JP4894722B2 - Fire detector - Google Patents

Description

  The present invention relates to a fire detector that determines the presence or absence of a fire from the smoke density in a monitoring space.

  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 sound waves (for example, ultrasonic waves).

  As shown in FIG. 17, the fire detector includes a sound source unit 1 capable of transmitting ultrasonic waves, a control unit (not shown) that controls the sound source unit 1, and ultrasonic waves transmitted from the sound source unit 1. And a signal processing unit (not shown) for determining whether or not there is a fire based on the output of the wave receiving element 3. The signal processing unit is estimated by smoke concentration estimation means for estimating 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. Fire determining means for comparing the smoke concentration with a predetermined threshold value to determine whether or not there is a fire. That is, when smoke particles enter the monitoring space, the sound pressure of the ultrasonic waves from the sound source unit 1 decreases before reaching the wave receiving element 3, and the attenuation amount of the output of the wave receiving element 3 is substantially equal to the smoke concentration in the monitoring space. Since it increases in proportion, the presence or absence of a fire can be determined by estimating the smoke density based on this attenuation.

  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. .

  However, in the above-described ultrasonic fire detector, the sound source unit 1 and the receiving element 3 are caused by changes over time (for example, aging degradation) and changes in the surrounding environment (for example, changes in temperature, humidity, atmospheric pressure, etc.). As a result, characteristic changes occur in the sound source unit 1 and the wave receiving element 3, and the attenuation from the reference value of the output of the wave receiving element 3 may fluctuate regardless of the smoke density in the monitoring space. That is, the sound pressure of the ultrasonic wave transmitted from the sound source unit 1 changes or the sensitivity of the wave receiving element 3 changes according to the time-dependent change of the sound source unit 1 or the wave receiving element 3 or the change in the surrounding environment of the fire detector. By changing, the attenuation amount from the reference value of the output of the receiving element 3 fluctuates, and as a result, there is a possibility that a non-fire report or a misreport is generated.

  The present invention has been made in view of the above reasons, and in the configuration for determining the presence or absence of a fire based on the amount of attenuation of ultrasonic waves in the monitoring space, the sound source unit or the It is an object of the present invention to provide a fire detector that does not cause non-fire reports or false alarms due to the influence of characteristic changes that occur in a wave receiving element.

  According to the first aspect of the present invention, a sound source unit capable of transmitting a sound wave, a control unit for controlling the sound source unit, a wave receiving element for detecting the sound pressure of the sound wave transmitted from the sound source unit, and an output of the wave receiving element A signal processing unit that determines the presence or absence of a fire based on the signal processing unit, the signal processing unit from the sound source unit to the receiving element through the propagation path having a different path length in the monitoring space between the sound source unit and the receiving element Sound pressure ratio calculation means for calculating the sound pressure ratio between a plurality of transmitted sound waves, and smoke concentration estimation for estimating the smoke density in the monitoring space based on the amount of change from the initial value of the sound pressure ratio calculated by the sound pressure ratio calculation means And a fire 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 value.

  According to this configuration, the sound pressure ratio calculation means can detect the sound between the plurality of sound waves respectively propagated from the sound source unit to the receiving element through the propagation paths having different path lengths in the monitoring space between the sound source unit and the receiving element. Since the pressure ratio is calculated, even if the sound pressure of the sound wave transmitted from the sound source changes or the sensitivity of the receiving element changes according to changes over time or the surrounding environment, these changes Does not affect the sound pressure ratio calculated by the sound pressure ratio calculation means. Therefore, in the smoke concentration estimation means for estimating the smoke density in the monitoring space based on the amount of change from the initial value of the sound pressure ratio calculated by the sound pressure ratio calculation means, the sound source section or Smoke density can be estimated without being affected by changes in the characteristics of the receiving element, and as a result, non-fire reports and misreports will not occur due to the effects of the above-mentioned characteristic changes that occur in the sound source section and receiving element. .

  According to a second aspect of the present invention, in the first aspect of the invention, the sound source unit is capable of transmitting a plurality of types of sound waves having different frequencies, and the signal processing unit includes the type of suspended particles present in the monitoring space and Storage means for storing relational data between the output frequency of the sound source unit according to smoke density and the amount of change from the initial value of the sound pressure ratio, and the sound pressure ratio for each sound wave of each frequency transmitted from the sound source unit And particle type estimation means for estimating the type of particles floating in the monitoring space using the relationship data stored in the storage means, and the smoke concentration estimation means at the particle type estimation means When the estimated particle is a smoke particle, the smoke density in the monitoring space is estimated based on an amount of change from an initial value of the sound pressure ratio with respect to a sound wave of a specific frequency.

  According to this configuration, in the signal processing unit, the particle type estimation unit floats in the monitoring space using the sound pressure ratio for each sound wave of each frequency transmitted from the sound source unit and the relational data stored in the storage unit. When the particle estimated by the particle type estimation means is a smoke particle, the smoke concentration estimation means determines the type of particle based on the amount of change from the initial value of the sound pressure ratio with respect to the sound wave of a specific frequency. Since the smoke concentration in the monitoring space is estimated, 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. Compared with a light-reducing smoke detector, non-fire reports due to steam can be reduced, and it is also suitable for use in kitchens and bathrooms.

  According to a third aspect of the present invention, in the second aspect of the present invention, the storage means includes, as the relation data, an output frequency of the sound source unit and a rate of change obtained by dividing an amount of change from an initial value of the sound pressure ratio by an initial value. It is characterized by storing related data.

  According to the present invention, even when the initial value of the sound pressure ratio varies according to the output frequency of the sound source unit, the relational data between the output frequency of the sound source unit and the rate of change from which the influence of the variation of the initial value of the sound pressure ratio is removed By using, it is possible to estimate the type of particles floating in the monitoring space without being affected by the fluctuation of the initial value of the sound pressure ratio.

  According to a fourth aspect of the present invention, in the second or third aspect of the invention, the sound source unit includes a single sound wave generating element capable of transmitting the plurality of types of sound waves, and the control unit includes a plurality of sound wave generating elements. The sound source unit is controlled so that seed sound 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 the case where a plurality of sound wave generating elements capable of transmitting various sound waves are provided.

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

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

  According to a sixth aspect of the present invention, in the invention according to the fifth aspect, the sound source section includes the heating element portion formed on one surface side of the base substrate, and the heating element portion 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 base 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 sound wave becomes high, and the power consumption can be reduced.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the smoke density estimation means is based on a change rate obtained by dividing a change amount from an initial value of the sound pressure ratio by an initial value. It is characterized by estimating smoke density in the monitoring space.

  According to this configuration, since the smoke density in the monitoring space is estimated based on the rate of change in the sound pressure ratio from which the influence of the variation in the initial value of the sound pressure ratio has been removed, if the smoke density in the monitoring space is the same, the sound pressure ratio Regardless of the initial value, the smoke density estimation results can be made uniform.

  The invention of claim 8 is the invention according to any one of claims 1 to 7, wherein the propagation path between the sound source unit and the receiving element is selected from a plurality of propagation paths having different path lengths. A route selection unit for selecting the sound source is provided, the control unit controls the sound source unit so that sound waves are intermittently transmitted from the sound source unit, and the sound pressure ratio calculation means includes a route selection unit. The sound pressure ratio between the plurality of sound waves propagated from the sound source unit to the wave receiving element is calculated in each state in which the propagation paths having different path lengths are selected.

