Pengantar Pengendalian Proses

steamgloomyΗλεκτρονική - Συσκευές

15 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

81 εμφανίσεις

Process Control

Priyatmadi 2008









1

Pengantar Pengendalian Proses

Priyatmadi

Jurusan teknik Elektro

FT UGM

Process Control

Priyatmadi 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 Control

Priyatmadi 2008









3

PROCESS TYPE


Self
-
regulating Processes


Manual controlled processes


Automatic controlled process


Process Control

Priyatmadi 2008









4

Self
-
regulating Processes


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

steam
out

cold water
in

hot water out

steam
in

heat exchanger

Process Control

Priyatmadi 2008









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Manual Control

Process Control

Priyatmadi 2008









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Automatic Control

TT

TIC

I/P

4
-
20 mA

4
-
20 mA

3
-
15psi

Set point

Cold water in

hot water out

steam in

Plant

Controller

Sensor

+

-

Set point

Process Control

Priyatmadi 2008









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Process Control Classification


Manual Control


Automatic Control



Feedback Control


Feed forward Control




Arithmetic control


Logic Control



Analog Control


Digital Control



Process Control

Priyatmadi 2008









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Controller Development


Pneumatic controllers


Electronic analog controllers


Supervisory control computers


Distributed Control Systems (DCS)


Fieldbus technology

Process Control

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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 Control

Priyatmadi 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 Control

Priyatmadi 2008









11

Pneumatic Controller Installation

T
F
2
T
2
Thermocouple
millivolt signal
Transmitter
Pneumatic
Controller
3-15 psig
T
sp
Air
F
1
T
1
Thermowell
3-15 psig
Air
Process Control

Priyatmadi 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 Control

Priyatmadi 2008









13

Electronic Controller Installation

T

F

2

T

2

Thermocouple

millivolt signal

Transmitter

4
-
20 ma

Electronic

Analog

Controller

3
-
15 psig

4
-
20 ma

T

sp

I/P

Air

F

1

T

1

Thermowell

Process Control

Priyatmadi 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 Control

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Supervisory Control Computer

Printer
Video Display
Unit
Interfacing
Hardware
Analog
Control
Subsytem
Alarming
Functions
Supervisory Control Computer
Data Storage
Acquisition
System
...
Process Control

Priyatmadi 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.

Process Control

Priyatmadi 2008









17

DCS Architecture

Process Transmitters and Actuators
Data Highway
(Shared Communication Facilities)
Local
Console
Local
Control
Unit
..............
Data
Storage
Unit
Host
Computer
System
Consoles
PLC
Local
Control
Unit
Local
Console
Process Control

Priyatmadi 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 Control

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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 Control

Priyatmadi 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 Control

Priyatmadi 2008









21


Fieldbus Architecture

Plant-Wide Network
.................
Smart
Sensors
Smart Control
Valves and
Controllers
Local
Area
Network
Smart
Sensors
Smart Control
Valves and
Controllers
Local
Area
Network
Fieldbus Network
Fieldbus Network
a