GB2309080A

GB2309080A - Light scattering type smoke sensor

Info

Publication number: GB2309080A
Application number: GB9707434A
Authority: GB
Inventors: Tetsuya Nagashima
Original assignee: Hochiki Corp
Current assignee: Hochiki Corp
Priority date: 1993-09-07
Filing date: 1994-09-02
Publication date: 1997-07-16
Anticipated expiration: 2014-09-02
Also published as: GB2309079B; GB2309080B; GB2309079A; GB9707433D0; GB9707434D0

Description

is 1 _Or 2309080 LIGHT SCATTERING TYPE SMOKE SENSOR L(CAT,E The present

invention relates to a light scattering type smoke sensor for sensing_smoke by detecting light scattered by smoke.

In a light scattering type smoke sensor of this kind, labyrinth members constitute a smoke detecting chamber which allows smoke to efficiently enter from the outside and cuts off light entering from the outside, and optical axes of light emitting and receiving sections are disposed in such a manner that their optical axes intersect each other in the smoke detecting chamber to detect light scattered by the smoke.

As a light emitting device constituting the light emitting section, such a conventional light scattering type smoke sensor uses an infrared LED (light emitting diode) having a relatively wide directional angle of 30 to 60. Conseguently, the scattering angle at which the optical axes of the light emitting and receiving sections intersect, and the shapes and reflection angles of the labyrinth members have to be designed so that the light receiving section is prevented from directly receiving 1 i g h t of the relatively wide directional angle from the.nirared LED.

- i 1 ' ,-A In the convent ional light scattering type smoke sensor, the light emitting device has a relatively wide directional angle. When the sensor is constructed to reduce its therefore, a part, oLE direct 1 i g h t - From the 1 -1 g h ?-- e -n 11: n g device and light reflected by the labyrinth members enter the light receiving device, thereby increasi.ng the zerc-po-nc level. This croduces a problem in that such a sensor cannot he constructed in a thin form.

The zero-pcii:: level means an output of t h e 1 i ch i receiving device obtained when there is no smoke in the smoke detecting chamber. if the licht receivIng device receives reflected light when there is no smoke in the smoke detecting chamber, the zero-point level is naturally increased so as to deteriorate the SIN ratio and reliability.

If the placing a lens device in order light emitting section may be assembled by or the like in front crE the light emitting to reduce the directional angle of the ligh! em-ttin:7 section tc Zh_in the sensor, the p_reduction ccsz cf the light emitting section is increased and a positional error in assembly between the light emitting device and the lens causes the light beam to be deviated in direction so that the sensor have to be assembled in a high!,,- accurate manner to -irn,,z)air the pr2duct-i,,-itv thereof.

In a light scattering type smoke sensor of this kind, the light receiving section has to reCeive only light by smoke. rjamely, the Qos.L'--Jons, shapes and ancles 2 - of the labyrinth members have to be designed so that the light receiving section is prevented from receiving direct light from the light emitting section multi-reflected light which is reflected at a plurality of times by the labyrinth members. However, the conventional light scattering type smoke sensor is designed without paying sufficient ccnsidera7-ion on this point, thereby producing a problem in that the zero-point level is increased.

Recently, in the view point of the i-zerior of a room, external appearance of a device or the like, the demand for constructing a sensor of this kind in a thin form is increasing.

in the above-described conventional light scattering type smoke sensor, however, the light emitting device has a relatively wide directional angle. Even when the sensor is constructed so as to have a thin form, therefore, direct light from the light emitting device is vertically reflected by the ceiling and bottom faces of the smoke detecting chamber, and the reflected light and light which is again reflected by these faces and the labyrinth members enter the light receiving device to increase the zero-point level. This produces a problem in that such a sensor cannot be constructing in a thin CD r rp,. In addition, when the ceiling and bottom 'Laces of the smoke detecting chamber are soiled, the ze--3- point level is turther increased.

- 3 To comply with this, a configuration in which a throttle (opening) or a hood is disposed in front of the licht emitting device may be emoloved. However, this conil.-.L'guration has problems in that all the light emitted from the light emitting device cannot eLfec:-i,,-ely be used, and that the cost of the sensor is increased.

The configuration in which a throttle (opening) for reducing the projecting area ell the light emitting device is disposed can prevent the le,.,el being increased.

