Comparison Of System Configurations With Standard And Fault-Tolerant Communication - Siemens SIMATIC S7-400H System Manual

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, we may assume a total operating time of all redundant
automation systems of 300,000,000 hours. We have received reports of the failure of four
redundant automation systems in total.
This proves an assumed MTBF of 3000 years to be 95 % reliable.
The MTBF values assessed as being real are:
Type I b, CCF = 2 % Approx. 5.68 acres
Type I b, CCF = 0.2 % Approx. 29.65 acres
Type I differs from an average redundant automation system only in the use of a redundant
power supply. So the above analysis is rather pessimistic.
A.2.3 Comparison of system configurations with standard and fault-tolerant
communication
The next section shows a comparison between standard and fault-tolerant communication
for a configuration consisting of a fault-tolerant system, a fault-tolerant CPU operating in
stand-alone mode, and a single-channel OS.
The comparison only took account of the CP and cable communication components.
Systems with standard and fault-tolerant communication
Standard communication
Fault-tolerant communication
S7-400H
System Manual, 09/2007, A5E00267695-03
Characteristic values of redundant automation systems
A.2 Comparison of MTBF for selected configurations
Base line
1
Factor
approx. 80
319