Can the data sampling interval be adjusted during an active OPC trend session in OPC Expert?
Changing OPC Trend Sampling Time During an Active Session
OPC Expert’s OPC Trend module allows users to configure the data capture interval for each subscribed item. The OPC Trend module retrieves data through OPC subscriptions, and the update rate for those subscriptions determines how frequently new values are delivered to the trend display. Adjustments to this rate affect how the trend behaves going forward from the point of the change.
How Update Rates Are Configured
Each item subscribed in OPC Expert has an update rate that governs how frequently the OPC server reports new values to OPC Expert. This rate can be modified within the subscription settings. When the rate is changed, the OPC server receives the updated subscription request and begins reporting at the new interval. The trend will reflect data at the new sampling rate from that point forward, while the previously captured history remains unchanged.
Effect on Trending and Archiving
The OPC Trend module displays data as it arrives from the OPC subscription. If you reduce the sampling interval to capture faster-changing data, the trend will update more frequently and accumulated data density will increase from that point onward. If you increase the interval to reduce data volume during a steady-state period, the trend will update less frequently. In both cases, the historical data already captured in the archive is preserved at its original resolution and remains accessible for review.
Practical Considerations
When investigating a specific fault or transient condition, tightening the sampling interval temporarily allows for finer-grained capture of the event timeline. Once the investigation is complete, the interval can be relaxed to reduce storage and processing load. OPC Expert’s built-in Historian retains all captured data regardless of interval changes, so no retrospective data is lost when the sampling rate is adjusted.
Relevant Tools
OPC Expert (OPC Trend Software): The trending module that manages subscriptions, displays live and historical data, and supports configuration of update rates for individual items.
OPC Expert (Archive OPC Data): Works alongside the trend module to preserve captured data at its original resolution regardless of subsequent sampling rate changes.
The ability to adjust sampling rates within an active session gives engineers the flexibility to respond to changing process conditions without stopping and restarting their monitoring configuration.