Honeywell 7800 Series Installation Instructions Manual page 20

RM7838B, RM7838C 7800 SERIES RELAY MODULES
Initiate
The RM7838B,C enters the INITIATE sequence when the
Relay Module is initially powered. The RM7838B,C can
also enter the INITIATE sequence if the Relay Module
verifies voltage fluctuations of +10/-15 percent or
frequency fluctuations of ±10 percent 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 is initiated and displayed on the KDM for at least
five seconds. When the tolerances are met, the INITIATE
sequence restarts. If the condition is not corrected and the
hold condition exists for four minutes, the RM7838B,C
locks out. Causes for hold conditions in the INITIATE
sequence:
a. AC line dropout detection.
b. AC line noise that prevents a sufficient reading of
the line voltage inputs.
c. Low line voltage brownouts.
The Alarm, terminal 3, is energized during INITIATE
(RM7838B only).
Standby
The RM7838B,C remains in STANDBY until the Burner
Control Switch is closed. Two seconds before leaving
STANDBY, the shutter circuit is energized and verifies that
no flame is present. The Alarm, terminal 3, is energized
until flame is sensed (RM7838B only).
Normal Startup PURGE
Purge timing is determined by the plug-in purge timer:
• RM7838B with ST7800A Purge Timer provides 15
purge timing options from 2 seconds to 30 minutes.
• RM7838C with ST7800C Purge Timer provides 15
purge timing options from 7 seconds to 45 minutes.
NOTE: The ST7800A Purge Timer will not fit in the
RM7838C and the ST7800C Purge Timer will not
fit in the RM7838B.
1. Closing the burner control switch starts the
recirculating/exhaust blower. PURGE sequence
begins when power is applied to the RM7838B,C
through the recirculating/exhaust blower airflow
switch, Stop Station, and the limit string to terminal
6. The Run/Test switch and all microcomputer-
monitored circuits must also be in the correct
operating state.
2. The RM7838B,C Relay Module commands the firing
rate motor to the high purge rate position by closing
a circuit between terminals 12 and 13. PURGE
timing begins when the High Fire Switch closes,
providing input to terminal 19. Four minutes, 15
seconds are provided for the High Fire Switch to
close. A jumpered High Fire Switch adds 30 seconds
to the PURGE timing.
3. Valve Proving Tests are conducted in Before, Split, or
Both Valve Proving option is selected. The
RM7838B,C will sequence the Main Valves to
conduct the VP tests concurrently with Prepurge
(beginning 10 seconds into purge).
• Some applications exist that do not use
combustion airflow switch to power terminal 7.
Power is available on terminal 7 at the same time
32-00211—01
terminal 6 is powered, either through lockout
interlock switches or just a jumper. Leave JR3
intact (as received) for these applications.
• Systems using a combustion blower (connected
to terminal 5) require the Combustion Airflow
Switch to close, powering terminal 7. Remove JR3.
The RM7838B,C will energize the Combustion
Blower (terminal 5) to conduct the VP testing. If
purging time is remaining, terminal 5 will be
turned Off.
When the VP testing is complete, the prepurge timing will
be displayed where it is at and complete purge. If purge
timings are complete the dampers will be moving to the
low fire position.
4. The Pre-Ignition Interlocks must remain closed
throughout Prepurge (except during valve testing),
otherwise the RM7838B,C will lockout.
5. When the PURGE timing is complete, the
RM7838B,C commands the firing rate motor to the
low fire position by closing a circuit between termi-
nals 13 and 14. Four minutes, 15 seconds are pro-
vided for the motor to reach the low fire position.
6. When the Low Fire Proving Switch is proven (input
on terminal 18), the RM7838B,C commands the
Combustion Blower to turn on through terminal 5. A
jumpered Low Fire Switch adds 30 seconds to the
PURGE timing.
7. Five seconds are provided for the Combustion
Blower Airflow Switch at terminal 7 to close and sta-
bilize. Safety shutdown occurs if the Combustion
Blower Airflow Switch does not close or if it opens
during ignition trials or RUN.
8. The RM7838B,C waits indefinitely for the Start Input
to terminal 21. If Start Input is on, the RM7838B,C
will hold 60 seconds, then go to a lockout.
9. The Alarm is powered during PURGE timing
(RM7838B only).
Ignition Trials
Ignition trials begin when the momentary Start input is
received at terminal 21 of the RM7838B,C
1. Pilot Flame Establishing Period (PFEP):
a. When the PFEP begins:
(1) The pilot valve and ignition transformer,
terminals 8 and 10, are energized.
(2) Five seconds into PFEP, Ignition terminal 10
is de-energized.
(3) Flame must be proven by the end of the ten-
second PFEP (four seconds if Configuration
Jumper JR1 is clipped) to allow the sequence
to continue. If a flame is not proven by the
end of PFEP, a safety shutdown occurs.
(4) During PFEP, the Low Fire Switch must
remain closed. If it opens, a safety shutdown
occurs.
(5) The Preignition Interlock input is ignored
throughout the Ignition Trial state.
(6) The RM7838B alarm output stops when
flame is proven.
(7) The RM7838B automatically sequences to
Main Flame Establishing Period (MFEP).
2. Main Flame Establishing Period (MFEP):
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