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http://blog.9cbs.net/kind_li/archive/2002/12/25/10993.aspx
OPC standard - Do you know?
These articles are all colredent, not the article I wrote, I am just a summary. But in any case, I hope you can learn from this article to the OPC standard.
What is OPC?
OLE for process control - OLE for process control is an industrial standard, which is the world's leading automation and soft, hardware companies and Microsoft's cooperation. This standard defines how to use the Microsoft operating system to exchange automated real-time data between PC-based clients. Organization to manage this standard is the OPCOPC Foundation. The foundation of the foundation is more than 220 worlds. Including almost all of the world's control systems, instrumentation and process control systems are main suppliers. The Pioneer of the OPC Foundation-A "Special Working Group" consisting of Fisher-Rosemount, Rockwell Software, Opto 22, Intellution, and Intuitive Technology, developed a basic and operational operation after a year of work OPC specification. The standard of the simplified first phase was released in August 1996.
With the introduction of the DCOM technology supported by Windows 95 in February 1997, the newly established OPC Foundation in September 1997 revised the OPC specification, adding some standards such as data access, and the OPC specification has been further improved. OPC is based on Microsoft's Distributed Internet Application (DNA) architecture and Component Object Model (COM) technology, which is designed according to easy scalability. The OPC specification defines an industrial standard interface, which makes COM technology to apply applications such as process control and manufacturing automation. OPC is a communication standard for an OLE / COM mechanism as an application. OLE / COM is a customer / server mode with the advantages of language independence, code reuse, and easy integration. The OPC specifies the interface function, regardless of the form of on-site equipment, customers access to a unified manner, ensuring the transparency of the software to the customer, so that the user is completely detached from the low-level development.
OPC efficiency
The development of the OPC standard has now been 5 years. In this past five years, many industry-leading manufacturers have developed a variety of OPC servers and client applications. In the actual engineering, it has also passed many tests and tests. Tetrapak with Switzerland as an example, its data acquisition system based on OPC server technology guarantees that the update time for more than 500 data points is 200 milliseconds.
In Softing's OPC server performance test, the local OPC application is tested for DCOM-based distributed applications, respectively.
In order to ensure the credibility of the test, two low-grade computers are particularly selected. It is configured as follows:
Hardware: CPU: Pentium 90MHz processor RAM: 48 or 64M software: Windows NT 4.0
In the local test, the OPC client test application and the OPC server are mounted on the same PC. In DCOM-based distributed OPC application test, the OPC client test application runs on the second remote PC. Test results: Whether in the local or two computers, 5,000 process variables can be transmitted between OPC servers and clients within 1 second. For only 500 process variables, just 100 milliseconds. Thus, OPC is considered to be very suitable for collecting a large number of dynamic process variables in a short update rate.
Advantages of OPC
The benefits of using OPC specification design systems:
With standard Windows system interfaces, hardware manufacturers have reduced the number of interface programs provided by their devices to one, and software manufacturers also 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. The OPC specification is based on OLE / DCOM, while OLE / DCOM supports network protocols such as TCP / IP, so that individual subsystems can be physically separated from different nodes of the network.
OPC is encapsulated by an application (OPC server) as an object-oriented principle, and only the interface method is exposed to the outside, and the customer calls this method in a unified manner to ensure the transparency of the software to the customer, so that users It is completely detached from the low-level development.
The OPC implements remote calls that make the application's distribution of the system-hardware distribution, which makes the system hardware configuration, making the system's application range.
Using OPC specification, it is easy to configure the system, which greatly simplifies system complexity, which can greatly reduce software development cycles, improve software operation reliability and stability, and facilitate the upgrade and maintenance of the system.
The OPC specifies the interface function, regardless of the form of on-site equipment, customers access to the unified manner, thereby achieving the openness of the system, which is easy to implement interfaces with other systems.
