JP5166991B2 - Airborne particle measurement system - Google Patents

Description

  The present invention relates to a suspended particle measuring system for measuring the concentration of suspended particles present in a monitoring space.

  Conventionally, suspended particles (smoke particles, dust, etc.) that exist in the monitoring space are used for the purpose of determining the presence or absence of a fire by measuring the smoke concentration, for example, and managing the state of the clean room used in the semiconductor manufacturing process. Suspended particle measurement systems that measure the concentration of steam, steam, etc.) have been proposed.

  As this type of suspended particle measuring system, a system that measures the concentration (number) of suspended particles using scattered light of suspended particles of laser light is known (see, for example, Patent Document 1 and Patent Document 2). Here, the suspended particle measuring system described in Patent Document 1 irradiates the suspended particles with one of the laser beams divided into two by a demultiplexer to generate scattered light, and frequency shifts the other laser beam. Then, the number of suspended particles is measured using an optical heterodyne method in which the synthesized light is combined with the scattered light, and the combined light is received by a photodetector to detect and process a beat signal. On the other hand, the suspended particle measuring system described in Patent Document 2 scans laser light emitted from a laser oscillator with a polygon mirror having a plurality of mirror surfaces, and has a rectangular opening for scattered light from the suspended particles of the scanned light. It is detected by a CCD camera through a mask, and the concentration of suspended particles is measured based on the detected scattered light.

  By the way, as described above, the suspended particle measurement system using the scattered light by the suspended particles of the laser beam scans the demultiplexer for dividing the laser beam and the laser beam in addition to the laser light source and the photodetector (or CCD camera). There is a problem that an optical member such as a polygon mirror is required, and the system is large, large, and expensive.

  In order to solve the problems of the suspended particle measuring system using the scattered light described above, the present applicant has proposed a suspended particle measuring system that measures the concentration of suspended particles using sound waves (for example, ultrasonic waves).

  As shown in FIG. 18, the suspended particle measurement system includes a sound source unit 1 capable of transmitting sound waves, a control unit (not shown) that controls the sound source unit 1, and a sound wave transmitted from the sound source unit 1. A wave receiving element 3 that detects sound pressure, and a signal processing unit (not shown) that measures the concentration of suspended particles existing in the monitoring space between the sound source unit 1 and the wave receiving element 3 based on the output of the wave receiving element 3. Z)). The signal processing unit includes concentration estimation means for estimating the concentration of suspended particles in the monitoring space based on the attenuation amount from the reference value of the output of the wave receiving element 3. That is, when particles enter the monitoring space, the sound pressure from the sound source unit 1 decreases before reaching the receiving element 3, and the attenuation of the output of the receiving element 3 is approximately equal to the concentration of suspended particles in the monitoring space. Since it increases in proportion, the presence or absence of a fire can be determined by estimating the concentration of suspended particles based on this attenuation.

  In the above-described acoustic wave type floating particle measurement system, an optical member necessary for the floating particle measurement system using scattered light is not required. Therefore, the system can be simplified and can be made small and inexpensive.

  However, in the above-described sonic-type suspended particle measurement system, 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 amount from the reference value of the output of the wave receiving element 3 fluctuates regardless of the concentration of suspended particles in the monitoring space. Accuracy may be reduced.

Therefore, the present applicant adds sound pressure ratio calculating means for calculating the sound pressure ratio between a plurality of sound waves propagated from the sound source unit 1 to the wave receiving element 3 through propagation paths having different path lengths to the signal processing unit. A configuration is further considered in which the estimation means estimates the concentration of suspended particles in the monitoring space based on the amount of change from the initial value of the sound pressure ratio. Specifically, two sets of the tone generator section 1a having different distances from one another, 1b (see FIG. 1) and wave receiving element 3a, 3b provided (see FIG. 1), one of the tone generator section through the propagation path of the path length L ₁ The ratio of the sound pressure of the sound wave transmitted from 1a to the wave receiving element 3a and the sound pressure of the sound wave transmitted from the other sound source unit 1b to the wave receiving element 3b through the propagation path of the path length L ₂ (> L ₁ ) is defined as the sound pressure ratio. Calculated by sound pressure ratio calculation means.

