CN101135631A - Particle monitor, smoke detector and method of construction thereof - Google Patents

Abstract

The present invention relates to a particle monitor adapted to determine the presence of predetermined particles in a detection zone, comprising: at least one emitter adapted to irradiate light onto the detection area, the irradiated light comprising light of a second level of brightness; a receiver assembly proximate the detection area and adapted to receive light scattered from the detection area, the receiver assembly having a primary stop and a lens stop, the primary stop being positioned relative to the emitter such that the secondary light is directed away from the lens stop. The invention also relates to a method of constructing a receiver assembly in a particle detector, comprising the steps of: providing at least one emitter adapted to irradiate light onto the detection area, the irradiated light comprising light of a second level of brightness; a primary stop and a lens stop are provided, the primary stop being positioned relative to the emitter such that the secondary light is directed away from the lens stop. The particle monitor and the smoke detector have high sensitivity to smoke and cannot give an alarm by mistake due to dust, and can be used for ventilation, air-conditioning or pipeline monitoring, building, fire fighting or safety monitoring.

Description

Particle monitor, smoke detector and method of construction

This application is a divisional application of Chinese Patent Application No. 200480031342.4 with the filing date of October 20, 2004, entitled "Improvement of Particle Monitor and Its Method".

technical field

The present invention relates to the field of detection, analysis and/or determination of substances or particles suspended in fluids.

In a particular form, the invention relates to smoke detectors for detecting undesired pyrolysis or combustion in substances. In another form, the invention relates to smoke detectors of the early detection type that may be used for ventilation, air conditioning, or duct monitoring of particular areas. In yet another form, the invention relates to surveillance monitoring, such as building, fire, or security monitoring. In yet another form, the invention relates to environmental monitoring, such as the monitoring, detection and/or analysis of fluids, zones, areas and/or surrounding environments, including commercial and industrial environments.

Obviously, the invention has wide applicability and the particular forms described above are given by way of example only, without limiting the scope of the invention to these forms.

Background technique

The present inventors established a recognition that the types of smoke produced in various pyrolysis and combustion environments are different. Fast burning flames tend to produce large quantities of very small solid particles that can aggregate into irregular shapes to form soot. Conversely, the early stages of pyrolysis tend to produce smaller quantities of larger liquid particles (with high boiling points), often present as suspended dust particles that can coalesce to form larger, translucent spheres.

The inventors have also established a recognition that detection of a slow increase in number of relatively large particles over a sustained period typically indicates a pyrolysis or incomplete combustion (smoldering) condition, whereas rapid detection of a large Small particles without early pyrolysis or incomplete combustion indicate the use of arson, including the use of accelerants.

The inventors have also established the recognition that dust particles result from the abrasive or athermal decomposition of natural substances or organisms in the environment and that these particles are generally very large compared to smoke particles.

The inventors have also established the following realizations:

Traditional point-type smoke detectors were originally designed for ceiling mounting in the area to be protected. These detectors have low sensitivity to detect the presence of undesired pyrolysis in the presence of large quantities of gas passing through the monitored area, thus impairing the ability of the detector to sense the presence of undesired pyrolysis.

To overcome these drawbacks, highly sensitive inhalation smoke detectors have been developed and are often deployed on ducts to monitor an area. These detectors provide detection hundreds of times more sensitive than traditional point-type detectors. These suction systems utilize negative pressure through air pumps, and also utilize dust filters to reduce unwanted dust contamination, which contaminates detectors, or is indistinguishable from smoke detection causing false alarms to be triggered.

The smoke detectors preferred for use in suction systems are turbidimeters. This is a detector sensitive to particles of various sizes, such as those produced in fires, or in the early stages of overheating, pyrolysis, or incomplete combustion.

Prior art optical smoke (or airborne particle) detectors typically use a single light source to illuminate the detection zone likely to contain such particles. The use of two light sources has been proposed for some detectors. Particles scatter some of this light to one or more receiver elements (or sensors). The signal output from the receiver element is used to trigger the alarm signal.

Other detectors utilize a laser beam, usually in the near-infrared wavelength range, that provides a polarized monochromatic light source. However, these detectors are not considered true turbidimeters because they tend to be overly sensitive to certain particle size (particle size) ranges at the expense of other size ranges.

A drawback of the detectors described above is their relative insensitivity to early pyrolysis and incipient fires, as well as the very small particle characteristics of some fast burning fires.

Ionization smoke detectors, on the other hand, use a radioactive element such as americium to ionize the air in the detection chamber. These detectors are more sensitive to very small particles from flammable fires, but less sensitive to larger particles from pyrolysis or incomplete combustion. They have also been found to be more prone to venting to displace ionized air within the detection chamber and thereby trigger false alarms. This creates a practical limit to its useful sensitivity.

Other smoke detectors use xenon lamps as the single light source. Xenon lamps produce a continuous spectrum similar to sunlight, including the ultraviolet, visible, and infrared wavelength ranges. Particles of all sizes can be detected with this light source, and the detector produces a signal proportional to the mass density of the smoke, which is characteristic of a true turbidimeter. However, this detector cannot characterize the type of fire since it cannot discern (distinguish) specific particle sizes. Also the xenon light (source) has a relatively short lifetime of about 4 years and its light intensity is known to vary, which affects the sensitivity.

The inventors have also realized that in order to provide a wide output range in sensitivity, prior art detectors provide an analog-to-digital converter (ADC) for applying the smoke concentration data to the microprocessor. With careful design, essentially the entire capacity of the ADC is used to represent the maximum smoke concentration, eg (typically) 20%/m. ADCs running at 8-bit resolution are efficient, while ADCs of 10 bits or greater are more expensive and require larger microprocessors. It has been found that a 10 bit ADC allows dividing the concentration of 20%/m into 1024 steps, each step representing an increment (gain) of 20/1024 = 0.02%/m. So the levels are 0, 0.02, 0.04, 0.06, etc., with no possibility for finer increments. At low smoke levels, this is considered a very coarse resolution, making it difficult to finely set alarm thresholds. However, at high smoke concentrations, a resolution of 0.02%/m is unnecessary, eg the ability to set alarm thresholds at 10.00%/m or 10.02%/m is of little benefit. It is therefore considered that the resolution of the prior art detectors is too coarse at low smoke concentrations and too fine at high smoke concentrations.

Any discussion of documents, devices, acts or knowledge contained in this specification is intended to illustrate the context of the invention. It should not be taken as an admission that any material forms part of the prior art base or common general knowledge in relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.

It is an object of the present invention to provide a particle detection device and method capable of improved detection, identification and/or analysis of particles, pyrolysis, incomplete combustion (smoldering), and/or fire events and dust, A corresponding improvement in the detection of fluid-borne particles is thereby provided.

Another object of the present invention is to provide a particle detection device suitable for use in conjunction with a pipeline or as a stand-alone detector and/or monitor.

It is a further object of the present invention to alleviate at least one drawback associated with the prior art and to provide one or more improvements associated with particle detectors and/or monitors and methods thereof.

Contents of the invention

According to various aspects of the present invention, the monitoring, surveillance, determination, detection and/or analysis of particles, environments, fluids, smog, zones, or areas may include the presence of particles and/or particle Determination of characteristics.

In this regard, the present invention provides, in one aspect, a method and apparatus for determining the presence of particles of approximately a predetermined size or size range in a fluid sample, the method comprising the steps of: illuminating the sample with light of a first wavelength, Obtaining a first response signal representative of the first irradiation, irradiating the sample with light of a second wavelength, obtaining a second response signal representative of the second irradiation, and determining a sample having the size or the size range by comparing the first and second signals the presence of particles.

Preferably, the illumination is horizontally and/or vertically polarized.

In another aspect of the present invention there is provided a gain control apparatus adapted to provide gain control in a particle monitor, said apparatus comprising a first gain stage having a first amplifier, a second gain stage having a second amplifier, and a voltage or current controlled feedback (means) from the output of the second gain stage to the input of the first gain stage so that the frequency response of the amplifier is not affected by said feedback (signal).

In yet another aspect of the present invention, a method of determining a maintenance interval for a particle monitor is provided, the method comprising the steps of: determining the presence of dust particles, providing detection of the presence of the particles, and providing maintenance when the detection reaches a predetermined threshold. instruct.

