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OPC FAQCan I run an OPC Server as a Windows service and what would be the benefits?

An OPC Server can execute as a Windows service. The benefit of this operation is the

OPC Server will start with the Operating System. t will even ta!e the identity of theOperating System which is desirable in some cases.

Some OPC Servers cannot execute as a Windows Service. This will either re"uire a user

to be logged on to the PC# or some other application to initiate the operation of the OPCServer.

Can I use my HMI software to tunnel OPC data between PCs?

$any products can be used to as an OPC tunnel. Some people use an %$ or even their

%istorian to provide OPC Tunneling services. %owever# in most cases# an OPC tunnel provides a far easier way to transfer data since the OPC tunnels are typically

 preconfigured for the specific tas! of transferring data rather than visuali&ing or storingit.

Can OPC be configured to work on inu!?

Classic OPC was based solely on $icrosoft's (CO$ for data transportation.

Conse"uently# OPC applications typically reside on Windows. There are ports of (CO$to other operating systems )such as *inux+. Conse"uently# OPC will wor! on those

systems as well.

With OPC ,A the OPC -oundation wrote its own services for the data transportation.The OPC -oundation is providing source code to developers who can then port the

technology to any operating system.

Can OPC be configured to work on Microsoft Windows "ista #$ bit?

Classic OPC )based on (CO$+ wor!s on any operating system that supports (CO$.

$icrosoft ista supports (CO$ )even in the /0 bit version+# thus OPC will wor! on

Windows ista /0 bit. n addition# OPC also functions properly between 12 and /0 bitsystems.

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Can OPC %& '%nified &rchitecture( be used on non)Windows O*erating Systems?

Classic OPC was based solely on $icrosoft's (CO$ for data transportation.

Conse"uently# OPC applications typically reside on Windows. There are ports of (CO$to other operating systems )such as *inux+. Conse"uently# OPC will wor! on those

systems as well.

With OPC ,A the OPC -oundation wrote its own services for the data transportation.The OPC -oundation is providing source code to developers who can then port the

technology to any operating system.

+o I have to u*date all com*uters to the same OPC distributable *ackage?

OPC provides specifications that enable applications to communicate with each other. As

vendors release their software# and apply patches and upgrades# they provide differentexecutables )distributable pac!ages+. %owever# to ensure successful OPC

communication# users do not need to ensure that all their applications have the samereleases. While this may be a good practice in some situations# it is not necessary. OPC

compliant applications that support the same release of an OPC specification will be able

to communicate with each other regardless of their vendor's release.

+o I need to add my OPC a**lications 'OPC clients and OPC servers( to the list of e!ce*tions in my

anti virus software '&vg, Panda antivirus, &vast, -as*ersky, Mc&fee, Microsoft +efender, Microsoft

Windows Security .ssentials, /orton, Symantec, etc(?

Antivirus software detects viruses and other malware )tro3ans# worms# etc+. Anti virus

applications protect your computer from unwanted activities. These applications should

not catch OPC servers because the servers are not harming the computer. %owever# it is

 possible future automated updates may incorrectly flag your OPC applications.Therefore# you should add your OPC clients and servers to the exception list so that they

will not be accidentally stopped in the future.

/ote0 these anti4virus applications are only one part of a cyber security measures. Toimprove your protection# you should also deploy firewalls on each computer# and restrict

user account access. -or an automated solution# refer to OPC 5escue.

.rror with CSI+12345265+)7.5C)$$d8)4C56)$.339#4:#;3;<

Problem6 When trying to configure (CO$ components within (CO$C7-8# Windows

issues the following (CO$ configuration warning6

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The CLSID {1F87137D-0E7C-44d5-8C73-4EFFB68962F2}, item

C:!I"D#!SS$%tem32&'em&mi()*%e+ee .d tit/e i)%t !I )*ide)

S'%$%tem Se)ed %t h% the .med */e ((ID, 't i% .t )e)ded .de)ECLSSES;##T((Id+ D $ &i%h t )e)d it<

Cause6 n Windows 9P# the most common cause of this problem is the following

Windows ,pdate6Se)it$ =(dte ) !i.d&% > ?B956572@

,nfortunately# this update is only valid on Windows 2::1 )as per $icrosoft;sdocumentation+. Adding to the complexity# not all Windows 9P installations are affected

 by this update.

