GB2335737A - Smoke detector with particle sensor - Google Patents

Abstract

A fire detector which utilizes a discrete smoke particle counter incorporates a laser diode as a source of coherent light. An aerosol channel permitting one-at-a time particle flow is located adjacent to the diode, at either an output port thereof or formed so as to intersect a region of stimulated emission, thus reducing the output of the diode. A light amplitude sensing element such as a photodetector, is configured so as to detect variations in light intensity in response to the presence of individual airbome smoke particles. A modulated signal from the detector can be processed to determine smoke type and concentration so as to establish the presence or absence of a fire profile. Either unidirectional or bidirectional flow of particles can be provided using valveless solid state actuators. Multi-channel outputs can be provided using a single source with multiple sensors or multiple source/sensor pairs.

Description

2335737 SMOKE DETECTOR WITH PARTICLE SENSOR

Field of the Invention:

The invention pertains to smoke detectors. More particularly, the invention pertains to such detectors configured to sense and count individual particles of smoke.

Back2round of the Invention:

Fire detectors have been recognized as valuable safety tools in that they can usually be expected to provide an early warning of a developing fire condition in a region. Known fire detectors utilize a variety of different types of sensors. For example, thermodetectors are used to sense increasing ambient temperature. Smoke detectors, having ionizatioz or photoelectric sensors, detect the presence of airborne particulate matter in a region being supervised. Gas detectors sense the presence and concentration of one or more gases.

is While known detectors are useful, they are designed to sense the presence of a selected macro-condition. For example, thermosensors will generally sense the temperature of air moving in a region being supervised. In this regard, the temperature characteristics of individual air molecules are not being sensed. Rather, pluralities of molecules are being sensed to provide an average temperature indication. Similarly, both ionization- type and photoelectric-type smoke detectors sense the concentration of smoke in a region. This includes a large number of smoke particles.

As a result of their sensing approaches, known detectors have limitations in terms of energy requirements reduction, size reduction and manufacturing cost reduction which can be achieved. It would be desirable to be able to take advantage of current integrated circuit processing technology. and to create a physically small, inexpensive, low-power smoke sensor. Preferably, such a detector would respond to individual smoke particles, as opposed to responding to the presence of large numbers of particles, so as to provide information pertaining to the type of smoke and concentration.

Summga of the Invention:

A low-power solid state particle sensor incorporates a laser diode as a source of coherent light. Known laser diodes have beam output ports of the order of 1 by 5 microns. Preferably, laser diodes having the smallest possible output ports will be used. Output ports having dimensions on the order of 1 micron by 1 micron are suitable.

In one aspect, a flow path dimensioned to permit the serial flow of spaced apart, individual, smoke particles is positioned adjacent to the output port.

The flow path preferably would have dimensions comparable to those of the known size of smoke particles, on the order of 3 microns for example. Typical smoke particle size is known to be on the order of. 1 to 1 micron. It is also known that such particles tend to self-center in flow channels and tend not to cluster along the channel walls.

In yet another aspect, a photosensor, such as a photo diode, Pan be positioned adjacent to the output port of the source with a portion of the flow path therebetween. Hence, as smoke particles move through the flow path, each of them will pass one at a time in front of the beam modulating same.

The output electrical signal from the sensor is indicative of the size and the velocity of the particle which is in effect obscuring the radiant energy beam. Modulated output signals from the sensor will be presence in response to each of the smoke or aerosol particles passing through the flow path. Alternately, the sensor can be oriented so as to detect light reflected off of individual particles.

A fire detector which utilizes a discrete smoke particle sensor incorporates a laser diode as a source of coherent light. An -aerosol channel is located adjacent to the diode, at either an output port thereof or formed so as to intersect a region of stimulated emission. A light amplitude measuring element, such as a photodetector, is configured so as to detect variations in light intensity in response to the presence of individual airborn.- smoke particles.

A modulated signal from the detector can be processed to determine smoke type and concentration so as to establish the presence or absence of a fire profile. In one aspect. circuitry can be provided for analyzing the size of sensed particulate matter to determine fire type. Circuitry for determining the distance between particles can be used to establish smoke concentration. Pattern recognition circuitry can be used for analysis purposes.

