O2 Volts

[Jay Wallace]

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