Pressure Changes; Humidity Changes; Temperature Changes - MSA Orion G Operating Manual

Chapter 7, Performance Specifications

Pressure Changes

The Orion G 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
temperature-of-use for the least effect.
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