Principal Technical Features; Sequence Of Operation - Honeywell 7800 Series Installation Manual

RM7885A 7800 SERIES RELAY MODULES
4. Mount the RM7885A by aligning the four L-shaped
corner guides and knife blade terminals with the
bifurcated contacts on the wiring subbase and
securely tightening the two screws without
deforming the plastic.
Mounting Other System
Components (Fig. 7)
Refer to the applicable specifications for mounting other
system components.
PRINCIPAL TECHNICAL
FEATURES
The RM7885A 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. AC line power errors occurred, see Operation.
b. Four minute INITIATE period has been exceeded.
2. STANDBY Period:
a. Flame signal is present after 40 seconds.
b. Intermittent pilot valve terminal is energized.
c. Main valve terminal is energized.
d. Internal system fault occurred.
3. SAFE START CHECK:
a. Flame signal is present.
b. Intermittent pilot valve terminal is energized.
c. Main valve terminal is energized.
d. Internal system fault occurred.
4. IGNITION Period:
a. Intermittent pilot valve terminal is not energized.
b. Start Switch is energized longer than 15 minutes.
c. Main valve terminal is energized.
d. Internal system fault occurred.
5. RUN Period:
a. No flame is present.
b. Pilot valve terminal is not energized.
c. Main valve terminal is not energized.
d. Internal system fault occurred.
OPERATION

Sequence of Operation

The RM7885A has the operating sequences listed below;
see Fig. 2. The RM7885A LEDs provide positive visual
indication of the program sequence: POWER, PILOT,
FLAME, MAIN and ALARM.
NOTE: The alarm will sound until a flame is sensed.
32-00215—01
Initiate
The RM7885A enters the INITIATE sequence when the
relay module is initially powered. The RM7885A 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 RM7885A locks out. Causes for hold conditions in the
INITIATE sequence:
a. AC line dropout detection.
b. AC line noise that can prevent a sufficient read-
ing of the line voltage inputs.
c. Brownouts caused by a low line voltage.
d. Line frequency out of range.
Standby
The RM7885A is in the STANDBY mode after completing
the INITIATE startup or when the Stop Switch is pressed.
The POWER LED blinks every four seconds, signifying that
an internal hardware check is completed. The alarm LED
is also lit and the external alarm (if used) is activated.
Normal Start-Up
When the Start Switch is pressed, the ignition transformer
is energized and power is applied to terminal 10 of the
relay module. If all microprocessor monitored circuits are
in the correct state, the relay module starts a Safe Start
Check and Ignition Trials.
Safe Start Check (Two Seconds)
The RM7885A conducts a two-second Safe Start Check
and verifies that critical loads are in the proper state prior
to startup and that no flame is present in the combustion
chamber.
Ignition Trials
Following the Safe Start Check, the RM7885A provides
power to the Intermittent Pilot Valve, terminal 8, and turns
on the PILOT LED. When flame is proven, the FLAME LED
lights, the ALARM LED turns off, and the relay module
turns on the Main Valve and the MAIN LED. The Start
Switch can be released, which shuts off the ignition
transformer.
NOTE: The Pilot Valve follows the Start Switch until the
flame is proven. Then it controls the RM7885A
(for example, pushing and releasing the Start
Switch turns on and off the ignition transformer
and the pilot valve until the flame is proven). Not
releasing the Start Switch causes a shutdown
after 15 minutes.
Run
The RM7885A is now in RUN and remains in RUN until the
Stop Switch is pressed or a limit opens terminal 6.
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