Measuring and testing – Gas analysis – Detector detail
Patent
1992-06-18
1993-07-13
Warden, Robert J.
Measuring and testing
Gas analysis
Detector detail
338 34, 422 83, 422 98, 436151, H01C 700, G01N 2704
Patent
active
052263096
ABSTRACT:
A highly sensitive and selective sensor for the detection of halogenated compounds comprises a bead of sodium lanthanum fluoride silicate, having the molecular formula NaLa.sub.4 (SiO.sub.4).sub.3 F, in which are embedded two noble metal electrodes, preferably a straight platinum wire near the center and a helical platinum wire near the periphery of the bead. A current passing through the helical wire maintains the sensor temperature at about 550.degree. C. by resistive heating. The electrical resistance between the two wires is deduced from measurements of the current passing through a fixed external resistor when a substantially constant voltage, preferably about 4 volts, is applied between the wires. A decrease in the measured resistance is an indication of the presence of a halogenated compound in the sample of air to which the bead is exposed. The sensor is preferably controlled by a microprocessor or microcomputer that also performs data processing. This system not only detects a halogenated compound of interest, but also measures its concentration.
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Cao Zhuang
Stetter Joseph R.
Dawson E. Leigh
Illinois Institute of Technology
Warden Robert J.
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