GB1581495A - Smoke detector - Google Patents

Description

(54) SMOKE DETECTOR (71) We, CHLORIDE INCORPORATED, a Corporation organised under the laws of the State of Delaware, United States of America, of 5200, West Kennedy Boulevard, Tampa, Florida, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement.

This invention relates to a smoke detector operating on the reflected light principle, so that when smoke is present at greater than a certain concentration in ambient air entering the detector, a light detector can give an alarm signal that there is a danger of fire.

An object of the invention is to provide a smoke detector which is reasonably quick in response to the presence of smoke particles above the certain concentration while yet is unlikely to give false alarms.

According to the present invention, a smoke particle, or like, detector comprises a chamber, a pair of recesses opening into a wall of the chamber and having axes which intersect, a light source in one recess for illuminating the chamber, and a light detector in the other recess positioned to receive light from the source not directly, but after reflection by particles carried by fluid in the chamber, and a fluid flow passage opening into the chamber in the part of the wall between the recesses.

Preferably the air is arranged to flow from outside into the chamber through the said fluid flow passage, and out through an exit passage in an opposite wall of the chamber, and the chamber has a large cross-sectional area in rela tion to the area of the inlet passage to tend to cause the air to eddy as it enters the chamber, so that smoke carried by the air becomes fairly quickly fairly uniformly dispersed throughout the chamber, and an accurate detection can be achieved quickly.

The position of the fluid flow passage, whether for entrance or exit of air, in the cham ber wall between the two recesses tends to pre vent build-up of dust between the recesses which could cause a false alarm.

The light source and light detector are di rected so as to illuminate, and respond to, the air in the chamber itself rather than the air entering or leaving the chamber, through the fluid flow passage.

The invention may be carried into practice in various ways, and one embodiment will now be described by way of example with reference to the accompanying drawings; in which: Figure 1 is an exploded view of the compon ents of the detector housing, and Figure 2 is a plan view of the bottom portion of the detector housing with certain components shown in the assembled position.

Referring to the drawings there is illustrated a smoke detector which comprises a housing hav ing a base portion 10 an upper portion 12, a cover 14, and an air-directing plate 16.

The base portion 10 and the upper portion 12 may conveniently be formed of moulded plastic, and having mating internal portions, to be more fully described hereinafter, that form a smoke chimney 18, a smoke chamber 20 having an entrance port 22 and an exit port 24 disposdd generally opposite each other, and recesses 26 and 28 for receiving, respectively, a light source 30 and a photo-cell 32 and associated fodusing lenses 34 and 36.

The photocell is connected to suitable cir cuitry (not shown) to actuate an alarm 37 when an electrical characteristic of the photo cell (such as resistance, in the case of a photo resistive device) changes a predetermined amount. Such circuits are well known in the art.

The entrance port 22 is in the form of a narrow slot leading from an entrance chamber .38, the upper side of which is positioned below an opening 40 in the cover 14.

The air directing plate 16 is provided with radial vanes 42 which rest against the top of the cover 14 and direct air moving across the detector to the centre of the plate, where it is drawn into the entrance chamber 38.

To create a continuous small flow of air through the detector, a heating resistor 44 is mounted in the chimney 18. The detector is intended for mounting on a wall with the chimney in the vertical position, or for moun ting on a ceiling. When mounted on a wall, the heat from the resistor causes a flow of air up the chimney and out an exhaust vent 46, drawing air through the chamber 20 from the entrance chamber 38. When the detector is mounted on a ceiling, the fact that the resistor is higher than the opening 40 in the cover 14 causes a flow of air to occur through the detector when in this position.

If smoke is present in the incoming air, it appears in the air passing through the entrance slot 22; however, due to the laminar flow resulting from the low velocity of the air, it may not be uniformly distributed therein, and the dimensions of the air stream coming out of the slot are not great enough to cause an adequate photo-cell response unless the smoke concentration is much higher than the concentration at which it is desired that the alarm be actuated. However, as the air passes through the chamber, swirls of eddies form on both sides of the air flowing across the chamber, due to the frictional effect of the air flowing across the chamber, due to the frictional effect of the air flow between the ports 20 and 22.

Hence if the incoming air contains smoke, smoke-filled eddies form on both sides of the direct path between the entrance and exit ports.

It is not clear whether the air flow in the eddies is turbulent or laminar; however, even if the flow is laminar the effect of the greater volume of smoke-filled air is to provide a greater surface from which light is reflected onto the photo-cell and therefore provides a greater photo-cell response, for a given concentration of smoke in the ambient air, than would be obtained from viewing only the air-smoke mixture passing through the entrance slot.

The light source 30 is positioned and directed to illuminate the chamber and the photo-cell is positioned and directed to view the illuminated chamber at an angle of about 135a to the axis of the light beam, to take advantage of the "forward scatter" effect.

The entrance port 22 preferably is narrower than its height, and has a cross-sectional area smaller than that of the exit port, or any other portion of the air flow passages, so that the velocity of flow into the chamber from the entrance port is higher than the velocity out of the chamber.

It is believed that maximum diffusion of the smoke-laden air throughout the chamber is thereby obtained.

The positioning of the slot 22 between the recess 28 containing the photo-cell and the re cess 26 containing the light source presents a build-up of a continuous surface layer of dust or lint therebetween, so that the possibility of a false alarm from such cause is eliminated.

Although in the illustrated embodiment the port between the recesses containing the photo cell and the light source is the inlet port, it will be understood that in some cases the photo-cell and the light source can be positioned on oppo site sides of the exit port.

In some installations more positive means of creating air flow through the chamber, such as a pump, may be used. In such case turbulent flow may exist in the entrance port, in which event the size of the chamber may be reduced.

