A Technical Comparison DCS versus PLC’s Presented By Jim Cushman Emerson Process Management Power & Water Solutions
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Evolution in Automation Instrumentation
Process Controls
Loop Controllers
DCS
PID loops Electrical
Integrated Control Factory Automation
Relays
µP Control PLCs
Logic sequences
Low cost Compact
1970 [File Name or Event] Emerson Confidential 27-Jun-01, Slide 2
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1980
1990
Field Intelligence, Comm Tech, IT Integration
PlantWeb
2000
History of PLC
Developed from Automotive Assembly and Factory Automation where discrete points are used Developed to replace mechanical timers and solid state relays Evolved where process restart is not a major concern but processing speed is important Designed with digital logic as the most important design feature
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 3
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History of DCS
Evolved from single loop controllers
Evolved from analog based signal handling
Evolved with extensive involvement from the process control end-users
Developed with alarm handling, diagnostics and fail safe as important design feature
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 4
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DCS Designed with Latest Technology
Windows or Solaris platform “Off-the-shelf” Pentium controller “Off-the-shelf” Ethernet network Oracle configuration database Oracle historical process data AutoCAD control builder (varies between vendor)
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 5
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CTLRCTLR
CTLRCTLR
DCS Architecture Realtime Data Server
(Single point failure here)
PLC-MMI Architecture
DCS - SCADA Configuration Control Room
Local Site CTLR CTLR
Ovation eDB Engineer
RS232 or Ethernet Redundant SCADA Servers
Ovation Network
Redundant PLC/RTU Radios RS232 or Ethernet
Remote Site [File Name or Event] Emerson Confidential 27-Jun-01, Slide 7
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In
Out
Radio Repeater Repeater Site
Comparison Of PLC & DCS Operator Interface
PLC HMI have a separate database from the control system and needs to be configured separately. Database consistency is a major issue Alarms and faceplates have to be specially configured PLC station to station communications are tedious and are via third party integrators
Requires the use of network servers, external hard disks with huge configuration effort
Limited OPC server functionality
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 8
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DCS HMI is part of the single integrated database
DCS has built in feature in the HMI as standard and optimized for handling alarm messages and data from controllers
Real time integration is available via a serial card, OPC, or NetDDE.
Transaction integration is via Historian.
Comparison of PLC & DCS Configuration Vs Programming
PLC Programming is usually the familiar ladder logic
PLC Programming requires writing of logic for alarms and signal conditioning
Challenge to write analog PID control using ladder logic
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 9
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DCS configuration uses graphical function blocks that follow SAMA standards
DCS configuration comes with alarms and signal conditioning as standard, part of the database parameters
It is generally easier to understand a Boolean Logic Block diagram than separate analog logic diagram and ladder logic diagram
DCS Windows Edition Developer Studio
System Configuration
Tools
System Database Tools
Control Builder
Graphics Builder
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 10
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Comparison of PLC & DCS Control Algorithms
PLC does not have standard algorithms and requires programmers to build the logical conditions and equations from scratch
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 12
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Besides having a standard library of algorithms such as PID, lead-lag, etc., DCS also features other in DCS such as drag-and-drop configuration and graphical configuration.
DCS Developer Studio
The DCS System Database manages all items in the system – – – –
Input, output and calculated points Control modules Process graphics System configuration
This allows simplified engineering via standard drag & drop functionality – Drag & drop points, control, graphics and system configuration to desired locations – Download changes
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 13
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Data and Event Historian of PLC & DCS Operator Interface
Data historian is often a basic package supplied by the HMI software vendor
Little analysis and exporting capability
Difficult to integrate a sophisticated historian package and requires a new configuration database
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 14
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DCS uses a sophisticated historian engine as a standard.
The link and configuration is integrated within the single database of DCS. Analysis of cause and effect can be done.
DCS Operator Interface - HMI
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 15
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DCS eDB Historian Architecture Features Distributed Data Scanners
Data scanning is de-coupled from the eDB database server
Scanners to be available for DCS, WDPF and OPC
Scans process values and sends exceptions, aggregates and messages to the eDB
Scanner buffer stores during brief network or server outages
eDB Historian TCP/IP Network DCS
WDPFII
Does not rely on process data network — requires only TCP/IP Third-Party WEStation Controller OPC Server
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 16
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Alarm Management of PLC & DCS Operator Machine Interface
Certain alarms and faceplates have to be specially configured Very basic alarm handling capability that is built for discrete industry
Difficult to bring maintenance bits/flags into alarm system.
