Specify Whether ClearSCADA is to Constantly Poll an Outstation During an Open Line Call

This section applies to PSTN outstations and outstations that are configured to use PSTN fallback.

PSTN calls to an outstation can be initiated using the One Shot action or the Open Line action. With a One Shot call, ClearSCADA dials the outstation to collect that outstation’s data and then ends the call. With an Open Line call, the outstation remains online for a configurable period (specified using the Maximum Call Length field (see Define an Outstation’s PSTN Properties in the ClearSCADA Guide to Advanced Drivers)).

Use the Poll When Online check box on the PSTN tab to specify whether ClearSCADA is to send integrity polls to the outstation during an Open Line call, once it has retrieved the data from that outstation and performed any user requests.

The Poll When Online check box is selected by default. This results in ClearSCADA sending integrity polls to the outstation while the line remains open. Such polls are constant, but do take into account the PSTN channel’s Scan Parameters settings (such as the Inter Message Delay).

Clear the Poll When Online check box if ClearSCADA is not to constantly poll the outstation once it has retrieved the outstation’s data and the line is still open. This may be preferable if, for instance, the DNP3 outstation is being used to route data to other outstations, or is performing other tasks. If the check box is cleared, ClearSCADA will poll the outstation at the poll rates specified on the outstation’s DNP3 tab for the duration of the call.