Abstract:
A system for analyzing smoke has a plurality of units, wherein each unit includes an optical emitter for alternately directing horizontally and vertically polarized light along a beam path, and into a smoke cloud, to generate scattered light. A horizontally polarized detector and a vertically polarized detector are positioned at different locations, but at a same distance and scattering angle relative to the beam path. Each unit has a different wavelength. A computer receives signals from the detectors of all units, in response to each emitter, for analysis of the smoke.

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to smoke analyzers. More particularly, the present invention pertains to optical devices that are used for smoke analyzers. The present invention is particularly, but not exclusively useful as an optical unit for generating signals to analyze smoke, wherein the signals are based on polarization, wavelength and scattering angle considerations. 
     BACKGROUND OF THE INVENTION 
     Particles of different sizes and shapes (i.e. different materials) can become suspended in air for any of several different reasons. Tiny, condensed water droplets or ice crystals that become suspended in the atmosphere as clouds are a good example of this phenomenon. Clouds of particles, other than water, that may become suspended in air, such as dust and smoke, are also well known examples of the phenomenon. Unfortunately, smoke can be generated with many types of materials that will most likely cause undesirable consequences. In any event, and particularly in the case of smoke, it may be desirable or necessary to identify the type(s) of particles that constitute the smoke cloud. 
     Physically, it is well known that different types of particles, when suspended in air as a cloud, will affect light differently. In particular, it is known that particles in a cloud will scatter the light that is incident on the cloud and, depending on the nature of the particles in the cloud, the incident light will be scattered in a predictable and detectable manner. Importantly, the measurable characteristics of the scattered light depend on at least three significant factors. For one, if the incident light is polarized, when it is incident on particles in a cloud the light may change its polarization. If so, the polarization of the scattered light will be different from that of the incident light. For another, the wavelength (λ) of the incident light that interacts with the particles in the cloud will determine the extent of scattering. Further, detection of the scattered light will be influenced by where the detector is located relative to the beam path of the incident light (i.e. a scattering angle (θ)). In summary, the detection of a signal that is generated when light is scattered by a smoke cloud is dependent on the polarization of the incident light, the wavelength (λ) of the incident light, and the scattering angle (θ) where the detector happens to be located. 
     For purposes of the present invention, the above factors are important because different smoke and dust particles will scatter a same incident light beam differently. Further, it can be shown that relatively benign particles, though detectably different, have characteristically similar responses. Accordingly, as a group, they can be differentiated from the group of responses that are characteristically different and are typical of potentially hazardous or toxic particles (e.g. petrochemicals). 
     In light of the above, it is an object of the present invention to provide an optical unit for a smoke analyzer system that evaluates signals received from light scattered by a smoke cloud to determine whether the smoke includes particularly hazardous or toxic materials. Another object of the present invention is to provide an optical unit for a smoke analyzer system that generates signals for evaluation, wherein the signals are based on polarization, wavelength and scattering angle considerations. Yet another object of the present invention is to provide an optical unit for a smoke analyzer that is easy to use, is simple to manufacture and is comparatively cost effective. 
     SUMMARY OF THE INVENTION 
     A system for analyzing smoke includes a plurality of optical units, wherein each unit includes an optical emitter (E) and a pair of detectors. Each emitter is computer controlled to alternately direct a beam of horizontally polarized light (λ H ), or a beam of vertically polarized light (λ V ) along a beam path through a smoke cloud. Further, the emitters of the different optical units are controlled by the computer for sequential operation. 
     In addition to its emitter, each optical unit includes a horizontally polarized detector (D H ) and a vertically polarized detector (D V ). Both detectors are positioned at different locations having a same distance and a same scattering angle (θ) relative to the beam path. Preferably, the detectors are coplanar with the emitter and are therefore on directly opposite sides of the beam path. In operation, the horizontally polarized detector (D H ) generates a signal S HH  in response to λ H , and it generates a signal S VH  in response to λ V . Similarly, the vertically polarized detector (D V ) generates a signal S HV  in response to λ H , and it generates a signal S VV  in response to λ V . 
     For a preferred embodiment of the present invention, three coplanar optical units are used. Thus, respective emitters (E 1 , E 2  and E 3 ) are positioned on a circumference of a circle, with a separation arc length of 4θ between adjacent emitters. Within this arrangement, the emitter (E 1 ) of a first optical unit generates λ H  and λ V  having a same first wavelength (λ), the emitter (E 2 ) of a second optical unit generates λ′ H  and λ′ V  having a same second wavelength (λ′), and the emitter (E 3 ) of a third unit generates λ″ H  and λ″ V  having a same third wavelength (λ″). Importantly, each emitter is sequentially and individually activated by the computer for a predetermined time interval to simultaneously generate response signals (S) in all detectors of the system. 
     The computer is also used for evaluating all of the response signals “S” for an analysis of the smoke. More specifically, this task is accomplished by computing a polarization ratio ρ(θ): wherein
 
