JP4894724B2 - Fire detector - Google Patents

Description

  The present invention relates to a fire detector.

  2. Description of the Related Art Conventionally, as a fire detector that detects smoke generated in the event of a fire, a scattered light type smoke detector (see, for example, Patent Document 1) and a dimming smoke detector (see, for example, Patent Document 2) are known. Yes. Here, the scattered light type smoke detector is configured to receive light scattered by smoke particles of light irradiated to the monitoring space from a light projecting element made of a light emitting diode element by a light receiving element made of a photodiode. In addition, if smoke particles are present in the monitoring space, the amount of light received by the light receiving element is increased due to the generation of scattered light. Therefore, the presence or absence of smoke particles can be detected based on the amount of increase in the amount of light received by the light receiving element. On the other hand, the dimming smoke detector is configured so that light emitted from the light projecting element is directly received by the light receiving element, and smoke particles are present in the monitoring space between the light projecting element and the light receiving element. If it is present, the amount of light received by the light receiving element is reduced, and therefore the presence or absence of smoke particles can be detected based on the amount of light received by the light receiving element.

By the way, the scattered light type smoke detector needs to be equipped with a labyrinth body as a countermeasure against stray light, so when there is little air flow, the time until smoke particles enter the monitoring space in the event of a fire increases, and the response There was a problem with sex. In addition, there is a problem that the dimming smoke detector may generate a report due to the influence of background light (a non-fire report will be generated) even though no fire has occurred. . In addition, the separate-type dimming smoke detector needs to align the optical axes of the light projecting element and the light receiving element with high accuracy, and there is a problem that it takes a lot of work.
JP 2001-34862 A JP 61-33595 A

  In order to solve the problems of the photoelectric fire detector described above, the present applicant has proposed a fire detector that detects the presence or absence of smoke using ultrasonic waves (see FIG. 2).

  The fire detector includes a sound source unit 1 capable of transmitting ultrasonic waves, a control unit 2 that controls the sound source unit 1, a wave receiving element 3 that detects sound pressure of ultrasonic waves transmitted from the sound source unit 1, And a signal processing unit 4 for determining the presence or absence of a fire based on the output of the wave receiving element 3. The signal processing unit 4 includes smoke concentration estimation means 41 that estimates the smoke concentration in the monitoring space between the sound source unit 1 and the wave receiving element 3 based on the attenuation amount from the reference value of the output of the wave receiving element 3, and the estimation A smoke type judgment means 42 for judging the presence or absence of a fire by comparing the smoke concentration and a predetermined threshold value. That is, since the attenuation amount of the output of the wave receiving element 3 increases substantially in proportion to the smoke concentration in the monitoring space, the presence or absence of a fire can be determined by estimating the smoke concentration based on this attenuation amount.

  This ultrasonic fire detector can eliminate the influence of background light, which is a problem with photoelectric fire detectors, and eliminates the need for a labyrinth that is required for scattered light smoke detectors. Smoke particles easily diffuse into the monitoring space in the event of a fire, improving responsiveness compared to scattered light smoke detectors and reducing non-fire reports compared to dimming smoke detectors. .

  By the way, in the ultrasonic fire detector described above, in order to maximize the amount of change in the output of the wave receiving element 3 relative to the amount of change in smoke density (that is, the amount of change in the received sound pressure at the wave receiving element 3). It is conceivable to increase the power supplied to the sound source unit 1 within a range in which the sound source unit 1 is not damaged and increase the sound pressure of the ultrasonic wave transmitted from the sound source unit 1.

  However, even if the sound pressure of the ultrasonic wave transmitted from the sound source unit 1 is increased, the ultrasonic wave diffuses between the sound source unit 1 and the wave receiving element 3, thereby determining whether smoke particles exist in the monitoring space. Regardless of this, the sound pressure of the ultrasonic wave received by the wave receiving element 3 decreases. As a result, there is a problem that the amount of change in the output of the wave receiving element 3 with respect to the amount of change in smoke density is relatively small, and the SN ratio is small.

  The present invention has been made in view of the above-described reasons, and improves the SN ratio in a configuration in which the presence or absence of a fire is determined based on the amount of ultrasonic attenuation in the monitoring space between the sound source unit and the receiving element. The purpose is to provide a fire detector.

  In the invention of claim 1, a sound source unit capable of transmitting an ultrasonic wave, a control unit for controlling the sound source unit, a wave receiving element for detecting the sound pressure of the ultrasonic wave transmitted from the sound source unit, and a wave receiving element A signal processing unit for determining the presence or absence of a fire based on the output of the signal, the signal processing unit is a monitoring space between the sound source unit and the receiving element based on the attenuation from the reference value of the output of the receiving element Smoke density estimation means for estimating the smoke density of the smoke, and smoke type judgment means for judging the presence or absence of a fire by comparing the smoke density estimated by the smoke density estimation means with a predetermined threshold, at least in part The diffusion preventing member that has inner surfaces arranged so as to face each other and that narrows the diffusion range of the ultrasonic waves by passing the ultrasonic waves from the sound source unit through the space between the opposed inner surfaces is transmitted from the sound source unit. And disposed on a propagation path of an ultrasonic wave received by the wave receiving element.

  According to this configuration, the diffusion has an inner surface arranged so that at least a part thereof faces each other, and narrows the diffusion range of the ultrasonic wave by passing the ultrasonic wave from the sound source unit through the space between the opposed inner surfaces. Since the prevention member is disposed on the propagation path of the ultrasonic wave transmitted from the sound source unit and received by the wave receiving element, the ultrasonic wave from the sound source unit passes through the space between the opposing inner surfaces. By suppressing diffusion, it is possible to suppress a decrease in sound pressure due to diffusion of ultrasonic waves between the sound source unit and the receiving element. Therefore, the sound pressure of the ultrasonic wave received by the wave receiving element when there is no smoke particle in the monitoring space can be maintained high, and the amount of change in the output of the wave receiving element with respect to the amount of change in smoke concentration is relatively large, There is an advantage that the SN ratio is improved.

  According to a second aspect of the present invention, in the first aspect of the invention, the diffusion preventing member is formed of a cylindrical body that is formed in a cylindrical shape and has an inner surface along the longitudinal direction as the inner surface.

  According to this configuration, since the ultrasonic wave from the sound source part passes through the inner space of the cylinder surrounded on the four sides by the inner surface, for example, diffusion having a pair of planes facing only in one direction as the inner surface Compared with the case where the prevention member is used, the diffusion of the ultrasonic wave between the sound source unit and the wave receiving element can be surely suppressed, and therefore the decrease in the sound pressure due to the diffusion of the ultrasonic wave can be further suppressed. .

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the sound source unit can transmit a plurality of types of ultrasonic waves having different frequencies, and the signal processing unit exists in the monitoring space. Storage means for storing relationship data between the output frequency of the sound source unit according to the type of suspended particles and the smoke concentration and the attenuation from the reference value of the output of the receiving element, and each of the waves transmitted from the sound source unit Particle type estimation means for estimating the type of particles floating in the monitoring space using the output of the receiving element for each ultrasonic wave of the frequency and the relational data stored in the storage means, and The smoke concentration estimation means is configured to detect smoke concentration in the monitoring space based on an attenuation amount from a reference value of the output of the wave receiving element with respect to an ultrasonic wave of a specific frequency when the particle estimated by the particle type estimation means is smoke particle. Is estimated.

  According to this configuration, in the signal processing unit, the particle type estimation unit uses the output of the receiving element for each ultrasonic wave of each frequency transmitted from the sound source unit and the relational data stored in the storage unit. Estimate the type of particles floating in the monitoring space, and when the particles estimated by the particle type estimation means are smoke particles, the smoke concentration estimation means uses the output standard of the receiving element for ultrasonic waves of a specific frequency. Since the smoke concentration in the monitoring space is estimated based on the amount of attenuation from the value, it is possible to identify, for example, smoke particles and steam by estimating the type of particles floating in the monitoring space in the particle type identifying means. Therefore, it is possible to reduce non-fire reports caused by steam as compared with the scattered light smoke detector and the reduced light smoke detector, and it is also suitable for use in the kitchen or bathroom.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the storage means is an attenuation obtained by dividing an attenuation amount from the reference value of the output frequency of the sound source unit and the output of the receiving element by the reference value as the relation data. It stores the relationship data with the rate.

  According to the present invention, even when the reference value of the output of the receiving element varies according to the output frequency of the sound source unit, the attenuation rate from which the influence of the variation of the output frequency of the sound source unit and the reference value is removed, and By using the relationship data, it is possible to estimate the type of particles floating in the monitoring space without being affected by the fluctuation of the reference value.

  According to a fifth aspect of the present invention, in the third or fourth aspect of the invention, the sound source unit includes a single sound wave generation element capable of transmitting the plurality of types of ultrasonic waves, and the control unit includes a sound wave generation element. The sound source unit is controlled so that a plurality of types of ultrasonic waves are sequentially transmitted.

  According to this configuration, it is possible to reduce the size and cost of the sound source unit as compared with a case where a plurality of sound wave generating elements capable of transmitting various types of ultrasonic waves are provided.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the sound source section has a wave transmitting surface that vibrates air facing an incident side end surface on which the ultrasonic waves are incident on the diffusion preventing member. And having a width dimension equal to or greater than the distance between the inner surfaces in the opposing direction of the inner surfaces.

  According to this configuration, since the ultrasonic wave transmitted from the transmission surface of the sound source unit travels along the inner surface in the space between the inner surfaces of the diffusion preventing member, the ultrasonic wave is reflected by the inner surface. Ultrasonic interference does not occur, and a decrease in sound pressure due to interference can be avoided. For example, when the diffusion prevention member is a straight tubular cylinder, the ultrasonic wave transmitted from the transmission surface of the sound source section travels as a plane wave in the cylindrical body, so that the ultrasonic wave is reflected on the side surface along the longitudinal direction of the cylindrical body. As a result, no ultrasonic interference occurs, and a decrease in sound pressure due to the interference in the cylinder can be avoided.