In yet another aspect of the present invention, a particle monitoring chamber is provided that includes a first lens operatively associated with an illumination source, a second lens for focusing incident light onto a receiver element, and a lens for primarily blocking light. Scatter (diverge) directly from the first lens to enter the main diaphragm of the second lens.

In another aspect of the present invention, there is provided a method and apparatus for determining the velocity of a fluid flowing through a given area, the method comprising the steps of: providing a first sensor at a location of lower flow velocity in a fluid flow path, at A relatively higher flow rate location in the fluid flow path provides a second sensor having a temperature characteristic substantially similar to that of the first sensor, and the flow rate is determined based on detection of the cooling effect of fluid flowing through the first and second sensors .

In addition, according to another aspect of the present invention, there is provided a method and apparatus for installing a casing on a pipeline, the method comprising the steps of: providing at least one joint piece coupled with the casing, positioning the casing at The fitting is shaped to substantially fit the piping profile near the installation area near the installation area of the pipe, and the housing is connected using the fitting.

The present invention also provides a monitor for monitoring the presence, concentration and identity of particulates in a fluid medium, comprising:

at least one emitter adapted to irradiate light to the detection region, the irradiating light comprising light of a second level of brightness;

a receiver assembly proximate to the detection region and adapted to receive light scattered from the detection region, the receiver assembly having a primary diaphragm and a lens diaphragm, the primary diaphragm positioned relative to the emitter such that secondary light is directed away from the lens aperture.

Wherein, the main diaphragm is suitable for shielding the secondary light from the lens diaphragm.

A particle monitor according to the present invention, further comprising: in the receiver assembly, the receiver aperture positioned relative to the main aperture such that light of the tertiary brightness reflected from the main aperture does not impinge on the in the receiver element.

A particle monitor according to the invention, further comprising an emitter diaphragm associated with at least one emitter. Therein, the emitter aperture is adapted to shield the emitter light directly incident on the main aperture or the lens aperture.

A particle monitor according to the invention wherein the main aperture is larger in size than the lens aperture.

A particle monitor according to the invention, wherein the emitter is also adapted to provide light of the first level of brightness. Wherein the first-order light provides light of the first-order brightness in a cone; the second-order light is provided outside the cone-shaped light.

A particle monitor according to the invention wherein a portion of the tertiary light passes through a lens close to the lens stop. Wherein the lens is a biconvex lens. Wherein the lens has a relatively long focal length. Wherein the lens has two convex surfaces. Light scattered by the particles therein also passes through the lens. Wherein the spherical aberration of the lens enhances the separation of the light scattered by the particles from the tertiary light.

A particle monitor according to the present invention, wherein the tertiary light is unwanted light.

The invention also relates to a smoke detector comprising the monitor of the invention. Wherein the detector is a point detector. Alternatively, the detector is a suction detector.

A particle monitor according to the present invention, wherein the monitor is a point detector.

A particle monitor according to the invention, wherein the monitor is a suction detector.

A method of incorporating a receiver assembly in a particle detector adapted to determine the presence of particles within a detection region, the method comprising the steps of:

providing at least one emitter adapted to irradiate light to the detection region, the irradiating light comprising light of a second level of brightness;

A main stop and a lens stop are provided, the main stop being positioned relative to the emitter so that the secondary light is directed away from the lens stop.

The method according to the invention, wherein the main diaphragm is arranged in the receiver assembly.

The method according to the invention, wherein the lens stop is arranged in the receiver assembly.

The method according to the invention, wherein the main diaphragm is adapted to shield the lens diaphragm from secondary light.

The method according to the present invention further comprises: in the receiver assembly, providing a receiver diaphragm positioned relative to the main diaphragm such that light of the tertiary brightness reflected from the main diaphragm does not impinge on the vicinity of the receiver diaphragm. in the receiver element.

The method according to the invention further comprises providing an emitter stop in combination with at least one emitter. Wherein the emitter diaphragm is provided in such a way that the emitter light is shielded from being directly incident on the main diaphragm or the lens diaphragm.

The method according to the invention, wherein the emitter is also adapted to provide light of the first level of brightness. Wherein the first-order light provides light of the first-order brightness in a cone; the second-order light is provided outside the cone-shaped light.

A method according to the invention wherein a portion of the tertiary light passes through a lens close to the lens stop. Light scattered by the particles therein also passes through the lens. The method according to the present invention further includes utilizing the spherical aberration of the lens to enhance the separation of the light scattered by the particles from the tertiary light.

According to the method of the present invention, wherein the tertiary light is unwanted light.

A smoke detector constructed to operate in accordance with the method of the present invention. Wherein the detector is a point detector. Alternatively, wherein the detector is a suction detector.

A particle monitor constructed to operate in accordance with the method of the present invention. Wherein the monitor is a point monitor. Alternatively, wherein the monitor is a suction monitor.

The invention also provides a logarithmic signal as an output to trigger a threshold or alarm of the detector. It refers to a signal whose amplitude can be compressed according to a logarithmic function or scale. The logarithmic signal may represent various characteristics of the detected particles, such as presence, number, frequency, concentration and/or duration.

Essentially, in one aspect of the invention, different wavelengths, various wavelength ranges and/or polarizations are used to detect predetermined particles in a fluid.

Essentially, in another aspect of the invention, the subtraction of the two signals or the ratio of the two signals provides a more measurable output indicative of particle and particle size detection.

Essentially, in another aspect of the invention, this output indicative of particle detection is amplified from two signals.

Other and preferred aspects are disclosed in the description and/or are defined in the appended claims forming a part of the description of the invention.

The present invention has been found to yield advantages such as reduced size, cost and energy consumption while achieving the highest industry standards for sensitivity, reliability, maintenance intervals and minimization of false alarms, and/or for Monitoring for the presence of smoke and/or dust particles in the environment makes it possible to provide very high sensitivity to smoke without false alarms due to dust.

Throughout this specification, reference is made to various different light sources with specific wavelengths. Light sources and wavelengths are mentioned only because they are currently commercially available light sources. It should be understood that the principles underlying the invention are equally applicable to light sources of different wavelengths.

Monitors may include the mentioned detectors or similar devices.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating the preferred embodiment of the invention, have been given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be appreciated from the detailed description. It will become apparent to those skilled in the art.

Description of drawings

By referring to the following description of preferred embodiments in conjunction with the accompanying drawings, those skilled in the relevant art can better understand the further disclosure content, purpose, advantages and aspects of the present application, and the accompanying drawings are only provided by way of illustration, and Not intended to limit the present invention, in the accompanying drawings:

Figure 1 shows the results of blue light at 430nm wavelength and red light at 660nm wavelength on particles in the entire particle size range;

Figure 2 shows the results of blue light 430nm wavelength and green light 530nm wavelength on particles in the entire particle size range;

Figure 3 shows the results of blue light at 470nm wavelength and infrared light at 940nm wavelength on particles in the entire particle size range;

Fig. 4 shows the result after the relative subtraction of the red light signal from the blue light signal;

Figure 5 shows the result after the relative subtraction of the green light signal from the blue light signal;

Fig. 6 shows the result after relatively subtracting the infrared light signal from the blue light signal;

Figure 7 shows the change in particle size over time for various types of combustion agents;

Figure 8 shows the comparative response of the infrared and blue channels to smoke from various combustion agents and/or various stages of fire growth;

Figure 9 shows the relative ratio of channel B output and channel A output for a given combustion agent in response to airborne particles during tracking;

Figure 10 shows a schematic block diagram of a smoke detector according to one embodiment of the present invention;

Figure 11 shows a circuit diagram of a form of gain controlled amplifier according to an embodiment of the present invention;

Figures 12 and 13 illustrate preferred control room geometry including indicating light paths;

Figure 14 illustrates the use of a lenticular lens according to an aspect of the invention;

Fig. 15 shows the relevant operation of the aspheric lens according to one aspect of the present invention;

Figure 16 illustrates the use of an aspheric mirror according to an aspect of the present invention;

Figure 17 illustrates the relative operation of a lenticular lens according to an aspect of the present invention; and

Fig. 18 shows an example of mounting the detector unit to the plumbing fixture.

