MSA ORION - Environment and Oxygen Sensor Readings; Humidity Changes; Pressure Changes; Temperature Changes

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 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
o
C of the
temperature-of-use for the least effect.
Table 7-5. OXYGEN - Typical Performance Specifications
RANGE
0 to 25% O
2
RESOLUTION
0.1% O
2
REPRODUCIBILITY
0.3% O
2
, for 2 to 25% O
2
RESPONSE TIME
90% of final reading
30 seconds (normal temperature
range)*
3 minutes (extended temperature
range)
Chapter 7, Performance Specifications Operating Manual
7-4