US3922655A - Smoke or fire detector - Google Patents

Abstract

The detector comprises a light source and a photosensitive cell located in a container which allows entry of smoke but is impervious to exterior light. Any smoke entering the container affects the cell by reflecting the light from the source onto the cell or by obscuring to a varying extent the light from the source. The light source is a liquid-state or solid-state component and preferably a semiconductor component.

Description

United States Patent l l [l l 3,922,655

Lecuyer Nov. 25, 1975 [54l SMOKE R FIRE DETECTOR 3,409,885 ll/l968 Hall I I I I I 340/237 S 3.474435 l0/l969 White et al,.., 340/237 S U51 Dame Leclyeri Le Fran 3,655,289 4/I972 Walker I I I 356/207 x 73 Assignefil La Detecion Electronique Francaise 3 727,056 4/l973 Enemark .2 340/237 5 X Protecbal vanves' France FOREIGN PATENTS OR APPLICATIONS [22] Filed: Mar. 6, 1973 l,086,870 /1967 United Kingdom 340/237 S l,222,35l 2/1971 United Kingdom 340/237 S [2!] Appl. No: 338,480

Primary Examiner-l0hfl W. Caldwell Foreign Application Priority Data Assistant ExaminerDaniel Myer Mar 7, I972 France .4 724078I2 y. g Or Fi g ll, Mi n. May 26, 1972 France I. 72.19006 Zinn & Macpeak [52] US. Cl. 340/237 5; 250/574; 356/207 57 ABSTRACT [51] Int. Cl. G08B 21/00 Th d t t 4 m d h t 58 Field of Search 4. 340/237 5; 356/207, 208; r 6 comPr'ses a p O 250/574 sItIve cell located In a contaIner which allows entry of smoke but is impervious to exterior light. Any smoke [56] References Cited entering the container affects the cell by reflecting the light from the source onto the cell or by obscuring to UNITED STATES PATENTS a varying extent the light from the source The light 3 31 Fr ygang .4 3 5 source is a liquid-state or solidstate component and 2,437,071 3/l948 Cahusac et al. .I 340/237 S preferably a Semiconductor component 2,537,028 l/l95l Cahusac et al. 340/237 S X 3,226,703 l2/l965 Finkle 340/237 S 9 Claims, 5 Drawing Figures I P 1 I T d I I I 3 5l RIje 7 L1; RELAY 52 OR T0 ALARM R :3 THYRISTOR U.S. Patent N0v.25, 1975 Sheet10f3 3,922,655

U.S. Patent Nov. 25, 1975 Sheet20f3 3,922,655

SMOKE on FIRE DETECTOR The present invention relates to smoke or fire detectors and more particularly to optical detectors of this type.

Heretofore, two types of optical smoke detectors have usually been employed.

The first type is based on the principle of the measure of the obscuration of a source of light by the smoke whereas the second type employs the Tyndall effect and permits measuring the light reflected by particles of smoke when the latter pass through a beam of light issuing from a source of light.

A drawback of these known detectors is that the production of the beam of light essential to the detection requires the use of a light source whose operation is based either on the emission of light from a hot body (an incandescent lamp for example) or on the emission of light from an arc in a gas (neon lamp).

These light sources have a relatively short life, are brittle and sensitive to shocks (the filament is brittle or the electrodes are very close to each other) and have a very low efficiency.

Moreover, when an optical fire detector includes such a light source, the power supplied to the latter requires energy of the order of a watt which results, for a detector installation including a number of detectors, in a high total consumption of energy which must be, moreover, supplied permanently.

As concerns incandescent light sources in particular, they have a very wide spectrum of emission of light whereas the detector usually has a photodetector which is responsive to only a small part of this spectrum.

Further, arc lamps, although selective in respect of their spectrum, require a relatively high voltage supply.

An object of the present invention is to provide a smoke or fire detector which does not possess the drawbacks resulting from the use of the aforementioned light sources.

The invention provides an optical smoke or fire detector comprising a light source and a photoelectric cell which is placed in a container which is impervious to the exterior light but which smoke is capable of penetrating so as to act on said cell by reflection of the light issuing from the light source or by obscuration of the light source, and means for using the signal furnished by said cell, wherein said light source is acomponent in the solid or liquid state and preferably semiconductor component.

The utilisation of such a component results in particular in a very low consumption of energy, a very low voltage power supply and a prolonged detector life.

