Technology that uses a tunable laser to detect small quantities of methane gas will allow gas leaks to be identified more quickly and accurately, according to its developers.
The Vogue project, which includes researchers from Siemens and the University of Glasgow, has built a portable imaging system that uses the spectral absorption of gas to detect leaks from a distance of up to 30m.
A laser is directed at a surface from where a leak is suspected, such as a wall or road. The surface scatters a small proportion of the light back towards the instrument, where it is collected using a lens. Analysis of the optical absorption spectrum of the returned light allows calculation of the level of gas in the intervening space.
A reference cell containing a sample of the gas to be detected is integrated into the laser module. By calibrating the laser’s signal beam with the gas in the cell, users can tell when gas of the same absorption rate is present.
Bob Rhodes, who worked as part of the Vogue project for UK company Semelab, helped develop the laser module for the system. ‘We used a laser that is tunable through the range where we expected the absorption-rate of the gas to be. If the signal beam bounced back with the same absorption band, then you knew the same gas had been detected as is in the reference cell,’ said Rhodes.
The Vogue system also produces an image of the leak to allow quick, accurate analysis of the area where it is occurring.
During testing, the laser was sensitive enough to detect leaks with flow rates of less than five litres/min, and which were the equivalent of a gas cloud just 1mm thick.
The electronics were then miniaturised so that the commercial prototypes produced by Siemens and Glasgow University are no larger than a handheld camera.
The system can be used to detect a number of different gases. However, as the DFB (Distributed Feedback) lasers used are only tunable within a narrow field of around three to four nanometers, the laser and the gas it is going to detect must be roughly within the same range.
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