 7otes6

o Clic!ing the <=es< or <7o< buttons does not solve the problem

o This is /O= caused by a dis! drive corruption or failure

o =ou do /O= need to reformat your computer 

Suggested action6 ,ninstall <Se)it$ =(dte ) !i.d&% > ?B956572@<. %owever#

if you are already in the process of reinstalling Windows# simply ensure you do not apply

this update.

How can I ac>uire data from an OPC Server through a firewall?

To configure OPC communication to pass through a firewall# you must open a port for(CO$ communication and provide application exceptions. Specifically# you must

configure your firewall as below.#C C/ie.t C .iA)ti.: -irst# you must provide exceptions for (CO$;s end4point

mapping )>P$AP+ functions on TCP port ?1@. =ou must also provide exceptions for

OPC Client applications.#C Se)*e) C .iA)ti.: -irst# you must provide exceptions for (CO$;s end4point

mapper )>P$AP+ on TCP port ?1@. Then you must provide exceptions for both the OPC

Server as well as Opc>num.(CO$ will ta!e over from there# and will only re"uire enabling 0 ports to establish

communication. *uc!ily# (CO$ will find these ports automatically.

(CO$ can also be configured to pass information across static )or fixed+ ports so it canwor! well with external or hardware firewalls. n this case# only 2 ports will benecessary.

OPCT;s *evel 26 OPC Security and *evel 06 Advanced OPC Pro3ects cover this

configuration extensively. -or automated firewall configuration# refer to OPC 5escue.Additional resources6

o iew data and diagnose compatibility problems www.Opc>xpert.com. OPC

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>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#

and much more.

o Training classes )physical and online+ at http6www.opcti.comTraining4

Schedule.aspx

How can I ac>uire data from an OPC Server through a router?

OPC wor!s seamlessly through most routers. %owever# any router that provides 7AT

)7etwor! Address Translation+ services will stop (CO$ from wor!ing. This is because

the OPC Server PC must be able to address the OPC Client PC directly.n practice# most routers that are internal to a sitecompany do not use 7AT. %owever#

5outers that provide communication to the nternet typically use 7AT and will stop OPC

communication. f your OPC applications are separated by a router that uses 7AT# you

will have to either use Tunneling technology or use OPC ,A )which uses web4services toestablish communication instead of (CO$+.

How can I diagnose the cause of an OPC interface to sto* collecting data?

n general# there are three ways to diagnose a failure in communication.

-irst# loo! at the log files of both OPC applications. Often they will indicate if theapplication failed to receive a re"uest# or failed to receive a reply. The log files will also

indicate whether or not the application sent a re"uest for a reply. This will help you toisolate the cause of the problem and determine whether the source of the

miscommunication was on the OPC Client or Server end. 7ote that the amount of

information in a log file is controlled by that application's vendor. OPC specifications donot specify the type of information to log. 7evertheless# logging any information that

would help a person find the cause of problem is good practice.

Second# loo! at the Windows event log to find out if there were any errors logged by

Windows. This will also help you to isolate the cause of the problem.Third# use a third4party application to log the OPC communication between the OPC

Client and OPC Server. These applications )often called <sniffers< or <loggers<+ simplycapture the communication between the OPC Client and server and record all the calls ina log file. The integrator can then read through the file and determine the cause of the

 problem.

Additional resources6

o iew data and diagnose connectivity problems www.Opc>xpert.com. OPC

>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#

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and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com

o Training classes )physical and online+ at http6www.opcti.comTraining4Schedule.aspx

How can I use OPC across different com*uter domains?

OPC applications can communicate with each other even when they are on different

Windows (omains. The tric! to getting communication wor!ing is Windows

Authentication on both the OPC Client and OPC Server PCs.-irst# the OPC Server PC must recogni&e the ,ser Account of the OPC Client PC.

