When connecting OPC DA and OPC UA systems, when should you use OPC Bridge versus OPC Tunneler in OPC Expert?
OPC Bridge and OPC Tunneler are both available within OPC Expert and both can connect OPC DA and OPC UA systems, but they address different architectural needs. OPC Bridge is the right choice when you need to actively replicate or transfer data items between two OPC servers. OPC Tunneler is the better fit when you need to extend an existing OPC connection transparently across a network, particularly when DCOM configuration is impractical or when security requirements demand encrypted transport.
What OPC Bridge Does
OPC Bridge operates as an OPC client to two servers simultaneously. It reads data from a source OPC server and writes it to a destination OPC server, item by item, based on a configuration you define. This makes it ideal for scenarios where two separate control systems or devices need to share specific process values, and you want precise control over which items are bridged, in which direction, and under what conditions. You can bridge OPC DA to OPC DA, OPC UA to OPC UA, or any combination of the two. The setup is done visually through the drag-and-drop interface or in bulk through CSV configuration files.
What OPC Tunneler Does
OPC Tunneler is designed to make an OPC connection that would normally require DCOM work transparently across a network, without exposing the underlying DCOM layer at all. It wraps OPC Classic or OPC UA communication in a standards-based secure transport, allowing an OPC client to connect to a remote OPC server as if both were local. Tunneling is not about replicating specific items from one server to another; it is about extending the reach of an existing OPC client-server pair across a network boundary. It supports half-tunnel configurations, where only one instance of OPC Expert is needed on one side of the connection.
Choosing Between the Two
If your goal is to move data from a specific set of tags on one server into another server so that a second system can read them, OPC Bridge is the appropriate tool. If your goal is to allow an existing OPC client application to reach a remote OPC server securely without reconfiguring DCOM or opening broad firewall rules, OPC Tunneler is the right approach. In some deployments, both tools are used together: tunneling handles the secure remote connectivity while bridging handles the item-level data replication between systems at each site.
Relevant Tools
OPC Bridge is the OPC Expert feature for item-level data replication between OPC servers, supporting mixed DA and UA configurations with drag-and-drop setup and bulk CSV configuration. OPC Tunneler is the OPC Expert module for secure, DCOM-free connectivity across networks, using OPC UA and standards-based transport to extend OPC Classic and OPC UA connections without system modifications.
Both tools solve real problems in OPC integration, and the choice between them comes down to whether you are replicating data between servers or extending the reach of an existing OPC connection. In complex environments, combining both approaches gives you the most flexibility.