In this configuration, even if a characteristic change occurs in the sound source unit 1 or the receiving element 3 according to a change with time or a change in the surrounding environment, the characteristic change uniformly affects the plurality of sound waves having different propagation path lengths. The sound pressure ratio calculated by the sound pressure ratio calculating means is not affected. Therefore, in the concentration estimating means for estimating the concentration of the suspended particles based on the amount of change from the initial value of the sound pressure ratio, the characteristic change of the sound source unit 1 and the receiving element 3 due to the change over time and the change of the surrounding environment. The concentration of suspended particles can be estimated without being affected, and as a result, the accuracy of concentration measurement does not deteriorate due to the influence of the characteristic change occurring in the sound source unit 1 and the wave receiving element 3.
JP-A 63-63944 Japanese Patent Laid-Open No. 7-229826

By the way, when the sound wave propagates in the air, the sound pressure decreases due to absorption attenuation and diffusion attenuation in the air. Therefore, in the sound wave type suspended particle measurement system, the sound wave transmitted from the sound source unit 1 is the wave receiving element 3. The sound pressure decreases before reaching. Here, drop rate B ₁ of the sound pressure due to absorption attenuation and diffusion _damping, B ₂ can be either expressed as a function of the path length x of the propagation path, the sound pressure reduction rate B ₁ due to absorption decay B _{1 =} e ^{-Α · x} , the sound pressure decrease rate B ₂ due to diffusion attenuation is expressed by 1 / (2πx). In short, if the sound pressure of the sound wave transmitted from the sound source unit 1 is P ₀ , the sound pressure P _x received by the wave receiving element 3 is expressed by the following equation.

  Here, α in the above formula is an attenuation coefficient of absorption and attenuation of sound waves by air, and the attenuation coefficient α is expressed as a function of the temperature, humidity, and atmospheric pressure of air as a medium and the frequency of sound waves. (Reference 1: HEBass et al., “Atmospheric absorption of sound: Further developments”, The Journal of the Acoustic Society of America, 1995, Volume 97, Issue 1, p. 680-683). Therefore, the attenuation coefficient α may change due to changes in the surrounding environment (for example, changes in temperature, humidity, atmospheric pressure, etc.).

When the attenuation coefficient α changes, the sound pressure ratio may fluctuate regardless of the concentration of suspended particles in the monitoring space. That is, when the attenuation coefficient α is changed, the sound pressure reduction rate B ₁ due to absorption attenuation of sound waves received at the wave receiving element 3 varies, the across multiple acoustic path length x is different propagation paths since a difference in amount of change sound pressure reduction rate B ₁ is generated, the sound pressure ratio varies by the attenuation coefficient α is changed, the accuracy of results in density measurement may be reduced.

  The present invention has been made in view of the above-mentioned reasons, and an object thereof is to provide a suspended particle measurement system in which the accuracy of concentration measurement does not decrease due to the influence of a change in attenuation coefficient due to a change in the surrounding environment. And

The invention according to claim 1 is a sound source unit capable of transmitting sound waves, a control unit for controlling the sound source unit, a wave receiving element for detecting sound pressure of sound waves transmitted from the sound source unit, and an output of the wave receiving element And a signal processing unit for measuring the concentration of suspended particles existing in the monitoring space between the sound source unit and the receiving element, and the signal processing unit passes through the propagation paths having different path lengths in the monitoring space. A sound pressure ratio calculating means for calculating a sound pressure ratio between a plurality of sound waves respectively propagated from the sound wave to the receiving element, and a concentration estimation for estimating the concentration of suspended particles in the monitoring space based on the sound pressure ratio calculated by the sound pressure ratio calculating means Caused by a change in the attenuation coefficient based on the attenuation coefficient estimated by the attenuation coefficient estimating means estimated by the attenuation coefficient estimating means and the attenuation coefficient estimating means for estimating the attenuation coefficient of the sound wave absorption attenuation in the monitoring space in the absence of airborne particles Remove the fluctuation of the sound pressure ratio A sound pressure ratio correcting means for correcting the pressure ratio urchin the sound, said possess a sound speed measuring means for determining the speed of sound in the monitored space, each wave are arranged to face each other in the traveling direction of the sound waves transmitting from the tone generator A pair of reflecting surfaces are provided, the sound source unit and the receiving element are respectively disposed on the reflecting surfaces, and each reflecting surface is curved to collect sound waves from the sound source unit. The sound pressure ratio calculating means calculates a sound pressure ratio between a sound wave directly propagated from the sound source unit to the wave receiving element and a sound wave reflected by a reflecting surface and propagated to the wave receiving element. The sound pressure ratio correcting means corrects the sound pressure ratio based on the sound speed obtained by the sound speed measuring means so as to remove the fluctuation of the sound pressure ratio due to the change in the sound speed .