In this configurazion, ho.wever, all the l-ic7ht ernitted 1from the light emitting device cannot effectively be used, with the result that the signal level due to light scattered by smoke is lowered.

The invention has been conducted in view of the above Problem,5 in the conventional light scattering device. It is an object ci: the invention to provide a scattering type smoke sensor in which the zero-point level of the detection output of a light receiving section can be lowered to a level as low as possible, thereb-,; enhancing the reliability. It is another object of the invention to provide a light scattering type s,-,.oke sensor in which, when the sensor is constructed in a thin form, the zero-point: level of the detec-,ion output be lowered, thereb.,- the In order to attain the objects, the light scattering type smoke sensor of the invention comprises: a plurality of labyrinth members for facilitating an inflow of smoke entering from the outside, and for cutting off light entering from the outside; a plurality of smoke inlets each of which is formed by a space between paired ones of the labvrinth members, the paired labyrinth members being adjacent to each other; A- smoke detecting chamber which is formed in a center portion by the labyrinth members; a light emitting device for radiating light toward the smoke detecting chamber, the light emitting device having a half-value anale of substantially 10' or less; and a light receiving device for detecting light scattered by the smoke in the smoke detecting chamber, the light receiving device having an optical axis which intersects in the smoke detecting chamber an optical axis of the light emitting device at a scattering angle in the range of substantially '00 to 80'. One of the labyrinth members is a labyrinth member which intersects the optical axis of the light emitting device in a substantially center portion of the member, and which has a reflecting face for reflecting light radiated from the light emitting device, and the re-Flecting face reflects the liQht in a direction opposite to the light receiving device.

In the light scattering type smoke sensor,even when the accuracy of assembling the light emitting device and the light receiving device is low or the optical axis c-.' the light emitting de.,ice is deviated, a:)art of direct from the - 5 light emitting section and light reflected by the lab. ri nth members are prevented from entering the light recei,.-.L'ng section. Therefore, the zero-point level can be lowered by such a simple structure.

Particularly, in order to attain another object of: the present invention, a thinned light t-,,,pe smoke sensor according to the invention a light scattering type smoke sensor comprises: a plurality of labyrinth members for faci lite- n- an inflow of smoke entering Erom the outside, and for cutz:inc off:

light entering from the outside; a pluralitv of smoke inlets each c-,' which is f=med by a space bet-ween paired ones c.,' the labyrinth members, the paired labyrinth members being adjacent to each other; a smoke detecting chamber which is formed in a cenzer portion b.,, the labyrinth members; a light emittina device for radiating light toward the smoke detecting chamber; and a light receiving device fo-- detecting light scattered by the smoke in the smoke detecting chamber, the light re-je-J-,,-;,ng device having an optical axis which intersects in the smoke detecting chamber an optical axis of the light emitting device.

The projecting area heght of a face Cf o-t-ical axis of the of the light emitting device is within a the lab,,,,rinth member which - inters-act-c the light emitting device. In this case, the projecting area means an area of the inside 3f --he hall' value anz Tn the scattering type smoke sensor, the,ertic:al direct light from --he ligh 6 regard i ng t: emittin- device is reflected only by the labyrinth member intersecting the optical axis of the light emitting section, and is not reflected by the ceiling 1. ace and the bottom face of the smoke detecting chamber so that the zero- point le-.,el _is lowered.

is In the accompanying drawings, Fig. 1 is a diagram showing a plan view and a side section view of an embodiment of the sca--r-e.-.Lngtype smoke sensor according to the invention; Fig. section view 2(a) is a diagram showing a plan view and a side of the embodiment of the light scattering type smoke sensor according to the invention; Fig. 2(b) is a diagram showing a plan view oil the embodiment of the light scattering type smoke sensor according to the invention; Fig. 3 is a diagram showing a lighr emitting device used in the light scattering type smoke sensor according to the invention; Fig. 4 is a diagram showing a half-value angle of a light emitting device used in the light scatterinc type smoke sensor according to the invention; Fig. 5 is a diagram of a first embod,,ent- c the licht scattering type smoke sensor according to the inveniion; Fig. 6 is a diagram of a second embedimeni of the s,:atter.,ng type smoke sensor according to the -inven--ion; 1 0 Fig. 7 is a diagram showing the relationship between the projected plane projected by a light emitting section and an window of a light receiving section in the second embodiment of the light scattering type smoke sensor according to the invention; Fig. 3 is a diagram showing the relationship bet-ween the projected plane projected by the light emitting section and a viewing field of the light receiving section in the second embodiment o:E the light scattering:llipe smoke sensor ac--ordin: to the invention;

