Pilz PSS SB FT, Basic license - Manual (Page 39)

5-9 Modular Block System: Burner Management
Fault diagnostics
Error types
On programmable safety systems from the PSS-range, a distinction is
made between two types of errors. On the one hand there are errors which
are detected and evaluated through the PSS operating system, and on the
other there are errors which are detected and evaluated through the user
program. The reaction to these two types of errors is different.
Where errors are detected through the operating system, the FS section of
the PSS will switch to a STOP condition and all outputs will be switched off
safely.
Where errors are detected through the user program, only the configured
error reaction will occur. Errors that are detected via an MBS standard
function block belong to this second type of error.