Siemens SIMATIC S7-400H - Page 445

Characteristic values of redundant automation systems
A.2 Comparison of MTBF for selected configurations
S7-400H
System Manual, 03/2012, A5E00267695-11
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Table A-1 MTBF factors of the redundant I/Os
Module MLFB MTBF factor
CCF = 1%
Digital input modules, distributed
DI 24xDC24V 6ES7 326–1BK00–0AB0 approx. 5
DI 8xNAMUR [EEx ib] 6ES7 326–1RF00–0AB0 approx. 5
DI16xDC24V, Alarm 6ES7 321–7BH00–0AB0 approx. 4
Analog input modules, distributed
AI 6x13Bit 6ES7 336–1HE00–0AB0 approx. 5
AI8x12Bit 6ES7 331–7KF02–0AB0 approx. 5
Digital output modules, distributed
DO 10xDC24V/2A 6ES7 326–2BF00–0AB0 approx. 5
DO8xDC24V/2A 6ES7 322–1BF01–0AA0 approx. 3
DO32xDC24V/0.5A 6ES7 322–1BL00–0AA0 approx. 3
Summary
There are now several thousand applications of redundant automation systems in the field,
in various configurations. To calculate the MTBF, we assumed an average configuration.
Based on experience in the field, an assumption of MTBF of 3000 hours is 95% reliable.
The system MTBF value calculated is about 230 years for a system configuration with
redundant CPU 417-5H.