Historian Data & Trending
A SCADA historian stores time-series data long-term, the foundation for trend-based troubleshooting.
A historian database stores tag values (sensor readings, equipment status) at a set interval over long periods, distinct from the live, real-time-only data shown on an HMI screen.
Trend graphs built from historian data reveal gradual drift, cyclical patterns, and step changes that are invisible when only looking at an instantaneous reading.
Historian data retention and backup policy matters; a system that only retains a few months of history limits the ability to investigate a slowly developing problem or support a regulatory data request.
Compression settings on historian data (how much precision is sacrificed to save storage) should be reviewed periodically, since overly aggressive compression can smooth away exactly the short-duration spikes worth investigating.
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