Overview
The advantages of using OPC
Comparison and assessment of technologies
References

OPC (OLE for Processes Control) is a standard mechanism for communicating to numerous data sources, either devices on the factory floor, or a database in a control room.

OPC is designed to allow client applications access to plant floor data in a consistent manner. With wide industry acceptance OPC will provide many benefits:

• Hardware manufacturers only have to make one set of software components for customers to utilize in their applications.
• Software developers will not have to rewrite drivers because of feature changes or additions in a new hardware release.
• Customers will have more choices with which to develop World Class integrated manufacturing systems.

Overview

OPC is the technological basis for the convenient and efficient link of automation components with control hardware and field devices. Furthermore, it provides the condition for integration of Office products and information systems on the company level such as Enterprise Resource Planning (ERP) and Manufacturing Execution Systems (MES). Process data on the field level can be presented in an Excel sheet. Status data and production data on the control level can be archived in a database without any problems via OPC or can be further processed in a production planning system.

OPC today is based on Microsoft’s Distributed Component Object Model (DCOM). All definitions of DCOM (objects, interfaces, methids, etc.) thus also apply to OPC.

OPC servers can be accessed by clients written in a large number of programming languages, including C++, Visual Basic, and script languages.

The advantages of using OPC

Hardware manufacturers - manufacturers of devices that provide or need data (e.g. PLC, barcode reader, measuring instruments) or manufacturers of PC plug-in cards that enable access to such devices (e.g. field bus boards, measuring systems).	The product can be used by all OPC-compatible systems in the market and is not limited to an individual system for which a corresponding solution (i.e. specific drivers) must be developed. Due to the existence of standardized interfaces and the interoperability related to them, there is no need to become familiar with the specific requirements of other systems. The Time-to-Market for new device generations is significantly reduced as only one OPC server has to be updated, not a large number of drivers or DDE servers. The effort needed for support is also reduced as only one product has to be supported.
Software manufacturers - manufacturers of applications for the acquisition, visualization, or processing of data of the above mentioned devices and for sending data to those devices.	Software manufacturer The product can be used with all devices and communication protocols on the market that make available an OPC interface. The manufacturer no longer has to develop corresponding solutions (specific drivers). Due to the existence of standardized interfaces and the interoperability related to them, there is no need to become familiar with the specifications of other devices and communication protocols. The time needed for support is considerably reduced as many products to be supported (product specific drivers up to now) no longer exist.
System integrator - prepares complete solutions based on the products available on the market.	System integrator Flexibility in the choice of product is considerably increased, as is, consequently, the number of projects that can be processed. The time needed for integration and training is considerably reduced, as OPC provides a standardized interface which remains the same for all products.
End user - uses solutions based on OPC products.	End user OPC provides additional flexibility (distribution of components, use of new technologies, choice between products, etc.) during the design of the overall system as products of various manufacturers can be combined. The increasing variety of products available on the market should, in the future, lead to a noticeable reduction of costs with increasing quality and user comfort. By relying on an acceptable standard in this sector, investments will be better protected.

Comparison and assessment of technologies

	Product-specific drivers	DDE	OPC
Standardization	No	No	Yes
Interoperability	No	Limited either to standard DDE or to the respective dialects (e.g. FastDDE, AdvancedDDE).	Yes
Performance	Very high performance as the solutions are optimized as to the specific application.	DDE is based on the exchange of messages. This is slow. DDE dialects improve efficiency by putting more data into one message.	Very high performance.
Remote access	No	Yes (through NetDDE)	Yes (Distributed COM)
Interactions	Generally not available.	No	Yes
Standardization	No	No	Yes. OPC defines a large number of methods, which can be used for exchanging additional information between client and server.
Complexity	Many manufacturers provide toolkits with which drivers can be created quickly for corresponding systems. A new system requires additional time to learn.	Toolkits are available from manufacturers. As the variety of DDE shapings is not very high, familiarization with them is rarely necessary. Programming of DDE applications without toolkits is very difficult.	Learning DCOM programming is timeconsuming. There are toolkits that help minimize this time.
Availability on other platforms	There are only a few systems available for different platforms.	DDE is only available for Windows operating systems.	OPC components are limited to systems where DCOM is available. These are primarily Windows systems. The new OPC and XML specification being under construction additionally allows the use of OPC components on operating systems without DCOM.

References

Futher information about OPC can be obtained from www.opcfoundation.org.