Appendix: Safe torque off (STO) 403
24 V auxiliary voltage load (I/O, panel load, used fieldbus or STO circuits; max.
200 mA) of the drive supplying the STO circuit (see section Control connection data
on page 369). When using external supply, all analog grounds (AGND) of the drives
must be chained together.
Note: Daisy chaining lowers the total system safety integrity level, which needs to be
calculated case by case for each system.
Start-up and commissioning
Always test the operation and reaction of the STO function before commissioning.
Technical data
STO components
STO safety relay type
STO connection
STO cable
General requirements IEC 61508 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 100 mA per contact
Maximum switching delay
between contacts
200 ms
Example 1 Simple SIL3 approved safety relay
Type and manufacturer PSR-SCP- 24UC/ESP4/2X1/1X2 by Phoenix Contacts
Approvals EN 954-1, cat 4; IEC 61508, SIL3
Example 2 Programmable safety logic
Type and manufacturer PNOZ Multi M1p by Pilz
Approvals EN 954-1, cat 4; IEC 61508, SIL3; and ISO 13849-1, PL e
Input for external STO
supply
24 V DC ± 10%, load 25 mA
Input impedance R
in
= 2 kohm
Load 12 mA / channel
Output Maximum load 200 mA depending on I/O load
Type 2×2 cables, low voltage, single shielded, twisted pair cable
Conductor size 1.5…0.25 mm
2
(16…24 AWG)
Maximum length Max. 25 m between STO inputs and the operating contact
Tightening torque 0.5 N·m (4.4 lbf·in)
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