OMM-0153_E
• 5/11/2023 Technical Support • (800) 526-0288 • Mon-Fri, 8 am - 5 pm EST Page 89 of 124
CENTURION Installation, Operation & Maintenance Manual
SECTION 9: O2 TRIM OPERATION
Figure 9-2 graphically shows the functional logic of the O
2
Trim system and how the blower
voltage (BV), O
2
Limits, and air/fuel ratio interact during an O
2
Trim 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 Water Heater or application.
Figure 9-2 shows how the controller would react to an O
2
% reading above the upper limit. It will
reduce the blower voltage (BV) until the O
2
% reading is within the Target Range, provided the
BV adjustments are within the limits for that fire rate. The control will then store this as the new
BV calibration setting until changed manually or by another O
2
Trim function cycle.
Figure 9-2: O
2
Trim Logic
Once the system operational stability conditions are met, the O
2
Trim system will:
1. Lock the fire rate at the current position that needs adjustment to the air/fuel ratio.
2. The
Demand
LED will flash once per second to indicate that the trim function has started.
3. Check the oxygen levels inside the combustion chamber:
•
If oxygen levels are within the set range, O
2
Trim releases control.
•
If oxygen levels are outside the set range, O
2
Trim will adjust Blower Voltage to bring
the Water Heater back to the Target O
2
value.
This process repeats until the target oxygen range is achieved or the unit reaches the allowable
blower voltage limit.
9.2 O
2
Sensor Calibration
O
2
sensor calibration can be initiated by
pressing the Calibrate button on the Edge’s
O
2
Sensor
screen
(
Main Menu
→
Calibration
→
Input/Output
→
O
2
Sensor
). Connect the combustion
analyzer to the exhaust to perform the O
2
sensor calibration. Once the calibration starts, the
Edge ignites the unit and waits 2 minutes for the sensor to settle. Enter the O
2
reading from the
analyzer to complete the calibration process.
