information to the controller

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17
Q

What is a set point?

A

The desired value of the process variable

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18
Q

What is the difference between an open-loop and a closed-loop control system?

A

An open-loop system is a manual system, it is not self correcting, and the controlling device operates independently of the process variable
A closed-loop system is automatic, self correcting, and the controller relies on feedback from the process variable to modify it.

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19
Q

5 system elements of a closed-loop control system

A

Process variable
Set point
Sensor
Controller
Actuator

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20
Q

Difference between continuous and discontinuous control system

A

Continuous system supplies variable power
Discontinuous supplies full power or no power

21
Q

Transducer

A

Generally a sensor used for automatic control
Converts energy in to a form suitable for the controller

22
Q

Analog sensor signal

A

Supplies continuous variable output that varies smoothly

23
Q

Digital sensor signal

A

Is displayed in fixed, discrete steps

24
Q

Common type of sensors

A

Motion
Force
Fluids
Temperature
Light

25
Q

3 types of motion

A

Linear: motion in a straight line
Angular: The rotary movement of a shaft in degrees clockwise or counter-clockwise from a reference position
Rotary: Typically the speed of rotation of a shaft and its direction

26
Q

Sensor of force

A

Bonded wire strain gauge
Wire bonded to a plastic sheet in grid form

27
Q

How does a bonded wire strain gauge work?

A

When force is applied to the column it’s overall length reduces
This change is transferred to the wire of the gauge
When the wire is compressed it’s effective length reduces
Cross sectional area increases
This translates into an overall reduction in resistance

28
Q

Types of fluid pressure sensors

A

Bourdon tube
Bellows
Diaphragm
Piezoelectric pressure transducer

29
Q

Fluid flow sensors

A

Orifice plates and manometers
Magnetic flow meter

30
Q

Liquid level sensors

A

Float liquid level sensor
Capacitive liquid level sensor
Ultrasonic wave

31
Q

Temperature sensors

A

Resistive temp. sensor
Resistance temp. detector
Thermistors
Thermocouple
Bimetallic sensor

32
Q

Light sensors generally work on one of the following principles…

A

Photoemission: electrons liberated from material when light energy falls on it
Photoconduction: resistance of material is reduced with light
Photovoltaic: voltage is generated in a cell due to light falling on it

33
Q

What is a transducer?

A

A device that converts one form of energy into another

34
Q

List 4 basic principles used to sense linear motion

A

Resistance change
Inductance change
Capacitance change
Transformer coupling change

35
Q

What resistance parameters are changed when a strain gauge is subjected to a compression force?

A

Decrease in length and increase in cross sectional area

36
Q

How can a piezoelectric crystal work as a sensor?

A

It can separate charges (create voltage) according to the amount of mechanical pressure applied.

37
Q

3 basic principles used in light sensors

A

photoemission
photoconduction
photovoltaic

38
Q

Function of a transmitter

A

Accept sensor information and provide standard types of output signals for transmission over long distances

39
Q

How does a bourdon tube work?

A

It is a semicircle of slightly flattened steel. As pressure in the tube increases, it straightens.

40
Q

How do bellows work?

A

Fluid pressure can be applied from either end, the bellow expands ans pressure increases.

41
Q

What does a controller typically consist of?

A

A comparator and an output section

42
Q

What does the comparator do?

A

Generates an error signal by measuring how far away the feedbacksignal is from the set-point signal.

43
Q

Negative feedback is?

A

Desired.
The error signal is the difference between the set point and the feedback signal.

44
Q

Positive feedback is?

A

Undesired.
Connection error or wrong selection of system components.
sum of set point and feedback signals.

45
Q

Four basic modes of control?

A

On/Off
Proportional
Proportional plus integral
Proportional plus integral plus derivative (PID)

46
Q

What is the difference between positive and negative feedback?

A

Positive is the sum of set-point and feedback signal
Negative is the difference of set-point and feedback signal

47
Q

What are the general classifications of actuators?

A

Electrical
Hydraulic
Pneumatic

48
Q

Function of actuator?

A

Receive signal from controller, modify process variable accordingly

LVL 4 ELEC (8 decks)

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