  According to this configuration, a sound wave transmitted from a single sound source unit can be propagated to a single receiving element through propagation paths having different path lengths. The sound pressure ratio between a plurality of sound waves received by the receiving element can be calculated. Therefore, the calculated sound pressure ratio is not affected by variations in characteristic changes that occur between multiple sound source units or variations in characteristics that occur between multiple receiving elements, and as a result, the sound pressure ratio is calculated. Accuracy is improved.

  The invention of claim 9 is the invention of any one of claims 1 to 7, wherein a plurality of propagation paths having different path lengths are formed between the sound source section and the receiving element, The sound pressure ratio calculating means calculates a sound pressure ratio between a plurality of sound waves transmitted from the sound source unit and transmitted through the propagation paths having different path lengths to the receiving element.

  According to this configuration, a sound wave transmitted from a single sound source unit can be propagated to a single receiving element through propagation paths having different path lengths. The sound pressure ratio between a plurality of sound waves received by the receiving element can be calculated. Therefore, the calculated sound pressure ratio is not affected by variations in characteristic changes that occur between multiple sound source units or variations in characteristics that occur between multiple receiving elements, and as a result, the sound pressure ratio is calculated. Accuracy is improved. In addition, since the sound pressure ratio is calculated for the sound waves simultaneously transmitted from the sound source unit, the calculated sound pressure ratio is not affected by variations in sound pressure caused by the driving timing of the sound source unit.

  According to a tenth aspect of the present invention, in any one of the first to seventh aspects, the pair of reflecting surfaces are arranged so as to face each other in the traveling direction of the sound wave transmitted from the sound source unit and reflect the sound wave, respectively. The sound pressure ratio calculating means calculates a sound pressure ratio between a plurality of sound waves having different numbers of reflections from the sound source unit to the wave receiving element before being propagated to the wave receiving element. To do.

  According to this configuration, even a sound wave transmitted from a single sound source unit and propagated to a single receiving element passes through propagation paths having different path lengths depending on the number of times reflected by the reflecting surface. Propagated. In short, a sound wave transmitted from a single sound source unit can be propagated to a single receiving element through propagation paths having different path lengths, and transmitted from a single sound source unit and transmitted by a single receiving element. It is possible to calculate a sound pressure ratio between a plurality of received sound waves. Therefore, the calculated sound pressure ratio is not affected by variations in characteristic changes that occur between multiple sound source units or variations in characteristics that occur between multiple receiving elements, and as a result, the sound pressure ratio is calculated. Accuracy is improved. In addition, since the sound pressure ratio is calculated for the sound waves simultaneously transmitted from the sound source unit, the calculated sound pressure ratio is not affected by variations in sound pressure caused by the driving timing of the sound source unit. Further, the use of the reflective surface can reduce the size of the fire detector relative to the path length.

  According to an eleventh aspect of the present invention, in the tenth aspect of the invention, the reflecting surface is formed of a concave curved surface that is curved so as to collect sound waves from the sound source section on the other reflecting surface. .

  According to this configuration, even if the reflection on the reflecting surface is repeated, the sound wave is not easily diffused. Therefore, it is possible to suppress a decrease in sound pressure due to the sound wave diffusion between the sound source unit and the wave receiving element. As a result, the sound pressure of the sound wave received by the wave receiving element in a state where 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 twelfth aspect of the present invention, in the invention of the eleventh aspect, the sound source unit and the wave receiving element are on the reflection surfaces different from each other, and are incident and reflected as plane waves on the other reflection surface. Is arranged at a position for focusing.

  According to this configuration, the sound wave that reaches the reflection surface on the receiving element side while spreading radially from the sound source unit is reflected as a parallel wave on the reflection surface on the sound source unit side by the reflection surface, and then reflected on the sound source unit side. By being reflected by the surface, the focal point is formed at the position of the wave receiving element on the reflection surface on the wave receiving element side. Therefore, it is possible to reliably suppress a decrease in sound pressure due to diffusion of sound waves while propagating from the sound source unit to the wave receiving element. As a result, there is an advantage that the SN ratio is further improved.

  Since the present invention estimates the smoke concentration in the monitoring space based on the amount of change from the initial value of the sound pressure ratio calculated by the sound pressure ratio calculating means, the sound source unit and the receiving element due to changes over time and changes in the surrounding environment The smoke concentration can be estimated without being affected by the characteristic change of the sound, and there is an effect that the non-fire report or the misreport is not caused by the influence of the characteristic change generated in the sound source unit or the receiving element.

(Embodiment 1)
As shown in FIG. 2, the fire detector of the present embodiment has a pair of sound source units 1a and 1b capable of transmitting ultrasonic waves (hereinafter referred to as the sound source unit 1 when the two sound source units 1a and 1b are not particularly distinguished). A control unit 2 that controls the sound source units 1a and 1b, and a pair of wave receiving elements 3a and 3b that detect the sound pressure of the ultrasonic waves transmitted from the sound source units 1a and 1b (hereinafter, both wave receiving elements 3a). , 3b is referred to as a receiving element 3) and a signal processing unit 4 that determines the presence or absence of a fire based on the output of each of the receiving elements 3a, 3b. Here, the sound source unit 1 and the wave receiving element 3 that transmit and receive ultrasonic waves are employed. However, the sound source unit 1 and the wave receiving element 3 are not limited to ultrasonic waves, but may be anything that transmits and receives sound waves. .

  Here, the sound source unit 1 and the receiving element 3 are a set of the first sound source unit 1a and the first receiving element 3a, and the second sound source unit 1b and the second receiving element 3b. As shown, the sound source sections 1a and 1b and the wave receiving elements 3a and 3b constituting each set are arranged to face each other on one surface side of the circuit board 5 (see FIG. 17) made of a disc-shaped printed board. . The circuit board 5 is provided with a control unit 2 and a signal processing unit 4. 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 receiving element, 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 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 propagating 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; The sound source unit 1 is intermittently driven so that ultrasonic waves are intermittently transmitted from the sound source unit 1.

  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.

Here, the sound source units 1a and 1b and the wave receiving elements 3a and 3b are arranged so that the distance between them is different for each group. In this embodiment, the first sound source unit 1a and the first receiving unit are arranged. An arrangement is employed in which the distance between the second sound source unit 1b and the second wave receiving element 3b is longer than the distance from the wave element 3a. Thereby, as shown in FIG. 1A, the ultrasonic wave Sw1 transmitted from the first sound source unit 1a and the ultrasonic wave Sw2 transmitted from the second sound source unit 1b are received by the sound source unit 1. Through the propagation paths having different path lengths in the monitoring space between the wave elements 3, the waves are propagated to the wave receiving elements 3 a and 3 b forming a pair. That is, the propagation path of the ultrasonic wave Sw1 transmitted from the first sound source unit 1a and received by the first wave receiving element 3a is a separation distance between the first sound source unit 1a and the first wave receiving element 3a. has a path length L _1, whereas, the propagation path of the ultrasonic Sw2 is reception in the second wave receiving element 3b is transmitting from the second sound source unit 1b, a second tone generator 1b second It will have a separation distance between the wave receiving element 3b as the path length L _2. In addition, you may provide the partition which separates both propagation paths so that the ultrasonic waves Sw1 and Sw2 from each sound source part 1a, 1b may not interfere with each other.