Fig. 9 is a diagram of a third embodiment c,-- the light scattering type smoke sensor according to the invention; Fig. 10 is a diagram of a fourth embodiment of the light scattering type smoke sensor according to the invention; Fig. 11 is a graph showing the relationship between a half-value angle of a light emitting device and an 5/N ratio in the light scattering type smoke sensor accc)rc.ng to the invention; and Fig. 12 is a.graph showing the relationship between a scattering angle and a zero-ocinz output in the light S-attering type smoke sensor aczording to the invention.

Hereinaf:ter, the detailed description cl' the preferred c-E the cresent invention will be reference to the acc-ompanying drawings.

p - is Fig. 1 shows a plan view of an embodiment of the light scattering type smoke sensor according to the invention, and a section view and an appearance of a holder for a light emitting devic:e 12 as seen from the side, and Fig. 2 shc-.,7s a section view and an appearance of a holder for a light receiving device 13 as seen from the side. in the side views sho...;n in 1 and 2, the light emitting device 12, the light receiving device 13, and an insect net 5 are not shown.

In Figs. 1 and 2, a smoke detecting section body 2 is formed in a substantially cylindrical shape, and an upper wall 8 is attached to the ceiling. On the upper wall 8, a pluralty of labvri,n.--h members 9 are fcrme-J in a standing manner so that a smoke detecting chamber is formed in an area surrounded by the labyrinth members 9. The labyrinth members 9 are formed in such a manner they facilitate the inflow of smoke from the outside, and cut off light entering from the outside. Smoke inlets Sa formed by spaces bet-ween adjacent labyrinth members 9 are covered by an insect net 5 surrounding the labyrinth members so that insects are prevented from invadinz the smoke detecting chamber and scattering light. An opening of the bottom is opposite to the upper wall 8) o_f the smoke detecting section body 2 is covered by a cover which is not shown.

On the upper wall 3, moreover, holders 10 and -11, and a light- shielding plate I"11 are disposed in a standing manner. The holders 10 and 11 are formied as recess oortions in which z /2 the light emitting device 12 and the light receiving device 13 for detecting smoke are resPectively accommodated in such a manner that optical axes of the light emittinz device 12 and the light receiving device 13 intersect each other at the center of the smoke detecting chamber constituted by the labyrinth members light radiated by reaching the light are respectively restricting their device 13 does not 9. The licht shielding plate 14 the light emitting device 12 from receiving device 13. The holders prevents directly and 11 provided with windows 22 and 21 -0viewing fields so that the light receiving directly receive light emitted by the light emitting device 12. The light emitting device 12 and the holder 10 having the window 22 constitute a light emitting section for detecting smoke, and the light receiving device 12 and the holder 11 having the window 21 constitute a light receiving section for detecting smoke.

It is oreferable that the licht emitting device 12 accommodated in the holder 10 is a device having a so-called half-value angle el of substantially 10' or less as shown in Figs. 3 and 4. half-value angle means an angle at which the output power P is reduced to a half value. In the light emitting device 12, preferably, its front end is formed by an epoxy lens 12 or the like so that light radiated by a tip 12b is converged, thereby attaining the half-value angle 61 of substantially 10' or less.

- 10 1 In order that the viewing field of the light receiving device 13 in the smoke detecting chamber is restricted only to the front area thereof, the labyrinth member 91 which intersects the optical axis of the light emitting device 12 is longer than the other labyrinth members 9, and a gap 20 is formed between L-he front end of the labyrinth member 91 and the light shielding plate 14. A width of the aap 20, for example, about 3 to 5 mm. All the labyrinth members 9 are structured in such a manner that front end faces 011a -thereof are not directed to the light emitting face of the light emitting de,,--ice 12, and the flat portions 91b which are reflecting faces for reflecting the light are formed at such an angle that they reflect light radiated by the light emitting device 12 not in the direction toward the light receiving face of the light receiving device 13, but in the direction toward the outside for escape. Namely, each of the labyrinth members 9 has the end face 91a at the end adjacent to the smoke detecting chamber, which the face is directed away from the light emitting windo-w 22 of the light emitting device 12, and the flat portions 91b reflect the light in a direction opposite to the window 21 of the light receiving device 13.

