Rockwell Automation Allen-Bradley Compact GuardLogix 5370 Controller Application Technique page 21

IMPORTANT The 1734-IB8S is not included in the safety function because it is used only for actuator feedback monitoring. The PFH for this complete safety function,
with the sensor, logic, and actuator subsystems, is 3.13E-8, which consumes 31.3% of the PLe bandwidth. The PL for the complete safety function is PLe.
Functional Safety Data Required for Determining the Performance Level of Electromechanical Devices
Because these contactors are electromechanical devices, the safety contactor data includes the following:
• Mean Time to Failure, dangerous (MTTFd)
• Diagnostic Coverage (DCavg)
• Common Cause Failure (CCF)
The functional safety evaluations of the electromechanical devices include the following:
• How frequently they are operated
• Whether they are effectively monitored for faults
• Whether they are properly specified and installed
SISTEMA calculates the MTTFd by using B10d data that are provided for the contactors along with the estimated
frequency of use, entered during the creation of the SISTEMA project. The estimated frequency for this example was
once per hour, 24 hours per day, 365 days per year. The number of operations that are entered into the SISTEMA
example for the contactor subsystem was 8760 annually.
Door Locking and Monitoring with a 442G Access Box and an Integrated Safety Controller Safety Function
Rockwell Automation Publication SAFETY-AT129B-EN-P - November 2018 21