In the present embodiment, both sound source units 1a and 1b have the same characteristics, both receiving elements 3a and 3b have the same characteristics, and both sound source units 1a and 1b have the same conditions (for example, ) And the receiving elements 3a and 3b are used under the same conditions (for example, DC bias voltage). Here, the surrounding environment (for example, temperature, humidity, atmospheric pressure) of the fire detector is set to a predetermined state, and the sound source unit 1 and the wave receiving element 3 are not changed over time (for example, before shipment). When no suspended particles (including smoke particles) enter the monitoring space, the ultrasonic waves Sw1 and Sw2 from the sound source units 1a and 1b have different path lengths L as described above, as shown in FIG. ₁ , L ₂ , by passing through the propagation paths respectively, the sound pressures P ₁₀ , P ₂₀ (super wave received by the first wave receiving element 3 a when received by the wave receiving elements 3 a, 3 b) The sound pressure of the sound wave Sw1 is P ₁₀ and the sound pressure of the ultrasonic wave Sw2 received by the second receiving element 3b is P ₂₀ ). That is, since the ultrasonic wave transmitted from the sound source unit 1 is the sound pressure is to be attenuated according to the path length of the propagation path at the time of propagating the monitoring space, the second source through the propagation path of the path length L ₂ the sound pressure _{P 20} of an ultrasound Sw2 from part 1b transmitted to the second wave receiving element 3b from the first sound source unit 1a through the propagation path of the path length _L 1 _{(<L 2)} in the first wave receiving element 3a It becomes lower than the sound pressure _{P 10} of an ultrasound Sw1 transmitted. The control unit 2 does not need to drive both the sound source units 1a and 1b at the same time, but controls each of the two sound source units 1a and 1b so that the total of the ultrasonic wave transmission time is the same.

  Incidentally, as shown in FIG. 2, the signal processing unit 4 calculates the sound pressure ratio between the ultrasonic waves Sw1 and Sw2 received by the first wave receiving element 3a and the second wave receiving element 3b, respectively. Smoke density for estimating the smoke density in the monitoring space between the sound source unit 1 and the wave receiving element 3 based on the sound pressure ratio calculation means 40 and the amount of change from the initial value of the sound pressure ratio calculated by the sound pressure ratio calculation means 40 The sound pressure ratio calculated by the sound pressure ratio calculating means 40, the fire determining means 42 for determining the presence or absence of fire by comparing the smoke density estimated by the smoke density estimating means 41 with a predetermined threshold, and the sound pressure ratio calculating means 40. Storage means 43 for storing. The signal processing unit 4 is configured by a microcomputer, and each of the means 40 to 43 is realized by mounting an appropriate program on the microcomputer. The signal processing unit 4 is also provided with an A / D converter for analog-digital conversion of the output signal of the wave receiving element 3.

Here, sound pressure ratio calculating means 40, the sound pressure of the ultrasonic Sw2 that through propagation path of the path length _{L 2} transmitted from the second sound source unit 1b in the second wave receiving element 3b, the path length _L 1 _{(<L 2} ) Divided by the sound pressure of the ultrasonic wave Sw1 transmitted from the first sound source unit 1a to the first wave receiving element 3a through the propagation path of) is calculated as the sound pressure ratio. The initial value of the sound pressure ratio is such that the surrounding environment of the fire detector is set to a predetermined state as described above, the sound source unit 1 and the wave receiving element 3 are not changed with time, and suspended particles in the monitoring space In the state of FIG. 1A in which no sound enters, the sound pressure ratio R ₀ (= P ₂₀ / P ₁₀₎ calculated by the sound pressure ratio calculation means 40 by transmitting an ultrasonic wave from the sound source unit 1 to the wave receiving element 3. ) And stored in the storage means 43 in advance. Further, instead of setting the calculated sound pressure ratio R ₀ as an initial value, an equivalent initial value may be set (set on a program) at the design stage.

The smoke density estimation means 41 compares the sound pressure ratio _RS calculated by the sound pressure ratio calculation means 40 with the initial value _R0 of the sound pressure ratio stored in advance in the storage means 43, and determines the difference between them (ie, the initial value). The smoke density in the monitoring space is estimated based on the amount of change in the sound pressure ratio R _S from R ₀ . As will be described in detail later, the amount of change from the initial value R ₀ of the sound pressure ratio R _S calculated by the sound pressure ratio calculation means 40 increases substantially in proportion to the smoke density in the monitoring space. If a relational expression between the smoke density and the amount of change is obtained based on the relational data with the amount of change and stored in the storage means 43, the smoke density can be estimated from the amount of change using the relational expression. it can.

  The fire determination means 42 determines “no fire” when the smoke concentration estimated by the smoke concentration estimation means 41 is less than the above threshold, while “fire is present” when the smoke concentration is equal to or greater than the above threshold. It judges and outputs a fire detection signal to the control part 2. Here, when receiving the fire detection signal from the fire determination means 42, the control unit 2 controls the drive input waveform to the sound source unit 1 so that an alarm sound composed of sound waves in the audible range 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. Note that the output destination of the fire detector signal from the fire determination means 42 is not limited to the control unit 2 and may be output to an external notification device, for example.

According to the configuration described above, when characteristic changes occur in the sound source unit 1 and the wave receiving element 3 due to changes over time of the sound source unit 1 and the wave receiving element 3 and changes in the surrounding environment, they are shown in FIG. a first sound pressure _{P 11} of an ultrasound Sw1 to be received at the wave receiving element 3a as, each of the sound pressure _{P 21} of an ultrasound Sw2 to be received at the second wave receiving element 3b 1 ( The sound pressure ratio R ₁ (= P ₂₁ / P ₁₁ ) calculated by the sound pressure ratio calculation means 40 is changed (reduced here) from the respective values (P ₁₀ , P ₂₀ ) of a), but FIG. Is substantially the same as the initial value R ₀ (= P ₂₀ / P ₁₀ ) calculated in the state (that is, R ₁ = R ₀ ). However, in the example of FIG. 1B, it is assumed that there are no suspended particles (including smoke particles) entering the monitoring space. That is, the characteristic change of the sound source unit 1 due to the time change of the sound source unit 1 and the change of the surrounding environment similarly occurs in both the first and second sound source units 1a and 1b, and the time change of the wave receiving element 3 changes. Since the characteristic change of the wave receiving element 3 due to the change of the surrounding environment and the first and second wave receiving elements 3a and 3b occur in the same manner, these characteristic changes are calculated by the sound pressure ratio calculating means 40. It does not affect the sound pressure ratio R ₁ that.

On the other hand, when smoke particles (or other suspended particles) enter the monitoring space between the sound source unit 1 and the wave receiving element 3, the first wave receiving element 3a receives the smoke as shown in FIG. that the sound pressure _{P 1S} ultrasonic Sw1, from each of the sound pressure _{P 2S} ultrasonic Sw2 to be received at the second wave receiving element 3b each value in Fig. _{1 (a) (P 10,} P 20) Not only fluctuates (here, decreases), but also the sound pressure ratio R _S (= P _2S / P _1S ) calculated by the sound pressure ratio calculation means 40 is an initial value R ₀ (which is calculated in the state of FIG. 1A). = P ₂₀ / P ₁₀ ) (ie, R _S ≠ R ₀ ). That is, when smoke particles enter the monitoring space, the sound pressure of the ultrasonic wave from the sound source unit 1 decreases before reaching the wave receiving element 3, but the attenuation of the sound pressure at this time is an ultrasonic wave in the monitoring space. Depends on both the distance propagated and the smoke density in the monitoring space, the sound pressure ratio R _S is the path length L ₁ of the propagation path between the sound source unit 1a and the wave receiving element 3a, and the sound source unit 1b and the wave receiving element 3b. It changes from the initial value R _{0 by} an amount corresponding to the difference (L ₂ −L ₁ ) with the path length L ₂ of the propagation path between and the smoke density in the monitoring space.

