OPC Access Path Parameters

In some instances, an OPC server might have several ways to access a particular item. For instance, a particular server, which communicates by means of modem, might have multiple modems at its disposal. It might be desired that certain items in the OPC server are always accessed using a particular modem, the fastest of the group, for example. OPC allows you to specify this preference by using the Access Path <OPCAccessPath> value.

An access path is optional, provided in addition to the Item ID (the tag address), which is provided as a recommendation to the server, regarding how to access the data.

Note: The availability, format, and use of access paths is server-specific. Refer to your OPC server documentation for details relevant to your server.

[OPCAccessPaths]<IOServerName>.<IODeviceName>=<OPCAccessPath>

where:

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

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

• <OPCAccessPath> = Access path to set up communications to the OPC server.

This parameter is not normally required with most OPC servers.

The Plant SCADA OPC client driver supports specification of a single access path for each configured I/O device using the [OPCAccessPaths] section of the Citect.ini file.

To specify the access path for a particular device, add an entry to the ini file in the format <IOServerName>.<IODeviceName>. For example, to specify that the access path COM1: should be used for the I/O device OPC1 on I/O server IOServer1, add the following entry to the Citect.ini file:

[OPCAccessPaths]
IOServer1.OPC1=COM1:

Multiple entries are also acceptable:

[OPCAccessPaths]
IOServer1.PLC1=PLC4
IOServer1.PLC2=TestPLC