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Principal Technical Features; Operation - Honeywell 7800 Series Installation Instructions Manual

Relay modules
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RM7897A1002, RM7897C1000 7800 SERIES RELAY MODULES
Once the system is in operation, the settings of the postpurge
time can be viewed under Diagnostics, using your S7800
Keyboard Display Module.

PRINCIPAL TECHNICAL FEATURES

The RM7897 provides all customary flame safeguard
functions as well as significant advancements in safety,
annunciation, and system diagnostics.
Safety Shutdown (Lockout) Occurs if:
1. INITIATE PERIOD
a. Purge card is not installed or removed.
b. Purge card is bad.
c. Configuration jumpers have been changed (after
200 hours)—Fault Code 110.
d. AC line power errors occurred, see Operation.
e. Four minute INITIATE period has been exceeded.
2. STANDBY PERIOD
a. Airflow lockout feature is enabled and the airflow
switch does not close after ten seconds or within the
specified purge card timing.
b. Flame signal is detected after 240 seconds.
c. Ignition/pilot valve terminal is energized.
d. Main valve terminal is energized.
e. Delayed main valve terminal is energized
(RM7897C).
f.
Internal system fault occurred.
g. Purge card is removed.
h. Purge card is bad.
i.
PreIgnition Interlock open.
3. PREPURGE PERIOD
a. Airflow lockout feature is enabled and the airflow
switch opens.
b. Ignition/pilot valve terminal is energized.
c. Main valve terminal is energized.
d. Delayed main valve terminal is energized
(RM7897C).
e. Internal system fault occurred.
f.
Purge card is removed.
g. Purge card is bad.
h. Flame signal is detected for 30 seconds.
i.
Preignition interlocks open during standby.
4. PILOT FLAME ESTABLISHING PERIOD (PFEP)
a. Airflow lockout feature is enabled and the airflow
switch opens.
b. No flame signal at end of PFEP.
c. Ignition/pilot valve/intermittent pilot valve terminal is
not energized.
d. Main valve terminal is energized (RM7897A).
e. Delayed (second stage) main valve terminal is
energized (RM7897C).
f.
Internal system fault occurred.
g. Purge card is removed.
h. Purge card is bad.
5. MAIN FLAME ESTABLISHING PERIOD (MFEP)
(RM7897A, terminal 21; RM7897C, terminal 8)
a. Airflow lockout feature is enabled and the airflow
switch opens.
b. Ignition terminal is energized.
c. Ignition/pilot valve terminal is not energized.
d. Main valve terminal is not energized.
e. Delayed main valve terminal is energized.
66-1151
f.
Loss of flame signal.
g. Internal system fault occurred.
h. Purge card is removed.
i.
Purge card is bad.
6. RUN PERIOD
a. No flame present (JR2 removed).
b. Airflow lockout feature is enabled and the airflow
switch opens.
c. Interrupted pilot valve terminal is energized
(RM7897A, terminal 21; RM7897C, terminal 8).
d. Main valve terminal is not energized.
e. Delayed main valve terminal is not energized
(RM7897C).
f.
Internal system fault occurred.
g. Purge card is removed.
h. Purge card is bad.
i.
Ignition terminal is energized.

OPERATION

Sequence of Operation
The RM7897A,C has the operating sequences listed below;
see Fig. 2 and 3. The RM7897A,C LED provide positive visual
indication of the program sequence: POWER, PILOT, FLAME,
MAIN and ALARM.
Initiate
The RM7897A,C Relay Module enters the INITIATE sequence
when the relay module is powered. The RM7897A,C can also
enter the INITIATE sequence if the relay module verifies
voltage fluctuations of +10/-15% or frequency 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 not met, a hold
condition is initiated and displayed on the optional KDM for at
least five seconds; when met, the INITIATE sequence
restarts. If the condition is not corrected and the hold condition
exists for four minutes, the RM7897A,C locks out. Causes for
hold conditions in the INITIATE sequence:
1. AC line dropout detection.
2. AC line noise that can prevent a sufficient reading of the
line voltage inputs.
3. Low line voltage brownouts.
The INITIATE sequence also delays the burner motor starter
from being energized and de-energized from an intermittent
AC line input or control input.
Standby
The RM7897A,C 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 relay module to continue into the PREPURGE
sequence.
Normal Start-Up Prepurge
The RM7897A,C Relay Module provides PREPURGE timing,
selectable with ST7800 Purge Timer cards, from two seconds
to thirty minutes with power applied and the operating control
indicating a call for heat.
12

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