Process Control and Data Acquisition SystemsCM4120Chemical Plant Operations

Distributed Control System (DCS) ArchitectureUsed for continuous control of chemical processingControl functions are distributed throughout redundant, deterministic networked computer architectureI/O interface and level 1 control functionsadvanced control functionshuman interfaceDCS replaced mainframe computer controllersAdded a high level of robustness to control systemsPre-configured functionality geared toward process industries, but a relatively high cost

Programmable Logic Controller (PLC) ArchitectureUsed 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 PLCs are relatively low cost

In chemical processing, often are used along side DCS

SCADA Supervisory Control and Data Acquisition SystemScalable 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

Rockwell Automation ProcessLogix DCS and OSISoft PI in PSCCWE NetworkPI ServerPI is process data management system External historized and real-time data requests are served thru PI ServerOperator Stations and other internal data users communicate thru PLX ServerControl executes at PLX Controller

ProcessLogix How it worksControl Room network is Windows 2000 domain PSCCPDC is PI ServerControl system configuration is done thru PLX Server creates configuration databasePLX server stores configuration database and stores/updates an active, real-time databaseOperator stations access process thru PLX server

ProcessLogix How it worksCommunications via ControlNetController configuration is downloaded to PLX ControllerPLX Controller continuously updates copy of active database at PLX serverPLX Controller continuously executes all control logic, alarming, PID loops, indicators, etc.Controller continues to function, even after loss of communication w/ server

ProcessLogix How it worksI/O cards are specific to device requirements4-20 mA input, 4-20 mA output24 VDC input, 24 VDC output, etc.A pair of wires runs from each device back to the I/O cardTypically 8 to 16 devices per I/O card

PLX Controller Cabinet

Field Junction CabinetSingle pairs from field device

Field Devices TransmittersWiring to field junction cabinetThermocouple headTemperature transmitterWiring from transmitter to measuring elementLevel transmitter

Field Devices TransducerWire prs. to transducersCurrent to pneumatic transducersAir lines to control valvesSingle pr. cable from field termination cabinetSolenoids for 2-position air-actuated ball valvesAir lines to ball valvesWire prs. to solenoids

Field Devices Regulatory Control ValveAir line from transducerActuator w/ positionerControl valveBlock valvesBypass valve

Field Devices Ball Valve w/ ActuatorAir line from solenoidActuatorBall valve bodyProcess line

PI Plant Information SystemPI is a process data historization/ data retrieval systemPI server (Steam) is PDC for control room network and is also on WE networkPI data are available anywhere on campus networkPIPC is Excel add-inProcessBook is graphical tool for viewing process and process dataPI Server- OPC Interface

PI Plant Information SystemData Historian system is required part of process management systemLong-term data storage/ retrieval systemOptimizes use of hard drive storage space and permits quick recall of archived dataIncludes data retrieval software toolsOSISoft, Inc. PI systemImport process data into supervisory control or process monitoring applicationsLink process control systems with business management systemsProvide data for production and compliance reporting

PI How it worksA PI tag is configured for every piece of data you want to archiveCollected tags are scheduled to retrieve data periodically or upon the occurrence of an eventData are brought into the archive thru a filtering and compression algorithmData are not archived unless they pass the filter and compression testsWhen data are retrieved from the archive and presented in a series, the individual points are extrapolated between the stored dataTags can also be manually entered lab data