Smoke Detector With At Least One Smoke Measuring Chamber

Abstract

A device for the detection of smoke or combustion aerosols comprising a supporting member for attachment to the ceiling of a room and a housing dependent therefrom enclosing a detection chamber. This housing is provided with openings for the entry of the ambient or surrounding atmosphere into the confines of the smoke detection chamber. These openings are arranged in two different zones, wherein the opening or openings in an upper zone are spaced at a maximum of 20 mm. from the room ceiling upon which the device is to be mounted and the opening or openings in the lower zone are arranged at the underside or bottom of such housing.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an improved device for the detection of smoke or combustion aerosols which is of the type incorporating at least one smoke detection or measuring chamber consisting of a mounting portion, typically in the form of a support or socket plate, adapted to be secured to the ceiling of a space in which the presence of smoke is to be detected, and a depending housing fastened to the mounting portion and surrounding a smoke detection or measuring chamber, this housing being pierced by apertures or openings permitting entrance of the surrounding air into the detection chamber.

The purpose of a smoke detector is to detect at as early a stage as possible the appearance of smoke or combustion aerosols resulting from the presence of a fire. In this regard, problems of transport play a decisive part. The appearance of smoke at the location of the fire is not sufficient to produce the response of the smoke detector and thus to initiate an alarm condition. To achieve this end, it is necessary that a sufficient quantity of smoke is transported into the detection chamber of the smoke detector. Within the detection chamber the smoke or aerosol particles may then be detected in known manner, for example, by the scattering of light from the path of light emitted by a light source (optical smoke detector), by the alteration of a current in an ionization chamber (ionization fire alarm), or by other techniques such as measurement of changes in conductivity, humidity or ion density of the air in the space.

It is therefore extraordinarily important for all types of smoke detectors, in order to ensure for the earliest possible response of the detector and the sounding of an alarm, to take into account the dispersion characteristics of the smoke from the seat of combustion. It is therefore usual during the design of fire alarm installations to determine the most suitable locations for mounting the smoke detectors through experimental research by trying out different possible locations of a fire.

The manner of smoke dispersion in a space or area has, however, formerly received little consideration in the design and construction of smoke detection devices. It has principally been sought to make the detection chamber as accessible as possible to the surrounding air. In a number of known devices, for example the detection chamber is separated from the external atmosphere merely by a grid-like hood, or by a hood with relatively large grid-like apertures. However, such constructions possess the disadvantage that they are subject to the collection of heavy deposits of environmental dust.

In optical fire alarms the employment of a largely open detection chamber is impossible, since the entrance of external light must be prevented. To this end, the entrance apertures are so formed that there is no direct path from outside into the detection chamber, and light can only enter the chamber after multiple reflections. Hence, the transport of smoke into the detection chamber is correspondingly hindered, which naturally affects the response conditions of the alarm.

It has become known for ionization fire alarms that the detection sensitivity is optimum when the field strength in the detection or measuring chamber is less than 5 V/cm. This relatively low field strength results in the phenomena that the velocity of the ions in the measuring or detection chamber is relatively low. In an open measuring chamber, therefore, even a low velocity of the ambient air is sufficient to affect the ionization current in the detection chamber. Thus, it is necessary to screen ionization fire alarms with low field strength by additional wind screens which, however, again hinders the transport of smoke into the measuring or detection chamber and results in a delayed response of the fire alarm installation.

SUMMARY OF THE INVENTION

Accordingly, there is a real need in the art for an improved smoke detector which effectively overcomes the aforementioned drawbacks of the prior art constructions. A primary objective, therefore, of this invention is to provide just such an improved smoke detector which effectively fulfills this need and obviates the above-mentioned disadvantages associated with the prior art smoke detection devices.

Still a further significant object of the present invention relates to an improved smoke detector which enables the smoke to enter much more rapidly and easily into the detection or measuring chamber, so that an alarm may be given during an early stage of the development of a fire.

Yet a further significant object of the present invention relates to an improved smoke detection apparatus of the mentioned type which facilitates entry of the smoke particles or combustion aerosols into the measuring chamber thereof without impairing the operational integrity of this smoke detection apparatus.

Another noteworthy object of the present invention relates to improved design of smoke detection apparatus wherein the openings or apertures facilitating the entry of smoke or combustion aerosols into the confines of the measuring or detection chamber are arranged at the housing of the smoke detection apparatus in such a fashion that not only is there ensured for a much improved entry of such smoke or combustion aerosols into the measuring chamber without impairing the operational reliability of the smoke detection apparatus, but furthermore, these openings are arrayed in such a way upon the housing that the appearance of the smoke detection apparatus is not diminished or rendered offensive to the eye.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the smoke detection device of the present invention is manifested by the features that the openings provided at the housing enclosing the smoke detection or measuring chamber are arranged in two different zones. Hence, the opening or openings of the upper zone at most possess a spacing of 20 mm. from the room ceiling upon which the smoke detection device is to be mounted, and the opening or openings in the lower zone are arranged at the underside or bottom of such housing.

