PROCESS CONTROL IT62 - PowerPoint PPT Presentation

Title: PROCESS CONTROL IT62


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PROCESS CONTROL (IT62)

• Syllabus
• Chapter 1 Controller Principles
• Chapter 2 Analog Controllers
• Chapter 3 Control Loop Characteristics
• Chapter 4 Controllers, Converters, Transmitters
  Relays
• Chapter 5 Process ID Symbols and Drawings

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• Textbooks
• Process Control Inst. Technology (7th Edn) by
  C.D.Johnson, Pearson Education Pub.2003. For
  Chapter 1, 2 and 3
• Instrument Engineers Handbook Vol. 1-Process
  Measurement, Vol. 2-Process Control, by Bela J.
  Liptak, Chilton Book Company. For Chapter 4 5

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COURSE OVERVIEW

• The course provides a fundamental knowledge to
  instrumentation engineer regarding the
  implementation of process control techniques in
  the process industries.
• The course also provides a basic knowledge about
  process instrumentation drawing symbols and
  diagrams.

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COURSE OBJECTIVE

• To make instrumentation technology students to
  become familiar with process control techniques
  tools.
• At the end of this course you will be in a
  position to measure, acquire, control tune the
  process parameters in process industries.

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INTRODUCTION TO PROCESS CONTROL

• Process
• In general, process constitutes a sequence of
  events in which a raw material will be converted
  into finished product.
• Any system composed of dynamic variables,
  usually involved in manufacturing production
  operations.

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• Control
• The methods/techniques to force parameters or
  variables in the environment / process to have
  specific values.
• Control System
• All the elements necessary to accomplish the
  control objective i.e. regulation of some
  parameters to have specific or desired values

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• Process Control
• It deals with the elements and methods of
  control system operations used in industry to
  control industrial processes.

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PROCESS CONTROL PRINCIPLE

• Objective of process control is to regulate the
  value of some quantity.
• Regulation It means to maintain a quantity or
  variable at some desired value regardless of
  external influences.

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Process An Example-Level of Liquid in a tank

• Qout gt Qin Level drops
• Qout lt Qin Level rises

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Human Aided Control

• Definition
• Example Control of liquid level in a tank

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Automatic Control System

• Definition
• Example Control of liquid level in a tank

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Some Definitions Related to Process Control

• Controlled Variable The process variable
  regulated by process control loop.
• Controlling Variable The process variable
  changed by the final control element under the
  command of controller to effect regulation of
  controlled variable.
• Setpoint The desired value of a controlled
  variable in process control loop.

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• Error The algebraic difference between the
  measured value of variable and setpoint.
• Controller The element in a process control loop
  that evaluates error of the controlled variable
  and initiates corrective action by a signal to
  controlling variable.
• Dynamic variable The process variable that can
  change from moment to moment because of unknown
  sources.

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ELEMENTS OF PROCESS CONTROL

• Process
• Measurement
• Error Detector
• Controller
• Control Element

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PROCESS CONTROL BLOCK DIAGRAM
p Controller output c Controlled variable b
measured value of c e Error signal r Set
point u Controlling variable Fig. Block
diagram of basic process control loop.
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Example
Fig. Physical diagram for flow process control
system
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Final Control Element
I/P Converter, Actuator, Valve
Controller
(Error Detector)
(Controller)
Pipe Flow
r
Process
Orifice plate, DP Cell, P/I Converter
Measurement
Fig. Block diagram for flow process control
system.
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ANALOG DATA REPRESENTATION

• Analog Standards for representing range of
  variable in Process Control Systems
• Current Signal 4 to 20 mA
• Pneumatic Signal 3 to 15 psi (20 to 100kPa)

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Why Current Signal?

• Current is used instead of voltage because the
  system is then less dependent on load.

Fig. Transmission of current signal is
independent of line resistance
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FINAL CONTROL OPERATION
Fig. Elements of Final Control Operation
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Chapter-1CONTROLLER PRINCIPLES
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OBJECTIVES

• Define understand the process characteristics,
  process system parameters
• Describe the discontinuous and continuous
  controller modes
• Describe the composite controller modes
• Compare and differentiate discontinuous and
  continuous controller modes, and their advantages
  applications.

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PROCESS CHARACTERISTICS

• Selection of controller modes is a function of
  process characteristics.
• Important Process Characteristics
• Process Equation
• Process Load
• Process Lag
• Self Regulation

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Example

• Process Parameters
• TL Liquid temperature (controlled variable)
• QA Input flow rate
• QB Output flow rate
• TA Ambient Temp.
• TO Inlet temperature of liquid
• TS Steam Temp.
• QS Steam flow rate (Controlling variable)

Fig. Control of liquid temperature in a tank by
process control
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1. Process Equation

• The process equation is a function which
  describes the process and provides the
  information about other process parameters which
  influence the controlled variable.
• For liquid temperature control the process
  equation is
• TL f (QA, QB, QS, TA, TS, TO)

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2. Process Load

• The process load refers to set of all process
  parameters excluding the controlled variable.
• Nominal Set
• Nominal Load
• Nominal value
• Process Load Change
• Transient Load Change Example

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3. Process Lag

• Process lag refers to the time consumed by the
  process itself to bring the controlled variable
  to setpoint value during load change. Example

4. Self-regulation

• Some processes adopt to stable value without
  being regulated via process control loop.