Login (DCU Staff Only)
Login (DCU Staff Only)

DORAS | DCU Research Repository

Explore open access research and scholarly works from DCU

Advanced Search

Development of a fibre optic sensor for methane gas

Sweeney, Jude (1994) Development of a fibre optic sensor for methane gas. Master of Science thesis, Dublin City University.

A fibre optic sensor for methane gas using the "differential absorption" referencing technique has been designed and constructed. Infra red light in the 1.66pm spectral region is absorbed by methane and this is the operating principle of the sensor. The system employs a novel LED, manufactured by GEC Marconi Ltd., as an infra red light source. The LED couples more power into single mode fibre than any other device of its type which is commercially available. The light is transmitted to a gas cell via single mode fibres and a fibre optic coupler, where some of it is absorbed according to the concentration of methane present. Two optical interference filters with transmissions at absorbing and non-absorbing spectral regions, respectively, are used in dual wavelength referencing mode to remove any interferences from non gas dependent parameters (e.g. dust in the cell). A calibration curve for the sensor is determined by plotting the values of the attenuated light signals against the corresponding concentrations of methane in the gas cell. A full characterisation of each component of the system was undertaken and the systems overall performance determined. The system has a limit of detection of 0.077% CH4. This is a factor of 18 below the specification requirement for the project, which is 1.25% CH4 in air (i.e. 25% of the Lower Explosive Limit). The= system has a resolution of 0.025% CH4 and shows both good repeatability and reproducibility. The main problem associated with the system is the critical temperature dependence of the optical interference filters, whose transmissions vary with temperature changes of 0.1°C and therefore affect the system stability.
Item Type:Thesis (Master of Science)
Date of Award:1994
Supervisor(s):MacCraith, Brian
Uncontrolled Keywords:Fiber optics; Methane sensing; Sensors and detectors
Subjects:Physical Sciences > Physics
DCU Faculties and Centres:DCU Faculties and Schools > Faculty of Science and Health > School of Physical Sciences
Use License:This item is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 License. View License
ID Code:19433
Deposited On:02 Oct 2013 15:02 by Celine Campbell . Last Modified 02 Oct 2013 15:02

Full text available as:

[thumbnail of Jude_Sweeney_20130723152753.pdf]
PDF - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader


Downloads per month over past year

Archive Staff Only: edit this record