AFR Measurement Offsets
The main menu selection of "OFFSETS" allows the user to bias the displayed, recorded, and
output AFRs for each AFR sensor by an entered amount. The entered offset acts across the
entire range of measured AFRs. Separate offset values are maintained for each of the AFR
units choices (AFR, φ, λ or %O
2
). For example, if the measured AFR is 14.6 and the offset
is -0.1, the displayed AFR will be 14.5. The offset AFRs are used for display, recording, and
outputs.
AFR Measurement Calibration (“AIR CAL”)
The selection of "AIR CAL" from the main menu field-calibrates the AFR measurement
function with air as the calibration gas. “AIR CAL” requires that the user enter the %O
2
in
air in Setup - Constants - Fuel & Air (on page 21) and only needs to be performed if the
AFRecorder does not display this entered value when the AFR sensor is held in stationary
air. AFR measurement calibration will be needed when the AFR sensor degrades and/or
when atmospheric pressure conditions change due to altitude and weather changes.
The procedure for air calibration is:
1. Put the AFR sensor in stationary air.
2. After 20 minutes:
a. If the AFRecorder shows "%O2: ##.#" for AFR (where ##.# is the %O
2
in
air) then the AFR measurement function does not require calibration.
b. If the AFRecorder does not show "%O2: ##.#" then select "AIR CAL" from
the main menu, followed by the AFR sensor to calibrate (left or right), and
initiate calibration. Note that the correct %O
2
in air must be entered in
Setup - Constants - Fuel & Air (on page 21).
The "AIR CAL" procedure takes approximately 10 seconds. Upon
completion, the "AGE FACTOR" will be displayed. The age factor of a new
AFR sensor at the same atmospheric conditions under which it was factory
calibrated is 1.0. This will change with sensor degradation and/or changes
in atmospheric conditions. “AIR CAL” will correct for sensor degradation
and/or changes in atmospheric pressure (those resulting from weather and
altitude changes). The “AGE FACTOR” will decrease as the sensor ages.
If any AFR sensor parameter (Io
2
, Ico, Ih
2
, I
1
or I
2
) is entered (including reentering the same
number) (see Setup - Constants - AFR Sensor_L, Sensor_R on page 20 and Unit-Specific
Information on page 43), the AFRecorder assumes that a new sensor is being used and
resets the "AGE FACTOR" to 1.00. The effect of this is to negate all AFR sensor field
calibration and to return the AFRecorder to the factory-delivered AFR sensor calibration.
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