  According to a seventh aspect of the present invention, the sound source unit according to any one of the first to sixth aspects of the present invention is characterized by applying a thermal shock to the air due to a change in temperature of the heat generating unit accompanying energization of the heat generating unit. It is characterized by generating sound waves.

  According to this configuration, the sound source unit has a flat frequency characteristic, and the frequency of the generated ultrasonic wave can be changed over a wide range. It is also possible to transmit single-pulse ultrasonic waves with little reverberation from the sound source unit.

  The invention according to claim 8 is the invention according to claim 7, wherein the sound source section is formed with the heating element portion on one surface side of the base substrate, and the heating element portion and the base on the one surface side of the base substrate. It is characterized by having a thermal insulation layer comprising a porous layer provided between the substrate and thermally insulating the heating element and the base substrate.

  According to this configuration, since the heat insulating layer is made of a porous layer, the heat insulating property of the heat insulating layer is improved compared to the case where the heat insulating layer is made of a non-porous layer. The ratio of the sound pressure of the ultrasonic wave becomes high, and low power consumption can be achieved.

  According to a ninth aspect of the present invention, in the first or second aspect of the present invention, the control unit has a resonance frequency exceeding that based on a propagation distance of an ultrasonic wave transmitted from the sound source unit and received by the receiving element. Controlling the sound source unit to continuously transmit a sound wave from the sound source unit over a transmission time longer than a propagation time required for the ultrasonic wave to propagate from at least the sound source unit to the receiving element. It is characterized by that.

  According to this configuration, resonance occurs in the space between the inner surfaces of the diffusion prevention member, and the sound pressure of the ultrasonic wave transmitted from the sound source unit increases, so the change in the output of the wave receiving element with respect to the amount of change in smoke concentration The amount increases and the signal to noise ratio improves. In addition, in the ultrasonic wave reflected by the sound source unit or the receiving element due to resonance, the effective transmission distance is extended according to the number of reflections, and the amount of change in the output of the receiving element with respect to the amount of change in smoke density is more It gets bigger.

  According to a tenth aspect of the present invention, in the invention according to any one of the third to fifth aspects, the control unit resonates based on a propagation distance of an ultrasonic wave transmitted from the sound source unit and received by the receiving element. A plurality of types of ultrasonic waves that have different frequencies and are continuously transmitted over a transmission time longer than a propagation time required for the ultrasonic waves to propagate from at least the sound source unit to the receiving element. The sound source unit is controlled to transmit from the unit.

  According to this configuration, resonance occurs in the space between the inner surfaces of the diffusion prevention member, and the sound pressure of the ultrasonic wave transmitted from the sound source unit increases, so the change in the output of the wave receiving element with respect to the amount of change in smoke concentration The amount increases and the signal to noise ratio improves. In addition, in the ultrasonic wave reflected by the sound source unit or the receiving element due to resonance, the effective transmission distance is extended according to the number of reflections, and the amount of change in the output of the receiving element with respect to the amount of change in smoke density is more It gets bigger.

  According to an eleventh aspect of the present invention, in the ninth or tenth aspect of the present invention, in the diffusion preventing member, the space between the inner surfaces through which the ultrasonic waves from the sound source portion pass is superfluous at both end surfaces in the ultrasonic wave propagation direction. The sound source section is closed by a reflecting surface that reflects sound waves, the sound source unit is disposed on one reflecting surface, and the wave receiving element is disposed on any reflecting surface.

  According to this configuration, in the diffusion preventing member, the space between the inner surfaces through which the ultrasonic waves from the sound source portion pass is ultrasonic waves at both ends in the ultrasonic propagation direction, as in the case where the acoustic tube having both end surfaces closed is resonated. Since the pressure change is maximized, the wave receiving element detects the sound pressure of the ultrasonic wave at the site where the pressure change due to the ultrasonic wave is maximized. That is, the change amount of the output of the wave receiving element with respect to the change amount of the smoke density can be maximized.

  According to a twelfth aspect of the present invention, in the ninth or tenth aspect of the present invention, the space between the inner surfaces through which the ultrasonic waves from the sound source portion pass in the diffusion preventing member is superfluous at both end surfaces in the propagation direction of the ultrasonic waves. Closed by a reflection surface that reflects sound waves, the sound source unit is disposed on one reflection surface, and the inner surface along the propagation direction is at a position where the pressure change due to the ultrasonic wave from the sound source unit is maximized. The wave receiving element is arranged.

  According to this configuration, since the wave receiving element is disposed at a position where the pressure change due to the ultrasonic wave from the sound source portion is maximized on the inner surface of the diffusion preventing member, the output of the wave receiving element with respect to the amount of change in smoke density Can be increased as much as possible. In addition, when resonance is generated in a space where both end faces are closed by a reflecting surface, resonance is caused by reflection of ultrasonic waves on the reflecting surface, and in particular, ultrasonic waves with a short wavelength have only minute irregularities on the reflecting surface. However, when the sound is reflected by the reflecting surface, the sound pressure is reduced. However, according to the structure of claim 12, since the wave receiving element is provided on the inner surface along the propagation direction of the ultrasonic wave, the reflecting surface is provided. Compared with the case where a wave receiving element is provided, the reflecting surface can be a flat surface with less unevenness, and as a result, the sound caused by resonance can be prevented without obstructing the reflection of the ultrasonic wave on the reflecting surface by the wave receiving element. The pressure can be increased.

  According to a thirteenth aspect of the present invention, in the twelfth aspect of the invention, the control unit causes the sound source so that an ultrasonic wave having a length obtained by dividing the distance between the reflecting surfaces by a natural number is transmitted from the sound source unit. The wave receiving element is arranged at an intermediate position between the reflecting surfaces.

  According to this configuration, since the ultrasonic wave having a length obtained by dividing the distance between the reflecting surfaces by a natural number is transmitted from the sound source unit, the pressure change due to the ultrasonic waves is always the maximum at the intermediate position between the reflecting surfaces. It becomes. Therefore, even if the frequency of the ultrasonic wave is different as long as the wavelength condition described above is satisfied, only at the wave receiving element arranged at the intermediate position between the two reflecting surfaces, the pressure change due to the ultrasonic wave is maximized. Sound pressure can be detected, and the cost can be reduced compared to the case where receiving elements are arranged at a plurality of locations.

  According to a fourteenth aspect of the present invention, in the invention according to any one of the ninth to thirteenth aspects, the control unit corrects a frequency of an ultrasonic wave transmitted from the sound source unit according to a change in sound velocity due to a temperature change. It has a correction means.

  According to this configuration, even if the resonance frequency based on the propagation distance of the ultrasonic wave may fluctuate due to a change in sound velocity due to a temperature change, the frequency of the ultrasonic wave transmitted from the sound source unit is adjusted by the frequency correction unit. Since the resonance frequency after the fluctuation is corrected, resonance surely occurs and the sound pressure of the ultrasonic wave increases.

  The invention according to claim 15 is the invention according to claim 14, wherein the frequency correction means is based on a time difference from when the sound source section transmits an ultrasonic wave until the ultrasonic wave is received by the receiving element. The frequency is corrected using the speed of sound obtained in this way.

  According to this configuration, in the frequency correction unit, the frequency is corrected using the speed of sound obtained based on the time difference from when the sound source unit transmits an ultrasonic wave until the ultrasonic wave is received by the receiving element. The configuration can be simplified as compared with the case where a means for obtaining the sound speed is separately provided.

  Since the present invention can suppress a decrease in sound pressure due to the diffusion of ultrasonic waves between the sound source unit and the receiving element, the ultrasonic wave received by the receiving element in a state where there is no smoke particle in the monitoring space. The sound pressure of the sound wave can be kept high, the amount of change in the output of the wave receiving element with respect to the amount of change in smoke density is relatively large, and the SN ratio is improved.

(Embodiment 1)
As shown in FIG. 2, the fire detector according to the present embodiment includes a sound source unit 1 capable of transmitting ultrasonic waves, a control unit 2 that controls the sound source unit 1, and an ultrasonic wave transmitted from the sound source unit 1. A wave receiving element 3 that detects sound pressure and a signal processing unit 4 that determines the presence or absence of a fire based on the output of the wave receiving element 3 are provided. Here, as shown in FIG. 1, the sound source unit 1 and the wave receiving element 3 are disposed so as to face each other on the one surface side of the circuit board 5 made of a disk-shaped printed board. A control unit 2 and a signal processing unit 4 are provided. Between the sound source unit 1 and the wave receiving element 3, a cylindrical body 6 described later formed in a cylindrical shape is disposed. In addition, a sound absorbing layer (not shown) for preventing the reflection of the ultrasonic wave transmitted from the sound source unit 1 is provided on the one surface of the circuit board 5, so that the super wave transmitted from the sound source unit 1 is provided. A sound wave can be prevented from being reflected by the circuit board 5 and incident on the wave receiving element 3, and interference of the reflected wave can be prevented. In particular, a continuous wave is transmitted as an ultrasonic wave transmitted from the sound source unit 1. It is effective when using.

  In the present embodiment, a sound wave generating element that generates an ultrasonic wave by applying a thermal shock to air as described later is used as the sound source unit 1 to transmit an ultrasonic wave having a reverberation time shorter than that of a piezoelectric element. In addition, as the wave receiving element 3, a capacitance type microphone is used in which the Q value of the resonance characteristics is sufficiently smaller than that of the piezoelectric element and the generation period of the reverberation component included in the received wave signal is short.

  Here, as shown in FIG. 3, the sound source unit 1 includes a heat insulating layer (heat insulation) made of a porous silicon layer on one surface (upper surface in FIG. 3) side of a base substrate 11 made of a single crystal p-type silicon substrate. Layer) 12 is formed, and a heating element layer 13 made of a metal thin film is formed on the surface side of the heat insulating layer 12 as a heating element portion, and is electrically connected to the heating element layer 13 on the one surface side of the base substrate 11. A pair of pads 14 and 14 are formed. The planar shape of the base substrate 11 is a rectangular shape, and the planar shapes of the thermal insulating layer 12 and the heating element layer 13 are also rectangular. An insulating film (not shown) made of a silicon oxide film is formed on the surface of the base substrate 11 where the thermal insulating layer 12 is not formed on the one surface side.

