Comparison Of Mtbf For Selected Configurations; System Configurations With Centralized I/Os - Siemens SIMATIC S7-400H System Manual

Characteristic values of redundant automation systems
A.2 Comparison of MTBF for selected configurations
A.2

Comparison of MTBF for selected configurations

The following sections compare systems with a centralized and distributed I/Os.
The following framework conditions are set for the calculation.
● MDT (Mean Down Time) 4 hours
● Ambient temperature 40 degrees
● Buffer voltage is safeguarded
A.2.1

System configurations with centralized I/Os

The following system containing one CPU (e.g. 417-4H) operating in stand-alone mode
forms the basis for the calculation of a reference factor which defines the multiple of the
availability of other systems with centralized I/Os compared to the base line.
Fault-tolerant CPU in stand-alone mode
Fault-tolerant CPU in stand-alone mode (e.g. 417-4H)
Redundant CPUs in different racks
Redundant CPU 417-4H in a split rack, CCF = 2 %
Redundant CPU 417-4H in separate racks, CCF = 1 %
316
Factor
1
Factor
20
Factor
38
System Manual, 09/2007, A5E00267695-03
S7-400H