Therefore the ,ser Account of the OPC Client must exist in the Active (irectory )locatedon the (omain Controller+ of the OPC Server PC. Alternatively# the OPC Server PC must

have a local ,ser Account setup for the OPC Client application.

Second# the OPC Client PC must recogni&e the ,ser Account of the OPC Server PC.Therefore the ,ser Account of the OPC Server must exist in the Active (irectory

)located on the (omain Controller+ of the OPC Client PC. Alternatively# the OPC Client

PC must have a local ,ser Account setup for the OPC Server application.

All this can be made easier if the S )nformation Systems+ or T )nformationTechnology+ staff setup a Trust between the two Windows (omains. This will ensure that

all ,ser Accounts will be automatically synchroni&ed between the two (omains.

How do I know when my OPC Server has lost its connection with its data source 'such as a PC,

+CS, &nalyer, etc(?

OPC Servers that lose communication with their data source )such as a P*C# (CS#

Analy&er# etc+# should indicate that the process values now have <Bad uality<. naddition# they should also indicate the reason for this <Bad uality<. -or example# an

OPC Server can indicate the uality value is <Bad< because it lost communication with

the data source# or the item in "uestion is <out of range< or there was a <Sensor -ailure<#etc.These "uality values can clearly indicate that the loss of communication was due to a

failure between the OPC Server and its data source# rather than a communication

 problem between the OPC Client and OPC Server. endors can choose to implement thistype of diagnosis in their OPC Server or not. Therefore# some OPC Servers provide no

diagnosis at all.

The ability to diagnose problems and pass the results in a uality parameter is an

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important feature that will help you to differentiate between various vendors. OPC

specifications provide a list of possible error values.

How do Workgrou*s and +omains affect OPC connectivity via +COM?

Computers on a Wor!group do not use an external PC )(omain Controller with the

Active (irectory+ to help with the process of Authentication. nstead# they rely on their

own information for Authentication.Suppose an OPC Client application# which resides on a Wor!group# communicates with

an OPC Server on a (omain. n this case# the OPC Client application's ,ser Account

must either exist on the (omain Controller )of the OPC Server PC+# or on the OPCServer PC itself. -urthermore# the ,ser Account of the OPC Server must exist on the

OPC Client application's PC.

Suppose that an OPC Client application that resides on a (omain communicates with anOPC Server on a Wor!group. n this case# the OPC Client application's ,ser Account

must exist on the OPC Server PC itself. -urthermore# the ,ser Account of the OPC

Server must either exist on the (omain Controller )of the OPC Client PC+# or the OPCClient application's PC.

How does OPC read and write data from and to a PC?

An OPC Server provides data to an OPC Client application )such as an %$# %istorian#

etc+ using OPC. %owever# an OPC Server always uses a non4OPC method to exchangedata with a P*C.

-or example# suppose an OPC Server communicates with a P*C using the $odbus

 protocol. n this case# the OPC Server will as! the P*C for specific memory addressesthat contain the data that the OPC Server re"uires. This is done using the $odbus

 protocol. The P*C provides all the responses to the OPC Server using $odbus as well.

This way# the OPC Server can read data from# and write data to the P*C using $odbus.The OPC Server then converts the data it retrieves from the P*C )using $odbus+# to

OPC <format#< and sends the data to an OPC Client application.

n every case# the OPC Server must !now something very specific about the P*C towhich it connects. At minimum# it needs to !now the protocolAP spo!en by the P*C.

%owever# in most cases# the integrator needs to configure the OPC Server for the specificinformation the P*C contains# which will change from pro3ect to pro3ect. n every case#

once the integrator configures the OPC Server properly# any OPC Client application canretrieve data from the OPC Server without having to !now anything about the P*C or its

configuration.

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How does the *erformance of OPC com*are with communication over a serial line?

OPC can transfer tens of thousands of values per second. Some OPC Servers have been

cloc!ed at over ?::#::: values per second. On the other hand# serial communicationtypically provides data transfer rates of around 1:: values per second# or a little more.

Thus# OPC does not add a new communication bottlenec!. Typically bottlenec!s are a

result of non4OPC related factors such as external networ! limitations.

