Curtis 1212S Manual,
Rev. B
39
APPENDIX B: EN 13849 COMPLIANCE
Curtis has analyzed each safety function and calculated its Mean Time
To Dangerous Failure (MTTFd) and Diagnostic Coverage (DC), and designed
them against Common Cause Faults (CCF). The safety-related performance of
the Curtis 1212S is summarized as follows:
Safety Function
Designated MTTFd
DC
CCF PL
Architecture
Score
Crushing
*
2
≥
22 yrs
≥
60% 70 b
Crushing
**
2
≥
22 yrs
≥
60% 70 b
Loss of stablility
***
2
≥
22 yrs
≥
60% 70 b
*
due to unintended or uncontrolled movement
**
through loss of STO/braking
***
from excessive speeds, as specified by vehicle limits
EN1175 specifies that traction and hydraulic electronic control systems
must use Designated Architecture 2 or greater. This design employs input, logic,
and output circuits that are monitored and tested by independent circuits and
software to ensure a high level of safety performance (up to PL=d).
Mean Time To Dangerous Failure (MTTFd) is related to the expected
reliability of the safety related parts used in the controller. Only failures that
can result in a dangerous situation are included in the calculation.
Diagnostic Coverage (DC) is a measure of the effectiveness of the control
system’s self-test and monitoring measures to detect failures and provide a safe
shutdown.
Common Cause Faults (CCF) are so named because some faults within
a controller can affect several systems. EN13849 provides a checklist of design
techniques that should be followed to achieve sufficient mitigation of CCFs.
All circuits used by a safety function must be designed in such a way as to
score 65 or better on the CCF score sheet as provided by EN13849 table F.1.
Performance Level (PL) categorizes the quality or effectiveness of a safety
channel to reduce the potential risk caused by dangerous faults within the system
with “a” being the lowest and “e” being the highest achievable performance.
Contact Curtis technical support for more details.