Detailed ways

In the described embodiment at least two channels are mentioned, one channel A using wavelengths such as red or infrared wavelengths and the other channel B using wavelengths such as blue wavelengths. Other channels may be used, such as channel C, which uses wavelengths such as the green wavelength. Other wavelengths may also be used in accordance with the present invention, as will become apparent in the following description. In general, it is preferred if the reading established by the longer wavelength rivals that established by the shorter wavelength. More preferably, the longer wavelength is subtracted from the shorter wavelength. A ratio can also be used to compare wavelength readings.

wavelength of light

In one aspect of the present invention, the inventors have determined that the wavelength of light employed critically affects the sensitivity of the device to particle size. Bohren CF and Huffman DR in "Absorption and Scattering of Light by Small Particles", ISBN 0471-05772-X describe the scattering (divergence) of light from particles in various size ranges.

It has been established that the Mie equation is suitable for examining particles within the size range of conventional smoke and dust. Fast-burning fires tend to produce very large quantities of very small carbonaceous particles, which can aggregate into irregular shapes to form soot. In contrast, the early stages of pyrolysis tend to produce smaller quantities of larger liquid particles (with high boiling points), usually in aerosols, which can coalesce to form larger translucent spheres or small liquid droplets (microdroplets). Dust particles are generally produced by mechanical abrasion and have irregular shapes that can be approximated by larger spheres for modeling purposes. A source of smoke or dust is unlikely to be monodisperse (comprising one particle size), but more likely to be polydisperse, with a range of sizes that follow a Gaussian distribution. The inventors have found that a typical standard deviation for the size distribution is around 1.8 to 2.

The distribution of airborne particles in cities was also found to be bimodal, with peaks at about 0.1 microns and 10 microns. Typically, smoke particles are in the range of 0.01 micron to 1 micron, while airborne dust particles are in the range of 1 micron to 100 microns. However, there is some overlap at the 1 micron boundary, since in nature the smallest dust particles are smaller than the largest possible smog particles.

The inventors have also determined that certain particle sizes are more easily discerned by certain (different) wavelengths of light. Assuming this, we use two wavelengths of incident light. The light can be anywhere from blue to red (and infrared). An example is light in the range from 400nm (blue light) to 1050nm (red light). For example, 430nm (blue light) and 660nm (red light) may be used.

By applying Mie theory to particle sizes with a population mean diameter in the range of 0.01 microns to 10 microns and using a standard deviation of 1.8, Figure 1 shows incident light at two wavelengths (430nm (blue light) and 660nm (red light) light)), each of which is unpolarized, vertically polarized, or horizontally polarized, and is emitted at the same angle with respect to the optical axis.

In Fig. 1, the blue light system in the results (B=unpolarized blue light, BV=vertically polarized blue light, BH=horizontally polarized blue light) is very suitable for the detection of smoke and dust, while the red light system in the results (R, RV and RH) are also good for dust detection, but are weaker at detecting a wide range of smoke particles due to the lack of response to small particles. All the curves in Figure 1 cluster together above about 0.8 microns, while there are significant differences between the curves for particle sizes below 0.8 microns. Optimum separation of vertical blue light (BV) and horizontal red light (RH) is achieved. These curves cannot be effectively separated at larger diameters. Periodicity (edge effects or resonances) in the curve is caused by phase cancellation and enhancement due to interactions between a given wavelength and a given particle size.

If we instead examine the combination of wavelengths 430nm (blue light) and 530nm (green light), the results shown in Figure 2 are obtained. Here, the individual graphs are more similar to each other, and it is difficult to separate the curves above about 0.5 microns.

The wavelengths chosen for illustration are limited to those of commercially available emitters. Based on the information obtained in Figure 2 (530nm), the results for orange light (620nm) are similar to Figure 1 (660nm).

The results for blue light (470nm) and infrared light (940nm) are shown in FIG. 3 . In FIG. 3, the wavelength separation is basically an octave. It can be seen that the curves are more clearly separated in the region below 1 micron (the standard boundary between smoke and dust).

While this has some advantages in operating monitors at even more widely separated wavelengths, currently available technology is a limiting factor. The receiver element used to detect scattered light is a PIN photodiode with enhanced blue light response. Due to the peak response at 850nm, the response decreases by about 30% at 400nm and 1050nm, so for practicality, the emitter wavelength is currently limited to this range. Of course, if another receiver element is available, the wavelength of the light entering the particle can be changed to achieve greater separation.

From the above conclusions, it can be seen that in one embodiment of the present invention, the wavelengths used for the two emitters to illuminate the particles to be detected should preferably be blue/ultraviolet light in the range of 400nm to 500nm and red light in the range of 650nm to 1050nm. light/infrared light.

In another aspect of the invention, it has been found that more reliable "triggers" can be produced if the results of the received signals are compared to each other, for example, by comparing ratios or by mutual subtraction (i.e., subtracting one signal from the other) Or a detection signal that indicates the presence of particles of a size of interest in applications to which the monitor of the present invention is suitable. So, for example, if the monitor of the present invention is configured as a "smoke" monitor, then smaller particles should be of more interest than larger (dust) particles. Thus, the inventors have realized that for smoke monitors, for example, blue light has been found to respond to smaller as well as larger particle sizes, while infrared light only responds to larger particles. By acquiring a signal based on a "blue light" response signal that is less than an "infrared light" response signal, the monitor can be set to have a relatively high responsivity to small particles and a low or zero responsivity to larger particles .

For example, Figure 4 shows the results of subtracting red horizontal (polarized) (RH), red unpolarized (R), or red vertical (polarized) (RV) data from blue (B) data . Monitors set up in these ways respond with higher sensitivity (with the best sensitivity from the B-RH combination) to particles smaller than 1 micron. To avoid confusion, the results for BH and BV are not shown, but they are consistent.

Subtraction of GH, G and GV from B yields the results of FIG. 5 for comparison with FIG. 4 . Relatively small particle sizes are easier to discern than larger (dusty) particle sizes, although edge effects are significant.

Figure 6 shows the result after subtracting IRH from B. Other results are omitted for clarity. Also shown are some published data on average particle sizes obtained for incense, cotton wicks, toast, and Portland cement (a dust substitute).

It can be seen that the monitor used to perform this subtraction has a suitable sensitivity to conventional smoke types and is able to reject dust to a considerable extent (relatively).

From this subtractive aspect, yet another aspect of the present invention has been developed in that a properly constructed gain amplifier can be utilized to provide an appropriate output signal for use by an alarm or other warning device or system. This aspect will be more fully disclosed below.

In addition to the two wavelengths disclosed above, if a third or other wavelength could be used, it would be possible to identify not only small and large particles, but also particles of other (intermediate) sizes, depending on the wavelength used.

dual channel design

According to one aspect of the invention, by using a two-channel design to provide another characteristic, as described herein, by subtracting the A (reference) channel from the B (sample) channel (or vice versa), we can achieve the zero point balance. It has been found that this balance does not change significantly if the background of the monitoring chamber changes over time. The present inventors have realized that as the monitoring chamber ages or becomes contaminated over a long period of time (ie a time greatly extended by the use of dust filters), the background light level can change. The benefit of channel subtraction is that since both channels (especially to dust buildup) respond essentially the same, their effects cancel out, which minimizes any change over time in the output from the summing circuit. It is worth noting that the signal obtained from dust does not depend on it being airborne - or that it can stay on the surface. The same holds true for any matter larger than dust - dusty agglomerates or even (walls).

According to maintenance standards, this shift towards zero due to contamination is considered a valuable characteristic.

Signal Level Analysis

The invention is further disclosed with reference to its application to smoke detectors. However, it is worth noting that the invention is not limited to this application.

Conventional ceiling (ceiling) mounted "optical" smoke detectors typically provide a sensitivity equivalent to an obscuration of about 10%/m (3%/ft) for generating an alarm. The benchmark for very high sensitivity smoke detection requires at least two orders of magnitude higher sensitivity, equivalent to an alarm set point at levels below 0.1%/m obscuration over the entire range. Eccleston, King and Packham (Eccleston AJ, King NK and Packham DR, 1974: The Scattering Coefficient and MassConcentration of Smoke from some Australian Forest fires, APCA Journal, v24 no11) have shown that for eucalyptus forest fire smoke, the 0.1%/m level corresponds to With a visual range of 4km and a smoke concentration of 0.24mg/m ³ . Such a high sensitivity enables early detection of pyrolysis and thus provides the earliest warning of a potential fire in a building with a low false alarm rate.

