OPC Write from SQLTags

I have a few tags that control PLC outputs of status lights:

Works ok, but if something happens, say, an ice storm comes through and you’re without power for a while (gotta love Michigan), the outputs, of course reset to zero. Unfortunately, they never update back to the Tag SQLTag value. Is there any way to periodically force a write?


bumpity-bumpity-bump-bump-bump. (I’ll get a whole drum riff going pretty soon…) :mrgreen:

This is a bit trickier than it might seem at first. Right now it’s only writing when the value of the expression has changed. In this situation, it doesn’t know what the value of the writeback address is, so it can’t check and write any time they’re different. The possible solutions would be 1) Subscribe to that address and write when they’re not equal or 2) Write each time.

The third option would be a transaction group that let you easily map tags to tags. This has been requested a lot, and is hopefully going to make its way into 7.3. Right now, you can work this up one way or another, but it might take a bit of work. For example, if you want your expression to be in a SQLTag, you’ll need to make a group that has a reference to both the source and target tags, and then an expression that references the first and targets the second.


Rats. I figured that was going to be it, but it’s good to know that changes are in the air!

Thanks, Colby.