204 Appendix: Safe Torque Off (STO)
Technical data
STO safety relay type
General requirements EN 61508 and/or EN 61511 and/or
EN ISO 13849-1
Output requirements
No. of current paths 2 independent paths (one for each STO path)
Switching voltage capability 30 V DC per contact
Switching current capability 10 mA per contact per drive
Maximum switching delay
be
tween contacts
<200 ms
Internal supply/multiple
un
its
Maximum length of safety
circui
t from operating contact
to most distant drive
30 m (98.4 ft)
Maximum number of drives in
circuit
16
External supply/multiple
units
External power supply 24 V DC
+10% SELV
Current requirement 20 mA per connected drive
Example 1 Simple SIL3 approved safety relay
Type and manufacturer PSR-SCP- 24UC/ESP4/2X1/1X2 by Phoenix
Co
ntacts
Approvals EN 954-1, cat 4; EN 61508, SIL3
Example 2 Programmable safety logic
Type and manufacturer PNOZ Multi M1p by Pilz
Approvals EN 954-1, cat 4; EN 61508, SIL3; and
EN ISO 13849-1, PL e
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