The labyrinth member 91 intersects the optical axis of the light emitting device 12 at a substantially center portion of the reflecting face of the labyrinth member 91. Preferablv, the position of the labyrinth member 91 is adjusted in accordance with the length of the member as follows.

Embodiments of the invention which are applied to the above-described light scattering type smoke sensor will be described.

I) First Embodiment Fig. 5 is a diagram showing a first embodiment of the light scattering type smoke sensor according to the invention.

The light emitting device 12 has a so-called half-value angle el of substantially 10' or less at which the output power P is reduced to a half value. The light emitting device 12, and the light receiving device 13 are disposed in such a manner that a scattering angle e2 at which their optical axes intersect each other is in the range of substantially 601 to 0 The labyrinth member 91 which intersects the optical axis of the light emitting device 12 is formed in such a manner that the reflecting face does not face the light receiving race or the light receiving device 13 and forms a reflection angle e3 of substantially 450 to the optical axis of the light emitting device 12. When an extension face of the labyrinth member 91 which inte--sects the optical axis of the light emitting device 12 are nearer to the center of the smoke detecting chamber than those of the window 21 of the light receiving face 21 of the light receiving device 13 as shown in Fig. 2(b), for example, the reflecting face does not 'Lace the light receiving face of the light receiving device 13.

12 is The light emitting device 12, and the light receiving device 13 are disposed in -the following manner: The angle at which. the optical axes of the devices intersect each other, namely, the scattering angle e2 is set to be substantially 60' or more so that the light receiving device 13 does not directly receive light emitted by the light emitting device 12, and also to be substantially 80' or less so that the light receiving device 13 does not receive primary reflected light which is reflected by the labyrinth member 91.

Preferably, the above-mentioned angle 62 formed by the holders 10 and 11 which are shown in Fig. 2 and into which the light emitting device 12 and the light receiving device 13 are to be accommodated is set to be substantially 70'.

The labyrinth members 9 are formed in such a manner that the front end faces 91a are not directed to the light emitting face of the light emitting device 12, and at such angles that the flat portions 91b do not reflect light radiated by the light emitting device 12 in the direction toward the light receiving face of the light receiving device 13, but 1 iL reflect the light in the direction toward the outside for escape. In order to reflect light from the light emitting device 12 in the direction opposite to the light receiving device 13, the labyrinth member 101 is preferably formed in such a manner that, for example, the angle e3 to the optical axis o' light emitting device 12 is substantially 45'.

13 II) Second Embodiment Fig. 6 is a diagram showing a second embodiment of the light scattering type smoke sensor according to the invention. In the figure, positions of components are approximately indicated. In order to facilitate the illustration, the smoke detecting body 2 is formed in a substantially cylindrical shape or has the shape in the horizontal direction which is substantially circular, and the light emitting device 12 is apparently located at a point A on the circle.

In order that the light receiving device 13 does not receive primary reflected light which is reflected by the labyrinth member 91 intersecting the optical axis of the light emitting device 12 located at the position A, the labyrinth member 91 is formed in such a manner that the reflecting face does not face the light receiving face of the light receiving de;ice 13 and the reflection angle to the optical axis AD of the light emitting device 12 is substantially 45', and the light receiving device 13 is disposed in such a manner that its viewing field does not include an area of the reflecting 'Lace of the labyrinth member 91 and passes a substantially center por--icn 0 of the smoke detecting chamber. The labyrinth member 1,31 intersects the optical axis at a substantially center portion of the reflecting face of the labyrinth member 91. The position of the labyrinth member 011 have to be --djusied in acccrdance with the length of the member.

