# Specifying derived tag expression in a UDT Parameter

**URL:** <https://forum.inductiveautomation.com/t/specifying-derived-tag-expression-in-a-udt-parameter/33667>\
**Category:** Ignition Early Access\
**Created:** [April 3, 2020, 5:08pm UTC](https://forum.inductiveautomation.com/t/specifying-derived-tag-expression-in-a-udt-parameter/33667 "2020-04-03T17:08:29Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![md.szyman](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/md.szyman/32/9240_2.png) [@md.szyman](https://forum.inductiveautomation.com/u/md.szyman)\
**Post date:** [April 3, 2020, 5:08pm UTC](https://forum.inductiveautomation.com/t/specifying-derived-tag-expression-in-a-udt-parameter/33667/1 "2020-04-03T17:08:29Z")

</div>

Is it possible to specify a derived tag expression in a UDT parameter? For instance, I want the expression from the parameter to be `{source}/25.4` but it’s being converted to `null/25.4`, which I imagine is because it’s trying to substitute the parameter `source` which doesn’t exist. Is it possible to prevent the parameter from trying to interpret other parameters like this? I tried escaping like `\{source\}/25.4` but that didn’t seem to work. Surrounding the parameter value in quotes didn’t work either, i.e. `"{source}/25.4"`