Process Control Priyatmadi 2005 1 Pengantar Pengendalian Proses Priyatmadi Jurusan teknik Elektro FT...

Process ControlPriyatmadi 2005 1

Pengantar Pengendalian Proses

PriyatmadiJurusan teknik Elektro

FT UGM


Overall Course Objectives

• Develop the skills necessary to function as an industrial process control engineer.– Skills

• Tuning loops

• Control loop design

• Control loop troubleshooting

• Command of the terminology

– Fundamental understanding• Process dynamics

• Feedback control


Control Relevant Aspects of Control Loop Hardware

• Necessary for control loop troubleshooting:– To determine if each subsystem (control

computer, actuator system, and sensor system) is functioning properly

– To understand the proper design and operation of all the components that make-up each of the subsystems of a control loop


Process Control Classification• Manual Control• Automatic Control

• Feedback Control• Feed forward Control

• Analog Control• Digital Control


Manual Control


Automatic Control

TT

TIC

I/P

4-20 mA4-20 mA

3-15psi

Set point

Cold water in

hot water outsteam in

PlantController

Sensor

+

-

Set point e(t) m(t) c(t)


Control Diagram of a Typical Control Loop

F1

T1

T

F2

T2

TCController

ActuatorSystem

TT

SensorSystem


Components and Signals of a Typical Control Loop

T

F2

T2

Thermocouplemillivolt signal

Transmitter4-20 maDCS

ControlComputer

A/D

3-15 psig

D/A4-20 ma

OperatorConsole

Tsp

I/PAir

F1

T1

Thermowell


Controller Development

• Pneumatic controllers

• Electronic analog controllers

• Supervisory control computers

• Distributed Control Systems (DCS)

• Fieldbus technology


Pneumatic Controllers - Phase I

• Introduced in the 1920’s

• Installed in the field next to the valve

• Use bellows, baffles, and nozzles with an air supply to implement PID action.

• Provided automatic control and replaced manual control for many loops


Pneumatic Controllers - Phase II

• Transmitter type pneumatic controllers began to replace field mounted controllers in the late 1930’s.

• Controller located in control room with pneumatic transmission from sensors to control room and back to the valve.

• Allowed operators to address a number of controllers from a centralized control room.


Pneumatic Controller Installation

T

F 2

T 2


TransmitterPneumaticController

3-15 psig

T sp

Air

F 1

T 1

Thermowell

3-15 psigAir


Electronic Analog Controllers

• Became available in the late 1950’s.

• Replaced the pneumatic tubing with wires.

• Used resistors, capacitors, and transistors based amplifiers to implement PID action.

• Outsold pneumatic controllers by 1970.

• Allowed for advanced PID control: ratio, feedforward, etc.


Electronic Controller Installation

T

F2

T2


Transmitter4-20 maElectronic

AnalogController

3-15 psig

4-20 ma

Tsp

I/PAir

F1

T1

Thermowell


Computer Control System

• Based upon a mainframe digital computer.

• Offered the ability to use data storage and retrieval, alarm functions, and process optimization.

• First installed on a refinery in 1959.

• Had reliability limitations.


Supervisory Control Computer

PrinterVideo Display

Unit

InterfacingHardware

AnalogControl

Subsytem

AlarmingFunctions

Supervisory Control Computer

Data StorageAcquisition

System

...


Distributed Control System- DCS

• Introduced in the late 1970’s.

• Based upon redundant microprocessors for performing control functions for a part of the plant. SUPERIOR RELIABILITY

• Less expensive per loop for large plants.

• Less expensive to expand.

• Facilitates the use of advanced control.


DCS Architecture

Process Transmitters and Actuators

Data Highway(Shared Communication Facilities)

LocalConsole

LocalControl

Unit..............

DataStorage

Unit

HostComputer

SystemConsoles

PLC

LocalControl

Unit

LocalConsole


DCS and Troubleshooting

• The data storage and trending capability of a DCS greatly facilitate troubleshooting control problems. That is, the sources of process upsets can many times be tracked down through the process by trending a group of process measurements until the source of the process upset is located.


Control Relevant Aspects of a DCS

• The most important control aspect of a DCS is the cycle time for controller calls. The shortest cycles times are typically around 0.2 seconds while most loops can be executed every 0.5 to 1.0 seconds. These cycle times affect flow control loops and other fast control loops.


Fieldbus Technology

• Based upon smart valves, smart sensors and controllers installed in the field.

• Uses data highway to replace wires from sensor to DCS and to the control valves.

• Less expensive installations and better reliability.

• Can mix different sources (vendors) of sensors, transmitters, and control valves.

• Now commercially available and should begin to replace DCSs.


Fieldbus Architecture

Plant-Wide Network

.................

SmartSensors

Smart ControlValves andControllers

LocalArea

Network

SmartSensors

Smart ControlValves andControllers

LocalArea

Network

Fieldbus NetworkFieldbus Networka

Process Control Priyatmadi 2005 1 Pengantar Pengendalian Proses Priyatmadi Jurusan teknik Elektro FT...

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