# Instance of data types doesn't fire value changed event

**URL:** <https://forum.inductiveautomation.com/t/instance-of-data-types-doesnt-fire-value-changed-event/35446>\
**Category:** Ignition\
**Tags:** ignition80\
**Created:** [June 9, 2020, 8:48am UTC](https://forum.inductiveautomation.com/t/instance-of-data-types-doesnt-fire-value-changed-event/35446 "2020-06-09T08:48:22Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![chester.sun](https://avatars.discourse-cdn.com/v4/letter/c/85f322/32.png) [@chester.sun](https://forum.inductiveautomation.com/u/chester.sun)\
**Post date:** [June 9, 2020, 8:48am UTC](https://forum.inductiveautomation.com/t/instance-of-data-types-doesnt-fire-value-changed-event/35446/1 "2020-06-09T08:48:22Z")

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Tag is an indirect OPC tag, OPC Item Path : [machineID]c\_Time  
Instance of the tag, machineID is set, and value is read from PLC, but the value changed event isn’t fired.  
The script is a simple print hello world.  
If I use direct tag by hardcoding machineID, the value changed event fires.