  In the above-described sound source unit 1, when current is passed between the pads 14 and 14 at both ends of the heating element layer 13 to cause a sudden temperature change in the heating element layer 13, the air (medium) that is in contact with the heating element layer 13. A sudden temperature change (thermal shock) occurs (that is, a thermal shock is applied to the air in contact with the heating element layer 13). Accordingly, the air in contact with the heating element layer 13 expands when the temperature of the heating element layer 13 rises and contracts when the temperature of the heating element layer 13 decreases. Therefore, by appropriately controlling energization to the heating element layer 13 Ultrasonic waves that propagate in the air can be generated. In short, the sound wave generating element constituting the sound source unit 1 generates an ultrasonic wave propagating through the medium by converting a rapid temperature change of the heat generating body layer 13 accompanying energization to the heat generating body layer 13 into expansion and contraction of the medium. Therefore, it is possible to transmit single-pulse ultrasonic waves with less reverberation compared to the case where ultrasonic waves are generated by mechanical vibration like a piezoelectric element.

In the sound source unit 1 described above, a p-type silicon substrate is used as the base substrate 11, and the heat insulating layer 12 is formed of a porous layer made of a porous silicon layer having a porosity of about 60 to about 70%. Therefore, a porous silicon layer serving as the thermal insulating layer 12 can be formed by anodizing a part of the silicon substrate used as the base substrate 11 in an electrolytic solution composed of a mixed solution of hydrogen fluoride and ethanol. (Here, the porous silicon layer formed by the anodic oxidation treatment contains a large number of nanocrystalline silicon composed of microcrystalline silicon having a crystal grain size on the order of nanometers). Since the porous silicon layer has a lower thermal conductivity and heat capacity as the porosity becomes higher, the thermal conductivity and heat capacity of the heat insulating layer 12 are made smaller than the heat conductivity and heat capacity of the base substrate 11, and heat insulation is performed. By making the product of the thermal conductivity and heat capacity of the layer 12 sufficiently smaller than the product of the thermal conductivity and heat capacity of the base substrate 11, the temperature change of the heating element layer 13 can be efficiently transmitted to the air. In addition, efficient heat exchange occurs between the heating element layer 13 and the air, and the base substrate 11 can efficiently receive the heat from the heat insulating layer 12 and release the heat of the heat insulating layer 12 to generate heat. It is possible to prevent heat from the body layer 13 from being accumulated in the heat insulating layer 12. Note that the porosity formed by anodizing a single crystal silicon substrate having a thermal conductivity of 148 W / (m · K) and a heat capacity of 1.63 × 10 ⁶ J / (m ³ · K) is 60%. The porous silicon layer is known to have a thermal conductivity of 1 W / (m · K) and a heat capacity of 0.7 × 10 ⁶ J / (m ³ · K). In this embodiment, the heat insulating layer 12 is composed of a porous silicon layer having a porosity of approximately 70%, the heat conductivity of the heat insulating layer 12 is 0.12 W / (m · K), and the heat capacity is 0.00. It is 5 × 10 ⁶ J / (m ³ · K).

  The heating element layer 13 is made of tungsten, which is a kind of refractory metal, but the material of the heating element layer 13 is not limited to tungsten, and for example, tantalum, molybdenum, iridium, aluminum, or the like may be adopted. In the sound source unit 1 described above, the thickness of the base substrate 11 is 300 to 700 μm, the thickness of the heat insulating layer 12 is 1 to 10 μm, the thickness of the heating element layer 13 is 20 to 100 nm, and the thickness of each pad 14. However, these thicknesses are only examples and are not particularly limited. Further, Si is adopted as the material of the base substrate 11, but the material of the base substrate 11 is not limited to Si, and for example, it can be made porous by anodic oxidation treatment of Ge, SiC, GaP, GaAs, InP or the like. Other semiconductor materials may be used, and in any case, a porous layer formed by making a part of the base substrate 11 porous can be used as the heat insulating layer 12.

As described above, the sound source unit 1 generates ultrasonic waves in accordance with the temperature change of the heating element layer 13 due to energization of the heating element layer 13 via the pair of pads 14 and 14. When the drive input waveform composed of the drive voltage waveform or the drive current waveform applied to is a sine wave waveform having a frequency of f1, for example, the frequency of the temperature oscillation generated in the heating element layer 13 is ideally the frequency of the drive input waveform f1. The frequency f2 is doubled, and an ultrasonic wave having a frequency approximately twice that of the drive input waveform f1 can be generated. That is, the above-described sound source unit 1 has a flat frequency characteristic and can change the frequency of the generated ultrasonic wave over a wide range. Further, in the sound source unit 1 described above, for example, a half-cycle solitary wave of a sine wave waveform is applied between the pair of pads 14 and 14 as a drive input waveform, so that a single-pulse ultrasonic wave of approximately one cycle with little reverberation is generated. Can be generated. By using such single-pulse ultrasonic waves, interference due to reflection is less likely to occur, so that the sound absorbing layer can be made unnecessary. Further, in the sound source unit 1, since the heat insulating layer 12 is formed of a porous layer, the heat insulating layer 12 is compared with a case where the heat insulating layer 12 is formed of a non-porous layer (for example, a SiO ₂ film). As a result, the heat generation efficiency is improved, the efficiency of ultrasonic generation is increased, and the power consumption can be reduced.

  Although not shown, the control unit 2 that controls the sound source unit 1 gives a drive input waveform to the sound source unit 1 to drive the sound source unit 1, and a control circuit that includes a microcomputer that controls the drive circuit; It consists of

  Further, as shown in FIG. 4, the capacitance type microphone constituting the wave receiving element 3 has a rectangular frame-shaped frame 31 formed by providing a window hole 31a penetrating in the thickness direction in the silicon substrate. And a cantilever-type pressure receiving portion 32 disposed on one surface side of the frame 31 so as to straddle two opposing sides of the frame 31. Here, a thermal oxide film 35, a silicon oxide film 36 covering the thermal oxide film 35, and a silicon nitride film 37 covering the silicon oxide film 36 are formed on one surface side of the frame 31, and one end of the pressure receiving portion 32. Is supported by the frame 31 via the silicon nitride film 37, and the other end faces the silicon nitride film 37 in the thickness direction of the silicon substrate. Further, a fixed electrode 33a made of a metal thin film (for example, a chromium film) is formed on the surface of the silicon nitride film 37 facing the other end of the pressure receiving portion 32, and the silicon nitride film 37 at the other end of the pressure receiving portion 32 is formed. A movable electrode 33b made of a metal thin film (for example, a chromium film) is formed on the opposite side of the opposite surface. A silicon nitride film 38 is formed on the other surface of the frame 31. The pressure receiving portion 32 is constituted by a silicon nitride film formed in a separate process from the silicon nitride films 37 and 38 described above.

  In the wave receiving element 3 composed of a capacitive microphone having the configuration shown in FIG. 4, a capacitor having the fixed electrode 33a and the movable electrode 33b as electrodes is formed, so that the pressure receiving portion 32 receives the pressure of the dense wave. As a result, the distance between the fixed electrode 33a and the movable electrode 33b changes, and the capacitance between the fixed electrode 33a and the movable electrode 33b changes. Therefore, if a DC bias voltage is applied between pads (not shown) provided on the fixed electrode 33a and the movable electrode 33b, a minute voltage change occurs between the pads according to the sound pressure of the ultrasonic waves. The sound pressure of ultrasonic waves can be converted into an electric signal.

  By the way, the signal processing unit 4 includes a smoke density estimation unit 41 that estimates the smoke density in the monitoring space between the sound source unit 1 and the wave receiving element 3 based on the attenuation amount from the reference value of the output of the wave receiving element 3. The smoke type estimation means 42 for comparing the smoke density estimated by the smoke density estimation means 41 with a predetermined threshold value to determine the presence or absence of a fire, and the sound source unit 1 transmits the ultrasonic wave, and then the ultrasonic wave A sound speed detecting means 43 for obtaining the sound speed based on the time difference until the wave receiving element 3 receives the wave, a temperature estimating means 44 for estimating the temperature of the monitoring space based on the sound speed obtained by the sound speed detecting means 43, Thermal type determination means 45 that compares the temperature estimated by the temperature estimation means 44 with a specified temperature to determine the presence or absence of a fire is provided. The signal processing unit 4 is configured by a microcomputer, and each of the means 41 to 45 is realized by mounting an appropriate program on the microcomputer. The signal processing unit 4 is provided with an A / D converter for analog-digital conversion of the output signal of the wave receiving element 3.

  The smoke density estimation means 41 estimates the smoke density based on the attenuation amount from the reference value of the output of the wave receiving element 3 that detects the sound pressure of the ultrasonic wave from the sound source unit 1. If the frequency of the transmitted ultrasonic wave is constant, the amount of attenuation increases approximately in proportion to the smoke concentration in the monitoring space, so the smoke concentration is based on the relationship data between the smoke concentration and attenuation measured in advance. If the relational expression between and the amount of attenuation is obtained and stored, the smoke density can be estimated from the amount of attenuation using the relational expression. The smoke type determination means 42 determines “no fire” when the smoke concentration estimated by the smoke concentration estimation means 41 is less than the above threshold value, while “no fire” when it exceeds the threshold value. And the fire detection signal is output to the control unit 2. Here, when the control unit 2 receives the fire detection signal from the smoke type determination means 42, the control unit 2 controls the drive input waveform to the sound source unit 1 so that an alarm sound including an audible sound wave is generated from the sound source unit 1. . Therefore, since the alarm sound can be generated from the sound source unit 1, it is not necessary to separately provide a speaker for outputting the alarm sound, and the entire fire detector can be reduced in size and cost.

