CC to PICList as of possible interest.


I tried using a Zinc-Air cell as an O2 sensor REALLY roughly (seemed like a
cheap way to make a sensor) and cell voltage seemed to be very insensitive
to Oxygen concentration (as you suggest it would be). Stored O2 appears to
be a major problem.  I'll be trying it again in due course with  a little
more finesses (hopefully). We bought a batch of "real" Oxygen sensors but
even in 100 volume (I think it was) they cost around $US45 AFAIR. These DO
produce a linear pO2 versus Voltage response. Being an electrochemical cell
they have a finite lifetime and they drift severely so you need to
calibrate them before every use. Fortunately there is an easy cheap and
fairly accurate source of 20.8%-Oxygen calibration gas available. (Or, if
you want to argue, 20.95 +/- 0.01% - yep, the ranges don't coincide-
depends who you listen to :-)).

Diversion:

Q.:     Zinc Air cells have superb energy densities - about twice that of
Alkaline.Good for spacecraft?
A        :-(  - No




Russell McMahon

From: JimSwen@aol.com <JimSwen@aol.com>
To: henry@spsystems.net <henry@spsystems.net>

>I have always thought that zinc-air hearing-aid batteries might make
decent
>pO2 sensors.
>
>Just looking at their voltage wouldn't work, of course.
>The voltage would be something like the log of pO2, a weak function, and
>subject to stored O2 every time it got a good exposure.
>
>But the sensor was run as a current source into a virtual-ground meter
input,
>with a small diffusive air leak,
>the current might be proportional to pO2 with a response time of under a
>minute.
>
>This might be useful for monitoring inert-gas vs oxygen.
>I never got around to trying it.
>Has anybody tried this or heard of it?
>
>Jim S