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item Controller BL 1-04 /C
― Product manual
to the safe state (STO) and for the tolerance time with regard to the OSSD signals (buffer time). These values depend on the
input voltage.
The time response is described in section 8.11.2 Time response on page 48.
4.5.4 Discrepancy time
The transition between the safe and unsafe state is initiated by level changes at the control inputs STOA and STOB of the ser
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vo drive. In accordance with the specification of the safety function, both levels must be identical. Otherwise, an error message
will be generated. The finite state machine in the servo drive monitors the driver supply voltage as a result of the actuation of
the control inputs. Usually, these level changes do not occur exactly at the same time, e.g. due to component tolerances or
bouncing outputs of safety control systems. The firmware tolerates this as long as the second input follows within a predefined
time, the so-called discrepancy time. If it is exceeded, the servo drive will generate an error message.
A discrepancy time of 100 ms is preset. Recommendation: Ensure to always switch STOA and STOB simultaneously.
In addition, to the integrated STO circuit, the finite state machine in the servo drive has its own status. Due to the evaluation
of the discrepancy time, this finite state machine may reach the "safe state" only with a considerable delay. Consequently, this
state can only be signalled via the digital outputs or a fieldbus with a considerable delay. The power output stage has already
been "switched off safely" when this happens. The status of the finite state machine is processed every 10 ms.
4.5.5 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 8.11.1
Electrical data of the STO function on page 47.
4.5.6 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.
4.5.7 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 detect
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ed, 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.