The invention arises from the observation that because of the heat developed in a fire the smoke or aerosol particles resulting at the seat of combustion at first rise vertically upwards until laterally deflected by an obstruction, usually the ceiling of the room, and then flow downwards again at the side walls of the room. In an overwhelming number of applications, fire alarms are mounted in rooms which have a flat ceiling and vertical walls. In these cases there results directly above the seat of the fire a flow of air directed vertically upwards, but on the ceiling, except for the position directly above the seat of the fire, the air flow is horizontal.

Investigations of fires in different spaces have now led to the recognition that during the early stages of a fire the smoke is transported along the ceiling mainly in the form of a thin layer some 2 - 3 centimeters thick. In order to ensure for the best possible transport of smoke into the detection chamber it is therefore advantageous, on the one hand, to provide entrance openings or apertures at as small a possible a distance from the ceiling of the room through which the smoke can enter into the detection chamber when the detector is not positioned directly above the seat of the fire, and, on the other hand, to provide entrance openings or apertures in the bottom of the detector housing so that as early as possible response is achieved if the detector is positioned directly above the seat of the fire. In addition, damming up or choking of the flow from beneath is prevented if the air can again leave the detection chamber through apertures which are situated as far up as possible at the housing of the smoke detection device.

It is sufficient to provide apertures only in an upper zone lying close under the room ceiling and in a lower zone in the underside of the housing, the other surfaces of the housing being closed. There is thus ensured that not only does the transport of smoke into the detection chamber take place very rapidly, but furthermore the effects of wind and drafts, or in the case of an optical detector, the effect of ambient or scattered light is prevented by the lateral screening.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. 1 shows a partly sectional elevational view of an optical smoke detector designed according to the teachings of the invention;

FIG. 1a is a cross-sectional view of the detector device illustrated in FIG. 1, taken substantially along the line A--A thereof;

FIG. 2 shows a partly sectional elevational view of a first embodiment of ionization type fire alarm;

FIG. 3 depicts in sectional elevation another embodiment of ionization fire alarm;

FIG. 4 is a schematic representation of a typical circuit diagram employed with the ionization detector according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawings, the optical fire alarm illustrated in FIG. 1 consists of a base or mounting portion 1 which serves for mounting the fire alarm device to a horizontal surface 2, usually the ceiling of a room. To base 1 is secured a dependent housing 3 which surrounds a detection or measuring chamber 4. The detection chamber 4 includes a light source 5, for example an incandescent or glow lamp or a discharge lamp specially suitable for pulse operation, e.g. a glow-discharge lamp and a photocell 6. By the term "photocell" there is to be understood any known light-sensitive electrical device such as vacuum or gas-filled photocells, a phototransister, photodiode or photoconductor. A screen 7 prevents light from the lamp 5 falling directly upon the photocell 6. The photocell 6 can therefore receive light only when the light radiated by the lamp 5 in the detection chamber is scattered by particles in the detection chamber, for example smoke particles or combustion aerosols. When the amount of this scattered light exceeds a predetermined amount the photocell triggers an alarm signal. The appropriate electric circuitry necessary for this purpose may be fitted, for example, in the intermediate space 8 in the base 1 and may be so constructed that an alarm is given both by an alarm indicating lamp 9 on the fire alarm device and over conductors or wires to a suitable alarm device at a central signal station.

The housing 3 of the smoke detector possesses a number of openings or apertures 10 and 11 which are arranged in two different zones. In the embodiment of exemplary smoke detection device here shown, by way of example, the oval, almost circularly formed apertures 10 in an upper zone are arranged as near as possible to the upper margin of the housing 3, so that the distance of these apertures or openings 10 from the mounting surface 2, e.g. the ceiling, is less than 20 millimeters. The apertures 10 are arranged in a ring completely around the housing 3, so that when smoke flows across the ceiling in a relatively thin layer in any direction whatever, sufficient smoke enters into the detection or measuring chamber 4 to trigger an alarm. For this reason a generally cylindrical symmetrical construction is very suitable, although embodiments of rectangular or polygonal form in plan are also possible, so long as such smoke entry openings or apertures are provided at every side or lateral surface. Moreover, the form of these openings or apertures 10 is also optional.

Now, at the underside of the housing or casing 3 there are situated the openings or apertures 11 which permit enough smoke-containing air to enter the detection chamber 4 when a vertical flow of air appears. These apertures 11 may be, for example, formed as a wire grid which occupies the whole underside of the housing 3. Furthermore, the underside of the housing 3 need not be planar or flat as shown in the exemplary embodiment of FIG. 1, but may be domed or in the form of a spherical segment, a truncated cone, or possess some other suitable geometrical form.

