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How To Handle Subscribing To An Inactive OPC Item
06 Sep 2021 09:58 #10183
by Bishop
How To Handle Subscribing To An Inactive OPC Item was created by Bishop
I am busy investigating edge cases within our subscription workflow and have noticed that one may Subscribe to an inactive OPC Item (Or even one that does not exist) and still receive a handle back from the EasyDAClient.
The ItemChanged method is then still called for this inactive/non-existent OPC Item, which then raises the error below from within our event handler system.
The ItemChanged method is then called every 60 seconds on the same inactive/non-existent OPC Item and the above error is raised, as can be seen in the image below.
Is this simply an internal default, where the EasyDAClient performs a read on all subscriptions every 60 seconds to compare against previous values?
Is this a known issue with subscribing to an inactive/non-existent OPC Item?
I would ideally like to handle this internally to not subscribe to an OPC Item if it does not exist or is inactive.
Any help with regard to the above issue would be extremely helpful.
Many thanks,
Brett.
The ItemChanged method is then still called for this inactive/non-existent OPC Item, which then raises the error below from within our event handler system.
*** Failure {http://opcfoundation.org/DataAccess/}E_UNKNOWN_ITEM_NAME: OPC NET API failure result "E_UNKNOWN_ITEM_NAME".
+ The client method called was 'ItemChanged'.The ItemChanged method is then called every 60 seconds on the same inactive/non-existent OPC Item and the above error is raised, as can be seen in the image below.
Is this simply an internal default, where the EasyDAClient performs a read on all subscriptions every 60 seconds to compare against previous values?
Is this a known issue with subscribing to an inactive/non-existent OPC Item?
I would ideally like to handle this internally to not subscribe to an OPC Item if it does not exist or is inactive.
Any help with regard to the above issue would be extremely helpful.
Many thanks,
Brett.
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