DIY-WB.....AFR vs Vout equations

[NickG]

In preparation of building and using the DIY-WB O2 sensor, I wanted to
somehow relate the voltage output by the controller to an actual AFR. Using
the WB-Vout text included in the plans and an online polynomial solving
page, I have derived some equations relating the Vout to AFR. I'm listing 3
equations; the higher the order, the more accurate the equation is:

Note: the term 'x' below is the voltage output by the controller.

for n=3:

AFR = -25.2818 + 54.1746x - 27.7675x^2 + 5.01153x^3

for n=4:

AFR = 50.4636 - 95.2203x + 80.3494x^2 - 29.0507x^3 + 3.94727x^4

for n=5:

AFR = 110.714 - 244.07x + 225.008x^2 - 98.2133x^3 + 20.226x^4 - 1.51015x^5

One way to use these equations is with a data acquisition board and Excel.
By importing the captured WB O2 voltage into a spreadsheet, the above
formulas can be used to calculate the AFR from the captured voltage.

Nick



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