MSA SIRIUS Instruction Manual page 51

RESPONSE NOTES:
* Some compounds may reduce the sensitivity of the combustible gas sensor by poiso-
ning or inhibiting the catalytic action or by polymerizing on the catalytic surface.
For an instrument calibrated on Pentane, multiply the displayed %LEL value by the con-
version factor above to get the true %LEL.
These conversion factors should be used only if the combustible gas is known.
These conversion factors are typical for a SIRIUS Multigas Detector. Individual units
may vary by ±25% from these values.
Table 9. OXYGEN – Typical Performance Specifications
RANGE
RESOLUTION
REPRODUCIBILITY** 0.7% O
RESPONSE TIME
* See Table 5. Instrument specification, NOTE
** See Table 14. PID Typical Performance Specifications. NOTE
Environment and Oxygen Sensor Readings
A number of environmental factors may affect the oxygen sensor readings, including chang-
es 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%, 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 envi-
ronment 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 at a
temperature within 30 °C of the temperature-of use for the least effect.
0 to 25% O
2
0.1% O
2
for 0 to 25% O
2
90% of final reading
Performance Specifications
2
30 seconds with sample line and
probe (normal temperature range*)
3 minutes with sample line and
probe (extended temperature range*)
8
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