Honeywell 7800 Series Manual page 24

RM7800E,G,L,M
OPERATION
STANDBY
The RM7800 is ready
to start an operating se-
quence when the operat-
ing control determines a
call for heat is present. The burner switch, limits, operating
control and all microcomputer monitored circuits must be in
the correct state for the RM7800 to continue into the
PREPURGE sequence.
NORMAL START-UP
PREPURGE
The RM7800 provides
a PREPURGE timing se-
lectable from two seconds
to 30 minutes with power applied and the RM7800 operating
control indicating a call for heat:
a. Running Interlocks, Preignition Interlocks, Burner
Switch, Run/Test Switch, Lockout Interlocks and all micro-
computer monitored circuits must be in the correct operat-
ing state.
b. The blower motor output, terminal 5, is powered to
start the PREPURGE sequence, except for the RM7800E.
The firing rate motor is driven to the high fire position. The
PREPURGE timing for the RM7800E,L does not begin
until the Lockout Interlock String and High Fire Switch are
both closed. The blower motor output for the RM7800E is
not energized until the High Fire Switch is closed.
c. The Preignition Interlock input must remain closed
throughout PREPURGE; otherwise, control returns to
the STANDBY state and holds (30 seconds) for the
RM7800G,M or safety shutdown for the RM7800E,L
occurs.
d. The Lockout Interlock or Running Interlock inputs
(interlock circuit including Airflow Switch) must close by ten
seconds into PREPURGE; otherwise, a recycle to the begin-
ning of PREPURGE for the RM7800G,M will happen or a
safety shutdown for the RM7800E,L occurs.
e. After the firing rate motor reaches the PREPURGE
rate position and PREPURGE timing is completed, the
firing rate motor will drive to the low fire position,
RM7800E,G,L.
f. When the firing rate motor reaches low fire position,
the Low Fire Switch, terminal 18, input must be energized
before entering the Ignition Trial state.
IGNITION TRIALS
a. Pilot Flame Estab-
lishing Period (PFEP):
1. With the firing
rate motor at the low fire position:
a. The pilot valve and ignition transformer, termi-
nals 8, 10 and 21, are energized. The RM7800M
has an intermittent pilot valve, terminal 21. The
RM7800G has an interrupted or intermittent
pilot valve, terminal 21, depending on the selec-
tion of configuration jumper 2. The RM7800E,L
has a fifteen second interrupted pilot valve,
terminal 21. All the RM7800s have a ten second
interrupted pilot valve/ignition, terminal 8.
b. During PFEP , the Low Fire Switch must remain
closed. If it opens, a safety shutdown occurs.
c. The Preignition Interlock input is ignored
STANDBY
Total Cycles 132
PURGE 00:30
Total Hours 396
PILOT IGN 00:10
Fault History
throughout the Ignition Trial state.
2. Flame must be proven by the end of the four or ten
second PFEP to allow the sequence to continue. If
flame is not proven by the end of PFEP, a safety
shutdown occurs.
3. With flame proven, the ignition, terminal 10, is de-
energized for early spark termination.
b. Main Flame Estab-
lishing Period (MFEP):
1. The RM7800E,L
has a selectable
ten second or fif-
teen second MFEP. After the Ignition Trials, and
with the presence of flame, the main fuel valve,
terminal 9, is powered. If a flameout occurs, the
RM7800 will lockout within .8 or 3 seconds, de-
pending on the Flame Failure Response Time
(FFRT) of the amplifier.
2. The RM7800G has a ten second, fifteen second or
thirty second MFEP. After the Ignition Trials, and
with the presence of flame, the main fuel valve,
terminal 9, is powered. If a flameout occurs, the
RM7800 will lockout within .8 or 3 seconds, de-
pending on the FFRT of the amplifier.
3. The RM7800M has a ten second MFEP. After the
Ignition Trials, and with the presence of flame, the
main fuel valve, terminal 9, is powered. If a flame-
out occurs, the RM7800 will lockout within .8 or 3
seconds, depending on the FFRT of the amplifier.
RUN
1. A ten second stabi-
lization period occurs at
the beginning of the RUN
period.
2. The firing rate motor releases to modulation
(RM7800E,G,L).
3. The RM7800 is now in RUN and will remain in RUN
until the controller input, terminal 6, opens, indicating that the
demand is satisfied or a limit has opened.
POSTPURGE
The RM7800 provides
a fifteen second POST-
PURGE following the
completion of the RUN
period. The blower motor output is powered to drive all
products of combustion and any unburned fuel from the
combustion chamber. It also supplies combustion air to
burn fuel being purged from the fuel line downstream of the
fuel shutoff valve.
1. The main fuel valve and intermittent pilot valve,
terminals 9 and 21, are de-energized and the firing rate motor
is commanded to the low fire position to begin the
POSTPURGE period.
2. The Preignition Interlock closes within the first five
seconds of POSTPURGE.
3. After the fifteen second POSTPURGE period is com-
pleted, the RM7800 reenters STANDBY.
24
MAIN IGN 00:15
Flame Signal 2.7V
RUN
Expanded Annun.
POST PURGE 00:12
Device RM7800L