1 process control and data acquisition systems cm4120 chemical plant operations
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Process Control and Data Acquisition Systems
CM4120
Chemical Plant Operations
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Distributed Control System (DCS) Architecture
Used for continuous control of chemical processing Control functions are distributed throughout redundant,
deterministic networked computer architecture– 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
Used for control where the devices are primarily discrete (the controlled devices are energized/de-energized and the inputs are open/closed circuit)
Provide very fast response (< .1 sec) to system changes
Typical applications are packaging, material conveyance, and waste water treatment
Very little, if any pre-configured functionality, but PLC’s are relatively low cost
In chemical processing, often are used along side DCS
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SCADA – Supervisory Control and Data Acquisition System
Scalable systems that provide some additional level of control and data acquisition “above” the controller, DCS and/or PLC level
Typically use non-redundant TCP/IP communications and therefore are not considered appropriate for direct process control
Built upon non-proprietary, off-the-shelf hardware
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
WE Network
PI Server
Control RoomControl RoomNetwork SwitchNetwork Switch
Operator Stations
ProcessLogix Server
PLX Controllerand I/O Cards
Plant Area – valves, xmitters
PI is process data management system
“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
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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
ProcessLogix – How it works
Control RoomControl RoomNetwork SwitchNetwork Switch
Operator Stations
ProcessLogix Server
PI Server
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ProcessLogix – How it works
ProcessLogix Server
PLX Controllerand I/O Cards
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.
Controller continues to function, even after loss of communication w/ server
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ProcessLogix – How it works
PLX Controllerand I/O Cards
Plant Area – valves, xmitters
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
8 pr. cables from field junction cabinet
Zener barriers
I/O cards
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
Wiring to field junction cabinet
Thermocouple head
Temperature transmitter
Wiring from transmitter to measuring element
Level transmitter
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Field Devices – Transducer
Wire prs. to transducers
Current to pneumatic transducers
Air lines to control valves
Single pr. cable from field termination cabinet
Solenoids for 2-position air-actuated ball valves
Air lines to ball valves
Wire prs. to solenoids
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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
Actuator
Ball valve body
Process line
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PI is a process data historization/ data retrieval system
PI server (Steam) is PDC for control room network and is also on WE network
PI data are available anywhere on campus network
PIPC is Excel add-in
ProcessBook is graphical tool for viewing process and process data
PI – Plant Information System
PI Server- OPC Interface
Control RoomControl RoomNetwork SwitchNetwork Switch
Operator Stations- PIPC- ProcessBook
ProcessLogix Server- OPC Server
WE Network- PIPC- ProcessBook
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PI – Plant Information System
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
– 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
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