Industrial Data Collection

Global – October 29, 2026 -- Industrial historians should default to data-change subscriptions for continuously monitored OPC UA process variables and reserve polling for explicitly periodic records, according to collection guidance tied to TDengine TSDB-Enterprise.

Polling leaves a blind spot between reads

A polling client issues Read requests at a fixed interval, so a ten-second poll fetches the latest value every ten seconds whether or not it changed. If a motor status flips from 0 to 1 and back to 0 inside that window, both surrounding polls return 0. A shorter interval cuts the risk but raises load, and it never removes the gap between samples.

Polling fits periodic reporting, slow-changing values that need regular records, and servers with weak subscription support. A quality report requiring one temperature record per minute, including unchanged periods, is a polling case.

Global – October 27, 2026 -- The right OPC UA collection rate is the slowest configuration that still preserves the process behavior needed for operations and historical analysis, and it is set across five separate stages rather than one "scan rate." Device updates, server sampling, subscription publishing, filtering and historian storage each have their own timing. Treating them as one setting can add load without adding information, or hide a pressure transient the historian was expected to explain.

Server sampling cannot beat the source update rate

A PLC may update a temperature every 500 milliseconds while the OPC UA server refreshes its internal value once per second. A client request to sample every 100 milliseconds then re-reads the same value or detects changes no sooner than the server exposes them.