O2-sensor and lambda

[Mattias Nyberg]

Does the O2-sensor measure lambda?

The O2-sensor measure the concentration of O2 in
the exhaust gases. This is not equivalent or
proportional to the lambda value.
The relation is as follows (from Heywood):

              Ma    [CO2]+[CO]/2+[H2O]/2+[NO]/2+[NO2]+[O2]
(A/F) = 4.77*----*-----------------------------------------
              Mf            [HC]+[CO]+[CO2]

where [..] means concentration, and Ma is the mole-mass of
air and Mf is the mole-mass of fuel.

In a linear lambda sensor, we can measure the O2
concentration but this is obvously not the same
as the lambda value. What is the error made?
Is it really lamdba that is interesting for the catalyst,
or is it the O2-concentration?

Mattias Nyberg