Transcript Control and Data Acquisition Systems

Process Control and Data
Acquisition Systems
CM4120
Chemical Plant Operations
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Distributed Control System (DCS)
Architecture
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Used for continuous control of chemical processing
Control functions are distributed throughout redundant,
deterministic networked computer architecture
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I/O interface and level 1 control functions
advanced control functions
human interface
DCS replaced mainframe computer controllers
Added a high level of robustness to control systems
Pre-configured functionality geared toward process
industries, but a relatively high cost
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Programmable Logic Controller (PLC)
Architecture
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Used for control where the devices are primarily discrete
(the controlled devices are energized/de-energized and the
inputs are open/closed circuit)
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Provide very fast response (< .1 sec) to system changes
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Typical applications are packaging, material conveyance,
and waste water treatment
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Very little, if any pre-configured functionality, but PLC’s
are relatively low cost
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In chemical processing, often are used along side DCS
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SCADA – Supervisory Control and Data
Acquisition System
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Scalable systems that provide some additional level of
control and data acquisition “above” the controller, DCS
and/or PLC level
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Typically use non-redundant TCP/IP communications and
therefore are not considered appropriate for direct process
control
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Built upon non-proprietary, off-the-shelf hardware
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Very useful in large plant environments where data from
many sources must be collected
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Rockwell Automation ProcessLogix DCS
and OSISoft PI in PSCC
PI is process data management system
WE Network
“External” historized and real-time data
requests are served thru PI Server
Operator Stations and other “internal” data
users communicate thru PLX Server
Control executes at PLX Controller
Plant Area – valves, xmitters
PI Server
Control Room
Network Switch
ProcessLogix
Server
PLX Controller
and I/O Cards
Operator Stations
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ProcessLogix – How it works
Control Room network is
Windows 2000 domain – PSCC
PDC is PI Server
Control system configuration is
done thru PLX Server – creates
configuration database
PLX server stores configuration
database and stores/updates an
active, real-time database
Operator stations access process
thru PLX server
PI Server
Control Room
Network Switch
ProcessLogix
Server
Operator Stations
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ProcessLogix – How it works
Communications via ControlNet
Controller configuration is
downloaded to PLX Controller
PLX Controller continuously updates
copy of active database at PLX server
PLX Controller continuously
executes all control logic, alarming,
PID loops, indicators, etc.
ProcessLogix
Server
PLX Controller
and I/O Cards
Controller continues to function, even
after loss of communication w/ server
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ProcessLogix – How it works
Plant Area – valves, xmitters
PLX Controller
and I/O Cards
I/O cards are specific to device requirements
•4-20 mA input, 4-20 mA output
•24 VDC input, 24 VDC output, etc.
A pair of wires runs from each device back to the I/O card
Typically 8 to 16 devices per I/O card
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PLX Controller Cabinet
PLX controller
I/O cards
Zener barriers
8 pr. cables from
field junction cabinet
2nd I/O chassis
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Field Junction Cabinet
Single pairs from
field device
8 pr. Cables to
controller cabinet
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Field Devices – Transmitters
Level transmitter
Wiring to field
junction cabinet
Thermocouple head
Wiring from
transmitter to
measuring element
Temperature
transmitter
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Field Devices – Transducer
Solenoids for 2-position
air-actuated ball valves
Single pr. cable
from field
termination cabinet
Air lines to
ball valves
Current to pneumatic
transducers
Air lines to
control valves
Wire prs. to solenoids
Wire prs. to transducers
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Field Devices – Regulatory Control Valve
Air line from transducer
Actuator w/ positioner
Control valve
Block valves
Bypass valve
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Field Devices – Ball Valve w/ Actuator
Air line from
solenoid
Ball valve body
Actuator
Process line
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PI – Plant Information System
PI is a process data historization/
data retrieval system
WE Network
- PIPC
- ProcessBook
PI server (Steam) is PDC for
control room network and is also
on WE network
PI data are available anywhere on
campus network
PI Server
- OPC Interface
Control Room
Network Switch
ProcessLogix
Server
- OPC Server
PIPC is Excel add-in
ProcessBook is graphical tool for
viewing process and process data
Operator Stations
- PIPC
- ProcessBook
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PI – Plant Information System
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Data Historian system is required part of process
management system
Long-term data storage/ retrieval system
Optimizes use of hard drive storage space and permits
quick recall of archived data
Includes data retrieval software tools
OSISoft, Inc. PI system
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Import process data into supervisory control or process monitoring
applications
Link process control systems with business management systems
Provide data for production and compliance reporting
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PI – How it works
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A PI “tag” is configured for every piece of data you want to
archive
Collected tags are “scheduled” to retrieve data periodically or
upon the occurrence of an event
Data are brought into the archive thru a filtering and
compression algorithm
Data are not archived unless they pass the filter and compression
tests
When data are retrieved from the archive and presented in a
series, the individual points are extrapolated between the stored
data
Tags can also be manually entered – lab data
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