Honeywell 7800 Series Manual page 26

RM7888A
OPERATION
Initiate State
The Initiate state will be entered when the RM7888A is
powered. The sequence will transition to the Standby state
after a ten second period. However, if any condition exists
that could prevent reliable operation of the RM7888A, the
sequence will remain in the Initiate state until the condition
is corrected. These conditions include the detection of the
loss of ac power, insufficient ac power level, incorrect ac
line frequency, and excess noise present on the ac line. A
ten second stabilization period occurs after the condition is
corrected before the sequence transitions to the Standby
state. Also, any condition that is detected will remain annun-
ciated for a minimum of five seconds.
Standby State
Standby states for the DSI sequences are the same as
those for the Pilot sequences. See Pilot Configuration Igni-
tion Trials.
WARNING
The user of the RM7888A is responsible for pro-
viding an effective purge that meets the approval
of the authority having jurisdiction for a particular
installation. The RM7888A does not directly moni-
tor 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, causing damage, serious injury
or death.
NOTE: When special function 1 is energized, the RM7888A
will sequence to the initial DSI state based on the setting
of the configuration jumpers. A hold, as previously de-
fined, will prevent the sequence from exiting the Standby
state.
Normal—Part 1
The Normal—Part 1 state is entered only from the
Standby state with the Limits Complete signal and @Low
Fire input on, and special function 1 energized. On entry,
the Air Valve will be commanded off, the Ignition and Pilot
(Low Fire Valve) outputs are commanded on, and Low Fire
position is commanded. The Main Valve and Flame Proven
outputs are commanded off. The RM7888A will lockout if
the @Low Fire input becomes de-energized after the first
two seconds of the Normal—Part 1 state. A one- to two-
second transition state precedes the Normal—Part 1 state
so the Low Fire switch has at least three seconds (total) to
stabilize. This reduces the chance of a nuisance lockout due
to a contact bounce on the @Low Fire input. The RM7888A
will lockout if the Limits Complete is de-energized.
65-0175
For the first four seconds, the Normal—Part 1 state
attempts to establish a Pilot (Low Fire Valve) flame. At the
end of the first four seconds, the Ignition output is com-
manded off. If flame has not been established, a lockout
will occur. With flame established, an indefinite hold will
occur if special function 2 is de-energized and the Flame
Proven output is commanded on. Otherwise, with flame
established and special function 2 energized, the Normal—
Part 2 state is entered.
WARNING
The Flame Proven output is an RM7888A safety
output with an output status monitored by the
RM7888A. This output is used by external equip-
ment which can respond to the signal. The end
user must assure that the Flame Proven output
cannot be misinterpreted. Misinterpretation of this
signal could create a hazardous situation, result-
ing in fire or explosion that can cause damage,
serious injury or death.
Normal—Part 2
Upon entry, the igniter is commanded off, the Flame
Proven output is commanded on, and the Main Fuel Valve
and Air Valve are commanded on. The Pilot (Low Fire)
Valve remains on. The commanded Low Fire motor posi-
tion is unchanged. This state will continue for five seconds.
A flame failure will result in a lockout. A lockout will also
occur if the @Low Fire input becomes de-energized during
this state. Special function terminal 2 is ignored during this
timed period. At the end of the timed period, the sequence
will go back to the end of the Normal—Part 1 state if
special function 2 is de-energized. If special function 2 is
energized and special function 4 is de-energized, a Hold
will occur. If special function 4 is energized, the sequence
will proceed to the Normal—Part 3 state.
Normal—Part 3
All commanded outputs remain unchanged. The igniter
is commanded off and Flame Proven output, Pilot (Low
Fire Valve), Main Fuel Valve and Air Valve are com-
manded on. The sequence will lockout if the Limits Com-
plete is de-energized or a flame failure occurs. The se-
quence will lockout if special function 2 is de-energized.
and special function 4 is energized. If special functions 2
and 4 are energized , the motor position will be Modulated.
If special function 2 is energized and special function 4 is
de-energized, the commanded motor position will be the
Low Fire position and an alarm will occur if the Low Fire
input is de-energized after four minutes. If special func-
tions 4 and 2 are both de-energized, an alarm will occur if
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