In order to improve the stability of the detector with respect to temperature and to avoid a drift in the point of rest of a detector of the aforementioned type, the photoelectric cell preferably comprises two photosensitive elements and the detector includes means for acting on said elements respectively by the absorption or obscuration of the light issuing from the light source and by reflection of said light through the medium of particles of smoke which may enter the container.

These features afford several notable advantages over known detectors, namely:

The photosensitive elements may operate in the region of their characteristics corresponding to a low ohmic value so that an improved stability of the measurement is achieved The two phenomena of absorption and reflection are employed simultaneously which have reverse effects on the two photosensitive elements of the cell so that considerable sensitivity results.

On the other hand, the exterior variations (for exam ple, temperature and ageing) have equal effects on the two elements, so that these variations do not affect the point of rest of the detector.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a sectional view of a smoke or fire detector according to a first embodiment of the invention;

FIG. 2 is the circuit diagram of such a detector;

FIG. 3 is a sectional view of a smoke or fire detector according to a second embodiment of the invention;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3, and

FIG. 5 is a circuit diagram of the detector shown in FIGS. 3 and 4.

FIGS. 1 and 2 show a smoke or fire detector according to a first embodiment of the invention and operating by the Tyndall effect.

This detector comprises a cylindrical container 1 preferably made in two parts la and lb which are interconnected by suitable means, as by flanges 2 and screw and nut assemblies 20.

The lower part In has three circular openings 3, 4 and 5 which are masked inside the container by associated screens 3a, 4a, 5a mounted at a distance from the wall of the container so as to constitute labyrinths for the light coming from the exterior.

These screens are covered with a black coating or layer 6, as a mat paint, on the face thereof facing the associated opening. Further, the openings themselves are bordered by mat black coatings 7 so that light which enters by way of the openings 3, 4 and S is ab sorbed as soon as it enters the container, whereas any smoke is free to enter the container.

Two coaxial sleeves 8 and 9 are secured to the vertical wall of the container 1. Their axis is perpendicular to the axis of the latter. The sleeve 8 is adapted to support a source of light 10 with its associated concentrating lens 100. The sleeve 9 has an internal coating of an absorbent coating 11, for example a coating of mat black paint.

The light source 10 is constituted by a component in the solid state. Preferably, it comprises a semiconductor device such as an electro-luminescent diode whose emission spectrum is usually within a very narrow wave band such as the red band ranging from 0.64 to 0.68 micron, the yellow band ranging from 0.58 to 0.62 micron or a green band ranging from 0.52 to 0.56 micron. These diodes are made from a doped material such as gallium arsenide or gallium phosphor, the doping imparting the required colour to the light emitted. For example, there is employed a diode of the type manufactured by Hawlett Packard, reference No. 5082-4403, by Texas Instruments Incorporated, reference No. PL 209 or by General Electric Company, reference No. SSL 22.

Such sources result in the detector consuming a very small amount of electricity, of the order of 20 mW, for an electroluminescent diode, whereas the operating voltage is of the order of a volt.

A printed circuit card 12 is clamped between the flanges 2 of the parts Ia and lb of the container. It has in its centre a circular opening 13 in which is secured a sleeve 14 which is coaxial with the container 1 and supports at its upper end a photosensitive cell 15, such as a photoresistor. The sensitivity range of this photoresis' tor is chosen in accordance with the light source employed and preferably it has its maximum sensitivity in the emission range of this source. The printed circuit card 12 is connected to three conductors 16, 17, 18, the conductors 16 and 17 supplying power to the detector and the third conductor 18 serving to transmit an alarm signal.

A supervising or indicator lamp 19 is provided in the lower wall of the container so as to provide a visual indication of whether the detector is in the alarm condi tion or not. This lamp 19 is connected to the perforated card by a conductor 20.

The components of the detector are shown in the circuit diagram of FIG. 2.

The light source 10 is permanently connected to the supply conductors l6 and 17 through a stabilizing resistor 21. The photosensitive cell is also connected to the supply conductors l6 and 17 through a resistor 22 which forms therewith a voltage divider whose ratio is modified in accordance with the action on or irradiation of the cell 15. The measure signal received at the intermediate junction point 23 of the divider is applied to a thyristor 24 which is connected in series with the lamp 19. The line 18 is connected to the junction of these two components.

