Pilz PSS SB FT, Basic license - Manual (Page 28)

4-4
Intended Use
Modular Block System: Burner Management
SB154: Control and position monitoring of valves
SB154 monitors the status of a valve. It changes the valves' position after
the corresponding input prompt, monitors the direction of a positional
change and checks the reaction time.
The contact bounce time lasts for one cycle, if a change in position occurs.
SB155: Pre-purge
SB155 monitors the limit switch for the maximum position of the air
damper or the maximum air flow during the pre-purge time.
If the limit switch isn’t activated by the air damper during the pre-purge
time, or if the maximum air flow for pre-purge is not achieved, SB155
resets its enable.
SB156: Tightness control
SB156 checks the tightness (seal) of the safety valves, the main valves
and, if present, the exhaust valves.
Tightness monitoring must be called up separately. If an error occurs, the
enable is reset and a shutdown occurs.
SB157: Several ignition attempts
SB157 counts the number of ignition attempts. After a failed ignition, a
signal is issued for another attempt, after which the step sequence can
immediately start the initial ignition step.
SB157 also monitors the time between the ignition attempts and the
establishment of a flame.