Abstract: The OPC specification is an industrial standard developed by the OPC Foundation, which specifies the interface between process control and automation software and industrial field devices. The technical specifications of OPC technology, OPC standards, and the benefits of OPC specifications design systems and outlined its main applications at home and abroad, and the main role of OPC technology in applications also analyzed. OPC represents the development direction of process control system communication standards within a period of time. Key words: OPC; process control; technical specifications; interface
1. The production of OPC technology With the continuous development of industrial production, industrial control software has made great progress. However, due to the expansion of production scale and the improvement of process complexity, industrial control software design faces huge challenges, which is to integrate quantities and types of live information. In traditional control systems, information sharing between smart devices and intelligent devices and control system software is implemented by drivers, and different manufacturers have different drivers, forcing industrial control software to include The more underlying communication modules. In addition, since the driver of relative applications generally does not support changes in hardware features, the upgrade and maintenance of industry control hardware and software is extremely inconvenient. Also, at the same time, two customer applications generally cannot read and write the same device, because they have different, independent drivers, while operating the same device, may cause access to conflicts, even Leading the system crashes. The emergence of OPC technology is well solved these problems. OPC is an abbreviation for Object Linking and Embedding (OLE) for Process Control, which is the application of Microsoft's object links and embedded technology in process control. The OPC uses the OLE / COM / DCOM technology, using customer / server mode, providing a unified standard for the object-oriented development of industrial automation software, this standard defines the application Microsoft operating system exchange automation between PC-based clients Data method. After this criteria, hardware developers will replace software developers to develop unified OPC interface programs for their hardware products, and software developers can exempt the development of the driver, give full play to their own specialties, put more energy into To the development of its core products. This not only avoids the reproducibility of development, but also improves the opening and interoperability of the system.
2. OPC Specification Overview OPC is an industrial standard, which is built by some world-renowned automation systems and hardware, software companies and Microsoft (Microsoft). OPC includes a set of interfaces, attributes, and methods, providing users for process control and industrial automation applications. Microsoft's OLE / COM technology defines how a variety of different software components interacts and share data, allowing OPC to provide general interfaces for communication between various process control devices, regardless of the software and devices. Its development is listed in Table 1. Table 1 OPC Standard Rate Version Content Data Access 3.0,2.0,1.0 Data Access Specification ALARMS AND Events 1.10, 1.00 Alarm and Event Specification Historical Data Access 1.0 Historical Data Access Specification BATCH 2.0, 1.0 Batch Process Specification SECURITY 1.0 Security Specification Compliance 2.00 .2 Data Access Standard Test Tools OPC XML 1.00, 0.18 Process Data XML Specification OPC Exchange 1.0 Data Exchange Specification OPC Commands is Developing Command Specifications OPC Common I / O Obsuscies OPC Complex Data is developing complex data specification The implementation of OPC technology consists of two parts, the OPC server and the OPC client application section. Its application model is shown in Figure 1. The OPC server completion is to collect data information of field devices, and then transfer to OPC client applications through standard OPC interfaces. The OPC client receives data information through standard OPC interfaces. During specific implementation, users can use their own needs to select the appropriate specifications. The data access specification provides a method of accessing real-time process data; alarms and event specifications provide a mechanism for notifying client programs or an alarms; historical data access specification is used to provide users to be stored in the process The historical data in the data archive file, the database, or the remote terminal device and the method of analyzing these historical process data. Other specifications are not hereby introduced. 3. The benefits of using OPC specification design 1) Adopt standard Windows system interfaces, hardware manufacturers reduce the number of interface programs provided by their equipment to one, software manufacturers only need to develop a set of communication interface programs. That is, it is conducive to software and hardware developers, more beneficial to end users. 2) The OPC specification is based on OLE / DCOM, and OLE / DCOM supports network protocols such as TCP / IP, so individual subsystems can be physically separated, distributed on different nodes of the network.