According to this configuration, the attenuation coefficient estimating means estimates the attenuation coefficient of the sound wave absorption attenuation by air in the monitoring space, and the sound pressure ratio correcting means removes the fluctuation of the sound pressure ratio due to the change of the attenuation coefficient. Thus, even if the attenuation coefficient may change due to changes in the surrounding environment, the change in the sound pressure ratio due to the change in the attenuation coefficient is the concentration of suspended particles estimated by the concentration estimation means. Does not affect. As a result, the accuracy of concentration measurement does not deteriorate due to the influence of the change in the attenuation coefficient due to the change in the surrounding environment.
Further, 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. A sound pressure ratio between a plurality of sound waves received by one 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. Further, the use of the reflective surface can reduce the size of the suspended particle measurement system relative to the path length. In addition, each reflecting surface is formed of a concave curved surface that is curved so as to collect the sound wave from the sound source unit once and collect the sound on the receiving element. Difficult to diffuse, and therefore, it is possible to suppress a decrease in sound pressure due to diffusion of sound waves between the sound source unit and the receiving element. As a result, the sound pressure of the sound wave received by the receiving element can be maintained high when there is no suspended particle in the monitoring space, and the amount of change in the output of the receiving element relative to the amount of change in the concentration of the suspended particles is relatively large. Thus, there is an advantage that the SN ratio is improved.

  According to a second aspect of the present invention, in the first aspect of the invention, the signal processing unit includes parameter acquisition means for measuring at least one of temperature, humidity, and atmospheric pressure in the monitoring space as a parameter, and the attenuation coefficient estimation. The means estimates the attenuation coefficient using the parameter.

According to this configuration, the attenuation coefficient is estimated using at least one of temperature, humidity, and atmospheric pressure in the monitoring space as parameters, so the attenuation coefficient can be estimated accurately while using parameters that can be acquired by a relatively simple method. can do.
According to a third aspect of the present invention, there is provided 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 a sound pressure of the sound wave transmitted from the sound source unit, and an output of the wave receiving element And a signal processing unit for measuring the concentration of suspended particles existing in the monitoring space between the sound source unit and the receiving element, and the signal processing unit passes through the propagation paths having different path lengths in the monitoring space. A sound pressure ratio calculating means for calculating a sound pressure ratio between a plurality of sound waves respectively propagated from the sound wave to the receiving element, and a concentration estimation for estimating the concentration of suspended particles in the monitoring space based on the sound pressure ratio calculated by the sound pressure ratio calculating means Caused by a change in the attenuation coefficient based on the attenuation coefficient estimated by the attenuation coefficient estimating means estimated by the attenuation coefficient estimating means and the attenuation coefficient estimating means for estimating the attenuation coefficient of the sound wave absorption attenuation in the monitoring space in the absence of airborne particles Remove the fluctuation of the sound pressure ratio Sound pressure ratio correction means for correcting the sound pressure ratio, and parameter acquisition means for measuring at least one of temperature, humidity and atmospheric pressure in the monitoring space as parameters, and the attenuation coefficient estimation means The receiving element has a fixed electrode and a movable electrode arranged opposite to each other, and a partition wall that separates the reference pressure chamber in which the atmospheric pressure is kept constant from the monitoring space. The movable electrode is disposed on a part of the partition wall, and the partition wall receives a sound wave from the monitoring space side, thereby changing the distance between the movable electrode and the fixed electrode and changing the capacitance between the movable electrode and the fixed electrode. And the parameter acquiring means includes barometric pressure measuring means for measuring the barometric pressure in the monitoring space based on the change in the capacitance .
According to this configuration, the attenuation coefficient estimating means estimates the attenuation coefficient of the sound wave absorption attenuation by air in the monitoring space, and the sound pressure ratio correcting means removes the fluctuation of the sound pressure ratio due to the change of the attenuation coefficient. Thus, even if the attenuation coefficient may change due to changes in the surrounding environment, the change in the sound pressure ratio due to the change in the attenuation coefficient is the concentration of suspended particles estimated by the concentration estimation means. Does not affect. As a result, the accuracy of concentration measurement does not deteriorate due to the influence of the change in the attenuation coefficient due to the change in the surrounding environment. In addition, according to this configuration, since the attenuation coefficient is estimated using at least one of temperature, humidity, and atmospheric pressure in the monitoring space as parameters, the attenuation coefficient can be accurately measured using parameters that can be obtained by a relatively simple method. Can be estimated well. Furthermore, since the atmospheric pressure in the monitoring space is measured using the output of the wave receiving element, there is an advantage that it is not necessary to add a new device for measuring the atmospheric pressure.

The invention of claim 4 is the invention of claim 2 or 3 , wherein the parameter acquisition means includes temperature measuring means for measuring the temperature of the monitoring space, and sound speed measuring means for obtaining the sound speed of the monitoring space, The attenuation coefficient estimating means uses the temperature measured by the temperature measuring means and the humidity calculated from the temperature and the sound speed obtained by the sound speed measuring means as the parameters.

  According to this configuration, since the humidity is calculated from the temperature measured by the temperature measuring unit and the sound speed obtained by the sound speed measuring unit, there is an advantage that it is not necessary to add a new device for measuring the humidity. .