  The sound speed detection means 43 obtains the sound speed using the distance between the sound source unit 1 and the wave receiving element 3 and the time difference. Moreover, the temperature estimation means 44 estimates the temperature of the said monitoring space from a sound speed using the well-known relational expression of the sound speed in air and absolute temperature. The thermal determination means 45 determines “no fire” if the temperature estimated by the temperature estimation means 44 is lower than the specified temperature, while “fire” if the temperature is higher than the specified temperature. And the fire detection signal is output to the control unit 2. Here, even when the control unit 2 receives the fire detection signal from the thermal determination unit 45, the drive input waveform to the sound source unit 1 is generated so that an alarm sound including an audible sound wave is generated from the sound source unit 1. To control.

  By the way, in the present embodiment, the cylindrical body 6 provided between the sound source unit 1 and the wave receiving element 3 functions as a diffusion preventing member that narrows the diffusion range of the ultrasonic wave from the sound source unit 1. It is arranged along the direction in which the sound source unit 1 and the wave receiving element 3 are opposed to at least a part of the propagation path of the ultrasonic wave so as to propagate the ultrasonic wave from the sound source unit 1 through the internal space. Specifically, the cylindrical body 6 is a straight tubular rectangular tube whose both end surfaces in the longitudinal direction are open. As shown in FIG. 1, one end surface in the longitudinal direction (the right end surface in FIG. 1) is used as the sound source unit 1. By being arranged close to each other, the one end surface is closed by the sound source unit 1, and the other end surface (left end surface in FIG. 1) is disposed to face the wave receiving element 3 with a predetermined interval. By providing the cylindrical body 6, the ultrasonic wave transmitted from the sound source unit 1 passes through the internal space of the cylindrical body 6 surrounded by the inner surface (inner surface) along the longitudinal direction of the cylindrical body 6. The diffusion is suppressed by passing through, so that a decrease in sound pressure due to the diffusion of ultrasonic waves between the sound source unit 1 and the wave receiving element 3 can be suppressed.

  Moreover, in the fire detector of the present embodiment, the surface of the heating element layer 13 (wave transmission surface) that vibrates the air as the medium in the sound source unit 1 is super-high in the cylinder 6 as shown in FIG. It is disposed opposite to the incident side end face (that is, the end face on the sound source unit 1 side) on which the sound wave is incident, and is formed in the same size or larger than the incident side end face. As an example, when the opening surface that is the incident side end face of the cylindrical body 6 is a 10 mm square, the surface of the heating element layer 13 is a 10 mm square. According to this configuration, since the rapid temperature change of the heating element layer 13 is uniformly transmitted to the entire area of the incident side end face of the cylinder 6, the ultrasonic wave transmitted from the sound source unit 1 is in the cylinder 6. Proceed as a plane wave. Therefore, the ultrasonic wave does not cause interference due to the reflected wave on the side surface along the longitudinal direction of the cylindrical body 6, and a decrease in the sound pressure of the ultrasonic wave due to the interference in the cylindrical body 6 can be avoided.

  As shown in FIG. 5B, when the sound source unit 1 is composed of a plurality of sound wave generating elements 1a and these sound wave generating elements 1a are driven simultaneously in synchronization, the plurality of sound wave generating elements 1a are arranged side by side. If the transmission surface of the sound source unit 1 to be formed is opposed to the incident side end surface of the cylindrical body 6 and is equal to or larger than the incident side end surface, the same effect as the example of FIG. 5A described above can be obtained. Can do. For example, when the opening surface that is the incident side end face of the cylindrical body 6 is a 10 mm square, the surface of the heating element layer 13 is arranged in a square shape of 10 mm square by arranging four sound wave generating elements 1 a each having a square shape of 5 mm square. It is sufficient to form the wave transmission surface.

  Further, in the present embodiment, the cylindrical body 6 having the configuration shown in FIG. 1 is illustrated, but the configuration of the cylindrical body 6 is not limited to that of FIG. 1. For example, as shown in FIG. 6 or a configuration in which one end face of the cylindrical body 6 is opposed to the sound source unit 1 with a predetermined interval as shown in FIG. When the central axis of the sound source unit 1 and the central axis of the wave receiving element 3 are not on the same axis, that is, when the wave receiving element 3 is arranged to be inclined with respect to the central axis of the sound source unit 1, FIG. As shown in FIG. 6, a cylindrical body 6 bent along the propagation path may be disposed in a part of the propagation path of the ultrasonic wave between the sound source unit 1 and the receiving element 3. Further, as shown in FIG. 9, both end surfaces in the longitudinal direction of the cylindrical body 6 are formed between the sound source unit 1 and the wave receiving element 3 by using the cylindrical body 6 having the same length as the interval between the sound source unit 1 and the wave receiving element 3. A closed configuration is also conceivable. However, in the configuration in which both end surfaces are closed, the inside of the cylindrical body 6 becomes a monitoring space, and therefore, a hole (not shown) for guiding smoke or the like is formed in the side surface along the longitudinal direction of the cylindrical body 6, for example. As shown in FIG. 10, an acoustic horn whose cross section perpendicular to the longitudinal direction becomes larger toward the end face (end face facing the wave receiving element 3) from which the ultrasonic wave is emitted may be used as the cylindrical body 6. Here, each cylinder 6 is not limited to a square cylinder but may be a round cylinder.

  In this embodiment, the fire detector signal output from the smoke determination unit 42 or the thermal determination unit 45 is output to the control unit 2, but is not limited to the control unit 2. You may make it output to a notification apparatus.

  In the fire detector according to the present embodiment described above, the smoke density estimation means 41 determines the monitoring space between the sound source unit 1 and the wave receiving element 3 based on the attenuation amount from the reference value of the output of the wave receiving element 3. The smoke density is estimated, and the smoke type judging means 42 compares the smoke density estimated by the smoke density estimating means 41 with a predetermined threshold value to judge the presence or absence of a fire. A photoelectric fire detector such as a light smoke detector can eliminate the influence of background light, which is a problem, and can eliminate the labyrinth required for the scattered light smoke detector, resulting in a fire. Occasionally, smoke particles are likely to diffuse into the surveillance space, so that responsiveness can be improved compared to scattered light smoke detectors, and non-fire reports can be reduced compared to dimmed smoke detectors.

  Further, in the present embodiment, the ultrasonic wave transmitted from the sound source unit 1 is provided by providing the cylindrical body 6 in at least a part of the ultrasonic wave propagation path between the sound source unit 1 and the wave receiving element 3. Diffusion is suppressed by passing through the internal space of the cylindrical body 6, and a decrease in sound pressure due to diffusion of ultrasonic waves between the sound source unit 1 and the wave receiving element 3 can be suppressed. The sound pressure of the ultrasonic wave received by the wave receiving element 3 can be maintained high in the absence of noise, and the amount of change in the output of the wave receiving element 3 relative to the amount of change in smoke density becomes relatively large. There is an effect of improving. Furthermore, the surface of the heating element layer 13 is disposed to face the incident side end face of the cylindrical body 6 and is formed to have the same size or larger than the incident side end face, so that interference within the cylindrical body 6 occurs. A decrease in the sound pressure of the ultrasonic wave due to can also be avoided.

  Furthermore, in the fire detector according to the present embodiment, the sound speed detection means 43 determines the sound speed based on the time difference from when the sound source unit 1 transmits an ultrasonic wave until the ultrasonic wave is received by the wave receiving element 3. The temperature estimation means 44 estimates the temperature of the monitoring space based on the sound speed obtained by the sound speed detection means 43, and the thermal type judgment means 45 compares the temperature estimated by the temperature estimation means 44 with the specified temperature. Therefore, it is possible to detect the fire even when the temperature rises at the time of the fire without using a separate temperature detecting element, and to detect the fire more reliably.

(Embodiment 2)
The basic structure of the fire detector of the present embodiment is substantially the same as that of the first embodiment, and the configuration of the control unit 2 and the configuration of the cylinder 6 are different from the fire detector of the first embodiment. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted suitably.

In the present embodiment, as shown in FIG. 9, a cylindrical body 6 having the same length as the distance between the sound source unit 1 and the wave receiving element 3 is used, and the sound source unit 1 and the wave receiving element 3 are arranged in the longitudinal direction of the cylindrical body 6. The structure which closed both end surfaces is adopted. At this time, each surface facing the internal space of the cylindrical body 6 in the sound source unit 1 and the wave receiving element 3 also functions as a reflection surface that reflects ultrasonic waves. With this configuration, the cylindrical body 6 has a specific resonance frequency, similar to a known acoustic tube whose both end faces in the longitudinal direction are closed. That is, when the longitudinal dimension of the cylinder 6 is L, the frequency f (wave propagation velocity) corresponding to the wavelength λ satisfying the relationship of L = (n / 2) × λ (where n is a natural number). (represented by f = c / λ as c) is the resonance frequency of the cylinder 6. Therefore, when a continuous wave of ultrasonic waves satisfying the relationship L = (n / 2) × λ is incident into the cylindrical body 6 from the end face in the longitudinal direction, at least a part of the ultrasonic wave is at both ends in the longitudinal direction of the cylindrical body 6. By repeating reflection on the surface, the reflected wave and the direct wave from the sound source unit 1 overlap and resonate, and the sound pressure of the ultrasonic wave increases with time as shown in FIG. To do. Thus, in the present embodiment, the control unit 2 controls the sound source unit 1 to transmit the ultrasonic wave having the resonance frequency unique to the cylinder 6 from the sound source unit 1, thereby causing resonance in the cylinder 6. The sound pressure of the ultrasonic wave from the sound source unit 1 is increased. In this case, in order to generate resonance in the cylindrical body 6, it is necessary to transmit ultrasonic waves of a plurality of periods exceeding L / λ (hereinafter referred to as m periods) from the sound source unit 1 instead of single-pulse ultrasonic waves. Therefore, the control unit 2 controls the sound source unit 1 so as to transmit a continuous wave of ultrasonic waves having an m (> L / λ) period from the sound source unit 1. In other words, the transmission time t _p (that is, t _p = m × λ / c) in which the ultrasonic wave is continuously transmitted from the sound source unit 1 propagates between both ends in the longitudinal direction of the cylindrical body 6. The sound source unit 1 is controlled by the control unit 2 so as to be longer than the propagation time t _s (that is, t _s = L / c) required (ie, t _p > t _s ). The wave receiving element 3 detects the sound pressure of the ultrasonic wave at the timing when the resonance occurs in the cylindrical body 6 and the sound pressure of the ultrasonic wave is saturated (“S” timing in FIG. 11). Usually, since the sound pressure of the ultrasonic wave is saturated when the transmission of the ultrasonic wave from the sound source unit 1 is completed, as an example, the wave receiving element 3 simultaneously ends the transmission of the ultrasonic wave from the sound source unit 1. It is conceivable to detect the sound pressure of ultrasonic waves.