3) OPC follows the object-oriented principle to encapsulates the application (OPC server) as an object, only exposing the interface method outside, and the customer calls this method in a unified manner to ensure that the software is transparency to the customer. The user is completely detached from the underlying development. 4) OPC implements remote calls, making the distribution of the application unrelated to the distribution of system hardware, facilitating the system hardware configuration, making the system application range. 5) Adopt OPC specification, easy to configure the system, greatly simplify system complexity, can greatly reduce software development cycles, improve software operation reliability and stability, easy to upgrade and maintenance. 6) The OPC specifies the interface function, regardless of the form of on-site equipment, customers access in a unified manner, thereby achieving the openness of the system, easy to implement interfaces with other systems. 4. The application of OPC technology is possible to solve industrial controls in a simpler system structure, longer life, lower price due to the use of OPC technology. At the same time, the connection between field devices and systems is also simpler, flexible and convenient. Therefore, OPC technology has been widely used in domestic industrial control in China. The main applications are as follows: 1) Data acquisition technology. OPC technology is usually widely used in data acquisition software. Nowadays, the products provided by many hardware vendors have standard OPC interfaces. OPC implements efficient and flexible data reading and writing between applications and industrial control devices, which can prepare the collection tasks that comply with the standard OPC interface. . 2) Historical data access. OPC provides a way to read historical data stored in process data archive files, databases, or remote terminal devices, and methods of operation, editing. 3) Alarm and event processing. When OPC provides an OPC server, a mechanism to send notifications to the OPC client when the OPC server setting event arrives, and can better capture various alarms and events in the control process and give corresponding deal with. 4) Data redundancy technology. Industrial control software development, redundant technology is the most important technology, which is the guarantee of long-term stability of the system. The use of OPC technology can be more convenient to implement software redundancy, and have better openness and interoperability. 5) Remote data access. With Microsoft's DCOM (Distributed Component Object Model) technology, OPC implements high performance remote data access capabilities, making data exchange between industrial control software more convenient.
5. OPC technology The role of OPC technology in industrial control is influence and application is basic and revolutionary, simply, its role is mainly manifested in several aspects: First, OPC solves the device driver Heterogeneous issues in development. With the continuous development of computer technology, the continuous improvement of user needs, the industrial control system of DCS (distributed control system) is more powerful, and the structure is increasing, and the scale is growing, and a set of industrial control systems often use it. Several or even more than ten different companies integrate a large system, but due to lack of unified standards, developers must write corresponding drivers for each device of the system, and when the hardware device is upgraded, When modified, the driver must also follow the modification. At the same time, if the control software of different companies is running in a system, there is also a risks of mutual conflict. With the OPC, since there is a unified interface standard, hardware manufacturers only need to provide a program that meets OPC technology, software developers also need to write an interface, and users can easily expand their devices. As long as they provide OPC support. All data exchanges are performed through the OPC interface, regardless of which specific manufacturers are provided. Second, OPC solves the problem of data exchange between heterogeneous network segments in the fieldbus system. The fieldbus system still has a variety of bus coexistence, so data exchange between system integration and heterogeneous control network segments face many difficulties. With the OPC as the integrated middleware of the heterogeneous network, as long as each bus segment provides its respective OPC servers, all OPC client software can access these OPC servers through the consistent OPC interface, thereby obtaining data of each bus segment; It is well possible to achieve data interaction between heterogeneous bus segments. Moreover, when the protocol version of a bus is upgraded, it is also necessary to upgrade the program corresponding to the bus. Third, OPC can act as a middleware accessing a proprietary database. In practical applications, many control software use a proprietary real-time database or historical database, which is developed by the developer of the control software. Access to such databases is not as easy as accessing the general database, only by calling the developer's API function or other special way. However, the API functions provided by different developers are different, which brings similar problems with hardware drives: To access the proprietary database of different monitoring software, you must write different code, which is obviously very cumbersome. Using OPC can effectively solve this problem, as long as the proprietary database developers can provide an OPC server accessing the database while providing a database, then use only the OPC client according to the requirements of the OPC specification when the user is accessible. There is no need to understand the specific interface requirements for this proprietary database. Fourth, OPC facilitates integration of different data, providing convenience to the management system upgrade to the control system. One of the current trends of the current control system is networking, and network technology is used inside the control system, and the control system and control system also network connection, constitutes a larger system, and the entire control system is also network connection, control The system is only a subnet of the entire enterprise network. OPC can also play an important role in achieving such a corporate network. In the information integration of enterprises, including field equipment and monitoring systems, monitoring systems between components, monitoring systems and enterprise management systems, as well as information integration between the monitoring system and the Internet, OPC as connectors, press one Set of standard COM objects, methods, and properties provide convenient information flow and exchange.
Whether it is a management system or a control system, whether it is a PLC (programmable controller) or DCS, or FCS (fieldbus control system), it can exchange information quickly and reliably with each other through OPC. In other words, OPC is a data interface specification for the entire enterprise network. Therefore, OPC enhances the functionality of the control system, enhancing the network's function, and improves the level of enterprise management. Finally, OPC enables control software to design, production, and development, respectively, and is conducive to independent third-party software suppliers, thus forming new social division of labor, more competitive mechanisms, providing more Good product. 6. As a gradual molded technology, OPC has received high attention from domestic and foreign manufacturers. Many companies have added support for OPC on the basis of the original product. Due to the unified interface of data access, the control system is further open to open, implement information integration and sharing, users can get more convenience. OPC technology has changed the original control system model, and a development opportunity and challenge proposed to domestic system manufacturers. It is in line with the OPC specification, and hardware has been widely used, which brings vitality to industrial automation.
