Honeywell 7800 Series Installation Instructions Manual page 23

A lockout will occur if the Low Fire input or the Limits
Complete becomes de-energized, or a flame failure
occurs, or Flame Proven output is de-energized. After the
first two seconds, a lockout will occur if the special
function 2 or 3 de-energize.
At the end of the ten second period, the pilot is
commanded off and a five second minimum flame
stabilization period begins. When the stabilization period
is completed, the RM7888A will respond to the status on
special function 4. If special function 4 is energized, the
sequence will proceed to the Release to Modulation state
(Run state).
If special function 4 is de-energized, the sequence will
remain indefinitely at the Main Flame Low Fire state. A
lockout will occur if the Pilot, Ignition or Main Valve
outputs are not in the commanded states, if the flame is
lost, if special function 2 or 3 becomes de-energized, or
Flame Proven output is de-energized.
Release to Modulation State (Run State)
When the Release to Modulation state is entered, the only
change in the commanded output status is the motor
position; it is commanded to Modulate instead of Low Fire.
The sequence will lockout if the Limits Complete becomes
de-energized, a flame failure occurs, special function 2 or
3 becomes de-energized, or Flame Proven output is
deenergized.
If the site configurable jumpers are configured to include
Pilot Relight (PV Return Sequence) Pilot Relight is
initiated as follows. When the motor position is Modulate
and the Low Fire input is energized during the Release to
Modulation state for a continuous time period of ten
seconds, the sequence will proceed to the Pilot Relight
state. Normally, the requirements of the process will be
sufficient to keep the modulating control above the Low
Fire position.
If the site configurable jumpers are configured to exclude
Pilot Relight (MV Lo Fire Sequence), Pilot Relight will not
be initiated; the burner modulates to Low Fire during the
Run state and remains there until the RM7888A is
commanded off (Standby).
Run-Low Fire (part of Run State)
If special function 4 becomes de-energized during the
Run state, the sequence will command the motor position
to Low Fire and start a 240-second timer. If the @Low Fire
input fails to energize or becomes de-energized after the
time period has expired while special function 4 remains
deenergized, the alarm output will be made active. If
special function 4 becomes energized, the time period
measurement will end and the normal Release to
Modulation (Run) state will be active.
Pilot Relight—PV Return Sequence Only
When the Pilot Relight state is entered, the Ignition, Pilot,
Main, and Air Valve will be commanded on, the motor
position will be commanded to Low Fire and a ten second
timer will be started. Flame Proven remains on.
The sequence will lockout if the Limits Complete
deenergizes or a flame failure occurs. Lockout will also
occur if the Low Fire input or special function 2 or 3
becomes deenergized during Pilot Relight.
RM7888A 7800 SERIES RELAY MODULE
At the end of the ten-second period, the Wait for Low Off
state is entered. The ignition, main valve and Air Valve are
commanded off, the Pilot remains commanded on, and
the motor is commanded to the Modulate position. The
Modulate position is commanded to detect a process load
increase by noticing that the modulating control has
requested a position other than the Low Fire position.
If the Low Fire input is de-energized during the Wait for
Low Off state for a continuous time period of five seconds,
the sequence will proceed to the Drive to Low Fire state.
Otherwise, the sequence will remain in the Wait for Low
Off state indefinitely while waiting for the modulating
control to request more heat by commanding a motor
position from Low Fire that signals that the process load
has increased and the burner will sequence back to the
Run state. The sequence will lockout if the special function
2 (terminal 17) becomes de-energized, but will ignore
special functions 3 and 4.
Drive to Low Fire
The purpose of the Drive to Low Fire state is to drive the
motor position back to Low Fire in preparation for return
to main fuel.
When the Drive to Low Fire Position state is entered, the
Ignition, Main Valve and Air Valve are commanded off, the
Pilot is commanded on, the motor position is commanded
to the Low Fire position and a 15-second timer is started.
If the 15-second time period expires, the sequence will
hold waiting for the Low Fire input to become energized
and the alarm output will be commanded on. The
sequence will proceed to the Main Train Fuel On state
when the Low Fire input becomes continuously energized
for three seconds. If special function 2 is de-energized, a
lockout will occur.
Lockout State
The Lockout State is entered when a timed sequence hold
expires or a signal is not in the required state. The
RM7888A Pilot Configuration sequence description
details the conditions under which the sequence will
lockout.
Pilot Sequence Timing Diagram
Fig. 21 shows the timing relationships between the
RM7888A inputs and outputs for each sequence state
described in the preceding paragraphs.
DIRECT SPARK IGNITION (DSI)
OPERATING SEQUENCE
The Direct Spark Ignition (DSI) configuration has three
distinct operating sequences that are entered from the
Standby/Standby Purge states. The sequences are:
• Normal sequence.
• High/Low Stepfire sequence.
• Off/On Stepfire sequence.
Each sequence is user-selectable using the configuration
jumpers. The sequence that is used is dictated by the
requirements of a particular application. Each sequence
consists of a burner operating sequence with several
states.
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