Curtis 1239E - Page 157

Return to TOC Curtis 1239E-1269E Manual, os 37.0 RevA – May 2021
APPENDIX B
pg. 153
To mitigate the hazards typically found in machine operations, EN13849 requires that safety functions
be dened; these must include all the input, logic, outputs, and power circuits that are involved in any
potentially hazardous operation. Two safety functions are dened for Curtis Enhanced AC Motor
Controllers: Uncommanded Powered Motion and Motor Braking Torque.
e Uncommanded Powered Motion safety function provides detection and safe shutdown in the
following circumstances: faulted throttle; improper sequence of forward/reverse switches, throttle,
and interlock; incorrect direction of travel; loss of speed control or limiting; uncommanded
movement; or movement at startup. e Braking Torque safety function provides detection and safe
shutdown in the event of the loss of braking torque or position/hill hold.
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).
e safety-related performance of the Curtis 1239E/1269E is summarized as follows:
Safety Function Designated Architure MTTFd DC CCF PL
Uncommanded
Powered Motion
2 >40 yrs >90% Pass d
Motor Braking Torque 2 >16 yrs >90% Pass c
EN1175 specifies that traction and hydraulic electronic control systems must use Designated
Architecture 2 or greater. is design employs input, logic, and output circuits that are monitored
and tested by independent circuits and soware 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 eectiveness 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 aect
several systems. EN13849 provides a checklist of design techniques that should be followed to achieve
sucient mitigation of CCFs. e CCF value is a pass/fail criterion.
Performance Level (PL) categorizes the quality or eectiveness 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.