When smoke enters the container 1, the light issued from the source 10 is reflected by the particles of smoke and the reflected energy acts on the photosensitive cell 15. On the other hand, in the absence of smoke, the light of the source is totally absorbed by the sleeve 9 and by the black faces of the container. If the amount of smoke exceeds a certain threshold value, the cell 15 increases the potential of the point 23 to such extent that the thyristor 24 is triggered. This returns the conductor 18 to the potential of the conductor 17.

The variation of this potential can be employed for actuating a suitable signalling device such as a siren or the like.

According to a modification which has not been illustrated in the drawings, the cell 15 may be placed directly in front of the light source 10, that is to say in the sleeve 9, so that the smoke, in obscuring the source, modifies the impedance of this cell and results in a variation in the potential of the junction 23.

The circuit shown in FIG. 2 is arranged in a conventional manner on the printed circuit card 12.

According to the second embodiment shown in FIGSv 3 and 4, the smoke detector comprises a cylindrical container 25 which is preferably of metal and comprises two assembled parts 250 and 25b, the part 250 having an internal flange 26 against which a printed circuit structure 27 bears. The latter comprises the electronic circuit of the detector.

The parts of the container 250 and 25b are assembled by means of flanges 28 gripping a plate 29 which forms in the container 25 two compartments 30a and 30b, the compartment 30b constituting the measuring compartment of the detector. The elements 27 and 29 are spaced apart by means of a spacer ring 31.

A photoelectric cell 32 is mounted at the center of the support plate 29 so as to be capable of receiving the light in the measuring compartment 30b This cell is of the differential type and comprises two photosensitive 4 elements 33 and 34 subjected to different levels of illumination.

The wall of the compartment b has inlet apertures 35 through which the smoke can enter the container. These apertures are masked by screens 36 mounted at a distance from the wall of the compartment 30b. The outwardly facing surfaces of the screens are preferably coated with an absorbent material 37 which is also provided on the inside of the peripheral edge portions of the apertures 35. Owing to this arrangement, the surrounding light is prevented from entering the compartment 30b. Formed in the wall of the latter is a housing 38 in which is mounted a source of light 39 of the solid state type as described hereinbefore in respect of the first embodiment of the invention. This source radiates light in a direction perpendicular to the axis of the cylindrical container 25 of the detector and therefore cannot directly act on the photosensitive elements 33 and 34.

The compartment 30b also encloses means for acting on the photosensitive elements 33 and 34 respectively by absorption of the light from the source 39 and by reflection of this light on the particles of smoke which may enter the compartment 30b by way of the apertures 35.

These means comprise, on one hand, a screen 40 constituted by a strip of opaque material, for example metal, secured to the wall of the compartment 30b by means of two tabs 41. Consequently, the screen 40 masks the element 34 from the source 39 and also from the light that this source 30 reflects on the walls of the container 30b.

A plate 42 having a reflecting surface 43 captures the light reflected by the walls of the compartment 30b and reflects it onto the photosensitive element 34. The plate 42 is mounted by means adjusting its position which comprise a screw 45 engaged in a tapped aperture 46 provided in the lower wall of the container 25. This screw terminates in a smooth portion 47 engaged in a sleeve 48 which is integral with the rear of the plate 42. It will be understood that when the screw 45 is rotated in the aperture 46, the plate moves vertically. In other words, by acting on the adjusting screw 45, it is possible to adjust the dimension of the lower portion of the plate 42 which reflects the light in the direction of the photosensitive element 34 and is not masked by the screen 40.

Thus, it is possible, in the absence of smoke in the detector, to balance exactly the quantities of light reach' ing the elements 32 and 33 respectively. In the absence of smoke, the quantity of light which acts on the photo sensitive element 33 is determined by reflection of the light issuing from the source 35 on the walls of the compartment 30b. The quantity of light reaching the photosensitive element 34 is determined by the rays which are received by the plate 42 and are also reflected from the walls of the compartment 30b, However, neither the element 33 nor the element 34 receives the light from the source 39 directly.

The detector further comprises a supervising or inspection lamp L mounted in the lower wall of the container 25.

FIG. 5 shows an embodiment of a circuit which may be employed in the detector shown in FIGS. 3 and 4. This circuit is supplied with d-c current by an exterior source (not shown) through lines 49 and 50. The voltage across these two lines is stabilized by a regulating device constituted by a transistor T a resistor R and a Zener diode Z,, these components being connected in the conventional manner.

