O2 sensor question

[Chad]

>Normally I would say "yes, exactly". The oxygen pump is operated by a
>pumping current, whose polarity is determined by either depleted or
>excess O2, and whose current level relates to the amount of depletion or
>excess, hence your curves. But from the description, I may be jumping to
>some conclusions. You mention "bias conditions" and a reference voltage;
>it sounds like those are set and the resultant current is measured. On
>the face of it, this sounds a bit different than the way the NTKs work.
>The NTKs require a feedback loop which the current pump is part of, and
>which is servo'd off the nernst measurement cell. As such, there isn't
>any biasing or reference per se. But here again, I might be leaning on
>words too heavily. They may infact work very similar and I'm just
>getting hung up on the terminology meself.
>
>Gar
>


You're right about the reference voltage.  A precision reference voltage is
applied, the correct temperature is set up, then the resulting current is
measured.  The control loop is set up to measure the voltage drop across the
heater to check it's temperature (adjusting if necessary), then measuring the
resulting current for O2 content.  Technically, I do think I misused the term
'bias conditions', what I mean to imply are the operating conditions that the
Bosch graphs are based upon.

Admittedly, I don't understand what the reference voltage does, I just know
that it needs to be there.  In the interest of learning, I'm going to try to
find some more info about the physical construction of this sensor.  It is my
first guess that the reference voltage is used to extract a given number of
oxygen atoms from the chamber, and the polarity and magnitude of the current
needed to pump oxygen back into equilibrium indicates the O2 concentration in
the chamber.  This is probably a hasty conclusion, but I would really like to
learn *exactly* what is going on.  Any insight from how NTKs work?

Chad

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