14 - The light receiving device 13 is cc)nrigured have a viewing field angle of substantially 20' or order not to directly receive light from the light device 12, moreover, one end of the v-indo-.. 21 cfreceiving device 13 is located at a posItion separated by substantially 15' or more f_---= one end light receiving section side (which is i n the so as to less. In emitting the light which is B of the direction opposite to the reflection direction of the labyrinth member 91) of the projected plane BC which is projected by the light emitting device 12 for the labyrinth member 91. In this case, the pr)jected plane means a plane which _Js a part oLLE the wall of the smoke detecting 2 where from the light emitting device 12 is not to receive secondary reflected light by the labyrinth member 91 and is then labyrinth member, further-more, -the licht end is 450 or more from the other end C of the side is in the reflection direction of the labyrinth member 91) opposite to the light receiving section of the projected plane BC.

iNext, the range of the scattering angle will be described with reference ?--o Figs. 7 and 8. -,.;her, a device having a so-called half-value angle 01 of 10 at which the outQut oower P is reduced to a half value is used as the surface of an inner the light emitted projected. In order which is reflected reflected by another rece-;-.-.;na device 13 is disposed in such a manner that one of the viewing field of the light receiving device 13 located at a position F which is separated by substantially - is discosed so as not to see the member 91 emitting device 1.2 as shown in Fig.. 7, the angle BOD subtended at the center 0 by an plane BD which is a half of the projected plane is 20'. As described above, in order that the light receiving device 13 does not directly receive light from the light emitting device 12, one end of the windo-w 21 of the light receivinc device 13 is located au the pos-t-3n E which is separated by substantially 15" or more from one end B of the light receiving section side of the projected plane BC projected by the light emittIng device 12 (the center of the window 21 is at 150 + ci), and the light receiving device 13 is reflecting face of the labyrinth in other wcrds, in the same manner as Embodiment 1, the labyrinth member 91 which intersects the optical axis of the light emitting device 12 is disposed in such a manner that the reflecting face does not face the light receiving face of the light receiving device 13.

When the optical axis of the light receiving device 13 passes the center 0 of the smoke detecting chamber so as not to;n=lude an area of the reflecting face of the labyrinth member 91, the diameter ct of the smoke detecting chamber is 50 mm, the window 21 is separated from the smoke detecting chamber center 0 by a distance of 10 mm, and the diameter t of the window is 5 mm, the angle a subtended at the smoke detecting chamber center 0 b-,- the area between optical axis of the light rec:eiving device 13 and one end (i.e., the po-sition E) of the 2-1 is as follows:

cy = tan' ( 2. 5 mmI 10 miii) 15C, Therefore, the scattering angle 6 formed bY the optical axis of the light emitting device 12 and that o..L= the light receiving device 13 is obtained from the following expression:

e = 20cl + 15-- + 15c = 500 with the result of 6 > 50'.

In order that the light receiving device 13 does not receive secondary reflected light due to the labyrinth members other than the labyrinth member 91, the light emitting device 12 and the light receiving device 13 are disposed in such a manner that, as shown in Fig. 8, the viewing field of the light receiving device 13 is located at the position F which is separated by substantially 451 or more (in the figure, 45' +) from the other end C of the projected of the light emitting device 12. When the viewing field angle of the light receiving device 13 is 200 as shown in Fig. 7, the angle 0 subtended at the smoke detecting chamber center 0 by the area between the optical axis of the light receiving device 13 and the position which is ser)arated by 45' from the other end C of the projected plane projected by the light emitting device 1-2 is obtained from the following expression:

25s-in = (25 10)sin20c ,. 0 = 280 - 25C Therefore, the scattering angle 0 in this case obtained from the following expression: e = 18oo - (200 + 4511 + 250) = 9011 2 with the result of e < 900. From Exs. (1) and (2), 50c < 6 < 900. According to the above-deszribed configuration, consequently, the condition of 50' < scattering angle e < go, which is considered to be appropriate for detectinc lic:ht scattered by smoke is attained, and moreover the condition of scattering angle E) 70' which is considered t:o be most appropriate is attained.

III) Third Embodiment Fig. 9 is a diagram showing a side view and a plan view of a third embodiment of the light scattering type smoke sensor according to the invention. In the figure, positions of components are approximately indicated.

in order to facilitate the illustration, the smoke detecting body 2 is formed in a substantially cylindrical shape or has the shape in the horizontal direction which is substantially circular, and the light emitting device 12 is apparently located at a point A on the circle. The light emitting device 12 located at the point A, and the labyrinth member 91 which intersects the optical axis of the light emittinci device 12 are disposed in such a manner that the projecting area (el in the figure) of the light emitting device - is - 12 is within the height H (i.e., the height of the interior of the smoke detecting chamber) of the face of the labyrinth member 91. In this case, the projecting area means an area of the inside of the half value angle. Specifically, the height H of the labyrinth member 91 In this case, the projecting of the half value angle.

