Sensor Connection Using The 4-Terminal Concept - Siemens SINUMERIK 840D sl Function Manual

Example of connecting a sensor
2 safety-related inputs (to read-in through 2 channels via SGE) and 1 standard test output (for
the forced checking procedure) are required to connect a sensor in a failsafe fashion. The test
output is fed from the power supply voltage of the safety input module. For sensors with a self-
test routine, the test output on the input module is not required. For the 3-terminal connection
concept we recommend that sensors with non-equivalence contacts are used (NC contact/NO
contact). If both signal cables have a P or M short-circuit - or are both interrupted - then a signal
state is obtained that is not logically permissible. This means, that a cross-circuit fault can be
detected by the non-equivalence concept without having to carry out any test.
Note
Cross-circuit fault detection in the input module is not required.
Figure 8-5
8.1.4

Sensor connection using the 4-terminal concept

With the 4-terminal concept, four terminals are required at the failsafe input module to connect
a sensor that utilizes a contact (e.g. Emergency Stop pushbutton). 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 failsafe input module.
The following applies to the safety-related sensor connection
2 safety-related inputs + 2 standard test outputs.
Safety Integrated
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
Sensor connection using failsafe inputs according to the 3-terminal concept
Connecting sensors and actuators
8.1 Safety-related input/output signals
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