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Performance evaluation of OPC-based I/O of a dynamic process simulator

As the use of dynamic process simulation in industry has increased, a need has emerged for an easy way to configure reliable and powerful data exchange between simulation applications and distributed control systems (DCS's). A system where the control applications and manmachine interfaces of the real DCS are connected to a simulation model of the process, can be used for building, tuning and testing the control system implementation, and for training the operators, independently from the plant hardware. OPC (OLE for Process Control) is a set of component specifications widely used in the automation domain for software application interoperability. OPC Data Access interfaces have been used e.g. for connecting DCS applications of multiple vendors to simulation models. This paper discusses architecture and design issues that affect the performance of the OPC data exchange in applications involving simulation. The performance test results of an OPC server designed according to the guidelines given show that OPC-based communication can offer sufficient data transfer capacity for most dynamic process simulation purposes. INTRODUCTION Dynamic process simulation has long been used in automation design and testing. For these purposes, it is often desirable to connect the simulation model to control application in a real DCS. If both systems support OPC data access specifications, the connection can be made using this technique. The concept has already been used for automation testing and for operator training. [1,2] The OPC-based connection has proved to be an easy-to-configure tool, but it lacks the ability to manage larger scale use. For instance, the transfer capacity of OPC servers has been too small for transferring a set of items comprising several thousands to tens of thousands values a second. The aim of this paper is to discuss the features that affect the performance of OPC data access based communication. The practical work has centered on the dynamic process simulator Apros (Advanced PROcess Simulator). Product has been developed by Technical Research Centre of Finland (VTT) and Fortum, and is available for modeling of combustion power plants, nuclear power plants and pulp and paper mills. The motivation for developing OPC was to find an easy way to communicate between numerous data sources in the field of automation. The costs of integrating equipment from different vendors can be significant. A considerable amount of engineering time may also be required in writing drivers for a typical supervisory-control software project. [3] OPC provides a plug-and-play software technology for automationand process control industries. It has rapidly attained worldwide de-facto standard status. One reason for this is that the OPC specification is built on the existing, widely used binary standard COM. [4] The OPC specification includes Data Access, Alarms & Events, Batch, Historical Data Access and OPC XML specifications. The most widely used is the Data Access (DA) specification. This paper mainly covers issues related to data access specification. As mentioned, OPC specification is build on COM. A DA OPC client can use either a custom interface or an optional automation interface. Figure 1 illustrates the situation.