Optional Site.Service Specifier in OPC Identifier

OPC > CygNet OPC Servers > CygNet OPC DA Server > Optional Site.Service Specifier in OPC Identifier

Optional Site.Service Specifier in OPC Identifier

It is possible to omit the Site.Service specifier from an OPC request from the CygNet OPC DA Server.

The CygNet OPC DA Server uses an OPC identifier when requesting data for a CygNet point from a CygNet current value service (for example, OPCIS, UIS). By default, the OPC identifier for a CygNet point is its fully qualified tag string. For example, the Facility Tag String format is MYSITE.UIS::MyWell.PDIFF;ALARMACK, which provides access to real-time data for alarm acknowledgment status (ALARMACK) for the MyWell differential pressure point (PDIFF) in MYSITE.UIS.

However, you can omit the Site.Service specifier and the period or colon(s) from the CygNet tag string when making an OPC item request.

To Omit the Site.Service Name

You can omit the Site.Service specifier from the OPC identifier, and create a text file containing a list of one or more default Site.Service names. At startup the CygNet OPC DA Server will read the text file, prepend the Site.Service name(s) from the list, add necessary periods or colons to the OPC identifier, and attempt to resolve the point.

Configure the OPC identifiers without a Site.Service specifier.
Create a default Site.Services text file using a text editor such as Notepad. Each Site.Service name must be listed on a separate line:

OpcServerDefaultSiteServices.txt

Save the file as OpcServerDefaultSiteServices.txt to the same directory where CygNetOPC.exe is located, for example, C:/CygNet/Support/OPC.
Restart the CygNetOPC.exe to read the OpcServerDefaultSiteServices.txt file.

Formatting and Tag Resolution Notes

Only three of the four CygNet tag string formats are supported:

CygNet Tag String Format Type	Accepted OPC Identifier Format (full tag string, no local text file)	Accepted OPC Identifier Format (with local text file*)
Tag String	Site.Service.PointID	not supported
Long Tag String	Site.Service:LongID	LongID
Full Tag String	Site.Service.PointID:LongID	PointID:LongID
Facility Tag String	Site.Service::Facility.UDC	Facility.UDC

* Site.Service: or Site.Service. or Site.Service:: will be prepended.

If the OPC item does not contain a Site.Service specifier and no default text file is provided, the OPC item will fail to resolve.

If the supplied Site.Service names yield more than one resolved tag, the OPC item request will fail.

If the specified OPC item is ambiguous and exists on multiple services listed in the default text file, the OPC item request will fail to resolve.

All resolution errors will be logged by the CygNet OPC DA Server to the CygNetOPC.log file.

If no default text file is provided, all OPC identifiers must contain a Site.Service specifier.