Siemens SIMATIC S7-400H System Manual page 313

The figure below shows the parameters included in the calculation of the MTBF of a system.
Figure A-2
Requirements
This analysis assumes the following conditions:
● The failure rate of all components and all calculations are based on an average
● The system installation and configuration is free of errors.
● All replacement parts are available locally, in order to prevent extended repair times due
● The MDT of the various components is four hours. The system's MDT is calculated based
● The MTBF of the components conforms to the SN 29500 standard, which corresponds to
● The calculations are made using the diagnostic coverage of each component.
● A CCF factor between 0.2 % and 2 % is assumed, depending on the system configuration.
S7-400H
System Manual, 09/2007, A5E00267695-03
MTBF
temperature of 40 °C.
to missing spare parts. This keeps the component MDT down to a minimum.
on the MDT of the various components plus the system structure.
MIL–HDBK 217–F.
Characteristic values of redundant automation systems
A.1 Basic concepts
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