More specifically, the smoke density in the monitoring space in the evaluation with the light-reducing smoke densitometer (light-reducing smoke detector) is C [% / m], 1 [m / m] with respect to the smoke density 1 [% / m]. The attenuation rate of the hit ultrasonic wave is α, the propagation length of the ultrasonic wave Sw1 transmitted from the first sound source unit 1a and received by the first receiving element 3a is L ₁ [m], When the path length of the propagation path of the ultrasonic wave Sw2 transmitted from the second sound source unit 1b and received by the second receiving element 3b is L ₂ [m], the first receiving element 3a receives the wave. The sound pressure P _1S of the ultrasonic wave Sw1 is expressed as P _1S ≈P ₁₀ (1-αCL ₁ ), and the sound pressure P _2S of the ultrasonic wave Sw2 received by the second wave receiving element 3b is P _2S ≈ It is represented by P ₂₀ (1-αCL ₂ ). Here, P ₁₀ and P ₂₀ represent the sound pressures of the ultrasonic waves Sw1 and Sw2 respectively received by the receiving elements 3a and 3b in the example of FIG. 1A, and L ₁ and L ₂ It is assumed that L ₁ <L ₂ <1. If P _1S and P _2S represented by the above equation and the initial value R ₀ = P ₂₀ / P ₁₀ of the sound pressure ratio are used, the sound pressure ratio R _S (= P _2S / P) of the sound pressures P _1S and P _2S the amount of change from the initial value _{R 0} of the _{1S) (i.e.,} R 0 -R _S) is expressed by the following equation.

R ₀ -R _S = R ₀ αC (L ₂ -L ₁ ) / (1-αL ₁ )
Here, if αL ₁ is sufficiently smaller than 1, then R ₀ −R _S = R ₀ αC (L ₂ −L ₁ ), and the change amount (R ₀ −R _S ) of the sound pressure ratio R _{S from} the initial value R _0. ) Is expressed in a form proportional to the path length difference (L ₂ −L ₁ ) and the smoke density C of the monitoring space. Therefore, if α, L ₁ , and L ₂ are known, the smoke density C [% / m] in the monitoring space is calculated based on the amount of change (R ₀ −R _S ) from the initial value R ₀ of the sound pressure ratio R _S. Can be estimated.

Also, smoke density estimation unit 41, smoke density of the sound pressure ratio _{R S} initial value divided by the rate of change variation in the initial value _{R 0} from _{R 0} in _{(R 0 -R S) / R} 0 monitored space based upon May be estimated. In the rate of change of the sound pressure ratio, the influence of the variation of the initial value _R0 that occurs between the fire detectors due to variations in the characteristics of the sound source unit 1 and the receiving element 3 that have occurred in the manufacturing process has been removed. If the smoke density is the same, the smoke density estimation results can be made uniform regardless of the initial value _R0 . Therefore, conversion to smoke density becomes easy.

Note that, under the above-described conditions, the sound pressure ratio R _S does not become larger than the initial value R ₀ due to the smoke particles flowing into the monitoring space (that is, R ₀ −R _S becomes a negative value). In the fire determination means 42, a negative threshold is not set for the smoke density output from the smoke concentration estimation means 41. Even if a negative smoke concentration is output from the smoke concentration estimation means 41, the fire determination The means 42 judges that there is a false detection and judges “no fire”.

According to the fire detector of the present embodiment described above, a plurality of super-waves respectively propagated from the sound source units 1a and 1b to the receiving elements 3a and 3b through a plurality of propagation paths having different path lengths L ₁ and L _2. The sound pressure ratio R _S between the sound waves Sw1 and Sw2 is calculated by the sound pressure ratio calculation means 40, and the smoke density estimation means 41 sets the amount of change from the initial value R ₀ of the sound pressure ratio R _S calculated by the sound pressure ratio calculation means 40. Since the smoke density in the monitoring space is estimated based on this, the sound pressure of the sound wave transmitted from the sound source unit 1 or the sensitivity of the wave receiving element 3 changes according to changes over time or changes in the surrounding environment. However, since these characteristic changes uniformly affect the plurality of ultrasonic waves Sw1 and Sw2, the smoke concentration estimation unit 41 estimates the change based on the change in the sound pressure ratio R _S of the plurality of ultrasonic waves Sw1 and Sw2. The smoke density is a shadow of the characteristic change It will not be affected. As a result, no non-fire report or misreport occurs due to the influence of the characteristic change generated in the sound source unit 1 or the wave receiving element 3.

(Embodiment 2)
The basic structure of the fire detector of this embodiment is substantially the same as that of the first embodiment, and a plurality of propagation paths having different path lengths are alternatively selected between the sound source unit 1 and the receiving element 3 for each one. This is different from the fire detector of the first embodiment in that it can be formed. 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, the fire detector is provided with a path selection unit that selectively selects an ultrasonic wave propagation path between the sound source unit 1 and the wave receiving element 3 from a plurality of propagation paths having different path lengths. The sound pressure ratio calculation means 40 calculates the sound pressure ratio between the plurality of ultrasonic waves propagated from the sound source unit 1 to the wave receiving element 3 in each state in which propagation paths having different path lengths are selected by the path selection unit. Here, the control unit 2 intermittently drives the sound source unit 1 so that ultrasonic waves are transmitted from the sound source unit 1 in each state where propagation paths having different path lengths are selected.

  As an example of the present embodiment, a configuration in which the linear distance between the sound source unit 1 and the wave receiving element 3 is variable as shown in FIG. In the example of FIG. 5, the wave receiving element 3 can be moved in a direction to be in contact with or separated from the sound source unit 1 by a moving mechanism (not shown), and this moving mechanism functions as a path selection unit. In this case, the sound source unit 1 may be moved with respect to the wave receiving element 3.

That is, after the first ultrasonic wave Sw1 is transmitted from the sound source unit 1 with the distance between the sound source unit 1 and the receiving element 3 set to L ₁ as shown in FIG. By moving the receiving element 3 in the direction away from the sound source unit 1 by the moving mechanism as shown in FIG. 5B, the distance between the sound source unit 1 and the receiving element 3 is set to L as shown in FIG. _{The second} ultrasonic wave Sw2 is transmitted from the sound source unit 1 in a state set to ₂ (> L ₁ ). Thus, the first ultrasonic Sw1 from the sound source unit 1, whereas is propagated to wave receiving element 3 through the propagation path of the path length L _1, 2-time ultrasonic wave from the sound source unit 1 for sw2, it will be propagated to the wave receiving element 3 through the propagation path of the path length L _2. Thereafter, the sound pressure ratio calculation means 40 calculates the sound pressure ratio between the ultrasonic waves Sw1 and Sw2.

  As another example of the present embodiment, as shown in FIG. 6, a plurality of types of cylindrical bodies 6a and 6b having different path lengths of ultrasonic propagation paths formed in the internal space are alternatively selected. A configuration in which the sound source unit 1 and the wave receiving element 3 are interposed is conceivable. In the example of FIG. 6, two types of cylinders 6a and 6b are replaced by a replacement mechanism (not shown), and this replacement mechanism functions as a path selection unit.