  As shown in FIG. 12, the sound source unit 1, the wave receiving element 3, and the cylindrical body 6 of the present embodiment are located on one end surface (left end surface in FIG. 12) in the longitudinal direction of the cylindrical body 6. The wave receiving element 3 is positioned on the other end surface in the longitudinal direction of the cylindrical body 6 (the right end surface in FIG. 12). Here, as is well known, in an acoustic tube whose both end faces in the longitudinal direction are closed, the pressure change due to the ultrasonic waves is maximized at both ends in the longitudinal direction. The sound pressure of the ultrasonic wave can be detected at the site where the change is maximum. In other words, the wave receiving element 3 can detect the sound pressure of the ultrasonic wave at the part that becomes the antinode of the sound pressure of the ultrasonic wave (that is, the node of the moving speed of the air) (“A” and “B” in FIG. 12). ”Represents the magnitude of the pressure change). As a result, the amount of change in the output of the wave receiving element 3 with respect to the amount of change in smoke density can be increased as much as possible. As shown in FIG. 13, the sound source unit 1 and the wave receiving element 3 are arranged side by side on one end surface in the longitudinal direction of the cylinder 6 (left end surface in FIG. 13), and the other end surface in the longitudinal direction of the cylinder 6 (see FIG. 13). Even when the right end surface in Fig. 13 is closed, the wave receiving element 3 can detect the sound pressure of the ultrasonic wave at the site where the pressure change due to the ultrasonic wave is maximized.

  Moreover, the configuration of the sound source unit 1 is not limited to the configuration of FIG. 12 and FIG. 13, and the sound source unit 1 is disposed on one end surface in the longitudinal direction of the cylindrical body 6 whose both end surfaces in the longitudinal direction are closed by reflecting surfaces as shown in FIG. Even if the wave receiving element 3 is arranged at a position where the pressure change due to the ultrasonic wave from the sound source unit 1 is maximized on the side surface along the longitudinal direction, the wave receiving element 3 is a part where the pressure change due to the ultrasonic wave is maximized. Ultrasonic sound pressure can be detected. That is, in an acoustic tube whose both end surfaces in the longitudinal direction are closed, the pressure change due to the ultrasonic wave is maximized not only at both ends in the longitudinal direction but also from one end surface along the longitudinal direction every λ / 2 (λ is the wavelength of the ultrasonic wave). As in the case where the wave receiving element 3 is disposed at any end face in the longitudinal direction by arranging the wave receiving element 3 at this position, the output of the wave receiving element 3 with respect to the amount of change in smoke density Can be increased as much as possible.

  FIG. 14B is an example in which the wave receiving element 3 is disposed at a position where the pressure change due to the ultrasonic wave from the sound source unit 1 is maximized on the side surface of the cylindrical body 6, specifically, the control unit 2. However, the sound source unit 1 is controlled so that an ultrasonic wave having a wavelength λ (that is, λ = L / n) having a length obtained by dividing the length L in the internal space of the cylindrical body 6 by the natural number n is transmitted from the sound source unit 1. As a premise, the wave receiving element 3 is arranged at the center of the cylindrical body 6 in the longitudinal direction (that is, at the intermediate position between both reflecting surfaces). In short, when the ultrasonic wave having the wavelength λ (= L / n) is transmitted from the sound source unit 1, the central portion in the longitudinal direction of the cylindrical body 6 is necessarily n times λ / 2 from one end surface in the longitudinal direction. Since the pressure change due to the ultrasonic wave is always the maximum, the wave receiving element 3 arranged at the center in the longitudinal direction of the cylindrical body 6 detects the sound pressure at the position where the pressure change due to the ultrasonic wave is maximum. can do. In this configuration, if the frequency of the ultrasonic wave is different as long as the above-described wavelength λ (= L / n) condition is satisfied, only the receiving element 3 disposed at the center in the longitudinal direction of the cylindrical body 6 The sound pressure can be detected at a position where the pressure change due to the ultrasonic wave is maximum, and the design of the cylindrical body 6 is easier than in the case where the wave receiving element 3 is arranged at a different position for each ultrasonic frequency. Become.

  Here, when an acoustic tube whose both end surfaces are closed is resonated, it resonates by reflection of ultrasonic waves at each end surface in the longitudinal direction. When reflected at the end face, the sound pressure is reduced due to interference. However, according to the configuration in which the wave receiving element 3 is arranged on the side surface along the longitudinal direction of the cylindrical body 6 as shown in FIG. Compared with the case where the element 3 is provided, the end surface of the cylindrical body 6 can be a flat surface with less unevenness. As a result, the wave receiving element 3 inhibits the reflection of ultrasonic waves at the end surface of the cylindrical body 6. It is possible to increase the sound pressure due to the resonance without doing so. In the configuration of FIGS. 12 to 14, the inside of the cylinder 6 becomes a monitoring space as in the configuration of FIG. 9. For example, the side surface along the longitudinal direction of the cylinder 6 has a hole for guiding smoke or the like ( (Not shown) is formed.

  By the way, since the speed of sound c, which is the propagation speed of ultrasonic waves, changes according to the absolute temperature of the medium, the resonance frequency of the cylindrical body 6 is not always constant and varies due to changes in the speed of sound due to changes in the temperature of the medium. Therefore, in order to accurately match the frequency of the ultrasonic wave transmitted from the sound source unit 1 with the resonance frequency of the cylindrical body 6, the frequency of the ultrasonic wave transmitted from the sound source unit 1 is corrected in accordance with the change in sound velocity due to the temperature change. There is a need. Therefore, in the present embodiment, the control unit 2 includes frequency correction means (not shown) that corrects the frequency of the ultrasonic wave transmitted from the sound source unit 1 in accordance with the change in sound speed due to the temperature change. Therefore, even if the resonance frequency of the cylinder 6 varies due to a change in the sound speed, the frequency of the ultrasonic wave transmitted from the sound source unit 1 is changed by the frequency correction means. Therefore, the resonance can be reliably generated in the cylindrical body 6. Further, this frequency correction means is based on the time difference from when the sound source unit 1 transmits ultrasonic waves to when the ultrasonic waves are received by the wave receiving element 3 in the sound speed detection means 43 described in the first embodiment. The frequency of the ultrasonic wave transmitted from the sound source unit 1 is corrected using the sound speed obtained in this way, and as a result, the configuration can be simplified as compared with the case where a means for obtaining the sound speed is separately provided.

  Specific examples of this embodiment will be given below. When the speed of sound c is 340 m / s and the longitudinal dimension L of the cylindrical body 6 is 34 mm, the frequency f () of the ultrasonic wave transmitted from the sound source unit 1 is satisfied in order to satisfy the relationship L = (n / 2) × λ. = C / λ) may be set to, for example, 100 kHz (n = 20) or 50 kHz (n = 10). That is, 100 kHz and 50 kHz are resonance frequencies of the cylindrical body 6, and by transmitting ultrasonic waves of these frequencies from the sound source unit 1, the sound pressure of the ultrasonic waves changes with time as shown in FIG. Increased by resonance. Here, as described above, it is necessary to control the sound source unit 1 so as to transmit a continuous wave of ultrasonic waves of m (> L / λ) period from the sound source unit 1, so that the control unit 2 is, for example, 100 kHz The sound source unit 1 is controlled so as to continuously transmit ultrasonic waves from the sound source unit 1 for 100 cycles, and in the case of 50 kHz, about 50 cycles. In this configuration, the sound pressure of the ultrasonic wave detected by the wave receiving element 3 at the timing at which resonance occurs in the cylinder 6 and the sound pressure of the ultrasonic wave is saturated (timing “S” in FIG. 11) The sound pressure is several tens of times that when a single-pulse ultrasonic wave is transmitted and received in a configuration without the body 6.

Further, in the present embodiment, a configuration in which both end surfaces in the longitudinal direction of the cylindrical body 6 are closed is illustrated, but not limited to this configuration, for example, the longitudinal direction of the cylindrical body 6 as illustrated in FIG. 1 described in the first embodiment. Alternatively, a configuration in which only one end face is closed (the other end face is opened) may be employed. In the configuration of FIG. 1, the cylindrical body 6 has a specific resonance frequency in the same manner as a known acoustic tube whose one end surface in the longitudinal direction is closed. That is, when the longitudinal dimension of the cylindrical body 6 is L, the wavelength λ satisfies the relationship L = (1/4 + n / 2) × λ (where n = 0, 1, 2, 3,...). The corresponding frequency f (= c / λ) is the resonance frequency of the cylinder 6. Therefore, when a continuous wave of ultrasonic waves satisfying the relationship of L = (1/4 + n / 2) × λ enters the cylindrical body 6 from the end face in the longitudinal direction, at least a part of the ultrasonic waves is longitudinal in the cylindrical body 6. The reflection wave and the direct wave from the sound source unit 1 overlap and resonate by repeating the reflection at both end surfaces of the sound wave, and the sound pressure of the ultrasonic wave as time elapses as shown in FIG. Will increase. Therefore, even when the configuration of FIG. 1 is adopted, if the sound source unit 1 is controlled in the control unit 2 so that the ultrasonic wave having the resonance frequency inherent to the cylinder 6 is transmitted from the sound source unit 1, the cylinder body. 6 can resonate and increase the sound pressure of the ultrasonic wave from the sound source unit 1. In this case, in order to cause resonance in the cylindrical body 6, the control unit 2 transmits a continuous wave of ultrasonic waves having a period of m (> L / λ) from the sound source unit 1 instead of a single-pulse ultrasonic wave. The sound source unit 1 is controlled so that In other words, a transmission time t _p (= m × λ / c) for continuously transmitting ultrasonic waves from the sound source unit 1 is required for the ultrasonic waves to propagate between both ends in the longitudinal direction of the cylindrical body 6. The sound source unit 1 is controlled by the control unit 2 so as to be longer than the time t _s (= L / c) (that is, t _p > t _s ). When one end face is an open end as shown in FIG. 1, as is well known, an ultrasonic sound pressure node (that is, an antinode of air moving speed) is generated slightly outside the open end by ΔL. If the length L used for obtaining the resonance frequency is corrected by the above ΔL (correction of the opening end), a more accurate resonance frequency can be obtained.

