Redundancy Mode "Off" (0) - ABB S900 Manual

Hide thumbs

Table Of Contents

Table of Contents

I/O System S900

Communication Interface for PROFIBUS DP, CI920

voter treats both lines identically in all respects, so that different slaves (S900

systems) of a trunk – with the lines properly working – can be operated on

different lines. Each CI920 of the I/O System S900 is allocated its own station

address (or none, in case of LR_NONE). The station address of the redundant

Communication Interface and the redundancy operating mode is passed to the

passive Communication Interface by the active Communication Interface

after it has started up.

If the PROFIBUS line fails (the one the active Communication Interface uses

to handle the user data communication with the master), the active

Communication Interface recognizes this fact. As a consequence, the two

CI920 of the I/O System S900 swap their PROFIBUS station addresses. The

previously passive Communication Interface becomes the active CI920 and

vice versa. Now the master tries to include the active CI920 on the redundant

line in the cyclic data exchange. Since the lines cannot be diagnosed during

the start-up period and the redundant line could also be defective, the start-up

(time) is monitored by the active CI920. When the active CI920 achieves the

cyclic data exchange with the master, time monitoring is stopped, since now

the line could be monitored. If the active CI920 does not achieve the cyclic

data exchange with the master within the predefined start-up time (default

setting = 8 s), another redundancy toggle is performed. For the time used for

redundancy toggling and the startup time the module outputs retain their last

valid values. If the cyclic data exchange could not be achieved after the first

redundancy toggle, the originally active CI920 sets the module outputs to the

parameterized safety condition/value after expiration of the startup time and

after switching back to the originally active CI920. Retaining the input values

during redundancy switching can only be ensured by the master system. The

S900 ensures that already the first data telegram to the master will contain

valid input data when entering the cyclic data exchange. This cannot be

ensured for cyclic HART variables.