That is, the first ultrasound from the sound source unit 1 in a state in which a straight tube and insert the cylindrical body 6a of the tube length L ₁ between the sound source unit 1 and wave receiving element 3 as shown in FIG. 6 (a) Sw1 6b, the cylindrical bodies 6a and 6b are replaced by a replacement mechanism as shown in FIG. 6B, thereby bending between the sound source unit 1 and the receiving element 3 as shown in FIG. 6C. The second ultrasonic wave Sw2 is transmitted from the sound source unit 1 in a state where the cylindrical body 6b having the tube length L ₂ (> L ₁ ) is inserted. Thus, the first ultrasonic Sw1 from the sound source unit 1 is to be propagated to the wave receiving element 3 through the interior space of the cylindrical body 6a of tube length L ₁ (propagation path of the path length L ₁₎ in contrast, the second ultrasonic Sw2 from the sound source unit 1 that through the interior space of the tubular body 6b of tube length L ₂ (propagation path of the path length L ₂₎ is propagated to the wave receiving element 3 Become. Thereafter, the sound pressure ratio calculation means 40 calculates the sound pressure ratio between the ultrasonic waves Sw1 and Sw2.

  Here, according to the configuration of FIG. 6, since the cylinders 6 a and 6 b are provided between the sound source unit 1 and the wave receiving element 3, the ultrasonic waves transmitted from the sound source unit 1 are Since the diffusion is suppressed by passing through the internal space of 6b and the decrease of the sound pressure due to the diffusion of the ultrasonic wave between the sound source unit 1 and the receiving element 3 can be suppressed, there is no smoke particle in the monitoring space In this state, the sound pressure of the ultrasonic wave received by the wave receiving element 3 can be kept high, and 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 large. As a result, the SN ratio is improved. There is an effect.

  In the example of FIG. 6, the sound source unit 1 and the receiving element 3 are arranged so as to face each opening end face of the cylinders 6 a and 6 b, and the inside of each cylinder 6 a and 6 b is a monitoring space. Therefore, for example, holes (not shown) for guiding smoke or the like are formed in the side surfaces along the longitudinal direction of the cylinders 6a and 6b.

  In the fire detector of the present embodiment described above, the ultrasonic waves transmitted from the single sound source unit 1 can be propagated to the single wave receiving element 3 through the propagation paths having different path lengths. The sound pressure ratio between a plurality of ultrasonic waves transmitted from the sound source unit 1 and received by the single receiving element 3 can be calculated. Therefore, the sound pressure ratio calculated by the sound pressure ratio calculation means 40 is not affected by the variation in characteristic change that occurs between the plurality of sound source units 1 or the variation in characteristic change that occurs between the plurality of receiving elements 3. This leads to improvement in calculation accuracy of the sound pressure ratio.

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

(Embodiment 3)
The fire detector of the present embodiment has a basic configuration substantially the same as that of the first embodiment, and a plurality of propagation paths having different path lengths are formed between the sound source unit 1 and the receiving element 3 each one. Is 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, the ultrasonic wave transmitted from the sound source unit 1 is branched into a plurality of propagation paths having different path lengths and propagated to the wave receiving element 3 through each propagation path. Here, the sound pressure ratio calculating means 40 calculates the sound pressure ratio between a plurality of ultrasonic waves that reach the wave receiving element 3 through propagation paths having different path lengths.

As an example of this embodiment, as shown in FIG. 7A, a plurality of types of cylinders 6 a and 6 b having different propagation lengths of ultrasonic waves formed in an internal space are used as a sound source unit 1 and a wave receiving element 3. It is conceivable to intervene in parallel with each other. That is, between the sound source unit 1 and wave receiving element 3 as shown in FIG. 7 (a), the a cylindrical body 6a of a straight tubular pipe length L _1, a curved shape tube length L _{2 (>} L ₁ ) cylinders 6b are arranged in a plane orthogonal to the direction in which the sound source unit 1 and the receiving element 3 face each other, and the ultrasonic waves from the sound source unit 1 are applied to both the cylinders 6a and 6b. It branches so that it may pass through the internal space of each cylinder 6a, 6b. Accordingly, the ultrasonic wave transmitted from the sound source unit 1 is branched into the first and second ultrasonic waves Sw1 and Sw2 at the entrances (the left end face in FIG. 7A) of both the cylinders 6a and 6b. while being propagated in the wave receiving element 3 1 ultrasonic Sw1 is through the interior space of the cylindrical body 6a of tube length L ₁ (propagation path of the path length L _1), second ultrasonic Sw2 is tube length L ₂ It will be propagated to the wave receiving element 3 through the interior space of the cylindrical body 6b (the propagation path of the path length L _2). Thereafter, the sound pressure ratio calculation means 40 calculates the sound pressure ratio between the ultrasonic waves Sw1 and Sw2.

Here, at the timing when each of the ultrasonic waves Sw1 and Sw2 arrives at the wave receiving element 3, as shown in FIG. 7B, a time difference Td corresponding to the difference between the path lengths L ₁ and L ₂ of the propagation path is generated. This time difference Td is obtained by dividing the difference between the path lengths L ₁ and L ₂ by the speed of sound. In order to distinguish the ultrasonic waves Sw1 and Sw2 in the wave receiving element 3, it is necessary to keep the period during which the ultrasonic waves Sw1 and Sw2 are received by the wave receiving element 3 within the time difference Td.

That is, for example, the sound velocity at 340m / s, when the frequency of the ultrasonic wave transmitted from the sound source unit 1 is 100kHz, ultrasound period 10 [mu] s, since the wavelength 3.4 mm, the path length _L 1, _{L 2} When the difference is set to 68 mm, if the wave number of the ultrasonic wave exceeds 20, the ultrasonic waves overlap each other, and the wave receiving element 3 cannot distinguish the ultrasonic waves Sw1 and Sw2. Therefore, by adjusting the difference between the path lengths L ₁ and L ₂ and the wave number of the ultrasonic wave transmitted from the sound source unit 1 at one time, the ultrasonic waves do not overlap each other. When reducing the difference between the path lengths L ₁ and L ₂ in order to reduce the size of the fire detector, the temperature of the heating element layer 13 accompanying the energization of the heating element layer 13 as described in the first embodiment is used. It is useful to employ a sound source unit 1 that is configured to generate an ultrasonic wave by applying a thermal shock to the air by a change and that can transmit a single-pulse ultrasonic wave with little reverberation.

  Furthermore, according to the configuration of FIG. 7A, since the cylinders 6 a and 6 b are provided between the sound source unit 1 and the wave receiving element 3, the ultrasonic waves transmitted from the sound source unit 1 are cylindrical. Diffusion is suppressed by passing through the internal spaces 6a and 6b, and a decrease in sound pressure due to diffusion of ultrasonic waves between the sound source unit 1 and the 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.

  In the example of FIG. 7, the sound source unit 1 and the receiving element 3 are arranged so as to face each opening end face of the cylinders 6 a and 6 b, and the inside of each cylinder 6 a and 6 b is a monitoring space. Therefore, for example, holes (not shown) for guiding smoke or the like are formed in the side surfaces along the longitudinal direction of the cylinders 6a and 6b.

