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Revision 6/F3590
©
Moffat Ltd, February 2005
and provide gas to the burner. At the same
time the ignition control will generate a high
voltage ignition spark sequence conveyed to
the ignition electrodes mounted at the front of
the burner and oven through a high tension
ignition cable. The spark and earth ignition
electrodes will spark across the end gap
between these two to ignite the burner.
On successful ignition of the burner the third
electrode, being a flame rectification rod, will
be in the burner flame. This provides the
ignition control with confirmation that the
burner is lit by establishing a micro-amp
current from the electrode to earth through the
flame due to combustion flames being ionised
and therefore able to conduct minute electrical
currents. The flame electrode is connected to
the ignition control with an insulated wire
conductor.
If this ignition sequence occurs correctly the
spark sequence will be stopped and the
burner will continue to operate until the
thermostat switches off and shuts down the
ignition control and consequently closes the
gas solenoid valve.
Should the ignition control not sense the
burner flame within a fixed ignition / spark
sequence period, the ignition control will lock-
out and turn off the gas solenoid valve on
220-240 volt models. Lock-out condition
requires the oven thermostat to be switched
off before operation can be restarted. On 110
volt models only, an unsuccessful ignition
attempt will be followed by a 30 second purge
with the gas control valve shut, then
re-attempt ignition automatically. 2 re-ignition
retries will be attempted. If unsuccessful the
ignition control will then lock-out and shut the
gas valve off.
If the ignition control loses the burner flame
during an on period, a re-ignition attempt will
be started automatically. If this is unsuccess-
ful the ignition will go to lock-out mode.
NOTE:
Different voltage and market models
have different ignition sequence and
re-ignition specifications. Refer to appendix A
for specific model details.
The gas solenoid valve also includes the gas
regulator and on installation is adjusted to
achieve correct burner gas operating
pressure.
The G32M and G32MS Turbofan convection
ovens feature a Roast-and-Hold system which
can be used to automatically set the oven to a
fixed holding temperature at the end of a
timed cooking period. When the Roast-and-
Hold switch is turned On the switch will illumi-
nate and switch on a relay found inside the
control panel, at the base of the control hous-
ing next to the door microswitch. When the
relay is switched ON a normally closed switch
pole on the relay is opened and the normal
power supply to the oven thermostat is iso-
lated. A second normally open switch
pole is closed and this provides power to the 3
hour roast timer.
If the roast timer is in the Hold (vertical)
position the timer switch contacts will be in
their normally closed position and supply
power directly to the Hold thermostat located
behind the control panel. The Hold
thermostat is factory set to 75°C (167°F) and
will supply power to the ignition and gas
burner as required to maintain its preset
temperature.
The thermostat heating light will also cycle
On/Off as the Hold thermostat maintains
temperature.
In the Roast-and Hold mode the 3 hour timer
can be set to a selected roasting time. During
this time period the normally open switch
contacts of the timer are closed. The timer
has two change over switches and in this
position one is used to supply power to its
timing motor and the other is used to switch
power directly to the main oven thermostat.
During the 3 hour timer run-down period the
oven temperature will be controlled by the
main oven thermostat to the set temperature
and operate as previously described.
When the 3 hour timer has run down and
reached the Hold position the two switch
contacts change over to their normally closed
position which isolates power from the timer
motor and the oven thermostat. It also
switches power back to the oven hold
thermostat. At this point the temperature
control is now maintained by the hold
thermostat as previously described. To
cancel the hold circuit the Roast-and-Hold
switch is turned Off. This turns off the relay
which removes power from the 3 hour timer
and closes the pole on the relay that feeds the
main oven thermostat. The Hold indicator
light above the 3 Hour timer will illuminate
whenever the oven is operating in hold mode
(Roast ‘n Hold selected, and 3 Hour timer at
zero position).