# Expression tags solving very slowly

**URL:** <https://forum.inductiveautomation.com/t/expression-tags-solving-very-slowly/6847>\
**Category:** Ignition\
**Created:** [July 11, 2013, 3:21am UTC](https://forum.inductiveautomation.com/t/expression-tags-solving-very-slowly/6847 "2013-07-11T03:21:37Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![easikwilson](https://avatars.discourse-cdn.com/v4/letter/e/a6a055/32.png) [@easikwilson](https://forum.inductiveautomation.com/u/easikwilson)\
**Post date:** [July 11, 2013, 3:21am UTC](https://forum.inductiveautomation.com/t/expression-tags-solving-very-slowly/6847/1 "2013-07-11T03:21:37Z")

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We have a customer project where we are noticing extremely slow solving of expression tags (like simple evaluation of a few bits to create an integer value taking 10 seconds). For instance, we look at the status of a bit with an OPC tag looking at data in a PLC, and we have an expression tag that looks at the value of that boolean OPC tag and does an “if” statement to provide a resulting tag value for that expression tag that is a string with either “Y” or “N”. We have other instances where we are using expression tags to create a integer number for the value of the expression tag using a “binEnc” based on the evaluation of several OPC tags bit values.

Any ideas???

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**Author:** ![diat150](https://avatars.discourse-cdn.com/v4/letter/d/a587f6/32.png) [@diat150](https://forum.inductiveautomation.com/u/diat150)\
**Post date:** [July 11, 2013, 1:10pm UTC](https://forum.inductiveautomation.com/t/expression-tags-solving-very-slowly/6847/2 "2013-07-11T13:10:18Z")

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how many expression tags and what is the scan class? I would think having only 10 tags vs 200000 expression tags would make a big difference in the answer.

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**Author:** ![anna](https://avatars.discourse-cdn.com/v4/letter/a/779978/32.png) [@anna](https://forum.inductiveautomation.com/u/anna)\
**Post date:** [July 12, 2013, 11:02pm UTC](https://forum.inductiveautomation.com/t/expression-tags-solving-very-slowly/6847/3 "2013-07-12T23:02:51Z")

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With a lot of tags on the same scan class, you will eventually start getting delays as the scan class goes through the tags sequentially. Assigning those tags to a less “busy” scan class with a different scan rate will help.

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**Author:** ![easikwilson](https://avatars.discourse-cdn.com/v4/letter/e/a6a055/32.png) [@easikwilson](https://forum.inductiveautomation.com/u/easikwilson)\
**Post date:** [July 13, 2013, 8:50pm UTC](https://forum.inductiveautomation.com/t/expression-tags-solving-very-slowly/6847/4 "2013-07-13T20:50:24Z")

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Folks,

Thank You for the advice, turns out it was the whole scan class thing and how being in a single scan call over-filled the thread. Have since broken up scan classes and performance is greatly improved. Thank You all! 😃