Tag Value Changes with Allow Back-fill Data Enabled

Ignition
1

Hello,

We have a tag provider with the Allow Back-Fill data option set to true. Which is reading data from a AB PLC 5 over a DH+ network. Regularly, we receive data out of order, when this occurs we see the value of the flips to the out of data value and then back to the current value when the next poll occurs.

I pretty sure I'm miss understanding how to use the feature effectively and I'd like clarification on if it is expected to see the tag value update.

We have a Query tag, that is inserting the PLC 5 tag on a event change into a DB. From experimenting, it looks like we'd be better off using a tag change script to update the database to avoid the out of order data.

We intend to migrate the functionality any way, but I'm more so just looking to gain a better understand the feature and how I can use it in the interim while we bring the facility up to date.

2

This feature should have no effect with drivers like PLC5 (and most others) because timestamps and historical data are not sent by the device. The timestamp is essentially always the OPC server timestamp and there's no historical / multiple points in play.

You might want to work with support to figure out if what you're seeing is really what you're seeing, or if something else is going on.