According to a fifth aspect of the present invention, in the invention according to any one of the first, second, and fourth aspects, the sound velocity measurement unit is configured to transmit the propagation path for a plurality of sound waves to be calculated by the sound pressure ratio calculation unit. The speed of sound is calculated by dividing the difference in length by the time difference required for each of the plurality of sound waves to propagate from the sound source unit to the receiving element.

  According to this configuration, the sound speed of the monitoring space can be calculated using a plurality of sound waves detected by the receiving element to calculate the sound pressure ratio, so a new device is added to measure the sound speed. There is an advantage that there is no need to do.

  The present invention has an effect that the accuracy of concentration measurement does not decrease due to the influence of a change in attenuation coefficient due to a change in the surrounding environment.

  In the following embodiments, as an example of the suspended particle measurement system of the present invention, an example of measuring the concentration of smoke particles in the monitoring space for the purpose of determining whether or not a fire has occurred, is not limited to this example. The suspended particle measurement system of the present invention can be used to measure the concentration of various suspended particles (smoke particles, dust, steam, etc.) in the monitoring space.

(Embodiment 1)
As shown in FIG. 1, the suspended particle measuring system of the present embodiment is a pair of sound source units 1a and 1b capable of transmitting ultrasonic waves (hereinafter referred to as the sound source unit 1 unless the sound source units 1a and 1b are 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 (hereinafter referred to as both wave receiving elements) that detect the sound pressure of the ultrasonic waves transmitted from the sound source units 1a and 1b. 3a and 3b are referred to as receiving elements 3 when not particularly distinguished), and the concentration of suspended particles existing in the monitoring space between the sound source unit 1 and the receiving elements 3 based on the outputs of the receiving elements 3a and 3b. And a signal processing unit 4 for measuring. 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 units 1a and 1b and the wave receiving elements 3a and 3b constituting each set are arranged to be opposed to each other on one surface side of the circuit board 5 (see FIG. 18) 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. 2, 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. 2) 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. 3, the capacitive microphone constituting the wave receiving element 3 is a rectangular 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 including the capacitance type microphone having the configuration shown in FIG. 3, 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. 4A, the first ultrasonic wave Sw1 transmitted from the first sound source unit 1a and the second ultrasonic wave Sw2 transmitted from the second sound source unit 1b are defined. In the monitoring space between the sound source unit 1 and the wave receiving element 3, the wave is transmitted to the wave receiving elements 3 a and 3 b forming a pair with each other through propagation paths having different path lengths. In other words, the propagation path of the first ultrasonic Sw1 to be received at the first wave receiving element 3a is closed the distance between the first sound source unit 1a and the first wave receiving element 3a as the path length L ₁ On the other hand, the propagation path of the second ultrasonic wave Sw2 received by the second receiving element 3b is the distance L ₂ between the second sound source unit 1b and the second receiving element 3b. Will have. 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, and atmospheric pressure) of the suspended particle measurement system is set to a predetermined state, and the sound source unit 1 and the wave receiving element 3 are not changed with 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 are different in path length 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.

  By the way, as shown in FIG. 1, 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. 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 concentration of suspended particles in the monitoring space between the sound source unit 1 and the wave receiving element 3 is estimated. Concentration estimation means 41 and storage means 43 for storing the sound pressure ratio calculated by the sound pressure ratio calculation means 40 are provided.

  The signal processing unit 4 is further provided with an attenuation coefficient estimating means 44 for estimating an attenuation coefficient, which will be described later, and a sound pressure ratio correcting means 45 for correcting the sound pressure ratio. A basic configuration of the signal processing unit 4 excluding the sound pressure ratio correction unit 45 will be described. The signal processing unit 4 is constituted by a microcomputer, and each of the means 40 to 45 is realized by mounting an appropriate program on the microcomputer. The signal processing unit 4 is also provided with an A / D converter (not shown) that performs analog-digital conversion on 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 ambient environment of the suspended particle measurement system is set to a predetermined state as described above, the sound source unit 1 and the receiving element 3 are not changed over time, and are further suspended in the monitoring space. The sound pressure ratio R ₀ (= P ₂₀ / P) 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 in the state of FIG. ₁₀ ), which is 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 concentration estimation means 41 compares the sound pressure ratio R _S calculated by the sound pressure ratio calculation means 40 with the initial value R ₀ of the sound pressure ratio stored in the storage means 43 in advance, and the difference between them (ie, the initial value R). _The amount of suspended particles in the monitoring space is estimated based on the change amount of the sound pressure ratio _RS from 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 in proportion to the concentration of suspended particles in the monitoring space. If a relational expression between the concentration of suspended particles and the amount of change is obtained on the basis of the relational data between the concentration of particles and the amount of change, and stored in the storage means 43, it is suspended from the amount of change using the relational expression. The concentration of particles can be estimated.

