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Process Control and Data Acquisition Systems

Process Control and Data Acquisition Systems. CM4120 Chemical Plant Operations. Distributed Control System (DCS) Architecture. Used for continuous control of chemical processing Control functions are distributed throughout redundant, deterministic networked computer architecture

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Process Control and Data Acquisition Systems

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  1. Process Control and Data Acquisition Systems CM4120 Chemical Plant Operations

  2. 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

  3. 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

  4. 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

  5. Control Room Network Switch Plant Area – valves, xmitters ProcessLogix Server Operator Stations PLX Controller and I/O Cards Rockwell Automation ProcessLogix DCS and OSISoft PI in PSCC • 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 WE Network PI Server

  6. PI Server Control Room Network Switch ProcessLogix Server Operator Stations 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

  7. ProcessLogix Server PLX Controller and I/O Cards 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. • Controller continues to function, even after loss of communication w/ server

  8. Plant Area – valves, xmitters PLX Controller and I/O Cards ProcessLogix – How it works • 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

  9. PLX controller I/O cards Zener barriers 8 pr. cables from field junction cabinet 2nd I/O chassis PLX Controller Cabinet

  10. 8 pr. Cables to controller cabinet Field Junction Cabinet Single pairs from field device

  11. Field Devices – Transmitters Wiring to field junction cabinet Level transmitter Thermocouple head Wiring from transmitter to measuring element Temperature transmitter

  12. Field Devices – Transducer Single pr. cable from field termination cabinet Solenoids for 2-position air-actuated ball valves Air lines to ball valves Current to pneumatic transducers Wire prs. to solenoids Wire prs. to transducers Air lines to control valves

  13. Field Devices – Regulatory Control Valve Air line from transducer Actuator w/ positioner Control valve Block valves Bypass valve

  14. Field Devices – Ball Valve w/ Actuator Air line from solenoid Ball valve body Actuator Process line

  15. WE Network - PIPC - ProcessBook Control Room Network Switch ProcessLogix Server - OPC Server • Operator Stations • PIPC • - ProcessBook PI – Plant Information System • 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 Server - OPC Interface

  16. 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

  17. 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

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