  As another example of the present embodiment, as shown in FIG. 8A, one cylindrical body 6a is omitted, and an ultrasonic wave transmitted directly from the sound source unit 1 to the wave receiving element 3 is a first ultrasonic wave Sw1. The reflection surface 7 along the direction in which the sound source unit 1 and the receiving element 3 are arranged as shown in FIG. 8B is formed on the side of the sound source unit 1 and the receiving element 3, and the sound source unit The ultrasonic wave directly transmitted from 1 to the wave receiving element 3 is defined as the first ultrasonic wave Sw1, and the ultrasonic wave transmitted from the sound source unit 1 and then reflected by the reflecting surface 7 and transmitted to the wave receiving element 3 is transmitted to the second wave receiving element 3. A configuration using ultrasonic waves Sw2 is also conceivable.

  In the fire detector of the present embodiment described above, the ultrasonic waves transmitted from the single sound source unit 1 can be propagated to the single wave receiving element 3 through the propagation paths having different path lengths. The sound pressure ratio between a plurality of ultrasonic waves transmitted from the sound source unit 1 and received by the single receiving element 3 can be calculated. Therefore, the sound pressure ratio calculated by the sound pressure ratio calculation means 40 is not affected by the variation in characteristic change that occurs between the plurality of sound source units 1 or the variation in characteristic change that occurs between the plurality of receiving elements 3. This leads to improvement in calculation accuracy of the sound pressure ratio. Moreover, since the sound pressure ratio is calculated for the ultrasonic waves transmitted from the sound source unit 1 at the same timing, the calculated sound pressure ratio is not affected by variations in sound pressure caused by the drive timing of the sound source unit 1.

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

(Embodiment 4)
The fire detector of the present embodiment has a basic configuration substantially the same as that of the first embodiment, and forms a plurality of propagation paths having different path lengths between the sound source unit 1 and the receiving element 3 each one. Moreover, the point which provided the pair of reflective surface which reflects the ultrasonic wave transmitted from the sound source part 1 is different from the fire detector of Embodiment 1. 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, the first and second reflecting surfaces 7a and 7b are arranged so as to face each other in the traveling direction of the ultrasonic wave transmitted from the sound source unit 1 (the left-right direction in FIG. 9). Has been. Each of the reflection surfaces 7a and 7b reflects ultrasonic waves. The wave receiving element 3 is disposed on the first reflection surface 7a, and the sound source unit 1 is disposed on the second reflection surface 7b. Here, the sound pressure ratio calculating means 40 calculates the sound pressure ratio between a plurality of ultrasonic waves having different numbers of times of reflection by the reflecting surfaces 7 a and 7 b before being propagated from the sound source unit 1 to the wave receiving element 3.

  That is, the ultrasonic wave directly transmitted from the sound source unit 1 to the wave receiving element 3 as shown in FIG. 9 is set as the first ultrasonic wave Sw1, and after being transmitted from the sound source unit 1, is reflected by the first reflecting surface 7a. Furthermore, an ultrasonic wave transmitted to the wave receiving element 3 by being reflected by the second reflecting surface 7b is referred to as a second ultrasonic wave Sw2. Thus, the path of the propagation path between the first ultrasonic wave Sw1 with 0 reflections on the reflection surfaces 7a and 7b and the second ultrasonic wave Sw2 with 2 reflections on the reflection surfaces 7a and 7b. The lengths are different, and the sound pressure ratio calculation means 40 calculates the sound pressure ratio of these ultrasonic waves Sw1 and Sw2. Here, in order to enable the wave receiving element 3 to distinguish the ultrasonic waves Sw1 and Sw2, the difference in path length between the ultrasonic waves Sw1 and Sw2 and the wave number of the ultrasonic waves transmitted from the sound source unit 1 at once are adjusted. This is the same as in the third embodiment in that the ultrasonic waves do not overlap each other.

  By the way, in this embodiment, each reflective surface 7a, 7b consists of a concave curved surface curved in the shape which collects a reflected wave on the other reflective surface 7a, 7b. Furthermore, the sound source unit 1 and the wave receiving element 3 are disposed on the reflecting surfaces 7a and 7b at positions where the reflected ultrasonic waves incident on the other reflecting surfaces 7a and 7b and reflected are focused.

  In short, as shown in FIG. 10 (a), the ultrasonic wave that has reached the first reflecting surface 7a on the receiving element 3 side while spreading radially from the sound source unit 1 arranged on the second reflecting surface 7b is By being reflected by the first reflecting surface 7a, it becomes a parallel wave with respect to the second reflecting surface 7b on the sound source unit 1 side as shown in FIG. 10B, and then reflected by the second reflecting surface 7b. As shown in FIG. 10C, the focal point is formed at the position of the wave receiving element 3 on the first reflecting surface 7a. Therefore, even if the reflection on the reflecting surfaces 7a and 7b is repeated, the ultrasonic wave is difficult to diffuse, and the path length of the propagation path is the same for the ultrasonic wave propagating linearly and the ultrasonic wave propagating radially. Interference due to the phase shift of the. Therefore, 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. As a result, the change amount of the output of the wave receiving element 3 with respect to the change amount of the smoke density becomes relatively large, and the SN ratio is improved.

  According to the configuration described above, since the ultrasonic wave transmitted from the single sound source unit 1 can be propagated to the single wave receiving element 3 through the propagation paths having different path lengths, the single sound source unit 1 It is possible to calculate a sound pressure ratio between a plurality of ultrasonic waves that are transmitted from and received by a single receiving element 3. Therefore, the sound pressure ratio calculated by the sound pressure ratio calculation means 40 is not affected by the variation in characteristic change that occurs between the plurality of sound source units 1 or the variation in characteristic change that occurs between the plurality of receiving elements 3. This leads to improvement in calculation accuracy of the sound pressure ratio. Moreover, since the sound pressure ratio is calculated for the ultrasonic waves transmitted from the sound source unit 1 at the same timing, the calculated sound pressure ratio is not affected by variations in sound pressure caused by the drive timing of the sound source unit 1.

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

  By the way, the fire detector of each said embodiment may be provided with the diffusion prevention member which narrows the diffusion range of the ultrasonic wave from the sound source part 1. FIG. That is, in the examples of FIGS. 6 and 7, the cylinders 6a and 6b provided between the sound source unit 1 and the wave receiving element 3 function as diffusion preventing members, but diffusion prevention other than the cylinders 6a and 6b. A member may be applied. For example, in the configuration of the fourth embodiment, as shown in FIG. 11, a pair of diffusion prevention plates 6 ′ can be used as a diffusion prevention member that narrows the diffusion range of ultrasonic waves from the sound source unit 1.

  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 surfaces facing each other. The sound source unit 1 and the wave receiving element 3 are sandwiched between the one surface so as to propagate the ultrasonic wave from the sound source unit 1 through the space between the surfaces. By providing the diffusion prevention plate 6 ′ in this manner, the ultrasonic wave transmitted from the sound source unit 1 is suppressed from being diffused by passing through the monitoring space surrounded by the one surface of the diffusion prevention plate 6 ′. Therefore, 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.

(Embodiment 5)
The basic structure of the fire detector of the present embodiment is substantially the same as that of the first embodiment, 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, and description is abbreviate | omitted suitably.