How does the *erformance of OPC +& using COM com*are with OPC %& using Web Services?

nitial tests with the binary data transportation for OPC ,A show that Classic OPC

)based on (CO$+ is faster for small messages# while OPC ,A is faster for largemessages. 7evertheless# context is most important. Both Classic OPC and OPC ,A can

transfer tens of thousands of values per second# whereas most control systems are unableto !eep up with a fraction of this data transfer rate. Conse"uently# OPC ,A is not

expected to add another bottlenec! to the communication systemD 3ust as classic OPC)which was OPC before ,nified Architecture+ does not add a communication bottlenec!

today.

How fast can an OPC Server transfer values?

OPC can transfer tens of thousands of values per second. Some OPC Servers have beencloc!ed at over ?::#::: values per second.

How many different OPC Clients can connect to an OPC Server?

The OPC specifications do not limit the number of OPC Clients that can connect to an

OPC Server. %owever# vendors might set their own limits for various commercial#

 performance# security# and other reasons.

How many different OPC Servers can be connected to a single OPC Client a**lication?

OPC specifications do not limit the number of OPC Servers to which a Client can

connect. %owever# vendors might set their own limits for various commercial# performance# security# and other reasons.

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How many OPC Servers can I install on a single PC?

The OPC specifications do not limit the number of OPC Servers that can be installed ona single PC. %owever# vendors might set their own limits for various commercial#

 performance# security# and other reasons.

How *o*ular is the OPC Historical +ata &ccess 'OPC H+&( s*ecification? Has it heavily *enetrated

industry?

The most popular OPC Specification today is OPC (ata Access )(A+. OPC %(A is a

distant second# while OPC Alarms E >vents )AE>+ is a very distant third. 7evertheless#as more users demand standardi&ed access to their historical process data# OPC %(Acontinues to gain ground. Already all the ma3or historian vendors support OPC %(A.

How well does OPC *erform from a com*uter resource *ers*ective?

There are many factors that affect computer resource usage. 7evertheless# consider thefollowing. Applications that use (CO$ abound in the world of S )nformation

Systems+. This is the reason the OPC -oundation selected (CO$ as the platform ofchoice for OPC. Also (CO$ is already loaded in Windows by default. Therefore# theamount extra resources used by OPC applications are minimal.

I am trying to connect to an OPC Server using a *articular *roduct 'name withheld(, but I am

having difficulty@ What is the +COM configuration for both the Client and Server?

The various OPC specifications state how an OPC Server should communicate with anOPC Client. %owever# the OPC specifications do not state how each product should be

configured. To find out how to configure a specific OPC application )such as an OPCServer or a Client application+# you must consult the specific product documentation.There are many reasons an OPC Client application will fail to connect to an OPC Server.

The single most common reason is a failure to pass the Windows authentication process.

The OPC Training nstitute's website covers many of these reasons in detail. Ourwhitepapers )available for free+ list various error conditions# their causes# and how to

solve them using a step4by4step guide.

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In light of the OPC %& '%nified &rchitecture( s*ecification, should I avoid OPC Servers based on the

+& '+ata &ccess( s*ecification?

There is no need to delay purchases of OPC (A to wait for OPC ,A products. This is because OPC ,A is bac!wards compatible with OPC (A. As well# ntegrators and

vendors will be able to retrofit any OPC (A product with an OPC ,A wrapper that the

OPC -oundation provides.

Is there a ste* by ste* guide on how to configure an OPC Server?

The various OPC specifications state how an OPC Server should communicate with an

OPC Client. %owever# the OPC specifications do not state how each product should beconfigured. To find out how to configure a specific OPC application )such as an OPCServer or a Client application+# you must consult the specific product documentation.

Is there an easy way to configure OPC for multi)tag data structures on PCs?

The beauty of OPC is that once the OPC Server has information# any OPC Client caneasily retrieve it without having to worry about the specific P*C format. %owever#

configuring an OPC Server to communicate with a P*C ta!es some wor!. A commonissue is what to do about data sources )P*Cs or (CSs+ that have a specific structure forthe data. With OPC (ata Access )(A+# the most common mechanism to describe the data

is to simply use a common naming convention. Thus# <-C?:?.P< provides the Process

ariable# <-C?:?.SP< provides the Setpoint# etc.

