Which of the following is NOT a key function of a data historian?

A data historian primarily serves functions related to data collection, storage, and analysis over time. Its core functions include storing large amounts of historical data, analyzing performance trends to help in decision-making, and generating reports that summarize this data for further insights.

Controlling equipment directly is not a key function of a data historian. Instead, data historians typically interface with control systems and other tools to gather data, but they do not execute control actions themselves. They provide valuable insights based on historical performance data, allowing operators and engineers to make informed decisions, but they do not interact with the process in a control capacity. This distinction clarifies that data historians focus on data management rather than direct control activities.