According to the above-described configuration, when the sound source unit 1 or the receiving element 3 undergoes a change in characteristics due to a change over time of the sound source unit 1 or the receiving element 3 or a change in the surrounding environment, as shown in FIG. the sound pressure _{P 11} of an ultrasound Sw1 to be received at the first 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 4 ( Although the sound pressure ratio R ₁ (= P ₂₁ / P ₁₁ ) calculated by the sound pressure ratio calculation means 40 varies (decreases in this case) from each value (P ₁₀ , P ₂₀ ) of a), 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. 4B, 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 floating particles such as smoke particles enter the monitoring space between the sound source unit 1 and the wave receiving element 3, the ultrasonic wave received by the first wave receiving element 3a as shown in FIG. The sound pressure P _{1S of} Sw1 and the sound pressure P _2S of the ultrasonic wave Sw2 received by the second receiving element 3b vary from the values (P ₁₀ , P ₂₀ ) in FIG. In addition, the sound pressure ratio R _S (= P _2S / P _1S ) calculated by the sound pressure ratio calculation means 40 is not limited to the initial value R ₀ (= P ₂₀ ) calculated in the state of FIG. / P ₁₀ ) (ie, R _S ≠ R ₀ ). That is, when suspended particles enter the monitoring space, the sound pressure of the ultrasonic wave from the sound source unit 1 decreases until it reaches 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 traveled by and the concentration of suspended particles in the monitoring space, the sound pressure ratio R _S is the path length L ₁ of the propagation path between the sound source section 1a and the wave receiving element 3a, the sound source section 1b, and the received wave. It changes from the initial value R _{0 by} an amount corresponding to the difference (L ₂ −L ₁ ) from the path length L ₂ of the propagation path between the elements 3 b and the concentration of suspended particles in the monitoring space.

Specifically, the concentration of suspended particles (smoke particles) in the monitoring space in the evaluation with a light-reducing smoke densitometer (light-reducing smoke detector) is C [% / m], and the concentration of suspended particles is 1 [ % Is the attenuation rate of ultrasonic waves per [m] relative to [% / m], and the path length of the propagation path 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], and the propagation length 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 The sound pressure P _1S of the ultrasonic wave Sw1 received by the wave receiving element 3a is represented by P _1S ≈P ₁₀ (1-αCL ₁ ), and the ultrasonic wave Sw2 received by the second wave receiving element 3b The sound pressure P _2S is represented by P _2S ≈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. 4A, and L ₁ and L ₂ are as follows. 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 concentration C of suspended particles in the monitoring space. Therefore, if α, L ₁ , and L ₂ are known, the suspended particle concentration C [% / m in the monitoring space 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.

The concentration estimating unit 41, the change rate obtained by dividing the amount of change from the initial value _{R 0} in the sound pressure ratio _{R S} at the initial value _{R 0} of the suspended particles _{(R 0 -R S) / R} 0 monitored space based upon The concentration may be estimated. In the rate of change of the sound pressure ratio, the influence of the variation of the initial value R ₀ generated between the suspended particle measurement systems due to the variation in the characteristics of the sound source unit 1 and the receiving element 3 generated in the manufacturing process is removed. If the concentration of suspended particles in the space is the same, the estimation result of the suspended particle concentration can be made uniform regardless of the initial value _R0 . Therefore, conversion to the concentration of suspended particles is facilitated.

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 flow of suspended particles into the monitoring space (that is, R ₀ −R _S becomes a negative value). In the unlikely event that a negative value is output from the concentration estimation means 41, it is determined that there is no false particle detection and no suspended particles have entered the monitoring space.

According to the suspended particle measurement system of the present embodiment described above, a plurality of sound beams propagated from the sound source units 1a and 1b to the wave 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 ultrasonic waves Sw1 and Sw2 is calculated by the sound pressure ratio calculation means 40, and the concentration 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 concentration of suspended particles 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 in accordance with changes over time or changes in the surrounding environment. Even if this occurs, these characteristic changes uniformly affect the plurality of ultrasonic waves Sw1 and Sw2, and therefore the concentration estimation unit 41 determines the change based on the change in the sound pressure ratio R _S of the plurality of ultrasonic waves Sw1 and Sw2. Estimated suspended particles The density is not affected by the characteristic change. As a result, the accuracy of measurement of the concentration of suspended particles in the monitoring space does not decrease due to the influence of the characteristic change that occurs in the sound source unit 1 and the receiving element 3, and the measurement result of the concentration of suspended particles (smoke particles). Therefore, there is an advantage that non-fire reports and misreports do not occur when judging the presence or absence of a fire.

