Geo SCADA Expert can retrieve current data from each Modbus controller at one of eight Normal frequencies, which you specify on the Modbus tab of the relevant Outstation Form (see Define the Data Retrieval Intervals).
Under certain circumstances, you might want to ‘promote’ a controller’s scan rate, so that its data is retrieved at a more frequent rate. Specify this rate using the eight Promoted intervals on the same tab. Use the Promote when Displaying Points check box on the Direct tab of the Outstation Form to specify whether scanning is automatically promoted while a controller’s points are on display (see Define Whether an Outstation is Promoted While its Points are on Display). (You can manually promote scanning using a controller’s Promote Scanning pick action—see Temporarily Increasing the Scan Rate.)
Use the Retrieval Interval field on each Point Form to specify which of the eight Normal and Promoted retrieval interval combinations apply to each point (see Configure Common Point Properties). Whenever one or more retrieval intervals expire, the driver will attempt to poll the controller for the data for those points on which the intervals have expired.
Example:
A controller includes this configuration:
Normal Retrieval Interval 1: 5 Seconds
Normal Retrieval Interval 2: 10 Seconds
One of the analog points on the controller has this configuration:
Address: 30001
Retrieval Interval: Interval 1
Another analog point on the controller has this configuration:
Address: 30002
Retrieval Interval: Interval 2
The above configuration results in the driver scanning point addresses 30001 and 30002 together at 10 second intervals, in addition to scanning address 30001 every other 5 seconds. (As 30001 is scanned at 5-second intervals and 30002 at 10-second intervals.)
You can also assign a Scan Group to each point (other than those for which Geo SCADA Expert only retrieves historic data), to provide confidence that the point’s data is still up-to-date, even if the point has not changed for some time at the controller. Be aware that Geo SCADA Expert will attempt to poll a controller for current data whenever any of the points’ Scan Group intervals expires (see Configure Common Point Properties). Typically, a Scan Group interval should be a multiple of a point’s Retrieval Interval.