Operation - Honeywell 7800 SERIES Manual

Sequence of Operation
The RM7890 has the following operating sequences, see
Figs. 13 and 15.
INITIATE
The RM7890 enters the INITIATE sequence if the Relay
Module verifies voltage fluctuations of +10/-15% or fre-
quency fluctuations 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 and will be displayed on the optional VFD for at
least five seconds. When the tolerances are met, the INI-
TIATE sequence will restart. If the condition is not corrected
and the hold condition exists for four minutes, the RM7890
will lockout. Causes for hold conditions in the INITIATE
sequence are:
• AC line dropout is detected.
• AC line frequency error caused by using a 60 Hz device
on a 50 Hz line or vice versa.
• AC line noise that can prevent a sufficient reading of
the line voltage inputs.
• Brownouts caused by a low line voltage.
STANDBY
The RM7890 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 RM7890 to continue into the SAFE-START
CHECK.
Fig. 13—RM7890A,B sequence.
LED
DISPLAY
BURNER
START
OPERATING
CONTROLLER
AND LIMITS
FLAME
SIGNAL
00 00
SAFE-
INITIATE STANDBY
START
POWER POWER POWER
LIMITS AND BURNER CONTROL CLOSED
SAFE START CHECK
1 MAIN FUEL VALVE WILL BE ENERGIZED DURING PFEP IF FLAME IS PROVEN.
2 RM7890A1031 PFEP IS FIXED 30 SECOND.
NORMAL START-UP SAFE-START CHECK
(EXCEPT RM7890C)
The RM7890 verifies that a flame does not exist and
proceeds into the Ignition Trial. If a flame is present, the
RM7890 will recycle to the STANDBY period. If the critical
loads are not in the correct state, a safety shutdown occurs.
IGNITION TRIALS
a. Pilot Flame Establishing Period (PFEP):
1. The pilot valve and ignition transformer, terminals
8 and 10, are energized. The RM7890A,B has an
intermittent pilot valve, terminal 8.
2. Flame must be proven by the end of the 4 or 10
second PFEP (30 second for RM7890A1031) 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 and the main valve, terminal 9, is
energized.
RUN
The RM7890 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.
SELECTABLE SITE-CONFIGURABLE JUMPERS
The RM7890 has two site-configurable jumper options,
see Fig. 16 and Table 3. The site-configurable jumpers should
be clipped with side cutters and the resistors removed from
the Relay Module.
10
2
PFEP
RUN
4 OR 10 SEC
POWER POWER
PILOT PILOT
FLAME FLAME
MAIN MAIN
ALARM
ALARM
10
IGNITION
INTERMITTENT PILOT 8
MAIN VALVE 9
+ 6
TO
FLAME PROVING
15
RM7890A,B,C

OPERATION

Operation
STANDBY
POWER
1
S S C
M5135B
65-0126—2