Introduction

Abstract

The use of PC- and software-based automation systems in industrial automation rapidly increased since the early nineties. Especially, Windows-based PCs are used for visualization and control purposes. One of the major efforts for the development of standardized automation software in the past years was the access to automation data in devices where an uncountable number of different bus systems, protocols, and interfaces are used. A similar problem for software applications did exist for the access to printers, where in old DOS days, every application needed to write its own printer drivers for all supported printers. Windows solved the printer driver problem by incorporating printer support into the operating system. This one printer driver interface served all applications that needed printer access. And these printer drivers are provided by the printer manufacturer and not by the application developers. Since vendors of Human Machine Interface (HMI) and Supervisory Control and Data Acquisition (SCADA) software had similar problems, a task force initiated by the companies Fisher-Rosemount, Rockwell Software, Opto 22, Intellution, and Intuitive Technology was founded in 1995. The goal of the task force was to define a Plug&Play standard for device drivers providing a standardized access to automation data on Windows-based systems. The result was the OPC Data Access specification released after short time in August 1996. The nonprofit organization that is maintaining this standard is the OPC Foundation. Nearly all vendors providing systems for industrial automation became member of the OPC Foundation. The OPC Foundation was able to define and adopt praxis relevant standards much quicker than other organizations. One of the reasons for this success was the reduction to main features and the restriction to the definition of APIs using the Microsoft Windows technologies Component Object Model (COM) and Distributed COM (DCOM). The focus on important features and the use of base Windows technologies allowed a quick adoption of the standard for the addressed use case. As a result of the experience from product developments, multi-vendor demonstrations, and interoperability workshops, version two of the OPC Data Access specification was introduced in 1998. Based on this version, a large number of products implemented the standard. OPC Data Access version two is still the most important interface for OPC products.