Gas detector

A gas detector that is arranged to sense the concentration levels of a target gas(es) within a gas sample from an environment surrounding the detector, comprising:

• a laser source(s) that is arranged to transmit radiation through the gas sample at a target wavelength(s) that corresponds approximately to the optimum absorption wavelength(s) of the target gas(es);
• an optical detector(s) that is arranged to sense the intensity of the radiation transmitted through the gas sample at the target wavelength(s) and generate a representative output intensity signal(s) for the target wavelength(s);
• and
• a control system that is arranged to operate the laser source(s) and optical detector(s), the control system having a current driver(s) that is arranged to drive the laser source(s) with a drive current signal(s) that is modulated with a sine wave and a triangle wave such that the signal(s) is simultaneously triangularly ramped and sinusoidally modulated to generate wavelength scanned, and frequency modulated, radiation at or about the target wavelength(s), and wherein the control system generates representative concentration level information relating to the target gas(es) within the gas sample based on the level of absorption of the radiation transmitted into the gas sample at the target wavelength(s) with reference to the representative output intensity signal(s) from the optical detector(s) for the target wavelength(s).

A gas detector that is arranged to sense the concentration levels of target gases oxygen, methane, carbon monoxide, and hydrogen sulphide, within a gas sample from an environment surrounding the detector, comprising:

• four laser sources corresponding to the four target gases, each laser source being arranged to transmit radiation through the gas sample at or about a target wavelength that corresponds approximately to the optimum absorption wavelength of its respective target gas;
• an optical detector or detectors that are arranged to sense the intensity of the radiation transmitted through the gas sample at each of the target wavelengths and generate representative output intensity signals for each of the target wavelengths;
• a gas space through which the gas sample from the environment may flow, the laser sources and optical detector(s) being arranged about the gas space such that the laser sources transmit radiation through the gas sample in the gas space for detection by the optical detector(s);
• an optical system located in the gas space into which the laser sources for carbon monoxide and hydrogen sulphide direct their respective radiation, the optical system being arranged to modify and increase the radiation transmission path length between the laser sources and optical detector(s) for the radiation relative to a direct transmission through the gas space such that the radiation transmission path length is in the range of 20 m-50 m for the radiation at the target wavelength of carbon monoxide and is in the range of 10 m-35 m for the radiation at the target wavelength of hydrogen sulphide;
• and
• a control system that is arranged to operate the laser sources and optical detector(s), and which generates representative concentration level information relating to each of the target gases within the gas sample based on the level of absorption of the radiation transmitted into the gas sample at each of the target wavelengths with reference to the representative output intensity signals from the optical detector(s) for each of the target wavelengths.

A portable hand-held gas detector that is arranged to sense the concentration levels of a plurality of target gases within a gas sample from an environment surrounding the detector, comprising:

• a housing having a gas space through which the gas sample from the environment may flow;
• a plurality of laser sources mounted within the housing about the gas space corresponding to the plurality of target gases, each laser source being arranged to transmit radiation through the gas sample in the gas space at or about a target wavelength that corresponds approximately to the optimum absorption wavelength of its respective target gas;
• an optical detector or detectors mounted within the housing about the gas space that are arranged to sense the intensity of the radiation transmitted through the gas sample at each of the target wavelengths and generate representative output intensity signals for each of the target wavelengths;
• and
• a control system that is arranged to operate the laser sources and optical detector(s), the control system comprising:
• one or more current drivers that are arranged to drive the laser sources with a pre-determined pattern of pulsed drive current signals so as to activate each laser source to transmit radiation at its respective target wavelength sequentially in a pre-determined pattern and cyclical manner one at a time;
• and
• a lock-in-amplifier that is arranged to sequentially amplify and filter that output intensity signals from the optical detector(s) at each of the target wavelengths one at a time in a synchronous manner according to the sequential activation of the corresponding laser sources,
• and wherein the control system generates and outputs representative concentration level information relating to each of the target gases within the gas sample based on the level of absorption of the radiation transmitted into the gas sample at each of the target wavelengths with reference to the filtered and amplified representative output intensity signals from the lock-in-amplifier for each of the target wavelengths.