Use the Minimum Secondary Scan Interval to define the least amount of time in which secondary data extraction can take place per System Scan.
If the System Scan time expires and this minimum period has not elapsed then the scan time will be extended to accommodate the extra time required to achieve the Minimum Secondary Scan time.
If all of the available logged data is retrieved before the minimum period has elapsed, then the Secondary Phase completes.
Specify the interval using the Minimum Secondary Scan field on the Form(s) for the Channel(s) via which each outstation communicates (see Define the Permitted Scan Durations). When defining the Minimum Secondary Scan, you need to consider the Recommended Settings for Scan Durations.
Example:
A driver scans four direct outstations that communicate with the server via a particular channel. The outstations have addresses 3, 4, 5, and 6.
The driver firstly scans the outstations on the channel for current data (the Primary Phase of the scan). As the scan starts, the System Scan time starts to elapse.
Once the current point data has been retrieved from the four outstations, the driver scans the outstations for any logged data (the Secondary Phase of the scan). However, the Primary Phase in this instance has left less System Scan time remaining then has been defined as the minimum time for a Secondary Phase. Therefore, the scan time is extended until the Minimum Secondary Scan time has elapsed.