ρ(θ)=σ HH (θ)/σ VV (θ)
 
with σ HH (θ) and σ VV (θ) each being a differential mass scattering cross section for horizontally polarized light and for vertically polarized light, respectively. In particular, for the present invention, the polarization ratio, ρ(θ), is used to identify smoke from a petrochemical (hydrocarbon) source.
 
     In addition to the optical units mentioned above, the system of the present invention also includes filters for minimizing noise in the response signals. One filter is for removing white noise from the response signals (S), and the other is for operationally tracking the emitters. Specifically, a pre-filter is connected to each of detectors to filter a substantially d.c. component (white noise) from the outputs of the respective detectors. Additionally, the system has an oscillator that is controlled by the computer and is connected to each of the emitters. As used for the present invention, the oscillator establishes a blink rate (e.g. 3 Hz) for the transmission of light beams (e.g. λ H  and λ V ) from the respective emitters. Also, a synchronous demodulator is connected directly to the oscillator, and in series with the prefilter, for tracking the blink rate of the emitter during generation of the response signals S. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a schematic drawing of a system for an optical smoke analyzer in accordance with the present invention; 
         FIG. 2  is a schematic drawing of an optical unit for use with the system of the present invention; 
         FIG. 3  is a schematic drawing of a plurality of optical units positioned for mutual operation as a system in accordance with the present invention; 
         FIG. 4  is a Table showing signals that are generated by the cooperative operations of light beam emitters and signal detectors for a system as shown in  FIG. 3 ; and 
         FIG. 5  is a graph of signal responses showing an exemplary difference between the optical responses of benign materials and those of hazardous materials. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , a system for an optical smoke detector in accordance with the present invention is shown and is generally designated  10 . As shown the system  10  includes a computer  12  that is directly connected with a sequencer  14 . In turn, the sequencer  14  is connected to a plurality of emitters, of which the emitters E 1 , E 2  and E 3  are exemplary. As intended for the system  10 , each of the emitters E are positioned to direct a laser beam  16  to a point  18  in a smoke cloud  20 . The light in the laser beam  16  will then be scattered as it passes through the smoke cloud  20 , and will be received by a plurality of detectors, of which the detectors D H , D V , D′ H , D′ V , D″ H , and D″ V  are exemplary.  FIG. 1  also shows that these detectors (D H , D V , D′ H , D′ V , D″ H , and D″ V ) are each connected, in sequence, to a pre-filter  22  and a tracking filter  24 . Further, the system  10  is shown to include an oscillator  26  that is connected between the computer  12  and each of the emitters E 1 , E 2  and E 3 , with the oscillator  26  also connected to the tracking filter  24 . 
     In detail, each of the emitters E 1 , E 2  and E 3  includes two light emitting diodes (LEDs) that are specifically interrelated to each other. Importantly, the laser light beams  16  that are emitted from the LEDs of a respective emitter E 1 , E 2  and E 3  have a same wavelength (λ). They have, however, a different polarization. Specifically, the emitter E 1  will alternately transmit a horizontally polarized light beam  16  of wavelength λ H , and a vertically polarized light beam  16  of wavelength λ V . Similarly, the emitter E 2  will transmit light beams  16  of wavelengths λ′ H  and λ′ V , while the emitter E 3  will transmit light beams  16  of wavelengths λ″ H  and λ″ V . Preferably, λ is substantially red light, λ′ is substantially green light, and λ″ is substantially blue light. As envisioned for the present invention, the transmission of light beams  16  from the respective emitters E 1 , E 2  and E 3  is controlled by the computer  12  through a concerted action of the sequencer  14  and the oscillator  26  to create signals S for use by computer  12  for generating an output  28 . 
