Process ControlPriyatmadi 2008 1

Pengantar Pengendalian Proses

PriyatmadiJurusan teknik Elektro

FT UGM

Process ControlPriyatmadi 2008 2

PROCESS CONTROL PRINCIPLE

• Process control is methods to force process parameter to have specific values.

• Objective to maintain the value of some quantity at some desired level regardless of influences.

Process ControlPriyatmadi 2008 3

PROCESS TYPE

• Self-regulating Processes

• Manual controlled processes

• Automatic controlled process

Process ControlPriyatmadi 2008 4

Self-regulating Processes

• The process outputs are not regulated, its value will easily change.

steam out

cold water in

hot water outsteam in

heat exchanger

Process ControlPriyatmadi 2008 5

Manual Control

Process ControlPriyatmadi 2008 6

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

Process ControlPriyatmadi 2008 7

Process Control Classification

• Manual Control

• Automatic Control

• Feedback Control

• Feed forward Control

• Arithmetic control

• Logic Control

• Analog Control

• Digital Control

Process ControlPriyatmadi 2008 8

Controller Development

• Pneumatic controllers

• Electronic analog controllers

• Supervisory control computers

• Distributed Control Systems (DCS)

• Fieldbus technology

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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

Process ControlPriyatmadi 2008 10

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.

Process ControlPriyatmadi 2008 11

Pneumatic Controller Installation

T

F 2

T 2

Thermocouplemillivolt signal

TransmitterPneumaticController

3-15 psig

T sp

Air

F 1

T 1

Thermowell

3-15 psigAir

Process ControlPriyatmadi 2008 12

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.

Process ControlPriyatmadi 2008 13

Electronic Controller Installation

T

F2

T2

Thermocouplemillivolt signal

Transmitter4-20 maElectronic

AnalogController

3-15 psig

4-20 ma

Tsp

I/PAir

F1

T1

Thermowell

Process ControlPriyatmadi 2008 14

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.

Process ControlPriyatmadi 2008 15

Supervisory Control Computer

PrinterVideo Display

Unit

InterfacingHardware

AnalogControl

Subsytem

AlarmingFunctions

Supervisory Control Computer

Data StorageAcquisition

System

...

Process ControlPriyatmadi 2008 16

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.

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DCS Architecture

Process Transmitters and Actuators

Data Highway(Shared Communication Facilities)

LocalConsole

LocalControl

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

DataStorage

Unit

HostComputer

SystemConsoles

PLC

LocalControl

Unit

LocalConsole

Process ControlPriyatmadi 2008 18

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.

Process ControlPriyatmadi 2008 19

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.

Process ControlPriyatmadi 2008 20

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.

Process ControlPriyatmadi 2008 21

Fieldbus Architecture

Plant-Wide Network

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

SmartSensors

Smart ControlValves andControllers

LocalArea

Network

SmartSensors

Smart ControlValves andControllers

LocalArea

Network

Fieldbus NetworkFieldbus Networka