FCU 500, FCU 505 · Edition 02.17
24
Temperature monitoring
4 .1 High temperature operation with safety
temperature monitor function (STM function)
As soon as the temperature in the furnace chamber
is above the spontaneous ignition temperature of the
gas/air mixture (> 750°C), the FCU signals to the down-
stream burner control units via the fail-safe HT output
that the furnace system is in High temperature mode
(HT). When the HT input is activated, the burner control
units switch to High temperature mode. They operate
without evaluating the flame signal and their internal
flame control is non-functional.
If the furnace temperature falls below the spontaneous
ignition temperature (< 750°C), the FCU disconnects
the HT output from the electrical power supply. As soon
as the signal to the HT inputs of the burner control
units is no longer present, the flame signals are once
again monitored by a UV sensor or flame rod.
In the event of a fault in a temperature monitoring com-
ponent (e.g. sensor discontinuity, sensor short-circuit)
or in the event of a mains failure, the flame control task
is transferred to the burner control units.
Either the temperature module integrated in the FCU..
H1 or an external safety temperature monitor (STM)
can be used for High temperature mode. Pre-purge
can be disabled for both versions in High temperature
mode, see page 86 (Pre-purge during high tempera-
ture operation).
4 .1 .1 With integrated STM
The integrated temperature module (STM) can be used
for high temperature operation. Pre-purge can be disa-
bled in High temperature mode, see page 86 (Pre-
purge during high temperature operation).
FCU 50x..H1
M
BCU 4xx..D
µC
9
BCU 4xx..D
µC
9
HT
18
6
6
HT
HT
5-8
STM