  In the fire sensor according to the present embodiment described above, the cylindrical body 6 transmits a continuous wave of ultrasonic waves having a resonance frequency inherent to the cylindrical body 6 and m (> L / λ) cycles from the sound source unit 1. 6 is caused to resonate and the sound pressure of the ultrasonic wave from the sound source unit 1 is increased, so that a decrease in sound pressure between the sound source unit 1 and the receiving element 3 can be further suppressed, and smoke The amount of change in the output of the wave receiving element 3 with respect to the amount of change in density is increased, and the SN ratio is further improved. Moreover, in the ultrasonic wave that repeats reflection at the end face in the longitudinal direction of the cylindrical body 6 due to resonance, the effective transmission distance is extended according to the number of reflections, and the ultrasonic wave is substantially the dimension in the longitudinal direction of the cylindrical body 6. It reaches the wave receiving element 3 through a transmission distance several times L. This also contributes to an increase in the amount of change in the output of the wave receiving element 3 with respect to the amount of change in the smoke density, as compared with the case where a non-resonant single-pulse ultrasonic wave is received by the wave receiving element 3. The attenuation of ultrasonic waves increases several times.

  Other configurations and functions are the same as those in the first embodiment.

  By the way, even if the cylindrical body 6 is not a complete cylindrical shape, for example, one that is opened to one side by forming a slit over the entire length in the longitudinal direction, the effect of resonance is slightly diminished. Generally, since it has a specific resonance frequency as in the above embodiment, the cylindrical body 6 used in the above embodiment may not be a perfect cylinder. That is, even if the cylindrical body 6 that is not completely cylindrical is used, resonance is generated in the cylindrical body 6 to increase the sound pressure of the ultrasonic wave from the sound source unit 1, and the wave receiving element 3 with respect to the amount of change in the smoke density is increased. It is possible to improve the amount of change in output.

(Embodiment 3)
The fire detector according to this embodiment uses a pair of diffusion prevention plates 6 ′ shown in FIG. 15 instead of the cylinder 6 as a diffusion prevention member that narrows the diffusion range of ultrasonic waves from the sound source unit 1. It differs from the fire detector of 1 or Embodiment 2.

  Each diffusion prevention plate 6 ′ is a flat plate having a rectangular shape in plan view, and the pair of diffusion prevention plates 6 ′ are arranged substantially in parallel so that one surface faces each other. Here, the pair of diffusion preventing plates 6 'narrows the diffusion range of the ultrasonic waves by passing the ultrasonic waves from the sound source unit 1 through the space between the one surface (inner surface) facing each other, The ultrasonic wave from the sound source unit 1 is propagated through the space between the one surface facing each other, so that the surface of the one surface is opposed to the sound source unit 1 and the receiving element 3 in at least a part of the propagation path of the ultrasonic wave. It arrange | positions in the form which makes a longitudinal direction correspond. Specifically, as shown in FIG. 15, the sound source unit 1 and the wave receiving element 3 are arranged so as to face each other in a straight line, and the pair of diffusion prevention plates 6 ′ is located between the one surface and the sound source unit. 1 and the wave receiving element 3 are interposed. Here, a space between the opposing one surfaces of the pair of diffusion prevention plates 6 ′ is a monitoring space, the sound source unit 1 is disposed at one end in the longitudinal direction of the monitoring space, and the wave receiving element 3 is the longitudinal length of the monitoring space. It is arrange | positioned at the other end part of a direction. By providing the diffusion preventing plate 6 ′ in this way, the ultrasonic wave transmitted from the sound source unit 1 is monitored space in which the upper and lower sides of FIG. 15 are surrounded by the one surface (inner surface) of the diffusion preventing plate 6 ′. By passing through, diffusion is suppressed, and hence a decrease in sound pressure due to diffusion of ultrasonic waves between the sound source unit 1 and the wave receiving element 3 can be suppressed.

  According to this configuration, since both end faces in the width direction of the monitoring space are open, the ultrasonic wave from the sound source unit 1 is surrounded by the inner surface of the cylindrical body 6 as in the first embodiment. Compared to a passing configuration, the effect of suppressing the diffusion of ultrasonic waves is reduced, but smoke or the like is easily guided into the monitoring space.

  In the present embodiment, an example in which a pair of diffusion prevention plates 6 'facing each other is used as a diffusion prevention member is shown. However, the present invention is not limited to this example, and at least a part of the inner surface is disposed so as to face each other. The diffusion preventing member that narrows the diffusion range of the ultrasonic wave by passing the ultrasonic wave from the sound source unit 1 through the space between the opposing inner surfaces is transmitted from the sound source unit 1 and received by the wave receiving element 3. Any configuration may be used as long as it is disposed on the propagation path of the sound wave.

  Other configurations and functions are the same as those in the first or second embodiment.

(Embodiment 4)
The basic structure of the fire detector of the present embodiment is substantially the same as that of the first to third embodiments, and the configurations of the control unit 2 and the signal processing unit 4 are different as shown in FIG. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1-3, and description is abbreviate | omitted suitably.

By the way, the inventors of the present application indicate that the output frequency of the sound source unit 1 and the unit attenuation rate of the sound pressure as shown in FIG. 17 according to the type of suspended particles in the monitoring space between the sound source unit 1 and the wave receiving element 3. I got the knowledge that the relationship is different. Here, the sound pressure (hereinafter referred to as a reference sound pressure) received by the wave receiving element 3 in the absence of suspended particles in the monitoring space is defined as I ₀ , a dimming smoke densitometer (a dimming smoke detector). (I ₀ −I _x ), where I _x is the sound pressure received by the wave receiving element 3 in a state where suspended particles having a concentration of x% / m exist in the monitoring space. The value represented by / I ₀ is defined as the sound pressure attenuation rate, and in particular, the attenuation rate when x = 1 is defined as the unit attenuation rate. Here, it is assumed that the reference sound pressure I ₀ and the sound pressure I _x are detected under the same conditions except for the presence or absence of suspended particles in the monitoring space. “A” in FIG. 17 is an approximate curve (the black circle is measured data) showing the relationship between the output frequency and the unit attenuation rate of sound pressure when the suspended particles are black smoke particles, and “B” is the suspended particles. Approximate curve showing the relationship between the output frequency of white smoke particles and the unit attenuation rate of sound pressure (black square is measured data), “C” is the output frequency when the floating particles are steam particles It is an approximate curve (black triangle is measurement data) showing the relationship with the unit attenuation rate of sound pressure, and the unit attenuation rate shown here is when the distance between the sound source unit 1 and the receiving element 3 is set to 30 cm. The data for each output frequency. Further, each data at the right end in FIG. 17 is data when the output frequency is 82 kHz, and FIG. 18 shows the result of normalizing the unit attenuation rate of each output frequency with the data when the output frequency is 82 kHz as 1. . In short, in FIG. 18, the horizontal axis represents the output frequency, and the vertical axis represents the relative unit attenuation rate. The size of white smoke particles is about 800 nm, the size of black smoke particles is about 200 nm, and the size of steam particles is about several μm to 20 μm.

  Based on the above knowledge, in the present embodiment, the control unit 2 controls the sound source unit 1 so that plural types of ultrasonic waves having different frequencies are sequentially transmitted from the sound source unit 1, and the signal processing unit 4. Is at least the reference output of the wave receiving element 3 (the output of the wave receiving element 3 with respect to the reference sound pressure), the output frequency of the sound source unit 1 and the wave receiving element corresponding to the type of floating particles present in the monitoring space and the concentration of floating particles 3 relative data of the relative unit attenuation rate of the output (data extracted from FIG. 18 described above), unit attenuation rate at a specific frequency (for example, 82 kHz) with respect to smoke particles (data extracted from FIG. 17 described above) Is stored in the monitoring space using the storage means 48 storing the signal, the output of the wave receiving element 3 for each ultrasonic wave transmitted from the sound source unit 1 and the relational data stored in the storage means 48. Particle seeds The particle type estimation means 46 for estimating the frequency, and when the particles estimated by the particle type estimation means 46 are smoke particles, the attenuation from the reference value of the output of the wave receiving element 3 with respect to the ultrasonic wave of a specific frequency (for example, 82 kHz) Smoke density estimation means 47 for estimating the smoke density in the monitoring space based on the quantity, and smoke type judgment for judging the presence or absence of a fire by comparing the smoke density estimated by the smoke density estimation means 47 with a predetermined threshold Means 42.

