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Implementing Mission Critical Data

Connectivity with OPC Eric Murphy,P.Eng-2008

From oil rening to industrial manufacturing to powergeneration, no matter what business people are in,

they depend on certain systems to run their business.

Today’s world turns on the uninterrupted ow of data

and communications and to keep it owing, OPC plays

an increasingly mission-critical role in the enterprise. 

In the early days of OPC adoption, systems tended to

be limited to supervisory applications, history collectionand auxiliary data systems. This was due to a reluctan

to use PC based platforms in the control environment.

As Microsoft operating systems and Ethernet based

communications became more reliable and accepted,

major control system vendors introduced operator

stations, engineering consoles and application platform

running on PC hardware. These factors coupled with

the rise of OPC as the preferred communication

standard led to an accelerating penetration of OPC intomission critical architectures. OPC is now a cornerstone

component of many mission-critical or near safety-

critical applications such as turbine-compressor

monitoring, burner management systems, rail system

management, radiation detection and reporting, and

many more. This has signicantly increased the need t

assure that OPC can deliver reliable 24 - 7 operations.

 

Execve Smm

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What DoES MiSSion CritiCal MEan?

While there are differences of opinion about the denition of mission-criticalapplications, the general consensus of what “mission critical” means centers onthe following attributes: 

• Critical role: The role of software in fullling the mission must be crucialto the successful performance of the organization in which it is used.

• Critical view: The operational or controlling view of the system must bemaintained at all times to ensure safe or proper operation.

• Critical data: Environments which monitor, store, support andcommunicate data cannot lose or corrupt the data without compromisingtheir core function.

 Once an application or components of an architecture are deemed to bemission critical, the next step is determining what can go wrong. A basicOPC system is comprised of an OPC client on one PC, communicating over

the network to an OPC server on another machine. This involves multipleopportunities for system failure, including hardware faults, software oroperating system incidents, and cabling or network routing failures.

What iS thE Solution?

One guiding principle for OPC mission-critical design is that the infrastructureis only as reliable as its components. The entire system must be made faulttolerant and able to remain functional in the event of a failure of one of thecomponents. Adding redundant components signicantly increases both faulttolerance and system reliability. In response to this need many OPC vendorsare supplying products that enable OPC redundancy at multiple levels in theOPC architecture. A common system conguration is the three tier redundancymodel.

oPC thrEE tiEr rEDunDanCy MoDEl

As the name implies, this model applies redundant software andcommunication channels at the three major levels of the architecture; the OPCclient application, the OPC server and the end device or data source.

Often in mission critical systems, the controller or data collection device is of a fault tolerant design and is implemented in a redundant primary/secondaryconguration. In order for an OPC server collecting data from these devicesto seamlessly handle the dual conguration, it needs to have been designedto support device level redundancy. This means that a single OPC server canfail between two devices congured as a redundant pair, in a timely fashionwithout any action required by the OPC client. Increasingly more OPC vendorsare offering OPC servers that support device or communication channel

redundancy, particularly for controllers that are commonly installed in aredundant conguration.

One guiding principle for OPC

mission-critical design is that

the infrastructure is only as

reliable as its components.

The entire system must be

made fault tolerant and able

to remain functional in the

event of a failure of one of the

components.

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Server level redundancy behaves in a similar manner, in that a single OPC

client can fail between two OPC servers that have been implemented asa redundant primary/secondary pair. Typically this requires that the OPCvendor has implemented the redundancy functionality as part of the OPCclient design. However, due to the nature of the OPC standard, server levelredundancy is possible even if the OPC client has not been designed forredundancy. Since any OPC client can communicate with any OPC server, aredundancy enabled middleware application or broker can be inserted intoany OPC architecture. The OPC redundancy wedge proxies all communicationbetween the OPC client and the redundant OPC server pair and handlesall aspects of the failover, such as how and when failover occurs, initiatingconnections, OPC item management and clean up.

The nal tier, application level redundancy often encompasses morefunctionality than just the OPC client connections. A typical congurationinvolves two applications running as a redundant pair that are continuouslyexchanging ‘heartbeat’ messages or status information. In the event thesecondary application losses communication to the primary application, it

will establish a connection to the OPC server and assume the data collectionresponsibilities.