Some OPC Servers are aware of structures in the device to which they are supposed toconnect. n this case# the OPC Server can configure itself automatically for the scenario

above. Other OPC Servers do not have a predetermined structure and re"uire ntegrators

to set these up repeatedly for each pro3ect. The ability for an OPC Server to automaticallyconfigure itself to a P*C# or do so with minimal integrator interaction is a !ey

differentiator between OPC Servers. The OPC Training nstitute encourages you to find

out how a server handles configuration at the time pro3ect re"uirements are set.

My OPC client a**lication *eriodically loses connectivity to the OPC server@ When I check again, the

connection works@ How can I diagnose intermittent OPC communication *roblems?

OPC and (CO$ provide a highly reliable data communication base# which is suitable

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for critical 209F operations. Connections should never stop )drop+ without explanation.

 7evertheless# factors beyond (CO$;s control may stop connections and include any ofthe following6

o  7etwor! connection may terminate due to cable disconnections or networ!

appliance )switch# router# gateway# etc+ failures

o OPC servers may terminate due to two main reasons6

o >xpected6 A user may shutdown an OPC server 

o ,nexpected6 OPC servers may terminate unexpectedly due to a variety of

reasons )bugs# lac! of resources availability# manual termination# etc+

o The computer hardware may fail

o >tc.

>ach of failure condition is uni"ue. To diagnose these problems in real4time# deploy any

of the following6

o $anually monitor the system for connectivity problems )not recommended+

o ,se a process historian to continuously capture real4time data and networ!

conditions at the time of failure

o ,se event monitoring software capture and diagnose real4time problems

n all these cases# OPC 5escue can be a valuable first4line of defense to help you

diagnose real4time connectivity problems.

What actions and errors must an OPC a**lication log?

OPC Specifications do not re"uire applications to log any data specifically. 7evertheless#

logging any information that would help a person find the cause of a problem is good

 practice. $ost OPC applications provide some logging facilities. The OPC Trainingnstitute recommends that ntegrators base a part of their OPC product selection on the

application's error logging facilities# which help ntegrators reduce their time to diagnose

 problems and improve pro3ect success.

What are the security holes when working with OPC?

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$icrosoft's (CO$ provides a highly secure and robust platform for applications to

setup their communication. Classic OPC )before OPC ,A+ uses (CO$ as its

transportation platform. Therefore# an OPC application is# in essence# a (CO$

application. OPC only re"uires the standard configuration that any other (CO$application re"uires. When properly configured# OPC applications do not open any new

security vulnerabilities for (CO$.%aving noted the above# many people disable security to get their (CO$ )and OPC

applications+ wor!ing for the first time. This is a valid practiceD however# ntegrators

$,ST remember to restore the security bac! when they are done. -ailure to do this willcause a security hole. n this case# it would be the ntegrators themselves that are the

cause of the security hole and not OPC technology in and of itself.

What are the standard +COM error messages?

$icrosoft Windows defines the standard (CO$ error messages. (CO$ errors typically begin with a <:xG::< code. Classic OPC )previous to OPC ,A+ uses (CO$ as its

transportation mechanism. Thus# OPC states what information must transfer# and (CO$

handles the transfer itself. (CO$ also handles security aspects such as authenticationand encryption.

There are a multitude of reasons for an OPC Client application to fail to connect to an

OPC Server due to (CO$ problems. The OPC Training nstitute's website covers manyof these reasons in detail. Our whitepapers )available for free+ list various error

conditions# their causes# and how to solve them using a step4by4step guide.

What are the standard OPC error messages?

OPC specifications provide a list of possible error values and messages. endors can

choose whether or not they want to implement these.

The ability to diagnose problems and pass the results in a uality parameter is an

important feature that will help you to differentiate between various vendors.

What +COM settings are re>uired for connecting OPC Servers between two different domains?

OPC applications can communicate with each other even when they are on different

Windows (omains. The tric! to getting communication wor!ing is WindowsAuthentication on both the OPC Client and Server PCs.

