OPC UA Historians Need Alarm Records, Not Just Tag History
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Global – October 27, 2026 -- A pump pressure trend shows when a value left its normal range but cannot show which alarm changed state, what severity the server reported, or when an operator acknowledged it. Those answers sit in separate OPC UA records, and historian designs must decide which questions each record has to answer.
Tag history stores values, not alarm lifecycles
An OPC UA client collects a variable through a monitored item. When DataChange criteria are met, the server sends a DataValue that the historian can store with source timestamp, server timestamp, and StatusCode, depending on the collector mapping. Sampling, deadbands, queues, and timestamp selection determine how much process behavior survives.