7.9 Safety function STO
A frequently required application task is the safe torque off and the protection of personnel
against unintentioned restarting of drives. The S700 servo amplifier offers, even in the basic
version, a two channel STO function (Safe Torque Off). The function blocks the trigger
pulses of the power transistors (pulse inhibitor).
Advantages of the safety function STO:
the DC bus link remains charged up, since the mains supply line remains active
only low voltages are switched, so there is no contact wear
very little wiring is required
single or dual channel control possible
SIL2 or SIL3 solutions possible
The STO safety function corresponds to stop category 0 (uncontrolled stopping) acc. to EN
60204-1. The safety function STO can be operated from external safety switch gears
(relays), from a safe external control (semiconductor output or driven contact) or from the
built-in safety card S1-2 (➜ # 155) or S2-2 (➜ # 153).
SIL2 / PLd solutions can be implemented with single-channel or dual-channel control with
simple safety switching devices.
A SIL3 / PLe solution requires a safety control that periodically tests the safe switching of
the pulse inhibitor by analyzing the feedback (status) signal.
7.9.1 Safety characteristic data
The subsystems (servo amplifiers) are totally described for safety technics with the char-
acteristic data SIL CL, PFHD and TM..
Unit Operation
Mode
EN 13849-1 EN 62061 PFHD [1/h] TM [Years]
STO1/2 Enable single channel PLd, Cat.3 SIL CL 2 7.05E-08 20
STO1-Enable+
STO2-Enable
dual channel PLd, Cat.3 SIL CL 2 7.05E-08 20
STO1-Enable+
STO2-Enable+
STO-Status
dual channel +
periodical
testing
PLe, Cat.4 SIL CL 3 1.38E-09 20
S748-772 Instructions Manual | 7 Technical description
Kollmorgen | kdn.kollmorgen.com | July 2019 41
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