OPC UA Technology Solutions

What is OPC UA?

OPC UA (Open Platform Communications Unified Architecture) is a vendor-independent standard for industrial data exchange, maintained by the OPC Foundation and standardised as IEC 62541. Unlike a pure transport protocol, OPC UA also describes what the data means: a machine exposes its values as an information model, with data types, units, methods and relationships. A client can browse this model and understand the data without knowing the machine in advance.

How OPC UA is used in the IIoT

OPC UA is the common interface for getting data out of controllers, machines and plants, for example for MES, production data acquisition, OEE analysis or condition monitoring. Many current controllers from Siemens, Beckhoff, B&R or Bosch Rexroth have a built-in OPC UA server. For entire machine classes there are Companion Specifications that define how, for instance, an injection moulding machine (EUROMAP 77) or a machine tool (umati) describes its data. Machines from different vendors thus speak the same language.

OPC UA or MQTT?

OPC UA traditionally follows the client-server model: a client connects to a machine and reads or subscribes to values. This is ideal for connecting individual machines but scales less well when hundreds of machines have to feed many applications. That is where MQTT is strong. Many architectures therefore combine both: OPC UA at the machine, MQTT for distribution. With OPC UA PubSub, OPC UA can now also send its information models over MQTT itself.

How an OPC UA connection is structured

On the machine side, the OPC UA server runs either directly in the controller or in an upstream gateway. It publishes an address space with objects, variables and methods that a client can browse. The client, such as an MES, an edge platform or a visualisation tool, logs on with a certificate and subscribes to the values it needs. Changes are then pushed to it automatically instead of it having to poll cyclically. The standard connection runs over TCP on port 4840.

What to consider when choosing

First check whether your existing controllers already include an OPC UA server or whether it needs to be licensed. Older machines without OPC UA are connected through gateways that translate Profinet, Modbus or S7 protocols. Certificate management, often underestimated in operation, also matters, as does whether a Companion Specification exists for your machine class. Using one saves a lot of mapping work later.