Most very high sensitivity smoke detectors today utilize an optical (monitoring) chamber with an infrared solid state laser diode. The long wavelength of infrared light is good for detecting the larger airborne particle properties of dust and smoke aerosols from some types of fires, but is poor at detecting the very small particles contained in other fires. Conventional solid-state lasers, preferably operating at shorter visible wavelengths, are expensive or do not operate reliably at elevated ambient temperatures (60°C). To overcome these difficulties, in a preferred embodiment of the invention applied to smoke detectors, it was decided to use light emitting diode (LED) emitters operating at the blue end (470nm) of the visible spectrum.

As will be explained further below, the monitor arrangement incorporates such a blue light emitter arranged at a 60° angle to the axis of the receiver element within the optical monitoring chamber. The monitor also included a reference emitter at 940nm (infrared light) positioned at the same angle, but horizontally opposite the blue emitter. With an effective emitter illumination cone angle of 10°, this configuration provides a relatively optimal setup that maximizes the sensitivity of the system while minimizing background light that could interfere with receiver elements.

For a specified smoke density (0.1%/m), comprising (say) particles with a material mean particle size of 0.3 μm (with an actual geometric standard deviation of 1.8), Weinert (WeinertD, 2002: Assessment of Light Scattering from Smoke Particles for A Prototype Duct-mounted Smoke Detector, unpublished) has determined that in the monitor setup used, the signal strength received by such smoke by irradiation with an unpolarized blue light source is on the order of 4.5E-8 per unit of irradiation. The Weinert data at 470 nm and 940 nm are plotted and shown in FIG. 3 . Crucially, this means that, due to unwanted residual reflections from the monitoring chamber walls, the "background" light intensity received by the element must be at least 8 orders of magnitude lower than the emitter beam intensity in order not to interfere with the desired light signal (scattered from smoky).

In one form, a blue light emitter is specified to have a luminous intensity of 40 candela (cd) at a drive current of 500 mA. By definition, the power level of 1 cd is 1.464 mW per steradian (sr), so the rated power is 1.464*40=58.6 mW/sr. The 5° half angle is converted to 2π(1-cos(5))=0.024sr, so the output power is 58.6*0.024=1.4mW. Incidentally, at this drive current, the transmitter voltage drop is 4.0V, so if a 0.1% duty cycle is used, the input power to the transmitter is 0.5*4.0*0.001=2.0mW, which is more than its maximum power draw Dispersion rating is 1% smaller.

Thus, at a pulser power output of 1.4mW, the scattered light signal directed to the element for the setup used is 1.4*4.5E-8=6.3E-5μW. This level of illumination is directed and focused onto the receiver element, which is the PIN photodiode in the receiver module. The component is specified to have a sensitivity of 0.2A/W at 400nm, changing to 0.31μA/μW at 470nm. Thus, at a specified 92% (uncoated) lens transmission, the signal converted by the illuminated element is 0.31*6.3E-5*0.92=1.8E-5 μA.

In one form, the receiver module includes a three-stage AC-coupled pulse pre-amplifier comprising a current-to-voltage converter followed by two voltage amplifiers. The converter is an operational amplifier with a PIN photodiode connected differentially between the inverting and non-inverting inputs, ignoring the series resistance. The feedback resistor could be 3.9M (shunted with 3.9pF), so at mid-band frequencies, for an input signal of 1µA, the output from this stage would be 3.9E6*1E-6 = 3.9V/µA. In response to the specified element illumination, the output becomes 3.9*1.8E-5=7.0E-5V or 70μV.

In one form, the next two stages are op amps each with a mid-band gain of 10, so the receiver module output under the specified illumination should be 7.0 mV. A standard full-scale output level for signal processing may be 3V, so the main amplifier voltage gain would be 3/7.0E-3=429. Using two similar stages, such an amplifier would require a gain of 21 per stage. In practice a gain of 17 per stage has been found to be sufficient to produce the nominal 0.1%/m sensitivity required for full scale.

Undoubtedly, the sensitivity of all smoke detectors depends on particle size, and a meaningful standard would need to specify this size (or range of sizes). However, the perfect international benchmark for performance is the VESDA MK3 monitor recently manufactured by Vision Systems Australia using a xenon light source. In fact, this light source is comparable to blue light emitters because of the spectral characteristics of xenon lamps, combined with the spectral response of PIN photodiodes and light from small suspended particles or molecules that favor short wavelengths such as 1/ ^λ4 Scattering, determined to be benchmarked for xenon-based monitors has a characteristic wavelength of 470 nm, the same as for blue emitters. For this, reliable gases such as nitrogen and FM200 are continuously available as standards (which is not possible with infrared laser based detectors).

As mentioned above, the monitor employs two emitters operating at different wavelengths. Referring to Figure 3, for larger particles (>1μ), the design goal is to generate the same signal level at the element from the IR signal as is the case for the blue light signal. At an infrared wavelength of 940 nm, the receiver element has a sensitivity of 0.55 μA/μW (comparable to 0.31 μA/μW at 470 nm). Since the light transmittance of the lens at 940nm remains 92%, and because all relevant equations are linear and the geometry is relatively uniform, the output power of the infrared light emitter can be reduced by a coefficient of 0.31/0.55=0.56. Since the IR light emitter has a power level of 343mW/sr (comparable to the blue light emitter's 58.6mW/sr) at 500mA, the required drive current for the IR light emitter becomes 500*0.56* 58.6/343 = 48mA. If polarizing filters are used, the drive current needs to be increased in order to overcome losses in such filters.

At the desired transmitter drive settings, the small background signal caused by cumulative reflections from the monitoring chamber walls should be at approximately the same (very low) level for either transmitter as seen from the receiver element. level. This requires monitoring the reflection (or absorption) of the walls of the chamber to be largely independent of differences in the wavelength used. Therefore, in the absence of any smoke in the monitoring room, the differential voltage between the dual channel outputs should be close to zero (or can be adjusted to be so).

By introducing smoke into the monitoring chamber, the voltage on each channel should increase, but the differential voltage between channels may often not be zero. This differential voltage provides an indication of the properties of the airborne particles. Figure 6 shows the sensitivity obtained when the infrared channel is subtracted from the blue channel. This result can be used to highlight the presence of particles smaller than 1 μm mass average particle size. Figure 6 includes straight lines consistent with published data for mass average particle sizes of particles produced from some existing materials (Portland cement "dust", toast, cotton wicks, and incense). The differential voltage should be zero or slightly negative in the first instance (large particles), but significantly positive in the other three instances (small particles). This shows the possibility of distinguishing dust while maintaining good smoke detection.

The particle size in the smoke aerosols can vary substantially depending on the combustion agent used, the temperature and time period (period), and the airflow conditions that determine the oxygen supply, cooling and dilution of the smoke. In Figure 7, data from Cleary, Weinert, and Mulholland (Cleary TG, Weinert, DW, and Mulholland GW, 2001: Moment Method of obtaining Particle Size Measures of Test Smokes, NIST) were averaged to create a graph of suspended particle size , the suspended particles were generated by four combustion agents, cooking oil (glass dish on electric stove), toast (oven), polyurethane foam (incomplete combustion or smoldering) and beech wood blocks (electric stove). It can be seen that in each case the average particles are initially small, increase in size and then fall as the combustion agent is completely consumed. As a summary, it can be said that the detection of small particles is important for the earliest possible warning of early fires. Other data show that the suspended particulate mass concentration reaches its highest value in the second half of each period plotted and decreases towards the end.

Figure 8 provides a more extensive comparison of the relative responses of the two channels, expected in published particle size order, for a large number of species. Here, the response of Portland cement (a dust substitute) has been normalized by reducing the infrared light emitter signal by a factor of 0.64. Data for Douglas fir and rigid polyurethane (Bankston et al; Bankston CP, Zinn BT, Browner RF and Powell EA, 1981: Aspects of the Mechanisms of Smoke Generation by Burning Materials, Combustion and Flame no 41 pp273-292) show that radiant heat The progression of the three different phases of the release rate, which should generate corresponding differential voltage signals.

Roughly and for reasons previously stated, Figure 8 can be taken as a comparison of the expected performance between standard xenon based and current laser based (infrared light) detectors.

