OPC UA (OPC Unified Architecture) is a platform-independent, open standard for exchanging industrial data securely between machines, controllers and software, published by the OPC Foundation and standardized as IEC 62541.
OPC UA succeeded OPC Classic, which depended on Microsoft Windows COM/DCOM. The OPC Foundation released it in 2008. It runs on PLCs, embedded devices, PCs and cloud servers across operating systems.
Two things set it apart from simpler protocols. First, an information model: data is not a flat list of values but a browsable structure of objects, variables, methods and events, with types. A client can discover what a server offers. Companion specifications define standard models for equipment classes such as machine tools, robots and analyzers. Second, built-in security: X.509 certificates for application authentication, signing and encryption of messages, user access control and auditing.
OPC UA supports two communication patterns. Client/server is request-response, used for reading, writing and calling methods. Publish/subscribe (PubSub) sends data to many receivers through middleware, which can include MQTT. A common confusion is to treat OPC UA and MQTT as rivals. They overlap but solve different problems: OPC UA defines rich data semantics; MQTT is a lightweight transport. Many architectures use both. In practice, security features are often left disabled at commissioning, which defeats their purpose.
Questions about OPC UA
What is the difference between OPC UA and OPC Classic?
OPC Classic depended on Microsoft Windows COM/DCOM. OPC UA succeeded it, was released by the OPC Foundation in 2008, and runs on PLCs, embedded devices, PCs and cloud servers across operating systems.
What security does OPC UA have?
Security is built in: X.509 certificates for application authentication, signing and encryption of messages, user access control and auditing. In practice, these features are often left disabled at commissioning, which defeats their purpose.
Related terms
MQTT
MQTT is a lightweight publish/subscribe messaging protocol, an OASIS standard, in which devices send messages to named topics on a broker and any subscribed application receives them.
Unified namespace (UNS)
A unified namespace (UNS) is an architecture pattern in which plant and business systems publish their current data to one shared, hierarchically organized hub, usually an MQTT broker, instead of exchanging it through point-to-point integrations.
Industrial IoT (IIoT)
Industrial IoT (IIoT) is the network of sensors, instruments, and machines in industrial settings that are connected to computers and software to collect and use operational data.
PLC (programmable logic controller)
A PLC (programmable logic controller) is a ruggedized industrial computer that reads inputs from sensors, runs a user program, and drives outputs such as motors and valves in real time.
ISA-95
ISA-95 is an international standard series, also published as IEC 62264, for integrating enterprise business systems with manufacturing control systems.