Siemens Sinumerik 840D sl Function Manual page 198

Connecting Sensors/Actuators
7.1 Safety- -relevant input/output signals
Example of an actuator connection
2 outputs (to control through 2 channels via SGA) and 1 standard test input (for the
forced checking procedure) are required to connect an actuator in a safety--related
fashion. The test input is the feedback signal from the load circuit and is fed from
the power supply voltage of a standard input module. The user should derive this
as directly as possible from the process quantity.
Actuator control P/M switching:
The actuator is directly controlled using a plus potential (P--switching) and minus
potential (M--switching). If the actuator is not a qualified component (safety compo-
nent or component with fault exclusion), then in the case that the actuator fails, the
user must apply additional cascaded measures in order to bring the process into a
safe condition.
Example:
The process quantity, e.g. hydraulic pressure, is switched using a standard valve
that is controlled in a safety--related fashion. A pressure sensor signals the status
of the process quantity. If the valve can no longer switch due to a fault condition,
then using a safely controlled standard contactor, the motor that is generating the
pressure, is shutdown. The advantage of this particular version is that components
can be used that are already available as standard. As to whether this solution can
be used, must be confirmed as a result of the risk assessment (see Fig. 7-3).
IM 151--1
F--DO
High Feature
PROFIBUS
with PROFIsafe
When OK, only the valve
is switched. The pump
remains powered--up.
In the case of a fault, the
feedback signal from the
pressure sensor is not
received, the pump motor is
additionally switched.
Figure 7-3 Cascaded shutdown using fail--safe outputs
In other cases a second actuator must be connected in series in the load circuit
(see Fig. 7-4).
7-198
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) - - 10.2015 Edition
DI
PM--E F
ET 200S PROFIsafe
Feedback signal
24 V load
Shutdown,
circuit,
channel 1
valve
Shutdown, 400 V load
channel 2 circuit, motor
Feedback signal
Pressure
sensor
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10/15