ABB MicroFlex e190, User Manual, Page: 191 / 210

Appendix: Safe Torque Off (STO) 191
Wiring principles
The Safe Torque Off connector is X4 on MicroFlex e190 drives.
Wiring principles are shown in the diagrams below. See chapter Technical data for
the cable specification and possible safety relay types.
• The wiring to each STO input must be routed separately.
• Wiring the STO inputs in accordance with the following diagrams provides Safety
Integrity Level 3 (SIL3). It is not permissible to control both STO inputs from one
safety circuit, as this does not provide SIL3 protection.
• The Safe Torque Off (STO) function provides a stop function equivalent to
‘stop category 0’ according to EN 60204-1.
• The STO element is classified as type A, according to EN 61508-2.
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Connected components
Ensure that all components controlling the STO inputs, including cabling, do not
cause the STO inputs to become constantly powered (a ‘dangerous failure’) or
constantly unpowered (a ‘safe failure’).
Diagnostic pulses produced by Safe Digital Output devices are not recognized by the
MicroFlex e190, and will not activate the STO function provided they have a period of
less than 1 ms.

Short circuit testing
Short circuit conditions on the STO inputs must be tested within the proof test
interval.

Power supply
It is recommended to use the 24 V DC supply provided on pin 4 of connector X4. This
supply is derived from the bus voltage (if present) or from the optional 24 V logic
supply on connector X2 (if present).
If an external 24 V DC power supply is connected to X4 it must fulfill the following
criteria:
• It must be a Safety Extra Low Voltage (SELV) supply.
• It must be suitable for the desired safe application and safety integrity level.
• It must be protected against over voltages.
• It must limit the output voltage under all fault conditions <60V.
• It must be TüV certified to EN 60950.

Drive enable input
If an additional hardware ‘drive enable’ input is used to control the drive, it must not
be wired as part of the STO input circuit.