SI-MRT-XX-105 [2]

A Technical ComparisonA Technical Comparison

DCS versus PLC’sPresented

By

Jim Cushman

Emerson Process Management

Power & Water Solutions

[File Name or Event]Emerson Confidential27-Jun-01, Slide 2

SI-MRT-XX-105 [2]

Relays

Electrical

Instrumentation

Loop

Controllers

Integrated

Control

Process Controls

DCS

Field Intelligence,

Comm Tech,

IT Integration

PlantWeb

Evolution in AutomationEvolution in AutomationEvolution in Automation

1970 1980 1990 2000

Low cost

Compact

Factory Automation

µP Control

PLCs

PID loops

Logic sequences

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History of PLCHistory of PLCHistory 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

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History of DCSHistory of DCSHistory 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

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DCS Designed with Latest TechnologyDCS Designed with Latest DCS Designed with Latest TechnologyTechnology

� 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)

DCS Architecture

PLC-MMI Architecture

Realtime

Data

Server

(Single point

failure here)

CTLRCTLR CTLRCTLR

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Remote Site

Redundant

RadiosPLC/RTU

RS232 or Ethernet

Repeater Site

In Out

Radio Repeater

eDBOvation

Engineer

Redundant

SCADA Servers

Ovation Network

RS232 or Ethernet

Control Room

DCS - SCADA ConfigurationDCS DCS -- SCADA ConfigurationSCADA Configuration

CTLRCTLR

Local Site

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Comparison Of PLC & DCSOperator InterfaceComparison Of PLC & DCSComparison Of PLC & DCSOperator InterfaceOperator 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

� 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.

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Comparison of PLC & DCSConfiguration Vs ProgrammingComparison of PLC & DCSComparison of PLC & DCSConfiguration Vs ProgrammingConfiguration Vs Programming

� PLC Programming is usuallythe familiar ladder logic

� PLC Programming requires writing of logic for alarms and signal conditioning

� Challenge to write analog PID control using ladder logic

� DCS configuration uses graphical function blocks that follow SAMAstandards

� 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

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DCS Windows EditionDeveloper StudioDCS Windows EditionDCS Windows EditionDeveloper StudioDeveloper Studio

� System Configuration

� Tools

� System Database Tools

� Control Builder

� Graphics Builder

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Comparison of PLC & DCSControl AlgorithmsComparison of PLC & DCSComparison of PLC & DCSControl AlgorithmsControl Algorithms

� PLC does not have standard algorithms and requires programmers to build the logical conditions and equations from scratch

� 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.

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� 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

DCS Developer StudioDCS Developer StudioDCS Developer Studio

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Data and Event Historian of PLC & DCS Operator InterfaceData and Event Historian of PLC & Data and Event Historian of PLC & DCS Operator InterfaceDCS Operator Interface

� Data historian is often a basic package supplied by the HMI software vendor

� Little analysis and exportingcapability

� Difficult to integrate a sophisticated historianpackage and requires a new configuration database

� DCS uses a sophisticated historianengine as a standard.

� The link and configuration is integrated within the single database of DCS. Analysis of cause and effect can be done.

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DCS Operator Interface - HMIDCS Operator Interface DCS Operator Interface -- HMIHMI

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DCS DCS eDBeDB Historian Architecture Features Historian Architecture Features Distributed Data ScannersDistributed Data Scanners

OPC Server

WEStation

DCS WDPFII

Third-Party

TCP/IP

Network

eDBHistorian

eDBHistorian

Controller

� 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

� Does not rely on process data network — requires only TCP/IP

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Alarm Management of PLC & DCSOperator Machine InterfaceAlarm Management of PLC & DCSAlarm Management of PLC & DCSOperator Machine InterfaceOperator 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

� DCS alarm management is built upon the strength of DCS

� DCS enhances alarm management by

– minimizing nuisance alarms

– simplifying alarm tracing

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DCS Operator Station FunctionsDCS Operator Station FunctionsDCS Operator Station Functions

