3.3.6   OPC Comport Properties

The OPC Comport is associated with one OPC Server.  If you have multiple OPC Servers, you must configure an OPC Comport to each Server.  All OPC Devices on the same Comport are associated with one OPC Server.

OPC is an acronym for OLE for Process Control.  It is an industry standard introduced by Microsoft based on DCOM. The WebAccess Device driver is an OLE Client.  Hardware manufactures typically supply an OPC Server to provide access to real-time data. Most OPC Servers allow tags to be "browsed" and "imported".  WebAccess provides an OPCTool.exe that allows tags to be "imported" after you have configured an OPC Comport and at least one OPC Device.

The OPC Server software is usually is installed on the SCADA node (a Local OPC Server). 

The OPC Server software can also be installed on another PC (a Remote OPC Server) that is not the SCADA Node. A TCP/IP network connection (usually a LAN or Intranet) is used to communicate to the "remote" OPC Server from the SCADA Node. The remote OPC Server must have either WebAccess Project Node software or OPC Service installed.

Figure 3-8Comport Properties - OPC

Comport Number

In the OPC port properties, this is a Virtual number used for reference.  It can be any number. The only consideration might be to avoid conflicts with another device driver (i.e. a Serial Comport) which requires the comport number to match that of the physical interface.

The connection from the OPC Server to the PLC or automation device may be a Serial Port, TCP/IP or proprietary network card. Hence, it is possible to have a Serial connection to the device, but use the OPC Port type in WebAccess.  

If the OPC Server uses a Serial Comport, it is okay to use that same number as the OPC Comport number.  This has the added advantage of reducing confusion.

Auto Recover Time

Auto Recover Time is the Time to wait before attempting to re-establish communications with the OPC Server.  It is recommended to accept the default of 60 seconds.  If communications to the OPC Server is unusually slow due to software, communications or network issues, you might consider increasing this value.  If communications to the OPC Server fails frequently, you may want to decrease this number in order to have WebAccess try to re-establish communications sooner. 

If communications to the Server Fails (i.e. exceeds Timeout for a remote OPC Server or drops in a Local Server), WebAccess will wait the Auto Recover Time before trying to re-establish communications.  WebAccess will drop any "open handles" and re-establish new "software links" to the OPC Server. WebAccess will try to restart the OPC Server if the OPC Server is not running.


User defined field for reference. This appears only in Project Manager.