Selective leak-detector for natural gas

A selective detector apparatus of natural gas and of other combustible gases which is designed to distinguish between natural gas on the one hand, which is composed principally of a mixture of methane and ethane having a ratio between 100:1 and 20:1, and on the other hand other combustible gases such as methane, ethane, CO, H.sub.2, gasoline vapors, propane or others, the apparatus comprising:

• an NDIR detector channel sensitive to methane gas and providing a first output signal which varies as a function of the concentration of methane gas;
• an NDIR detector channel sensitive to ethane gas and providing a second output signal which varies as a function of the concentration of ethane gas;
• a non-specific combustible detector sensitive to combustible gases and providing a third output signal when combustible gases are present;
• a gas analysis chamber having a gas inlet and a gas outlet and including said NDIR detectors and said non-specific combustible detector;
• first ratio determining means receiving said first and second signals and providing a ratio output signal indicating the ratio of methane to ethane;
• first comparator means indicating the presence of natural gas when said first ratio falls in the range between 100:1 and 20:1;
• and further comparator means receiving said first and third output signals and said ratio signal to provide an indicator of and identity of other combustible gases or H.sub.2 or CO.