By the way, the inventors of the present application show the unit change rate of the output frequency and the sound pressure ratio of the sound source unit 1 as shown in FIG. 13 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 ratio (hereinafter referred to as the initial sound pressure ratio) between the ultrasonic waves received by each of the receiving elements 3a and 3b in a state where no suspended particles exist in the monitoring space is R ₀ , a dimming smoke densitometer. Sound between ultrasonic waves received by each of the receiving elements 3a and 3b in a state where suspended particles having a concentration of s [% / m] are present in the monitoring space, as evaluated by the (dimming smoke detector). When the pressure ratio is R _S , the value represented by (R ₀ −R _S ) / R ₀ is defined as the rate of change of the sound pressure ratio, and in particular, the rate of change when s = 1 is defined as the unit rate of change. To do. Here, the initial sound pressure ratio R ₀ and the sound pressure ratio R _S are calculated under the same conditions except for the presence or absence of suspended particles in the monitoring space. “A” in FIG. 13 is an approximate curve (the black circle is measured data) showing the relationship between the output frequency and the unit change rate of the sound pressure ratio when the suspended particles are black smoke particles, and “B” is the suspended particles. Approximate curve (black square is measured data) showing the relationship between the output frequency and the unit change rate of the sound pressure ratio when white smoke particles are used. “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 change rate of the sound pressure ratio, and the unit change rate shown here is the path length L of the propagation path of the ultrasonic wave between the sound source unit 1a and the receiving element 3a. ₁ and data for each output frequency when the difference (L ₂ −L ₁ ) between the path length L ₂ of the ultrasonic wave propagation path between the sound source unit ₁ b and the wave receiving element 3 b is set to 30 cm. Each data at the right end in FIG. 13 is data when the output frequency is 82 kHz, and FIG. 14 shows the result of normalizing the unit change rate of each output frequency with the data when the output frequency is 82 kHz as 1. . In short, in FIG. 14, the horizontal axis represents the output frequency, and the vertical axis represents the relative unit change 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 the relational data between the output frequency of the sound source unit 1 and the relative unit change rate of the sound pressure ratio according to the initial sound pressure ratio R ₀ for each output frequency, the type of suspended particles present in the monitoring space, and the suspended particle concentration (Data extracted from the above-mentioned FIG. 14), the unit change rate (data extracted from the above-mentioned FIG. 13) of the sound pressure ratio at a specific frequency (for example, 82 kHz) with respect to the smoke particles is stored in the storage means 43, and the sound source The output of the sound pressure ratio calculation means 40 (the sound pressure ratio R _S between the ultrasonic waves received by the wave receiving elements 3 a and 3 b) and the storage means 43 for each ultrasonic wave transmitted from the unit 1. Relationship Particle type estimation means 44 for estimating the type of particles floating in the monitoring space using the data is provided. Here, the smoke concentration estimation means 41 outputs the initial sound pressure ratio of the output of the sound pressure ratio calculation means 40 for the ultrasonic wave of a specific frequency (for example, 82 kHz) when the particles estimated by the particle type estimation means 44 are smoke particles. The smoke density in the monitoring space is estimated based on the amount of change from _R0 .

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 sound pressure ratio calculation means 40 calculates the sound pressure ratio R _S between the ultrasonic waves received by the wave receiving elements 3 a and 3 b for various types of ultrasonic waves. (Step S11). The particle type estimation means 44 obtains the rate of change of the sound pressure ratio R _S calculated for each output frequency from the initial sound pressure ratio R ₀ (step S12), and at 20 kHz relative to the rate of change of the sound pressure ratio when the output frequency is 82 kHz. The ratio of the change rate of the sound pressure ratio is calculated (step S13). In the storage means 43, as the relation data between the output frequency of the sound source unit 1 and the relative unit change rate of the sound pressure ratio, the ratio of the relative unit change rate at 20 kHz to the relative unit change rate at the output frequency of 82 kHz. (In the case of FIG. 14, white smoke is 0, black smoke is 0.2, and steam is 0.5), and the particle type estimation means 44 stores the ratio of the calculated change rate in the storage means 43. Compared with the stored relational data, the type of particles having the closest ratio of change rate among the relational data is estimated as particles floating in the monitoring space (step S14). Here, if the estimated particles are smoke particles, the process moves to the smoke concentration estimation means 41 (step S15). In this case, in the case of white smoke, as shown in FIG. 16, the relationship between the smoke density measured by the dimming smoke densitometer and the rate of change of the sound pressure ratio is data that can be represented by a straight line, and other particles Therefore, the smoke concentration estimating means 41 calculates the ratio of the estimated change of the sound pressure ratio with respect to the ultrasonic wave of a specific frequency (for example, 82 kHz) to the unit change rate in the storage means 43 for the estimated particle type. 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 fire determination means 42 compares the smoke density estimated in step S16 with a predetermined threshold (for example, a smoke density that is 10% / m in the evaluation with the dimming smoke densitometer), and the estimated smoke density. Is less than the threshold value, it is determined that there is no fire. On the other hand, if it is greater than the threshold value, it is determined that there is a fire, and a fire detection signal is output to the control unit 2.

  In the above example, the particle type estimation means 44 uses the rate of change of the sound pressure ratio when the output frequency is 82 kHz and the rate of change of the sound pressure ratio when the output frequency is 20 kHz, but the combination is limited to these output frequencies. Instead, different combinations of output frequencies may be used. Furthermore, the rate of change of the sound pressure ratio with respect to more output frequencies may be used, and in that case, the accuracy of estimation of the particle type can be improved. In the present embodiment, the smoke density estimation means 41 targets one frequency as the specific frequency, but targets a plurality of frequencies as the specific frequency, and calculates the 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 44 is realized by mounting an appropriate program on the microcomputer.

  In the present embodiment, the sound wave generating elements described in the first embodiment are used as the sound source units 1a and 1b, respectively, and the control unit 2 described above sequentially applies the frequencies of the drive input waveforms to be given to the sound source units 1a and 1b. By changing, a plurality of types of ultrasonic waves having different frequencies are sequentially transmitted from the sound source units 1a and 1b. 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, as described above, the sound wave generation elements described in the first embodiment are used as the sound source units 1a and 1b, respectively, so that the ultrasonic waves that are sequentially transmitted can be ultrasonic waves having different frequencies. Therefore, the cost can be reduced as compared with the case where a plurality of piezoelectric elements having different resonance frequencies are used as the sound source units 1a and 1b, respectively, and a continuous wave ultrasonic wave is transmitted from each piezoelectric element.

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 change rate of the sound pressure ratio is stored in the storage unit 43 has been shown. Accordingly, since it is the amount of change (R ₀ −R _S ) of the sound pressure ratio R _{S from} the initial sound pressure ratio R ₀ that changes for each output frequency of the sound source unit 1, the relational data stored in the storage means 43 is: Any data indicating the relationship between the output frequency of the sound source unit 1 and the amount of change of the sound pressure ratio R _{S from} the initial sound pressure ratio R ₀ may be used. For example, instead of the above-mentioned relative unit change rate, the sound pressure ratio R _S the amount of change from the initial sound pressure ratio R ₀ and the sound pressure ratio R _S of the initial sound pressure ratio R ₀ of the amount of change from dividing by initial sound pressure ratio R ₀ rate of change, or stores relationship data employing the unit change ratio means 43 You may make it memorize.

