Understanding Data Transfer

iFIX applications retrieve real-time data from an OPC server through requests. The most important iFIX application is the iFIX WorkSpace since it puts the most load on the network.

Objects in an operator display update by polling the OPC server. Each animated object has a configurable refresh rate. This rate determines how often each link requests the current value from the OPC server. When the OPC server is an iFIX SCADA server, object update rates are grouped together and sent as one transaction, up to 16 kilobytes at a time. If the request or response for that group exceeds 16 kilobytes, it is broken up into 16-kilobyte packets.

If more than one picture is open at the same time that has objects to the same SCADA server, there is a separate group for each picture.

When animated objects communicate with a third-party OPC server, data is sent and received according the server's requirements. Refer to your OPC documentation for more information.

Alternative Way of Changing the Refresh Rate

If you find that network traffic is too high with the existing refresh rates and changing them all individually is too time consuming, it is possible to affect them all with one .INI setting. In the FixUserPreferences.ini file in the iFIX Local folder, add the following lines to control the actual refresh times:

[OPCEDARefresh]

SetRefreshtoActual=TRUE

When set to TRUE, the OPC groups refresh the data at the specified refresh rate.  Anything other than TRUE will maintain the normal behavior which is to update the data at 2 times the refresh rate. Normally, the update rate is twice the object refresh rate because under certain timing conditions, the refresh would not reflect the updated data.

WARNING: Be aware that alarms could be lost if you configure the OPCEDA refresh rate to equal the objects' refresh rate.

See Also