8 STO (safe torque off)
8.5.5 Test pulses
Temporary test pulses from safety control systems are tolerated, i.e. they do not trigger
any STO function request.
The tolerance with regard to test pulses from sensors with OSSD signals is rated for the
operating range as per section 12.11.1 Electrical data of the STO function on page 230.
8.5.6 Auxiliary supply [X3]
The servo drive with an integrated STO function provides a switchable 24 V output
DOUT0 at [X3]. It can be used for the supply of external active sensors.
8.5.7 Additional diagnostics functions
The following functions integrated in the servo drive are not certified in accordance with
the Machinery Directive 2006/42/EC. They are functional extensions and offer additional
diagnostics options.
Error messages that are generated by the integrated STO circuit, e.g. when the
discrepancy time is exceeded, are registered and evaluated by the non-safety-relevant
finite state machine of the servo drive. If the conditions for an error state are detected, an
error message will be generated. In this case, it cannot be absolutely guaranteed that the
power output stage has been switched off safely.
The integrated STO function does not have any inherent error assessment mechanisms
and it cannot indicate any errors.
Acknowledgement of error messages
When error messages are acknowledged, all of the acknowledgeable errors concerning
the functional safety technology will also be acknowledged at the same time. See
section 8.11 Diagnostics and fault clearance on page 207.
The servo drive monitors the status of the control inputs STOA and STOB.
This enables the firmware of the servo drive to detect the request of the STO safety
function ("Safe Torque Off") and various non-safety-oriented functions will be performed:
l Detection of the disconnection of the driver supply for the power semiconductors
by the integrated STO circuit
l Deactivation of the drive control and also of the actuation of the power
semiconductors (PWM)
l Deactivation of the holding brake actuation (if configured)
l Finite status machine of the servo drive including an assessment of the actuation
(discrepancy time monitoring)
l Detection of application-related error states
l Hardware diagnosis
l Status and error indication via displays, digital outputs, fieldbuses, etc.
Product manual BL 4000-C Page 199 of 298
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