OPC Tag Grouping From Different OPC DA Servers To OPC UA

In this comprehensive tutorial, we'll explore the process of grouping OPC tags from various OPC DA servers to OPC UA. This guide will cover essential concepts, step-by-step instructions, and troubleshooting tips to help you efficiently manage and consolidate your industrial data communication.

1. Introduction to OPC DA and OPC UA

1.1 What is OPC DA?

OPC DA (Data Access) is a classic OPC protocol used for real-time data communication in industrial automation. It allows OPC clients to connect to OPC servers and access OPC data and tag values from PLCs and other devices. OPC DA operates on a client-server model, where the OPC server acts as a data provider, and the OPC client subscribes to receive updates. This protocol has been widely used for years, but has limitations in terms of security and cross-platform compatibility. OPC DA is primarily designed for use within Windows environments, which can limit its application in modern, diverse industrial networks.

1.2 What is OPC UA?

OPC UA (Unified Architecture) is a more advanced and versatile protocol developed by the OPC Foundation to address the limitations of OPC DA. It provides a unified architecture for industrial data communication that is platform-independent and offers enhanced security features. In OPC UA, data is also organized in a hierarchical structure called an address space. This allows for more flexible and meaningful representation. OPC UA servers can be configured to support different security levels, including encryption and authentication, ensuring secure data transmission across local networks and the Internet.

1.3 Why migrate from OPC DA to OPC UA?

Migrating from OPC DA to OPC UA offers numerous benefits for industrial automation systems. OPC UA provides enhanced security features, including encryption and authentication, which are crucial in today's interconnected industrial environments. It also offers platform independence, allowing for easier integration across different operating systems and devices. The main advantage is that it doesn't use Windows specific things like DCOM and works on top of TCP/IP. This helps connect programs on computers with different operating systems, both new and old.

2. Understanding Tag Grouping

2.1 What are OPC tags?

OPC tags are individual data points in an industrial automation system that represent specific pieces of information, such as sensor readings or equipment status. These tags serve as the basic units of data exchange between OPC servers and clients. They are the basic units of data exchange between OPC servers and clients. In OPC DA, tags are arranged into OPC items within OPC groups, whereas in OPC UA, they form a part of a hierarchical address space.

The attributes of each OPC tag typically include a unique identifier, data type, value, quality, and timestamp. The tag value indicates the current state or measurement of the associated variable, while the quality indicates the data's reliability.

2.2 Why group tags from different servers?

Grouping tags from different OPC DA servers into a unified OPC UA server offers several advantages in industrial automation. It allows for centralized data management, reducing the complexity of maintaining multiple server connections. By consolidating tags, you can create a single point of access for all your critical data, simplifying client applications and improving overall system efficiency. If you are sharing your OPC UA server through public networks, such as the Internet, you should only open a single TCP port number, which will improve your system security.

Moreover, aggregating tags from diverse servers into OPC UA provides a means of modernizing outdated systems while preserving compatibility with the existing OPC DA infrastructure, thereby facilitating a more seamless transition to more advanced industrial communication protocols.

2.3 Benefits of tag grouping in OPC UA

Tag grouping in OPC UA offers numerous benefits for industrial automation systems. It allows for more efficient data organization and management, enabling users to create logical structures that reflect their processes or equipment hierarchies. This improved organization can lead to easier navigation and quicker access to relevant information for operators and engineers. Additionally, tag groups in OPC UA can be assigned specific properties, such as update rates or security settings, allowing for fine-tuned control over data access and performance.

Another significant advantage of tag grouping in OPC UA is the ability to optimize network traffic and server resources. By grouping related tags together, you can configure subscription rates and execution modes that balance real-time data needs with system performance. This can result in more efficient use of bandwidth and reduced load on both the OPC UA server and clients. Furthermore, tag grouping facilitates implementation of security policies, as access controls can be applied at the group level, streamlining the process of managing user permissions and data visibility across the system.

