Siemens SINUMERIK 840D sl Function Manual page 158

Safety functions integrated in the system/drive
7.8 Safety software cams and safety cam track (SN)
Tolerance for SN
Owing to variations in the clock cycle and signal run times (signal propagation times), the cam
signals of the two monitoring channels do not switch simultaneously and not precisely at the
same position. A tolerance bandwidth can therefore be specified for all cams using the following
machine data/parameters. Within this bandwidth, the signal states for the same cam may be
different in the two monitoring channels.
For 840D sl:
MD36940 $MA_SAFE_CAM_TOL
for SINAMICS S120:
p9540 SI Motion SCA (SN) tolerance (Control Unit)
Note
The lowest possible tolerance bandwidth (less than 5-10 mm) should be selected for the "safe
software cams" function. It makes sense to parameterize the cam tolerance greater than or
equal to the actual value tolerance.
Effect when SN responds
Safe referencing
When defining cam positions, please note that the function only monitors the actual position
thus making (predictive) sensing of cam signals impossible.
The cams are only considered as being safe if they were safely referenced. This is the reason
that the user must interlock this SGA in the SPL with the cam SGAs.
Response times
Response times without cam synchronization
typical 1 interpolation clock cycle + 1.5 monitoring clock cycles
maximum 1 position controller clock cycle + 4 monitoring clock cycles + 2 interpolation clock
cycles + 3 PLC cycles
Response times with cam synchronization
typical 1 interpolation clock cycle + 2.5 monitoring clock cycles
maximum 1 position controller clock cycle + 5 monitoring clock cycles + 2 interpolation clock
cycles + 3 PLC cycles
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WARNING
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
Safety Integrated