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counter-clockwise until the CAL LED (orange) is off, then turn the potentiometer slowly
clockwise until the CAL LED just lights. If the CAL POT cannot be turned to where the
CAL LED is off then the sensor is bad.
Fuel Type Compensation
The AFM1000 assumes a fuel H:C ratio of 1.85 and an O:C ratio of zero. If a fuel of a
different composition (H:C=m, O:C=p) is used, Equation 2 can be used to compensate (i.e.
correct) the AFM1000's output.
AFRcorr = [(2.368 x (m - 2p + 4)) / (m + 16p + 12)] x AFR
where: AFRcorr is the AFR for the fuel of H:C=m and O:C=p composition.
AFR is the AFR output by the AFM1000.
The relationship between the analog output (Vout) and the AFR for methanol (race car
"alcohol") is:
AFR = 0.888 x Vout + 3.55 (methanol only)
The relationship between the analog output (Vout) and the AFR for ethanol (corn alcohol) is:
AFR = 1.235 x Vout + 4.94 (ethanol only)
The relationship between the analog output (Vout) and the AFR for M85 is:
AFR = 1.050 x Vout + 4.22 (M85 only)
The relationship between the analog output (Vout) and the AFR for CH
AFR = 2.366 x Vout + 9.46 (natural gas only)
Pressure Compensation
All wide-range exhaust sensors have a pressure sensitivity. Errors occur when the sensor is
operated at pressures different from the pressure at which it was calibrated.
pressure come about from changes in weather, altitude changes, and engine backpressure.
There is no sensitivity to pressure at stoichiometric (Lambda = 1) conditions. The sensitivity
gets greater the further from stoichiometric the engine is operated. Increases in pressure
make the sensor read further from stoichiometric (i.e. if lean, reads leaner, if rich, reads
richer). For example, an increase in exhaust pressure of 127 mmHg above the calibration
pressure (which would result from calibrating at 1 mile above sea level and then driving
down to sea level) would make a 12.65 AFR engine read 12.50 or a 16.77 AFR engine read
17.00. To compensate for pressure use Equation 7:
[Equation 2]
[Equation 3]
[Equation 4]
[Equation 5]
(natural gas) is:
4
[Equation 6]
Changes in
5
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