# OPC data mode as subscription vs polled

**URL:** <https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972>\
**Category:** Ignition\
**Created:** [November 2, 2022, 7:04am UTC](https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972 "2022-11-02T07:04:36Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Dharani\_T](https://avatars.discourse-cdn.com/v4/letter/d/bc8723/32.png) [@Dharani\_T](https://forum.inductiveautomation.com/u/Dharani_T)\
**Post date:** [November 2, 2022, 7:04am UTC](https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972/1 "2022-11-02T07:04:36Z")

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Hi,

I have an opc tag in which data are getting read only if the opc data mode is in Polled state.  
But when i check in opc quick client, subscription is working. But when i set OPC mode as subscription it is displaying as "Uncertain initial value"  
What is the cause of this issue and how to overcome

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<div class="post-metadata">

**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:** [November 2, 2022, 11:42am UTC](https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972/2 "2022-11-02T11:42:23Z")

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What OPC server? (There are some buggy external servers that have this behavior.)

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<div class="post-metadata">

**Author:** ![Dharani\_T](https://avatars.discourse-cdn.com/v4/letter/d/bc8723/32.png) [@Dharani\_T](https://forum.inductiveautomation.com/u/Dharani_T)\
**Post date:** [November 2, 2022, 11:53am UTC](https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972/3 "2022-11-02T11:53:21Z")

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OPCUA expert .

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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:** [November 2, 2022, 11:58am UTC](https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972/4 "2022-11-02T11:58:25Z")

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UaExpert is a client

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<div class="post-metadata">

**Author:** ![Dharani\_T](https://avatars.discourse-cdn.com/v4/letter/d/bc8723/32.png) [@Dharani\_T](https://forum.inductiveautomation.com/u/Dharani_T)\
**Post date:** [November 2, 2022, 11:59am UTC](https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972/5 "2022-11-02T11:59:55Z")

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Sorry. Win CC RT Advanced

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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:** [November 2, 2022, 12:04pm UTC](https://forum.inductiveautomation.com/t/opc-data-mode-as-subscription-vs-polled/65972/6 "2022-11-02T12:04:40Z")

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Oh, that's definitely one of the "buggy external servers"...

You can set the log level for the loggers you get searching "OpcUaSubscriptionModel" and "OpcUaSubscriptionSynchronizer" to DEBUG or TRACE and see if there's an error when creating the monitored item for some reason.

Or make sure the connection has no security and set up a Wireshark capture.

[https://docs.inductiveautomation.com/display/DOC81/Diagnostics+-+Logs#DiagnosticsLogs-ChangingLoggingLevels](https://docs.inductiveautomation.com/display/DOC81/Diagnostics+-+Logs#DiagnosticsLogs-ChangingLoggingLevels)