Instrumentation and Control - Process Control Fundamentals.pdf - automatyka - seithe

Instrumentation & Control

Process Control Fundamentals

Table of Contents

Introduction..................................................................................................................................................... 1

Performance Objective ............................................................................................................................. 1

The Importance of Process Control ............................................................................................................... 1

Learning Objectives.................................................................................................................................. 1

The Importance of Process Control................................................................................................................. 2

Process...................................................................................................................................................... 2

Process Control ........................................................................................................................................ 2

Reduce Variability ............................................................................................................................. 2

Increase Efficiency ............................................................................................................................ 3

Ensure Safety ..................................................................................................................................... 3

Control Theory Basics .................................................................................................................................... 4

Learning Objectives.................................................................................................................................. 4

The Control Loop............................................................................................................................................. 5

Three Tasks ...............................................................................................................................................5

Process Control Terms ....................................................................................................................................6

Process Variable.......................................................................................................................................6

Setpoint .....................................................................................................................................................6

Measured Variables, Process Variables, and Manipulated Variables.....................................................7

Error .........................................................................................................................................................7

Offset.........................................................................................................................................................8

Load Disturbance .....................................................................................................................................8

Control Algorithm.....................................................................................................................................8

Manual and Automatic Control ................................................................................................................9

Closed and Open Control Loops ..............................................................................................................10

Components of Control Loops and ISA Symbology ...................................................................................... 11

Learning Objectives.................................................................................................................................. 11

Control Loop Equipment and Technology ....................................................................................................... 12

Primary Elements/Sensors........................................................................................................................ 12

Transducers and Converters..................................................................................................................... 13

Transmitters .............................................................................................................................................. 13

Signals ...................................................................................................................................................... 14

Pneumatic Signals ............................................................................................................................. 14

Analog Signals................................................................................................................................... 14

Digital Signals ................................................................................................................................... 15

Indicators.................................................................................................................................................. 15

Recorders.................................................................................................................................................. 16

Controllers................................................................................................................................................ 16

Correcting Elements/Final Control Elements .......................................................................................... 18

Actuators................................................................................................................................................... 18

Fundamentals of Control

Table of Contents

ISA Symbology .................................................................................................................................................19

Symbols ................................................................................................................................................... 20

Pumps .............................................................................................................................................. 21

Piping and Connections .................................................................................................................. 22

Identification Letters............................................................................................................................... 23

Tag Numbers........................................................................................................................................... 23

ISA Symbology Review ........................................................................................................................... 26

Controller Algorithms and Tuning ...............................................................................................................27

Learning Objectives.................................................................................................................................27

Controller Algorithms.....................................................................................................................................28

Discrete Controllers ................................................................................................................................28

Multistep Controllers................................................................................................................................29

Continuous Controllers ............................................................................................................................29

Why controllers need tuning? ...........................................................................................................................31

Gain ..........................................................................................................................................................31

Proportional Mode ..........................................................................................................................................33

Proportional Gain ....................................................................................................................................33

Proportional Band ....................................................................................................................................33

Limits of Proportional action ...................................................................................................................34

Determining the Controller Output..........................................................................................................34

Proportional Action- Closed Loop........................................................................................................... 35 .

Integral Mode ................................................................................................................................................. 37

Integral Action ........................................................................................................................................ 37

Open Loop Analysis................................................................................................................................ 37

Closed Loop Analysis ............................................................................................................................. 38

Reset Windup .......................................................................................................................................... 39

Summary ................................................................................................................................................. 40

Derivative Mode .............................................................................................................................................. 41

Derivative Action .................................................................................................................................... 41

Rate Summary ......................................................................................................................................... 44

Process Control Loops.....................................................................................................................................46

Learning Objectives..................................................................................................................................46

Single Control Loops .......................................................................................................................................47

Feedback Control .....................................................................................................................................47

Examples Of Single Control Loops..................................................................................................................48

Pressure Control Loops............................................................................................................................49

Flow Control Loops..................................................................................................................................49

Level Control Loops .................................................................................................................................50

Temperature Control Loops .....................................................................................................................51

iii

Fundamentals of Control

Table of Contents

Multi-Variable / Advanced Control Loops ......................................................................................................52

Multivariable Loops .................................................................................................................................52

Feedforward Control ................................................................................................................................53

Feedforward plus Feedback .....................................................................................................................54

Cascade Control ..................................................................................................................................... 55

Batch Control ......................................................................................................................................... 56

Ratio Control .......................................................................................................................................... 56

Selective Control..................................................................................................................................... 57

Fuzzy Control ......................................................................................................................................... 57

Fundamentals of Control

Introduction

Control in process industries refers to the regulation of all aspects of the process. Precise control of level,

temperature, pressure and flow is important in many process applications. This module introduces you to

control in process industries, explains why control is important, and identifies different ways in which

precise control is ensured.

The following five sections are included in this module:

The importance of process control

Control theory basics

Components of control loops and ISA symbology

Controller algorithms and tuning

Process control systems

As you proceed through the module, answer the questions in the activities column on the right side of each

page. Also, note the application boxes (double-bordered boxes) located throughout the module. Application

boxes provide key information about how you may use your baseline knowledge in the field. When you see the

workbook exercise graphic at the bottom of a page, go to the workbook to complete the designated exercise

before moving on in the module. Workbook exercises help you measure your progress toward meeting each

section’s learning objectives.

P ERFORMANCE O BJECTIVE

After completing this module, you will be able to determine needed control loop components in specific

process control applications.

Fundamentals of Control

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