Why OPC UA Is Becoming the Standard in Modern Industry
Industry 4.0 requires standardized data exchange between PLCs from different manufacturers, SCADA, MES, ERP, and the cloud. OPC UA (OPC Unified Architecture), developed by the OPC Foundation, has been the de facto standard since 2008—adopted by Siemens, Schneider Electric, Rockwell, Beckhoff, Bosch, and most major manufacturers.
Compared to Modbus, OPC UA offers:
- Native security — encryption, authentication, security policies.
- Rich data model — objects, nodes, types, methods, events, alarms.
- Interoperability — compatibility between vendors without manual mapping.
- Contextual information — data includes its unit, valid range, and timestamp.
- Reliability — quality status (Good/Bad/Uncertain) for each value.
OPC UA to Cloud Architecture
The OPC UA Subscription model is more efficient than Modbus polling: the OPC UA server notifies the client only when a value changes (or exceeds a deadband threshold), reducing bandwidth consumption.
OPC UA vs. Modbus: A Comparison
| Critère | Modbus RTU/TCP | OPC UA |
|---|---|---|
| Native Security | Aucune | TLS + X.509 Certificates |
| Data Model | Flat Registers (Integers) | Objects, types, methods, alarms |
| Exploring the Facilities | Manuelle | Automatic (browse the tree) |
| Alarms and Events | Integrated A&E | |
| Metadata (unit, range, etc.) | ||
| Interopérabilité | Basique | Standardized Profiles by Sector |
| Hardware Compatibility | ★★★★★ (universal) | ★★★ (modern amenities) |
| Implementation Complexity | Faible | Moderate to high |
OPC UA and Modbus are not mutually exclusive—they coexist. A modern industrial gateway supports both: OPC UA for newer PLCs (S7-1500, M262, CP600, etc.) and Modbus RTU/TCP for existing equipment.
Compatibility by Manufacturer
Siemens
- S7-1200 / S7-1500: built-in OPC UA server, configurable via TIA Portal.
- S7-300 / S7-400: via IE CP module (e.g., CP 343-1) or external OPC UA server.
- WinCC: built-in OPC UA DA server.
Schneider Electric
- Modicon M262, M580: native OPC UA server.
- M340, M221: via EcoStruxure Machine Expert (OPC UA server add-on).
- EcoStruxure EcoDataCenter: OPC UA for energy equipment.
Beckhoff TwinCAT 3 includes a full-featured OPC UA server with support for OPC UA profiles for IEC 61131-3.
Rockwell Automation ControlLogix, CompactLogix: OPC UA access via the RSLinx Enterprise server or third-party connectors.
OPC UA Security Best Practices
- Security Policies — Use at least
Basic256Sha256withSign & Encrypt. Never useNonemode in production. - Certificates — Each client and server has a unique certificate. The gateway connects only to servers whose certificates it has validated.
- VPN — Even with secure OPC UA, do not expose port 4840 directly to the Internet. Use a VPN as the transport layer.
- Whitelist — The OPC UA server must only accept connections from the gateway’s IP addresses.
- Audit — Enable OPC UA auditing (AuditEventType) to log all connections and changes.
The Eziwan Approach
The Eziwan Gateway implements an OPC UA client that connects to your PLC servers, subscribes to the configured nodes, and publishes the data to the Eziwan Cloud via MQTT and VPN. Configuration is visual—no need to know OPC UA syntax: you simply navigate the PLC’s data tree and select the variables to monitor.
For more information: Modbus Cloud, Industrial MQTT, and remote site monitoring.