Honeywell 7800 Series Manual page 27

the Low Fire input is de-energized anytime after four min-
utes and a lockout will occur after a total of eight minutes has
elapsed. If special functions 2 and 4 are de-energized, the
sequence will return to the end of the Normal—Part 1 state
when the Low Fire input is energized (after a two- to three-
second Debounce period). Otherwise, the Normal—Part 3
state will proceed to Standby when special function 1 be-
comes de-energized.
NOTE: For High/Low Stepfire and Off/On Stepfire se-
quences, the @Low Fire input (Low Fire switch) is not
used but must be jumpered to prevent a Hold condition
in Standby.
High/Low Stepfire—Part 1
High/Low Stepfire—Part 1 is entered only from the
Standby state with Limits Complete and @Low Fire inputs
energized and special function 1 energized. Upon entry to
this state, the Igniter and the Pilot (Low Fire Valve) are
commanded on, and the motor position is commanded to
Low Fire. The Main Valve, Air Valve and Flame Proven
outputs are commanded off.
HIGH/LOW STEPFIRE—PART 1 LASTS FOR FOUR
SECONDS.
The @Low Fire input is ignored during this state, and
special functions 2, 3 and 4 are ignored. If, at the end of the
timed period, the flame has not been established, a lockout
will occur. Otherwise, with flame established, the High/
Low Stepfire—Part 2 is entered.
High/Low Stepfire—Part 2
Upon entry to this state, the Pilot (Low Fire) Valve is
commanded on, the Igniter and Main Valve are commanded
off, the Flame Proven output is commanded on, the com-
manded motor position is Low Fire and a two-second timer
is started. A lockout will occur if a flame failure occurs.
Special functions 3 and 4 are ignored.
The High state will be entered if special function 2 is
energized and the two-second timer has expired. Other-
wise, High/Low Stepfire—Part 2 continues. The @Low
Fire input is ignored during this state.
High State
Upon entry to High State, the Main and Air Valves are
commanded on, and the Pilot (Low Fire Valve) and Flame
Proven outputs are commanded on. A two-second timer is
started. The commanded motor position is changed from
Low Fire to Modulate. A lockout will occur if a flame failure
occurs. The @Low Fire input and special functions 3 and 4
are ignored.
The High/Low Stepfire—Part 2 state will be re-entered
if special function 2 is de-energized and the two-second
time has expired. Otherwise, High State will continue until
special function 1 is de-energized, causing entry to Standby.
Off/On Stepfire—Part 1
Off/On Stepfire—Part 1 is entered only from the Standby
state, with Limits Complete, @Low Fire and special func-
tion 1 energized. When Off/On Stepfire—Part 1 is entered,
the igniter, Pilot (Low Fire Valve) and Air Valve are com-
manded on, while the Main Valve and Flame Proven are
commanded off. The commanded motor position is Modu-
late. Part 1 lasts for four seconds.
The flame signal and @Low Fire inputs are ignored
during this state while a Pilot/Low Fire (flame) is being estab-
lished. The sequence will lockout if Limits Complete be-
comes de-energized. Special functions 2, 3 and 4 are ignored.
At the end of the time period, if the flame has not been
established, a lockout will occur. Otherwise, with the flame
established, Off/On Stepfire—Part 2 is entered.
Off/On Stepfire—Part 2
When On/Off Stepfire—Part 2 is entered, the igniter is
commanded off and the Pilot (Low Fire) Valve, Main Valve
and Flame Proven are commanded on. The commanded
motor position remains at modulate. Special functions 2, 3
and 4 are ignored. The RM7888A will lockout if a flame
failure occurs. The @Low Fire input is ignored during this
state. The sequence will lockout if the Limits Complete
becomes de-energized. Off/On Stepfire—Part 2 proceeds to
Standby if special function 1 becomes de-energized.
Lockout
Lockout is entered when a timed sequence hold expires
or a signal is not in the required state. The RM7888A DSI
configuration sequence description details the conditions un-
der which the sequence will lockout.
Figs. 21 through 23 show the timing relationship be-
tween the RM7888A inputs and outputs for each sequence
state during DSI Normal, DSI High/Low Stepfire and DSI
Off/On Stepfire sequences.
27
RM7888A
OPERATION
65-0175