Pilz PSS SB FT, Basic license - Manual (Page 131)

Modular Block System: Burner Management 6-87
Programming guidelines
• ENBL
The negative edge of the enable ENBL from SB158 must set a flag to “0”
for the duration of one PSS-cycle. This pulse flag must be supplied to the
AND-operation before the global input
ERR or to the AND-operation
before the global input CHAI from 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 occurs a controlled shutdown is carried out, when
AuSt = 1 with re-start
CHAI: If an error occurs a safety shutdown is carried out.
A programming example can be found in Chapter 8 under “Managing
enables”.
• Resetting the sequence
To ensure the valve seal when a shutdown occurs, the operand used for
the
ENBL from SB152 must be assigned to the input parameter SyOK
from SB158.
If the
ENBL from SB152 changes from 0 to 1, SyOK of SB158 is also set.
The SB149 “sequence control” detects the positive edge and resets the
whole sequence as well as
NEXT from SB158.
• Driving the safety valve VAV1
The situation could arise where the safety valve VAV1 is driven
simultaneously by SB156 “Tightness Control” and SB158 “Ignition”.
Solution: Assign different flags to the output parameter VAV1 from
SB156 for VAV1 and the output parameter VAV1 from SB158 for VAV1.
After calling up the SB, perform an OR-operation on both flags and drive
the corresponding peripheral output with the result of this logic operation.