# Tag change not firing on initial event **URL:** \ **Category:** General Discussion\ **Tags:** ignition81\ **Created:** [April 11, 2024, 3:48pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692 "2024-04-11T15:48:44Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![rfolkes](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@rfolkes](https://forum.inductiveautomation.com/u/rfolkes)\ **Post date:** [April 11, 2024, 3:48pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692/1 "2024-04-11T15:48:44Z")
Within a UDT i have a expression tag (exprtag1) that takes 2 other tag values (value1, value2) expr = (value2-value1)\*.4 exprtag1 is set to Event Driven execution mode value1, value2 are OPCUA tags there is a tag change script on exprtag1 ```auto def valueChanged(tag, tagPath, previousValue, currentValue, initialChange, missedEvents): if currentValue.quality.good: system.tag.writeBlocking("[.]../Parameters.Deadband", currentValue.value) ``` to write the value to a parameter. Everything appears to be working except when tag is initially created. When UDT instance is created the parameter value remains null even though exprtag1 = 0.4 If I then change value1 or value2 the parameter gets updated. why isn't this running on initialchange? ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [April 11, 2024, 3:53pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692/2 "2024-04-11T15:53:45Z")
Are you sure the quality is good on that initial change? You might be getting a quality change event after the UDT starts up. ---
**Author:** ![rfolkes](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@rfolkes](https://forum.inductiveautomation.com/u/rfolkes)\ **Post date:** [April 11, 2024, 4:06pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692/3 "2024-04-11T16:06:05Z")
shouldn't a quality change from bad --\> good also trigger the tag change ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/2/c/2c8313f6f0896522b29f28a647e5fcdf6a764550.png) ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [April 11, 2024, 4:09pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692/4 "2024-04-11T16:09:33Z")
Hmm. Not sure. Try logging everything before your quality check. ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [April 11, 2024, 4:12pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692/5 "2024-04-11T16:12:47Z")
BTW, `writeBlocking()` is not safe to use in a tag event, in most cases. Use `writeAsync()` instead. ---
**Author:** ![rfolkes](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@rfolkes](https://forum.inductiveautomation.com/u/rfolkes)\ **Post date:** [April 11, 2024, 5:53pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692/6 "2024-04-11T17:53:59Z")
```auto def valueChanged(tag, tagPath, previousValue, currentValue, initialChange, missedEvents): logger = system.util.getLogger("myLogger") logger.info("TagChangeExecuted value="+str(currentValue.value)+'- tagPath='+str(tagPath)) if currentValue.quality.good: system.tag.writeAsync("[.]../Parameters.Deadband", currentValue.value) ``` Seems if I just do a few tags at a time it works fine. When my script adds a lot of tags at once it seems to randomly work and not work. I can't get consistent results. Other similar set of tags I used this script ```auto def valueChanged(tag, tagPath, previousValue, currentValue, initialChange, missedEvents): logger = system.util.getLogger("myLogger") logger.info("TagChangeExecuted"+str(currentValue.value)) if currentValue.quality.good: system.tag.writeAsync("[.]../Parameters.Deadband", currentValue.value) ``` and I can see in the log where the tags are created ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/0/2/023e33af770bab6dafac6b15fdc3becd6445e35c.png) then later in log where they update with values and tag change runs again ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/a/3/a3535ebcb12028b5d4a6dc3be8ee75e4fa72cbbd.png) but this time there are only 5 entries instead of 9. (However in this case all 9 executed the tag change and had the value of "8" updated.) However within the other set of tags I have seemingly random ones - delete all the tags and run the script to recreate them again and everything comes up correctly except differrent tags will have a null/default value for the parameter.deadband while others will be updated. Tag creation is by script command..system.tag.configure ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [April 11, 2024, 5:59pm UTC](https://forum.inductiveautomation.com/t/tag-change-not-firing-on-initial-event/88692/7 "2024-04-11T17:59:56Z")
Keep in mind that these events will queue if you have many trying to run at once--the default tag event workqueue has only three threads. Something similar for expression tag execution. These are probably combining in pathological ways when you try to create many quickly.