  By the way, the suspended particle measuring system of the present embodiment includes an attenuation coefficient estimating means 44 for estimating an attenuation coefficient of ultrasonic absorption attenuation by air that changes in accordance with changes in the surrounding environment, in addition to the basic configuration described above, and an attenuation coefficient. The signal processing unit 4 includes sound pressure ratio correction means 45 that corrects the sound pressure ratio based on the attenuation coefficient estimated by the estimation means 44. Hereinafter, the attenuation coefficient estimating unit 44 and the sound pressure ratio correcting unit 45 will be described.

That is, as described above, the sound pressure of the ultrasonic wave transmitted from the sound source unit 1 is reduced due to absorption attenuation and diffusion attenuation in the monitoring space even in the absence of suspended particles. The rate B ₁ can be expressed as B ₁ = e ^{−α · x} using the path length x of the propagation path. Here, α is an attenuation coefficient of absorption attenuation, and it is known that the attenuation coefficient α is expressed as a function of the temperature, humidity, atmospheric pressure of the medium (air) and the frequency of the ultrasonic wave (reference) Reference 1). Since the frequency of the ultrasonic wave is determined by the control unit 2, the attenuation coefficient estimating means 44 estimates the attenuation coefficient α using at least one of the temperature, humidity and atmospheric pressure of the monitoring space as parameters.

  In the present embodiment, the temperature measuring means 46 for measuring the temperature of the monitoring space and the sound speed measuring means 47 for measuring the sound speed in the monitoring space are provided as components of the parameter acquisition means for measuring the parameters, and are attenuated. The coefficient estimating means 44 estimates the attenuation coefficient α using the temperature measured by the temperature measuring means 46 and the humidity of the monitoring space calculated from the temperature and the sound speed measured by the sound speed measuring means 47 as parameters. In other words, the sound velocity C in the monitoring space can be expressed as a function of the temperature T, the water vapor pressure E, and the atmospheric pressure P in the monitoring space as shown in the following equation. Therefore, when the atmospheric pressure P is assumed to be 1 (atm), the sound velocity C And the temperature T are obtained, the water vapor pressure E is obtained from the following equation, and the humidity of the air can be calculated from the water vapor pressure E.

  The temperature measuring means 46 may measure the temperature from the output of a thermistor, thermocouple, temperature sensor IC, or the like. The speed of sound C (m / s) can be simply expressed as C≈331.5 + 0.6 T as a function of the temperature T (degrees Celsius) of the monitoring space, and the speed of sound measuring means 47 is measured by the temperature measuring means 46. The sound speed may be estimated from the result.

As another example, the sound velocity measuring unit 47 propagates the first and second ultrasonic waves Sw1 and Sw2 received by the first and second wave receiving elements 3a and 3b, respectively, as shown in FIG. A configuration in which the speed of sound in the monitoring space is calculated by dividing the path length difference (L ₂ −L ₁ ) of the path by the time difference Δt 0 (see FIG. 6A) of the timing of receiving the ultrasonic waves Sw 1 and Sw 2. There may be. That is, the path length difference (L ₂ −L ₁ ) between the propagation paths of the ultrasonic waves Sw1 and Sw2 is a constant value, but the time difference Δt0 changes according to the sound speed of the monitoring space as shown in FIG. 6B. Therefore, the change in sound speed can be obtained as a change in (L ₂ −L ₁ ) / Δt0. 6A shows the first and second ultrasonic waves Sw1 and Sw2 received by the wave receiving element 3 in a state where the initial value R ₀ (= P ₂₀ / P ₁₀ ) of the sound pressure ratio is calculated. FIG. 6B shows the waveforms of the first and second ultrasonic waves Sw1 and Sw2 received by the wave receiving element 3 when only the sound velocity in the monitoring space is changed from this state. In this configuration, it is not necessary to add a thermistor, thermocouple, or temperature sensor IC device to measure the speed of sound, and the number of parts of the suspended particle measurement system can be reduced.

Based on the attenuation coefficient α obtained as described above, the sound pressure ratio correction means 45 varies the output (sound pressure ratio R _S ) of the sound pressure ratio calculation means 40 resulting from the attenuation coefficient α from the initial value R _0. The sound pressure ratio _RS is corrected so as to cancel the minute.

