Glossary · Industrial communication
OPC UA client
Also known as: OPC UA client application
German: OPC-UA-Client
In OPC UA, a client is an application that connects to an OPC UA server, opens a secure channel and a session, and uses the server's services to browse its address space, read and write values, call methods and subscribe to data changes and events.
- Industrial communication
- Standards
In one sentence
An OPC UA client connects to a server over a secure channel and session to browse, read, write, call methods and subscribe to data.
Example
An MES acts as OPC UA client to the servers of the six machines on a packaging line and subscribes to their state and good-count variables instead of polling them.
How it applies
- Engineering: Clients can browse a server's OPC UA address space at runtime, but robust integrations address nodes by stable NodeIds or browse paths defined by a companion specification rather than by display names.
- Integration: Subscriptions with monitored items report changes at a configured sampling and publishing interval, which puts less load on the network and the server than cyclic reads.
- Security: The client must trust the server's certificate and the server the client's. Accepting every certificate automatically or connecting with security mode None removes the protection the OPC UA security policy is meant to provide.
- Documentation: The documentation team documents which servers a client connects to, the nodes it reads or writes, sampling intervals, the user account and the certificate exchange procedure.
Client-server vs. PubSub
In client-server communication each client opens its own session to the server. OPC UA PubSub sends data one-to-many without sessions, which suits many receivers and cloud connections.