化工自动化仪表双语课：Chapter 1_Introduction_student.pdf

Chapter1Introduction

1ProcessControlSystem

2ImportantTerms,ObjectiveandBlockDiagramofAutomatic

ProcessControl

3RegulatoryandServoControl

4TransmissionSignalsofControlSystemandOtherTerms

5ControlStrategies

6TimeResponseofControlSystem-PerformanceCriteria

Summary

1

1ProcessControlSystem

•Example–HeatExchanger

•Manualprocesscontrol

•Automaticprocesscontrol

•Feedbackcontrol

2

1ProcessControlSystem-ExampleofaProcess

Example

3

1ProcessControlSystem

Tofixideas,letusconsideraheatexchangerbelowinwhichaprocess

fluidisheatedbycondensingsteam.

Thepurposeofthisunitistoheattheprocessfluidfromsomeinlet

temperature,Ti(t),uptoadesiredoutlettemperature,T(t).

Theenergygainedbytheprocessfluidisprovidedbythelatentheatof

condensationofthesteam.

Inthisprocessmanyvariablescanchange,causingtheoutlettemperature

todeviatefromitsdesiredvalue.Ifthishappens,someactionmustbe

takentocorrectforthisdeviation.

Example

4

1ProcessControlSystem

Automaticprocesscontrolisconcernedwithmaintaining

processvariablesatadesiredoperatingvalue,inwhich

Processvariablesincludetemperatures,pressures,flows,

compositions,andthelike.

Importantprocessvariablesarethoserelatedtosafety,product

quality,andproductionrates.

Why?

•Asweshallseeintheensuingpages,processesaredynamicin

nature.

•Changesarealwaysoccurring.

•Andifactionsarenottaken,theimportantprocessvariables

willnotachieve