OPC Servers support a registration mechanism to put the appropriate entries into the Geo SCADA Expert registry. Registration occurs automatically whenever an application that supports the OPC protocol is installed. This section of the guide provides information for administrator level users should registration not appear to have occurred as expected, or should Geo SCADA Expert not be able to access an OPC server.
Geo SCADA Expert can communicate with three types of OPC server—In Process, Local, and Remote (see Configuring the OPC Server Properties). In Process servers are registered using RegSvr32; Local (executable) servers are registered through the /RegServer command line option; Remote servers need registering on both the server and client machines. Registration on Geo SCADA Expert systems is done through the Geo SCADA Expert Control Panel applet.
The OPCEnum service is installed automatically when you install Geo SCADA Expert as a server. The OPCEnum service offers an effective method of locating remote OPC servers, provided that the service is also available on the remote devices.
When searching for remote OPC servers, Geo SCADA Expert will initially use the OPCEnum service. The Geo SCADA Expert Simple OPC Driver will attempt to connect to the OPCEnum service on the remote machine. If the OPCEnum service is not available on the remote machine(s), Geo SCADA Expert will revert to using the Category Manager to browse for OPC servers.
This feature was introduced by the OPC foundation during the OPC DA 2 specification. Previously, a server included an extra OPC key under its Class Identifier (CLSID) to indicate that it was an OPC server. New servers should register themselves using both mechanisms—that is, using the Category Manager and using the OPC key under the CLSID.
Some very old servers only use the OPC key technique and as such, are not visible to Geo SCADA Expert (run OLE View in ‘Expert’ mode to see the OPC categories that are listed in the ‘Grouped By Component Category’ section). Old OPC servers that are not visible to Geo SCADA Expert need upgrading if Geo SCADA Expert is to communicate with them using the OPC protocol.