Transaction Group - Tag change monitoring

Ignition
1

Hello,
I am using a transaction group to save a plc udt to a database.

It is running only in OPC to DB mode.

I want it to save data whenever the monitored datapoint changes, each datapoint has a ID tag which is incremented every time the datapoint changes.

However the system sometimes hangs with the source value equaling the latched value, but the datapoint has not been uploaded to the database.
Has anyone encountered this issue?

image
image1171×389 136 KB

The latest ID saved in the database was 47, the next ID is 48 but the transaction group seems to have missed the change.

ignition version is 8.1.27

2

Ok,
I believe I have resolved the issue.

The problem seemed to be that the tag used as the trigger sometimes transitioned to true after the tag used to watch for change. therefore the transaction group didn't 'see' the required tag change.

I fixed by adding an ID_monitor tag as a Run-always expression item.
the tag contained the expression:

if({[.]DataAvailable},
{[~]ID},
0)

The ID_monitor tag is used as the tag to watch for change.
This ensures that the ID can be witnessed to change after the trigger is true.