Infrared gas sensing apparatus and method

A gas sensing apparatus for sensing gas that absorbs infrared light at a first wavelength, the gas sensing apparatus comprising:

• an infrared source that emits the infrared light;
• a wavelength tunable filter that selectively allows passage of the infrared light at a specific wavelength;
• a control circuit that includes a measurement circuit and a check circuit, the measurement circuit controlling the wavelength tunable filter, so that the wavelength tunable filter allows passage of the infrared light at the first wavelength and outputs a first filtered infrared light, the check circuit controlling the wavelength tunable filter, so that the wavelength tunable filter allows passage of the infrared light at a second wavelength and outputs a second filtered infrared light;
• an infrared detector that detects a first amount of the first filtered infrared light and a second amount of the second filtered light;
• and
• a housing for accommodating the infrared light source, the wavelength tunable filter, and the infrared detector, the housing having an inlet for introducing the gas therein, wherein
• the measurement circuit calculates concentration of the gas based on the first amount of the first filtered infrared light,
• the check circuit checks whether the wavelength tunable filter operates normally by comparing the second amount of the second filtered infrared light with a reference value,
• the second wavelength is within a wavelength range where atmospheric gases do not absorb the infrared light,
• the check circuit controls the wavelength tunable filter, so that the wavelength tunable filter allows passage of the infrared light at a third wavelength and outputs a third filtered infrared light, the third wavelength being within the wavelength range,
• the infrared detector detects a third amount of the third filtered infrared light as the reference value, and,
• the check circuit calculates a ratio between the second amount and the third amount and checks whether the wavelength tunable filter operates normally based on a deviation of the ratio from one.