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AVEVA™ Plant SCADA

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OPC Device-specific Parameters

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  • Last UpdatedJul 07, 2025
  • 2 minute read

For each OPC I/O device you can specify parameter conditions that override the default global settings. To do this, use the following format in the [OPC] section of the Citect.ini file.

[OPC]<IOServerName>.<IODeviceName>.<Parameter>=<Value>

where:

  • <IOServerName> = Name of I/O server configured in Plant SCADA .

  • <IODeviceName> = Name of I/O device configured for OPC communications.

  • <Parameter> = Parameter of the I/O device being overridden.

  • <Value> = Value of the overriding parameter being set.

Note: There are also a number of status tag parameters that you can override global settings for in the [OPCStatusTags] section of the Citect.ini file. For more information see OPC Status Tag Parameters.

The following device-specific parameters are supported.

[OPC] Parameter

Allowable Values

Default Value

Description

Active

0 - deactivate tag.

1 - leave tag active.

Value of the LeaveTagsActive parameter.

Allows user to individually override the global default LeaveTagsActive parameter to specify whether tags should be left active or inactive for a particular OPC I/O device.

Replace the placeholders <IOServerName> and <IODeviceName> in the parameter with the names of the OPC 'I/O Server' and 'I/O Device' you want to override and have remain active.

Determines whether individual OPC tags are left active even though Plant SCADA is no longer requesting them from the driver. Normally tags are made inactive 5 seconds from the last time they are requested.

See the LeaveTagsActive parameter in Driver-specific Citect.ini Parameters.

Update

0 to 32000 (milliseconds)

Scan rate specified in the Address field of the Boards settings.

Allows the user to individually override the.Default.Update parameter to specify the tag update rate for a particular I/O device. The update rate is the frequency with which the OPC server polls the device for values and updates its own cache.

Replace the placeholders <IOServerName> and <IODeviceName> in the parameter with the actual names of the OPC I/O server and I/O device you want to override with a specific update rate.

This parameter controls polling performed by the OPC server, not by Plant SCADA. The scope of the parameter is communication between the OPC server and a device, not between the OPC server and Plant SCADA.

UseAsyncWrites

0 - use synchronous writes.
1 - use asynchronous writes.

0

Determines whether writes are synchronous or asynchronous.

Note: UseAsyncWrites=1 is only valid when [OPC]UseOPC2=1, since OPC1 does not support asynchronous writes.

UseOPC2

0 – Individual OPC2 support disabled (Use OPC 1.0a interface).

1 – Individual OPC2 support enabled (Use OPC DA2 interface).

Value of global UseOPC2 parameter

Allows users to individually override the global default UseOPC2 parameter and to specify whether to use OPC 1.0a or OPC 2.0 for a particular I/O device.

Replace the placeholders <IOServerName> and <IODeviceName> in the parameter with the actual names of the OPC I/O server and I/O device you want to override and have with a particular version OPC interface.

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