GB1190583A - Improvements in or relating to Gas Detectors - Google Patents

Abstract

1,190,583. Luminescent materials and uses thereof. MINISTER OF POWER. 19 Jan., 1968 [19 Oct., 1966], No. 46674/66. Heading C4S. [Also in Division G1] A gas detector comprises a source of radiation causing luminescence in a material retained by a porous or permeable matrix. The gas to be detected, e.g. oxygen, interacts with the luminescent material causing a reduction in the luminescence intensity, which is detected and measured, and recorded or used to operate a warning device. In the particular embodiment described, an ultra-violet glow lamp 6 is used to excite fluorescence in a luminescent material carried by a porous glass plate 9. The fluorescent radiation is detected through an ultra-violet absorbing filter 13 by a photo-cell 14. A reference photo-cell viewing the lamp 6 through a filter 7 similar to filter 8 which is ultra-violet transmissive, is connected in a bridge circuit with the cell 14 so as to compensate for light source intensity fluctuations. The device may be used in two ways. The partial pressure of oxygen in the atmosphere outside the casing may be measured, since the air can diffuse through walls 1, which are of sintered metal, to reach the luminescent material. The molecules of oxygen interact with the excited luminescent molecules and cause a quenching of the luminescent energy and thus a reduction in light out- . put. Alternatively, a sample of gas to be monitored may be passed through chamber 10 via inlet and outlet pipes 11, 12. The device may be calibrated with samples of known oxygen content. Alternative photo-electric and optical arrangements.-Filter 8 may be a Woods glass filter and filter 13 a combination of blue and yellow filters. The detector may be photo-conductive (e.g. CdS cells) or photo-voltaic, or a photo-multiplier may be used. To avoid reflected or scattered light from the source reaching the detector and the use of filters, different configurations of source, matrix element and detector from that shown may be used, e.g. a detector arranged behind or beside the source or viewing a luminescent element attached to a prism. Various two-path systems are described. In those using two detectors, the reference detector instead of viewing the source itself (as shown), views luminescent material not affected by the test gas or material affected by a standard quenching gas, e.g. air. A single detector, two-path system may be used, a light chopper, prisms and mirrors being used to alternately illuminate the detector with sample and reference beams. Luminescent and matrix materials.-Rapid response and high quenching efficiency are obtained using a polycyclic aromatic hydrocarbon such as fluoranthene or pyrene adsorbed in the pores of a porous, glass matrix. The luminescent material is dissolved in cyclohexane for application to the glass, and the solvent evaporated off. These materials are less efficient if carried on a polyethylene, polystyrene or silicone or natural rubber matrix. Naphthalene is also mentioned as a possible luminescent material. The matrix may be protected by a layer of activated charcoal from contaminating vapours. Activation sources.-The following may be used to activate luminescence: a tungsten filament lamp, with or without a suitable phosphor, and using a heat filter; low pressure mercury discharge tube with U.V. transmitting envelope or phosphor; a nuclear radiation source (by itself or with a phosphor); a semiconductor glow or arc discharge source with a phosphor.