Although the illustrated embodiment of the invention is designed for use with a gaseous medium, the principles of the invention may be adapted for use in devices for measuring or detecting particles or turbidity in fluids.

Sinee certain other changes apparent to one skilled in the art can be made in the illustrated embodiment of the invention, it is intended that all matter contained herein be interpreted in an illustrative and not a limiting sense.

WHAT WE CLAIM IS: 1. A smoke particle, or like, detector comprising a chamber, a pair of recesses opening into a wall of the chamber and having axes which intersect, a light source in one recess for illuminating the chamber, and a light detector in the other recess positioned to receive light from the source not directly, but after reflection by particles carried by fluid in the chamber, and a fluid flow passage opening into the chamber in the part of the wall between the recesses.

2. A detector as claimed in Claim 1 including a second fluid flow passage opening into the chamber.

3. A detector as claimed in Claim 2 in which the second passage is in a wali opposite the wall into which the first fluid flow passage opens.

4. A detector as claimed in any of the preceding claims including means for driving air from outside the detector into the chamber by way of the passage, or one of the passages.

5. A detector as claimed in Caim 4 in which the driving means comprises a heater positioned in a chimney or like passage leading from the chamber.

6. A detector as claimed in any of the preceding claims in which the cross section of the chamber is substantially greater than the area of the first fluid flow passage.

7. A detector as claimed in any of the Claims 26 in which the cross sectional area of one fluid flow passage is greater than that of the other, 8. A detector as claimed in any of the preceding claims in which the axis of one or each recess is inclined to the wall of the chamber into which it opens.

9. A smoke particle, or like, detector constructed and arranged substantially as herein specifically described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. the entrance chamber 38. When the detector is mounted on a ceiling, the fact that the resistor is higher than the opening 40 in the cover 14 causes a flow of air to occur through the detector when in this position. If smoke is present in the incoming air, it appears in the air passing through the entrance slot 22; however, due to the laminar flow resulting from the low velocity of the air, it may not be uniformly distributed therein, and the dimensions of the air stream coming out of the slot are not great enough to cause an adequate photo-cell response unless the smoke concentration is much higher than the concentration at which it is desired that the alarm be actuated. However, as the air passes through the chamber, swirls of eddies form on both sides of the air flowing across the chamber, due to the frictional effect of the air flowing across the chamber, due to the frictional effect of the air flow between the ports 20 and 22. Hence if the incoming air contains smoke, smoke-filled eddies form on both sides of the direct path between the entrance and exit ports. It is not clear whether the air flow in the eddies is turbulent or laminar; however, even if the flow is laminar the effect of the greater volume of smoke-filled air is to provide a greater surface from which light is reflected onto the photo-cell and therefore provides a greater photo-cell response, for a given concentration of smoke in the ambient air, than would be obtained from viewing only the air-smoke mixture passing through the entrance slot. The light source 30 is positioned and directed to illuminate the chamber and the photo-cell is positioned and directed to view the illuminated chamber at an angle of about 135a to the axis of the light beam, to take advantage of the "forward scatter" effect. The entrance port 22 preferably is narrower than its height, and has a cross-sectional area smaller than that of the exit port, or any other portion of the air flow passages, so that the velocity of flow into the chamber from the entrance port is higher than the velocity out of the chamber. It is believed that maximum diffusion of the smoke-laden air throughout the chamber is thereby obtained. The positioning of the slot 22 between the recess 28 containing the photo-cell and the re cess 26 containing the light source presents a build-up of a continuous surface layer of dust or lint therebetween, so that the possibility of a false alarm from such cause is eliminated. Although in the illustrated embodiment the port between the recesses containing the photo cell and the light source is the inlet port, it will be understood that in some cases the photo-cell and the light source can be positioned on oppo site sides of the exit port. In some installations more positive means of creating air flow through the chamber, such as a pump, may be used. In such case turbulent flow may exist in the entrance port, in which event the size of the chamber may be reduced. Although the illustrated embodiment of the invention is designed for use with a gaseous medium, the principles of the invention may be adapted for use in devices for measuring or detecting particles or turbidity in fluids. Sinee certain other changes apparent to one skilled in the art can be made in the illustrated embodiment of the invention, it is intended that all matter contained herein be interpreted in an illustrative and not a limiting sense. WHAT WE CLAIM IS:

1. A smoke particle, or like, detector comprising a chamber, a pair of recesses opening into a wall of the chamber and having axes which intersect, a light source in one recess for illuminating the chamber, and a light detector in the other recess positioned to receive light from the source not directly, but after reflection by particles carried by fluid in the chamber, and a fluid flow passage opening into the chamber in the part of the wall between the recesses.

2. A detector as claimed in Claim 1 including a second fluid flow passage opening into the chamber.

3. A detector as claimed in Claim 2 in which the second passage is in a wali opposite the wall into which the first fluid flow passage opens.

4. A detector as claimed in any of the preceding claims including means for driving air from outside the detector into the chamber by way of the passage, or one of the passages.

5. A detector as claimed in Caim 4 in which the driving means comprises a heater positioned in a chimney or like passage leading from the chamber.

6. A detector as claimed in any of the preceding claims in which the cross section of the chamber is substantially greater than the area of the first fluid flow passage.

7. A detector as claimed in any of the Claims 26 in which the cross sectional area of one fluid flow passage is greater than that of the other,

8. A detector as claimed in any of the preceding claims in which the axis of one or each recess is inclined to the wall of the chamber into which it opens.

9. A smoke particle, or like, detector constructed and arranged substantially as herein specifically described with reference to the accompanying drawings.