Either unidirectional or bidirectional flow of particles can be provided using valveless solid state actuators. Alternately, particulate flow can be induced thermally.

In another aspect, a plurality of detectors can be arranged in an array. In such arrangements, both absorption and scattering can be employed to produce signals indicative of the presence of particulate matter, particle size and concentration. Alternately, a plurality of laser sources, emitting light of different frequencies, can be used. Further, the location of one or more of the photodetectors can be varied relative to the source.

In another, particulate matter that has been sensed can be illuminated by a second source, a second laser of perhaps a different output frequency. This injection of radiant energy into individual particles may produce a change in particle size or other discernable characteristics. The particles, exhibiting the altered characteristics can be sensed again for "before" and "after" analysis.

Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embents thereof, from the claims and from the accompanying drawings.

Brief Descripti :on of the Drawings:

Fig. 1 is a side elevational view of a particle counter in accordance with the present invention; Fig. 1A is an enlarged view of a region of the detector of Fig. 1; Fig. 2 is a top plan view of the particle counter of Fig. 1; Fig. 3 is an enlarged, side elevational view of a portion of the particle counter of Fig. 1; Fig. 4A is an enlarged, side elevational view of an alternate form of a laser source; Fig. 4B is an enlarged, side elevational view of yet another forTn of a laser source; Fig. 5 is a partial, enlarged, side elevational view of yet another form of a laser source; Fig. 6 is a side elevational view of a particle counter as in Fig. 1 which incorporates a solid state, valveless, particle moving pump; Fig. 6A is an enlarge view of portion of the pump of Fig. 6; Fig. 7 is an enlarged side elevational view of an alternate form of a particle counter incorporating a solid state pump; Fig. 8A is a side elevational, view of a particle counter which incorporates a photosensor array; and Fig. 8B is an enlarged, side elevational view of a particle counter which incorporates an array of sources and sensors; and Fig. 9 is an enlarged side elevational view of yet another form of a multi source particle counter.

Detailed Description of the Preferred Embodiments:

While this invention is susceptible of embodiment in many different forms, there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.

it is recognized that smoke particles vary over a range in the order of 0. 1 to 1. 0 micron in diameter. They tend to be on the order of 10: 100 microns apart at a 2% per foot obscuration level.

It is also recognized, at constant obscuration levels, that smaller particles which are indicative of hotter fires will be closer together. Additionally, different materials burn under different conditions and will produce different particle size distributions. Hence, the varying characteristics of smoke particles can be used, in combination with the particle concentration, for purposes of reflecting, scattering, absorbing or obscuring one or more beams of radiant energy, on a particle basis.

Fig. 1 illustrates a particle counting system 10 in accordance with the present invention. The system of Fig. 1 along with various described alternates can be used to implement physically small, inexpensive, low energy smoke detectors. It is effective to count and analyze characteristics of individual smoke particles.

The system 10 includes a solid state lasing source of radiant energy 12. The source 12 could be implemented for example as a solid state laser diode. Such diodes are known to emit a monochromatic beam of radiant energy from an output port in response to applied electrical energy. An optically resonant channel or cavity is formed at a p-n junction of the laser diode. The ends of the channel are bounded by reflecting surfaces or planes. In known laser diodes, the output port is located at one end of the channel.

The system 10 also includes a sensor 14. The sensor 14 could be implemented as a photodiode for example.

lle elements 12, 14 are supported spaced apart from one another on a base 16. The system 10 can be incorporated into a housing 16a. It can be powered by a battery or other electrical source 18 and contain control circuitry 18a.

In the embodiment of Fig. 1, the particle sensor 14 is displaced from an output port 12a of the laser 12 by a distance corresponding to a width dimension of a smoke particle flow path 20, illustrated in more detail in Figs. 1A, 2 and 3.

The flow path 20 has dimensions which are of the same order of magnitude as the dimensions of smoke particles of the type being counted or sensed. For example, the flow path 20 could be configured so as to have width and depth dimensions on the order of 3 microns by 3 microns. With such dimensions, smoke particulate matter such as particles Pl, P2, and P3 can be caused to flow individually and spaced apart from one another through the channel 26.

