FCU 500, FCU 505 · Edition 02.17
81
Parameters
12 .2 .4 Low air pressure protection
Parameter 15
Equipment fitted with forced or induced draught
burner(s) shall be fitted with devices for proving ad-
equate air flow during pre-purge, ignition and operation
of the burner. Any failure of the air flow must trigger a
safety shut-down or fault lock-out at any time during
pre-purge, ignition or operation of the burners, depend-
ing on the requirement of the standard.
The air monitor must be checked when there is no flow
before start-up, for example by stopping the combus-
tion air supply or by interrupting the air signal air
min.
to
terminal 47 of the FCU (using a 2/3-way valve). As soon
as the combustion air supply is stopped or the signal is
interrupted, the fan will start. To start pre-purge, the air
monitor must indicate adequate flow for purging. The
flow must be detected within a timeout (250 s). After
the elapse of this timeout, the FCU will perform a shut-
down, depending on the function selected in param-
eter 15.
Parameter 15 = 0: OFF; the function is not required
Parameter 15 = 1: with safety shut-down
A safety shut-down will be performed if there is no input
signal.
Parameter 15 = 2: with fault lock-out
A fault lock-out will be performed if there is no input
signal.
Air flow monitoring during the post-purge time can only
be selected if it has also been activated for pre-purge.
For further information on the function of the signal
inputs to monitor the minimum air pressure (air
min.
, ter-
minal 47) and air flow (terminal 48) during pre-purge,
see page 89 (Air flow monitoring during pre-purge).
12 .2 .5 Safety time during operation t
SB
Parameter 19
This parameter can be used to adjust the reaction time
of the FCU to the failure of the flow detectors for air and
gas to the requirements of the system.
When selecting the reaction, compliance with the re-
quirements of the relevant system standard must be
ensured.