Regarding the horizontal direction, in order that the light receiving device 13 does not receive primary reflected light due to the labyrinth member 91 which intersects the optical axis of the light emitting device 12, the labyrinth member 91 is formed in such a manner that the reflecting face does not face the light receiving face of the light receiving device 13 and forms a reflection angle of substantially 450 to the optical axis AD of the light emitting device 12. In the same manner as Embodiment 1, the light receivina device 13 is disposed in such a manner that its viewing field does not include the reflecting face of the labyrinth member 101 and passes a substantially center portion 0 of the smoke detecting chamber. The light receiving device 13 is disposed so as not to receive direct light -Erom the light emitting device 12 and also secondary reflected light which is reflec-ted by the labyrinth member 91 and is then reflected by another labyrinth member.

in the embodiment, when the distance between the apparent position _k of the light emitting device 12 and the is substantially 20 mm or less. area means an area oL the inside 19 remotest position of the reflecting face of the labyrinth member 91 is indicated by L, and the height of the labyrinth member 91 is indicated by 11, the embodiment is so configured that a so-called half-value angle el at which the output Dower P of the light receiving device 13 is reduced to a half value becomes as follows:

el < tan-" H/2L In a thin smoke sensor in which the height H of the interior of the smoke detecting chamber is 20 mm or less, the light emitting device 12 of el < 100 is selected in consideration of variation in an assembling process.

According to this configuration, direct light from the light emitting device 12 is reflected only by the labyrinth member 91 and is not reflected by the ceiling face and the bottom -Lace (the face opposite to the ceiling Lace) of the smoke detecting chamber, and therefore the zeropoint level can be lowered.

IV) Fourth Embodiment Fig. 10 is a diagram showing a side view and a plan vie-w of a fourth embodiment of the light scatter-ing type smoke sensor according to the invention. In the figure, positions of components are approximately indicated. In order to facilitate the illustration, the smoke detecting body 2 is formed in a substantially cylindrical shape or has the shape in the horizontal direction which is substantially circular, and the - 20 is light emitting device 12 is apparently located at a point A on the circle. The light emitting device 12 located at the point A is disposed in such a manner that a so-called halfvalue angle 61 at which the output power P is reduced to a hal.L value is substantially 5 to 100 and the radiation range is within the height H (i.e., the height of theinterior c-E the smoke detecting chamber) of the face of the labyrinth member 91 which intersects the optical axis of the light emitting device 12. Specifically, the height H c-f the labyrinth member 91 is substantially 20 mm or less.

Regarding the horizontal direction, in order that the light receiving device 13 does not receive primary reflected light due to the labyrinth member 91 which intersects the optical axis of the light emitting device 12, the labyrinth member 91 is formed in such a manner that the reflecting face does not face the light receiving 'Lace of the light receiving device 13 and forms a reflection angle of substantially 451 to the optical axis AD of the light emitting device 12. The light receiving device 13 is disposed in such a manner that its viewing field does not see the reflecting face of the labyrinth member 91 and the optical axis passes a substantially center portion 0 of the smoke detecting chamber - which is ahead of the front end of the labyrinth member.9l. In the same manner as::'mdod-.m.ent 1, also, the light receivJng device 13 is disposed so as not to receive direct licht from the lic:'1-lt emitting device 12 and secondary reflected light which has been 21 reflected by the labyrinth member 91 and is then reflected by another labyrinth member.

In order to confirm the effect cl the above-described embodiment, experiments shown in Figs. 11 and 12 were conducted.

Fig. 11 shows experimental data obtained in measurements in which light emitting devices respectively having half-value angles el of 4', 7', 7.5', 9', 13', 15', and 20' were used to measure their SIN ratios. As seen from the figure, the S/1,1 ratio increases as the half-value angle 61 increases to 9', and decreases as the half-value angle el further increases beyond 90. Since a device having a half-value angle 61 of substantially 10' or less is used as the light emitting device 12, it is possible to improve the SIN ratio.

