Environment And Oxygen Sensor Readings; Pressure Changes; Humidity Changes; Temperature Changes - MSA Orion plus Mode D'emploi

Environment and Oxygen Sensor Readings

A number of environmental factors may affect the oxygen sensor
readings, including changes in pressure, humidity and temperature.
Pressure and humidity changes affect the amount of oxygen actually
present in the atmosphere.

Pressure Changes

The Orion plus oxygen sensor is designed to compensate for ambient
pressure changes in the area of instrument operation. If pressure
changes rapidly (e.g., stepping through airlock) the oxygen sensor
reading may temporarily shift, and possibly cause the detector to go into
alarm. While the percentage of oxygen may remain at or near 20.8%,
the total amount of oxygen present in the atmosphere available for
respiration may become a hazard if the overall pressure is reduced to a
significant degree.

Humidity Changes

If humidity changes to any significant degree (e.g., going from a dry, air
conditioned environment to outdoor, moisture laden air), oxygen levels
can change up to 0.5%. This is due to water vapor in the air displacing
oxygen, thus reducing oxygen readings as humidity increases. The
oxygen sensor has a special filter to reduce the affects of humidity
changes on oxygen readings. This effect will not be noticed
immediately, but slowly impacts oxygen readings over several hours.

Temperature Changes

The oxygen sensor has built-in temperature compensation. However, if
temperature shifts dramatically, the oxygen sensor reading may shift.
Zero the instrument to within 30°C of the temperature-of-use for the
least effect.
7-7