S7-400H fault tolerant PLC
Based on standard SIMATIC S7-400 modules, the S7-400H is a fault tolerant (redundant) PLC which drastically reduces the risk of production downtime. Its fault tolerant structure makes the S7-400H ideally suited to applications in which MTTR and downtimes need to be reduced or avoided where possible, e.g. for energy generation / distribution, the chemical industry, mining, transport, etc.
The fault tolerance is achieved by means of two parallel central controllers whose CPUs are connected by means of fiber optic conductors and which control the I/O through redundant PROFIBUS DP lines. Redundant I/O is presently under development. Once
this is available, it will be possible to compensate failing I/O in addition to failing CPU and PROFIBUS. In the event of an error, there is a bumpless transfer of control, i.e. the intact standby device takes over execution at the point of interruption, with no loss of information.