# Scan Class -OPC Tag Communication Issue **URL:** \ **Category:** Ignition\ **Tags:** ignition81, vision\ **Created:** [July 29, 2025, 6:00am UTC](https://forum.inductiveautomation.com/t/scan-class-opc-tag-communication-issue/109036 "2025-07-29T06:00:19Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![sk\_venkatesh](https://avatars.discourse-cdn.com/v4/letter/s/c57346/32.png) [@sk\_venkatesh](https://forum.inductiveautomation.com/u/sk_venkatesh)\ **Post date:** [July 29, 2025, 6:00am UTC](https://forum.inductiveautomation.com/t/scan-class-opc-tag-communication-issue/109036/1 "2025-07-29T06:00:19Z")
i am using Ignition 7.8.2 Version , OPC -UA Module is 3.8.2 and OPC Com module is 3.8.2. Issue is whenever i try to change the scan class for tag , it starts communicating, i have craeted different scan class with 10 sec, 11sec. i have attached screenshot for ref. Kindly advise met to get rid of this issue. My requirement is without changing scan class, my tag must communicate. ---
**Author:** ![Cody\_Morgan](https://avatars.discourse-cdn.com/v4/letter/c/db5fbb/32.png) [@Cody\_Morgan](https://forum.inductiveautomation.com/u/Cody_Morgan)\ **Post date:** [July 29, 2025, 7:52am UTC](https://forum.inductiveautomation.com/t/scan-class-opc-tag-communication-issue/109036/2 "2025-07-29T07:52:24Z")
The screenshot didn't make it into your post. You'll probably need to provide a lot more context to get decent help. (Configs, logs, screenshots, or even video of the behavior) ---
**Author:** ![sk\_venkatesh](https://avatars.discourse-cdn.com/v4/letter/s/c57346/32.png) [@sk\_venkatesh](https://forum.inductiveautomation.com/u/sk_venkatesh)\ **Post date:** [July 29, 2025, 10:28am UTC](https://forum.inductiveautomation.com/t/scan-class-opc-tag-communication-issue/109036/3 "2025-07-29T10:28:00Z")
![Scan class](https://us1.discourse-cdn.com/inductiveautomation/original/3X/8/e/8e97ffd0d4ffae8ee06ac9a21441725d7cd0a3ec.jpeg) ![Scan class1](https://us1.discourse-cdn.com/inductiveautomation/original/3X/0/e/0ebc0275fa4af0d87ce1b2e3aee8bed9a942c35c.jpeg) ![Tag address](https://us1.discourse-cdn.com/inductiveautomation/original/3X/7/8/78372da4549197449413d9d7c0e16bc85106a7a2.jpeg) ![Null Tag](https://us1.discourse-cdn.com/inductiveautomation/original/3X/4/3/430ca0dd679dd1008659e4862d981bd7ecf35c43.jpeg) Thanks for reply. If i change the scan class, Null will disappear and Quality will become good. I tried creating new scan class also with different scan rate of 1200 ms. But no use. All Machines with PLC will communicatwe via Codesys OPC. I can able to see those tags fetching with good quality in OPC Quick Client . But it fails to get good quality in UDT Tag Browser.Kindly advise. ---
**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:** [July 29, 2025, 12:46pm UTC](https://forum.inductiveautomation.com/t/scan-class-opc-tag-communication-issue/109036/4 "2025-07-29T12:46:44Z")
Your best bet is to upgrade to 7.8.5, the last version in the 7.8 series. You are likely experiencing a bug. However, there are many 3rd party OPC servers that do not follow the standards (and that old Ignition isn't great, either), and you will likely need to upgrade to modern Ignition (8.1) to get the necessary bug fixes and work-arounds. Meanwhile, what changed to break the communcation? (If these are **new** PLCs you are trying to add to **old** Ignition, do not expect success.) ---
**Author:** ![sk\_venkatesh](https://avatars.discourse-cdn.com/v4/letter/s/c57346/32.png) [@sk\_venkatesh](https://forum.inductiveautomation.com/u/sk_venkatesh)\ **Post date:** [July 30, 2025, 4:49am UTC](https://forum.inductiveautomation.com/t/scan-class-opc-tag-communication-issue/109036/5 "2025-07-30T04:49:56Z")
Thanks [pturmel](https://forum.inductiveautomation.com/u/pturmel)Leader