In optical detectors it is necessary to prevent external light from entering into the detection chamber 4. Even when, in order to overcome the effects of external light, the lamp is operated in a pulsed condition, with a correspondingly tuned receiver circuit, disturbances and false alarms may occur if it should happen that an external light source has the same frequency. The detection chamber 4 must therefore be additionally screened against the entry of light, but this screening should hinder as little as possible the entrance of air. In the embodiment illustrated, this additional screening consists of vertical lamellae 12, which are in part bent and interfit with one another in such a manner that no direct optical path extends from the exterior to the interior of the detection chamber. On the other hand, at least one flow path for the passage of air extends from each external opening into the interior of the chamber, each said flow path being composed of joined rectilinear portions which do form oblique angles at their junctions. None of the paths in the detection chamber includes an acute angled bend, which would greatly hinder the circulation of air. In this manner it may be ensured that no direct light can enter the detection chamber, but that the circulation of air is hindered as little as possible. A further advantage of the illustrated arrangement of bent lamellae 12 is that the photocell 6 does not receive any light emitted by the lamp 5 and reflected only once on a wall surface.

FIG. 2 depicts an ionization fire alarm device which consists of a supporting or mounting member 13 in the form of a base plate or socket which serves for attachment of the fire alarm device to a horizontal surface 14, such as the ceiling of a room. To the mounting member 13 there is secured or arranged a downwardly depending housing 15 enclosing a detection or measuring chamber 16. Chamber 16 includes a central electrode 17 which carries a radioactive substance 18. The air in the measuring or detection chamber 16 is ionized by this source of radiation 18 and an ion current flows between the central electrode 17 and the housing 15 which forms the other electrode of the ionization chamber. If smoke or combustion aerosols appear in the detection chamber 16, this ion current changes. In order to be able to evaluate this change of current the detection chamber 16 is connected in series with a resistance element, here shown as constituted by a reference ionization chamber 19 which is approximately inaccessible to smoke particles. The common central electrode 17 which carries a further radioactive preparation or substance 20 within the reference chamber 19, is connected with an electric circuit which triggers an alarm over conductors or leads connected with an alarm installation and actuates an individual indicating or alarm device 21 at the detector proper. This electric circuit is advantageously constructed as a printed circuit 22, which may be fitted to one of the surfaces of the mounting member 13, as shown. This flat arrangement in which the space occupied by the electrical circuit 22 is positioned centrally within the ionization fire alarm device and does not extend downwards more than 30 millimeters from the ceiling permits air to flow freely through the detection chamber 16. For the same reason, the reference ionization chamber 19 is recessed into the support or mounting surface 14 above the mounting member 13.

The housing 15 is provided in its cylindrical upper part with a ring of openings or apertures 23, here shown as vertical slits, though they may take other forms. The separation of these slits from the mounting surface 14 again amounts to less than 20 millimeters, so that smoke flowing in a thin layer in any direction whatever across the surface 14 may traverse the detection chamber 16 without any substantial hindrance. In the underside of the housing 15 are situated further narrow openings or apertures 24 which ensure that when a flow of air rises from beneath, the smoke-containing air likewise enters the detection chamber 16 without substantial hindrance. In this case apertures 23 afford free exit for the rising air and prevent any damming up or choking of the flow in the detection chamber 16. The form of the lower apertures 24 is again optional; they may be, for example, constructed as a screen or grid or as radial slits.

FIG. 3 shows a further embodiment of ionization fire-alarm device which is particularly suitable for use when any damage to the supporting surface is to be avoided, or where a technical appearance would be damaging, for example, in elegantly appointed or model rooms, museums, dwelling houses, and so on. Despite this, the technical advantages approximate those which are obtained in the embodiments previously described.

Thus, it will be observed that to the ceiling 25 of the room is fastened a mounting or supporting member 26 in the form of a base plate or socket, which here has the shape of a truncated cone, so that smoke-containing air flowing across the ceiling is guided to the upper rim of a housing 27. The cylindrical or somewhat conical housing 27, of which the generatrices preferably are inclined to the vertical at an angle not exceeding 10.degree., again encloses the detection or measuring chamber 30 provided with a central electrode 28 carrying a radioactive preparation or substance 29. There is again recessed into the mounting member 26 a reference ionization chamber 31 with a further central electrode 32 likewise carrying a radioactive preparation or substance 33. The reference ionization chamber 31 is made so flat that a neat mounting of the device on the supporting surface 25 is possible without the central electrode 28 projecting too far downwards. The electrical circuit 34 of the ionization fire alarm device is in the form of an encapsulated integrated circuit disposed between the two central electrodes 28 and 32, as shown.

