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

Connecting Sensors/Actuators
7.1 Safety-relevant input/output signals
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-crosswise data comparison and forced checking proce-
dure 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-relevant sensor connection:
The following applies to the safety-relevant actuator connection:
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-relevant
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.
7-170
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 03.2006 Edition
2 safety-relevant inputs + 1 standard test output.
2 safety-relevant outputs + 1 standard test input.
© Siemens AG, 2006. All rights reserved
03.06