A representative smoke particle, such as P2, when passing in front of a beam of radiant energy 12b, emitted from output port 12a will, at least in part, obscure a portion of the radiant energy incident on the photo diode 14. This obscuration characteristic of individual smoke particles traveling through the channel 20 will in turn result in the photodiode 14 emitting a varying electrical signal indicative of decreasing and increasing amounts of radiant energy incident upon the detector 14 as individual smoke particles, such as the particle P2, pass through the beam 12b along the channel 20.

With the exemplary dimensions illustrative of the channel 20, the passage of individual particles of smoke can be counted. Additionally, as discussed subsequently, the type of smoke particles and information pertaining to concentration level can also be deduced using the system 10. Hence, the output signal from the diode 14 which will vary in accordance with the size, velocity and concentration of the passing particulate matter can be analyzed by subsequent processing circuitry so as to ascertain if the sensed particulate matter is exhibiting a fire profile. Reflective or scattered light could also be sensed without departing from the spirit and scope of the present invention.

It will be understood that the particulate matter, Pl, P2.. Pn tend to pass along the center axis of the channel 20. Such particulate matter does not tend to be attracted to and/or adhere to the surfaces of the laser 12 or sensor 14 as it is flowing therebetween.

While the system 10 is configured with the channel 20 positioned between the output port 12a of the laser 12 and the displaced diode 14, alternate configurations do not depart from the spirit and scope of the present invention.

For example, Fig. 4A illustrates an alternate configuration of a laser diode 30. The diode 30 is formed of a semiconductor body 32 having a p-n junction of a type known to be effective in producing laser oscillation.

A photodiode 34 is coupled to an end of the body portion 32 at an output port. A flow channel 36 is formed in part in the body 32 of the diode 30. The flow channel 36 provides a pathway through which stimulated optical emissions must pass in connection with generating the required optical oscillation which is characterized by a monochromatic output beam.

The channel 36 passes, in part, transversely through the body, substantially perpendicular to the direction of travel of the stimulated emission through the body 32. This configuration makes it possible for the smoke particulate matter passing through the channel 36 to interfere with the optical oscillation process. This in turn reduces the output radiant energy. This reduction or variation can be in turn sensed by photodiode 34.

Fig. 4B illustrates an alternate wherein a laser diode 30a is formed in a semiconductor body 32a. In the embodiment of Fig. 4B, a channel 36a is formed through the body 32a concentric with a channel through which the stimulated emission travels. The presence of smoke particulate matter in the channel will interfere with the optical oscillation process and can be sensed by an adjacent photo sensor 34a as discussed above.

Yet another alternate is illustrated in Fig. 5. In Fig. 5, a system 40 is illustrated which incorporates a lasing semiconductor 42 and an associated photo diode 44. The photo diode 44 is located at a first end 42a of the lasing semiconductor 42. A radiant energy output port 42b is located adjacent toyhoto sensor 44.

A smoke particle channel 46 is formed between a second end 42b of the semiconductor 42 and a reflective element 48. In order to effect an optically resonate conditiorf, i.e., to cause the necessary stimulated emission to generate an output monochromatic beam at the output port 42b, the semiconductor body 42 cooperates with the reflector 48. As illustrated in Fig. 5, radiant energy, Rl, emitted from surface 42b travels to reflector element 48, is reflected therefrom and re-enters the lasing channel 42d of the body 42 thereupon contributing further to the optical resonance.

The presence of smoke particulate matter, Pl, P2 in the channel 46 interferes with the optical resonating process. As illustrated in Fig. 5, the passage of particulate matter, such as particle Pl, through the channel 46 will in part block the travel of radiant energy R1 from the channel 42d to the reflective element 48. If 'not blocked on the way to the reflective element 48, the radiant energy RV may be blocked by the particulate matter P1 on the return trip from the reflective element 48. In this instance, output signals from the photo sensor 44 can be expected to provide an indication of particulate travel through the channel 46 due to interference with the optical or resonance process. The structure of Fig. 5 can be expected to provide an enhanced signal to noise ratio since the particulate matter in the channel 46 impairs both the outgoing radiation R1 as well as reflected, returning radiation Rl.'.

