OFS (OPC Factory Server) #ClientAlive Feature Explanation

Description

The #ClientAlive feature in OFS OPC Factory Server is used to monitor whether an OPC client connection remains active.

Product Line

OFS

OPC Factory Server

Behavior

The #ClientAlive variable is a write-only system variable. Because it cannot be read, OPC clients such as OFSClient display it with Bad Quality. This behavior is expected and does not indicate a malfunction. The variable can still be written to correctly.

The OPC client must write to #ClientAlive within the configured timeout period. For example, if the timeout is set to 4 seconds, the variable must be written at least once within that time period. If no write occurs before the timeout expires, OFS automatically closes all active OPC Groups associated with that client.

In SCADA environments, closing OPC Groups may impact other variables in the same group and can lead to data loss or unexpected application behavior if the timeout is reached unintentionally.

Because #ClientAlive cannot be read, its activity cannot be monitored through OPC reads or browsing. Verification of correct operation is only possible by reviewing the OFS system logs, where write activity and timeout events are recorded.

If a readable indication of communication health is required, customers may use a standard readable variable and periodically toggle its value instead of using #ClientAlive.

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