Fge 1 - oPC tee te reddc Mde

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In some cases data collection is deemed critical due to regulatoryrequirements, such as the data required for U.S. Environmental ProtectionAgency (EPA) reporting. A real world use case is the Continuous EmissionsMonitoring Systems (CEMS) used to collect data for the Environmental Groupat Santee Cooper. The CEMS system provides information on gas turbineoperation to ensure environmental standards are enforced. This criticalsystem must function correctly and the data stream must be continuous.Emission reporting requires a minimum 98% uptime. Failure to meet reportingstandards could result in nes and other penalties. Santee Cooper usesMatrikonOPC products in a multiple level OPC redundancy architecture toensure meeting this requirement.

Santee Cooper Automates

Processes to Gain Step Change

in Efciency. Read the whole

case study for the full details

on how OPC redundancy can be

used in real world situations.

Fge 2 - Mpe te reddc Mde

Although the stability of off-the-shelf computer hardware and operatingsystems has improved signicantly over the last few years, system failurescan and still do occur. A proper redundant OPC architecture can prevent thesecomponent failures from leading to loss of control or a disruption of electrical

service. In order to ensure the constant operation of their OPC applications,industry leaders turn to OPC vendors and products like MatrikonOPC that

provide mission critical redundancy. Power generation, transmission, anddistribution utilities provide critical services to people every day. MatrikonOPCand their OPC redundancy products ensure their crucial control data is alwaysavailable.

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MoPC reddc Be ffes semesssfwe s mpemes dve eve eddc

sppg b oPC Da d a&E.

te MoPC reddc Be (orB) ebes es mpeme f eddc ssems

e dvge f oPC ecg. orB s desged f oPC ppcs ms seedd dwe d/ sfwe ceve e ges degee f cmmc eb.ORB can even be retrotted to current systems since ORB functions with any OPC server, regardlessf ved.

Fees cde:

• Support for multiple, same server, redundant pairs• Spp f oPC Da d oPC a&E• Ss gs ebe c wc oPC Seves e dw• Mpe eves f eddc• F spp f MoPC tee• Powerful event engine integration (trigger on item deviation, threshold, rate of change,

quality, etc.)• nw e bmpess fve ebes orB be DCoM mes

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aBout thE author 

Eric Murphy, BSc, PEng, is a Chemical Engineer with a ProcessControl specialization and an OPC expert. Eric has been a part of the OPC community since its early beginnings. Eric is heavily involved with theOPC Foundation and currently acts as the chair forthe OPC Historical Data Access (HDA) working group. Eric is also amember of the OPC Technical Advisory Council (TAC) and an active

member of the OPC Unied Architecture (UA) working group.Eric has worked for companies including Honeywell and MatrikonOPC, holdingpositions including software development architect,OPC R&D Manager, OPC Project Manager and OPC QA Manager.Eric has acted as chief consultant on hundreds of OPC projectswhere he has architected standards based OPC solutions.

You can often nd Eric presenting online as the featured speakerfor webcasts or at industry related events such as ISA Expos, OPC

Conferences and other events.

For MorE inForMation on oPC arChitECturESFor more information on OPC Redundancy and other OPC topics, besure to follow up with these associated titles on our website athttp://www.MatrikonOPC.com

oPC reddc – Pwe f PeveAlthough the stability of off-the-shelf computer hardware and operatingsystems has improved signicantly over the last few years, system failurescan and still do occur. A proper redundant OPC architecture can prevent thesecomponent failures from leading to loss of control or a disruption of electrical

service. In order to ensure the constant operation of their OPC applications,industry leaders turn to OPC vendors and products like MatrikonOPC thatprovide mission critical redundancy

Cse Sd: oPC reddc Cc P appcsSibur-Tumen Uses OPC Redundancy in Critical Plant Application.

 “With MatrikonOPC’s OPC Redundancy Broker, there has been no systemdowntime and no data loss.” Said Yuri Simakov, Chief of Industrial AutomationDepartment, Sterling Group. Read the case study to nd out how.