Fig. 6 illustrates yet another aspect of the system 10. In view of the dimensions of the channel 20, it is preferable to provide a form of propulsion for the particulate matter to cause same to pass along the channel 20. For example, a fan could be used to create a positive pressure condition to cause particulate matter to flow through the channel 20. Alternately, a fan can be used to crate a negative pressure condition to drawn particulate matter through the channel 20.

Solid state devices could be used for the purpose of drawing particulate matter into the channel 20 and expelling the same therefrom. For example, a solid state pump 60 can be provided at one end of the channel 20 to provide reciprocal motion of particulate matter in the channel 20 in response,to an applied electrical signal.

It is recognized that piezoelectric elements, often used to generate audible alarms in smoke detectors, do so by physically oscillating back and forth analogously to the way of the center of the end of a steel drum moves when depressed. This oscillatory mode, when moving in a first direction, can be used to draw particulate matter into the channel 20. When moving subsequently opposite the first direction, the particulate matter will be expelled from the channel 20. Hence, the piezo element provides a form of a solid state valveless pump which will draw in available particulate matter for counting and analysis, one particle at a time, and will expel that particulate matter subsequently.

Alternately, heat generated by absorbing radiant energy from the laser sources can be used as a vehicle for causing a flow of particulate matter through the channel 20.

Fig. 7 illustrates another configuration which utilizes a piezoelectric element for the purpose of drawing particulate matter into a channel. The particle counter 10a of Fig. 7 includes a laser source 12-1, and photodetector 14-1. The channel 20-1 extends therebetween.

-g- A piezoelectric flexing element 64 carries the photodiode 14-1. In response to applied electrical energy, the piezo element 64 flexes moving the photodiode 14-1 axially relative to the source 12-1 thereby drawing particulate matter into the channel 20-1 therebetween.

The system 10a thus illustrates another form of a valveless, solid state pump which can be used to cause a flow of particulate matter, one particle at a time, past the sourceldetector combination 12-1114-1. This will in turn produce a varying electrical output from the detector 14-1 which can be analyzed with respect to type of smoke and concentration thereof.

It will be understood that if desired an appropriate filter can be positioned at the entrance to the channel 20 to exclude therefrom, nonsmoke airborne particulate matter such as hair, dust and the like.

Fig. 8A illustrates another form of a particle counting system 10b.

This system incorporates a laser source 12-2 and a photodiode array 14-2 displaced from the output port of the source 12-2 with a particulate channel 20-2 extending therebetween. - - The array 14-2 can be unplemented m either two dimensional or three dimensional form. The various members of the array 14-2 respond to both - absorbed and scattered radiant energy as particulate matter, such as particle P1 travels through the channel 20-2. The use of an array such as the array 14-2 which could be implemented with a plurality of solid state detectors formed on a single substrate and hence be very small, makes it possible to carry out multichannel analysis on individual smoke particles.

Another form of multichannel structure can be implemented with a bank of parallel sources 12-3, 12-4.. 12-n as illustrated in Fig. 8B. The laser sources of Fig. 8B can be configured so as to generate light beams of different frequencies. The outputs from the respective photosensors in response to individual particles being detected thereby can be used also to carry out multichannel analysis of the characteristics of the smoke particles and concentration to determine the presence of a fire profile.

It will be understood that the various detected particles can be used by associated control circuitry 18a to form distributions of particle size or distributions of other fire-related characteristics for analysis purposes. The distributions can in turn be used to determine presence of a fire profile. The circuitry 18a can, if desired, be local to the source 12. Alternately, it can be in part local and in part remote at a common communications unit or panel.

Multichannel particle counters of type illustrated in Figs. 8A and 8B in turn make it possible to create distributions of detected particles or characteristics of detected particles based on a degree of blocked light, indicative of particle size as well as distance between particles, indicative of smoke concentration. They can provide these inputs, for example, to pattern recognition circuitry for analysis purposes.

Fig. 9 illustrates yet another form of a particle counting/analyzing, multiple source/detector system 70. The system 70 includes a plurality of analysis lasers 72a, 72b along with associated sensors 74a and 74b. A channel 76a extends therebetween.

