Applies To:
  • CitectSCADA
  • OPC driver version 1.11.10.000
Summary:
If an OPC device is defined with more than 32766 variable tags assigned to it then the OPC driver will not subscribe to all the tags correctly.

When CitectSCADA starts the I/O server will report that the unit has come online successfully.
If any read requests are sent to the device it will report Unit Offline. The I/O server will then bring the unit online again and the process repeats.
 

Solution:
It is unwise to create a single OPC device with this number of variable tags, if nothing else the device is likely to take a very long time to come online due to the time it takes to subscribe to each tag.

In this situation it is recommended to create multiple I/O devices that all address the same OPC server. Each of these devices should have less than 32767 tags defined against them.

This article supersedes Q3400.
 
Keywords:
OPC unit offline hardware alarm  

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