What is a SCADA historian and what data does it typically store?

• A. A time-stamped process data repository that stores tag values, trends, events, and historical reports for analysis.
• B. Real-time data only with no history
• C. Only alarm logs
• D. Only user login events

Answer: (A)

A SCADA historian is a time-stamped data repository that stores historical process data for analysis. It collects tag values from sensors and controllers, preserves trends for plotting how measurements change over time, records events such as state changes and operator actions, and provides historical reports for performance, fault analysis, and optimization. The timestamps enable correlation across data streams and reconstruction of what happened in the system. This makes the description of a time-stamped repository storing tag values, trends, events, and historical reports the best fit. Real-time data only with no history wouldn’t support retrospective analysis; alarm logs alone don’t cover the full range of process data, and user login events pertain to security rather than everyday process data.