Process Control and Data Acquisition Systems

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