I5

Question 1

Process variable

Answer 1

The variable that is controlled

Question 2

Sensor

Answer 2

Measures and senses the process variable, provides feedback to controller

Question 3

Actuator / Controlled device

Answer 3

Alters the process variable

Question 4

Set Point

Answer 4

Provides information to the controller about desired value of process variable

Question 5

Error (signal)

Answer 5

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

Question 6

Controlling device / controller

Answer 6

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

Question 7

Open Loop control system

Answer 7

Controlled manually

Question 8

Open-loop system operator

Answer 8

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

Question 9

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.

Answer 9

Not self correcting, Open-loop.

Question 10

Closed-loop control system

Answer 10

Controlled automatically

Question 11

Closed-loop system is also called

Answer 11

Closed-loop feedback control system

Question 12

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

Answer 12

Because an automatic system requires feedback from the process variable

Question 13

Discontinuous control system

Answer 13

full power is applied or removed to modify the process variable

Question 14

Continuous control system

Answer 14

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

Question 15

3 examples of process variables

Answer 15

Motor speed
Fluid pressure
Liquid level
Room temperature
Liquid flow

Question 16

What is the function of a sensor?

Answer 16

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

Question 17

What is a set point?

Answer 17

The desired value of the process variable

Question 18

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

Answer 18

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.

Question 19

5 system elements of a closed-loop control system

Answer 19

Process variable
Set point
Sensor
Controller
Actuator

Question 20

Difference between continuous and discontinuous control system

Answer 20

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

Question 21

Transducer

Answer 21

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

Question 22

Analog sensor signal

Answer 22

Supplies continuous variable output that varies smoothly

Question 23

Digital sensor signal

Answer 23

Is displayed in fixed, discrete steps

Question 24

Common type of sensors

Answer 24

Motion
Force
Fluids
Temperature
Light

Question 25

3 types of motion

Answer 25

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

Question 26

Sensor of force

Answer 26

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

Question 27

How does a bonded wire strain gauge work?

Answer 27

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

Question 28

Types of fluid pressure sensors

Answer 28

Bourdon tube Bellows Diaphragm Piezoelectric pressure transducer

Question 29

Fluid flow sensors

Answer 29

Orifice plates and manometers Magnetic flow meter

Question 30

Liquid level sensors

Answer 30

Float liquid level sensor Capacitive liquid level sensor Ultrasonic wave

Question 31

Temperature sensors

Answer 31

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

Question 32

Light sensors generally work on one of the following principles...

Answer 32

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

Question 33

What is a transducer?

Answer 33

A device that converts one form of energy into another

Question 34

List 4 basic principles used to sense linear motion

Answer 34

Resistance change Inductance change Capacitance change Transformer coupling change

Question 35

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

Answer 35

Decrease in length and increase in cross sectional area

Question 36

How can a piezoelectric crystal work as a sensor?

Answer 36

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

Question 37

3 basic principles used in light sensors

Answer 37

photoemission photoconduction photovoltaic

Question 38

Function of a transmitter

Answer 38

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

Question 39

How does a bourdon tube work?

Answer 39

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

Question 40

How do bellows work?

Answer 40

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

Question 41

What does a controller typically consist of?

Answer 41

A comparator and an output section

Question 42

What does the comparator do?

Answer 42

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

Question 43

Negative feedback is?

Answer 43

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

Question 44

Positive feedback is?

Answer 44

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

Question 45

Four basic modes of control?

Answer 45

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

Question 46

What is the difference between positive and negative feedback?

Answer 46

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

Question 47

What are the general classifications of actuators?

Answer 47

Electrical Hydraulic Pneumatic

Question 48

Function of actuator?

Answer 48

Receive signal from controller, modify process variable accordingly