Where the outstations on your system use only a single channel within a dual-channel set-up, you can configure those outstations to be in a shared outstation set, in which the outstations only communicate via a specified channel. The channels are identified as Line A and Line B (the channels are defined as Line A and Line B in the outstation set configuration).
Outstations that are ‘fixed on Line A’ cannot communicate with the ClearSCADA server via the alternate channel—‘Line B’ is unavailable. Similarly, outstations that are ‘fixed on Line B’ cannot communicate via Line A.
Fixed on Line A or B dual channel set-ups are used when an outstation only communicates via one direct channel, but that channel is used as part of a dual channel communications set-up (with other outstations that use both channels). Typically, this is the case when an outstation is located near to an existing dual channel set-up. It is more cost effective for the outstation to use one of the channels in the dual channel set-up than to set up a direct single channel set-up for the outstation.
In this example, the first two outstations in a set are connected to both direct channels (Line A and Line B). The set to which they belong is a shared set, and the outstations alternate between using Line A and Line B.
The last two outstations in the set use only one channel (Line A). These outstations, which have addresses 3 and 4, are in the same shared set, but have their communications fixed on Line A. The outstations communicate with the ClearSCADA server using only one direct channel.
To avoid the expense of installing an additional channel, the existing channel (Line A) is used for these outstations. As the outstations are of lesser importance than the other outstations in the set, it has been decided to avoid the expense of providing redundant communications, and so the outstations can only communicate on one channel.
To help provide the most efficient communications, the outstations with addresses 1 and 2 are configured to use Line B as the preferred channel. As such, they only use Line A (which is the line that is used by the outstations that can only communicate using one channel) if Line B is unavailable.
