OPC UA Companion Specifications: What They Are and When They Help

OPC UA's core standard defines how to transport typed data securely, but it says little about what a machine or a valve means. Companion specifications fill that gap by defining standardized information models for specific industries and device types - and they are the difference between exchanging data and exchanging meaning.

Why Companion Specs Exist

Without them, every integrator invents a tag structure: one project exposes temperature one way, another differently. A companion spec defines the object types, properties, and semantics once, so any OPC UA client that understands the spec can interpret data from any vendor that implements it.

Examples You Will Meet

• OPC UA for Machinery (VDMA): machine types and condition states for packaging, machine tools, robots, and more.
• OPC UA for Process Automation (PA-DIM): field device information for process industries.
• OPC UA for PLCopen: maps IEC 61131-3 concepts (tasks, programs, tags) into UA.
• OPC UA for Robotics (OPC Foundation / VDMA): robot kinematics and motion commands.
• OPC UA for AutoID: barcode and RFID reader integration.

Practical Advice

• When buying new equipment, request OPC UA with the relevant companion specification in the tender. If the vendor cannot say which spec they implement, you will get a proprietary tag dump.
• Prefer open, multi-vendor specs (OPC Foundation, VDMA) over single-vendor UA-like models.
• Still plan a mapping layer: even compliant devices expose different granularity, and the plant's naming conventions will still need to be applied somewhere.