OPC UA has become a bridge connecting enterprise-level computers and embedded automation components
OPC UA
OPC Unified Architecture (OPC Unified Architecture) is a new technology created by the OPC Foundation, which is more secure, reliable, and neutral (not related to suppliers), and is used for transmission from the manufacturing site to the production planning or enterprise resource planning (ERP) system Raw data and preprocessed information. Using OPC UA technology, all required information can reach every authorized application and every authorized person anytime and anywhere.
OPC UA is independent of the manufacturer, applications can communicate with him, developers can develop it in different programming languages, and support it on different operating systems. OPC UA makes up for the deficiencies of the existing OPC, adding important features such as platform independence, scalability, high availability, and Internet services.
OPC UA is no longer based on the Distributed Component Object Model (DCOM), but on the Service Oriented Architecture (SOA). OPC UA can therefore connect more devices.
Today, OPC UA has become a bridge between enterprise-class computers and embedded automation components-independent of Microsoft, UNIX or other operating systems.
1 Termination of Component Object Model (COM)/Distributed Component Object Model (DCOM)
The data exchange between traditional OPC applications is based on Microsoft's Component Object Model (COM) technology. Because the Windows operating system has been widely used worldwide, and at the same time it has promoted the use of Windows computers in automation, COM technology has also created conditions for the widespread use of OPC technology. In early 2002, Microsoft released a new .NET framework and announced the cessation of development of COM technology. Although this does not mean that the future Windows operating system does not support COM, as a result of the suspension, the basic technology of traditional OPC is no longer developed, sooner or later, it will be eliminated, so new replacement solutions must be sought.
Limitations of 2COM
In the 1990s, with the popularity of Windows computers, a set of features introduced by Microsoft's COM/DCOM technology has been highly appreciated by home computer users and industrial automation users. These features include copy and paste, drag and drop, link and embed. DCOM also provides a complete communication infrastructure with necessary security mechanisms, such as authorization, authentication, and encryption.
The DCOM security mechanism can realize the computer's remote access to data and programs. However, the DCOM security mechanism also poses challenges to installation engineers, system integrators and developers to manage projects, including OPC communications across PCs. Setting the DCOM security function correctly is a very difficult task and requires a lot of professional knowledge. As a result, installation engineers and system integrators routinely choose fast processes and adopt loose access authorizations on all networked OPC computers, causing most protections to fail and allowing unauthorized remote access.
This approach goes against the requirements of information technology (IT) security. During long-term operation, there may be a risk of damage caused by careless or sabotage. DCOM security settings often require a special ability, and configuring OPC communication functions is very easy.
3OPC communication through the firewall
In the automation industry, it has long been recognized that OPC communication needs to cross computer boundaries. This is another place where DCOM restricts traditional OPC communication. DCOM requires multiple ports, such as authentication, data transmission and a series of services to establish a connection.
Therefore, many ports have to be opened in the firewall to allow DCOM communication to pass through it. Each opening of a port on the firewall is a security hazard and provides a potential for hacker attacks. The tunnel technology in OPC UA is a widely accepted strategy that solves the problem of DCOM limitations in traditional OPC products.
4Using OPC on non-Windows platforms
In industrial applications, the almost "ubiquitous" Microsoft platform, using DCOM as a component of the operating system is an important factor for the rapid acceptance of traditional OPC. But at the same time, the integration concept of OPC is not effective when using other operating systems, because they do not support DCOM. For example, in the IT industry, this is the case when Unix or Linux systems are often used.
The same is true for automation, and some application areas explicitly refuse to use the Windows operating system. The field of embedded devices is another field where Windows is difficult (except for Windows CE or embedded XP). Here, complex applications are directly embedded in field devices, PLCs, operating panels and other devices. They run VxWorks, QNX, embedded Linux, RTOS, or other embedded operating systems without DCOM. The integration concept of using OPC in these fields is doomed to fail, because OPC requires DCOM as a technical basis, and this basis is missing in embedded systems.
5 Realize cross-platform OPC communication through Web services
With the release of the OPC XML-DA specification in 2003, the OPC Foundation demonstrated for the first time a way to be independent of the Windows platform and to overcome the limitations of DCOM. Today, many OPC XML-DA products demonstrate OPC technology based on Web services.
However, the data throughput of XML-DA communication is still not as good as that of DCOM, and the communication speed is 5 to 7 times slower. This speed is too slow for many automation requirements. The OPC communication function based on Web services is still useful because it realizes the ability to cross the operating system, but still needs to further improve the data transmission performance.
6 unified data model
So far, the traditional OPC technology has three different OPC servers-data access server, alarm and event server and historical data access server. If the user needs to obtain the current value of a temperature sensor, an event where the temperature exceeds a limit value, and a historical average value of the temperature, then he must send 3 requests and visit 3 servers.
It takes a lot of time for users to access process data, events and historical data in different ways. Therefore, unifying these three object models can make such things very simple, which is not only beneficial to suppliers of OPC products, but also to system integrators and users.
7Support complex data structure
One of the main applications of OPC is the operation and monitoring of serial communication or fieldbus networking equipment. In order to configure the device, the OPC client needs to write the data type to the device through the OPC server, including the meaning of the data structure element.
The OPC Foundation has created a method for describing complex data structures, namely complex data specifications. However, most traditional OPC products on the market today, with few exceptions, cannot use complex data specifications.
8 Ensure that communication does not lose data
The earliest defined data access allows the client application to periodically obtain the current state of the process data. If there is a problem with the physical communication connection between the OPC client and the remote OPC server, the data communication will be damaged. When the communication is damaged, the data transmitted to the OPC client will be changed or even lost.
This data loss is not critical in some data access applications, such as trend recording, process monitoring, or process display. But it is very critical in some applications. For example, OPC technology has become the basis of these areas, such as the chemical or petrochemical industries, where data must be recorded seamlessly.
In order to achieve this goal, suppliers need to implement special extension methods. They use a connection-based monitoring system to ensure that the disconnected communication is quickly detected. If the communication is disconnected, it can automatically reconnect. The data access server has data caching, redundancy, storage and forwarding functions. These extension methods are very useful, but they are not defined in the traditional OPC specification and will vary from vendor to vendor.
9 Increased protection against unauthorized data access
With the continuous growth of Ethernet-based communications in the automation industry, automation and office networks have become entangled. At the same time, the idea of ​​vertical integration has created new requirements, and this type of integration has also brought new security risks. OPC has also increased the use of remote maintenance and remote control concepts.
It is mentioned here again that unauthorized access to the periphery must meet stricter information security requirements. With the growth of cybercrime, espionage, and sabotage, information technology security is becoming more and more important-so there are security requirements for using OPC. Traditional OPC vendors have not developed proprietary preventive measures, so they cannot meet these safety requirements.
0 supports new command calls
In many applications, not only is it important to read and write values, but also to execute commands, such as starting or stopping a drive or downloading a file to the device. The OPC command specification defines the method of executing these commands, but this is only valid in OPC UA and cannot be used in traditional OPC.
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