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-irst# the OPC Server PC must recogni&e the ,ser Account of the OPC Client PC.

Therefore the ,ser Account of the OPC Client must exist in the Active (irectory )locatedon the (omain Controller+ of the OPC Server PC. Alternatively# the OPC Server PC must

have a local ,ser Account setup for the OPC Client application.

Second# the OPC Client PC must recogni&e the ,ser Account of the OPC Server PC.

Therefore the ,ser Account of the OPC Server must exist in the Active (irectory)located on the (omain Controller+ of the OPC Client PC. Alternatively# the OPC Client

PC must have a local ,ser Account setup for the OPC Server application.

All this can be made easier if the S )nformation Systems+ or T )nformationTechnology+ staff setup a Trust between the two Windows (omains. This will ensure that

all ,ser Accounts will be automatically synchroni&ed between the two (omains.

What is +COM error 7!477$7288 'Interface not registered(?

Windows reports error :xG::0:?@@ as6 nterface not registered. Programmers !now this

error as 5>8(BH>H(7OT5>8.

(CO$ errors typically begin with a <:xG::< code.This error typically occurs when applications are trying to use interfaces )or <features<

for which there is no record in the Windows registry.

To solve this problem# use 5egSvr12.exe )included with Windows+ to register specific

OPC (**s. OPC applications will begin wor!ing when you register these (**s properly because (CO$ will be able to find the interfaces.

The following resources are available on OPC Training nstitute;s website6

o iew data and diagnose compatibility problems www.Opc>xpert.com. OPC

>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#

and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com. OPC 5escue

also determines specific (**s to register.

o Training classes )physical and online+ at http6www.opcti.comTraining4

Schedule.aspx

f you are unable to find the right answer for your situation# please contact us and we will

help you ma!e the connection.

What is OPC self certification?

The OPC -oundation provides a test harness for OPC Client and OPC Server

applications. endors use this harness to ensure that their OPC applications can pass all

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the tests. f the OPC application passes all the tests# the endor can state that their

application is OPC Compliant. They are also able to post the results of their tests on theOPC -oundation's website.

=ou should as! all OPC vendors who state their applications are OPC compliant about

the last time that they attended an OPC nteroperability session and the results of the test.

What is O*c.num and why do I need it?

When an OPC Client application connects to a remote computer and attempts to browse

for OPC Servers# it is actually connecting to a copy of Opc>num on the remote PC.

Opc>num retrieves the list of OPC Servers on the computer on which it resides. Theinability to connect to Opc>num is typically a result of authentication failure. There are

other causes for a failure to connect to Opc>num. These reasons are listed on the OPC

Training nstitute's website in the whitepaper titled <Troubleshooting OPC and (CO$6uic! Start 8uide.<

What is the difference between a client and server?

The basic distinction between a client and server is <control.< Clients control servers.Clients tell servers what to do# while servers do as they are told.

The following factors will help you determine whether or not an application should be

 programmed as an OPC client or server6

o Push or *ull data0 OPC clients can pull data from OPC servers. They can also

 push data to OPC servers. n both cases they tell the server what to do.

o Synchronous or asynchronous communication0 OPC clients can initiate

synchronous and asynchronous calls to OPC servers. Again# the client is telling theserver what to do.

o Initiating communication0 OPC clients typically initiate communication with

OPC servers. %owever# in the case of callbac!s# OPC servers actually initiate replies

to OPC clients with data changes. n effect# the server behaves li!e a client. This

callbac! is technically in reply to a client;s initial re"uest# and so the client stillcontrols the server.

n contrast to OPC client applications# OPC servers always do as they are told.

What is the OPC Intero*erability session?

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The OPC nteroperability session is an event the OPC -oundation hosts three times every

year. (uring the event# OPC vendors gather to ensure their OPC Clients and OPC

Servers can communicate with each other. Thus# endor 9 tries to connect their OPC

Client application to vendor ='s OPC Server and also the OPC Server by endor I. Thesuccess andor failure results are posted on the OPC -oundation's web site.

=ou should as! all OPC vendors who state their applications are OPC compliant aboutthe last time they attended an OPC nteroperability session and the results of the test.

