Associated with: Shared or Switched outstation sets; Shared outstations (other than those for which communications is fixed on one channel)
Security permission required to access this pick action: Switch Line
Some simple driver channels support two lines and therefore also support the Switch Line pick action. Whenever the Switch Line pick action is supported, its functionality is summarized in the relevant driver-specific guide.
Most simple driver channels only support single connections and for such channels, any attempts to trigger the ‘Switch Line’ pick action or method in ClearSCADA will have no effect and will be ignored.
Shared and Switched outstations can communicate with ClearSCADA via either of two direct channels. With outstations on a Switched outstation set, all of the outstations have to use the same channel (see Switched Dual Channel). With outstations on a Shared outstation set, communications can be ‘shared’ between the channels, so that some outstations use one channel, and other outstations use the other channel (see Shared Outstations). The Balance status attribute indicates the percentage of outstations that are communicating via each line on a Shared outstation set.
With either setup, should ClearSCADA detect that communications on one channel (line) has failed, communications will usually switch to the other channel automatically. The exceptions to this are:
- Any Shared outstations for which communications is fixed on a particular line, or on which Heartbeating is used and this indicates that the other channel has also failed.
- Outstations in a Switched set, for which the other channel was last reported to be in a failed state.
If ClearSCADA detects that communications on both lines has failed:
- With Shared outstations on which Line Hunting is used, the driver will keep switching the line to test each line in turn, until one or both lines become healthy again.
- With Shared outstations on which Line Hunting is not enabled, the driver will switch once, away from the failed line that the outstations were using (if Heartbeating is used, the switch will only occur if the other channel is okay).
- With outstations in Switched sets, automatic switching will cease.
With Shared outstations and both Shared and Switched outstation sets, you can use the Switch Line pick action to force switching to continue, or to force outstation(s) to use a particular line. Use the pick action on a set to force each of the outstations on that set to switch (other than any fixed outstations); use the pick action on a Shared outstation to change communications on that outstation only (or, if the outstation is configured as a Group Master, the communications of both that outstation and its Group Slaves).
Select the Switch Line pick action to display the Switch Line window.
Select the required option from the combo box:
- Toggle Line—Switches communications to the channel (line) that is not presently being used. The lines are specified on the Outstation Set Form.
- Line A: <Full name of channel>—Switches communications to the channel that is designated Line A (as specified on the Outstation Set Form).
- Line B: <Full name of channel>—Switches communications to the channel that is designated Line B (as specified on the Outstation Set Form).
- Preferred Line—ClearSCADA checks whether the channel being used is the one that is designated as the Preferred Line. If not, communications is switched to the Preferred Line.
With a Shared outstation that is configured as Independent, the Preferred Line is specified on that outstation’s Form (see Define a Shared Outstation’s Switching Capabilities).
With a Shared outstation that is configured as a Group Slave, the Preferred Line is specified on the Group Master’s Outstation Form.
When using this pick action on a Shared Set, be aware that there may be a delay between individual outstations switching channels. Such a delay is specified on the Shared Set Form.
With both Switched and Shared outstations, should ClearSCADA detect that communications has failed on the chosen channel, it will automatically switch communications back to the other channel. With Switched Sets, ClearSCADA might need to detect that a specified number of outstations has failed before communications are switched back—such a requirement is specified on the Switched Set Form. This requirement does not apply should ClearSCADA detect that the channel itself has failed (for example, by detecting a COM port failure). In such circumstances, ClearSCADA will automatically switch communications back to the other channel, regardless of the number of outstations that it has detected as failed. Automatic switching of outstations in Switched Sets will not occur if the other channel was last reported to be in a failed state. With such a situation, use the Switch Line pick action to switch the outstations to the other channel once that channel is known to be healthy. (A channel’s state only updates when an attempt is made to communicate via that channel.) This also applies if ClearSCADA detect that both channels used by a Switched set have failed: once both channels are believed to be healthy, use the Switch Line pick action to switch the outstations to each of those channels. This will update each channel’s State in the database, allowing automatic switching to occur should the channel in use be detected as failed in future. For more information, see Switched Dual Channel.