Optical smoke detector

An optical smoke detector including a plurality of walls extending from a dark chamber in which an optical smoke sensor is located. The walls form passages in the detector which extend from smoke entrances on the outer perimeter to smoke ports that feed into the dark chamber. In construction, the smoke entrances extend substantially continuously around the perimeter of the smoke detector to allow the free entry of smoke into the dark chamber. Each wall is arranged to overlap the next so as to obstruct the direct rays of light from entering the dark chamber and a screen is disposed around the perimeter of the detector to prevent the entrance of insects into the dark chamber.

BACKGROUND OF THE INVENTION 
The present invention relates to optical smoke detectors. Such detectors 
direct a beam of light into a dark chamber which is shielded in as much as 
possible from ambient light. Air to be tested for the presence of the 
smoke will flow into the dark chamber and will scatter the light in the 
beam to initiate an alarm signal. 
DESCRIPTION OF THE PRIOR ART 
In the past, various arrangements have been utilized to allow smoke to 
enter a smoke detector. The United States patent to Steele et al U.S. Pat. 
No. 3,916,209 discloses forming the passages in a swirled shape so that 
air to be sampled and tested will flow through narrowing passages towards 
a terminal convergence point and then be diverted into a dark chamber 
which is disposed below the convergence point. In the United States patent 
to Steele, Ser. No. 777,043, filed Mar. 14, 1977, U.S. Pat. No. 4,124,298 
the optical sensing zone is located in a dark chamber formed by interior 
walls. Air to be tested enters through smoke entrances that are formed 
circumferentially and screens are disposed in each smoke entrance to 
prevent insects from entering the equipment and also reduce the passage of 
light into the dark chamber. 
SUMMARY OF THE INVENTION 
According to the present invention, the optical scanning detector includes 
a centrally located dark chamber and an adjacent smoke sensor. A plurality 
of walls extending from smoke entrances are disposed on the outer 
perimeter of the detector to smoke ports that open directly into the dark 
chamber. The walls cooperate to form passages of diminishing width for air 
to be sampled to flow from the smoke entrances to the smoke ports. They 
are arranged so that the entire perimeter of the smoke detector is free 
from obstructions, save for the width of the walls, thereby allowing air 
to be tested to enter throughout the entire periphery of the device. A 
screen is disposed in front of the smoke entrances to prevent insects from 
entering the passages and flying into the dark chamber. The screen 
contacts the walls only at their outer ends, if at all, thereby allowing a 
substantially unobstructed flow of air to be tested. Since the screening 
constitutes only a negligible obstruction in air flow, relative to the 
large sizes of the smoke entrances that extend around the entire perimeter 
of the detector, all air in the immediate area will flow through the 
passages and into the dark chamber.

DESCRIPTION 
The optical smoke detector of FIGS. 1 and 2 comprises a disk shaped base 1 
on which is secured an electronic circuit board 2, the circuit components 
being omitted. Attached to the circuit board is an optical block 3 
containing a light emitting diode (LED) 4 and a photocell 6. Light from 
the LED source 4 is directed out a passage in the light block on a first 
beam axis 7 to intersect a second axis 8 on which the cell 6 views through 
a passage to a smoke sensing zone Z. Light is scattered by smoke in the 
sensing zone to the cell 4, exciting the cell to an alarm response if the 
smoke exceeds a predetermined density. 
The intersection zone Z is located in a dark chamber 5 from which light is 
excluded so far as is possible while admitting smoke as freely as 
possible. The dark chamber is located between the optical block 3 and a 
cover 9 in the vertical dimension of FIG. 2 and within a molded plastic 
wall forming structure 11. The wall forming structure comprises a circular 
disk 12 interrupted centrally by a rectangular opening 14 modified at two 
opposite sides by dished out portions 16. Depending from three sides of 
the rectangular opening are flat walls 17 which fit closely around the 
optical block and obstruct ambient light entry from the circuit board side 
of the dark chamber, and which support the wall forming structure on the 
circuit board 2. A collar 30 covers the detector below the disk 12. It 
will be understood that reference to the vertical and up and down 
dimensions are with reference to the smoke detector as shown in the 
Figures and the detector may be installed on a wall or on a ceiling with 
vertical and horizontal dimensions reversed. Also while smoke entrances 
will be described it should be understood that, depending on the direction 
of smoke currents, entrances will at some times be exits. 
Of particular significance in the present invention are the walls and 
screening extending from the upper side of the disk 12 to the cover 9. A 
first set of circular walls 18 defining the outer boundary of the dark 
chamber form smoke ports 19 opening into the dark chamber. Preferably a 
baffle 21 is located inside each port 19. From the circular walls 18 
outwardly spiralled walls 22 extend to an outer periphery of the wall 
structure defined by a ring shaped screen 23. 
The cover 9 over the dark chamber is supported by and attached to the walls 
18, 21 and 22 extending upwardly from the disk 12 of the wall forming 
structure 11. The cover 9 and disk 12 have opposed annular grooves 29 and 
32 which receive and positively position the ring shaped screen 23 around 
the periphery of the detector. The outer ends 24 of the spiralled walls 
terminate at the periphery and adjacent outer ends 24 of the walls and 
form smoke entrances 26 at the periphery. Excluding the negligible 
dimension of the outer ends 24 of the spiralled walls 22, these smoke 
entrances extend in four quadrants completely, or substantially 
completely, around the available smoke entry area at the periphery thus 
maximizing the free entry of smoke toward the dark chamber. At the same 
time each spiralled wall 22, as extended continuously by the circular 
walls 18, overlaps its adjacent spiralled wall so that each adjacent wall 
pair forms an inwarldy spiralling and converging passage 26 from each 
smoke entrance to a smoke port 19, there being four such passages. 
By drawing a line from any spiralled wall outer end 24 through the adjacent 
passage 26 to the inner smoke port 19, it can be seen that direct light 
rays from the smoke entrance are blocked by the wall structure. Moreover, 
the wires of the screen 23 substantially obstruct light rays entering each 
quadrant of the screened periphery at an oblique angle obstructing 
approach to each port 19, but at the same time afford the maximum 
360.degree. area for radial entry of smoke into the passages 26 leading to 
the dark chamber. Test data indicate a substantial and significant 
increase in the speed in which an alarm level of smoke will be detected 
because of the maximized smoke entry characteristic of the present 
invention together with the decreased entry of ambient or external light. 
It should be understood that the present disclosure is for the purpose of 
illustration only and that this invention includes all modifications and 
equivalents which fall within the scope of the appended claims.