Honeywell 7800 Series Manual page 24

RM7888A
OPERATION
the motor is commanded to the Modulate position. The Mod-
ulate 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 com-
manded 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
DSI State Name
Normal—Part 1 (Main Flame
Establishing Period [MFEP])
Normal—Part 2 (Main Flame
Establishing Period [MFEP])
Normal—Part 3 (Run)
High/Low Stepfire—Part 1 (Main
Flame Establishing Period [MFEP])
High/Low Stepfire—Part 2 (Run)
Run—High
OFF/ON Stepfire—Part 1 (Main
Flame Establishing Period [MFEP])
OFF/ON Stepfire—Part 2 (Run)
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TABLE 7—DSI CONFIGURATION OPERATING SEQUENCE STATES.
Displayed Text
MAIN IGN 00:ss
MAIN IGN 00:ss
RUN
MAIN IGN 00:ss
RUN
RUN
MAIN IGN 00:ss
RUN
Fire input becomes continuously energized for three sec-
onds. 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 de-
tails the conditions under which the sequence will lockout.
Pilot Sequence Timing Diagram
Fig. 20 shows the timing relationships between the
RM7888A inputs and outputs for each sequence state de-
scribed 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 configura-
tion 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.
Normal sequence is used when the application requires
the burner flame to be modulated during the Run state.
Purpose
Establish a Low Fire flame. Display shows elapsed time
for Normal—Part 1.
Allow for main valve operators to be placed into the
normal operating condition while at Low Fire position.
Display shows elapsed time for Normal—Part 2.
Allow normal operation to take place where a modulating
control provides the motor position signal.
Establish a Low Fire flame. Display shows elapsed time.
Run with Low Fire flame while commanding Low Fire
for an indefinite time period. When the appropriate
special function signals are present, the sequence will
advance into the HI (Run at High Fire) state.
Run with a High Fire flame for an indefinite period. From
this state, the sequence can return to the Low Fire state
upon command without recycling. Commanded output
state is the same as Normal—Part 3, but special function
signals are different.
Establish a Low Fire flame. Display shows elapsed time.
Run with a high fire flame for an indefinite period.
Commanded output state is the same as Normal Part 3 but
special function signals are different.
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