9
T-Product · BCU 465 · 2006 April
BCU 4xx..D
STW
L1
DI
µ
C
BCU 4xx..D
DI
µ
C
>750
°
C
6
9
6
9
Caution:
In “high temperature
mode” (HT mode) the digital input
has been energized, the BCU oper-
ates without supervising the flame
signal. The safety function of the
flame control is deactivated.
This is only allowed if the furnace tem-
perature is high enough (>1400 °F),
to combust the gas reliably .
A suitable “FM” approved low limit
controller must be used to supply
the digital input “D1”. Consult lo-
cal regulatory agencies and your
insurance underwriter for additional
safety requirements and approved
controllers.
A safety temperature monitor with a
double thermocouple shall be used
to measure the temperature. A sen-
sor break or short-circuit, the failure
of a component or a supply failure
must result in the system being set
to a safe condition.
Only when the temperature in the
working chamber and/or the wall
temperature exceeds 1400 °F, volt-
age (115 Vac) may the digital input
be activated (see Terminal wiring).
If the system has been switched to
high temperature mode, the burner
control unit opens the gas valves re-
gardless of a flame signal. If the tem-
perature in the furnace chamber falls
below the ignition temperature, the
digital input must be de-energized
and the furnace must be operated
with flame control.
System Design Information
Operation of firing systems at temperatures above 1400 °F (760 °C)