Process Diagrams

Point Menu

Trends

Alarm System

Point Reviews

Options

� Compatible with Solaris

process diagrams

� Triggers display of trends,

graphics and point information

� 3-D graph option

� Drag & Drop trend building

with points

� Trend groups

� Alarm List, Alarm History,

Unacknowledged Alarms &

Reset List functions

� DCS alarm functionality - 4

high & 4 low limits

� Iconic and audible alarms

� Similar to Solaris but with

different look & feel

� DCS membrane keyboard

and dual-CRT options

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DCS Operator Station FunctionsDCS Operator Station Functions

� 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

Alarm System

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Comparison of PLC & DCSSmart Transmitter InterfaceComparison of PLC & DCSComparison of PLC & DCSSmart Transmitter InterfaceSmart Transmitter Interface

� PLC presently lack smart interfaces and have to use workaround solution

� Not proactive Field Bus and Open Architecture technologies

� HART is available with DCS

� DCS provides implementation to Foundation Fieldbus in a customer plant

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Manage

the

Process

DCS

Manage

the Field

Devices

AMS Inside

HART AI & AO

Modules

AMS Pass

Through SW

Control RoomMaintenance Shop

DCS with HART I/O Modules & AMSDCS with HART I/O Modules & AMSDCS with HART I/O Modules & AMS

CTLR CTLR

[File Name or Event]Emerson Confidential27-Jun-01, Slide 23

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AMS (Asset Management Software)AMS (Asset Management Software)AMS (Asset Management Software)

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Comparison of PLC & DCSDiagnostics and Failure HandlingComparison of PLC & DCSComparison of PLC & DCSDiagnostics and Failure HandlingDiagnostics and Failure Handling

� PLCs have relatively little diagnostic status and may only be indicative

� Limited use of diagnostic bits in logic

� 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 fieldinstruments including HART & Fieldbus.

� DCS I/O is selectable either in HOLD-LAST or FAIL-SAFE positions in the event of failure

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Comparison of PLC & DCSAdvanced ControlComparison of PLC & DCSComparison of PLC & DCSAdvanced ControlAdvanced Control

� PLC has limited advanced control features

� A primitive auto-tuningsoftware is all they can show

� 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”

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Comparison of PLC & DCSHardware FunctionalityComparison of PLC & DCSComparison of PLC & DCSHardware FunctionalityHardware Functionality

� PLC I/O does NOT support hot swap especially those in remote areas

� Limited redundancy options

� DCS cards have complete diagnostic and hot swapcapability

� DCS has redundancyoptions for most key hardware components

� A highly scalable system that allows you to add/change or upgradeworkstation, controller, I/O online.

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Lower Total Cost of OwnershipLower Total Cost of OwnershipLower 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

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You DecideYou DecideYou 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?

� DCS provide best value, highest return, lowest long term running cost.

AMS

Systems ComparisonSystems ComparisonSystems Comparison

Redundancy

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

Programming/Configuration

Drag & Drop Configuration Yes Some Some Some

Device Configuration Change Tracking

Yes No No No

Configuration Audit Trail Yes No No No

Systems Comparison (Cont’d.)Systems Comparison (ContSystems Comparison (Cont’’d.)d.)

Traditional Control Technology

Ovation Siemens PCS7

Rockwell ProcessLogix

Rockwell ControlLogix

Regulatory Yes Some Yes Some

Sequence Yes Yes Some Yes

Advanced Control Technology

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

Systems Comparison (Cont’d.)Systems Comparison (ContSystems Comparison (Cont’’d.)d.)

Service and Support

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

Systems Comparison (Cont’d.)Systems Comparison (ContSystems Comparison (Cont’’d.)d.)

System Management

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

System Architecture

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

Systems Comparison (Cont’d.)Systems Comparison (ContSystems Comparison (Cont’’d.)d.)

System Aspects

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