Connecting Sensors -- Actuators Using The 3--Terminal Concept - Siemens Sinumerik 840D sl Function Manual

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S a "2--terminal concept for sensors without test signals", if the two--channel
net (useful) signal to be tested automatically changes its level dynamically
as a result of the process. For example, for the input signals of a protective
door,
S a "2--terminal concept for sensors without test signals", if the sensor is a
safety--related component, e.g. light curtains,
S a "2--terminal concept for actuators without test signals", if the actuator is a
safety--related component, e.g. safety valves,
S a "2--terminal concept for actuators without test signals" if the feedback
signal can be checked using other useful signals. For example, for a valve
that indirectly switches a BERO via the process and this is available for
evaluation,
S a "2--terminal concept for actuators without test signals" if the function of the
mechanical system can be checked using other useful signals. For example,
for a brake that is checked using a separate brake test.
2. The signals "external STOPs" are processed internally in a special way:
S In order to increase the level of security that a requested "external STOP"
actually takes effect, the STOPs are internally exchanged between the two
channels. Failure of the stop control function in one channel does not
cause an error for these signals (in contrast to the mode changeover
signals, e.g. "SG/SBH active") in the crosswise data comparison.
While other signals can be subject to a forced checking procedure in parallel
and in both channels (and should be -- in order to avoid errors being trigge-
red by the crosswise data comparison), the "external STOPs" must be sub-
ject to a forced checking procedure one after the other in both channels.
7.1.3 Connecting sensors - - actuators using the 3- - terminal concept
Basic principle for safety- -related signal processing
With the 3--terminal concept, three terminals (signals) are required to connect a
sensor or actuator. Faults/errors in the sensors and actuators can be detected in
conjunction with the SPL--CDC and forced checking procedure or the forced
checking as a result of the process itself. The connecting cables are generally
monitored autonomously by the fail--safe I/O.
The following applies to the safety--related sensor connection:
The following applies to the safety--related actuator connection:
© Siemens AG 2015 All Rights Reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) - - 10.2015 Edition
2 safety--related inputs + 1 standard test output.
2 safety--related outputs + 1 standard test input.
Connecting Sensors/Actuators
7.1 Safety- -relevant input/output signals
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