Gas detection apparatus and method

A method of measuring the concentration of a first gas in a sample, the method comprising:

• providing a detector having a sensor responsive to a first wavelength, a sensor responsive to a second wavelength, and a sensor for taking reference readings;
• applying a lineariser function to each of the first and second absorption figures to calculate first and second concentration figures;
• calibrating the sensor for each wavelength for detecting the first gas such that the data at each wavelength gives the same reading when only the first gas is present in a sample;
• analysing a gas sample to obtain a first absorption reading at the first wavelength, a second absorption reading at the second wavelength and a reference reading;
• and
• calculating a first concentration figure (c1) and a second concentration figure (c2) using the reading at the first wavelength, the reading at the second wavelength and the reference reading, and calculating a corrected concentration figure (ccor) indicative of the actual concentration of the first gas in the sample using the equation ccor=c1−X·(c2−c1), in which X=A·(c1/c2)B, where A and B are constants for a particular pair of filter wavelengths chosen depending on the gases which are being looked for in the sample.

A method of identifying the presence of a first gas within a sample, the method comprising:

• providing a detector having a sensor responsive to a first wavelength, a sensor responsive to a second wavelength, and a sensor for collecting reference readings;
• analysing a gas sample to obtain a first absorption reading corresponding to the first wavelength, a second absorption reading corresponding to the second wavelength and a reference reading;
• calculating a first absorption figure using the first absorption reading and the reference reading, and a second absorption figure using the second absorption reading and the reference reading;
• applying a lineariser function to each of the first and second absorption figures to calculate first and second concentration figures;
• calibrating the sensor for each wavelength for detecting the first gas such that the data collected at each wavelength gives the same reading when only the first gas is present in a sample;
• and
• calculating the ratio of the first concentration figure to the second concentration figure, and using the ratio to identify whether only the first gas is present in the sample.

A selective gas detecting apparatus comprising:

• a sensor responsive to a first wavelength;
• a sensor responsive to a second wavelength, and;
• a sensor for collecting reference readings;
• and
• a processor, the processor being configured to:
• calculate a first absorption figure using the reading for the first wavelength and the reference reading, and a second absorption figure using the reading for the second wavelength and the reference reading;
• calculate first and second concentration figures by applying a lineariser function to each of the first and second absorption readings, the sensor for each wavelength being calibrated for detecting the first gas such that the reading for each wavelength is the same when only the first gas is present in a sample;
• calculate the ratio of the first concentration figure to the second concentration figure;
• and
• identify the gas which is present in the sample based on the calculated ratio.