The development of an Ultra Violet (UV) Differential Optical Absorption Spectroscopy (DOAS) fibre-optic sensor for
the monitoring of nitric oxide gases is described in this paper. Experimental results describing the operation of this
sensor with cylinder gases are presented. These experimental results are compared with existing published spectroscopic
absorption measurements. The sensor was developed to operate within an exhaust environment and demonstrate a low
susceptibility to interferences from other gases present. A LabVIEW program was created to interrogate the highest
absorbing wavelength for nitric oxide and calculate the concentrations present before outputting them to the user. The
lower limit of detection for the sensor was found to be 5ppm with response times of 3.4 seconds.
This paper describes a multipass absorption sensor based on an integrating sphere. The sphere has an internal coating
which is highly reflective (over 95%) in the near infrared region and this allows the detection of carbon dioxide (CO2)
gas at 2 &mgr;m. CO2 was detected using a light emitting diode as the emitter and a photodiode as the detector. A two inch
(50.8 mm) diameter integrating sphere was used as an absorption gas cell. A method of calculating the effective path
length of the integrating sphere is also presented. The latter is shown to be dependant on the reflectance of the sphere's
internal surface, the sphere's port fraction and the level of attenuation of the optical signal due to the gas present in the
sphere. Effective optical path lengths of 40 cm at the 2 &mgr;m region are reported. Experimental results demonstrating the
detection of CO2 using a two inch diameter integrating sphere are presented and these are compared to simulation results
based on a CO2 absorption over a 40 cm path length at 2 &mgr;m.
A fibre-optic sensor for the monitoring of hazardous exhaust gases based on absorption in the ultra-violet region is
described. The loss of light through a gas cell across the UV/VIS spectrum was utilised to determine the level of
absorption for three of the exhaust gases present in an exhaust. The measured absorption specific to each of these test
gases Nitrogen Dioxide (NO2), Sulphur Dioxide (SO2) and Nitric Oxide (NO) was used in a variation of the Beer-Lambert law to determine the absorption line intensities for each of the gases. Theoretical absorption line intensities for
each of the exhaust gases compared favorably with our measured results. A LabVIEW program was created and utilised
to interrogate the highest absorbing wavelength for each of the gases and absorption recorded at these specific absorbing
wavelength were then input along with our measured absorption line intensities into the Beer-Lambert law to determine
the concentrations of each of the gases present in the test cell. In this manner the concentrations were calculated
immediately and then output to the user eliminating the need for processing the data after testing. A lower detection
level of 1ppm for both NO2 and SO2 and in the order of 26ppm for NO was achieved.
An optical fibre based exhaust gas sensor has been developed from low-cost mid-infrared components which is capable of detecting carbon dioxide (CO2) emissions from both diesel and petrol engines. The optical fibre sensor is not cross sensitive to other gaseous species in the exhaust such as water vapour (H2O), carbon monoxide (CO), oxides of nitrogen
(NOx) or oxides of sulphur (SOx). Initial tests of this sensor on a modern diesel engine are outlined in this paper.
The reduction of harmful environmental pollutants which can have adverse effects on human health and the development of sensors capable of monitoring low concentrations of these pollutants is a major source of concern for many researchers today. This paper describes a multipass absorption cell used to detect and monitor the presence of several gases in the ultra violet and visible regions. An integrating sphere with a highly reflective internal coating (over 99%) was adapted in order to input and output various gases. Sulphur dioxide was detected in the ultra violet region, ozone in the visible and nitrogen dioxide in both the ultra violet and visible. This paper will report the generation of effective optical path lengths of up to 70 cm using a 5 cm diameter integrating sphere. This results in an optical sensor capable of detecting sulphur dioxide concentrations as low as 10 ppm, nitrogen dioxide concentrations as low as 4 ppm and ozone levels of the order of 500 ppm.
This paper describes two optical based sensors for the detection and quantification of vehicle exhaust pollutants. The first sensor consists of a single pass absorption cell. Broadband light from a deuterium/halogen source was transmitted through the cell from optical fibre and the resulting absorption is detected using a UV spectrometer which was also fibre coupled. The second approach includes an integrating sphere, which has been adapted for use as a multipass absorption cell. An ultraviolet LED was used as an emitter and a photodiode as the detector. Both were mounted directly on the sphere. The single pass absorption cell has been used to monitor nitric oxide, nitrogen dioxide and sulphur dioxide while the integrating sphere has been used to monitor nitrogen dioxide levels. Concentration levels of 10's of parts per million have been measured for each gas and sensor.