Non-dispersive infra-red (NDIR) sensors work by measuring the amount of IR light absorbed by the target gas in a fixed volume. Gas concentration is proportional to the amount of light absorbed as it passes through the gas.
The amount of light absorbed by the target gas, and hence measurement accuracy, is influenced by external environmental factors. The absorption of IR light is dependent on the number of gas molecules present in the fixed volume. Three factors influence the number of molecules in this fixed space, the gas concentration, gas temperature and gas pressure. To accurately measure gas concentration, it is therefore important to understand the effects of temperature and pressure.
The general behaviour of a gas, due to changes in temperature and pressure is based on well understood laws. However, the effects of temperature and pressure on the absorption of infra-red light by gas molecules and how they influence measurement accuracy are less well understood.
Changes in ambient temperature and pressure will induce CO2 concentration measurement errors unless corrected. This application note describes the impact of temperature and pressure on measurement accuracy and how these effects can be compensated. |
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