     Within the system  10 , the operational positioning and orientation of the emitters E 1 , E 2  and E 3 , relative to the detectors D H , D V , D′ H , D′ V , D″ H , and D″ V  will perhaps be best appreciated with reference to the optical unit shown in  FIG. 2  and generally designated  30 . For the optical unit  30 , it will be seen that a single emitter (e.g. E 1 ), and its associated detectors (i.e. D H  and D V ), are positioned on the circumference of a circle  32 . As shown, the circle  32  is centered on the point  18  in smoke cloud  20 . And, the laser light beam  16  (in this case, λ) is directed from the emitter E 1 , and through the point  18 , to a reference detector  34 . This reference detector  34  may be polarized or unpolarized. In order to properly orient the optical unit  30 , the reference detector  34  is positioned on the circle  32  diametrically opposite the emitter E 1 . As shown, the detectors D H  and D V  are then positioned opposite the path of light beam  16  from each other. And, they are respectively distanced from the reference detector  34  by a same arc length θ. As intended for the system  10 , which preferably includes three optical units  30 , the arc length θ will be equal to thirty degrees (30°). 
     A preferred layout of three optical units  30  for the system  10  is presented in  FIG. 3 . With reference to  FIG. 3  it is to be appreciated that for this configuration of the system  10 , the arc distance θ along the circumference of circle  32  will be the same from each detector D to an adjacent emitter E or to an adjacent reference detector (e.g. reference detector  34 ). This will then establish an arc distance of 4θ (i.e. 120°) between any two of the emitters E 1 , E 2  and E 3 . Further, it is also to be appreciated that as each of the emitters E 1 , E 2  and E 3  are activated, signals “S” will be simultaneously generated at all of the detectors D H , D V , D′ H , D′v, D″ H , and D″ V  in the system  10 . 
     By cross referencing  FIG. 3  with  FIG. 4 , the signal generation capability of the system  10  will be appreciated. As already disclosed, each emitter E in the system  10  is capable of transmitting a specific wavelength light with different polarizations (i.e. emitter E 1  transmits λ H  and λ V , E 2  transmits λ′ H  and λ′ V ; and E 3  transmits λ″ H  and λ″ V ). In the Table of  FIG. 4  the signals S are subscripted S (emitter)(detector) . This is done by identifying the polarization (H or V) of light transmitted by the emitter, as well as the polarization (H or V) of the particular detector D H , D V , D′ H , D′ V , D″ H , or D″ V  that generates the signal in response to light transmitted from the emitter E. [Note: primes are provided depending on wavelength or optical unit  30  association]. For example, when emitter E 2  activates its horizontally polarized light beam  16  (i.e. λ′ H ), the signals S (emitter)(detector)  that are generated by detectors D H , D V , D′ H , D′ V , D″ H , and D″ V  are respectively, S H′H , S H′V , S H′H′ , S H′V′ , S H′H″  and S H′V″ . 
     In the operation of the system  10 , the computer  12  uses the sequencer  14  to sequentially activate the LEDs of emitters E 1 , E 2  and E 3 . In concert with its operation of the sequencer  14 , computer  12  also uses the oscillator  26  to establish a so-called “blink rate” for the transmission of light beams  16  from the emitters E 1 , E 2  and E 3 . Accordingly, a sequence of light beams  16  having wavelengths and polarizations λ H , λ V , λ′ H , λ′ V , λ″ H , and λ″ V  are sequentially transmitted through the smoke cloud  20 , at the established “blink rate”. Consequently, for each sequence of light beams  16 , all of the signals S shown in  FIG. 4  are generated. 
     An important aspect of the system  10  is the combined use of the pre-filter  22  and the tracking filter  24 . In detail, the pre-filter  22  is used to eliminate the substantially d.c. component of background signals from the signals S. On the other hand, the tracking filter  24  is driven at the established “blink rate” to effectively isolate the received signals S. The isolated signals S can then be identified to correspond with times when a light beam  16  is being transmitted from an emitter E. 
     In accordance with the operation of system  10 , after they have been generated and filtered, all of the signals S (see  FIG. 4 ) are transferred to the computer  12 . The computer  12  then uses the signals S to calculate normalized polarization ratios, ρ(θ). Specifically, as used for the present invention a polarization ratio is calculated according to the expression:
 
ρ(θ)=σ HH (θ)/σ VV (θ)
 
wherein σ HH (θ) and σ VV (θ) are, respectively, a differential mass scattering cross section for horizontally polarized light, and a differential mass scattering cross section for vertically polarized light. As used by the system  10  of the present invention, the polarization ratio, ρ(θ), can then help identify smoke from a petrochemical (hydrocarbon) source. In particular, a succession of these normalization ratios are calculated and compared with empirical data to classify the origin of the smoke cloud  20 . As shown in  FIG. 5  this classification will provide an output  28  to determine whether particles in the smoke cloud  20  are in a group  36  of typically benign elements, or are in a group  38  of typically toxic elements (e.g. petrochemicals).
 
     While the particular Electro/Optical Smoke Analyzer as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.