Figure 9-2: Active O
2
Sensor Cycle Coverage Chart
Figure 9-3 graphically shows the functional logic of the AERtrim system and how the blower
voltage (BV), O
2
Limits, and air/fuel ratio interact during an AERtrim operation. The limits are
fixed presets within the controller. The target range is adjustable within these limits to allow the
user to select the optimal air/fuel ratio for a particular boiler or application.
Figure 9-3 shows how the controller would react to an O
2
% reading above the upper limit. The
controller will reduce the blower voltage (BV) until the O
2
% reading is within the Target Range,
provided the BV adjustments are within the BV limits for that unit at that fire rate. The control will
then store this as the new BV calibration setting until changed manually or by another cycle of
the AERtrim function.
NOTE:
When the O
2
sensor is off during the 10-hour O
2
Sensor OFF periods shown above, Modbus
sends an Oxygen Level of 99 (rather than 0) to the building automation system.
Figure 9-3: AERtrim Logic
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