Siemens SINUMERIK 840D sl Function Manual page 167

The specified machine data follow the generally valid rules when assigning the safety-related
inputs/outputs.
Cam range as supplementary information for the cam track
In the case of a fault, SGAs can assume a value of "0" (e.g. as a result of the cam
synchronization between monitoring channels, loss of the safety-related referencing etc.).
The user must take this into account so that when the SGAs are processed further, in a fault
condition, no unsafe (hazardous) machine states can occur (that means, for example, a
protective door is only enabled for a value of "1").
Further, the SGAs "cam range" may only be evaluated as supplementary information to SGA
"cam track". It is not permissible to evaluate the SGA "cam range" alone without evaluating
the SGA "cam track".
Hysteresis of cam SGAs
The hysteresis is applied both to the SGA "cam track" as well as to SGA "cam range" to prevent
signal flutter. This means the SGAs are therefore generated as follows in the two monitoring
channels, NCK and drive:
Figure 7-21
SN+TOL
As a result of the cam hysteresis, for increasing actual values, the cam SGAs do not switch
at the configured cam position (SN) but at the position increased by the cam tolerance
(hysteresis) (SN+TOL).
Users must carefully take this into consideration when configuring the cam positions and cam
tolerance.
Safety Integrated
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
WARNING
SGA "cam track" and "cam range" with hysteresis
WARNING
Safety functions integrated in the system/drive
7.8 Safety software cams and safety cam track (SN)
167