O2 Volts

[rr]

Jay Wallace wrote:
> 
> At 02:03 AM 5/20/99 -0400, you wrote:
> >rr wrote:
> >>
> >> >> Bruce Wrote:
> 
> snip...
> 
> >> Response's to different gases:
> >>
> >>         propane: rapid and long lasting, > 850mv.
> >>         R12: light response, quick to return to nominal, ~475mv.
> >>         acetylene: rapid and long lasted, > 750mv.
> >>         hold breath, breath through tube into can: no effect...
> >>         argon: light response, very short lived: ~70mv.
> >>         contact cleaner: medium response, ~650mv.
> >>                 (tricloroethane + diclorodifluoromethane)
> >>
> >>         (couldn't find any butane)
> >>
> >> Thinking about this, it makes sense. Once you reach stoich (450mv),
> >> how can you go higher? Only if the excess hc takes it there...
> >>
> >> The argon response, or lack thereof, is interesting.
> >You didn't report on the duration of the gas "shot".  Not sure it
> >matters, but I would have left whatever gas "running" for a fixed
> >amount of time in the can.  Or better yet, continously until end of
> >test.  Methinks I may have been motivated enough to do my own
> >experiments.
> >Shannen
> 
> I wouldn't be surprised if Shannen is on the right track here: Ar
> is heavier (denser) than air so it would sink to the bottom of
> whatever container that it is flowing into. You would need to flow
> long enough to displace all of the air before the tip of the sensor
> was surrounded by Ar.
> 
> One more thing that should be emphasized: a standard oxygen sensor
> is just an electrochemical cell with the output voltage
> proportional to the difference in oxygen concentration between the
> inside and outside (for a constant temperature) as long as the
> zirconia is hot enough to conduct. The output voltage is given by
> the Nernst equation. I _think_ that all of the experimental
> observations are consistent with this.
> 
> Jay

If I got an instant response, I really didn't run the gas much longer.
But for say, the argon, with a slow response, it was run for a while,
easily 30 to 60 seconds. Not real scientific, but I'm on a limited
time budget.

Another thought, in the back of my mind, I believe that o2 sensors
are built with a very thin film of platinum on the sensor cone. This
would act like a cat-con, burning any HC's and robbing the porous cone
of any o2. Including that o2 that has permated the cone material.

This may help explain the rapid reaction to hc's.


BobR.

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