What is the relationshi* between +COM and OPC?

Classic OPC relies on (CO$ for data transportation. That is# OPC specifies the formatof data that transfers between applications that use OPC. -or example# each OPC (ata

Access application must transfer a timestamp# "uality level and data value. t is notenough to simply pass along the data value itself. So while OPC states what information

must transfer between applications# (CO$ handles the transfer itself. (CO$ alsohandles security aspects such as authentication and encryption.

What *orts does +COM use?

(CO$ uses Port ?1@ to establish communication. Once the OPC Client and Server are

able to communicate# they will negotiate new port numbers for communicationdynamically. OPC applications typically use 0 ports. Once# the OPC Client and OPC

Server applications find the available ports# they use them and release traffic from port?1@.

When should I consider using an OPC =unneling *roduct?

(CO$ provides a versatile and secure platform for OPC communication. t is also freely

available with Windows. %owever# there are instances where (CO$ does not or cannot provide an acceptable solution# and ntegrators prefer to pay money to install an OPC

tunneling product from a vendor. The following lists the scenarios in which (CO$ OPCtunneling technology is preferred over (CO$6

o ntegrators don't !now how to configure (CO$. )This is the most common

reason people use OPC Tunneling.+

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o ntegrators don't !now how to configure the firewall. )This is the second most

common reason people use OPC Tunneling.+

o There is a re"uirement to use only a single port for OPC communication. )(CO$

typically uses 0 ports.+

o Communication timeouts must be closely controlled. )7ote that (CO$ recovers

very "uic!ly in most cases# but there are reported circumstances where timeouts ta!e

longer.+

o Communication has strict bandwidth restrictions that can only be overcome with

OPC Tunneling. )This is sometimes the case when bandwidth is restricted such as inoff4shore communication# or wireless telemetry communication.+

=ou should consider the following if you decide to use OPC Tunneling6

o (oes the Tunneling product provide >ncryption services# or does it send data <in

the clearJ< f >ncryption is available# does it provide an acceptable level of

encryptionJ (CO$ provides encryption services that enable it to !eep

communication secret on a networ!.

o (oes the Tunneling product provide Authentication services# or does it allow

anyone to connectJ Authentication prevents unauthori&ed users from connecting to adata source.

o (oes the Tunneling product provide centrali&ed administration of security

aspects# or must security be handled at each PCJ When using a (omain# (CO$enables users to have a single point for all aspects of security.

Whether you decide to use OPC Tunneling or (CO$# the OPC Training nstitute hopes

that you endeavor to learn (CO$ before you ma!e your decision. $ost people find(CO$ to be surprisingly logical once they understand how it wor!s.

Where does OPC get its timestam* from?

OPC Servers always send OPC Client applications information on the alue# uality# andTimestamp of an item. But some control systems do not provide a timestamp. n this

case# the OPC Server sends the PC timestamp# which is the only timestamp it has

available.When the OPC Server connects to control systems that have information on the

timestamp# the OPC Server has a choice. t can either use the timestamp from the control

system# or it can use the timestamp from the PC. Some OPC Servers even enable the

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integrator to ma!e this choice.

The ability to use the timestamp from the control system and even to select the source ofthe timestamp is a differentiating feature amongst OPC Servers. The OPC Training

nstitute recommends that System Architects investigate the timestamp re"uirements. -or 

example# a high4speed data ac"uisition to record a Se"uence of >vents )SO>+ typically

re"uires the timestamp to come from the control system. %owever# if the OPC Server isonly used in con3unction with an %$ )%uman $achine nterface+# the control system

timestamp may not be re"uired.

Why can I not AbrowseB an OPC Server?

When an OPC Client application connects to a remote computer and attempts to browse

for OPC Servers# it is actually connecting to a copy of Opc>num on the remote PC.

Opc>num retrieves the list of OPC Servers on the computer on which it resides. Theinability to connect to Opc>num is typically a result of authentication failure. There are

other causes for a failure to connect to Opc>num. These reasons are listed on the OPC

Training nstitute's website in the whitepaper titled <Troubleshooting OPC and (CO$6uic! Start 8uide.<

Additional resources6

o iew data and diagnose compatibility problems www.Opc>xpert.com. OPC

>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#

and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com

o Training classes )physical and online+ at http6www.opcti.comTraining4

Schedule.aspx

Why can I not see OPC Servers when browsing?

