Using IOT-Tree to Connect Various Devices and Output via OPC UA Server

IOT-Tree Server is an open-source IoT software that can serve as SCADA software for automation systems. It provides various capabilities including device connectivity, data organization and management, data sharing and utilization, message flow control logic, and human-machine interaction. Of course, you can also use this software simply as a data acquisition terminal or edge computing platform.

This is part of a series of articles on IOT-Tree Server. You can refer to other articles to learn more about the benefits IOT-Tree can bring you:

Using IOT-Tree Server to Connect Mitsubishi Q Series PLC via MC Protocol

Using IOT-Tree Server to Connect Siemens PLC S7–300/1200/1500

Using IOT-Tree Server to Connect Siemens PLC S7–200 via PPI (RS485)

The series also includes articles covering the complete process of using IOT-Tree to complete a specific project, very detailed, as follows:

Hands-on Guide to Computer Room Automation Monitoring — 10 Project Completion Summary

This article describes how IOT-Tree Server’s built-in OPC UA Server service supports outputting project data via OPC UA. This functionality is similar to Kepware software — essentially, IOT-Tree can also serve as an OPC UA software, and embedded devices running IOT-Tree in industrial settings can be used as OPC UA gateways.

1 Introduction to OPC UA

OPC UA (Open Platform Communications Unified Architecture) is a cross-platform industrial communication standard for secure and reliable data exchange between devices, systems, and services. It was developed by the OPC Foundation to address the limitations of traditional OPC (such as OPC DA) and to support modern Industrial IoT (IIoT) requirements.

Core Features Cross-platform: Supports Windows, Linux, embedded systems, etc., not dependent on a specific OS. Security: Built-in encryption (TLS/SSL), identity authentication (X.509 certificates), and permission management. Information Modeling: Describes complex data structures through the Address Space, supporting custom objects and variables. Extensibility: Integrates real-time data, historical data, alarms, and events.

Technical Architecture Communication Protocol: Supports TCP, HTTP/S, and WebSocket, adapting to different network environments. Information Model: Builds a hierarchical data model based on Nodes and References, compatible with OPC Classic and industry standards (e.g., PLCopen, ISA-95). Service Set: Provides basic services such as discovery, read, write, and subscribe, as well as advanced features like method calls.

Application Scenarios Industrial Automation: Connecting PLCs, sensors to SCADA/MES systems. Smart Manufacturing: Enabling device interoperability and digital twins. Energy Management: Monitoring power equipment status and energy consumption data.

Comparison with Traditional OPC OPC DA: Windows-only, relies on COM/DCOM, no built-in security mechanisms. OPC UA: Platform-independent, supports complex models, high security, suitable for cloud deployment.

2 IOT-Tree OPC UA Output Support

IOT-Tree Server directly provides external OPC UA Server support. This server is provided as a built-in service. In the IOT-Tree Server main management interface, click the “Settings” button under “Service Programs”, and you can see the “OPC UA Server” service in the popup dialog list. You can set the parameters of this service or control its start/stop, as shown:

This service can output data from one or more projects in IOT-Tree Server via OPC UA.

3 Setting Up OPC UA Server

Click the edit button to open the detailed parameter settings interface:

By default, the OPC UA Server is not enabled and uses port 4840. You can modify the port and enable the OPC UA Server.

You can set user authentication required for OPC UA Client access. Each line represents a user and password, formatted as follows:

user1=password11
user2=xxxxxxx

In the project list, you can see all projects contained in this IOT-Tree instance. You can select the projects you want to expose for OPC access.

The Trusted Certificates and Rejected Certificates sections below are for certificate management required by OPC UA Clients accessing this OPC UA Server. See the following section for details.

After successfully setting the above parameters, click the “Start Service” button in the Service list. When successful, this IOT-Tree Server instance now supports OPC UA Server.

4 Accessing with OPC UA Client

Install a “Matrikon OPC UA Explorer” on your computer. This article uses this software as the OPC UA Client. Open the software and click “Add New Server”. You can see the “Connect Server” area on the right directly displays the Local Discovery list. Because the configured OPC UA Server port is the default and this Client software runs on the same computer as IOT-Tree, the Client can directly discover our configured Server. If using a non-default port or different computer, you can manually enter the host and port, then click “Search” to find the corresponding Server, as shown below:

Expand the corresponding IOT-Tree OPC Server node to see the access methods available: Anonymous, Sign (Certificate), Sign (Certificate) & Encrypt.

Below that, you can also enter the username and password for connecting to the Server, which must match the user credentials configured above.

In the image above, we selected the Sign (Certificate) & Encrypt access method and entered the username and password. Click the “Connect” button. The connection will fail, as shown below:

This is because, under certificate verification connection mode, the Client automatically creates a certificate and submits it to the OPC UA Server. However, the Server automatically records the certificate on first access and rejects it. You need to trust the new Client certificate in the IOT-Tree OPC UA Server management interface.

Return to the OPC UA Server service management. Click the edit button. You’ll see the popup interface has changed: in the Rejected Certificates list, a connection certificate has appeared. Simply click the upward arrow button to set it as trusted, moving this certificate to the trusted list. This completes the trust operation for the accessing Client, as shown below:

Return to the “Matrikon OPC UA Explorer” software (note the username and password input), and click “Connect” again. The connection should succeed. In the successful connection dialog, you can find the corresponding project in the tree directory on the upper right. Expand and set the nodes to monitor, as shown below:

Note: Please start the IOT-Tree internal project and ensure it enters normal operation. You can then view the data changes of monitored nodes on the Client side. With this, the OPC UA Server is running normally and can provide a standard OPC UA interface for other systems such as ERP, MES, device management software, etc.