In short, when the attenuation coefficient α changes with changes in the surrounding environment (for example, changes in temperature, humidity, atmospheric pressure, etc.), the sound pressure reduction rate B ₁ (= e ^{−α · x} ) changes, and as a result, the sound pressure ratio R _S between the first ultrasonic wave Sw1 and the second ultrasonic wave Sw2 varies. In more detail, since the sound pressure reduction rate B ₁ represents is represented as a function of the path length x of the propagation path, the first and second ultrasonic Sw1 path length of the propagation path is different, between the Sw2, even the amount of change of the attenuation coefficient α is the same, a difference in amount of change the sound pressure reduction rate B ₁ is generated. Therefore, if the attenuation coefficient α changes, the sound pressure ratio _RS of the first and second ultrasonic waves Sw1 and Sw2 changes regardless of the concentration of suspended particles in the monitoring space.

Therefore, the sound pressure ratio correcting means 45 of the present embodiment, the to cancel the fluctuation of the sound pressure ratio R _S due to a change in the attenuation coefficient alpha, the sound pressure ratio R _S in accordance with the change of the attenuation coefficient alpha to correct. Specifically, the provided sound pressure ratio correcting means 45 in the subsequent stage of the sound pressure ratio calculating means 40 as shown in FIG. 1, the sound pressure ratio R _S calculated by the sound pressure ratio calculating means 40 is corrected by the sound pressure ratio correcting means 45 To the density estimation means 41. The correction value at this time is determined so as to remove the variation in the sound pressure decrease rate B ₁ due to the change in the attenuation coefficient α. As a result, the concentration estimating means 41 can estimate the concentration of suspended particles in the monitoring space using the sound pressure ratio R _S in which the variation from the initial value R ₀ caused by the change in the attenuation coefficient α is cancelled. Therefore, the change in the attenuation coefficient α due to the change in the surrounding environment does not affect the concentration of the suspended particles estimated by the concentration estimation means 41.

  Therefore, when determining the presence or absence of a fire from the measurement result of the concentration of suspended particles (smoke particles), non-fire reports and misreports due to the change in the attenuation coefficient α can be reduced, There is an advantage that the accuracy of judgment is improved.

(Embodiment 2)
The suspended particle measurement system according to the present embodiment includes a supersonic wave transmitted from the sound source unit 1 in order to form a plurality of propagation paths having different path lengths between each of the sound source unit 1 and the receiving element 3. The difference from the suspended particle measurement system of the first embodiment is that a pair of reflecting surfaces that reflect sound waves are provided. 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. 7, 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. 7). 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, as shown in FIG. 7, the ultrasonic wave (direct wave) directly transmitted from the sound source unit 1 to the wave receiving element 3 is the first ultrasonic wave Sw1, and the first reflection surface 7a is transmitted after being transmitted from the sound source unit 1. The ultrasonic wave (reflected wave) transmitted to the wave receiving element 3 by being reflected by the second reflection surface 7b and being reflected by the second reflection 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.

Note that if the number of reflections on the reflecting surfaces 7a and 7b is increased with respect to the second ultrasonic wave Sw2, the path length difference between the first ultrasonic wave Sw1 and the second ultrasonic wave Sw2 will increase, so that the monitoring space will Although the amount of change from the initial value R ₀ of the sound pressure ratio R _S when airborne particles enter the first wave reaches the receiving element 3 by increasing the path length of the propagation path of the second ultrasonic wave Sw 2. The sound pressure of the second ultrasonic wave Sw2 decreases. Accordingly, the number of reflections of the second ultrasonic wave Sw2 on the reflection surfaces 7a and 7b is the amount of change in the sound pressure of the second ultrasonic wave Sw2 received by the wave receiving element 3 and the sound pressure ratio _RS due to suspended particles. It is desirable to determine the balance.

Here, a time difference Δt0 (see FIG. 6A) corresponding to the difference between the path lengths L ₁ and L ₂ of the propagation path is generated at the timing at which each of the ultrasonic waves Sw1 and Sw2 reaches the wave receiving element 3. This time difference Δt0 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 Δt0.

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 the difference between the path lengths L ₁ and L ₂ is reduced in order to reduce the size of the suspended particle measurement system, as described in the first embodiment, the heating element layer 13 is energized as the heating element layer 13 is energized. It is useful to employ a sound source unit 1 that is configured to generate an ultrasonic wave by applying a thermal shock to air due to a temperature change and that can transmit a single-pulse ultrasonic wave with little reverberation.

  Further, in the present embodiment, as shown in FIG. 8, a pair of diffusion prevention plates 6 that narrow the diffusion range of the ultrasonic wave from the sound source unit 1 are further provided. Each diffusion prevention plate 6 is formed of 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 prevention plates 6 forms a gap having the same size as the height of the sound source unit 1 between the one surface, and the ultrasonic wave from the sound source unit 1 is passed through the gap to diffuse the ultrasonic wave. The range is narrowed, and 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 gap. That is, the pair of reflection surfaces 7 a and 7 b described above are formed between the diffusion prevention plates 6 so as to face each other in a plane along the one surface of the diffusion prevention plate 6. By providing the diffusion preventing 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 preventing plate 6, and the sound source unit The decrease in sound pressure due to the diffusion of ultrasonic waves between 1 and the wave receiving element 3 can be suppressed.