Even when the accuracy of attaching the light emitting device 12 to the holder 10 is low or the optical axis is deviated bv variation of the light emitting device 12 itsel-ft the output Dower of the light emitting device 12 can be set within the viewing field of the light receiving device 13, and the level of an output due to smoke is higher than that obtained in the case where a light emitting device having a large directional angle is used. Since the sensor is not required to inco- rporate a lens or the like, the sensor can be produced at a lower cost, and the deviation of a light beam

22 i 0 which depends on the assembling accuracy of a light emitting device and a lens does not occur.

Fic. 12 shows zerc-pc)-n: outputs cbr-Ained in the case where the lichremitting 12, having a angle el of 9' and the scatterina ancle 62 or the anzie at --he optical axes of the lich- --,iiicLinc device 12 and the light receivina device 13 intersect each other is char-,-3d frcr-,, 30' to 90' in t,'-ie steD of 10c and to L20: As seen from the ficure, the zero-L-c)int ouc:c)uz decreases as increases from 30.' to ncreases beycnd 701:1 As described range of 60' to 801, the optical axis of as to reflect light the angle 62 70'.' and increases as the an::!e above,the scattering ancle 62 is in the the labyrinth member 91 which intersects the licht emittinc: 1-2 is formed so from the light emitting device 12 in the dlirection opposite to the light receivinc 13, and the )izht receiving 13) does not receive primary li-jI'It due to the rnember 91. it is Dossible --c lower the zerD-Doint le.,-e-1.

means an output of the light obained wher.

there 15 nc smoke in the smoke detecting chan'--er. If the recelvinc: device easil.y receives reflected light when there is no sm-uke in the smoke chamber, the zero-point le!..el is naturally increased so that it, is to conduct the 3Uc--jmen-- cn and The zero--oint level 71 1 1 B - W OpIGIVAA, is Even when light emitted from the light emitting device 12 for detecting smoke is reflected several times by the flat portions 91b and front end edges of the labyrinth member 9 so as to be diffused in the smoke detecting chamber, the light receiving device 13 is shielded from the diffused light by the labyrinth member 91 and the light shielding plate 14. In addition, the viewing field of the light receiving device 13 is formed by the gap 20 and the windo-,., 21, so that the area of the viewina field is relatively small. Accordingly, it is z:)cssible to lower the zero-point level of the detection output of the light receiving device 13.

As a result, the SIN ratio can be improved, and hence the reliability can be enhanced. In addition, it is possible to provide a sufficient margin for various noises such as dust or dew formation. Furthermore, since the area which receives r':lec" ef. ted light in the smoke detecting chamber is limited, it is sufficient to put emphasis on the design of the labyrinth structure in the light receiving area. Thus, it becomes possible to increase the degree of freedom of the design of the labyrinth structure acainst the inflow of smoke and the optical dLsturbance.

As described above, in the first embodiment, the licht em-ttLng device has a so-called half-value angle e! of substantially 100 or less, the light emitting section, and the lzht 1-eceiving section are disposed in such a manner that a scattering angle at which their optical axes intersect- each 2 4 - other is in the range of substantially 60 to 801, and reflecting face of the labyrinth member which intersects optical axis of the light emitting section does not face light receiving the accuracy of light receiving the the the face of the light receiving section Even when assembling the light emitting device and the device is low or the optical axis is deviated by variation of the light emitting device itself, a thinned structure does not cause a part of direct light from the light emitting section and light reflected by the labyrinth members c) enter the light receiving section. Therefore, the zero-point level can be lowered by a simple structure.

In the second embodiment, the labyrinth member which intersects the optical axis of the light emitting section is discosed in such a manner that its reflecting face intersects the optical axis of the light receiving section at substantially 450, and the light receiving section is disposed in such a manner that its viewing field does not include an area of the reflecting face of the labyrinth member which intersects the optical axis of the light emitting section, and passes a substantially center portion of the smoke detecting chamber. Therefore, the light receiving section is prevented from receiving primary reflected light due to the labyrinth member which intersects the optical axis of the light emitting section, whereby the zero-Qc-int level of the detection output of' the light receiving section can be reduced to a as low as possible.

