Date: Fri, 3 Oct 2003 12:43:08 +0200
From: Olaf Trygve Berglihn
To: quest
Subject: Re: oxygen analyzer

* Corvino Gennaro

> Hy, 
> some of one guys, to know where to find some electronic circuit plan for to
> build any oxygen analyzer?

The O2-analyser is only a fuel cell.  The voltage over the cell is about
linear with O2 concentration in the cell.  So you only need a
millivoltmeter and a (linear) potmeter for calibration.  The fuel cells
have a normal working range around 0-50mV or 0-150mV, depending on
model.

You could also just calibrate a simple voltmeter using the scheme below.
You probably have a multimeter laying around already to burntest and
check your light and possibly scooter batteries.

Your calibration gas has O2 percentage of [O2]cal -- for Air ~ 20.8%.
Measure the voltage over the cell with your calibration gas; Ucal.
Measure the voltage over the cell with your unknown gas; Uunk.
The O2 percentage of your unknown gas [O2]unk is:

	[O2]unk = [O2]cal * Uunk/Ucal

Example: [O2]cal=20.8%, Ucal=8.0mV.
Your unknown gas reads Uunk=19.3mV.
Your unknown gas is then 20.8*19.3/8.0 = 50.2% O2.

Due to high temperature sensitivity and wear of the cell, you must
calibrate every time you use the cell.
 
-- 
Olaf Trygve Berglihn