Furthermore, for dual channel monitors, Figure 8 demonstrates increased sensitivity (4 or 5 times) to early fire incidents including pyrolysis and incomplete combustion compared to these infrared detectors while greatly reducing the sensitivity to source Possibility of sensitivity to false alarms from dust. This means no dust filter is required. In contrast, it is desirable to use dust filtration to minimize contamination and thereby maximize the maintenance interval and overall operational life of the monitor. Given that a good filter for dust can also trap smoke, the dust discrimination capability can be exploited to avoid unwanted false alarms caused by small amounts of dust that inevitably pass through the actual filter.

Also, because Channel A responds primarily to dust, the output from Channel A can be integrated (accumulated) over time (in months or years) to record the impact of the monitoring chamber and filter elements when distinguished from smoke. The actual exposure to dust thus makes it possible to determine and predict maintenance intervals depending on the (often unpredictable) surroundings. For example, the dust filter service interval may be determined based on an accumulated or counted number of detected dust readings. Once the count reaches or exceeds a predetermined threshold, the service indicator lights up or otherwise communicates. Preferably, the service indicator circuit should integrate the actual dust level and its duration.

logarithmic output

As mentioned above, to provide a wide output range of sensitivity, prior art detectors provide an analog-to-digital converter (ADC) for providing smoke concentration data to a microprocessor. With careful design, essentially all of the ADC's capacity is utilized to represent the maximum smoke concentration, eg (typically) 20%/m. ADCs operating at 8-bit resolution are useful, while ADCs of 10 bits or greater are more expensive and require larger microprocessors. It has been found that a 10-bit ADC allows dividing this 20%/m concentration into 2 ¹⁰ =1024 steps, each representing an increment of 20/1024=0.02%/m. So the levels are 0, 0.02, 0.04, 0.06, etc., without the possibility for finer increments. At low smoke levels, it is considered a very coarse resolution, making it difficult to finely set the alarm threshold. However, at high smoke concentrations, 0.02%/m resolution is unnecessary - for example, even having the ability to set alarm thresholds at 10.00%/m or 10.02%/m would be of little benefit. It is therefore considered that the resolution of the prior art detectors is too coarse at low smoke concentrations and too fine at high smoke concentrations.

However, according to this aspect of the invention, these prior art deficiencies described above are overcome by providing a logarithmic or deciles output range. According to the invention, the resolution has been found to be suitable for a given smoke concentration, ie fine at low smoke concentrations and coarse at high smoke concentrations. As illustrated, for the present invention, by using the logarithmic output range, the alarm threshold can be set at 0.010 or 0.011%/m at low smoke levels, and can be set at 10% at high smoke levels just as easily Set the alarm threshold at /m or 11%/m.

In other words, a logarithmic output is used for the entire wider smoke, recognizing that smoke is a very variable substance for which there is little benefit in measuring its density (concentration) to an accuracy greater than 2 significant digits. Concentration range and/or threshold setting provide advantageous sensitivity resolution.

smoke test results

A series of traces were carried out using smoke monitoring equipment constructed according to the present invention and constructed and assembled in accordance with the above disclosure of signal level analysis. The monitor is mounted on a 200mm diameter ventilation duct and a detector (probe) is inserted into the duct to sample the air passing through the duct. The inlet fan maintains a relatively continuous flow within the duct and ensures that airborne particles are thoroughly mixed with incoming fresh air. The outlet of the pipe is discharged through the flue. An electric furnace operating at about 350 °C was placed at the fan and duct inlet so that a small sample of the combustion agent could be placed on the electric furnace.

Since the fumes are entrained and mixed with the main stream of fresh air that is continuously drawn into the ducts from the test chamber, considerable dilution can occur with this device. This scenario was used to simulate a real protected environment where high levels of dilution would be expected in the early stages of early fire growth. Several different combustion agent samples were heated on an electric furnace to generate smoke suspended particles. In addition, some samples of dust released at the fan and duct inlets by agitation instead of an electric furnace were evaluated.

The outputs of the two monitor channels, A and B, are measured to provide the voltage excursion beyond the quiescent state (clean air) after airborne particles are introduced into the monitor.

Various combustion agent types were observed to generate smoke aerosols at different rates and concentrations. As the various combustion agents are heated and consumed, suspended particle size is expected to vary with time, and thus the relative output from channels A and B should vary accordingly. Figure 9 shows the channel B output expressed as a ratio of the channel A output in response to several particle sources (after correction to detect stable transients). These data are presented as ratios to account for the different airborne particle densities included (assuming we are now focusing on particle size). The length and position of each horizontal bar indicates the ratio of ranges that occurred during each follow-up trial. In many cases, the ratio quickly increases to a maximum value and then slowly decreases. In some cases, the ratio increases again at a lower value after one cycle. Some of these patterns (signals) were observed to be distinctly bimodal.

Figure 9 also shows the relative sensitivity of the monitors (in apparent order of average particle size) to these combustion agent and dust sources. Correspondingly, the nylon tubing initially produced the smallest particles (peak ratio 5.3). After halfway through the test, the ratio slowly decreased, and the combustion agent actually melted on the electric furnace and generated suspended particles for a relatively long time. Styrofoam had similar results. Combustion agents further down the graph tend to char and produce solid carbonaceous residues.

A heating wire test consisting of a 2m length of PVC insulated wire heated by a high current delivered by a 2V AC "range" transformer to simulate an overheated cable leading to early pyrolysis.

The solder resin results are from the melting of the shorter length turpentine cored solder, whose position in the table indicates the production of relatively large particles (high melting point droplets).

The results for steam are anomalous because the output readings obtained from boiling water sources are of a very small order of magnitude to generate an alarm condition, but the ratio includes the granularity set at the lower end of the graph. In contrast, in the case of various dust sources (including talc), all other sources produced large output readings, and only the channel output ratio was smaller.

There is obviously a huge difference based on particle size between smoke aerosols and dust, so it is possible to use this embodiment in generating an alarm to distinguish the smoke source needed for the alarm from the unwanted dust source.

In cases where the ratio is close to one, it can be understood that subtracting channel A (such as infrared light) from channel B (such as blue light) will result in a greatly reduced reading, thereby avoiding undesired alarms caused by these sources. In Subtracting channel A from channel B will still cause an alarm if the ratio is much higher than one. While the subtraction process does reduce the monitor's output for certain smoke types, it can in fact avoid adverse effects caused by dust sources. Desired alarms allow the monitor to operate at a higher sensitivity than would otherwise be the case.

Furthermore, these results are believed to be consistent with published data showing that for a variety of combustion agents, the primary particles released by pyrolysis are relatively small. Therefore, the type of monitor used here can provide the earliest warning of pyrolysis.

circuit description

Figure 10 schematically illustrates in block diagram one form of the invention for detecting smoke. The circuit drives a pair of light emitters 1 and 2, each having a different wavelength (color) and/or polarization characteristic. Each emitter is driven independently to provide light pulses of short duration (eg 0.4ms), optionally at intervals of, say, 150ms and 350ms. This enables the air quality to be updated twice per second, a high sampling update rate commensurate with low power consumption.

Part of the light scattered (divergent) from the airborne particles passing through the monitoring chamber 3 is received by optoelectronic elements (not shown) within the receiver module 4 . This signal is amplified in the receiver module 4 and sent to the main amplifier 5 with a gain controller 6 . The amplified signal then passes through a discriminator (discriminator) (comprising a pair of synchronous detectors 7, 8 and a pair of buffered sample-and-hold circuits 9, 10) which separates the signals originating from the two respective transmitters into In dual channels, use the number 9 to represent channel A, and the number 10 to represent channel B. Dual channels provide information about the type of particles in the air. Channel A is particularly responsive to dust particles, while channel B is primarily sensitive to smoke and somewhat to dust. This is because dust and smoke particles each cover a wide range of sizes, which can overlap to some extent. Therefore, in the subsequent circuit, the dust reading of channel A is subtracted from the smoke reading of channel B by means of adder 11 to obtain an indication signal which basically only provides smoke density (concentration).

The smoke density signal is applied to a threshold sensitive circuit 12 which operates a series of three lights and a relay 13 in response to the level of fire danger detected. These lights and relays are denoted, for example: A1 (warning, or level 1), A2 (activity, or level 2) and A3 (fire, or level 3). Typically these three alarm levels represent smoke densities approximately equivalent to 0.03, 0.06 and 0.10%/m obscuration rates, although the monitor can be adjusted to other settings, it should be understood that the signals and settings can be set to suit the present invention specific application.