  Below, the operation example of the fire detector of this embodiment is demonstrated with reference to the flowchart of FIG. First, a plurality of types of ultrasonic waves are sequentially transmitted from the sound source unit 1, and the output of the wave receiving element 3 for each ultrasonic wave is measured by the signal processing unit 4 (step S11). The particle type estimation means 46 obtains the sound pressure attenuation rate from the output of the wave receiving element 3 and the reference output stored in the storage means 48 for each output frequency (step S12), and the sound at the output frequency of 82 kHz. The ratio of the sound pressure attenuation rate at 20 kHz to the pressure attenuation rate is calculated (step S13). In the storage means 48, as the above relational data between the output frequency of the sound source unit 1 and the relative unit attenuation rate of the output of the wave receiving element 3, the relative unit at 20 kHz with respect to the relative unit attenuation rate at the output frequency of 82 kHz is stored. The ratio of the attenuation rate (in the case of FIG. 18, white smoke is 0, black smoke is 0.2, steam is 0.5) is stored, and the particle type estimation means 46 calculates the calculated attenuation rate ratio. Compared with the relational data stored in the storage means 48, the type of particle having the closest ratio of the attenuation rate in the relational data is estimated as the particle floating in the monitoring space (step S14). Here, if the estimated particles are smoke particles, the process proceeds to the processing in the smoke concentration estimating means 47 (step S15). Here, in the case of white smoke, as shown in FIG. 20, the relationship between the smoke density measured by the dimming smoke densitometer and the attenuation rate of the sound pressure is data that can be represented by a straight line. Therefore, the smoke concentration estimation means 47 is a unit stored in the storage means 48 of the attenuation factor of the output of the wave receiving element 3 with respect to the ultrasonic wave of a specific frequency (for example, 82 kHz) for the estimated particle type. A ratio with respect to the attenuation rate is calculated, and when the value of the ratio is y, it is estimated that the smoke density in the monitoring space corresponds to the smoke density y% / m in the evaluation with the dimming smoke densitometer (step S16). The smoke type determination means 42 compares the smoke density estimated in step S16 with a predetermined threshold value (for example, a smoke density that is 10% / m in the evaluation with the dimming smoke densitometer), and the estimated smoke. When the concentration is less than the above threshold, it is determined that “no fire”, while when it is equal to or greater than the above threshold, it is determined that “fire exists” and a fire detection signal is output to the control unit 2.

  In the above example, the particle type estimation means 46 uses the attenuation rate when the output frequency is 82 kHz and the attenuation rate when the output frequency is 20 kHz. However, the present invention is not limited to the combination of these output frequencies, and different combinations are possible. An output frequency may be used. Furthermore, attenuation rates for more output frequencies may be used, and in that case, the accuracy of estimation of the particle type can be improved. In this embodiment, the smoke density estimation means 47 targets one frequency as the specific frequency, but targets a plurality of frequencies as the specific frequency, and obtains an average value of the smoke density estimated for each specific frequency. In this case, the accuracy of smoke density estimation is improved. The signal processing unit 4 is constituted by a microcomputer, and the particle type estimation means 46, the smoke concentration estimation means 47, and the smoke type determination means 42 are realized by mounting an appropriate program on the microcomputer. Yes. The signal processing unit 4 is provided with an A / D converter for analog-digital conversion of the output signal of the wave receiving element 3.

  In the present embodiment, one sound wave generating element described in the first embodiment is used as the sound source unit 1, and the above-described control unit 2 sequentially changes the frequency of the drive input waveform applied to the sound source unit 1. A plurality of types of ultrasonic waves having different frequencies are sequentially transmitted from the sound source unit 1. Here, the control unit 2 changes the frequency of the ultrasonic wave transmitted from the sound source unit 1 from a lower limit frequency (for example, 20 kHz) to an upper limit frequency (for example, 82 kHz) in a predetermined frequency range (for example, 20 kHz to 82 kHz). . In the present embodiment, the control unit 2 is configured to control the sound source unit 1 so that four types of ultrasonic waves having different frequencies are sequentially transmitted from the sound source unit 1. The frequency of the ultrasonic wave to be waved is not limited to four types, but may be a plurality of types. For example, if two types are used, the control unit 2 and the signal processing unit are compared with the case where three or more types of ultrasonic waves are sequentially transmitted. 4 can be reduced, and the control unit 2 and the signal processing unit 4 can be simplified. In the present embodiment, since the sound wave generating element described in the first embodiment is used as the sound source unit 1 as described above, the ultrasonic waves sequentially transmitted can be converted into ultrasonic waves having different frequencies. The cost can be reduced as compared with the case where a continuous wave ultrasonic wave is transmitted from each piezoelectric element using a plurality of piezoelectric elements having different resonance frequencies as 1.

  Further, in the present embodiment, as in the second embodiment, as shown in FIG. 9, the cylindrical body 6 having the same length as the distance between the sound source unit 1 and the wave receiving element 3 is used, and the sound source unit 1 and the wave receiving element 3 are used. And adopting a configuration in which both end faces in the longitudinal direction of the cylinder 6 are closed, and the control unit 2 generates an ultrasonic wave having a resonance frequency inherent to the cylinder 6 and having an m (> L / λ) period as a sound source unit. By controlling the sound source unit 1 so as to be transmitted from 1, a resonance is generated in the cylindrical body 6 and the sound pressure of the ultrasonic wave from the sound source unit 1 is increased. In short, the control unit 2 controls the sound source unit 1 so that a plurality of types (for example, four types) of ultrasonic waves that are selected from the resonance frequency inherent in the cylinder 6 and have different frequencies are transmitted from the sound source unit 1. .

  Here, as in the example of FIG. 14 described in the second embodiment, the sound source unit 1 is arranged on one end surface in the longitudinal direction of the cylindrical body 6 whose both end surfaces in the longitudinal direction are closed, and the sound source unit among the side surfaces along the longitudinal direction. In the case where the wave receiving element 3 is arranged at a position where the pressure change due to the ultrasonic wave from 1 is maximized, λ / 2 (from the one end surface of the cylindrical body 6 for each frequency of the ultrasonic wave transmitted from the sound source unit 1 ( The receiving element 3 may be arranged at each position separated by n times the wavelength of the ultrasonic wave), but preferably the ultrasonic wave transmitted from the sound source unit 1 has a wavelength of λ = L / n. As shown in FIG. 14B, the wave receiving element 3 is arranged only at the central portion in the longitudinal direction of the cylindrical body 6 and the wave receiving element 3 detects ultrasonic waves of plural kinds of frequencies. You can do it. Thereby, compared with the case where the receiving element 3 is arrange | positioned in each different position for every frequency of an ultrasonic wave, the required number of the receiving elements 3 reduces and cost reduction is attained.

In the present embodiment, the example in which the relationship data between the output frequency of the sound source unit 1 and the relative unit attenuation rate of the output of the receiving element 3 is stored in the storage unit 48 has been shown. Since the amount of attenuation (I ₀ −I _x ) from the reference value of the output of the wave receiving element 3 changes for each output frequency of the sound source unit 1 according to the type of particle, the above relationship stored in the storage means 48 The data may be data indicating the relationship between the output frequency of the sound source unit 1 and the attenuation amount from the reference value of the output of the wave receiving element 3. Instead of the above relative unit attenuation rate, for example, the wave receiving element Attenuation amount from the reference value of the output of 3 or the attenuation value obtained by dividing the attenuation amount from the reference value of the output of the receiving element 3 by the reference value (I ₀ ), or related data adopting the unit attenuation rate You may make it memorize | store in the memory | storage means 48. FIG.

  In the fire detector of the present embodiment described above, in the particle type estimation unit 46, the relationship between the output of the receiving element 3 for each ultrasonic wave transmitted from the sound source unit 1 and the storage unit 48 is stored. The type of particles floating in the monitoring space is estimated using the data, and when the particle estimated by the particle type estimation unit 46 is a smoke particle, the smoke density estimation unit 47 uses the ultrasonic wave of a specific frequency. The smoke density in the monitoring space is estimated based on the attenuation amount from the reference value of the output of the wave receiving element 3 with respect to the smoke density, and the smoke type estimating means 42 uses the smoke density estimated by the smoke density estimating means 47 and a predetermined threshold value. In order to judge the presence or absence of a fire, it is possible to eliminate the influence of background light, which is a problem with photoelectric fire detectors such as scattered light smoke detectors and dimming smoke detectors, Rabi required for scattered smoke detectors Compared to light scattering type smoke detector to be able to eliminate the Nsu body can improve the response and the reduction of non-fire report is made possible as compared with the dimming smoke sensor. Moreover, since the particle type estimation means 46 can identify the smoke particles and steam by estimating the type of particles floating in the monitoring space, the scattered light type smoke detector and the dimming type smoke detector can be used. In comparison, non-fire reports due to steam can be reduced, making it suitable for use in kitchens and bathrooms. Further, since the white smoke particles and the black smoke particles can be discriminated by the particle type estimation means 46, it is also possible to use it for identifying the nature of the fire. In addition, it is possible to distinguish between dust and smoke particles floating when cleaning the room where the fire detector is installed or for electrical work behind the ceiling, so reduce non-fire reports caused by dust. Is also possible.

  By the way, in this embodiment, the sound source unit 1 is constituted by a single sound wave generating element, and the control unit 2 sequentially changes the frequency of the drive input waveform applied to the sound source unit 1, so that a plurality of types having different frequencies from the sound source unit 1 can be obtained. However, the sound source unit 1 may be composed of a plurality of sound wave generating elements having different output frequencies. In this case, an element that generates ultrasonic waves by mechanical vibration, such as a piezoelectric element, is used as each sound wave generating element, and each sound wave generating element is driven at the respective resonance frequency to be transmitted from the sound source unit 1. It is possible to increase the sound pressure of the ultrasonic wave and contribute to the improvement of the SN ratio. In addition to sequentially driving each sound wave generating element to send multiple types of ultrasonic waves, it is also possible to simultaneously drive multiple sound wave generating elements to send multiple types of ultrasonic waves simultaneously Become.

  In addition, individual receiving elements 3 may be provided for various types of ultrasonic waves. In this case, piezoelectric elements having a relatively large Q value of resonance characteristics are used as the receiving elements 3. The sensitivity of the wave receiving element 3 can be improved by using each wave receiving element 3 for receiving ultrasonic waves of the respective resonance frequencies. Furthermore, by simultaneously driving multiple sound wave generating elements and transmitting multiple types of ultrasonic waves, it is possible to detect the amount of attenuation of the sound pressure of multiple types of ultrasonic waves at the same time. It is possible to accurately estimate the type of suspended particles and the smoke concentration by detecting the attenuation of sound pressure for a plurality of types of ultrasonic waves without being affected by changes (for example, changes in the concentration of suspended particles). It is also conceivable that the sound wave generating element constituting the sound source unit 1 is also used as the wave receiving element 3. In this case, there is a reflection surface that reflects the ultrasonic wave transmitted from the sound wave generating element toward the sound wave generating element. Although necessary, the cost can be reduced by reducing the number of elements.

