FCU 500, FCU 505 · Edition 02.17
86
Parameters
12 .3 .7 Pre-purge during high temperature operation
Parameter 27
Parameter 27 can be used to define whether the fur-
nace start is performed with or without pre-purge in
High temperature mode. The internal or an external
STM can be used to detect the high temperature.
With the internal STM (FCU..H1), the FCU detects high
temperature operation using the limit value defined in
parameter 24.
With the external STM, the FCU detects high tempera-
ture operation by means of a high signal at terminal 66.
On FCUs with capacity control (FCU..F1, FCU..F2), the
actuator must be moved to ignition position or, if a fre-
quency converter is used, the fan must be accelerated
to ignition speed to start the burner. If the FCU..F1 is
used in conjunction with actuator IC 20, the ignition
position is approached via the purge position.
Parameter 27 = 0: OFF; no pre-purge is performed upon
furnace start-up
Parameter 27 = 1: ON; a pre-purge is performed at every
start regardless of the furnace temperature
