Operation - Honeywell 7800 Series Manual

RM7840E,G,L,M

OPERATION

Sequence of Operation
The RM7840 has the following operating sequences, see
Figs. 17, 18 , 19 and 20.
INITIATE
The RM78040 enters the INITIATE sequence when the
Relay Module is powered. The RM7840 can also enter the
INITIATE sequence if the Relay Module verifies voltage
fluctuations of +10/-15% or frequency flucuations of +/-10%
during any part of the operating sequence. The INITIATE
sequence lasts for ten seconds unless the voltage or frequency
tolerances are not met. When the tolerances are not met,
a hold condition will be initiated for at least five seconds.
When the tolerances are met, the INITIATE sequence will
restart. If the condition is not corrected and hold condition
exists for four minutes, the RM7840 will lockout. Causes for
hold conditions in the INITIATE sequence:
a. AC line dropout is detected.
b. AC line frequency error caused by using a 60 Hz device
on a 50 Hz line, or vice versa.
c. AC line noise that can prevent a sufficient reading of
the line voltage inputs.
d. Brownouts caused by low line voltage.
The INITIATE sequence also delays the burner motor
starter from being energized and de-energized from an inter-
mittent AC line input or control input.
STANDBY
The RM7840 is ready to start an operating sequence when
the operating control input determines a call for heat is
present. The burner switch, limits, operating limit control and
all microcomputer monitored circuits must be in the correct
state for the RM7840 to continue into the PREPURGE
sequence.
NORMAL START-UP PREPURGE
The RM7840 provides a selectable PREPURGE timing
from two seconds to 30 minutes with power applied and the
RM7840 operating control indicating a call for heat.
a. Running Interlocks, Preignition Interlocks, Burner
Switch, Run/Test Switch, Lockout Interlocks and all
microcomputer monitored circuits must be in the cor-
rect operating state.
b. The blower motor output, terminal 5, is powered to
start the PREPURGE sequence, except for the
RM7840E. The firing rate motor is driven to the high
fire position. The PREPURGE timing for the
RM7840E,L does not begin until the Lockout Inter-
lock string and High Fire Switch are both closed. The
blower motor output for the RM7840E is not energized
until the High Fire Switch is closed.
c. The Preignition Interlock input must remain closed
throughout PREPURGE; otherwise, the control re-
turns to the STANDBY state and holds (30 seconds)
for the RM7840G,M or safety shutdown for the
RM7840E,L occurs.
d. The Lockout Interlock or Running Interlock inputs
(interlock circuit including Airflow Switch) must close
by ten seconds or within specified purge card timing
into PREPURGE; otherwise, a hold or recycle back
to the beginning of PREPURGE for the RM7840G,M
will happen or a safety shutdown for the RM7840E,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,
RM7840E,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 Establishing Period (PFEP):
1. With the firing rate motor in the low fire position:
a. The pilot valve and ignition transformer, termi-
nals 8, 10 and 21, are energized. The RM7840M
has an intermittent pilot valve, terminal 21. The
RM7840G has an interrupted or intermittent
pilot valve, terminal 21, depending on the selec-
tion of configuration jumper JR2. The
RM7840E,L has a fifteen second interrupted
pilot valve, terminal 21. All the RM7840s have
a ten second interrupted pilot valve/ignition,
terminal 8.
b. During the PFEP, the Low Fire Switch must re-
main closed. If it opens, a safety shutdown occurs.
c. The Preignition Interlock input is ignored
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 Establishing Period (MFEP):
1. The RM7840E,L has a ten second or fifteen
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 RM7840
will lockout within .8 or 3 seconds, depending on
the Flame Failure Response Time (FFRT) of the
amplifier.
2. The RM7840G has a ten second or 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
RM7840 will lockout within .8 or 3 seconds, de-
pending on the FFRT of the amplifier.
3. The RM7840M 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 RM7840 will lockout within .8 or 3
seconds, depending on the FFRT of the amplifier.
18
Operation