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Thank you for your reply.

>Do you have any correlating numbers on the effect ?

 Not really though I have run several hours of testing, with run times of
between 20 minutes and 1.5 hours, with the miniox plumbed into the breathing
loop. I did not bother to record the drift upward in readings because they
were so small.  After exposures to what would be near 100% RH we found
increases in the readings of  ambient air of less than 1% immediately after
pulling it out of the loop.  For our purposes changes of a few percent are
immaterial.

>What about condensation inside the sensor ?
>Is this a problem in your design ?

We do get condensation on sensor but so far it has not caused any problems
we know of.  The ppo2 goes up and down in the loop based on metabolism and
air flow, it is possible that some of these variations are due to
condensation.  As time goes by during the test the variations seem to follow
the same pattern which says to me that the building humidity and
condensation are not affecting my readings in an erratic way.
>
>Does the O2 hysteresis of the sensor change
>with the humidity level ?

I know little about the electronics or inner workings of the sensors themselves.

>If the humidity level can vary a bit one could
>(for educational purposes at this point) ) integrate
>a humidity sensor and the O2 sensor (and what the heck,
>add a temperature sensor too) into one package.  Trouble is,
>the humidity sensors I have seen  all respond much faster to
>changes in the humidity than does the O2 sensors.  It's
>important to point out that I do not have first hand data
>on this aspect of O2 sensors.

Again with our application - confirming the rough ppo2 in our breathing loop
- small variations in our readings are not  a problem.  If we are actually
at .96 ata of o2 and our reading is 1.03 that is bang on for our purposes.
If the unit implodes, corrodes or reads .45 when I am at .96 then I will be
deeply concerned.

Inside the loop the RH should be constant near 100% after a few minutes so
we may be able to account for it simply by reducing the inital calibration
by some amount, but if the variations are as small as we have seen so far
why bother?

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