67
Safety Manual
00809-0200-5100, Rev GA
Parameters Related to the Safety Function
February 2017
Parameters Related to the Safety Function
A.4 Assumptions
Failure rates are constant, wear out mechanisms are not included
Propagation of failures is not relevant
The device is installed per manufacturer’s instructions
Failures during parameterization are not considered
Sufficient tests are performed prior to shipment to verify the absence of vendor and/or
manufacturing defects that prevent proper operation of specified functionality to
product specification or cause operation different from the design analyzed
Materials are compatible with process conditions
External power supply failure rates are not included
The mean time to restoration (MTTR) after a safe failure is 24 hours
The worst-case internal fault detection time is 90 minutes
Only the digital output is used for safety applications
The digital output signal is fed to a SIL 2 / SIL 3 compliant binary input board of a safety
PLC
Because the display is not part of the safety function, the failure rate of the display is not
considered in the calculation
All components that are not part of the safety function and cannot influence the safety
function (feedback immune) are excluded
For redundant parts the worst-case common cause factor of 5% for logic subsystems is
considered
A useful lifetime, based on experience, is approximately 15 years
The demand response time is 20 seconds. This is a worst-case delay between a change
in the measured process and the indication of the change at the safety digital output
To Next Page
Loading...
