OPC UA

A platform-independent industrial communication standard for exchanging plant data, with an information model and security built in.

OPC Unified Architecture is the successor to the older Windows-specific OPC DA. It is platform-independent, carries an information model that describes what each value means rather than only its address, and includes security as part of the specification.

It carries reads, writes, method calls and publish-subscribe, so read-only access is a configuration rather than a property of the protocol. For analytics it is usually the preferred acquisition path because that configuration is explicit: the application certificate establishes which client is connecting, and the server then grants browse and read permissions to a user or role without write permissions. The restriction is enforced by the control system itself and visible in its configuration.

Most modern DCS and PLC platforms offer a server as a licensed option. Where one already exists, reading through it involves no change to control logic, though the server side still changes: a certificate has to be trusted, a user or role assigned, the exposed namespace agreed and a firewall path opened. Where it does not, adding it is a change and needs the same approval as any other.