Siemens SINAMICS G120 Operating Instructions Manual page 234

Functions
8.10 Fail-safe function Safe Torque Off (STO)
Bit pattern test of fail-safe outputs and contact bounces of sensors
The inverter normally responds immediately to signal changes at its fail-safe input. This is
not required in the following cases:
1. When you interconnect the fail-safe input of the inverter with an electromechanical
2. Several control modules test their fail-safe outputs using bit pattern tests (on/off tests), in
If the signal to control STO is not "stable", then the inverter responds with a fault.
(Definition of a stable signal: Following a change to the F-DI input signals, the inverter
triggers an internal monitoring time. Up until the end of the time interval 5 x p9650, both input
signals must have a constant signal level. A constant signal level is a high or a low state, for
a period of at least p9650).
232
sensor, contact bounce may result in signal changes occurring, to which the inverter
responds.
order to identify faults due to either short or cross circuiting. When you interconnect the
fail-safe input of the inverter with a fail-safe output of a control module, the inverter
responds to these test signals.
A signal change during a bit pattern test usually lasts 1 ms.
Figure 8-27 Inverter response to a bit pattern test
Operating Instructions, 01/2011, FW 4.4, A5E02999804A AB
SINAMICS G120C Inverter