OPC related knowledge
1. COM - Common Object Model Component Object Model 2. OLE - Object Links and Embedded 3. Ole Automation - OLE Automation 4. DCOM - Distributed Component Object Model 5. ActiveX 6. DDE - Dynamic Data Exchange ( Dynamic Data Exchange)
OPC technical specifications
The OPC technical specification is based on Microsoft's OLE / COM technology, which defines a set of interface specifications. It includes an OPC automation interface (Automation Interface) and an OPC Table (CUSTOM Interface). In addition, the OPC technical specification is defined in the OPC server program and the client program to communicate interface or communication. 1 OPC object and interface: OPC server object provides methods for accessing (reading / writing) or communication of data sources, and the data source can be an I / O device on site, or other applications. By interface, the OPC client application can connect to the OPC server provided by one or more vendors. As shown in Figure 1. The OPC server encapsulates the type and name of the I / O control device and access data and the code for device operation. 2 OPC Data Access Specification: Overall, the OPC data access specification contains several objects: Server Object, group objects, item objects. The OPC server object maintains the information of the server, and is also a package container for the OPC group object. The OPC group object maintains its own information and provides an OPC item mechanism while managing OPC items. The OPC group provides a mechanism for customer application organization data, for example: a group can contain items for all data display panels and read and write data. In some special cases, you can also establish a connection to the client application and item in the group, and you can prohibit or allow this connection as needed. The OPC client application can also modify the number of refresh rates for the OPC server to submit data changes to the OPC client application. There are two types of OPC groups: public group (public or private). The public group can share multiple client programs, and the partial group is only for a certain client program. In each group, the client can define multiple OPC items. as shown in picture 2. The OPC item represents the connection to the data source in the server. From the Custom Interface Angle, an OPC item cannot be operated by an OPC client as an object, so an external interface is not defined in the OPC item. All operations for OPC items are performed using an OPC item's package container (OPC group) or OPC term. Each OPC item contains a value (Quality), Quality and Time Tags. The type of value (value) is Variant, the quality type is short. It should be noted that the item is not a data source, but is only connected to the data source. For example: labels that can enable OPC clients to access the OPC client in the DCS system. The OPC item should be seen as the indication of the data address, not the physical source of the data. 2.3 OPC Alarms and Events Specification: OPC Alarms Provide a mechanism. With this mechanism, the OPC client application can be notified when there is a specified event or alarm condition in the I / O device. With the OPC alarm and event specification interface, the OPC client application can set the events and conditions supported by the OPC server, and its current state is obtained. Here, the concept of alarms and events commonly used in process control is used. In unstrue, the alarms and events are not very obvious in meaning, and both can be interchangeable.
In OPC, a alarm is an abnormal condition, so it is a special case. One situation is a state named in the OPC Event Server (Event Server) or its included object, and this status is useful to the OPC client application. For example, the label FC101 can have the following related situations: upper limit alarm, upper limit alarm, normal, lower limit alarm, lower limit alarm. On the other hand, an event is very important to some changes that can be detected, and this change is very important to the OPC server and the I / O device thereof or OPC customers. An event may be related to some situations or may not be related to any situation. For example: The system changes from normal conditions to the upper limit alarm or changes from the upper limit to normal, this is the event related to some cases. However, the operation of the operator, the system configuration changes, the system fault is an event that is not related to the situation. The OPC client can get a notification of such special events. OPC Event Server Interface IopceventServer provides the OPC client to complete the following features: ● Decide the type of event supported by the OPC server. ● Register some specific events so that OPC customers can notify them when these events occur or use filters to define a subset of these events. ● Access or processing on the case implemented by the OPC server. In addition to the IOPCEventServer interface, the OPC event server also supports other interfaces that browsing the server implementation and managing the public group 2.4 OPC Historical Data Access (Historical Data Access "historical data engine can disperse storage Information is combined into an additional data source and supplies them to users or OPC clients that they are interested. At present, most historical data systems use their own dedicated interface distribution data, which cannot provide plug-and-play features, limiting the scope and function of their applications. In order to integrate historical data and various applications, historical information can be considered to be data for some data type. Currently, the OPC specification supports the following historical data servers: ● Simple trend data server. This server only provides raw data and simple storage. Data is typically the data type provided by the OPC data access server, often the form of [Numerical, Quality] tuple. ● Composite data compression and analysis servers. Such a server can provide the same data compression function as the original data storage, and provide data summary and data analysis functions such as mean, maximum, minimum, and so on. Support for data refresh and history of history, in addition, the history data can also record the annotation information of the data. OPC installation
These files are www.opcfoundation.org opc_aepcfoundation.org opc_aepcfoundation.rg opc_aeps.dll opccomn_ps.dll OpCfoundation.dll OpcProxy.dll AprxDist.exe opcProxy.dll AprxDist.exe opcProxy.exe, which is OPCNum.exe, is all OPC interface proxy file clients and server terms You must install these files *************************************************************************************** ********************* Do not cover the new version of the file when installing. ************ *********************************************************** *********** Installation steps: 1. Copy all files to Windows System32 directory. For example: Copy OpcProxy.dll C: / Winnt / System32 Copy Opccomn_ps.dll C: / WinNT / System32 COPY opc_aeps.dll c: / winnt / system32 copy opchda_ps.dll c: / winnt / system32 copy aprxdist.exe c: / winnt / system32 copy opcenum.exe c: / winnt / system32 2. installation proxy DLL files REGSVR32 opcproxy.dll REGSVR32 Opccomn_ps.dll regsvr32 opc_aeps.dll regr32 opchda_ps.dll 3. If there is no actXprxy.dll file in your Windows system directory, run aprxdist.exe program Aprxdist 4. Register OpCenum.exe opcenum / Re Gserver wants to learn more about OPC standards, please refer to the following website: OPC Foundation http://www.opcfoundation.org China Industrial Control Network OPC Forum http://www.gongkong.com/tech/forum/list38.asp