The emitter of the transistor T is connected to a re sistor R, which is connected to an electroluminescent diode which constitutes the light source 39 shown in FIGS. 1 and 2. This electroluminescent diode is connected to the line 50.

The junction point between the resistor R and the emitter of the transistor T is connected:

to the photosensitive cell 32 which, in the illustrated embodiment, is constituted by the two photosensitive elements 33 and 34 which are in this embodiment photoresistors;

to the source of a field effect transistor T to a voltage divider constituted by the series connection of a resistor R;,, a potentiometer P, and a resistor R the latter being connected to the line 50.

The control electrode of the transistor T, is connected to the junction point between the photoresistor elements 33 and 34, and the drain of the field effect transistor T is connected to the line 50 through a resistor R This resistor is also connected to the control electrode of a unijunction transistor T and to the line The cathode of this transistor T is connected through a resistor R to the line 50 and its anode is connected to the slider of the potentiometer P The junction point between the resistor R, and the transistor T is connected to an actuating device 51, such as a thyristor or an electromechanical relay, capable of controlling through a line 52 an alarm device outside the connector. The supervising lamp L is connected between the line 49 and the device 51.

This smoke detector operates in the following manner:

If a certain amount of smoke enters the compartment 30b, two distinct phenomena are produced:

The particles which arrive in the light beam issuing from the source 39 reflect a part of this light in the direction of the unmasked photosensitive element 33.

On the other hand, the particles of smoke which enter the space defined by the screen 40 and the walls of the compartment 30b, absorb the light reflected by the reflecting surface 43 of the plate 42.

In this way the photoelectric cell 32 is subjected to a double effect:

1. The resistance of the photosensitive element 33 decreases.

2. The resistance of the photosensitive element 34 increases.

There is therefore a reverse or differential effect on the two photosensitive elements upon entry of the smoke in the compartment 30b which considerably increases the sensitivity of the apparatus.

With reference to FIG. 5, it can be seen that if the resistance of the element 33 decreases and that of the element 34 increases, the voltage at their junction point 53 decreases. This voltage, applied to the high input impedance of the field effect transistor T appears at the low impedance constituted at the output of the field effect transistor T There is therefore a decrease in the voltage at the terminals of the resistor R, and, if this decrease exceeds a certain value (in other words, if the amount of smoke entering the detector exceeds a certain density), the unijunction transistor T is triggered and excites the device 51. Under these conditions, the lamp L lights up and an alarm signal is transmitted to the line 52.

The threshold level at which this detector reacts may be adjusted in a precise manner by means of the potentiometer P which is incorporated in the voltage divider R;,, T R,,.

Note that the circuit just described compensates for variation in the temperature. When a variation in the exterior temperature occurs, this occurs in the same manner for both photosensitive elements 33 and 34 so that the junction point 53 remains at a voltage value or point of rest which is fixed. The same is true when, owing to ageing, the characteristics of the elements 33 and 34 vary.

in the embodiment described hereinbefore, photoresistor elements have been employed. However, other photosensitive elements may be employed and the electronic circuit adapted accordingly.

In a modification, which has not been shown in the drawings, there may be provided, instead of the screen 40 and the reflecting plate 42, a light source (not shown) which acts directly on the photoresistor element 34. In this case, means must be provided for masking the photoresistor element 33 from this source.

The detectors according to the invention provided with a light source of the type described are strong and have a prolonged life with respect to detectors having incandescent lamps or lamps in which there is a discharge in a gas.

The sources employed are, moreover, advantageous in that they may be used with a certain modulation of their supply voltage so that the signal from the photosensitive cell may be coded in an analog or digital manner.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1. An optical smoke or fire detector comprising a cylindrical container, having a support plate attached to and extending across said container, a photosensitive cell having a housing mounted on said support plate, and first and second photosensitive elements mounted within said housing, said first photosensitive element connected to a first output thereof and said second photosensitive element connected to a second output thereof, each photosensitive lement having a signal output, the photosensitive cell being located in the container which is impervious to exterior light but which includes means allowing entry of smoke; a light source located in the container and oriented to radiate light in a direction perpendicular to the longitudinal axis of the container and perpendicular to the axes of said first and second photosensitive elements so as to direct light onto the wall of the cylindrical container; such that upon entry of smoke into the container, the light from the light source is reflected onto the first photosensitive element by particles of smoke, reflecting means located in said cylindrical container to further reflect light reflected by the wall of the container onto said second photosensitive element, said reflecting means located such that upon entry of smoke into the container the amount of light reflected onto said second photosensitive element is decreased; and electrical circuit means connected to the outputs of said cell for differentially associating the signals furnished by the photosensitive elements so as to be able to trigger an alarm signal, said light source being a solid state component.

