O2 Volts

[soren]

 Varying the amounts of HC, CO,
>CO2, and NOx don't affect the sensor. Only O2 quantity in relation to
>the sensor's reference changes voltage.  TPS senses TP whether output
>voltage increases or decreases with increased throttle angle.  Why do
>you think an "inverted" output from the O2 sensor makes it a Not O2
>sensor?



    A TPS has a supply voltage that can be modulated in either increasing or
decreasing fashion with increasing throttle angle, but the O2 sensor has to
make its own voltage.  My simple logic led me to the conclusion that the
compound that is being actually being sensed must be the one that provides
this positive voltage.
Then I remembered that the O2 sensor is actually a differential sensor, like
you said: it provides voltage based on the differential between the outside
reference air and the gases in the exhaust.  So my new hypothesis is that
the sensor is sensing O2, but it actually produces voltage from the
reference oxygen; when it is compared to an oxygen-poor environment in an
exhaust stream, there is a voltage differential across the ion-sensing
electrodes, and the voltage produced at the reference side goes up the
signal wire.  When the O2 is even on both sides, no voltage is produced.
    Of course, this would only apply to the zirconium type O2 sensors, the
titanium dioxide ones do actually use a reference voltage and act as a
variable resistor.
    So now what I want to see is someone test a sensor using sealed chambers
for both reference and exhaust sides, using O2, HCs, an inert gas such as
argon, and another gas containing negative ions (maybe one of the halogens)
as a control. :-p

Soren