In addition, the direct output 14 from channel A is used to indicate when the dust level is high independently of the smoke concentration level. This can also aid in testing, commissioning and demonstrations. The output also indicates when the monitor is in the process of identifying dirt.

Additional lamps and relays 13 may be provided as a "fail-safe" circuit applied to the summer 11 to provide a failure warning in the event the monitor fails to function properly with sufficient sensitivity. An analog output from summer 11 may also be provided for remote handling of fault and warning notifications. Optionally, the analog output may be provided from each of channels A and B to allow remote signal analysis and processing of fault and warning notifications.

A clock generator 15 can provide suitable timing signals when needed, and a power supply section 16 can distribute power to various parts of the circuit at appropriate voltages.

Desaturation of the output signal from the discriminator channel is necessary when very high smoke or dust concentrations are encountered. Such saturation would lose information about the relative signal levels produced by the two transmitters, thereby suppressing the discriminative function. First, the amplifier is provided with a large "headroom", enabling it to operate at full scale when, say, the signal level is half-saturated. Second, an automatic gain controller is provided. The DC output voltage from the discriminator channel is fed back to the gain control to ensure that saturation concentrations are not reached.

gain controller

Referring to FIG. 11 , the mid-band gain of the operational amplifier is determined by the ratio of the feedback resistance to the input resistance. For IC3a in Figure 11, the voltage gain is R4/R3, and for IC3b, the voltage gain is R6/R5. The high frequency breakpoints are determined by C4·R4 and C6·R6, while the low frequency breakpoints are determined by C1·(R1/R2), C3·R3 and C5·R5. The amplifier is DC coupled and the DC bias is set by R1 and R2.

The gain control device IC4 typically consists of an LDR (light dependent resistor) and LED (light emitting diode) closely coupled in a light-tight box. The LDR provides an adjustable resistance whose value is determined by the current delivered through the LED, which is externally controlled by R7. With no current through R7, the resistance of the LDR is virtually infinite, and at 10mA to 20mA the resistance drops to the range of 10kΩ to 100kΩ. Usually this LDR is connected across R4 or R6. This has the advantage in operation of increasing the high frequency breakpoint (C4·R4 or C6·R6), thereby upsetting the desired frequency response and phase characteristics of the amplifier. Additionally, it has been found that such an arrangement yields an incomplete dynamic range of gain control.

Since the two-stage circuit is non-inverting for the amplified signal, it is possible to connect the LDR from the output of the second stage (IC3b) to the input of the first stage (IC3a). This greatly increases the available effective dynamic range. Also, when IC4 is active, breakpoints C4·R4 and C6·R6 are not affected.

The current drive R7 is derived from the sample and hold voltage signals (high to low) of channel A and channel B, through Zener diodes (zener diodes) D5 and D6 to ensure that the gain control action does not take effect until the signal level is relatively large .

Importantly, the characteristics of the combination of LDR, LED and Zener diode are neither abrupt nor linear. It is non-linear and has the effect of providing a logarithmic gain function. Sudden changes in gain can cause instability or irregular behavior because high signal levels cause a sudden decrease in gain, which causes a sudden decrease in output, which in turn reduces drive to IC4, causing gain to increase again big. Also, this causes the alarm output relay to vibrate. The non-linear design allows for a small increase in output when the input goes high and provides control over a wide dynamic range.

The standard full-scale sensitivity of the monitor corresponds to an obscuration rate of 0.1%/m corresponding to the highest alarm threshold ("fire"), with intermediate alarm thresholds available below this level. By exploiting this logarithmic characteristic, it is possible to vary the set alarm output threshold so that higher level alarms can be within a non-linear range. In this way, sufficient resolution is provided to provide a first level of alarm (“warning”) at very low smoke densities (e.g. 0.01%/m), while the highest level of alarm can reach 1%/m, 10%/m or even higher.

monitoring room optics

Figure 12 shows ray diagrams of emitters operating at different wavelengths and/or polarizations. For clarity, the sample rays are shown according to their position at the center 1201, left or right end 1202 of the beam. Optionally, the beams are actually operated with short pulse durations. It can be seen that the light beams are formed by lensed emitters 1203, 1204 and limited by stops 1205, 1206 so as to pass through the center of the monitoring chamber, monitoring area or zone 1207. If smoke or dust is passing through this area 1207, these particles scatter a fraction of the beam's energy in multiple directions. Part of this energy is scattered in the direction of the main acceptance aperture 1208 and thus to the lens 1209 which focuses the energy onto the photocells in the receiver module 1210 . It is worth noting that intermediate diaphragms are dispensed with in this path, since stray light reflected by the monitoring chamber components and thus originating from unfavorable directions can be reflected by these intermediate diaphragms to be incident on the lens.

The direct beams 1201, 1202 then enter the absorbing channel 1211 where multiple reflections from the highly absorbing walls 1212 consume the light energy. This channel is designed to direct multiple reflected light towards the distal end of channel 1213 so that multiple reflections occur before any residual light appears. The combination of this absorption and the geometry of the main diaphragm for the monitoring chamber and the beam diaphragm avoids interference of light scattered from smoke or dust particles by residues of the initial beam.

Ray 1214 represents the area made sensitive to the photocell by the receive lens and primary diaphragm. It can be seen that the sensitive area is centered within the monitoring region 1207, but the photocell 1210 maintains sensitivity along the optical axis beyond this region. This extended sensitivity is limited by the absorbing region 1215 at the distal end of the monitoring chamber. The purpose of this design is to ensure that negligible light energy from the emitters 1203, 1204, which tends to interfere with the light scattered by the particles, can fall on this absorption region. This unwanted (undesired) light originates mainly from reflections from the emitter apertures 1205,1206. The combination of shading (shielding) of this absorbing region and reflecting stray light away from this region minimizes this disturbing light. In addition, the walls of the absorbing region are preferably colored black in order to absorb incident light.

FIG. 13 shows typical unwanted radiation reflected by emitter apertures 1205 , 1206 , which is prevented from reaching central absorbing region 1215 . The diagram also includes unwanted rays 1216 that pass through the primary diaphragm 1217 and are absorbed in the receive channel 1218 . In addition, as shown in the figure, the harmful rays 1219 reflected from the main aperture 1217 are focused outside the central axis of the photocells in the receiver module 1210, and by the photocells in the receiver module 1210 (shown as 1401 in FIG. 14 ) and is avoided.

A combination of all these methods is used to avoid interference with light scattered from airborne particles. The difficulty of this task can be appreciated from the fact that the intensity of scattered light is typically 100 million times lower than that of the emitter.

Referring again to FIG. 12, the brightness within the central cone of light 1202 from the emitter is considered the primary brightness within the monitoring room. This bright light is directed towards the absorption channel 1211, along which it is effectively absorbed after multiple reflections. Outside this central cone angle is the secondary brightness 1220 caused by the emitter's optics and emitter diaphragm reflections. Therefore, it is believed that the entire emitter diaphragm area must be bright in multiple directions. Correspondingly, the emitter diaphragm must be obscured from the perspective of the receiver or lens diaphragm, which can be achieved by the positioning of the main diaphragm 1217 . To achieve this shading, a straight line 1221 (shown in dashed line in FIG. shown) to set the geometry of the monitoring chamber. Given that the aim of embodiments of the invention is to produce a monitor with the smallest available size and the highest possible sensitivity, this geometry is considered to be a defined geometry.

Being outside the central emission cone 1202, the main aperture 1217 is exposed to light from the second level of brightness 1220 from the emitter apertures 1203,1204. Therefore, the main diaphragm 1217 reflects light of the third level of brightness 1219 in multiple directions. It's worth noting that in this discussion, "order of magnitude brighter" doesn't necessarily mean ten times brighter. Assuming that a black surface absorbs 99% of incident light and reflects only 1%, and this 1% is further reduced by scattering caused by non-specular reflection, the reduction in brightness may be on the order of 1000 times or more. Thus, the third level of brightness is not an exact measurement, but only provides a relative indication. A small portion of this tertiary brightness light 1219 will be reflected towards lens stop 1208 and lens 1209 . Lens 1209 will focus this unwanted light 1219 off the central axis of receiver element 1210 and be stopped by receiver diaphragm 1401 as shown in FIG. 14 . The use of biconvex lenses, longer focal lengths, and wider primary diaphragms enables unwanted rays (off-center axis) reflected from the primary diaphragm 1217 to fall onto the sides of the receiver element 1210 and can be absorbed by the receiver diaphragm. 1401 weakened.

