Associated with: Outstation sets; PSTN outstations or outstations with PSTN fallback; Slave PSTN outstations
Security permission required to access this pick action: Retrieve Data
When ClearSCADA executes a One Shot call, the server dials out to an outstation, retrieves its data, and then terminates the call. Use the One Shot pick action to instigate such a call. The pick action is typically associated with a Schedule, so that the One Shot calls occur automatically on a regular basis, without the need for user intervention. However, you can also use the One Shot pick action manually whenever required.
When a One Shot call is triggered on an outstation, ClearSCADA dials out to that individual outstation to retrieve its data.
When a One Shot call is triggered on an outstation set, if multiple PSTN channels are available, then multiple calls will run in parallel, as ClearSCADA will dial out to as many outstations as possible simultaneously. For example, if a set contains two outstations and two PSTN channels are available, ClearSCADA will dial both outstations at the same time. If there are three outstations in a set and only two PSTN channels available, then once the first call has completed, ClearSCADA will dial the third outstation. In each case, if there are more outstations then there are PSTN channels available, the server will dial the outstation with the lowest address first; once it has received the data from that outstation, it will terminate the call and dial the outstation that has the next lowest address, and so on. The telephone number that is used to contact each outstation is specified on the PSTN tab of the Outstation Form.
If the Preferred Channel pick action has been used to specify a particular channel, ClearSCADA will attempt to use that channel to dial out to the outstation(s) in preference to other PSTN channels.
Should an outstation have a large amount of data to report, the call will terminate once the outstation’s Maximum Call Length is reached, regardless of whether all of the data has been retrieved. With some types of outstation, you can use the Extend Line pick action to extend the length of such a call, in order to retrieve all of the data.
Whenever an action is triggered that requires ClearSCADA to exchange information with a PSTN outstation, ClearSCADA will automatically instigate a One Shot call to that outstation. Such actions include, for example, Control or Inching actions on points or pulse actions that are on a PSTN outstation. In such circumstances, ClearSCADA executes the actions, retrieves the data and then terminates the call.
For more information on PSTN communications, see PSTN Outstations and Communications in the ClearSCADA Guide to Advanced Drivers, and see Retrieving Data from PSTN Outstations in the ClearSCADA Guide to Advanced Drivers.
Use an outstation’s status attributes to ascertain information about the calls to that outstation (see Status Attributes Associated with Outstations on Advanced Drivers).
Also see Open Line, and see Promote Dial Out.