Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1991-09-20
1993-08-17
McGraw, Vincent P.
Optics: measuring and testing
By particle light scattering
With photocell detection
250574, 25022711, 356339, G01N 2149
Patent
active
052373860
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to particulate detecting and optical coupling arrangements. One such arrangement may be used within a system intended for sensing the presence of particulates within a gaseous or liquid medium; the medium is illuminated and the light scattered by any particulates present in the medium is collected by the optical coupling arrangement and transferred to a suitable photo-detecting device.
SUMMARY OF THE INVENTION
According to the invention, there is provided a particulate detecting arrangement, comprising light directing means for directing a beam of light into an area in which particulates may be present whereby the light is scattered by any such particulates, and light detecting means positioned to receive such scattered light and to respond to it and to detect it, characterised in that the light directing means is a laser and the light detecting means is an avalanching photo-diode.
According to the invention, there is also provided an optical coupling arrangement for collecting light present within a predetermined area as a result of the presence of particulates therein and for coupling the said light to light detecting means, characterised by an elongate optical member having a longitudinal dimension substantially greater that its transverse direction and extending longitudinally into the enclosure from wall means thereof and adapted to receive the said light and to transmit it to and to focus it onto the said light detecting means situated outside the enclosure.
According to the invention, there is further provided an optical coupling arrangement for focussing light onto light detecting means, characterised by lens means providing a thermal barrier.
DESCRIPTION OF THE DRAWINGS
Particulate detecting and optical coupling arrangements embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which:
FIG. 1 is a partial cross-section through one of the arrangements;
FIG. 2 is a partial cross-section through another of the arrangements; and
FIG. 3 is a partial cross-section through a further one of the arrangements .
DESCRIPTION OF PREFERRED EMBODIMENTS
The arrangement of FIG. 1 incorporates a chamber 10, part of whose wall is shown at 12, in which flows the medium in which the presence of particulates is to be sensed. The medium may be gaseous or liquid. A light source (not shown), preferably a laser beam, illuminates the medium within the chamber 10. Any particulates present within the medium will scatter the impinging light and the purpose of the optical coupling arrangement to be described is to collect the scattered light and to detect it by means of a photo-detector, thereby indicating the presence of the particulates.
The photo-detector is shown generally at 14 and comprises, in this example, an avalanche-type photo-detector. The sensitive area of the detector 14 is shown at 16 and it incorporates an integral light pipe 18 which conducts light from its face 20 to the sensitive area 16.
The optical coupling arrangement includes a graded index rod lens 22 which extends through a bore 24 in the wall 12 of the chamber 10 and has a face 25 which is optically coupled to the light pipe 18 and the face 20 of the photo-detector by means of a UV-cured adhesive 26. The rod lens 22 extends well into the chamber 10 and has a metal collar 28 attached adjacent its inner face 30 by means of UV-cured adhesive 32. The metal collar 28 supports a lens 34 which is in the form of a complete sphere and which is attached to the collar 28 by means of further UV-cured adhesive 36.
The photo-detector 14 has to be maintained at a stable temperature for effective operation. For this purpose, the detector is mounted within a metal block 40 and a Peltier-type solid state cooling device 42 is sandwiched between this block 40 and the wall 12 of the chamber. The Peltier device acts as a heat pump, collecting heat from the block 40 and the photo-detector 14 and transferring it to the wall 12 of the chamber
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patent: 4328488 (1982-05-01), Yanai et al.
patent: 4752131 (1988-06-01), Eisenlauer et al.
patent: 4799756 (1989-01-01), Hirschfeld
patent: 4859864 (1989-08-01), Smith
patent: 4896048 (1990-01-01), Borden
Kidde-Graviner Limited
McGraw Vincent P.
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