It can be expected that relatively precise control over the focus of the lens will be necessary in order to control the separation of unwanted (harmful) light from desired light. An aspheric lens 1501 with a shorter focal length is proposed (as shown in FIG. 15 ). This lens provides precise control of focus over the entire surface of the receiver element, avoiding spherical aberration and forming photographic quality images. Figure 15 illustrates the operation of such a lens 1501 in focusing scattered light received from particles detected in the monitoring region 1207 (Figure 12). FIG. 15 also shows the position of lens 1501 relative to main diaphragm 1217 , and element 1210 . However, FIG. 16 shows that with such an aspheric lens a part of the harmful light reflected from the main diaphragm falls on the element. This interferes with the desired signal.

Returning again to Figure 12, a thicker bi-convex lens (with two convex surfaces) is used and is shown in more detail in Figures 14 and 17 . As shown in Figure 14, the spherical aberration of this type of lens 1402 helps to improve the separation of these two sets of rays since the unwanted light 1219 arrives from a direction off the central axis. This separation is further facilitated by using longer focal lengths (and it has been found that the separation is proportional to focal length). In Fig. 17, it can be seen that it is possible to use a lenticular lens 1402, since there is no need to form an exact photographic image at the receiver element 1210, but only light rays to be collected, so the point of focus is less important than the involved ray channels. As such, the geometry of the receiver element 1210 and lens 1402 is preferably arranged such that the maximum amount of scattered light from the detected particles can fall on the receiver element (as shown, where the light substantially illuminates the element 1210 the entire surface of the element), while unwanted light is either blocked by the above-mentioned receiver diaphragm 1401 or allowed to pass through the sides of the element.

Hydrodynamics

From a hydrodynamic point of view, the design of the monitoring chamber is important. One embodiment of the present invention includes a micro duct probe for collecting continuous small but representative samples of the air flowing through ventilation ducts, as described, for example, by the inventors in co-pending U.S. patent application 2003/0011770 Disclosed detectors.

Referring to FIG. 13 , a fluid sample collected from the environment, such as air, is drawn into the monitoring chamber of the present invention through inlet 1301 , flows through the detection chamber and monitoring region 1207 ( FIG. 12 ), and exits through outlet 1302 . This makes it possible to use a larger filter 1303 that can effectively remove dust over long periods of operation without causing significant head loss (pressure drop). The preferred filter type in use is a macroporous, open foam filter of great depth. The smallest dust particles that the filter is designed to remove are typically at least 10 times smaller than the average pore size of the filter. The removal of dust is achieved as a result of Brownian motion (rapid thermal vibrations) by which the dust particles appear to be many times larger than their physical size. As the fluid flows through the deep filter, dust is statistically removed such that substantially all dust considered hazardous is removed before the fluid exits the filter outlet 1314 . It has been found that this minimizes the accumulation (contamination) of dust in the monitoring chamber, thereby greatly extending maintenance intervals. However, the open structure of the filter avoids the serious problem occurring in the prior art inhalation smoke detectors, namely the decrease in the sensitivity of smoke particle removal over time. Moreover, this filter is of the type in which the head loss in the filter does not increase appreciably as the filter is loaded with dust.

Typically, smoke particles are present in the range of 0.01 micron to 1 micron, while airborne dust particles are present in the range of 1 micron to 100 microns. However, there is some overlap at the 1-micron boundary because the smallest dust particles in nature are smaller than the largest possible smog particles. Therefore, it is inappropriate to think that a filter should be a good vacuum cleaner. To avoid reduced sensitivity to smoke, a small fraction of dust particles must therefore pass through the filter, which needs to be adjusted in other ways (as will be disclosed later).

The filter 1303 has mirrored diffusers 1312, 1313 on each side. The outlet face of the filter leads to diffuser 1313 which effectively recombines the fluid, makes a 90° turn and directs the fluid to channel 1304 . In the preferred embodiment of the invention, this channel is narrowed to a cross-sectional area still 5 times larger than the inlet pipe, thereby maintaining very low losses, but the local air velocity is about 8 times faster than at the outlet face 1314 of the filter. times.

In a preferred embodiment, two sensing devices 1305 , 1306 may be installed, one sensing device 1306 at the filter outlet and one sensing device 1305 within the constriction 1304 . In this setup, the sensor 1306 is subject to a relatively low velocity air flow from the filter so that very little cooling of the sensor occurs. Cooling of the sensor 1306 can be further prevented by means of the tube cover 1307 . Conversely, sensor 1305 is more fully exposed to a significantly higher velocity air flow, and is therefore easier to cool than sensor 1306 . Both sensors 1305, 1306 are preferably exposed to the same ambient air temperature. It may be preferable to use matched devices with known temperature dependencies, whereby the different cooling rates caused by the different air flow velocities to which they are exposed, can be used to generate different voltages across each sensor to a large extent Provides measurement of air velocity in a manner independent of ambient air temperature.

The sensor may be of the type disclosed in US Patent No. 4,781,065, however, the positioning of the sensor is uniquely different in the device of the present invention.

Also, in this device, the sensor is exposed to the airflow after it passes through the dust filter 1303, thus minimizing contamination. Contamination can affect the cooling characteristics of the sensors 1305, 1306, thereby reducing the accuracy of the air flow detection circuit.

The fluid then enters another diffuser 1308, which is also the light absorbing channel 1308 for the emitter 1203 (FIG. 12). When the airflow reaches the inlet of the absorption channel 1308, it is redirected to slow down to about 25 times less than the velocity at the inlet tube. Thus, very little loss is incurred during the flow of air through the channel 1308 , through the monitoring region 1207 ( FIG. 12 ) and into the second channel 1309 . Due to the slower velocity here, any residual dust particles (due to the filter 1303) that may be present in the airflow, smaller in number and size (because of the filter 1303), have very low impulse and thus cannot be suspended from the fluid by centrifugal force objects, thereby minimizing potential contamination within the vicinity of the monitoring area 1207. Where there is a centrifugal tendency for dust particles, the direction of their momentum is such that these particles are harmlessly deflected away from the main aperture 1217 .

The air flow is sucked into the second absorption channel 1309 and gradually and efficiently accelerated by diffusion so as to become matched to the exhaust outlet 1302 . The exhaust gases, such as dust, are then effectively returned to the sampled environment as described in above-cited US 4,781,065.

It has been explained how air flow passes through a series of stages in a way that minimizes losses and promotes laminar flow. Thus, the monitoring chamber is cleaned very efficiently and quickly with a fresh air sample, while only a very small amount of smoke remains. Despite the low local velocities caused by the large cross-sectional area, the response of the chamber assembly to changes in smoke concentration has proven to be very rapid and suitable for smoke monitoring and alarm purposes.

Since there is very little pressure drop within the monitor of the present invention, the absolute pressure at any point within the monitor is similar to that inside the pipe. Since there can be large pressure differentials between the inside of the pipe and the surrounding environment where the monitor is placed, the monitor must maintain a good pressure seal to avoid leaks at any point. The possibility of leakage is minimized by the design of the monitoring chamber, which consists of two similar halves joined in plan - a butt flange 1310 . Therefore, only one flat gasket is required to seal the monitoring chamber. In one embodiment, a thick sealing foam gasket is preferred because it easily accommodates changes in the plane of the flange in the monitoring chamber, thereby overcoming the small amount of bending and warping that may occur in injection molding. By extending the small side 1311 which overlaps at the central junction of the two monitoring chamber halves, the area of the monitoring chamber, especially the area close to the monitoring area 1207 which is sensitive to the light absorption capacity of the monitoring chamber wall, is hidden from the gasket . It is preferred that the actual contact between the two halves of the monitoring chamber is only on these sides, which greatly simplifies the need to make abutment planes.

The foregoing description has discussed in principle the use of pipe probes, however, in other embodiments of the invention, the probes may be replaced by other means to obtain a sample of the fluid to be monitored, such as air. Such other devices (disclosed in US 4,781,065) may be venturi devices in small bore pipes of eg 20mm diameter. This pipe can be connected to a suction pump or fan (aspirator) placed upstream or downstream of the Venturi. If placed downstream, multiple monitors can be connected to a single aspirator. Upstream of each monitor, small-bore piping can extend to the entire fire zone (fire zone). The sampling pipeline may be arranged as a network or a branched pipeline extending into the fluid area or region to be monitored or detected. Each of said conduits may include branch conduits. Each of the ducts and branch ducts may include a plurality of small holes to draw air into the duct in the vicinity of each hole. Components of the air sample from all of these holes are then drawn intermittently or relatively continuously into the venturi. The venturi is set up so that some of the air in the duct is drawn through the monitor so that the monitor can sense the presence of smoke or dust before the monitor airflows back into the duct. All the air is then sucked into the aspirator and expelled.

