OPC UA
Last updated on 16 October 2025
OPC UA communication protocol is a modern standard for industrial data exchange. You will find OPC UA everywhere — from PLCs and SCADA to MES and cloud — and it plays a central role in Industry 4.0 and Industrial IoT. In this documentation, we explain in simple terms what OPC UA is, what characteristics it has, which devices support it and how to set up a connection.
What is OPC UA
OPC UA (Open Platform Communications – Unified Architecture) was developed by the OPC Foundation as the successor to classic OPC DA. Instead of flat register access, OPC UA offers a service-oriented, platform-independent and secure architecture. Key advantages include platform independence (no more Windows/DCOM dependency), encryption and authentication, and standardized information models that add semantics to data.
Communication Models and Transport
OPC UA uses TCP/IP as base transport and supports two main modes: Client-Server for point-to-point communication and Publish-Subscribe (Pub/Sub) for efficient broadcast scenarios. For real-time applications, there is also support for UA Pub/Sub via UDP or TSN (Time Sensitive Networking).
Key Features of OPC UA
The core features of OPC UA that you will encounter in practice:
- Platform and vendor independent — runs on PLCs, PCs, embedded systems and in the cloud.
- Object-oriented data model — data are nested objects with attributes, methods and events.
- Built-in security — X.509 certificates, encryption and user authentication.
- Standardized information models — sector-specific models add semantics.
- Two communication models — Client-Server and Pub/Sub.
- Real-time support — UA Pub/Sub via UDP or TSN enables deterministic communication.
Supported Devices and Applications
OPC UA often functions as a bridge between OT and IT. Below you will find an overview of common devices and applications that support OPC UA.
| Application / device | Description |
|---|---|
| Modern PLCs | More and more PLCs (e.g. Siemens S7-1500, Omron NX/NJ, Beckhoff, B&R) have built-in OPC UA servers |
| SCADA and HMI systems | Can connect as OPC UA client to multiple PLCs simultaneously |
| Edge devices and gateways | Translate field protocols such as Modbus or FINS to OPC UA towards IT systems |
| MES / ERP systems | Can retrieve standardized process data via OPC UA |
| Cloud platforms and IoT hubs | Many cloud providers support OPC UA connectors for industrial data integration |
Setting up an OPC UA Environment
Setting up an OPC UA connection consists of configuring a server (usually the PLC or a gateway) and one or more clients (SCADA, MES or applications). Below are the usual steps.
1. Server configuration
- Activate the OPC UA server on the PLC or gateway.
- Set network parameters (IP address, port — default TCP 4840).
- Generate or upload security certificates (X.509).
- Define which variables, tags or objects are published.
- Set access rights per user or client.
2. Client configuration
- Add the server via Endpoint URL (e.g. opc.tcp://192.168.0.10:4840).
- Import the server certificate and accept it (trust list).
- Browse through the Address Space to discover available data objects.
- Connect and configure the desired subscriptions or method calls.
Security and Certificates
OPC UA uses X.509 certificates by default for authentication and encryption. Both client and server must trust each other’s certificates. This provides a much higher level of security than traditional protocols such as Modbus or FINS. Proper implementation of certificate management and policies is crucial for cybersecurity in industrial environments.
OPC UA Data Model and Address Space
Unlike classic register-based protocols, OPC UA works with a hierarchical object model. The data from a PLC is presented as a tree structure of nodes, each with attributes (value, data type, status), methods (executable functions, e.g. reset or start), events (asynchronous notifications such as alarms) and references that logically connect nodes to each other. This rich structure enables semantic interpretation and context, unlike flat register addressing of for example Modbus.
Example: Nodes and Methods
A node can have multiple attributes (Value, Timestamp, Quality), references to other nodes and methods that you can call. The Address Space is searchable, which facilitates discovery and model-driven integration.
Practical Tips
- Ensure that your network and ports are properly defined and secured.
- Use certificates and a trust list for all production clients and servers.
- Document information models so that integration with MES, SCADA and cloud systems is consistent.
- Test Pub/Sub and Client-Server scenarios for latency and determinism if real-time requirements apply.
- Keep track of firmware and certificate lifecycles; outdated certificates often unintentionally block access.
Where You Encounter OPC UA in your Architecture
You will often use OPC UA between PLCs and higher layers such as SCADA, MES and cloud platforms. It is the logical choice for integration in Industrial IoT environments and for implementations within Industry 4.0. If you are already working with cloud connectors or with a partner such as Remote, then OPC UA ensures a uniform and secure data flow towards IT systems and analytics.
In Summary
OPC UA communication protocol is the modern, secure and semantic standard for industrial data exchange. It combines platform independence, an object-oriented data model and built-in security (X.509) and is suitable for integration at all levels of the automation pyramid. Well-structured implementation improves interoperability between PLCs, SCADA, MES and cloud platforms and strengthens your cybersecurity strategy. For questions about integration and remote access, you can consult the documentation of your devices and integration platforms.