Gas sensors

A method of measuring a concentration of a gas, the method comprising the steps of:

• providing a gas sensor for measuring a concentration of a gas, the gas sensor comprising a light source configured to be switched on, to be power controlled to control light being emitted and to be switched off, a measurement volume, a detector configured to receive light that has passed through the measurement volume to output a photo detector signal, an adaptable filter disposed between the light source and the detector and having a measurement state in which the adaptable filter passes at least one wavelength band which is absorbed by the gas and a reference state in which said at least one wavelength band is attenuated relative to the measurement state;
• and a controller connected to each of the light source, the detector and the adaptable filter;
• switching on, with the controller, the light source at a start of a gas sensor operation period such that the light source emits a pulse of light above a predetermined threshold;
• switching off, with the controller, the light source at an end of the gas sensor operation period so as to enter a low power or shutdown mode, wherein the light source is switched off during the low power or shutdown mode;
• controlling, with the controller, power to the light source during said gas sensor operation period, including initiating an initial powering of the light source as a part of the light source emitting the pulse of light, and subsequent to said initiating an initial powering, controlling power to the light source during a measurement stage of the gas sensor operation period as a part of the light source emitting the pulse of light based on controlling the light source to a desired source temperature followed by the light source falling below the desired source temperature, controlling power to the light source during a dark signal stage, following the initial powering and prior to the measurement stage, of the gas sensor operation period as a part of the light source emitting the pulse of light and controlling power to the light source during a ramp-up time, after the dark signal stage and prior to the measurement stage, of the gas sensor operation period as a part of the light source emitting the pulse of light, based on controlling the light source to step-wise or continuously increase the source temperature to surpass the desired source temperature and thereafter to control the light source at the correct source temperature;
• switching, with the controller, the adaptable filter between the measurement state and the reference state comprising changing the adaptable filter between one said measurement state and one said reference state during said gas sensor operation period, subsequent to the light source reaching the desired source temperature and prior to the light source falling below the desired source temperature;
• sampling, with the controller, the photo detector signal during the dark signal stage, subsequent to initiating the initial powering of the light source and prior to the ramp-up time;
• sampling, with the controller, the photo detector signal with the adaptable filter in the measurement state during said measurement stage of the gas sensor operation period and prior to the light source falling below the desired source temperature;
• and
• sampling, with the controller, the photo detector signal with the adaptable filter in the reference state during the measurement stage of said gas sensor operation period, subsequent to the light source reaching the desired source temperature and prior to the light source falling below the desired source temperature.

A gas sensor for measuring a concentration of a gas, the gas sensor comprising:

• a light source configured to be power controlled to control light being emitted and to be switched off;
• a measurement volume;
• a detector configured to receive light that has passed through the measurement volume to output a photo detector signal;
• an adaptable filter disposed between the light source and the detector and having a measurement state in which the adaptable filter passes at least one wavelength band which is absorbed by the gas and a reference state in which said at least one wavelength band is attenuated relative to the measurement state;
• and
• a controller connected to each of the light source, the detector and the adaptable filter, the controller being configured:
• to switch on the light source at a start of a gas sensor operation period to control power to the light source such that the light source emits a pulse of light above a predetermined threshold during said gas sensor operation period and to switch off the light source at an end of the gas sensor operation period, wherein
• the control of power to the light source during said gas sensor operation period includes initiating an initial powering of the light source to preheat the light source to a temperature below a desired source temperature during a pre-heat stage of the gas sensor operation period as a part of the light source emitting the pulse of light;
• the control of power to the light source during said gas sensor operation period includes controlling power to the light source during a dark signal stage, following the initial powering as a part of the light source emitting the pulse of light;
• the control of power to the light source during said gas sensor operation period includes controlling power to the light source during a ramp-up time, after the dark signal stage as a part of the light source emitting the pulse of light, based on controlling the light source to step-wise or continuously increase the source temperature to surpass the desired source temperature and thereafter to control the light source at the correct source temperature;
• the control of power to the light source during said gas sensor operation period includes controlling power to the light source during a measurement stage of the gas sensor operation period as a part of the light source emitting the pulse of light based on controlling the light source to the desired source temperature following the ramp-up time, with the a measurement stage being followed by the light source falling below the desired source temperature;
• to sample the photo detector signal during the dark signal stage;
• to switch the adaptable filter between the measurement state and the reference state, including changing the adaptable filter between one said measurement state and one said reference state during the measurement stage;
• to sample the photo detector signal with the adaptable filter in the measurement state during the measurement stage and prior to the light source falling below the desired source temperature;
• and
• to sample the photo detector signal with the adaptable filter in the reference state during the measurement stage and prior to the light source falling below the desired source temperature.