Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1994-03-25
1995-08-08
Allen, Stephone B.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356336, 356438, 250237R, G01N 1506, G01N 2149
Patent
active
054401453
DESCRIPTION:
BRIEF SUMMARY
This invention relates to construction of a sampling chamber for pollution detectors particularly smoke detectors and particularly to various aspects of the chamber construction including a light absorber module, a flashlight reflector module both mountable in the chamber and a modified chamber construction.
DESCRIPTION OF PRIOR ART
Previous work in this field has culminated in several US patents in my name including U.S. Pat. No. 4,714,347--Flash Reflector, U.S. Pat. No. 4,665,311--Smoke Detecting Apparatus, U.S. Pat. No. 4,607,915--Light Absorber and U.S. Pat. No. 4,781,065--Anemometer.
Prior art pollution detectors comprised a sampling chamber which included a cylindrical cavity in a metallic tube comprising some thirty assembled and manufactured parts to absorb light reflected off the internal walls off the tube and including coupling tubes for allowing air flow through the chamber. Between the coupling tubes a sealed reflector and window for a Xenon flash tube was positioned to irradiate any polluting particles entrained in the sample air within the chamber. The chamber at one end included an extremely sensitive light detector and a light absorber at the other end acting to prevent any stray reflected light being retransmitted to the light receiver. The sampling chamber 10 includes a series of irises spaced along the length of the chamber adapted to absorb and dissipate light reflected off the walls of the chamber. Coupling tubes are provided to circulate ambient air from an area under fire surveillance or pollution surveillance into the chamber into a region which is subject to light from the flash tube.
It is intended that light scattered from tiny fragments and molecules entrained in the sample air are directed along the length of the sample tube to impinge on the light receptor to give a reading of pollution in the sample air. Extreme accuracy has been obtainable with the detector of my previous patents and it is the objective of the present invention to further improve the efficiency and ease of construction of the sampling chamber and the various components therein.
The light sensing apparatus comprises a solid state photo cell responsive to low levels of light connected to an impedance matching buffer stage, a gain controlled amplifier stage and an output amplifier stage; a gain control network controlled by a temperature sensor for receiving an amplified signal from said output stage the gain being adjustable to compensate the temperature dependence of the photo cell signal.
The absorber as described in U.S. Pat. No. 4,607,915 includes a central light receiving conical surface inclined by at least one annular truncated conical surface to provide at least one annular groove or valley surrounding the central cone and wherein one wall of the groove or valley is optionally undercut to shade the base of the groove or valley from direct impinging light.
The U-shaped reflector described in U.S. Pat. No. 4,714,347 includes a concave reflecting element to focus light from each cross-sectional element of the arc of ionised gas in a flash tube, the light output from the whole length of the tube being focussed into the central region of the sampling chamber.
DESCRIPTION OF INVENTION
The present invention relates to three specific aspects of contemplated improvements as disclosed in the following specification.
Sample Chamber Construction
The sample chamber is essentially of a two part preferably moulded plastic construction having a pair of matching interlocking pairs and including as an integral part a series of spaced interlocking baffles forming a series of irises spaced therealong when the two interlocking pairs are connected together and in position. The chamber includes simple tongue and groove connections incorporating a rubber seal. A focussing lens is held in one of the apertures for focussing reflected light onto the light receptor. The lens is frictionally held between resilient fingers integrally formed in the chamber body.
The interior surfaces of the sampling chamber are finished in
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Allen Stephone B.
I.E.I. PTY. Ltd.
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