Chapter 2 — Burner Operation and Control
Part No. 750-184 2-21
When the resistance ratio is equal, the motor stops in a position that
allows the proper fuel and combustion air flow to meet operating
demands.
A feature designed into the circuitry maintains the modulating
motor in the low-fire position during ignition and keeps it there until
the main flame is established. A low-fire switch, integral to the
motor, is actuated by the rotation of the motor. The switch must be
closed to establish that the damper and fuel metering valves are in
the low-fire position before the programmer commences into the
ignition period. During this time, neither the manual flame control
nor the modulating control have any control over the damper motor,
regardless of their setting.
An optionally equipped boiler uses a second integral switch to
establish that the motor has driven the damper to an open position
during the pre-purge period. The second integral switch closes, as
high fire position is approached, to complete an internal circuit in
the programmer to allow continuation of the programming cycle.
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