In this case, the apertures or openings of the upper zone may consist of a continuous annular slit 35, preferably not exceeding 8 millimeters in width, between the supporting member 26 and the housing 27, at a distance of less than 20 millimeters from the mounting surface 25 and not more than 10 millimeters from the supporting member 26. The housing 27 is connected with the supporting member 26 by widely spaced narrow bridges or ribs (not shown) which may interrupt the otherwise continuous slit. By this arrangement it may be ensured that the smoke-containing air easily deflected by the truncated conical mounting member 26 can flow without substantial hindrance into the detection chamber 30, and that an alarm can therefore be given at the earliest possible moment.

The apertures or openings of the lower zone are here formed as a continuous annular slit 36, preferably of a width not exceeding 5 mm. The bottom 37 of the housing may be flat or may be conical, the generatrices of the cone being inclined to the horizontal of an angle of not more than 10.degree., and is again fastened by narrow bridges or ribs (not shown) to the surrounding wall 27, these ribs may thus interrupt the otherwise continuous annular slit 36. It is an additional advantage of this construction that dust which enters the interior of the detection chamber 30 through the aperture or apertures 35 can fall out again through the aperture or apertures 36. It is noticable that by the limiting of the apertures to a minimum and by forming them as slits, which in suitable embodiments may appear to be merely grooves, very decorative embodiments may be constructed which may be employed even in rooms in which a technical appearance is undesirable. Despite the intrinsically disadvantageous small areas of the apertures, it is ensured by the arrangement of the apertures at advantageous positions in conjunction with the construction of the supporting member and a special construction of the detection chamber that the transport of smoke into the detection chamber is so little hindered that this ionization fire-alarm device does respond and yield an alarm at a very early or incipient stage in the development of a fire.

As shown in FIG. 4, ionization chamber 110 is electrically connected to any suitable detector-amplifier circuit generally represented as numeral 112. A conventional relay and alarm circuit 114 is also provided to operate in conjunction with the threshold detector-amplifier circuit 112. Thus, if smoke or combustion gases enter the measuring or ionization chamber 110, detector circuit 112 triggers the alarm. Typical circuitry which can be employed with the ionization device of the present invention has been disclosed in commonly assigned Swiss Pat. No. 446,131, published Mar. 12, 1968 which corresponds to U.S. Pat. No. 3,521,263. Additionally, U.S. Pat. No. 3,500,360 to N. Abe (issued Mar. 10, 1970) and U.S. Pat. No. 3,233,100 to Lampart (issued Feb. 1, 1966) also disclose suitable circuits.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. A device for the detection of smoke or combustion aerosols comprising a supporting member arranged for attachment to the ceiling of a room, a housing dependent from said supporting member and enclosing a detection ionization chamber, said chamber containing ionization means, said housing being provided with aperture means arranged in two separate zones defining an upper zone and a lower zone, said upper and lower zones being separated by a continuous impermeable zone, said aperture means of said upper zone being spaced substantially entirely not more than 20 millimeters from the room ceiling upon which the detection device is to be mounted and said aperture means of said lower zone being arranged at the bottom of said

2. The device defined in claim 1, wherein said aperture means of said upper

3. The device as defined in claim 1, wherein said aperture means of said

4. The device defined in claim 1, wherein said detection ionization chamber is responsive to smoke or combustion aerosols passing through said aperture means, said ionization chamber being connected electrically in

5. The device defined in claim 4, wherein said resistance element is a

6. The device defined in claim 4, wherein the space within the detection device occupied by said electrical circuit means is situated centrally in the detection device and does not extend downwards more than 30

7. The device defined in claim 1, wherein said aperture means of the upper zone are constituted by a substantially continuous annular aperture having

8. The device defined in claim 7 wherein said annular aperture is separated from said supporting member by a distance not exceeding 10 millimeters.

9. The device defined in claim 1, wherein said aperture means of the upper zone are constituted by substantially annular aperture means having a

10. The device defined in claim 1, wherein said aperture means of said lower zone are constituted by a substantially continuous annular slit

11. The device defined in claim 1, wherein said aperture means of said lower zone are constituted by slit means having a width not exceeding 8

12. The device defined in claim 1, wherein said housing is substantially

13. The device defined in claim 1, wherein said housing possesses the form of a truncated cone, the generatrices of which are inclined to the

14. The device defined in claim 1, wherein the bottom of said housing is

15. The device defined in claim 1, wherein the bottom of said housing possesses the form of a cone, the generatrices of which are inclined to

16. The device as defined in claim 4, wherein said detection chamber is equipped with an upper electrode and a lower electrode, said housing being devoid of said aperture means in the region thereof spanning between said upper electrode and said lower electrode.