Particulate matter can be injected into the channel 76a by a valveless solid state pump 76b. As particulate matter travels through the channel 76a, its presence can be detected by sensors 74a and 74b. Signals from these sensors can be processed as described above.

Disposed between sources 72a and 72b is another radiant energy source 72c. The purpose of the source 72c is to inject radiant energy or light into the particulate matter after it has passed source 72a and before it has passed source 72b. This process carries out a form of at least partial destructive processing of the various smoke particles potentially changing their characteristics in response to the injected energy from the source 72c.

The modified particulate matter or characteristics can in turn be Sensed by the photosensors 74b for comparison to signals generated by the sensor 74a and for further analysis. Where the pump 76b causes a reciprocal motion of particulate matter to occur, sensors 74a and 74b will detect particulate matter moving initially in a first direction and then opposite the first direction in response to the solid state pump 76b.

It will be understood from the above discussion that preferably a lasing source having an output port, corresponding to the area of the lasing channel, which is as small as possible, will be used so as to define an output beam having the smallest possible cross section. This can be expected to produce the greatest possible signal to noise ratio. Similarly, it will be understood that the size of the active area of the photodetector should be as small as possible to provide for an enhanced signal to noise ratio.

Preferably the output port from the source will have dimensions on the order of 1 micron by 1 micron. Also, preferably, the active area of the respective photodetector will be on the order of 1 micron by 1 micron.

It will also be understood that a plurality of photodetectors could be displaced varying distances from the output port of the respective laser source.

Analysis of signals from various displaced photodetectors can also be used for the purpose of establishing the presence of a fire profile.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims (15)

1. A system for detecting airborne combustion particulate matter comprising: at least one solid state source of radiant energy substantially of a predetermined frequency wherein a beam of energy exits the source from an output port of a selected area; a flow pathway for at, least a part of the particulate matter wherein the pathway intersects at least a portion of the radiant energy at a selected region such that the particulate matter therein affects the beam and wherein the pathway is dimensioned to promote a one-at-a-time flow of spaced apart particles; and a solid state sensor of radiant energy located adjacent to the output port and wherein the sensor generates an electrical signal indicative of the effects of the particulate matter. 1

2. A system as in claim 1 wherein the source is positioned within 5 microns of the sensor.

3. A system as in claim 1 wherein the pathway is formed in part in the source whereby the particulate matter will affect formation of the -beam.

4. A system as in claim 1 wherein particulate matter in the channel blocks, at least in part, the beam from being incident on the-sensor.

5. A system as in claim 3 wherein the source comprises a laser and wherein particulate matter in the pathway interferes with lasing of the source.

6. A system as in claim 5 wherein the pathway has a dimension, formed in part in the source that is less than 5 microns long.

7. A system as in claim 1 wherein the source comprises a laser diode, wherein the pathway has a region with a length of less than 5 microns and which extends between the output port and the sensor and wherein the sensor generates a varying output signal in response to the passage through the region of individual particles of combustion.

8. A system as in claim 1 which includes an aspirator for causing a flow of particulate matter along the pathway in at least one direction.

9. A system as in claim 8 wherein the aspirator is electrically energizable and includes a solid state activator.

10. A system as in claim 8 wherein the aspirator is valveless.

11. A system as.in claim 8 wherein the pathway is, in part, open to an adjacent region and wherein the element, when energized, causes particulate matter to move in a reciprocal fashion between the source and the sensor.

12. A system as in claim 8 which includes control circuitry, coupled at least to the sensor for responding to signals from the sensor.

13. A method, in accordance with Claim 1, of analyzing airbome particulate matter comprising: establishing a stream of spaced apart, individual, airborne particles; irradiating the particles, one at a time, with a sensing beam of substantially monochromatic energy; 1 sensing a modified beam characteristic indicative of an irradiated particle; and - processing a plurality of the sensed, modified characteristics.

14. A method as in claim 13 which includes irradiating the individual particles, subsequent to the sensing steD, with a modifying beam of radiant energy whereby parameters of at least some of the particles are modified.

15. A me as in claim 14 which includes irradiating the particles having modified parameters with a sensing beam and sensing the particles as modified.