Applies To:
  • CitectSCADA 5.20, 5.21, 5.30, 5.31, 5.40
Summary:
What is the limitation on the number of OPC tags per I/O Device? If we want to read more than this limit will we will have to split them over multiple I/O Devices? 

Solution:
The hard limit defaults to 32,000 tags per I/O device at present and can be increased adjusting the [OPCARRAYS]ArrayRecordBase parameter. Up to 65535 tags per I/O Device are theoretically possible.

Note that performance with OPC decreases at a mostly linear rate against an increase in the number of tags per I/O Device. With more than 4,000 tags per device, some users have found performance starts to be less than desirable. This depends as much on the Citect Driver as it does on the Citect project configuration, the speed and memory of the PC hardware, the OPC driver options chosen and performance of the given OPC Server.

UPDATED: This article is superseded by Q4220.

 
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