When an OPC Client application connects to a remote computer and attempts to browse

for OPC Servers# it is actually connecting to a copy of Opc>num on the remote PC.Opc>num retrieves the list of OPC Servers on the computer on which it resides. The

inability to connect to Opc>num is typically a result of authentication failure. There areother causes for a failure to connect to Opc>num. These reasons are listed on the OPC

Training nstitute's website in the whitepaper titled <Troubleshooting OPC and (CO$6

uic! Start 8uide.<Additional resources6

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o iew data and diagnose compatibility problems www.Opc>xpert.com. OPC

>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#

and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com

o Training classes )physical and online+ at http6www.opcti.comTraining4

Schedule.aspx

Why cant my OPC a**lication connect to an OPC Server?

There are many reasons an OPC Client application will fail to connect to an OPC Server.The OPC Training nstitute's website covers many of these reasons in detail. Our

whitepapers )available for free+ list various error conditions# their causes# and how to

solve them using a step4by4step guide.Additional resources6

o iew data and diagnose compatibility problems www.Opc>xpert.com. OPC

>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#

and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com

o Training classes )physical and online+ at http6www.opcti.comTraining4

Schedule.aspx

Why do I get +COM error 7!477$7;7;?

(CO$ errors typically begin with a <:xG::< code. Specifically# the :xG::0:2:2 error

appears in the OPC Client application when it fails to receive a callbac! from the OPCServer. The OPC Training nstitute's website has a whitepaper that provides details on

this error its various potential causes# and how to solve them using a step4by4step guide.

Additional resources6

o iew data and diagnose compatibility problems www.Opc>xpert.com. OPC

>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#

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and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com

o Training classes )physical and online+ at http6www.opcti.comTraining4Schedule.aspx

-or automated troubleshooting# refer to OPC >xpert# a software application to

troubleshoot OPC connections. f OPC >xpert fails to connect# it automatically informs

you of the problem# diagnoses the cause# and suggests a solution. OPC >xpert is free todownload# does not re"uire installation# and does not ma!e any changes to Windows

registry# so it is safe to use on your computer. (ownload at www.Opc>xpert.com.

Why do I get +COM error 7!47757778?

(CO$ errors typically begin with a <:xG::< code. Specifically# (CO$ >rror

:xG::F:::@ appears in OPC client applications when they try to connect to a server to

which they are refused access. This error could be caused under several conditions. 5eadthe full article to troubleshoot and repair this (CO$ error. The OPC Training nstitute's

website has a whitepaper that provides details on this error its various potential causes#

and how to solve them using a step4by4step guide.

Other resources6

o

iew data and diagnose compatibility problems www.Opc>xpert.com. OPC>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com

o Training classes )physical and online+ at http6www.opcti.comTraining4

Schedule.aspx

 

Why do I get +COM error 7!47757#9&?

Windows reports error :xG::F:/BA as6 The 5PC server is unavailable.(CO$ errors typically begin with a <:xG::< code.

The following resources are available on OPC Training nstitute;s website6

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o Whitepaper on <:xG::F:/BA< http6www.opcti.comerror4server4

unavailable.aspx

o iew data and diagnose compatibility problems www.Opc>xpert.com. OPC

>xpert also provides custom calculations# connectivity to >xcel# bridging# trending#and much more.

o Automated troubleshooting and diagnosis at www.Opc5escue.com

o Training classes )physical and online+ at http6www.opcti.comTraining4

Schedule.aspx

f you are unable to find the right answer for your situation# please contact us and we will

help you ma!e the connection.

Will making changes to +COM to accommodate OPC o*en any security holes?

$a!ing changes to (CO$ configuration to accommodate OPC communication does not

open any security holes or compromise security.

Will OPC work across a firewall?

OPC applications can be configured to wor! across firewalls. 5efer to %ow can ac"uire

data from an OPC Server through a firewallJ