  The other configurations and functions are the same as those of the first to third embodiments. For example, also in the fire detector of the present embodiment, the sound speed detecting means 43 is provided in the signal processing unit 4 as in the first embodiment shown in FIG. Further, a temperature estimation unit 44 and a thermal type determination unit 45 may be provided.

  By the way, in each of the above embodiments, the sound source unit 1, the control unit 2, the wave receiving element 3, and the signal processing unit 4 are provided on one circuit board 5 and housed in a container (not shown). And a sound source side unit provided with the control unit 2 and a reception side unit provided with the wave receiving element 3 and the signal processing unit 4 are configured as separate units to constitute a separate type fire alarm. May be. In this case, the cylindrical body 6 is provided in at least one of the sound source side unit and the wave receiving side unit, or is provided separately from the sound source side unit and the wave receiving side unit. Further, the sound source unit 1 is not limited to the sound wave generating element having the configuration shown in FIG. 3 described above. For example, a rapid temperature change of the heat generating unit accompanying energization of the heat generating unit with a thin aluminum plate as the heat generating unit. A sound wave may be generated by a thermal shock due to.

  Furthermore, the signal processing unit 4 periodically changes the output of the sound source unit 1 and the wave receiving element based on the output of the wave receiving element 3 with respect to an ultrasonic wave having a predetermined frequency (for example, 82 kHz which is the same as the specific frequency described above). If at least one of the control condition of the sound source section 1 by the control section 2 and the signal processing condition of the output of the receiving element 3 is changed so that the sensitivity fluctuation of 3 is canceled, the output fluctuation of the sound source section 1 Sensitivity fluctuations of the wave receiving element 3 can be periodically canceled, and long-term reliability is improved.

  Moreover, in each said embodiment, if the control part 2 is made to transmit the ultrasonic wave of the frequency which has an insect-proof effect from the sound source part 1, it can prevent that an insect penetrate | invades in the said monitoring space, Non-fire reports caused by insects can be reduced. Here, the control unit 2 may periodically transmit ultrasonic waves having a frequency having an insect-proofing effect separately from the ultrasonic waves having a frequency transmitted from the sound source unit 1 in order to estimate the smoke density. In order to estimate the smoke concentration, the frequency of the ultrasonic wave transmitted from the sound source unit 1 may be set to a frequency having an insect-proof effect.

The principal part of Embodiment 1 of this invention is shown, (a) is a schematic bottom view, (b) is a schematic side view. It is a block diagram which shows a structure same as the above. It is a schematic sectional drawing which shows the sound wave generation element used for the same as the above. The wave receiving element used for the above is shown, (a) is a partially broken schematic perspective view, and (b) is a schematic sectional view. (A) is a schematic perspective view which shows the principal part same as the above, (b) is a schematic side view which shows the other example of (a). It is a schematic side view which shows the other example same as the above. It is a schematic bottom view which shows another example same as the above. It is a schematic bottom view which shows another example same as the above. It is a schematic side view which shows another example same as the above. It is a schematic side view which shows another example same as the above. It is explanatory drawing which shows the sound pressure change by resonance of Embodiment 2 of this invention. It is a schematic side view which shows the principal part same as the above. It is a schematic side view which shows the other example same as the above. (A) is a schematic side view which shows another example same as the above, (b) is a schematic side view which shows the other example of (a). It is a schematic perspective view which shows the structure of Embodiment 3 of this invention. It is a block diagram which shows the structure of Embodiment 4 of this invention. It is explanatory drawing which shows the relationship between the output frequency of a sound source part same as the above, and the unit attenuation rate of a sound pressure. It is explanatory drawing which shows the relationship between the output frequency of a sound source part same as the above, and a relative unit attenuation factor. It is a flowchart which shows the operation example same as the above. It is explanatory drawing which shows the relationship between smoke density same as the above and the attenuation factor of the ultrasonic wave of a specific frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sound source part 1a Sound wave generation element 2 Control part 3 Receiving element 4 Signal processing part 6 Cylindrical body (diffusion prevention member)
6 'Diffusion prevention plate (Diffusion prevention member)
11 Base substrate 12 Thermal insulation layer 13 Heating element layer (heating element part)
41 Smoke density estimation means 42 Smoke type judgment means 46 Particle type estimation means 47 Smoke density estimation means 48 Storage means

Claims (15)

  A sound source unit capable of transmitting ultrasonic waves, a control unit for controlling the sound source unit, a receiving element for detecting the sound pressure of the ultrasonic wave transmitted from the sound source unit, and a fire based on the output of the receiving element A signal processing unit for determining the presence or absence of smoke, and the signal processing unit is configured to estimate smoke concentration in a monitoring space between the sound source unit and the wave receiving element based on an attenuation amount from a reference value of the output of the wave receiving element. It has density estimation means and smoke type judgment means for judging the presence or absence of a fire by comparing the smoke density estimated by the smoke density estimation means with a predetermined threshold, and is arranged so that at least a part thereof faces each other A diffusion preventing member that has a defined inner surface and that allows ultrasonic waves from the sound source unit to pass through the space between the opposing inner surfaces to narrow the diffusion range of the ultrasonic waves is transmitted from the sound source unit and received by the receiving element. A fire detector, which is disposed on a propagation path of ultrasonic waves.   The fire detector according to claim 1, wherein the diffusion preventing member is formed in a cylindrical shape and has a cylindrical body whose inner surface along the longitudinal direction is the inner surface.   The sound source unit can transmit a plurality of types of ultrasonic waves having different frequencies, and the signal processing unit is configured to output the output frequency of the sound source unit according to the type of suspended particles present in the monitoring space and the smoke concentration, and the Stored in the storage means for storing the relationship data with the attenuation amount from the reference value of the output of the receiving element, and the output of the receiving element for each ultrasonic wave transmitted from the sound source unit and stored in the storing means Particle type estimation means for estimating the type of particles floating in the monitoring space using the relationship data, and the smoke concentration estimation means is configured such that the particles estimated by the particle type estimation means are smoked. The smoke density in the monitoring space is estimated based on an attenuation amount from a reference value of the output of the receiving element with respect to ultrasonic waves of a specific frequency when the particles are particles. Fire detector.   The storage means stores, as the relationship data, relationship data between an output frequency of the sound source unit and an attenuation rate obtained by dividing an attenuation amount from a reference value of the output of the receiving element by a reference value. The fire detector according to claim 3.   The sound source unit includes a single sound wave generating element capable of transmitting the plurality of types of ultrasonic waves, and the control unit controls the sound source unit so that the plurality of types of ultrasonic waves are sequentially transmitted from the sound wave generating elements. The fire detector according to claim 3 or 4, characterized by:   In the sound source unit, a transmission surface that vibrates air is disposed to face an incident side end surface on which ultrasonic waves are incident on the diffusion preventing member, and the inner surface is equal to or more than a distance between inner surfaces in a direction facing each other. The fire sensor according to any one of claims 1 to 5, wherein the fire sensor has a width dimension of.   7. The sound source unit according to claim 1, wherein the sound source unit generates an ultrasonic wave by applying a thermal shock to air due to a temperature change of the heat generating unit accompanying energization of the heat generating unit. The fire detector according to claim 1.   The sound source unit is formed between the heat generating unit and the base substrate on the one surface side of the base substrate, and the heat generating unit and the base are formed on the one surface side of the base substrate. 8. The fire detector according to claim 7, further comprising a thermal insulation layer comprising a porous layer that thermally insulates the substrate.   The control unit transmits an ultrasonic wave having a resonance frequency based on a propagation distance of an ultrasonic wave transmitted from the sound source unit and received by the wave receiving element, and at least the ultrasonic wave propagates from the sound source unit to the wave receiving element. 3. The fire detector according to claim 1, wherein the sound source unit is controlled to continuously transmit the sound from the sound source unit over a transmission time longer than a propagation time required for the transmission. 4. .   The control unit transmits a plurality of types of ultrasonic waves having resonance frequencies based on a propagation distance of an ultrasonic wave transmitted from the sound source unit and received by the receiving element, each having a different frequency from at least the sound source unit. 4. The sound source unit is controlled to continuously transmit from the sound source unit over a transmission time longer than a propagation time required for an ultrasonic wave to propagate to the wave receiving element. The fire detector according to any one of claims 5 to 6.   In the diffusion preventing member, the space between the inner surfaces through which the ultrasonic waves from the sound source section pass is closed by reflection surfaces that reflect ultrasonic waves at both end surfaces in the ultrasonic wave propagation direction, The fire detector according to claim 9 or 10, wherein a sound source is disposed, and the wave receiving element is disposed on any of the reflecting surfaces.   In the diffusion preventing member, the space between the inner surfaces through which the ultrasonic waves from the sound source section pass is closed by reflection surfaces that reflect ultrasonic waves at both end surfaces in the ultrasonic wave propagation direction, A sound source is disposed, and the wave receiving element is disposed at a position where the pressure change due to the ultrasonic wave from the sound source is maximized on the inner surface along the propagation direction. The fire detector according to claim 10.   The control unit controls the sound source unit so that an ultrasonic wave having a length obtained by dividing a distance between the reflection surfaces by a natural number is transmitted from the sound source unit, and the receiving element is configured to receive both reflection surfaces. The fire sensor according to claim 12, wherein the fire sensor is disposed at an intermediate position.   The said control part has a frequency correction means which correct | amends the frequency of the ultrasonic wave transmitted from the said sound source part according to the change of the sound speed by a temperature change, The any one of Claim 9 thru | or 13 characterized by the above-mentioned. Fire detector as described in   The frequency correction means corrects the frequency using a sound speed obtained based on a time difference from when the sound source unit transmits an ultrasonic wave until the ultrasonic wave is received by the receiving element. The fire detector according to claim 14.

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