Transcript Control loop troubleshooting

Pengantar
Pengendalian Proses
Priyatmadi
Jurusan teknik Elektro
FT UGM
Process Control
Priyatmadi 2005
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Overall Course Objectives
• Develop the skills necessary to function as
an industrial process control engineer.
– Skills
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Tuning loops
Control loop design
Control loop troubleshooting
Command of the terminology
– Fundamental understanding
• Process dynamics
• Feedback control
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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
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Process Control Classification
• Manual Control
• Automatic Control
• Feedback Control
• Feed forward Control
• Analog Control
• Digital Control
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Manual Control
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Automatic Control
Cold water in
steam in
hot water out
3-15psi
Set point
TT
I/P
4-20 mA
Set point +
TIC
Controller
4-20 mA
Plant
Sensor
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Control Diagram of a Typical
Control Loop
Actuator
System
F1
F2
T1
T2
Sensor
System
Controller
TC
T
TT
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Components and Signals of a
Typical Control Loop
F1
F2
T1
T2
Thermowell
3-15 psig
T
Air
I/P
Operator
Console
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4-20 ma
Tsp
D/A
DCS
Control
Computer
Thermocouple
millivolt signal
A/D
4-20 ma
Transmitter
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Controller Development
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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
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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.
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Pneumatic Controller Installation
F1
F2
T1
T2
Thermowell
3-15 psig
T
Air
Tsp
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Pneumatic
Controller
Thermocouple
millivolt signal
3-15 psig
Air
Transmitter
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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.
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Electronic Controller Installation
F1
F2
T1
T2
Thermowell
3-15 psig
T
Air
I/P
4-20 ma
Thermocouple
millivolt signal
Tsp
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Electronic
Analog
Controller
4-20 ma
Transmitter
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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.
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Supervisory Control Computer
Video Display
Unit
Alarming
Functions
Printer
Supervisory Control Computer
Analog
Control
Subsytem
Interfacing
Hardware
Data Storage
Acquisition
System
...
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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
System
Consoles
Host
Computer
Data
Storage
Unit
PLC
Data Highway
(Shared Communication Facilities)
Local
Console
Local
Control
Unit
Local
Control
Unit
..............
Local
Console
Process Transmitters and Actuators
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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.
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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.
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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.
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Fieldbus Architecture
Plant-Wide Network
Local
Area
Network
Smart
Sensors
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.................
Smart
Sensors
Smart Control
Valves and
Controllers
Fieldbus Network
Local
Area
Network
Smart Control
Valves and
Controllers
Fieldbus Network
a
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