# Do calculation on OPC Tags

**URL:** <https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982>\
**Category:** Ignition\
**Created:** [May 7, 2025, 2:29pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982 "2025-05-07T14:29:55Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![Eugene49](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@Eugene49](https://forum.inductiveautomation.com/u/Eugene49)\
**Post date:** [May 7, 2025, 2:29pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/1 "2025-05-07T14:29:55Z")

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Opc source path shows unit in Celsius.

I need translate to Fahrenheit and import this to Tag Browser.  
I need this translation to be in tag level, so I can apply alarming in F units as well.

What is the best/short way to do this? other than using OPC and Expression Tag.

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**Author:** ![Transistor](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/transistor/32/3380_2.png) [@Transistor](https://forum.inductiveautomation.com/u/Transistor)\
**Post date:** [May 7, 2025, 2:32pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/2 "2025-05-07T14:32:25Z")

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Use the scaling feature on the tag definition. (Or switch to Celsius!)

> **[Tag Scaling Properties | Ignition User Manual](https://www.docs.inductiveautomation.com/docs/8.1/platform/tags/tag-properties/tag-scaling-properties)**
>
> Configuring a Tag's scaling will condition the data for use within the Ignition Designer. Scaling will take the raw PLC value driving a Tag, do some math, and use the resulting value as the value of that Tag. Scaling works both ways. When you write...

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [May 7, 2025, 2:51pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/3 "2025-05-07T14:51:04Z")

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Scaling can't handle this conversion, can it?

I think you need an expression tag, or derived tag if the conversion should work in both directions, i.e. the tag is writable.

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**Author:** ![Transistor](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/transistor/32/3380_2.png) [@Transistor](https://forum.inductiveautomation.com/u/Transistor)\
**Post date:** [May 7, 2025, 2:56pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/4 "2025-05-07T14:56:01Z")

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It does, as far as I can see.

 ![CtoF](https://us1.discourse-cdn.com/inductiveautomation/original/3X/7/a/7a4d0bc445be8cb811cb6181be2c51b2cad48b4c.png)

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<div class="post-metadata">

**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [May 7, 2025, 3:01pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/5 "2025-05-07T15:01:38Z")

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Huh, not sure why I thought that.

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<div class="post-metadata">

**Author:** ![Eugene49](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@Eugene49](https://forum.inductiveautomation.com/u/Eugene49)\
**Post date:** [May 7, 2025, 5:12pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/6 "2025-05-07T17:12:36Z")

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This is on OPC Tag, I am not sure what I can use for Fahrenheit Conversion:

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/f/5/f56c41a6037a4090716fa8bf3aaeb114f280b768.png)

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<div class="post-metadata">

**Author:** ![Transistor](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/transistor/32/3380_2.png) [@Transistor](https://forum.inductiveautomation.com/u/Transistor)\
**Post date:** [May 7, 2025, 5:17pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/7 "2025-05-07T17:17:23Z")

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I showed you in post #4!

0°C → 32°F  
100°C → 212°F

It's a linear scaling.

[![](https://us1.discourse-cdn.com/inductiveautomation/original/3X/9/e/9ef75bc47622dc58c36b72ba3e28ffd38a7fae9e.jpeg "John Finnemore's Souvenir Programme. Fahrenheit v Celsius") ](https://www.youtube.com/watch?v=nROK4cjQVXM)

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<div class="post-metadata">

**Author:** ![Eugene49](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@Eugene49](https://forum.inductiveautomation.com/u/Eugene49)\
**Post date:** [May 7, 2025, 5:25pm UTC](https://forum.inductiveautomation.com/t/do-calculation-on-opc-tags/105982/8 "2025-05-07T17:25:00Z")

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> [@Transistor](#):
>
> I showed you in post #4!

😱 Right it is linear equation.. My bad..