Is OPC Expert an OPC Server, an OPC Client, or Middleware?

Is OPC Expert an OPC server, or does it function purely as a middleware bridge between OPC clients and OPC servers?

OPC Expert contains both an OPC client and an OPC server within a single intelligent engine. It connects to one or more upstream OPC servers as a client, processes that data internally, and then exposes the result as a local OPC server to your application. This architecture is what makes features like redundancy, bridging, tunneling, and protocol conversion possible: OPC Expert sits in the middle of the data flow and manages it.

The Internal Architecture

When OPC Expert is running, it ingests data from upstream sources using its built-in OPC DA client and OPC UA client components. That data flows into OPC Expert’s processing engine, where features such as redundancy failover logic, calculations, bridging rules, and archiving can be applied. The processed data is then made available to your application through OPC Expert’s embedded OPC DA server and OPC UA server outputs.

From your application’s perspective, OPC Expert looks like a local OPC server. The application connects to it exactly as it would connect to any OPC server, using either DA or UA. The application has no visibility into whether OPC Expert is pulling data from a single remote server, managing a redundant pair, bridging between two incompatible OPC servers, or tunneling over a restricted network. All of that complexity is handled internally.

Why This Matters for Redundancy

The client-server architecture is precisely what makes OPC Expert’s redundancy feature work without modifying your existing application. Because OPC Expert presents a stable local OPC server endpoint to your application, the application continues to receive data from the same connection point regardless of what is happening on the upstream side. If the primary OPC server fails and OPC Expert switches to the standby, your application is unaware of the transition. It simply keeps receiving data from the local OPC Expert server as if nothing changed.

This is fundamentally different from asking your application to manage its own redundancy logic. Applications that connect directly to remote OPC servers must handle connection failures, retry logic, and failover themselves. By inserting OPC Expert between the application and the upstream servers, you retrofit redundancy into any existing application without changing a line of code or any application configuration.

Data Output Beyond OPC

While OPC DA and OPC UA are the primary output protocols, OPC Expert can also route data to other destinations from its internal engine. This includes SQL databases, Microsoft Azure, Amazon AWS, MQTT brokers, REST API endpoints, and Excel. These additional outputs are independent of the OPC server output and can be used simultaneously.

Related Tools

OPC Redundancy uses the client-server architecture described here to manage failover between primary and standby OPC servers. The embedded OPC server output is what allows your application to remain connected without interruption during a switchover.

OPC Bridge also relies on this architecture to transfer data between OPC servers. In a bridging scenario, OPC Expert connects to one server as a client and writes data into another server, with the internal engine managing the data routing and any conversion required between OPC DA and OPC UA.

Conclusion

OPC Expert is both an OPC client and an OPC server simultaneously. It connects to upstream OPC data sources as a client, applies processing logic internally, and presents the result as a local OPC server to downstream applications. This middleware architecture is what enables features like redundancy, bridging, tunneling, and protocol conversion to work transparently without requiring changes to existing applications or OPC servers.