Method for analysing a gas using an optical sensor

A device for determining an amount of a gas species in a gas, the device comprising:

• a light source configured to emit an incident light wave that propagates to the gas, the incident light wave lying in an absorption spectral band of the gas species;
• a measurement photodetector, configured to detect a light wave transmitted by the gas, at various measurement times, in a measurement spectral band, and to measure a measurement intensity thereof;
• a reference photodetector, configured to measure a reference intensity of a reference light wave emitted by the light source, in a reference spectral band, at the various measurement times;
• and
• a processor, programmed to implement actions, on the basis of the reference intensity and of the measurement intensity, the actions comprising, at each of the various measurement times:
• on the basis of the reference intensity measured by the reference photodetector, taking into account a correction function representative of a variation in an intensity of the incident light wave in the measurement spectral band relatively to an intensity of the incident light wave in the reference spectral band;
• and
• estimating an amount of the gas species, on the basis of:
• the measurement intensity measured by measuring, with the measurement photodetector, the measurement intensity of the light wave transmitted by the gas, in the measurement spectral band comprising the absorption spectral band,
• the reference intensity measured by measuring, with the reference photodetector, the reference intensity of the reference light wave, the reference light wave being emitted by the light source in the reference spectral band, and
• the correction function taken into account when taking into account the correction function representative of the variation in the intensity of the incident light wave in the measurement spectral band relatively to the intensity of the incident light wave in the reference spectral band;
• wherein:
• the correction function is established beforehand in a calibrating phase, by comparing, at various temperature levels, or at various supply-current levels, the light intensities emitted, by a test light source, in the measurement spectral band and in the reference spectral band, respectively, the test light source being considered to be representative of the light source used in emitting the incident light wave that propagates to the gas, at each measurement time;
• and
• during the calibrating phase, use is made of a calibration gas, the calibration gas comprising a concentration of the gas species, the concentration being constant or considered to be zero.

A method for measuring an amount of a gas species present in a gas, the gas absorbing light in an absorption spectral band, the method comprising:

• a) placing the gas between a light source and a measurement photodetector, the light source being configured to emit an incident light wave, the incident light wave propagating through the gas to the measurement photodetector, the light source being passed through by an electrical supply current, so as to bring the light source to a temperature value;
• b) illuminating the gas with the light source;
• c) measuring, with the measurement photodetector, a measurement intensity of a light wave transmitted by the gas, in a measurement spectral band comprising the absorption spectral band;
• and
• d) measuring, with a reference photodetector, a reference intensity of a reference light wave, the reference light wave being emitted by the light source in a reference spectral band;
• wherein b), c) and d) are implemented at a plurality of measurement times;
• the method further comprising, at each measurement time:
• e) on the basis of the reference intensity measured by the reference photodetector, taking into account a correction function representative of a variation in an intensity of the incident light wave in the measurement spectral band relatively to an intensity of the incident light wave in the reference spectral band;
• and
• f) estimating an amount of the gas species, on the basis of the measurement intensity measured in c), of the reference intensity measured in d), and of the correction function taken into account in e);
• wherein:
• the correction function is established beforehand in a calibrating phase, by comparing, at various temperature levels, or at various supply-current levels, the light intensities emitted, by a test light source, in the measurement spectral band and in the reference spectral band, respectively, the test light source being considered to be representative of the light source employed in b), at each measurement time;
• the calibrating phase is carried out using a theoretical expression that defines an emission intensity of the test light source as a function of the temperature of the test light source and of wavelength, the calibrating phase being carried out considering a wavelength in the measurement spectral band and a wavelength in the reference spectral band, respectively;
• and
• the calibrating phase comprises determining an ageing function, relating an ageing of the test light source, in the reference spectral band, to an ageing of the light source, in the measurement spectral band, the method being such that the correction function is determined on the basis of the ageing function.