OPC UA & Information Modelling

What does OPC UA information modelling consulting cover?

OPC UA information modelling consulting designs the address space from the machine's real signals.

This is for device manufacturers, machine builders and software vendors. We design the address space from the machine’s real signals, apply or extend the IEC 62541 companion specification that fits it, and build the servers and clients that expose it. Our own modelling tool generates NodeSet2 from base and companion specifications; it produced the EUROMAP 79 robot model for a delivered plastics and rubber machine. The engagement usually falls into one or more of these shapes:

• A model for a new product. OPC UA system design and architecture, from the machine’s signals to a NodeSet2 a customer’s MES can browse.
• A companion specification applied properly. IEC 62541 companion specification work, including extensions for signals the specification does not cover.
• Server or client development. OPC UA server and client development on embedded, Linux or Windows platforms.
• One endpoint over many machines. OPC UA aggregating server development, where the machines already speak OPC UA and the problem is fan-in. Our team has built the layer through which a remote ERP subscribed to several machines on one production line.
• A migration. OPC DA to OPC UA migration, or EUROMAP OPC UA version migration where the companion spec moved underneath a shipped product.
• The security model. OPC UA security model implementation, certificate and trust list management, and the policy migration described below.

We do not commission plants. The model, the server and the security design inside your product or platform are ours to build, and we test them with your engineers onshore and remotely.

What decides the outcome of an OPC UA project?

The information model, and it decides whether everything downstream is cheap or expensive.

Two vendors’ machines that both expose typed, companion-spec models can be consumed by one MES integration. The same two machines exposing bare tag lists need one integration each, then another when either changes. The cost does not appear at the machine; it appears every time somebody has to consume it. OPC DA to OPC UA migration is modelling work, not a protocol swap. A DA tag list carries the plant’s meaning implicitly, in naming conventions and in the knowledge of the people who built it. We make that meaning explicit as typed, structured data. Wrapping the same tag list in an OPC UA server without doing so carries the same problem forward.

Which companion specification applies to my machine?

Start by looking: most machine categories now have one, and building a private model beside it is a decision.

Plastics and rubber machinery has the EUROMAP series, and our delivered work sits there: EUROMAP 83 for the general type definitions, 77 for the injection moulding machine to MES interface, 79 for robots and handling devices. Machine tools have umati. VDMA has published across a long list of sectors, and the OPC Foundation maintains the full register. Two things regularly need deciding:

• How to extend the model where the specification does not reach, designed against the spec’s own type system, not a set of extra tags bolted on beside it.
• What happens when the companion spec moves version underneath a product already in the field. EUROMAP OPC UA version migration is a dedicated exercise, because a customer’s MES integration is bound to the types you shipped.

Which OPC UA stack should I build on?

The choice narrows once volume and support obligations are considered, and the licence rarely decides it.

We do not resell any of them. We port and integrate whichever you choose, and we give our recommendation on which and why before you decide.

What makes an OPC UA server slow?

Usually the access pattern, and occasionally the stack's own address-space design.

A client that polls reads every configured tag on a fixed interval whether or not anything changed, so five hundred tags across twenty machines produce the same load at three in the morning as they do mid-shift. Subscriptions with monitored items invert that: the server watches the values and notifies the client when they move, which is what the services were designed for.

• The address-space design is the smaller of the two effects. A static, compiled-in address space is marginally faster than one that has to fetch each value from an external store on every read.
• The tuning that gets skipped. Sampling interval and publishing interval are two different settings and are routinely set to the same number. Queue size and the discard policy decide which values in a burst are kept. A deadband stops a noisy analogue value generating traffic that nobody reads.

The model itself is the other half. An address space that is deep, flat in the wrong places or built from thousands of untyped variables is expensive to browse and to subscribe to, and no amount of client tuning recovers it. This is a second reason the modelling comes first.

Is an OPC UA information model a digital twin?

No, and the two meet at the data layer.

• What the model generates for a twin. A typed structure with real semantics that something else can subscribe to. That is the foundation, and it is a capability we have delivered, including a EUROMAP 79 robot model produced by our own modelling tool.
• What it does not do. OPC UA modelling does not include building Asset Administration Shells, behavioural or simulation models, or working on twin platforms such as Azure Digital Twins, MindSphere or Predix. The word “twin” gets stretched to cover all of these, so it matters which part of the design each piece actually covers.

What has changed in OPC UA security?

The SHA-1 policies are deprecated, and Basic256Sha256, Aes128_Sha256_RsaOaep and Aes256_Sha256_RsaPss are the live path.

A deployment still running either of the older two is running on something the standard has withdrawn.

The operational side is harder than the cryptographic side. Certificate and trust list management is what typically fails, often in year three, when a certificate expires on a machine nobody has logged into since commissioning. We treat certificate renewal and distribution as a deliverable, and where PubSub is in play, the security key service is part of the same design.

When does OPC UA need TSN underneath it?

OPC UA needs TSN when data has to arrive deterministically, within a bounded latency.

OPC UA PubSub over TSN integration is where the modelling and the network meet: the same information model, published over PubSub with a bounded delivery time. Our team has integrated OPC UA with TSN on an NXP i.MX Arm SoC under openIL, and a secured PubSub demonstrator held a 1 ms cycle with security active.

Below that sits the determinism engineering itself, the gate schedules, the drivers and the measurement, which is real-time Ethernet work, not data modelling. And where the requirement calls for DDS’s fine-grained, per-topic QoS control (reliability, durability, deadline) instead of OPC UA PubSub’s simpler publish/subscribe, the architecture belongs to a different family of middleware, which is what data distribution covers.