Process Control Priyatmadi 2005 1 Pengantar Pengendalian Proses Priyatmadi Jurusan teknik Elektro FT...
-
Upload
elinor-mathews -
Category
Documents
-
view
220 -
download
1
Transcript of 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
Process ControlPriyatmadi 2005 2
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
Process ControlPriyatmadi 2005 3
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 ControlPriyatmadi 2005 4
Process Control Classification• Manual Control• Automatic Control
• Feedback Control• Feed forward Control
• Analog Control• Digital Control
Process ControlPriyatmadi 2005 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 e(t) m(t) c(t)
Process ControlPriyatmadi 2005 7
Control Diagram of a Typical Control Loop
F1
T1
T
F2
T2
TCController
ActuatorSystem
TT
SensorSystem
Process ControlPriyatmadi 2005 8
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
Process ControlPriyatmadi 2005 9
Controller Development
• Pneumatic controllers
• Electronic analog controllers
• Supervisory control computers
• Distributed Control Systems (DCS)
• Fieldbus technology
Process ControlPriyatmadi 2005 10
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 2005 11
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 2005 12
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 2005 13
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 2005 14
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 2005 15
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 2005 16
Supervisory Control Computer
PrinterVideo Display
Unit
InterfacingHardware
AnalogControl
Subsytem
AlarmingFunctions
Supervisory Control Computer
Data StorageAcquisition
System
...
Process ControlPriyatmadi 2005 17
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 ControlPriyatmadi 2005 18
DCS Architecture
Process Transmitters and Actuators
Data Highway(Shared Communication Facilities)
LocalConsole
LocalControl
Unit..............
DataStorage
Unit
HostComputer
SystemConsoles
PLC
LocalControl
Unit
LocalConsole
Process ControlPriyatmadi 2005 19
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 2005 20
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 2005 21
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.