ABB ACS880-M04, Hardware Manual

Page: 152 / 195

152 The Safe torque off function
STO fault tracing
The indications given during the normal operation of the Safe torque off function are
selected by drive parameter
31.22 STO indication run/stop .
The diagnostics of the Safe torque off function cross-compare the status of the two
STO channels. In case the channels are not in the same state, a fault reaction
function is performed and the drive trips on an “STO hardware failure” fault. An
attempt to use the STO in a non-redundant manner, for example activating only one
channel, triggers the same reaction.
See the drive firmware manual for the indications generated by the drive, and for
details on directing fault and warning indications to an output on the control unit for
external diagnostics.
Any failures of the Safe torque off function must be reported to ABB.

Relevant failure modes
The STO trips spuriously (safe failure) and does not activate when requested.
A fault exclusion on the failure mode “short circuit on printed circuit board” is made
(EN 13849-2, table D.5). The analysis is based on an assumption that one failure
occurs at one time. No accumulated failures were analyzed.