162 Rockwell Automation Publication 2097-UM001D-EN-P - November 2012
Chapter 8 Kinetix 300 Drive Safe Torque-off Feature
Troubleshooting the Safe Torque-off Function
PFD and PFH Definitions
Safety-related systems can be classified as operating in either a Low Demand
mode, or in a High Demand/Continuous mode:
• Low Demand mode: where the frequency of demands for operation made
on a safety-related system is no greater than one per year or no greater than
twice the proof-test frequency.
• High Demand/Continuous mode: where the frequency of demands for
operation made on a safety-related system is greater than once per year or
greater than twice the proof test interval.
The SIL value for a low demand safety-related system is directly related to order-
of-magnitude ranges of its average probability of failure to satisfactorily perform
its safety function on demand or, simply, average probability of failure on demand
(PFD). The SIL value for a High Demand/Continuous mode safety-related
system is directly related to the probability of a dangerous failure occurring per
hour (PFH).
PFD and PFH Data
These PFD and PFH calculations are based on the equations from EN 61508
and show worst-case values.
This table provides data for a 20-year proof test interval and demonstrates the
worst-case effect of various configuration changes on the data.
PFD and PFH for 20-year Proof Test Interval
Error
Code
Fault Message
RSLogix (HIM)
Anomaly Potential Cause Possible Resolution
E39 DriveHardFault
(safe torque-off
HW Flt)
Safe torque-off function
mismatch. Drive will not
allow motion.
• Loose wiring at safe torque-off (STO)
connector.
• Cable/header not seated properly in
safe torque-off (STO) connector.
• Safe torque-off circuit missing +24V
DC.
• Verify wire terminations, cable/header
connections, and +24V.
• Reset error and run proof test.
• If error persists, return the drive to Rockwell
Automation.
ATTENTION: The safe torque-off fault (E39) is detected upon demand of the
safe torque-off function. After troubleshooting, a proof test must be performed
to verify correct operation.
Attribute Value
PFH [1e-9] 5.9
PFD [1e-3] 1.0
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