US 3524707 A
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Aug.A 18, 1970 J. E, HANSEN, SR., ET AL PULS'IINGA LIGHT SOURCE SMOKE DETECTOR Filed Aug. 14, v 12967 UnitedStates Patent O U.S. Cl. 356-103 3 Claims ABSTRACT OF THE DISCLOSURE An improved smoke detector enclosed in a cylindrical housing having an air smoke inlet at one end thereof in proximity to an internal air pump which causes any arnbient smoke present to pass into a path of collimated light reflections of which are detected by a photo cell and an auxiliary lamp for cancelling out any ambient light reections. The auxiliary lamp and collirnated light source being pulsed out of phase from a pulse generator.
CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part, of an application filed Oct. 23, 1965, Ser. No. 503, 421 for a Fire Detector by Julian E. Hansen, Sr., and Julian E. Hansen, Jr. now issued, Pat No. 3,417,392.
BACKGROUND OF THE INVENTION The present invention relates to a smoke detector and more particularly to an improved smoke detector for detecting extremely small changes in ambient smoke level.
The prior art smoke detectors which utilize the application of solid state photo-conductors to the measurement of small changes in back scattered or reected light as disclosed in the above-referenced co-pending application, have the disadvantage that Where the difference in conductivity of the photo-conductor brought about by the change of light is of the same order of magnitude as the direct current changes in conductivity of the photo-conductor, overall sensitivity is necessarily limited. These changes in conductivity are the result of the slow and almost continuous re-combination of the carriers in the photo-conductor which is particularly true of the cadmium sullide photo-conductors at low light levels and also temperature changes. This instability limits the sensitivity of these devices in lstrictly D C. circuits quite seriously.
According to the invention, a pulsed light is utilized to illuminate the media, resulting in a signal from the photo-conductor which consists of a train of pulses of an an amplitude determined by the amount of reected light reaching the photo cell. Utilizing this pulse light method, the bandpass of the system can be set to eliminate any direct current component as well as those changes occurring at a different frequency from that of the pulsing light. Hence, changes in the D.C. conductivity of the photo cell which may result from temperature or re-combination of carriers as outlined above, will have very little effect on the sensitivity since this component will not be seen.
Although this pulsed light received by the photo-conductor is principally from light scatter produced by smoke particles in the light beam, there will be some reflection from the walls of the housing containing the light source and the photo cell. The light reaching the photo-conductor from these surfaces cannot be distinguished from that produced by the smoke which, again, tends to place a limit on the sensitivity of the device. This second limitation 3,524,707 Patented Aug. 18., 1970 is largely eliminated by the use of a second light which is placed within the housings so that its illumination will fall directly on the photo-conductor. This light is also pulsed, but it is pulsed out of phase with respect to the light forming the columinated beam. The illumination reachingg the photo cell from this light is adjusted to the same intensity as the desired reflections reaching the photo cell from the inner surfaces of the housing of the device. The net result is essentially a constant low-level of illumination on the photo-conductor and therefore, essentially a zero output signal. Smoke in the system causing reections from the collimated light beam will not appreciably affect the light received from the second or auxiliary light and can, for practical purposes, be ignored. Hence, the sensitivity of this type of smoke detector has been increased in Atwo steps, the first being from the utilization of a pulsed light which largely eliminates the effect of the D.C. changes in conductivity of the photo-conductor and the second being utilization of a second pulsed light which is pulsed out of phase with the irst to substantially eliminate the eifects of scattered ambient light reaching the photo cell under quiescent conditions.
Actually, the system will detect very minute changes in reflected light regardless of cause. Hence, it could be' utilized to detect a change in ambient light levelor color spectrum changes as well as foreign particles such as smoke.
An object of the present invention is the provision of an improved smoke detector for detecting changes in ambient levels of smoke.
Another object is to provide an improved smoke detector in which drift, in the sensing elements, does not limit sensitivity.
A further object of the invention is the provision of an improved smoke detector utilizing a photo cell sensing element in which ambient reilected light is cancelled.
Yet another object of the invention is the provision of an improved smo-ke detector which is simple to construct, relatively inexpensive, and requires a minimum of maintenance and adjustment.
Other objects and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing in which the sole figure is a schematic representation of the preferred embodiment of the present invention.
