APPENDIX C
pg. 255
Return to TOC Curtis AC F2-A, F4-A, F6-A Motor Controllers – FOS 4.5 – April 2022
potentially hazardous operation. Two safety functions are dened for Curtis Enhanced AC Motor
Controllers: Uncommanded Powered Motion and Motor Braking Torque.
e Travel Control (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 start-up. e Braking Torque safety function provides
detection and safe shutdown in the event of the loss of braking torque, position/hill hold, or
emergency reverse.
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 F-Series controller are summarized as follows:
AC F2-A
Safety Function Category DC
avg
MTTF
d
PL CCF
Travel Control 2 94.2 % >293 yrs. D Pass
Prevent of Travel
(Interlock Braking)
2 91.5 % >163 yrs. D Pass
Emergency Reverse 2 91.6 % > 168 yrs D Pass
Speed Reduction (Limitation) 2 90.5 % > 185 yrs D Pass
Load Handling Control 2 94.8 % > 301 yrs D Pass
AC F4-A
Safety Function Category DC
avg
MTTF
d
PL CCF
Travel Control 2 74.4 % >366 yrs. D Pass
Prevent of Travel
(Interlock Braking)
2 66.6 % >215 yrs. D Pass
Emergency Reverse 2 69.8 % > 185 yrs D Pass
Speed Reduction (Limitation) 2 69.9 % > 186 yrs D Pass
Load Handling Control 2 66.3 % > 227 yrs D Pass
AC F6-A
Safety Function Category DC
avg
MTTF
d
PL CCF
Travel Control 2 84.3 % >453 yrs. D Pass
Prevent of Travel
(Interlock Braking)
2 77.0 % >287 yrs. D Pass
Emergency Reverse 2 79.0 % > 254 yrs D Pass
Speed Reduction (Limitation) 2 79.0 % > 254 yrs D Pass
Load Handling Control 2 77.4 % > 313 yrs D Pass
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