Siemens SINAMICS G120 CU240B-2 Operating Instructions Manual page 218

Functions
7.10 Safe Torque Off (STO) safety function
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).
An adjustable signal filter in the inverter suppresses temporary signal changes using bit
pattern test or contact bounce.
Figure 7-26
Note
The filter increases the inverter response time. The inverter only activates its safety function
after the debounce time has elapsed (parameters p9651 and p9851).
Note
Debounce times for standard and safety functions
The debounce time p0724 for "standard" digital inputs has no influence over the fail-safe
input signals. Conversely, the same applies: The F-DI debounce time does not influence the
signals of the "standard" inputs.
If you use an input as a standard input, set the debounce time at p0724.
If you use an input as fail-safe input, set the debounce time as described above.
218
Filter for suppressing temporary signal changes
Inverter with CU240B-2 and CU240E-2 Control Units
Operating Instructions, 07/2010, FW 4.3.2, A5E02299792B AA