It is worth noting that, preferably in the case of duct detectors or venturis, only a portion of the available air passes through the monitor. This portion of the air or air sample contains smoke and/or dust of the same density as the primary fluid. However, by carefully minimizing fluid flow through the monitor, the rate of dust buildup in the dust filter can be minimized, thereby maximizing service intervals without compromising monitor sensitivity.

In another alternative embodiment of the invention, instead of a venturi, the monitor can be connected directly to a small bore tube such as a 5mm inner diameter. This is suitable for running short distances such as a few meters. In this case, the entire air flow will pass through the monitor, but at a low flow rate, so it should not necessarily affect the maintenance interval. In order to achieve fast response times over long distances with small bore tubing, the pressure drop will be very high, forcing the use of aspirators with high pressure and high energy consumption

Monitor installation

Referring to FIG. 18 , a monitor 1801 (eg, a monitor according to the present invention) may be mounted on a flat-sided, rounded, or otherwise shaped surface, such as a pipe 1802 with a mounting fitting 1803 . The monitor 1801 may be fixed using, for example, screws, or other suitable means (not shown). During installation of the monitor, the joint 1803 is simply bent until the joint matches the surface of the monitor to which it is secured. For example, as shown in Figure 18, when installing on a pipe, the fittings are bent until they snap or match the surface of the pipe. The pipe can be as small as 200mm (8 inches) in diameter. The connector 1803 may be integrally formed with the housing of the monitor 1801, in which case slots (not shown) formed in the housing may confine the connector and allow the connector to bend without deformation so that Snaps to the surface of a pipe or other mounting surface. While the invention has been described in connection with specific examples thereof, it will be understood that the invention is capable of further modifications. This application is intended to cover generally any variations, uses or adaptations of the invention, the principles of the invention including those presently disclosed to the extent known or customary in the technical field to which the invention pertains, as well as the teachings set forth above as applicable to necessary device changes.

While the invention has been described in conjunction with specific embodiments thereof, it will be understood that the invention is capable of further modifications. This application is intended to cover the use or improvement of any variation of the invention generally following the principles of the invention, and includes deviations from the disclosure of this application from known or customary means in the technical field to which the invention pertains, and applicable Use or improvement of any variation of the invention of the essential features set forth above.

Since the present invention can be embodied in various ways without departing from the spirit of the essential characteristics of the invention, it should be understood that unless otherwise stated, the above-mentioned embodiments do not limit the invention, but should be defined by the appended claims. construed broadly within the spirit and scope of the defined invention. Various changes and equivalent arrangements should also be included within the spirit and scope of the present invention and appended claims. Accordingly, the specific embodiments are to be construed as illustrations of various ways of implementing the principles of the invention. In the appended claims, means-plus-function clauses are intended to cover structures as performing the recited function and not only structural equivalents but also equivalent structures. For example, although nails and screws are not structural equivalents because nails hold wood parts together with a cylindrical surface and screws hold wood parts together with a helical surface, in the case of wood parts, the nail and screws are equivalent structures.

When the specification uses "comprises/comprises", it is used to describe the existence of the stated features, integers, steps or components, but does not exclude one or more other features, integers, steps, components or combinations thereof The presence.

Claims (42)

1. one kind is suitable for use in determining the particle detector that has predetermined particle in the surveyed area, comprising:

At least one is suitable for light shining the transmitter of described surveyed area, and described irradiates light comprises the light of second level brightness;

Receiver assembly, near described surveyed area, and be suitable for receiving the light from described surveyed area scattering, described receiver assembly has key light door screen and lens stop, and described key light door screen is located with respect to described transmitter and made described second level light be directed avoiding described lens stop.

2. particle detector according to claim 1, wherein, described key light door screen is suitable for described lens stop is covered second level light.

3. particle detector according to claim 1 further comprises:

In described receiver assembly, the receiver diaphragm is with respect to described key light door screen and the location makes and do not incide near the receiver element that is arranged in the described receiver diaphragm from the light of the third level brightness of described key light door screen reflection.

4. particle detector according to claim 1 further comprises the transmitter diaphragm that combines with described at least one transmitter.

5. particle detector according to claim 4, wherein said transmitter diaphragm are suitable for covering transmitter light and are directly incident on described key light door screen or the described lens stop.

6. particle detector according to claim 1, wherein said key light door screen is bigger than described lens stop dimensionally.

7. particle detector according to claim 1, wherein said transmitter also is suitable for providing the light of first order brightness.

8. particle detector according to claim 7, wherein said first order light is provided as the light of the first order brightness of taper.

9. particle detector according to claim 8, wherein said second level light is outside described taper light.

10. particle detector according to claim 3, the part of wherein said third level light pass the lens near described lens stop.

11. particle detector according to claim 10, wherein said lens are biconvex lens.

12. particle detector according to claim 10, wherein said lens have long relatively focal length.

13. particle detector according to claim 10, wherein said lens have two convex surfaces.

14. particle detector according to claim 10, wherein the light of particle scattering also passes described lens.

15. particle detector according to claim 14, the spherical aberration of wherein said lens strengthen the light of described particle scattering and separating of described third level light.

16. according to each described particle detector in the claim 3,10 to 15, the only unwanted light of the wherein said third level.

17. a smoke detector comprises each described monitor in the claim 1 to 15.

18. a smoke detector comprises the described monitor of claim 16.

19. smoke detector according to claim 17, wherein said detector is a point detector.

20. smoke detector according to claim 17, wherein said detector is a suction detector.

21. according to each described particle detector in the claim 1 to 15, wherein said monitor is a point detector.

22. according to each described particle detector in the claim 1 to 15, wherein said monitor is a suction detector.

23. one kind is configured in method in the particle detector with receiver assembly, described particle detector is suitable for use in determining the endocorpuscular existence of surveyed area, said method comprising the steps of:

The transmitter that provides at least one to be suitable for light shining described surveyed area, described irradiates light comprises the light of second level brightness;

Key light door screen and lens stop are provided, and described key light door screen is located with respect to described transmitter and is made described second level light be directed avoiding described lens stop.

24. method according to claim 23, wherein said key light door screen is arranged in the described receiver assembly.

25. method according to claim 23, wherein said lens stop is arranged in the described receiver assembly.

26. method according to claim 23, wherein said key light door screen is suitable for described lens stop is covered second level light.

27. method according to claim 23 further comprises:

In described receiver assembly, the receiver diaphragm is provided, locate near the receiver element that makes the light of the late third level brightness of reflecting of described key light does not incide described receiver diaphragm with respect to described key light door screen.

28. method according to claim 23 further comprises the transmitter diaphragm that combines with described at least one transmitter is provided.

29. method according to claim 28, wherein said transmitter diaphragm makes and is not directly incident on the mode on described key light door screen or the described lens stop and provides to cover transmitter light.

30. method according to claim 23, wherein said transmitter also is suitable for providing the light of first order brightness.

31. method according to claim 30, wherein said first order light is provided as the light of the first order brightness of taper.

32. method according to claim 31, wherein said second level light is provided at outside the taper light.

33. method according to claim 27, the part of wherein said third level light are passed the lens near described lens stop.

34. method according to claim 33, wherein the light of particle scattering also passes described lens.

35. method according to claim 34 further comprises and utilizes described lens spherical aberration to strengthen the light of described particle scattering and separating of described third level light.

36. according to claim 27, each described method in 33 to 35, the only unwanted light of the wherein said third level.

37. smoke detector of constructing according to each described method operation in the claim 23 to 35.

38. according to the described smoke detector of claim 37, wherein said detector is a point detector.

39. according to the described smoke detector of claim 37, wherein said detector is a suction detector.

40. particle detector of constructing according to each described method operation in the claim 23 to 35.

41. according to the described particle detector of claim 40, wherein said monitor is a type monitor.

42. according to the described particle detector of claim 40, wherein said monitor is the suction-type monitor.

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