Ox sender actual function

[Mark Wilcutts]

Only when oxygen ions diffuse through the ZrO2 ceramic substrate do you
get a voltage on the sensor, perhaps the testers were misinterpreting the
results...  The voltage you get from the sensor is related to exhaust
oxygen concentration by

V = kT/2e ln(P(O2)_a/P(O2)_e)

where k = Boltzmann const
T = temp (absolute)
e = electron charge
P(O2)_a = oxygen partial pressure in air (~.2 bar)
P(O2)_e = oxygen partial pressure in exhaust

I believe the accepted lightoff temperature for ZrO2 sensors is 350 deg. C
(~650 deg. F).

On Mon, 9 Nov 1998, Gregory A. Parmer wrote:

> 
> > However, I believe here I once not to long ago heard someone mention that an
> > Oxygen sender in fact does not sense Oxygen as that would require higher
> > heat than present in most exhausts. That actually the sender senses carbon
> > particulate mater. What are the facts...
> 
> Apparently it senses CO and H.
> The following is taken from my beginnings of a FAQ that never got
> finished...it was posted by Dale Ulan on 28 Oct 94, I think.  This 
> version may be edited/abbreviated but a search of the archives will 
> get you the original post(s).  If you do the research and find the
> number of the mentioned SAE paper please let me know.  Isn't Dale 
> still here himself?
> -greg
> PS--the faq I started is at
> http://www.acesag.auburn.edu/~gparmer/efi/myfaq.html
> There are a few other O2 references also.
> 
> ------------------------------------------------------
> 
> About 1990, a few people from the EPA wrote an SAE paper on the subject of
> oxygen sensors. My copy of the paper is at school, so
>      I can't quote the names or give you the SAE paper number. But I can
> summarize it, because I was suprised, too.
>      The EPA was going to do a study of oxygen sensor aging and break-in
> periods, and quantify how this affects exhaust emissions. They
>      built a test setup with a heater (which would heat up the sensor and
> the gas it was exposed to), and a valving system that would allow
>      them to purge the test system with nitrogen gas, and then give
> samples of other gasses.
>      The most obvious test is to see what temperature was required for the
> sensor to sense oxygen. So they cranked up the O2 flow, and
>      started heating. The O2 sensor started to respond at about 800 or 900
> degrees C. No exhaust system operates at that under normal
>      road-load conditions.
>      At this point, they decided that their study should concentrate on
> this lack of O2 sensor activity. What they discovered was that the O2
>      sensor would respond to carbon monoxide and hydrogen. At normal
> operating temperatures, they concluded that the O2 sensor is not
>      capable of sensing oxygen at all. Few people seem to have read this
> paper, though, so most people out there think that the oxygen
>      sensor actually senses oxygen in a vehicle. It *can* sense oxygen,
> but it'll have to be glowing pretty bright to do it.
>      I would suggest going to your local technical library and finding
> this SAE article. It will be in one of the annual article abstract books,
>      somewhere between 1989 and 1993, and may be present in either the big
> thick SAE publication hardcovers, and/or in 'Sensors and
>      Actuators', an SAE special publication series (ref Dale Ulan --
> DIY_EFI email on 28 Oct 94). The output from an O2 sensor is shown
>      at http://www.bracken.co.uk/misc/ you will see a figure relating %
> O2, CO, H2, NOx etc to Lambda (ref Gus Cameron -- DIY_EFI
>      email on 24 Apr 1998).
> 
>