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9.4 Diagnostics
The STO safety function is monitored in the controller for
plausibility and operability.
9.4.1 STO status signal to control
Within the software, the status of the STO safety function
(1=OK, 0=STO triggered) is available at Input 15 on the I/O
level under device PM_DIDO.
If this status information is present in the application, this
must be assigned accordingly by the operator.
It is advisable to use the software input Emergency Stop.
Assignment is not necessary for safety reasons.
9.4.2 Fail-Safe state
If a fault in the safety technology is detected, e.g., if, for
example, control signals STO-A and STO-B have unequal
levels or there is a circuit defect, then a fault is triggered
internally. This fault can not be reset or can only be reset
by a restart, i.e., further start attempts no longer lead to the
turning on of the output drive.
It is assumed that there is an external fault and the
controller must be switched off. If the fault persists after
checking the external controller, then there is a defect in
the controller and it must therefore be replaced.
9.6.1 Passive circuit X41
Fig. 9-1:
The STO safety function can be requested by various devices. The switch S1 can be, for example, an Emergency Stop
switch, a safety door switch, a light curtain or a safety relay. The safety requirement is 2-channel via the switch S1and
leads to the 2-channel shutdown of the final stage - therefore, this structure is for Category 3. The auxiliary power supply
24 V for signal generation is provided on the interface.
9.6.2 Active circuit X41
Fig. 9-2:
Apex Tool Group
9.5 Time response
The control signals STO-A and STO-B are equivalent in
regards to their use, although the signals operate different
shutdown paths. They are described in terms of the time
response as a single, exchangeable STO signal.
The time from the shutdown of an STO signal to the activity
in the final stage of the controller is determined by the
external circuitry (see also9.3 Control signals STO-A and
STO-B, Page 18), including controllers connected in paral-
lel. The values given here refer to the Passive version (see
9.6.1 Passive circuit X41, Page 19) with a nutrunner con-
trol and the maximum cable length. The time response is
different for each layout and must be checked at startup to
see if it meets the minimum requirements.
9.6 Assembly and installation
When installing and wiring the signals, the requirements of
EN 60204-1 must be met. In this case, particular attention
must be paid to measures for short circuit fault exclusion.
For the STO cables 961924-xxx, the STO signals are indi-
vidually protected by a ground connection. The connection
to the first controller, and from controller to controller, must
not be longer than 60 m; in total in the system, a total
length of up to 1000 m is permitted for all of the STO con-
nections.
The following circuit examples show the intended wiring of
the STO interfaces. An analogous other use or connection
is not permitted.
P2552HW | 2021-04
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