The process of scanning (‘polling’) direct outstations for data differs with each advanced driver. This section explains the basic principles that apply to most advanced drivers. Use this section in conjunction with the relevant driver-specific documentation for comprehensive information on the scanning regime used by the driver(s) on your system, (Outstation Types and Communications Set-ups).
This section describes the scanning method used for direct outstations on many advanced drivers.
Many outstations on advanced drivers support current data—the present state or value of a point at the instance that the Geo SCADA Expert server requests current data from the outstation. Many outstations also support logged data—time stamped data that is stored at the outstation.
Scanning is the process of checking each of the outstations on a channel to assess whether any of those outstations have new current data or logged data. The data is then retrieved, processed and stored in the database, ready for use in Geo SCADA Expert. Each advanced driver on a Geo SCADA Expert system undertakes the scanning of the outstations that are associated with that driver.
The process of retrieving data differs, depending whether the outstation has a permanent connection to the server (‘direct communications’), or uses a dial-up modem and telephone line for all communications (‘PSTN communications’). With a PSTN outstation, communications are typically re-established each time the server requests data from the outstation
For information on the process used to scan direct outstations on many advanced drivers, see Scanning Process and Independent Connection Scanning Process.