What is a process historian and how is it integrated with SCADA?

Process historian collects, stores, and retrieves time-series process data efficiently using compression algorithms. Integration methods: OPC DA/HDA connection to SCADA server, direct polling of PLCs, or data forwarding from SCADA. Configuration: define tags (names, data types, engineering units), set collection rate (1 second to minutes depending on criticality), configure compression (deadband, deviation). Uses: trend analysis, regulatory compliance, performance analysis, root cause investigation, and reporting. Common historians: OSIsoft PI, Wonderware InSQL, GE Proficy, AspenTech IP.21. Ensure time synchronization and data integrity.