Difficult to relate alarms with operational philosophy
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 17
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DCS alarm management is built upon the strength of DCS
DCS enhances alarm management by – minimizing nuisance alarms – simplifying alarm tracing
DCS Operator Station Functions Process Diagrams
Compatible with Solaris process diagrams
Alarm System
Alarm List, Alarm History, Unacknowledged Alarms & Reset List functions
DCS alarm functionality - 4 high & 4 low limits
Iconic and audible alarms
Point Menu
Triggers display of trends, graphics and point information
Trends
3-D graph option
Drag & Drop trend building with points
Trend groups
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 18
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Point Reviews
Similar to Solaris but with different look & feel
Options
DCS membrane keyboard and dual-CRT options
DCS Operator Station Functions Alarm System
Tabs for mode switching between List, History,Unacknowledged, and Reset displays
Find function to locate alarm points
Title bars move for more or less information displayed
Moveable menu tool bar
Number of alarm windows configurable based on system limitations
Line-by-line printing of alarm messages to a local printer
User-selectable fonts; standard alarm fields displayed or removed by menu selection
Audible alarms use Wave files
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 19
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Comparison of PLC & DCS Smart Transmitter Interface
PLC presently lack smart interfaces and have to use workaround solution Not proactive Field Bus and Open Architecture technologies
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 21
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HART is available with DCS
DCS provides implementation to Foundation Fieldbus in a customer plant
DCS with HART I/O Modules & AMS Maintenance Shop
Control Room
Manage the Field Devices AMS Inside
Manage the Process DCS AMS Pass Through SW
CTLR
CTLR
HART AI & AO Modules [File Name or Event] Emerson Confidential 27-Jun-01, Slide 22
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AMS (Asset Management Software)
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 23
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Comparison of PLC & DCS Diagnostics and Failure Handling
PLCs have relatively little diagnostic status and may only be indicative
Limited use of diagnostic bits in logic
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 24
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All key diagnostic bits reflecting system health status can participate in logics for proper safety actions
DCS diagnostics allow us to drill down all the way to the field instruments including HART & Fieldbus.
DCS I/O is selectable either in HOLD-LAST or FAIL-SAFE positions in the event of failure
Comparison of PLC & DCS Advanced Control
PLC has limited advanced control features
A primitive auto-tuning software is all they can show
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 25
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DCS has all the depth and experience of implementing advanced control
DCS has a full suite of advanced control applications to improve yield and productivity known as “ Smart Process”
Comparison of PLC & DCS Hardware Functionality
PLC I/O does NOT support hot swap especially those in remote areas
DCS cards have complete diagnostic and hot swap capability
Limited redundancy options
DCS has redundancy options for most key hardware components
A highly scalable system that allows you to add/change or upgrade workstation, controller, I/O online.
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 26
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Lower Total Cost of Ownership
Total cost of ownership, including long term maintenance, upgrades, and replacement cost, is typically lower for a DCS. – – – – –
configuration savings start up savings long term maintenance upgrade/expansion change management vs. replacement
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 27
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You Decide
A PLC-HMI system will work. It will run your plant. It will do ladder logic. It will even do PID control. – – – –
Can you integrate well with external systems? Do you have easy to use Advanced Control? Do you have performance monitoring software? Do you have an integrated asset management solution?
AMS
DCS provide best value, highest return, lowest long term running cost.
[File Name or Event] Emerson Confidential 27-Jun-01, Slide 28
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Systems Comparison Ovation
Siemens PCS7
Rockwell ProcessLogix
Rockwell ControlLogix
Controller Redundancy
Yes
Some
Some
Some
Controller Power Supply Redundancy
Yes
Some
Some
Some
Communications Redundancy
Yes
Some
Some
No
Drag & Drop Configuration
Yes
Some
Some
Some
Device Configuration Change Tracking
Yes
No
No
No
Configuration Audit Trail
Yes
No
No
No
Redundancy
Programming/Configuration
Systems Comparison (Cont ’d.) (Cont’d.) Ovation
Siemens PCS7
Rockwell ProcessLogix
Rockwell ControlLogix
Regulatory
Yes
Some
Yes
Some
Sequence
Yes
Yes
Some
Yes
Fuzzy Logic
Yes
No
No
No
Neural Network Technology
Yes
No
No
No
Auto-Tune Technology
Yes
No
Some
Some
Multivariable Predictive Control
Yes
No
No
No
Traditional Control Technology
Advanced Control Technology
Systems Comparison (Cont ’d.) (Cont’d.) Ovation
Siemens PCS7
Rockwell ProcessLogix
Rockwell ControlLogix
24 x 7 Technical Support Worldwide
Yes
Some
Some
Some
Configuration Services
Yes
Yes
Some
Some
Hardware Maintenance Services
Yes
Some
Some
Some
Installation Services
Yes
Yes
Some
Some
Software Support & Upgrade Support
Yes
Some
Some
Some
Training
Yes
Yes
Some
Some
Single Source Supplier
Yes
Some
Some
Some
Service and Support
Systems Comparison (Cont ’d.) (Cont’d.) Ovation
Siemens PCS7
Rockwell ProcessLogix
Rockwell ControlLogix
Event Historian
Yes
Some
Some
Some
Sequence of Events Recording
Yes
Some
Some
Some
Asset Management
Yes
No
No
No
Global Database
Yes
No
No
No
Alarm Time Stamping
Yes
No
Some
Some
DCS / PLC Integration
Yes
Some
Some
Some
Scalable
Yes
Some
Some
Some
OPC Support
Yes
Some
Yes
Yes
Automated System Time Management
Yes
Some
Some
Some
Automated System Diagnostics
Yes
Some
Some
Some
System Management
System Architecture
Systems Comparison (Cont ’d.) (Cont’d.) Ovation
Siemens PCS7
Rockwell ProcessLogix
Rockwell ControlLogix
Time Synchronization Capability
Yes
No
No
No
Online Upgrade
Yes
No
No
No
Modifications without Shutdown
Yes
No
No
No
Support for Control in the Field
Yes
No
No
No
OPC Alarms and Events
Yes
No
No
No
Scalability
Yes
Some
Some
Some
I/O Simulation Capability
Yes
No
No
No
System Aspects
