Honeywell 7800 Series Manual page 23

2. During MAIN TRIAL, the Low Fire Switch Input
must be closed (RM7850A). If it opens, a safety
shutdown occurs.
3. After three or five seconds of MAIN TRIAL,
terminal 8 is de-energized for main stabilization.
Flame must remain proven during this period of
five seconds.
Run
The firing rate motor
releases to mod-
ulation.
The Relay Module 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 RM7830A or
RM7850A provides a two,
fifteen, or thirty second
POSTPURGE 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.
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 (RM7850A)
to begin the POSTPURGE period.
The Preignition Interlock Input is ignored during
POSTPURGE.
After the POSTPURGE period is completed, the Relay
Module reenters STANDBY.
Keyboard Display Module
The first line of the Vacuum Fluorescent Display (VFD)
provides current status of the burner sequence (STANDBY,
PURGE, PREIGNITION, SAFETY1, PILOT STAB., MAIN
TRIAL, RUN and POSTPURGE), timing information (PURGE,
SAFETY1, MAIN TRIAL and POSTPURGE) in minutes and
seconds, hold information (PURGE HOLD: T19) and lockout
information (Lockout, Fault Code, Message and Sequence),
RUN
Diagnostic info.
M1999A
POST PURGE 00:12
Device RM7850A
M10187
7800 SERIES RM7830A, RM7850A RELAY MODULE
see Fig. 17. The extreme right side of the first line will either
be blank or it will show a small arrow pointing to the second
line followed by a two-letter code (DI—Diagnostic Information
and Hn—Fault History Information). When the arrow and two-
letter code are displayed, it indicates the second line is
showing a selectable message submenu. The second line will
display selectable or preemptive messages. A selectable
message supplies information for flame strength, system
status indication, system or self-diagnostics and
troubleshooting (see Table 6). A preemptive message will
have parentheses around the message and supply a detailed
message to support the sequence status information. A
preemptive message can also be a lockout message. A
preemptive message will replace a selectable message to
support the sequence status information. It will also replace a
selectable message after 60 seconds if it or a lockout
message is available. The Relay Module LEDs provide
positive visual indication of the program sequence: POWER,
PILOT, FLAME, MAIN and ALARM.
FIVE WIRE CONNECTOR FOR COMMUNICATIONS.
SEQUENCE
REMOTE KEYBOARD DISPLAY AND
STATUS
REMOTE RESET
SELECTABLE
RUN/TEST
MESSAGE OR
SWITCH
PREEMPTIVE
MESSAGE
RESET
FLAME SIMULATOR
PUSH-
INPUT
BUTTON
SEQUENCE STATUS LEDs (POWER,
PILOT, FLAME, MAIN, ALARM)
Fig. 17. Keyboard Display Module and
sequence status LEDs (Table 5).
23
DI = DIAGNOSTICS
H1 = HISTORY
CAPTIVE
MOUNTING
SCREW
PLUG-IN
PURGE
CARD
KEYBOARD
DISPLAY
MODULE
RELAY
MODULE
FLAME
AMPLIFIER
FLAME CURRENT
TEST JACKS
M7702
65-0222