Safe torque off function 245
• The STO is a type A safety component as defined in IEC 61508-2.
• Relevant failure modes:
• The STO trips spuriously (safe failure)
• The STO does not activate when requested
A fault exclusion on the failure mode “short circuit on printed circuit board” has
been made (EN 13849-2, table D.5). The analysis is based on an assumption that
one failure occurs at one time. No accumulated failures have been analyzed.
• STO reaction time (shortest detectable break): 1 ms
• STO response time: 2 ms (typical), 5 ms (maximum)
• Fault detection time: Channels in different states for longer than 200 ms
• Fault reaction time: Fault detection time + 10 ms
• STO fault indication (parameter 31.22) delay: < 500 ms
• STO warning indication (parameter 31.22) delay: < 1000 ms
• Maximum cable length 300 m (984 ft) between activation switch (K) and drive
control board.
• The voltage at the INx terminals of each drive must be at least 13 V DC to be
interpreted as “1”. Pulse tolerance of input channels is 1 ms.
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