OPC Redundancy: Automatic Failover to a Backup OPC Server for SCADA

OPC Expert supports redundant OPC server configurations where two servers, one primary and one standby, are monitored simultaneously. When the primary server fails, OPC Expert switches to the standby automatically without manual intervention. The consuming application, whether a SCADA system or an Excel report, sees a single continuous data feed and is not disrupted by the transition.

How Redundancy Works in OPC Expert

OPC Expert monitors both the primary and standby OPC servers continuously. When it detects a failure condition on the primary server, it activates the standby and resumes data delivery. Failover triggers can be automatic, based on connection loss, or they can be configured to respond to specific conditions such as stale data values or threshold breaches. Once the primary server recovers, OPC Expert can optionally fail back automatically, restoring normal operation without requiring operator action.

Hot, Warm, and Cold Redundancy Options

OPC Expert offers three redundancy modes to match different operational requirements. Hot redundancy keeps the standby server in an active, subscribed state at all times so that failover is instantaneous and no data is lost during the transition. Warm redundancy maintains a connection to the standby but does not subscribe to data until a failover occurs, reducing network load at the cost of a brief reconnection delay. Cold redundancy holds the standby configuration ready but does not establish any connection until it is needed, which suits environments where standby availability is confirmed before failover begins.

Delivering a Single Output to SCADA

OPC Expert acts as an intermediary between the redundant source servers and the consuming SCADA system or Excel workbook. SCADA connects to OPC Expert as if it were a single server. The failover logic is contained entirely within OPC Expert, so the SCADA application requires no special configuration to support redundancy. This architecture means existing SCADA systems and Excel reports can benefit from redundant OPC connectivity without modification to those applications.

Relevant Tools

OPC Redundancy is the OPC Expert module that manages hot, warm, and cold failover between primary and standby OPC servers. It supports OPC DA and OPC UA and uses a visual drag-and-drop interface to configure redundant data connections.

OPC to Excel allows Excel workbooks to consume data from OPC Expert, benefiting from the same redundancy layer so that reports and real-time spreadsheet monitoring continue uninterrupted when a source server fails.

Summary

OPC Expert provides built-in redundancy that monitors two OPC servers and fails over automatically when the primary becomes unavailable. SCADA systems and Excel workbooks connect to OPC Expert as a single source, insulating them from server-level failures and maintaining continuous data availability.