  In the fire detector of the present embodiment described above, the particle type estimation unit 44 uses the sound pressure ratio for each ultrasonic wave transmitted from the sound source unit 1 and the relational data stored in the storage unit 43. The type of particles floating in the monitoring space is estimated, and when the particles estimated by the particle type estimation unit 44 are smoke particles, the smoke concentration estimation unit 41 calculates the sound pressure ratio with respect to ultrasonic waves of a specific frequency. The smoke density in the monitoring space is estimated based on the amount of change from the initial sound pressure ratio, and the fire determination means 42 compares the smoke density estimated by the smoke density estimation means 41 with a predetermined threshold value to determine whether there is a fire. Therefore, it is possible to discriminate between smoke particles and steam by estimating the type of particles floating in the monitoring space in the particle type estimation means 44, and the scattered light smoke detector and the dimming smoke detector. Compared to It is possible to reduce the non-fire report due care, also suitable for use in the kitchen or bathroom. In addition, since the particle type estimation means 44 can distinguish between white smoke particles and black smoke particles, it can also be used for identifying fire properties. 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, each sound source part 1a, 1b is comprised by the single sound wave generation element, respectively, and each sound source part is changed by changing the frequency of the drive input waveform which the control part 2 gives to each sound source part 1a, 1b. Although plural types of ultrasonic waves having different frequencies are sequentially transmitted from the units 1a and 1b, the sound source units 1a and 1b may be configured by 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, each of the receiving elements 3a and 3b may be provided with an individual receiving element for each type of ultrasonic wave. In this case, the Q value of the resonance characteristics of each receiving element is relatively low. The sensitivity of the receiving element can be improved by using a large piezoelectric element or the like and using each receiving element for receiving ultrasonic waves of the respective resonance frequencies. Furthermore, if a plurality of sound wave generating elements constituting each sound source unit 1a, 1b are driven at the same time and a plurality of types of ultrasonic waves are simultaneously transmitted from each sound source unit 1a, 1b, sound is generated for the plurality of types of ultrasonic waves. The amount of change in pressure ratio can be detected simultaneously, and the amount of change in sound pressure ratio can be detected for multiple types of ultrasonic waves without being affected by changes in the monitoring space over time (for example, changes in the concentration of suspended particles). Type and smoke density can be accurately estimated. 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.

  Other configurations and functions are the same as those in the first embodiment, and the sound source unit 1 and the receiving element 3 may be provided one by one in combination with any one of the configurations in the second to fourth embodiments.

  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. 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.

  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.

It is the schematic which shows the operation | movement of Embodiment 1 of this invention. 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. It is the schematic which shows the operation | movement of Embodiment 2 of this invention. It is the schematic which shows operation | movement of the other example same as the above. It is the schematic which shows the operation | movement of Embodiment 3 of this invention. It is the schematic which shows the other example same as the above. It is the schematic which shows the structure of Embodiment 4 of this invention. It is the schematic which shows operation | movement same as the above. It is a schematic perspective view which shows the other example same as the above. It is a block diagram which shows the structure of Embodiment 5 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 change rate of sound pressure ratio. 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 change rate. 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 change rate of the sound pressure ratio of a specific frequency. The principal part of a prior art example is shown, (a) is a schematic bottom view, (b) is a schematic side view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sound source part 1a 1st sound source part 1b 2nd sound source part 2 Control part 3 Wave receiving element 3a 1st wave receiving element 3b 2nd wave receiving element 4 Signal processing part 7a, 7b Reflecting surface 11 Base substrate 12 Heat Insulating layer 13 Heating element layer (heating element part)
40 Sound pressure ratio calculation means 41 Smoke concentration estimation means 42 Fire judgment means 44 Particle type estimation means L ₁ , L ₂ path lengths P ₁₀ , P ₂₀ , P _1S , P _2S sound pressure R ₀ initial value of R ₀ sound pressure ratio _RS sound pressure ratio Sw1, Sw2 ultrasound

Claims (12)

  A sound source unit capable of transmitting sound waves, a control unit for controlling the sound source unit, a receiving element for detecting the sound pressure of the sound waves transmitted from the sound source unit, and whether there is a fire based on the output of the receiving element A signal processing unit for determining, and the signal processing unit includes a plurality of sound waves propagated from the sound source unit to the receiving device through propagation paths having different path lengths in the monitoring space between the sound source unit and the receiving device. A sound pressure ratio calculating means for calculating the sound pressure ratio of the sound space, a smoke density estimating means for estimating the smoke concentration in the monitoring space based on an amount of change from the initial value of the sound pressure ratio calculated by the sound pressure ratio calculating means, and a smoke concentration estimating means A fire detector, comprising: a fire judgment means for judging the presence or absence of a fire by comparing the smoke concentration estimated in step 1 with a predetermined threshold value.   The sound source unit is capable of transmitting a plurality of types of sound waves having different frequencies, and the signal processing unit is configured to output an output frequency and the sound of the sound source unit according to the type of suspended particles present in the monitoring space and the smoke concentration. Using storage means storing relational data with the amount of change from the initial value of the pressure ratio, using the sound pressure ratio for each sound wave of each frequency transmitted from the sound source unit and relational data stored in the storage means Particle type estimation means for estimating the type of particles floating in the monitoring space, and the smoke concentration estimation means is a sound wave having a specific frequency when the particles estimated by the particle type estimation means are smoke particles. The fire detector according to claim 1, wherein the smoke density of the monitoring space is estimated based on an amount of change from the initial value of the sound pressure ratio with respect to the sound.   The storage means stores, as the relation data, relation data between an output frequency of the sound source unit and a change rate obtained by dividing a change amount from an initial value of the sound pressure ratio by an initial value. 2. Fire detector according to item 2.   The sound source unit includes a single sound wave generating element capable of transmitting the plurality of types of sound waves, and the control unit controls the sound source unit so that the plurality of types of sound waves are sequentially transmitted from the sound wave generating element. The fire detector according to claim 2 or claim 3, wherein   5. The sound source unit according to claim 1, wherein the sound source unit generates a sound wave by applying a thermal shock to the air due to a temperature change of the heat generating unit accompanying energization of the heat generating unit. The fire detector according to item 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. 6. The fire detector according to claim 5, further comprising a thermal insulation layer comprising a porous layer that thermally insulates the substrate.   7. The smoke density estimation unit estimates the smoke density in the monitoring space based on a rate of change obtained by dividing an amount of change from an initial value of the sound pressure ratio by an initial value. The fire detector according to any one of the above.   A path selection unit that selectively selects the propagation path between the sound source unit and the receiving element from a plurality of the propagation paths having different path lengths is provided, and the control unit receives sound waves from the sound source unit. The sound source unit is controlled so as to be transmitted intermittently, and the sound pressure ratio calculation means is configured to transmit the sound source unit from the sound source unit in each state where the propagation path having a different path length is selected by the path selection unit. The fire detector according to any one of claims 1 to 7, wherein a sound pressure ratio between a plurality of sound waves propagated to the wave receiving element is calculated.   A plurality of propagation paths having different path lengths are formed between the sound source section and the receiving element, and the sound pressure ratio calculating means transmits the propagation paths having different path lengths transmitted from the sound source section. The fire detector according to any one of claims 1 to 7, wherein a sound pressure ratio between a plurality of sound waves propagated to the receiving element through each of the sound receiving elements is calculated.   A pair of reflecting surfaces are provided so as to oppose each other in the traveling direction of the sound wave transmitted from the sound source unit, and each of the sound pressure ratio calculating means is configured to receive the sound receiving element from the sound source unit. The fire detector according to any one of claims 1 to 7, wherein a sound pressure ratio between a plurality of sound waves having different numbers of reflections before being propagated to the reflection surface is calculated.   The fire detector according to claim 10, wherein the reflection surface is a concave curved surface curved to collect sound waves from the sound source unit on the other reflection surface.   The sound source unit and the wave receiving element are on different reflection surfaces, respectively, and are arranged at positions where the sound waves reflected and incident on the other reflection surface as plane waves are focused. The fire detector according to claim 11.

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