Siemens SINAMICS G115D Operating Instructions Manual page 225

Function description
Discrepancy time for the simultaneity monitoring
The converter checks that the two input signals of the fail-safe digital input always have the
same signal state (high or low).
With electromechanical sensors (e.g. emergency stop buttons or door switches), the two
sensor contacts never switch at exactly the same time and are therefore temporarily
inconsistent (discrepancy). A permanent discrepancy signifies a fault in the fail-safe digital
input circuit, e.g. wire breakage.
When appropriately set, the converter tolerates brief discrepancies.
The discrepancy time does not extend the converter response time. The converter selects its
safety function as soon as one of the two F-DI signals changes its state from high to low.
Filter for suppressing short signals
In the following cases, an immediate converter response to signal changes of the fail-safe
digital inputs is not desirable:
• If a fail-safe digital input of the converter is interconnected with an electromechanical
sensor, signal changes can occur due to contact bounce.
• In order to identify faults due to short-circuit or cross faults, several control modules test
their fail-safe digital outputs with "bit pattern tests" (bright/dark test). If a fail-safe digital
input of the converter is interconnected with a fail-safe digital output of an open-loop
control module, then the converter responds with a bit pattern test.
The typical duration of the signal change within a bit pattern test:
– On test: 1 ms
– Off test: 4 ms
If the fail-safe digital input responds to many signal changes within a certain time, then the
converter responds with a fault.
SINAMICS G115D distributed drive
Operating Instructions, 12/2020, FW V4.7 SP13, A5E48681219B-002
Advanced commissioning
6.14 Safe Torque Off (STO) safety function
223