# Write a value from one PLC to other PLC through Ignition **URL:** \ **Category:** Ignition\ **Tags:** ignition81, perspective\ **Created:** [January 27, 2023, 9:31pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113 "2023-01-27T21:31:03Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![ANKIT\_BARAD](https://avatars.discourse-cdn.com/v4/letter/a/6f9a4e/32.png) [@ANKIT\_BARAD](https://forum.inductiveautomation.com/u/ANKIT_BARAD)\ **Post date:** [January 27, 2023, 9:31pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/1 "2023-01-27T21:31:03Z")
I have a reading coming from one plc to ignition, I want to send this reading to another PLC using ignition. How can I do this? ---
**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:** [January 27, 2023, 10:10pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/2 "2023-01-27T22:10:21Z")
Use a tag change script monitoring the one and writing unconditionally to the other. ---
**Author:** ![ANKIT\_BARAD](https://avatars.discourse-cdn.com/v4/letter/a/6f9a4e/32.png) [@ANKIT\_BARAD](https://forum.inductiveautomation.com/u/ANKIT_BARAD)\ **Post date:** [January 28, 2023, 3:20pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/3 "2023-01-28T15:20:42Z")
Do you have any example I can use? ---
**Author:** ![Matrix\_Engineering](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/matrix_engineering/32/19781_2.png) [@Matrix\_Engineering](https://forum.inductiveautomation.com/u/Matrix_Engineering)\ **Post date:** [January 28, 2023, 3:58pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/4 "2023-01-28T15:58:53Z")
[https://docs.inductiveautomation.com/display/DOC81/Tag+Event+Scripts](https://docs.inductiveautomation.com/display/DOC81/Tag+Event+Scripts) [https://docs.inductiveautomation.com/display/DOC81/system.tag.writeBlocking](https://docs.inductiveautomation.com/display/DOC81/system.tag.writeBlocking) ---
**Author:** ![justinedwards.jle](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/justinedwards.jle/32/37854_2.png) [@justinedwards.jle](https://forum.inductiveautomation.com/u/justinedwards.jle)\ **Post date:** [January 28, 2023, 7:54pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/5 "2023-01-28T19:54:02Z")
Just out of curiosity, is there a reason why PLC messaging isn't being used to transfer this information? ---
**Author:** ![ANKIT\_BARAD](https://avatars.discourse-cdn.com/v4/letter/a/6f9a4e/32.png) [@ANKIT\_BARAD](https://forum.inductiveautomation.com/u/ANKIT_BARAD)\ **Post date:** [January 28, 2023, 8:35pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/6 "2023-01-28T20:35:42Z")
PLCs are Allen Bradley and Siemens ---
**Author:** ![Gustavo\_Prado](https://avatars.discourse-cdn.com/v4/letter/g/b5e925/32.png) [@Gustavo\_Prado](https://forum.inductiveautomation.com/u/Gustavo_Prado)\ **Post date:** [January 28, 2023, 9:22pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/7 "2023-01-28T21:22:18Z")
You should consider using a gateway, like PLX31-EIP-PND (class 1), if the information you are sending from one plc to another are critical. Sorry if that's something you know, but just to make sure. Class 3 communication might have low priority in your rockwell processor and if enough overload occurs your communication through ignition (class 3) will get really slow, while class 1 communication will stay unaffected. ---
**Author:** ![ANKIT\_BARAD](https://avatars.discourse-cdn.com/v4/letter/a/6f9a4e/32.png) [@ANKIT\_BARAD](https://forum.inductiveautomation.com/u/ANKIT_BARAD)\ **Post date:** [January 28, 2023, 11:05pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/8 "2023-01-28T23:05:14Z")
Yes I have used gateway and aware of that. I just need one real value to be transferred. And I am looking for other solutions. Other recommendation are welcome ---
**Author:** ![Kyle\_Chase](https://avatars.discourse-cdn.com/v4/letter/k/9de0a6/32.png) [@Kyle\_Chase](https://forum.inductiveautomation.com/u/Kyle_Chase)\ **Post date:** [January 28, 2023, 11:38pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/9 "2023-01-28T23:38:24Z")
You could use the Ethernte/IP module from @pturmel if you wanted class 1 communications. However, for most things, using Ignition as a gateway would suffice. Just make sure you have a watchdog as well. ---
**Author:** ![Gustavo\_Prado](https://avatars.discourse-cdn.com/v4/letter/g/b5e925/32.png) [@Gustavo\_Prado](https://forum.inductiveautomation.com/u/Gustavo_Prado)\ **Post date:** [January 28, 2023, 11:44pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/10 "2023-01-28T23:44:48Z")
Thanks, good to know! ---
**Author:** ![gregory.sachs](https://avatars.discourse-cdn.com/v4/letter/g/e47774/32.png) [@gregory.sachs](https://forum.inductiveautomation.com/u/gregory.sachs)\ **Post date:** [February 2, 2023, 11:01pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/11 "2023-02-02T23:01:26Z")
I would recommend doing this via a timed script, not a tag change script. Tag changes can get missed, especially if one makes a save that restarts the script system. A timed script will always self correct. Set frequency of the script as needed for the application. As mentioned, if it is speed critical or application critical you might be better off with a hardware gateway. ---
**Author:** ![andrew.marano](https://avatars.discourse-cdn.com/v4/letter/a/e95f7d/32.png) [@andrew.marano](https://forum.inductiveautomation.com/u/andrew.marano)\ **Post date:** [February 7, 2023, 4:36pm UTC](https://forum.inductiveautomation.com/t/write-a-value-from-one-plc-to-other-plc-through-ignition/69113/12 "2023-02-07T16:36:53Z")
Another way we've accomplished this, is using SQL Bridge module to configure OPC-to-OPC transaction groups. We did this specifically for Allen-Bradley \<--\> Siemens, similar to the setup you mentioned.