2. A detector as claimed in claim 1, wherein said light source is an electroluminescent diode.

3. A detector as claimed in claim 1, wherein the container has reflecting inner surfaces, and said means for acting on the photosensitive elements comprise a screen placed in such manner with respect to the second photosensitive element as to mask the second photosensitive element from the light which issues from the light source and is reflected by the reflecting surfaces of the container, and a reflecting device capable of receiving a given quantity of said reflected light from the light source so as to direct it onto the second photosensitive element.

4. A detector as claimed in claim 3, wherein the reflecting device is movably mounted and an adjusting device is combined with the reflecting device to adjust the position of the reflecting device so that the quantity of light directed onto the second photosensitive element may be regulated.

5. A detector as claimed in claim 1, wherein the photosensitive elements are photoresistors,

6. A detector as claimed in claim 5, comprising ter minals of a source of voltage, the photoresistors being connected in series across the terminals and having a junction point, an impedance converting device connected to the junction point and having an output and an actuating device connected to the output of the impedance converting device.

7. A detector as claimed in claim 6, wherein the actu ating device comprises means for establishing a threshold value which is exceeded when a certain quantity of smoke enters the container.

8. A detector as claimed in claim 7, comprising an indicator lamp operatively connected to said actuating device so as to be lighted up when said actuating device is energized.

9. A detector as claimed in claim I, wherein the means allowing entry of smoke comprise light labyrinth means for precluding entry of light.

Claims (9)

1. An optical smoke or fire detector comprising a cylindrical container, having a support plate attached to and extending across said container, a photosensitive cell having a housing mounted on said support plate, and first and second photosensitive elements mounted within said housing, said first photosensitive element connected to a first output thereof and said second photosensitive element connected to a second output thereof, each photosensitive lement having a signal output, the photosensitive cell being located in the container which is impervious to exterior light but which includes means allowing entry of smoke; a light source located in the container and oriented to radiate light in a direction perpendicular to the longitudinal axis of the container and perpendicular to the axes of said first and second photosensitive elements so as to direct light onto the wall of the cylindrical container; such that upon entry of smoke into the container, the light from the light source is reflected onto the first photosensitive element by particles of smoke, reflecting means located in said cylindrical container to further reflect light reflected by the wall of the container onto said second photosensitive element, said reflecting means located such that upon entry of smoke into the container the amount of light reflected onto said second photosensitive element is decreased; and electrical circuit means connected to the outputs of said cell for differentially associating the signals furnished by the photosensitive elements so as to be able to trigger an alarm signal, said light source being a solid state component.

2. A detector as claimed in claim 1, wherein said light source is an electroluminescent diode.

3. A detector as claimed in claim 1, wherein the container has reflecting inner surfaces, and said means for acting on the photosensitive elements comprise a screen placed in such manner with respect to the second photosensitive element as to mask the second photosensitive element from the light which issues from the light source and is reflected by the reflecting surfaces of the container, and a reflecting device capable of receiving a given quantity of said reflected light from the light source so as to direct it onto the second photosensitive element.

4. A detector as claimed in claim 3, wherein the reflecting device is movably mounted and an adjusting device is combined with the reflecting device to adjust the position of the reflecting device so that the quantity of light directed onto the second photosensitive element may be regulated.

5. A detector as claimed in claim 1, wherein the photosensitive elements are photoresistors.

6. A detector as claimed in claim 5, comprising terminals of a source of voltage, the photoresistors being connected in series across the terminals and having a junction point, an impedance converting device connected to the junction point and having an output and an actuating device connected to the output of the impedance converting device.

7. A detector as claimed in claim 6, wherein the actuating device comprises means for establishing a threshold value which is exceeded when a certain quantity of smoke enters the container.

8. A detector as claimed in claim 7, comprising an indicator lamp operatively connected to said actuating device so as to be lighted up when said actuating device is energized.

9. A detector as claimed in claim 1, wherein the means allowing entry of smoke comprise light labyrinth means for precluding entry of light.

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