During the Secondary Phase Time, ClearSCADA attempts to scan those outstations that have secondary data available. Rather than scan each outstation for all secondary data, it ‘visits’ each outstation for a certain amount of time. During a ‘visit’, ClearSCADA retrieves as much secondary data as possible. At the end of the ‘visit’ it moves on to the next outstation. The maximum duration of a ‘visit’ is called the Maximum Secondary Scan per O/S.
The Maximum Secondary Scan per O/S allows ClearSCADA to use the Secondary Phase Time to scan a range of outstations. It is particularly effective when there are outstations with large amounts of secondary data available, as it stops ClearSCADA from using all of the available time scanning one outstation.
As long as ClearSCADA has completed a secondary scan of the outstations that have secondary data, it should be able to ‘re-visit’ the outstations. During the ‘re-visit’, ClearSCADA will attempt to retrieve any remaining secondary data (see Re-Visiting of Outstations During the Secondary Normal Phase).
To specify the Maximum Secondary Scan per O/S setting, you need to use the Channel Form. The time limit you specify will apply to each of the outstations that communicate via that channel. For more information, see Define the Permitted Scan Durations. Before specifying a time limit, you should also consider Recommended Settings for Scan Durations.