Browsing by Author "Pride, Russ D."

Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen Access
    Detection of a simulated gas leak in a wind tunnel
    (Iop Publishing Ltd, 2006-01-01T00:00:00Z) Hodgkinson, Jane; Shan, Q.; Pride, Russ D.
    This paper brings together considerations of gas leak behaviour and leak detector design and use, with a view to improving the detection of low-pressure natural gas leaks. An atmospheric boundary layer wind tunnel has been used to study ground-based releases of methane at full scale over distances of up to 3 m, under controlled conditions. These scales are relevant to the detection of natural gas leaks from mains and services using hand-portable gas detectors. The mean spatial distribution of the leaking gas plume was determined and used to test and fit a Gaussian dispersion model. This was used for subsequent analysis with respect to the ability of gas leak detectors to confirm and locate a leak. For ground-based leaks, gas concentrations drop rapidly with height such that instruments should ideally sample the air from within 100 mm of ground level. The rapid dilution of gas with distance from the source means that instruments with lower limits of detection, ideally of a few parts per million, have much improved ability to detect a leak from greater distances downwind. Finally, observations showed the variable temporal nature of the gas and the potential for confusion when sampling gas at a single point in time and space.
  • Thumbnail Image
    ItemOpen Access
    Field evaluation of a multi-point fibre optic sensor array for methane detection (“OMEGA”)
    (Society of Photo-optical Instrumentation Engineers (SPIE), 2000) Hodgkinson, Jane; Pride, Russ D.; Tandy, Chris; Moodie, Dave; Stewart, George
    A multi-point fibre optic sensor array for methane detection (“OMEGA”) has been developed and tested under semiquantitative field conditions. The new system employed wavelength modulation spectroscopy using a DFB laser source scanned across the Q6 methane line at 1.665•m. A branched fibre network connected the single source to up to 64 sensor heads. Controlled releases of natural gas were provided for test purposes within an array of four optical sensors and four pellistor reference sensors. An automated system delivered standard gases to each sensor, to enable routine calibration checks to be carried out. Agreement between the conventional and optical systems was excellent in the range 0-100% LEL (lower explosion limit). The optical system offers a simple, intrinsically safe design with a low cost of ownership per sensor head.
  • Thumbnail Image
    ItemOpen Access
    Imaging of methane gas using a scanning, open-path laser system
    (IOP Publishing Ltd, 2006-02) Gibson, Graham; van Well, Ben; Hodgkinson, Jane; Pride, Russ D.; Strzoda, Rainer; Murray, Stuart; Bishton, Steve; Padgett, Miles
    We have developed an imaging system for the detection and visualization of methane gas leaks. The system is based on a distributed feedback InGaAs laser diode emitting at 1.65μm, the beam from which is directed at neighbouring objects. The backscattered light is collected by a Fresnel lens and the gas concentration is deduced from the reduction in collected intensity as measured using a second derivative wavelength modulation technique. The incident laser and the collected beam are both scanned over an area to form an image of the gas emission. To ease the task of locating the source of the emission, we combine the resulting low-resolution image of the gas emission with a high-resolution colour image of the scene. Our results show that the system can image a gas cloud of 1mm effective thickness at a range of several metres, sufficient to detect a gas leak of 1 litre min−1 in light to moderate winds.
  • Thumbnail Image
    ItemOpen Access
    Methane-specific gas detectors: the effect of natural gas composition
    (Iop Publishing Ltd, 2010-10-31T00:00:00Z) Hodgkinson, Jane; Pride, Russ D.
    Certain gas sensors, particularly those based on optical spectroscopy, have enabled the detection of individual gas species such as methane with low cross-sensitivity to other gases. For gas-specific instruments used to measure natural gas leaks, this paper considers whether it is necessary to consider the other components of natural gas in addition to methane. We have quantified the effect of gas compositional variation on methane-based measurements on the ppm, %LEL and %volume scales. %LEL measurements, important for safety applications, are the most challenging for methane-specific detection. Acceptable levels of error have been drawn from gas detector standards and by comparison with established gas detectors. The fundamental error expected from a methane-specific detector, as a result of variations in gas composition, would be larger than this benchmark on the %LEL scale. However for gas-specific detection, measurement of an additional component such as ethane is shown to reduce the error to below the benchmark level. This has been demonstrated experimentally using an instrument based on tunable diode laser spectroscopy.
  • Thumbnail Image
    ItemOpen Access
    Modelling and interpretation of gas detection using remote laser pointers
    (Elsevier, 2006-04) Hodgkinson, Jane; van Well, Ben; Padgett, Miles; Pride, Russ D.
    We have developed a quantitative model of the performance of laser pointer style gas leak detectors, which are based on remote detection of backscattered radiation. The model incorporates instrumental noise limits, the reflectivity of the target background surface and a mathematical description of gas leak dispersion in constant wind speed and turbulence conditions. We have investigated optimum instrument performance and limits of detection in simulated leak detection situations. We predict that the optimum height for instruments is at eye level or above, giving an operating range of 10 m or more for most background surfaces, in wind speeds of up to 2.5 m s−1. For ground based leak sources, we find laser pointer measurements are dominated by gas concentrations over a short distance close to the target surface, making their readings intuitive to end users in most cases. This finding is consistent with the results of field trials.
  • Thumbnail Image
    ItemOpen Access
    An open-path, hand-held laser system for the detection of methane gas
    (Institute of Physics, 2005-06) van Well, Ben; Murray, Stuart; Hodgkinson, Jane; Pride, Russ D.; Strzoda, Rainer; Gibson, Graham; Padgett, Miles
    We have developed an open-path hand-held gas detector incorporating a distributed feedback InGaAs laser diode at 1.65 µm. Incorporated into a hand-held transceiver unit, the emitted laser beam is backscattered from nearby surfaces, collected and focused onto an amplified InGaAs detector using a 150 mm diameter plastic Fresnel lens. At ranges of 4–5 m, a typical backscattered signal is tens of nanowatts of laser light. Applying second derivative wavelength modulation spectroscopy gives a sensitivity to methane of better than 10 parts per million over a one metre path length. A number of demonstration units have been fabricated and successfully evaluated by end users.