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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

Process Control and Data Acquisition Systems


Chemical Plant Operations

Distributed control system dcs architecture
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

Programmable logic controller plc architecture
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

Scada supervisory control and data acquisition system
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

Rockwell automation processlogix dcs and osisoft pi in pscc

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

Processlogix how it works

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

Processlogix how it works1

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

Processlogix how it works2

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

Plx controller cabinet

PLX controller

I/O cards

Zener barriers

8 pr. cables from field junction cabinet

2nd I/O chassis

PLX Controller Cabinet

Field junction cabinet

8 pr. Cables to controller cabinet

Field Junction Cabinet

Single pairs from field device

Field devices transmitters
Field Devices – Transmitters

Wiring to field junction cabinet

Level transmitter

Thermocouple head

Wiring from transmitter to measuring element

Temperature transmitter

Field devices transducer
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

Field devices regulatory control valve
Field Devices – Regulatory Control Valve

Air line from transducer

Actuator w/ positioner

Control valve

Block valves

Bypass valve

Field devices ball valve w actuator
Field Devices – Ball Valve w/ Actuator

Air line from solenoid

Ball valve body


Process line

Pi plant information system

WE Network


- ProcessBook

Control Room

Network Switch



- 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

Pi plant information system1
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

Pi how it works
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