Daikin MicroTech III Operation Manuals page 133

Upon a call for heat, the controller will close digital output
(EXPB-DO1) and energize the R20A relay . Once the normally
open contacts of the R20A relay close 120V power is supplied
to terminal # 6 on the FSG . The FSG then energizes its
terminal #4, which powers the burner combustion air blower
motor (BM) and starts the 90 second prepurge cycle . The
controller will reposition the burner air valve to its maximum
open position via analog output EXPBAO_X7 for prepurge .
When the burner air valve reaches the full open position switch
(LS2) will 'make' and provide a digital input to the controller
(EXPB-DI_X3) . This digital input will initiate a 20 second timing
period in the controller . At the completion of the timing period,
the controller will begin to drive the burner air valve to its
minimum (low fire) position.
When the valve reaches the minimum position switch LS1 will
'make' and provide a digital input to the controller (EXPB-DI_
X2) indicating the controller's prepurge sequence is complete .
As soon as the FSG prepurge time expires FSG terminal #8
will energize relay R22 which will turn ON a digital input to the
controller (EXPB-DI-X1) . As soon as this digital input is 'made'
the controller will close digital output (EXPB-DO2) allowing the
combination gas valve(s) (GV1) to be energized .
After completion of the FSG prepurge period there will be a 10
second trial for ignition during which terminal #8 (combination
gas valve - GV1) and terminal #10 (ignition transformer - IT)
will be energized. If flame is being detected through the
flame rod (FD) at the completion of the 10 second trial for
ignition period, terminal #10 (ignition transformer - IT) will be
deenergized and terminal #9 (main gas valves - GV4 and
GV5 depending on burner size) will be energized and the
control system will be allowed to control the firing rate once the
heating stage timer (default 5 minutes) has passed .
After the flame has lit and been proven and the heating stage
time has passed, the controller will modulate (VM1) to the
required firing rate via analog output EXPB-AO_X7. In the
event the flame fails to ignite or the flame safeguard fails to
detect its flame within 10 seconds, terminals #4, 8, 9, and 10
will be de-energized, thus de-energizing the burner . The FSG
will then lockout and would require manual resetting . If the
FSG lockout occurs, FSG terminal #3 will energize the R24
alarm input status relay which will 'make' a digital input to the
controller (EXPB-DI_X4) .
When this digital input is 'made' the controller will drive VM1
to the closed position, de-energize digital output EXPB-DO2
and the prepurge sequence will be disabled and reset . If
the FSG terminal # 8 de-energizes R22 (EXPB-DI_X1) after
having it turned ON and the FSG is not OFF on safety lockout,
the prepurge sequence will start over . If an attempt is made
to restart the burner by resetting the FSG or if an automatic
restart is initiated after flame failure the earlier described
prepurge cycle with the wide open air valve will be repeated .
If the unit overheats, the high limit control (FLC) will cycle the
burner, limiting furnace temperature to the limit control set
point. The flame safeguard contains 'LEDS' (lower left corner)
that will glow to indicate operation .
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Typical Sequence of Operation (3-1 Gas)
When 120V power is furnished through the system ON/OFF
switch (S1), through the burner ON/OFF switch (S3), and
through the high limit control (FLC), terminal #6 on the flame
safeguard (FSG) is powered on a call for heat . Whenever
power is restored to the flame safeguard, the flame safeguard
will go through a 10 second initiation period before the
prepurge period will begin . The burner air control valve will be
at minimum position during OFF cycles .
Upon a call for heat, the controller will close digital output
(EXPB-DO1) and energize the R20A relay . Once the normally
open contacts of the R20A relay close, 120V power is supplied
to terminal # 6 on the FSG . The FSG then energizes its
terminal #4, which powers the burner combustion air blower
motor (BM) and starts the FSG prepurge cycle .
After completion of the FSG prepurge period there will be a 10
second trial for ignition during which terminal #8 (combination
gas valve - GV1) and terminal #10 (ignition transformer - IT)
will be energized. If flame is being detected through the flame
rod (FD) at the completion of the 10 second trial for ignition
period, terminal #10 (ignition transformer - IT) will be de-
energized and terminal #9 (main gas valves - GV4 and GV5)
will be energized and the control system will be allowed to
control the firing rate once the heating stage timer (default 5
minutes) has passed .
After the flame has lit and been proven and the heating stage
time has passed, the controller will modulate (VM1) to the
required firing rate via analog output EXPBAO_X7. In the
event the flame fails to ignite or the flame safeguard fails to
detect its flame within 10 seconds, terminals #4, 8, 9, and
10 will be de-energized, thus de-energizing the burner . The
FSG will then lockout and require manual resetting . If the
FSG lockout occurs, FSG terminal #3 will energize the R24
alarm input status relay which will 'make' a digital input to the
controller (EXPB-DI_X4) . When this digital input is 'made' the
controller will drive VM1 to the closed position . If the FSG
terminal 8 de-energizes relay R22 (EXPBDI_X1) after having
it turned ON and the FSG is not OFF on safety lockout the
controller will drive VM1 to the closed position . If an attempt
is made to reset the FSG or if an automatic restart is initiated
after flame failure, the FSG prepurge cycle will be repeated.
If the unit overheats, the high limit control (FLC) will cycle the
burner, limiting furnace temperature to the limit control set
point. The flame safeguard contains 'LEDS' (lower left corner)
that will glow to indicate operation .
133 OM 920-6 • MICROTECH UNIT CONTROLLER
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