Referring to the drawing, a cylindrical housing 11 has a dust filter 12 at one end and a smoke outlet aperture 13 at another end. A mounting member 14 having a passage 16 is positioned within cylindrical housing 11 and carries mounting members 17 and 18 to which are mounted a fan coil 19 and vibrating reed 21, respectively. 'Fan coil 19 has a pair of leads 22 passing through cylindrical housing 11. A mounting means 23 having an air passage 24 is also carried within cylindrical housing 11. Mounting means 23 carries a main lamp 26 and light baffles 27 and 28 having apertures 29 and 31, respectively. Mounting means 23 also carries photo cell 25. Auxiliary lamp 30 is mounted in cylindrical housing 11. Mounting plug 32 having a smoke outlet aperture therein, carries a 4light-absorbing baille 33.
Multi-vibrator 34 has one output connected to auxiliary lamp 30 and another output connected to main lamp 26. Photo cell 25 is connected to the input of passband amplifier 36, the output of which is connected to the indicator 37.
OPERATION In operation an A.C. current is supplied to fan coil 19 which vibrates vibrating reed 21 which pulls air in through dust filter 12 and passageways 16 and 24 in mounting means 14 and 23, respectively, through light aperture 31 in baie 28, around light-absorbing bale 33 and out through smoke outlet 13. At the same time, multi-vibrator 34 supplies a current to main lamp 26 and auxiliary lamp 30, but as can be seen, the two supplies are out of phase with each other. Hence, during the time the auxiliary lamp is receiving a pulse from multi-vibrator 34, main lamp 26 is not, resulting in their being excited out of phase, i.e., when one lamp is lighted, the other lam pis out. Quiescently, when there is no smoke in the system, reflected light from main lamp 26 will be seen by photo cell 25 resulting in a small output from photo cell 25 When there is no smoke to be detected. This is OIT-set by adjusting the variable resistance- 31 to supply an output from auxiliary lamp 30 which is equal in magnitude but opposite in phase. This will, in effect, cancel the input seen to passband amplifier 36 when there is no smoke in the system.
When smoke enters through dust filter 12 and hence, throughout the length of cylindrical housing 11, a portion of it is passed in the light lbeam from main lamp 26 resulting in an additional reflected light on photo cell 25. Since this smoke will have very little eiect on the direct light from auxiliary lamp 30, an output will be seen from photo cell 25 at the frequency of multi-vibrator 34. This output is passed through passband amplifier 3-6 and indicated in indicator 37. It has been found in the case of cadmium sulfide types of photo cells that a frequency on the order of one half of a cycle per second from multivibrator 34 yields excellent results. This frequency would be varied to an optimum frequency for any particular type of photo cell utilized.
It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.
What is claimed is:
1. A reected light detector comprising:
a sample chamber through which a test sample ows;
a primary pulsating light source of a predetermined frequency, said primary pulsating light source generating a predetermined pulsating light beam which is directed into said sample chamber;
a light sensitive means positioned in proximity to said primary pulsating light beam and out of said predetermined light beam for detecting ambient reflected light in said sample chamber from said primary pulsating light source when no test sample is in said sample chamber and light scattered by a test sample in said sample chamber;
indicating means connected tosaid light sensitive means for indicating relative intensity of pulsating light impinging thereon, said indicating means including passband means for eliminating substantially all frequencies outside of said predetermined frequency; and
an auxiliary pulsating light source positioned in illuminating proximity to said light sensitive means, said auxiliary pulsating light source being pulsed at said predetermined frequency in anti-phase with said primary pulsating light source and having an intensity substantially equal to said ambient reected light reaching said light sensitive means from said primary pulsating light source.
2. The reilected light detector of claim 1 and further including: electrical pulse generating means having irst and second outputs out of phase with each other, said first and second outputs being connected to said primary pulsating light source and said auxiliary pulsating light source, respectively, for pulsating said primary pulsating light source and said auxiliary pulsating light source in anti-phase with each other.
3. The reected light detector of claim 2 and further including: adjustment means for adjusting the relative amplitudes of said primary pulsating light source and said auxiliary pulsating light source.
References Cited UNITED STATES PATENTS 1,746,525 2/ 1930 Darrah. 1,828,894 10/ 1931 Freygang. 2,076,553 4/ 1937 Drinker et al. 2,877,453 3/ 1959 Mendenhall. 2,962,926 12/ 1960 Marak et al. 3,013,466 12/ 1961 Kaye. 3,045, 123 7 1962 Frommer. 3,078,756 2/1963 Barton et al. 3,127,464 3/ 1964 Gustavson. 3,317,736 5/1967 Herrick et al.
RONALD L. WIBERT, Primary Examiner W. A. SKLAR, Assistant Examiner U.S. Cl. X.R.