Applies To:
  • CitectSCADA

When I start up Citect and connect it to an OPC server, I occasionally get the hardware alarm "Data Not Yet Valid" and my points display as #COMs. In time, it sometimes recovers to display the true values of the points but again I occasionally get #COMs and the hardware alarm. What is happening here and how do I sort this out? 

This problem will generally only occur when the OPC server has a significant number of points to read from the PLC. What is happening is that the OPC server has started its reading process of points from the PLC, and before the process completes, the Citect system is trying to retrieve the OPC points data from the OPC server.

As all of the OPC points data have not been read yet to the OPC server from the PLC, the alarm is caused.

By setting the parameter:



we are able to display those points that have already been read, and the remaining points will display as zero initially (if the data is not yet valid) and then be updated to their true values when the OPC server reading operation has been completed.