Historian Tag Group in Driven Mode Occasionally Missing One-Second Sample

Ignition
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1

Currently, I am facing an intermittent issue with Ignition Tag Historian. I have configured a Driven Tag Group with a Boolean trigger tag that remains TRUE while the machine is running. The historian is configured to record data at 1-second intervals.

Most of the time, the data is logged correctly every second, but occasionally one second of data is missed, even though the trigger remains continuously TRUE.

For example:

16:27:36
16:27:37
16:27:38
16:27:39
16:27:40
16:27:42
16:27:43

Here, the 16:27:41 record is missing.

I would like to understand why this happens and whether a Driven Tag Group can occasionally skip an execution/sample due to Gateway load, tag execution timing, OPC communication, historian processing, or database delays.

My requirement is to reliably record one historian sample every second without missing any samples while the machine is running.

I have attached a screenshot showing the normal 1-second historian data logging for reference.

image
image940×282 106 KB

2

Yes. For any of the reasons you list. Possibly also GC stalls.

The only reliable way to guarantee this kind of recording is to use a buffer in the PLC, and use a pair of handshake tags to signal data available and acknowledge data stored to DB, per record. Usually combined with a scripted OPC read to ensure data is collected after the signal. (Ignition tags cannot actually do this part--they are entirely asynchronous to anything else, and OPC subscriptions do not guarantee any kind of delivery order.)