Start Up And Operation; Rm7897C & Rm7840L Flame Safeguard Controls Sequence - Beckett CG15 Manual

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Start Up and Operation

RM7897C & RM7840L Flame Safeguard
Controls Sequence
1. Initiate – The primary control enters the INITIATE
sequence when the control is first powered on
or power returns after an interruption. The initiate
sequence is a ten second delay during which the
control verifies line voltage stability.
2. Standby – The control enters STANDBY until the
limits, operating limit control, burner switch, and
all microcomputer-monitored circuits are in the
correct state.
3. Load Demand – Operating limit control contacts
close on drop in temperature (or pressure) and
initiates the start sequence.
4. Prepurge – The control will signal the PREPURGE
sequence when the airflow interlock and all switches
are in the correct state. The Prepurge sequence is
the amount of time the blower motor runs prior to
the ignition start sequence. Timing for the Prepurge
sequence is determined by a card mounted inside
the control module (typically 30 seconds). For the
RM7897C control, Prepurge is conducted with the
air damper in the low fire position. For the RM7840
control the air damper opens to the high fire position
for the timed prepurge period and returns to the low
fire position before releasing the control for ignition.
5. Trial for Ignition (TFI) – After the Prepurge
sequence has timed out, the ignition and main gas
valves will be energized. Because the burner has
direct spark ignition for the main flame, the flame
must be established and detected by the control
within 4 seconds or lockout will occur.
6. Flame Stabilization – The burner will operate in low
fire for 10 seconds before initiating high fire.
CG15, CG25, CG50 Burner Manual, Form No. 6104BCG50
7. Run – With a flame established and the control
continuing to detect a flame, the burner will operate
in the RUN mode until the load demand is satisfied
or a limit opens.
• For High/Low control wiring, if terminals RC1 and
RC2 are jumpered, the burner operates in the
Low-High-Off mode. The burner starts at Low and
goes to High after the flame stabilization period.
Flame is extinguished when the load is satisfied
or a limit opens, and the burner is sent to post
purge.
• For High/Low control wiring, if a high / low control
has been wired between terminals RC1 and RC2
the burner starts at Low and is released to go
to High after the flame stabilization period. It
can repeatedly cycle between low and high as
necessary to meet load demand until the load is
satisfied or a limit opens, and the burner is sent to
post purge.
• For modulating control wiring, the burner starts at
Low and is released to modulate after the flame
stabilization period. It can modulate between
low and high as necessary to meet load demand
until the load is satisfied or a limit opens, and the
burner is sent to post purge.
8. Load Satisfied – The fuel valves are closed. After
a 15 second post purge, the burner switches to idle
until the next call for operation.
This operation sequence is typical and for reference only.
The primary control could vary, depending on the customer
specification and code requirements. For the specific
operating sequence that applies to your installation,
consult the appliance manufacturer's directions, wiring
instructions, and control manufacturer's literature supplied
with your burner.
Section: Start Up And Operation — 21