A novel gas concentration monitor using a solid state modulator


Fairley, P.D. and Rutt, H.N. (2001) A novel gas concentration monitor using a solid state modulator. Sensors and Actuators B: Chemical, 75, (3), 192-196. (doi:10.1016/S0925-4005(01)00760-2).

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Description/Abstract

In this paper, we demonstrate the application of a novel solid state modulator in monitoring the concentration of a test gas. A widespread cost-effective method of gas concentration monitoring currently uses a blackbody source and pyroelectric detector combined with a filter to isolate the required infrared spectral region. Presently the intensity on the detector is modulated by either a mechanical chopper or by electrically-pulsing the source. The device described by this work uses a continuously-driven blackbody source with a novel solid state infrared modulator operating in the 8–14 μm band to generate the required change in intensity on the pyroelectric detector, eliminating the need for moving parts. The modulator may be incorporated into the detector’s optical window in a more-compact future device. The modulator operation is outlined, and the results of determining the concentration of SF6 test gas in a dedicated cell are compared for the solid state modulator and a mechanical chopper.

Item Type: Article
Additional Information: Thin films of titanium dioxide (TiO2) powder, dispersed in poly(vinylidenfluoride) and deposited on glass slides containing gold electrodes, are used as sensors for benzene, ethanol and methanol vapours at room temperature. The resistance of the films at a potential difference of 1.5 V is determined when the films are exposed to atmospheres containing these vapours with concentrations over the range 150–350 ppm. The relative resistance, ΔR, of the films increases linearly with increasing concentrations of the vapours (regression coefficients, r=0.90, 0.98 and 0.97 for benzene, methanol and ethanol, respectively). The findings are consistent with the TiO2 films having p-type semiconductor characteristics. The responses of the films are reversible with changes in ΔR of 0.042, 0.1 and 0.122% ppm−1 for benzene, ethanol and methanol, respectively. The response times to increasing concentrations of the vapours are about 1, 2 and 2 min for benzene, ethanol and methanol, respectively, and the corresponding values for decreasing concentrations 5, 6 and 6 min, respectively. The limit of detection for the vapours is about 10 ppm. With improvements in the sensitivity, selectivity and stability, the films could form the basis of a handheld instrument for the atmospheric monitoring of benzene.
ISSNs: 0925-4005 (print)
Related URLs:
Keywords: germanium, infrared, solid state, modulator, chopper, gas sensing, SF6
Subjects: T Technology > TP Chemical technology
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Divisions: University Structure - Pre August 2011 > Optoelectronics Research Centre
ePrint ID: 13667
Date Deposited: 12 Jan 2005
Last Modified: 27 Mar 2014 18:03
Contact Email Address: hnr@ecs.soton.ac.uk
URI: http://eprints.soton.ac.uk/id/eprint/13667

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