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T-Product · BCU 465 · 2006 April
Operation
Normal Start-up Sequence
for BCU 465
Safety Interlocks
Once air and gas flow safety limits
are proven, terminal #5 on the BCU
should be energized.
Switch Power “On”
When line voltage is applied to BCU
unit terminal #1, the microproces-
sor checks for proper line voltage,
frequency, and faults in all internal
electronic components.
Self-Check Time
The Valve Proof of Closure Switch
OCS must signal that the safety gas
valve is closed (115 Vac on terminal
#21).
The BCU also checks for any ex-
traneous flame signals. If no flame
signal is detected, the BCU unit
continues the start-up sequence. If
a flame signal is detected during the
self-check period (t
W
), the BCU waits
up to 25 seconds for the flame signal
to fade. If the flame signal fades, the
startup sequence will continue. If the
flame signal remains, the BCU will go
to fault lockout.
Trial for Ignition / Safety Period
on start-up
Once the self-check is complete and
a start signal is present at terminal
#4, the BCU will begin the trial for
ignition sequence. The gas valve
output terminal #12 (and terminal
#14 for BCU..O POC versions) and
the ignition transformer terminal #7
are energized. The ignition time (t z)
is constant and lasts for 3 or 6 sec-
onds depending on the safety period.
After the ignition transformer is de-
energized, the flame amplifier looks
for a flame signal. The flame signal
and the OCS contact must be OK
for operation within the safety period
on start-up.
For BCU without POC, contact
input terminal #14 (gas valve 2) is
energized after this time.
Normal Operation
Once the main flame is established
the BCU display window indicates
the program status. During normal
operation, “04” is displayed. This
indicates the burner is operating
normally without faults. To observe
the flame signal, push and hold the
reset/info button located on the front
of each BCU unit for 1 seconds. The
display will change to “01”. Release
the button and the flame current will
be displayed. The display will revert
back to the normal operation in ap-
proximately one minute.
