Pilz PSS SB FT, Basic license - Manual (Page 24)

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Safety
Modular Block System: Burner Management
Fault detection
The detection of errors and defects is an important function of the PSS, in
addition to pure control tasks.
Further information on the fault detection concept can be found in the PSS
“System Description”.
WARNING!
It is particularly important to detect open circuits and shorts within the
safety circuits (e.g. two-hand control devices, E-STOP etc.).
It is the responsibility of the user to select and apply an appropriate fault
detection system.
Feasibility test
Redundant input devices for safety functions must undergo a feasibility test
within the user program.
The plant must be stopped immediately if a feasibility error occurs. Similar
tests will also be required for other input devices.
If safety valves have feedback contacts, these must be evaluated
accordingly.
Fault prevention
Not all potential faults can be detected and managed. Such faults must be
excluded by suitable wiring methods.
Additional information on how to exclude potential errors can be found in
the BIA Handbook (BG Institute for Occupational Safety, St Augustin) or in
the directive VDI 2854:1991-06 (safety requirements on automated
manufacturing systems).