Browsing by Author "Davenport, John"
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Item Open Access Formaldehyde sensor using non-dispersive UV spectroscopy at 340nm(International Society for Optical Engineering; 1999, 2014-05-22T00:00:00Z) Davenport, John; Hodgkinson, Jane; Saffell, John R.; Tatam, Ralph P.; Berghmans, F.; Mignani, A. G.; De Moor, P.Formaldehyde is a volatile organic compound that exists as a gas at room temperature. It is hazardous to human health causing irritation of the eyes, nose and throat, headaches, limited pulmonary function and is a potential human carcinogen. Sources include incomplete combustion, numerous modern building materials and vehicle fumes. Here we describe a simple method for detecting formaldehyde using low resolution non-dispersive UV absorption spectroscopy for the first time. A two channel system has been developed, making use of a strong absorption peak at 339nm and a neighbouring region of negligible absorption at 336nm as a reference. Using a modulated UV LED as a light source and narrowband filters to select the desired spectral bands, a simple detection system was constructed that was specifically targeted at formaldehyde. A minimum detectable absorbance of 4.5 × 10-5 AU was estimated (as ΔI/I0), corresponding to a limit of detection of approximately 6.6 ppm for a 195mm gas cell, with a response time of 20s. However, thermally-induced drift in the LED spectral output caused this to deteriorate over longer time periods to around 30 ppm or 2 × 10-4 AUItem Open Access A measurement strategy for non-dispersive ultra-violet detection of formaldehyde in indoor air: Spectral analysis and interferent gases(Institute of Physics, 2015-12-14) Davenport, John; Hodgkinson, Jane; Saffell, John R.; Tatam, Ralph P.We have conducted an extensive review of published spectra in order to identify a region with potential for detection of formaldehyde in indoor air. 85 chemicals and chemical groups common to the indoor environment were identified, 32 of which had absorption spectra in the UV-vis region. Of these, 11 were found to overlap with the formaldehyde UV region. It was found that the region between 320 to 360 nm is relatively free from interference from indoor gases, with NO being the only major interferent. A method is proposed for a low resolution (3 nm) spectroscopic detection method, specifically targeted at formaldehyde absorption features at 327 nm with a reference at 334 nm. 32 ppb of NO was found to have a cross-sensitivity with equivalent magnitude to 100 ppb of formaldehyde. A second reference at 348 nm would reduce this cross-sensitivity.Item Open Access Noise analysis for CCD-based ultraviolet and visible spectrophotometry(Optical Society of America, 2015-08-17) Davenport, John; Hodgkinson, Jane; Saffell, John R.; Tatam, Ralph P.We present the results of a detailed analysis of the noise behavior of two CCD spectrometers in common use, an AvaSpec-3648 CCD UV spectrometer and an Ocean Optics S2000 Vis spectrometer. Light sources used include a deuterium UV/Vis lamp and UV and visible LEDs. Common noise phenomena include source fluctuation noise, photoresponse nonuniformity, dark current noise, fixed pattern noise, and read noise. These were identified and characterized by varying light source, spectrometer settings, or temperature. A number of noise-limiting techniques are proposed, demonstrating a best-case spectroscopic noise equivalent absorbance of 3.5×10−4 AU for the AvaSpec-3648 and 5.6×10−4 AU for the Ocean Optics S2000 over a 30 s integration period. These techniques can be used on other CCD spectrometers to optimize performance.Item Open Access Non-dispersive ultra-violet spectroscopic detection of formaldehyde gas for indoor environments(Cranfield University, 2018-02-21 11:11) Davenport, John; Hodgkinson, Jane; Tatam, RalphData to support the publication Non-dispersive ultra-violet spectroscopic detection of formaldehyde gas for indoor environments J. J. Davenport, J. Hodgkinson, J. R. Saffell and R. P. Tatam IEEE Sensors Journal DOI 10.1109/JSEN.2018.2795042Item Open Access UV spectroscopic instrumentation for formaldehyde detection in the indoor environment(Cranfield University, 2014-01) Davenport, John; Hodgkinson, Jane; Tatam, Ralph P.The aim of this project was to assess the feasibility of using UV spectroscopy for a simple detection system for formaldehyde gas in the indoor environment. Formaldehyde gas is hazardous to human health causing irritation of the eyes, nose and throat, headaches, limited pulmonary function and is a potential carcinogen. Formaldehyde derivatives are used in plywood and fibre board, carpeting, fabrics and some paints. The gas can be emitted from these materials and can build up in the indoor environment. Current methods for detecting formaldehyde gas that are simple, reliable and inexpensive are limited. A literature study of chemicals common to the indoor environment was carried out, and their UV absorption spectra compared to that of formaldehyde. 85 substances and substance groups were considered, 11 of which had absorption spectra that overlapped with the formaldehyde UV absorption band. A region was found between 320 and 360nm with very little spectral interference. Given the number of gases considered, this was a surprising result. Formaldehyde has several strong absorption peaks between regions of very low absorption, allowing for low resolution detection using a single LED source. Two prototype detection systems were developed. The first used a UV LED light source and used a beam splitter to provide one detection channel and one reference channel. The channels used narrow band (laser-line) optical filters. It was thoroughly optimised for noise performance, giving a best case limit of detection of 4.2ppm, limited by source fluctuation and shot noise, and LED thermal drift. Future developments could include a temperature controller inside the casing of the LED, or a multi- pass gas cell to increase sensitivity. With only two channels, the two filter system was susceptible to spectral interference from nitrogen dioxide and nitric acid. The second prototype system was developed using a novel method of passing un-collimated light through a laser-line filter to produce multiple wavelength channels with an angular spread. The principle was validated using two-channel detection with a limit of detection of 6ppm.