Question: How do you configure OPC redundancy failover in OPC Expert when the OPC server does not provide a heartbeat signal?
When an OPC server does not provide a dedicated heartbeat signal, OPC Expert allows you to define custom trigger conditions that serve the same purpose. Rather than relying on a heartbeat from the server, you configure OPC Expert to monitor observable data characteristics, such as whether specific values have become stale or whether a data quality flag has degraded, and use those conditions to determine when a failover should occur.
Custom Trigger Configuration
OPC Expert’s OPC Redundancy module includes both built-in automatic triggers and user-defined triggers. The built-in triggers detect standard conditions such as connection loss or communication timeout. The user-defined triggers allow you to specify conditions based on the actual data being read, for example, triggering a failover if a particular item has not changed within a defined time window, if a value exceeds or falls below a threshold, or if a data quality indicator moves from Good to Bad or Uncertain. This gives you fine-grained control over what constitutes a failure, even in the absence of a server-level heartbeat mechanism.
Data Staleness as a Heartbeat Proxy
A common approach when no heartbeat is available is to identify a data item on the OPC server that updates at a regular, predictable interval, such as a scan counter or a process variable that should never remain static for more than a few seconds during normal operation. You then configure OPC Expert to trigger a failover if that item stops updating within an acceptable window. This effectively uses a known-good data item as a proxy for server health, giving you the equivalent of a heartbeat without requiring the server to provide one natively.
Continuous Server Monitoring
OPC Expert continuously monitors the status of both the primary and standby servers in a redundant configuration. Even before a custom trigger fires, OPC Expert is tracking connectivity and data quality in real time. This means that obvious failures such as complete connection loss are detected and acted upon immediately through the automatic triggers, while subtler issues that would not cause a hard disconnect are handled by the custom conditions you configure.
Relevant Tools
OPC Redundancy is the OPC Expert module for managing hot, warm, and cold failover between primary and standby OPC servers, with both automatic and user-defined trigger options. Monitor OPC Data provides continuous real-time monitoring of OPC component health and can alert operators when specific conditions are detected, serving as a complementary visibility layer alongside the automated redundancy configuration.
The absence of a native server heartbeat does not prevent effective redundancy configuration in OPC Expert. By defining custom triggers based on data staleness or quality changes, you can achieve reliable failover detection that is tailored to the specific behavior of your OPC server environment.