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3.1 Composition of the controlled atmosphere
It is assumed that the standard composition of the atmosphere is a mixture of gases with the proportions
indicated in table 1.
Ingredient C [% vol] C [ppm]
Nitrogen 78.084 780 840
Oxygen 20.946 209 460
Argon 0.934 9 340
Carbon dioxide 0.0360 360
Neon 0.00181 18.18
Helium 0.00052 5.24
Methane 0.00017 1.70
Krypton 0.00011 1.14
Hydrogen 0.00005 0.50
Xenon 0.000008 0.087
Table 1: Typical composition of atmospheric air
3.1.1 Impact of the presence of a substance in a controlled atmosphere
These sensors combine the advantages and disadvantages of catalytic and semiconductor sensors, react to
most combustible gases, but also to chlorofluorocarbons, aerosols and the like. Therefore, the presence of
such vapours in the environment may trigger false alarms. Particular attention should be paid to:
vapours of paints and solvents, oil paints,
aerosols, perfumes, sprays,
vapours of spirit, gasoline,
condensing water vapour.
The prolonged presence of high working gas concentrations causes a decrease in the sensor's sensitivity.
3.1.2 Effect of oxygen concentration value
The concentration of oxygen affects the operation of the sensor. The sensor should operate in an
atmosphere of standard oxygen concentration.
3.2 Influence of temperature
The temperature of the measured atmosphere affects the characteristics of the sensor. Its influence in the
work of the sensor is compensated electronically.
3.3 Influence of pressure
Within the environmental parameters of the sensor, the influence of pressure on the measurement is
negligible.
3.4 Influence of moisture
Excess moisture affects the sensor's sensitivity. If water is condensed on the sensor and it stays on its
surface for a long time, a decrease in sensitivity will occur.
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p. 3/4 Appendix: PU-Z-033-ENG R02
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