Moreover, the window of the light receiving section is located at a position which is separated by substantially 150 or more from one end of the light receiving section side of the L projected plane which is projected by the light emitted from emitting section for the labyrinth member -which intersects the optical axis of the light emitting section, and the viewing field c-f the light receiving section is disposed at- a position which is separated by substantially 45 or more from the projected Plane projected by the light emitting section in the reflection direction of the labyrinth member. Therefore, the light receiving section is prevented from recei,,-ing direct light from the light emitting section and also secondary reflected light which has been reflected by the labyrinth member confronting the light emitting face of the light emitting section, and which is then reflected by another labyrinth member. Consecuently, the zerc-point level of the detection output of the light receiving section can be reduced, to a level as low as possible.

in the third embodiment, the projecting area of the be,,;;th-inthe the oPtical axis of the light emitting Pe,.:arding the vertical di------tion, therefore, dire--t light from the light emittin- de.--ice is reflected c)nlv by the ntersects the optical axis of the light is not reflected by the ceiling lace and L light emitting section is disposed so as to height of the face of the labyrinth member which 26 la'--vr-nth member which em-itting section, and the bottom -':ace of the smoke detecting chamber, whereby the zero-point level can be lowered.

In the fourth embodiment, a light s--attering type smoke sensor in which the height of the smoke det-acting chamber is 20 mm or less is ccnfigured so that a half-value angle of' the light emitting device is substantially 5 t-- 10'. Even when the sensor is to be thinned, therefore, r_he sens= is conficured in such a manner that direct l-ch _rom the emitting device is reflected only by the la-vr-inth member which intersects the optical axis of the light emitting section, and is not reflected by the ceiling face and the face of the smoke detecting chamber. Therefore, the zerGzc-i.nt level can be lowered.

27 e-oz S i l v lic:hz 1

Claims

1. A light scattering:ype smcke a _Iurality of labyrin:h members inflow of smoke entering from the outside, i 7 entering fzcm the outside; a smoke detecting chamber which is formed in a portion by said labyrinth members; light emitting means for radiating light smoke detecting chamber; and said smoke in said smoke detecting chamber, receiving means having an optical axis which 12 smcke ing chamber an optical axis of said light emitting 28 - DRIGINA1 16 height of a of one of the labvrinth members intersecting said 17 cotical axis o-' said emitt-inc means.

i

2 claim 1, wherein said o-f sa fa --= 0 -1abvr-n::h

3 member which intersects said opt---a- axis Of.: Said 1,,-,hz ZI e.m-;t-t-ng means is subs -;-- 11 20 mm or less.

i 3. A szatterinc: tvn= smoke sensor Z2 2 claim 2, where in sa id -1 -i=h-- emitt ing mea-s has a 3 angle c--- substanzially 5 to 1

4.

A. light scattering type smoke sensor according to claim 1, wherein, when a height of said lab-,-rinth member which 3 intersects said optical axis is indicated by H, and a distance between said light emitting means and a remotest position o -P reflecting Eace of said labyrinth member which intersects said 6 oDt-i--al axis is indicated by L, a hal..i'--,;-alue angle e c.E said 1 1 3 light receiving means sacisfies the following expression:

e < zan- H/2L,

5. A light scattering type smoke sensor a=cording to claiml, wherein said labyrint:, member said --:)t-ical axis is langer than other labyrinth members are 29 - E1Ap C)R1GiNA- i

6. A licht scatZerincl t_-Y'Pe EMCke -ze:s--r wherein a of claim 1, t nasses a substantially center nc-:-ion c-- said 1 -namzer.

7. A light scat--erinZ Z1/:)e SMicke Senscr 2 claim 1, wherein any po _int- 5 of 3 member wlliz'r, means are nearer cc smck=- detecting chamber than 6 i

8. A light scattering type smoke sensor ac--cordinz to 2 claim 1, wherein said ref lect ing _face c.-z sa I'd lab,,,r inth me. mber 3 intersects said optical axis of said light em, -i--ting means intersects said optical axis of said light emitting means a-- substantially 450.

1

9. A light scattering t-,,,ce smoke ser-.szr a:=crdn.g to 2 claim 8, wherein said C:.-: said fact-E c:f said 3 imernter which intersects said optical axis 0 f said means is substantialiv 20 mm,,r less.

10. A light scatzerinc type smoke claim 9, wherein light emitting means has a angle of substantially _; zc l'Ol'.

M-- BAD ONG IN -AI, 1 claim 9 1 A i'm 9, wherein said lighz szaizerLni Cype smcke sensor az::rding to labyrin=h member.

31 labyrin=h members which said smoke dece=cing 12ID OfRIGINAL