Hello,
I recently upgraded to Ignition 8 and noticed the Transaction Group Items boxes now have two columns for Value: Source and Latched. I can’t find anything in the documentation that describes the difference between the two. Can someone please elaborate on the difference and also what the benefit is of seeing both? I’m currently seeing discrepancies between the two so it’s confusing which value will be used when it’s triggered.
Thanks -
Source Value is your Actual Value of the Tag.
Latch Value is what you are writing to the database.
Value first comes to Source and then goes to latch and goes to database.
Can I do anything with the source value before it gets to latched value?
Use an expression item instead of a tag or OPC item.
I have a problem with Latch Value. It insert to database previous value not current value.
Any idea how to fix this issue?
Thanks,
Tam
That commonly happens when a non-trigger item is a tag. OPC doesn't have ordered delivery, so a trigger could fire before the rest of the tags are "fresh".
The answer is to replace the items that point at OPC tags with items that point directly at the OPC value, and set the transaction group to OPC "Read" mode. That causes a fresh read to happen just after the trigger, pulling in values that are certain to be "after" the trigger.
Thanks for quick relay. I am new Ignition. Where can I set the OPC to "Read" Mode.
I can't find "Read" in the Mode as shown below
Please! Advice
Thanks,
Tam
Advanced settings, upper right window if using default designer layout.
Change OPC mode from subscribe to read
Remember that the change in OPC data mode does not apply to tags. You must replace those members in your transaction with OPC Items, typically dragged from the OPC Browser (not the Tag Browser).
