OPC Servers support a registration mechanism to put the appropriate entries into the Windows 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 the driver not be able to access an OPC server.
The driver can communicate with three types of OPC DA server—In Process, Local, and Remote (see Configure the Advanced OPC Server). In Process and Local servers are present on the same machine as the main Geo SCADA Expert server. In a hot-standby system, which machine is In Process or Local, will change.
To connect to Remote systems you need to know the location of the servers. The Advanced OPC Driver provides you with the features to search and connect through to Remote OPC DA servers.
The OPC Foundation provide an OPC Server Browser called OpcEnum. This needs to be installed on the same machines as the OPC servers. If required it can be obtained from the OPC Foundation website. 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 machines.
When searching for OPC servers, the driver will initially use the OPCEnum service. The Geo SCADA Expert Advanced OPC Driver will attempt to connect to the OPCEnum service on the machine. If the OPCEnum service is not available on the machine(s), the driver will revert to searching the registry 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.