F_Quites; Maintenance Override Switch (Mos) - Siemens SIMATIC PCS 7 Operating Manual

7.10.2

F_QUITES

Using the "F_QUITES" F block, the OS can generate fail-safe pulses in the F program of the
automation system. You can find an application example for F_QUITES in "Implementing F
user acknowledgment in the OS", in Section Programming reintegration following module
errors or channel errors requiring acknowledgment (Page 110).
7.10.3

Maintenance Override Switch (MOS)

Maintenance Override gives you the option to set bypasses in the safety program from the
OS as well as the safety-oriented changing of F-parameters in the safety program of an F-
CPU from an OS.
A special safety protocol is used to make changes to F-parameters in safety mode. This
meets Safety Integrity Level requirements up to SIL3 in accordance with IEC 61508.
S7 F-systems offers the following for MOS:
● Four F-blocks, which you integrate into the CFC charts in your safety program:
– F_SWC_P: Central control of operation via the OS
– F_SWC_BO: Processing of an F_BOOL data type parameter for operation via the OS
– F_SWC_R: Processing of an F_REAL data type parameter for operation via the OS
– SWC_MOS: Interface for the display of the MOS function on the OS.
● A template for the temporal limitation of the change (SWC_TR)
● Associated faceplates, which you integrate into your OS.
Transaction for MOS
You can use MOS to modify an F-parameter in the safety program of an F-CPU if you
perform a specific sequence of operations on the OS within a specified period of time. The
entire change operation is known as a "transaction".
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
129