Pilz PSS SB FT, Basic license - Manual (Page 102)

6-58 Modular Block System: Burner Management
Standard Function Blocks
Programming guidelines
ENBL
The negative edge of the enable ENBL of SB155 must set a flag at “0” for
one PSS cycle. The pulse flag must be supplied to the AND-operation
before the global input
ERR or to the AND-operation before the global
input CHAI of SB152 “Burner: Start and operator elements”. The decision
to use ERR or CHAI depends on the user and the respective standards
regarding error reaction.
ERR: If an error is present a controlled shutdown occurs, if
AuSt = 1 with restart
CHAI: If an error occurs a safety shutdown is carried out.
A programming example can be found in Chapter 8 under “Managing
enables”.
Timing diagrams
Signal cycle with interrupted and uninterrupted pre-purge process
Polling the air pressure or the open posiiton of the air damper ( COND = 1)
during the pre-purge time ensures that over the total pre-purge a sufficient
quantity of air flows through the burner chamber.
If the air damper position is polled, the ventilator must be polled too. this
can take place in another program section.
SB155
If the input at COND input is missing while
the NEXT input is set, the ENBL and RDY
outputs are reset.
A recurring signal will not be accepted.
The NEXT input must be set once again. With the RDY output “Pre-purge criteria
fulfilled” is signalled.
This RDY-Signal is reset via the 1-0 edge
at the NEXT input after the pre-purge
time has elapsed. The COND signal is
then no longer necessary. The ENBL
signal remains at a constant “1” if no
interference occurs.