Siemens SIMATIC S7-400H System Manual page 443

Switched distributed I/O, PROFINET, CCF = 2 %
The estimate applies if the process allows for any device to fail.
S7-400H
System Manual, 03/2012, A5E00267695-11
Characteristic values of redundant automation systems
A.2 Comparison of MTBF for selected configurations
Factor
approx. 10
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