industrial//industrial data layer//OPC//OPC UA

2026-09-06

OPC UA (OPC Unified Architecture) is an industrial interoperability standard, the modern evolution of OPC, that exposes plant data through an information model of objects, variables, methods and hierarchies with semantics. It is platform independent, with no COM/DCOM and no Windows requirement, and has built-in security (certificates, encryption, authentication).

In that model, Boiler1 has a Temperature whose Value is 72.4, Unit is degrees Celsius, Quality is Good and Timestamp is such-and-such, and Compressor_17 exposes Speed, Temperature, State, Manufacturer and a Start() method.

That richness is the difference between a number and a datum, and it is why OPC UA is central to digitalization: a consumer can browse a server and discover what exists, with units and types, instead of reading a register map. Modbus moves a raw number to a numeric address and leaves the meaning in a PDF; OPC UA moves a named, typed, timestamped node with its quality, and the two live forty years apart in the same cabinet. (A schema-driven configurable data model in software solves the same problem in another world: the consumer discovers the structure of the data instead of hard-coding it.)

It belongs to the supervision layer. Below it the fieldbuses and EtherCAT close loops in microseconds to milliseconds; OPC UA, beside Modbus TCP and PROFINET's supervisory traffic, serves values to SCADA, historians and analytics on a scale of tens of milliseconds to seconds, and no fast loop should depend on it (determinism).

It runs over TCP/IP and so over any stack, including 4G and radio at a remote station (protocol stack). Modern PLCs embed an OPC UA server; a legacy plant gets one from the edge gateway, which reads Modbus, HART and PROFIBUS and exposes them as OPC UA nodes.

Every value can carry two clocks, a source timestamp set where it was measured and a server timestamp set where it was served, which is the distinction between event time and arrival time made part of the protocol.

Built-in security is a set of options, never a guarantee: a server deployed with the security policy None, with self-signed certificates accepted blindly or with anonymous login left on, is as open as Modbus. The protection is in the configuration, the certificate management and the network segmentation around it (cyber-physical security).

Its natural partner rather than rival is MQTT in the plant: OPC UA describes and serves data, MQTT distributes it; a common pattern publishes OPC UA structured payloads over MQTT.