GB
OPERATION MSA
26 ALTAIR 5 - Operating Manual
3. Operation
Instrument operation is dialog driven from the display with the aid of the
three function buttons (see chapter 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 vapour 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 have built-in temperature compensation. However, if temperature
shifts dramatically, the sensor's reading may shift.
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