The analyzer may show 100% oxygen if it is new or if the battery is low. Use the graduation wheel to adjust the arbitrary value shown by the instrument to the oxygen content of atmospheric air.
The display should read 21.0. The analyzer is now ready for use.
With the oxygen analyzer sensing tube pressed against the valve opening, gently open the cylinder valve. The mixture should not pass through the sensor under high pressure, a “quiet hiss” is sufficient for the analysis.
Wait until the reading on the instrument display stops changing and stops at the same value. This will be the percentage of of oxygen in your mixture. A small head of mixture for 30 seconds is usually sufficient to obtain accurate data.
The sensor must be pressed firmly against the cylinder vent (unless the instrument is equipped with an air sampling bag or adapter) so that the air stream does not trap outside air, otherwise the readings will be understated.
Do not cover the tube outlet of the analyzer with your hand, as a buildup of gas in the tube will give an overestimate of the oxygen content.
Most oxygen analyzers are very sensitive so do not open the cylinder valve abruptly to avoid damage.