# Using Derived tags to write data from one OPC tag to another **URL:** \ **Category:** Ignition\ **Tags:** perspective\ **Created:** [December 7, 2023, 3:11pm UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848 "2023-12-07T15:11:38Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Daniel\_Kareem\_Tabet](https://avatars.discourse-cdn.com/v4/letter/d/4da419/32.png) [@Daniel\_Kareem\_Tabet](https://forum.inductiveautomation.com/u/Daniel_Kareem_Tabet)\ **Post date:** [December 7, 2023, 3:11pm UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848/1 "2023-12-07T15:11:38Z")
Hey everyone, I am trying to pass data from one OPC tag (getting that data from a Modbus device using ignition's Modbus TCP driver) to another (standard OPC tag going to a PLC). I tried using a derived tag to do this. First, I defined the Source Tag Path as the OPC tag I want to write to. Then I defined the read expression as the OPC tag I would like to pass to the source tag path (i.e. the target OPC tag) using ignition's expression language. I set the write to {value} so I can write the value I'm reading to the source tag path. However this doesn't seem to write to my source tag as expected. I have confirmed I can write to the PLC tag on its own without any problems, so I'm feeling like I'm stuck on the derived tag write portion of it. Does anyone have any experience with writing data from one OPC tag to another with derived tags? Thanks in advance 🙂 ---
**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:** [December 7, 2023, 3:15pm UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848/2 "2023-12-07T15:15:20Z")
> [@Daniel\_Kareem\_Tabet](#): > > any experience with writing data from one OPC tag to another with derived tags I wouldn't expect anyone to have such experience (except negative), as that is not what they are for. Consider just placing a tag value change event on the source tag that performs a "fire-and-forget" `system.tag.writeAsync()` to send all new values to the target tag. (And will include one extra write at tag startup.) ---
**Author:** ![Daniel\_Kareem\_Tabet](https://avatars.discourse-cdn.com/v4/letter/d/4da419/32.png) [@Daniel\_Kareem\_Tabet](https://forum.inductiveautomation.com/u/Daniel_Kareem_Tabet)\ **Post date:** [December 7, 2023, 3:23pm UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848/3 "2023-12-07T15:23:00Z")
Thank you! I didn't think about trying that so I will give it a shot and let you know how that went. ---
**Author:** ![Daniel\_Kareem\_Tabet](https://avatars.discourse-cdn.com/v4/letter/d/4da419/32.png) [@Daniel\_Kareem\_Tabet](https://forum.inductiveautomation.com/u/Daniel_Kareem_Tabet)\ **Post date:** [December 8, 2023, 9:18am UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848/4 "2023-12-08T09:18:46Z")
It worked pretty smoothly, thank you! ---
**Author:** ![David\_Lopez](https://avatars.discourse-cdn.com/v4/letter/d/49beb7/32.png) [@David\_Lopez](https://forum.inductiveautomation.com/u/David_Lopez)\ **Post date:** [June 27, 2025, 3:04am UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848/5 "2025-06-27T03:04:12Z")
Hi, I have a similar issue. I'm working with a UDT to bypass an OPC tag to another. Using system.tag.writeAsync() works fine for few tags. However, when working with hundreds it takes a while to see the written value at the output tag. Is there any other way to trigger the Derivedexpressionsetter automatically? It only works if I clicked Enter on the derived tag ![java_FaLQ48KKPl](https://us1.discourse-cdn.com/inductiveautomation/original/3X/1/7/175b33a77d57be6b42e7112bc43f403d1e1b5561.gif) ---
**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:** [June 27, 2025, 6:12am UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848/6 "2025-06-27T06:12:42Z")
1. What's the name of the Tag Group in each of those tags? 2. What is the Rate setting for the Tag Group(s)? (This will determine how quickly the updates occur.) ![img5-eebcedc438de01a7da07a42b7eabcb9c](https://us1.discourse-cdn.com/inductiveautomation/original/3X/1/3/13823083b85f2aecbbbf62c9b6001dd8b2ffe6d0.png) ---
**Author:** ![David\_Lopez](https://avatars.discourse-cdn.com/v4/letter/d/49beb7/32.png) [@David\_Lopez](https://forum.inductiveautomation.com/u/David_Lopez)\ **Post date:** [June 27, 2025, 6:35am UTC](https://forum.inductiveautomation.com/t/using-derived-tags-to-write-data-from-one-opc-tag-to-another/82848/7 "2025-06-27T06:35:24Z")
Thank you for your response, they are working with the Default tag group 1000ms