MSA altair 5, Instruction Manual

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3. Operation
Instrument operation is dialog driven from the display with the aid of the
three Function buttons (see Section 2.2.1).
3.1. Environmental Factors
A number of environmental factors may affect the gas 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
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 vol%, the total amount of oxygen present in the atmosphere
available for respiration may become a hazard if the overall pressure is
reduced by a significant degree.
Humidity Changes
If humidity changes by any significant degree (e.g., going from a dry, air
conditioned environment to outdoor, moisture laden air), oxygen
readings can be reduced by up to 0.5 %, due to water vapor in the air
displacing oxygen.
The oxygen sensor has a special filter to reduce the effects of humidity
changes on oxygen readings. This effect will not be noticed
immediately, but slowly impacts oxygen readings over several hours.
Temperature Changes
The sensors are temperature compensated. However, if temperature
shifts dramatically, the sensor's reading may shift temporarily.
3-1