3. Step-by-Step Guide to Grouping Tags using Datatag Link Software

3.1 How to connect to OPC DA servers?

Connecting OPC DA servers with Datatag Link software requires several steps to ensure proper communication. First, launch the Datatag Link application and navigate to the server connection section. Here, you'll need to specify the OPC DA server details, including the server name, host computer or PLC IP address, and any required authentication credentials. It's crucial to ensure that the necessary DCOM configurations are in place, especially when connecting to remote OPC DA servers. It is preferable to install the software on the same computer as the OPC server.

Once the server details are entered, initiate the connection process. Datatag Link will attempt to establish communication with the OPC DA server. If successful, you'll be able to browse the available tags and OPC groups on the server. If you encounter any connectivity issues, consult the server documentation or consider contacting the software support team for assistance.

3.2 How to select and export tags?

After successfully connecting to the OPC DA servers, the next step is to select and export the desired tags. Use the tag browser functionality in Datatag Link to navigate through the available OPC groups and items. You can typically filter and search for specific tags based on criteria such as name or data type. Select the tags you wish to group and export to OPC UA.

The program also allows you to import multiple tags from an XML or CSV file. Use the "File" menu to export one tag and add all the others. For future reference and maintenance, remember to document your tag selection process.

3.3 What is the process for mapping tags to OPC UA?

Mapping tags from OPC DA to OPC UA involves creating a correspondence between the original OPC DA items and their new representation in the OPC UA address space. In Datatag Link, this process is easy to complete. You can just the source tag ID to another side and then select the corresponding data type. Of course, you can specify other tag ID or slightly transform the source tag name.

3.4 How to create tag groups in OPC UA?

Creating tag groups in OPC UA involves organizing the mapped tags into logical structures within the OPC UA address space. In Datatag Link, you'll typically use the dot as a delimiter of a data tag path in the OPC hierarchical structure. For example, Group1.SubGroup1.SubGroup2.TagName.

4. Configuring OPC Server

4.1 How to set up security for the OPC UA server?

Setting up security for the OPC UA server is crucial to protect your industrial data and ensure authorized access. Begin by configuring the server's security policies, which define the encryption and authentication methods used for client connections. OPC UA supports various security modes, including None, Sign, and Sign and Encrypt. It's recommended to use the highest level of security that your system can support, typically Sign and Encrypt, to ensure data integrity and confidentiality.

Next, set up user authentication and authorization. This involves creating user accounts or integrating with existing authentication systems. Define roles and access rights for different users or groups, ensuring that each has appropriate permissions for reading, writing, or browsing specific tag groups. Implement certificate-based security by generating and managing X.509 certificates for both the server and clients. This establishes trust between the components and prevents unauthorized access. Regular security audits and updates to these configurations are essential to maintain a robust security posture for your OPC UA server.

4.1 Testing the grouped tags using your favorite OPC client

To ensure proper functionality of your OPC UA server configuration, you should test the grouped tags. Begin by using an OPC UA client application to connect to your newly configured server. Verify that you can successfully establish a connection and browse the address space to locate your tag groups. The free UA Expert tool can be used for that. Make sure your groups are organized correctly and that all the tags are included.

Check data access and update functionality by carrying out read and write operations on various tags within the groups. Please ensure that the update rates and subscription behavior are in accordance with your configured group properties. Test different client scenarios, such as subscribing to multiple tag groups simultaneously, to validate performance under various conditions.

5. Troubleshooting Common Issues

5.1 What are frequent connectivity problems?

1. Frequent connectivity problems when grouping OPC tags from different OPC DA servers to OPC UA can arise from various sources. One common issue is network configuration problems, such as firewalls blocking necessary ports or incorrect IP addressing. Ensure that all required ports for OPC DA and OPC UA communication are open and properly configured.
2. Another frequent problem is DCOM configuration issues for OPC DA connections, especially when dealing with remote servers. Verify that DCOM settings are correctly set up on both client and server machines.
3. Authentication and security misconfigurations can also lead to connectivity problems. This includes incorrect usernames or passwords, mismatched security policies between clients and servers, or certificate issues in OPC UA and OPC DA connections.

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