What OPC UA actually is

What you will be able to do

• You can explain OPC UA to a colleague in two minutes without saying 'Industry 4.0'.
• You can read a specification reference like OPC 10000-4 and know what document it names.
• You can say what a version like 1.05.07 does and does not guarantee about interoperability.
• You can place OPC UA against MQTT, Modbus and PROFINET without treating them as rivals.

Syllabus

1. 1
   Read the problem OPC UA was built to solve

   Twelve vendors, twelve dialects, and integration as bespoke engineering every time. What that actually costs on a shop floor, and what a self-describing protocol changes.

   Asset A table of six real machine protocols with what each one carries and what it omits

   7 min
2. 2
   See what OPC UA moves that a byte protocol does not

   The same pressure reading over Modbus and over OPC UA, side by side: a register number versus a typed, named, ranged, timestamped value with a status.

   Asset A screenshot of the same value in a Modbus poller and in UaExpert, with both payloads written out

   8 min
3. 3
   Place OPC UA in the stack

   Fieldbus below, unified namespace and MES above. Why OPC UA is the semantic layer and not the cheapest transport, and why that trade is usually right and sometimes wrong.

   Asset A layer diagram naming real products at each level, with the protocol on each boundary

   6 min
4. 4
   Decode the three numbering schemes

   OPC 10000-4, IEC 62541-4 and 'Part 4' are one document. Companion specs use other series entirely. This lesson makes every later reference readable.

   Asset A conversion table between the three schemes plus the companion-spec series, with real examples

   7 min
5. 5
   Read a version number correctly

   1.05 is a release family; the fourth digit is an errata level. Why 'we support 1.05' is not an interoperability statement, and what to ask a vendor instead.

   Asset The published nodeset release dates for 1.05.04 through 1.05.07, with what changed between them

   6 min
6. 6
   Tell client-server from PubSub before you need either

   Two communication models in one standard. What each is for, and the fact that most plants never need PubSub at all.

   Asset A decision table mapping eight real data flows to the model that fits

   8 min
7. 7
   Meet the free servers you will use all course

   Three public OPC UA servers and three one-command local ones. Connect to one now and see an address space, before learning any theory.

   Asset Working connection to opc.tcp://opcua.umati.app:4840 in UaExpert, with the browse tree screenshotted

   9 min
8. 8
   Know what OPC UA does not do

   It is not real-time by default, not a database, not a scheduler, and it will not give you planned production time. Naming the boundaries now prevents a bad architecture later.

   Asset A list of five things teams routinely expect OPC UA to provide, and where each actually comes from

   11 min

Lab

Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.