Honeywell 7800 Series Installation Instructions Manual page 21

Pilot Configuration Sequence of
Operation
WARNING
The user of the RM7888A is responsible for
providing the correct signal to each special
function input terminal and must make sure that
safety is not compromised if an incorrect special
function input is applied.
Initiate
The RM7888A enters the INITIATE sequence when the
Relay Module is powered. The RM7888A also enters 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 will be initiated
and will be displayed on the Keyboard Display Module for
at least five seconds. When the tolerances are met, the
INITIATE sequence will restart. If the condition is not
corrected and the hold condition exists for four minutes,
the RM7888A will lock out. Causes for hold conditions in
the INITIATE sequence are:
• AC line dropout is detected.
• AC line noise that can prevent a sufficient reading of
the line voltage outputs.
• Brownouts caused by a low line voltage.
Standby
The Standby states include Standby-Off, Standby-Purge,
Standby-Control Cool, and Standby-Low Combustion Air
Only, and Standby-Hold. All Standby states command the
ignition, pilot and main off and will lockout if the feedback
signals indicate that one of those terminals is energized.
The Flame Proven output will be commanded off without
regard to the current Flame Sensed signal. After the first
three seconds of Standby, if the Flame Sensed signal
indicates flame, the special function inputs will be
ignored, the Air Valve will be commanded off and the
motor position commanded to Low Fire. The alarm output
will be commanded off.
The Standby state selected is based on the state of special
function inputs 1, 2, 3 and 4 (terminals 6, 17, 19 and 20).
A three-second transition period runs when the Standby
state is entered. This time period allows enough time for
the master system controller to set up the desired
combination of special function input signals so when the
time period expires, the required motor position command
and air valve output status are commanded. During the
time period, the motor control is commanded to the Low
Fire position, the Air Valve is commanded off, the special
function input terminals are ignored, and the safety loads
(Ignition, Pilot and Main Valve) are commanded off
immediately upon entering Standby.
RM7888A 7800 SERIES RELAY MODULE
When special function 1 is energized, a request for burner
operation is in effect, the Air Valve will be commanded off
and the LowFire motor position commanded. In this case,
special functions 2, 3, and 4 are ignored. The burner will
sequence to the Pilot Ignition state as soon as the Low Fire
input and the Limits Complete input are energized.
WARNING
The user of the RM7888A is responsible for
providing an effective purge that meets the
approval of the authority having jurisdiction for a
particular installation. The RM7888A does not
directly monitor the presence or absence of
airflow and cannot guarantee that the air valve
or fan is working. Failure to provide an effective
purge can result in a fire or explosion that can
cause damage, serious injury or death.
Standby-Hold
The RM7888A has a request to sequence out of standby
(special function terminal 1 is energized), but a condition
such as a de-energized Low Fire input or Limits Complete
input signal keeps the sequence in Standby.
When Special Function 1 is energized, the sequence will
hold for eight minutes while waiting for the Low fire signal
to become energized, with an alarm after four minutes of
hold. The sequence will hold for 120 seconds while waiting
for the Limits Complete signal to become energized. If
either time limit expires, a lockout will occur.
When Special Function 1 is de-energized, one of four
Standby states are possible. The Standby state in effect
depends on the status of the special function inputs. The
four Standby states are:
1. Off: the relay module is commanding the Low Fire
motor position and the Air Valve off.
2. Purge: The relay module is commanding the High
Fire motor position and the Air Valve on.
3. Control Cool: The relay module is commanding the
modulated motor position and the Air Valve on.
4. Low Combustion Air Only: The relay module is com-
manding the Low Fire motor position and the Air
Valve on.
If Special Function inputs 2, 3 and 4 are all de-energized,
the Standby-Off state is in effect: the Air Valve is
commanded off and the Low Fire state is ordered.
During Standby/Standby-Purge states, when special
function 1 is de-energized, special function terminals 2, 3
and 4 provide a signal that requests that the RM7888A
command a particular motor position and Air Valve status.
If any one or more of the special function inputs (terminals
17, 19, or 20) is energized, a Standby-Purge state is in
effect with the Air Valve commanded on and either Low
Fire, High Fire, or the modulated position commanded
(see Table 8).
Table 8 defines the combinations of special function
inputs and corresponding output state (Air Valve and
Motor Output) during Standby.
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