Ox sender actual function
Gregory A. Parmer
gparmer at acesag.auburn.edu
Mon Nov 9 16:30:00 GMT 1998
> 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).
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