Siemens SIMATIC S7-400H - Comparison of MTBFs for Selected Configurations

Characteristic Values of Redundant Programmable Logic Controllers
A-4
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
A.2 Comparison of MTBFs for Selected Configurations
The following sections compare systems with a central I/O.
The following framework conditions are set for the calculation.
• MDT (Mean Down Time) 4 hours
• ambient temperature 40 degrees
• buffer voltage is guaranteed
A.2.1 System Configurations With Central I/O
The following system with a standard CPU (e.g. CPU 417-4) is taken as a basis for
calculating a reference factor which specifies the multiple of availability that other
systems with a central I/O have, compared with the baseline.
Standard and fault-tolerant CPU in single operation
Standard CPU (e.g. CPU 417-4) Baseline
Mounting
rack, UR1
PS 407, 10 A CPU 417-4
SM 421
SM 422
1
Fault-Tolerant CPU in Single Operation (e.g. CPU 417-4H) Factor
Mounting rack,
UR1
PS 407, 10 A CPU 417-4H
SM 421
SM 422
1