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An Overview of OPC SECTION 17 Using CX-Supervisor as an OPC Client
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SECTION 17
Using CX-Supervisor as an OPC Client
This chapter introduces OPC Server to a new user, and explains how to use
CX-Supervisor as an OPC Client.
17-1 An Overview of OPC
OPC stands for OLE for Process Control, and is a standard published by the
OPC Foundation. The basic aim of the OPC standard is to allow hardware
vendors to produce software drivers (called OPC Servers) and for software
vendors to produce applications (called OPC Clients) which use a standard
method for data interchange. This allows software and hardware from different
vendors to be used together.
Based on Microsoft's OLE (now ActiveX), COM (component object model) and
DCOM (distributed component object model) technologies, OPC consists of a
standard set of interfaces, properties, and methods for use in process-control
and manufacturing-automation applications. The ActiveX/COM technologies
define how individual software components can interact and share data.
Backed by Microsoft's NT technology, OPC provides a common interface for
communicating with diverse process-control devices, regardless of the
controlling software or devices in the process. The goal of the standard is
Plug-and-Play, a concept developed by Microsoft and a number of other
companies a few years ago. By using a standard way of configuring computer
hardware (and software interfaces) automatically, a device will easily connect
to another and immediately work without the need for lengthy installation
procedures or complex configuration. Instead of having to learn how to use
100 or more custom toolkits, users will only have to learn one set of tools,
because all OPC drivers will work the same way. OPC's purpose is to compel
the automation industry suppliers to push all device drivers toward a standard
form. Essentially, OPC defines a common interface that permits interface
development work to be performed once and then easily reused. The OPC
standard requires hardware suppliers to provide front-line data collection and
distribution. They are the most familiar with how to access the device's internal
data efficiently. These devices then become OPC servers, providing data to
OPC client applications consistently. Application developers can then write
code in any language deemed appropriate.
The latest version of the OPC standard is version 2. This replaces the earlier
version 1 standard.
CX-Supervisor uses an OPC version 2 interface to connect to an OPC Server
which is version 2 compliant. Note that the OPC version 1 interface has been
superseded, and is not supported.
Users of CX-Supervisor may need some basic understanding of OPC. For
more information on OPC, see the OPC Foundation web site at
www.opcfoundation.org.
For instructions on configuring your DCOM settings for connection to remote
PCs, see Appendix A.
17-1-1 A Brief History of OPC Data Access
In the early 1990s a group of people from several important companies
involved in the creation of SCADA (Supervisory Control and Data Acquisition)
systems began meeting at Microsoft's headquarters in Redmond. Their
interests focused on the use of the Windows operating system within the
factory automation environment, in particular for the acquisition of real time