Data Persistence and Historical Logging

By default, Internal Tags run in the computer’s RAM (Volatile) memory. This means that data will be lost when the computer is turned off or if the power is cut. Wise SCADA offers two different mechanisms to protect your data:

1. Historical Logging

This feature saves the tag’s value to the Database (SQL) along with a timestamp.

• Purpose: To provide retrospective reporting, trend charts, and process analysis.
• How It Works: When the “Historical” setting is configured for a tag, values are archived in the database at defined intervals or upon change.
• Usage: Configured via the Historical Tags page.

2. Data Persistence (Persistence) – “Startup Memory”

This feature ensures that the tag starts with its last retained value when SCADA is closed and reopened.

• Purpose: To ensure system continuity (e.g., ensuring a set value or counter is not reset).
• How It Works: During a proper Shutdown/Exit process, Wise SCADA saves the final values of internal tags in memory to a special file in the project folder. When the program restarts, it reads this file and synchronizes the tags to their last values.

Critical Warning: Risk of Abnormal Shutdown and Data Loss

The Persistence feature works on a “Save on Exit” logic.

• The Risk: If a sudden power outage occurs, Windows crashes, or the SCADA process is forcibly terminated via “Task Manager,” the closing routine cannot execute. Therefore, the last values cannot be written to the file. The system will open using the data from the last successful save (or the default value).

Solution Recommendations:

• UPS Usage: Use an Uninterruptible Power Supply (UPS) that keeps the computer running long enough to shut down the program properly.
• Critical Data: For data where loss cannot be tolerated (such as production totals), it is recommended to use PLC Memory or Database (Historical) records instead of Internal Tags. PLCs are generally not affected by power outages as they have battery-backed memory.