Glossary · OPC Unified Architecture

OPC UA

OPC UA is an industrial communication standard that carries names, units and structure along with the values, addressing the limits of protocols that transmit numbers alone.

All terms Talk to an engineer

How it connects

Equipment server
Expose equipment data
Information model
Values, meaning and structure
Client
Read through a standard interface

Definition

OPC UA is an industrial communication standard that carries names, units and structure along with the values, addressing the limits of protocols that transmit numbers alone.

In more detail

Protocols like Modbus transmit values only; what a value means had to be looked up in documentation. OPC UA carries meaning with the data — name, unit, data type and position within the equipment model.

Security is part of the specification. Authentication, encryption and access control are standard features rather than bolt-on infrastructure.

The trade-off is weight. Older equipment often does not support it, and where it does, an optional module may be required. Real plants therefore run a mixture of OPC UA, Modbus and dry contacts, which is exactly why a layer that absorbs the difference is needed.

How it is used on the floor

Take structured data directly from relatively recent equipment.
Use the information model to reduce tag mapping work.
Meet security requirements between control and upper networks with standard features.

OPC UA versus classic OPC (OPC DA)

Classic OPC depended on Windows COM/DCOM, making firewall traversal and portability difficult. OPC UA was redesigned to run independently of the operating system. The name carries over; the architecture does not.