1 Process Control and Data Acquisition Systems CM4120 Chemical Plant Operations

2 Distributed Control System (DCS) Architecture n Used for continuous control of chemical processing n Control functions are distributed throughout redundant, deterministic networked computer architecture – I/O interface and level 1 control functions – advanced control functions – human interface n DCS replaced mainframe computer controllers n Added a high level of robustness to control systems n Pre-configured functionality geared toward process industries, but a relatively high cost

3 Programmable Logic Controller (PLC) Architecture n Used for control where the devices are primarily discrete (the controlled devices are energized/de-energized and the inputs are open/closed circuit) n Provide very fast response (<.1 sec) to system changes n Typical applications are packaging, material conveyance, and waste water treatment n Very little, if any pre-configured functionality, but PLC’s are relatively low cost n In chemical processing, often are used along side DCS

4 SCADA – Supervisory Control and Data Acquisition System n Scalable systems that provide some additional level of control and data acquisition “above” the controller, DCS and/or PLC level n Typically use non-redundant TCP/IP communications and therefore are not considered appropriate for direct process control n Built upon non-proprietary, off-the-shelf hardware n Very useful in large plant environments where data from many sources must be collected

5 Rockwell Automation ProcessLogix DCS and OSISoft PI in PSCC WE Network PI Server Control Room Network Switch Operator Stations ProcessLogix Server PLX Controller and 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

6  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 Room Network Switch Operator Stations ProcessLogix Server PI Server

7 ProcessLogix – How it works ProcessLogix Server PLX Controller and 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

8 ProcessLogix – How it works PLX Controller and 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

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

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

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

12 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

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 Actuator Ball valve body Process line

15  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 Room Network Switch Operator Stations - PIPC - ProcessBook ProcessLogix Server - OPC Server WE Network - PIPC - ProcessBook

16 PI – Plant Information System n Data Historian system is required part of process management system n Long-term data storage/ retrieval system n Optimizes use of hard drive storage space and permits quick recall of archived data n Includes data retrieval software tools n 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 n A PI “tag” is configured for every piece of data you want to archive n Collected tags are “scheduled” to retrieve data periodically or upon the occurrence of an event n Data are brought into the archive thru a filtering and compression algorithm n Data are not archived unless they pass the filter and compression tests n When data are retrieved from the archive and presented in a series, the individual points are extrapolated between the stored data n Tags can also be manually entered – lab data