Siemens SIMATIC PCS 7 Operating Manual page 131

At the "MODE" input of the "SWC_MOS" block, it is determined whether all three BOOL
values can be activated at the same time ("Norestrictions"), or if just one
("MutualExclBypass") BOOL value can be activated in each case.
The maximum activation period for the three BOOL values can be limited by using the
"SWC_TR" template. After placing the template and connecting the "AKT_TR" output with
the "AKT_TR" input of the "SWC_MOS" block, the further connections are established
automatically during compilation. The time can be triggered again from the OS before it
expires. Through configuring the "T_WARN" input to the "SWC_MOS" block, an alarm is
generated prior to the maximum time elapsing.
An "F_SWC_P" block is necessary for each shutdown group. It implements a special safety
protocol and monitors the required operator sequence from the OS. With the block's
"EN_SWC" input, the operation of all MOS functions in a shutdown group can be enabled
("1") or blocked ("0"). When the operation is locked, all activated signals are reset. At the
"MAX_TIME" input, the maximum time for the sequence of operations is set on the OS. If a
plant designation was assigned in the properties of the CPU, the "IDENT" input does not
have to be configured.
Example
The figure below shows an example of a temporally restricted maintenance function that is,
for example, required for a cyclic proof test at a fail-safe analog input and an error
acknowledgment:
Note
The figure is available in its original size as appendix to the manual in the ZIP download of
the checklists.
Compendium Part B - Process Safety (V8.2)
Operating Manual, 07/2016, A5E35031794-AB
7.10 Operating and changing safety-related parameters on a PCS 7 OS
Configuring the safety program
131