  Furthermore, in this embodiment, each reflective surface 7a, 7b consists of a concave curved surface (parabolic surface) each curved in a shape that reflects the reflected wave as a reflected wave that focuses on the other reflective surface 7a, 7b. The part 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 as a plane wave are focused. Thus, the ultrasonic wave transmitted from the sound source unit 1 and reflected by the first reflecting surface 7a is focused on the wave receiving element 3 by being reflected by the second reflecting surface 7b.

  In short, as shown in FIG. 9 (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. 9B, and then reflected by the second reflecting surface 7b. As shown in FIG. 9C, 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.

  Accordingly, it is possible to suppress a decrease in the sound pressure of the ultrasonic wave between the sound source unit 1 and the wave receiving element 3. As a result, the amount of change in the output of the wave receiving element 3 with respect to the amount of change in the concentration of suspended particles becomes relatively large, and the SN ratio is improved.

More specifically, if there is no reflection surface 7a, 7b, the ultrasonic wave transmitted from the sound source unit 1 is diffused and attenuated in the monitoring space, so that when it is received by the wave receiving element 3, the propagation path The sound pressure attenuates according to the path length. On the other hand, the second ultrasonic wave Sw2 reflected by the reflecting surfaces 7a and 7b is collected on the other reflecting surfaces 7a and 7b by being reflected by the reflecting surfaces 7a and 7b as described above. since consequently the diffusion attenuation is suppressed, the reflecting surface 7a, as compared with the ultrasonic waves are propagated the same path length L ₂ without being reflected by 7b, the attenuation of the sound pressure is reduced. In other words, the sound pressure P ₂₀ of the second ultrasonic Sw2 to be received at the wave receiving element 3, the reflective surface 7a, reception from the sound source unit 1 through the propagation path of the path length L ₂ without being reflected by 7b becomes larger than the sound pressure P ₂ of the ultrasonic wave propagated to the element 3, the resolution of the concentration of airborne particles is improved. In this case, the sound pressure _{P 20} of the second ultrasonic Sw2 can be represented by the product (A · _{P 2)} between the sound pressure _{P 2} and the sound-pressure increase coefficient A (> 1). The sound pressure increase coefficient is a coefficient representing the degree to which diffusion attenuation is suppressed by reflection of ultrasonic waves by the reflection surfaces 7a and 7b. The shape of the reflection surfaces 7a and 7b, the directivity of the ultrasonic waves, etc. It depends on.

  According to the configuration described above, the sound pressure ratio between the plurality of ultrasonic waves Sw1 and Sw2 transmitted from the single sound source unit 1 and received by the single receiving element 3 can be calculated. Compared to a configuration in which a plurality of ultrasonic waves Sw1 and Sw2 are transmitted from each individual sound source unit 1 and received by each individual receiving element 3, the sound pressure ratio calculated by the sound pressure ratio calculating means 40 is a plurality of sound sources. The calculation accuracy of the sound pressure ratio is improved by the amount that is not affected by the variation in the characteristic change that occurs between the units 1 or the variation in the characteristic change that occurs between the plurality of receiving elements 3. 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.

  In the case where the above-described diffusion preventing plate 6 is not provided, the effect of suppressing the diffusion of ultrasonic waves during reflection on the reflecting surfaces 7a and 7b is achieved by making the reflecting surfaces 7a and 7b be paraboloids, respectively. Can be enhanced the most.

By the way, in the suspended particle measurement system of the present embodiment, the sound pressure ratio correction means 45 outputs the output of the sound pressure ratio calculation means 40 caused by the change in sound speed based on the sound speed of the monitoring space measured by the sound speed measurement means 47 ( The sound pressure ratio R _S has a function of correcting the sound pressure ratio R _S so as to cancel the variation from the initial value R ₀ of the sound pressure ratio R _S ).

In short, when the sound speed in the monitoring space changes, the directivity of the ultrasonic waves in the monitoring space changes, and as a result, the sound pressure ratio _RS between the first ultrasonic wave Sw1 and the second ultrasonic wave Sw2 changes. More specifically, for example, when sinusoidal pulsed ultrasonic waves are transmitted from the sound source unit 1, the directivity coefficient (the angle θ = 0 °) is calculated using the angle θ with respect to the direction directly in front of the sound source unit 1. The coefficient (D ₁ (θ) indicating the magnitude of the sound pressure when the sound pressure is ₁ ) is expressed by the following equation. Note that Formula 3 is applied when 0 ≦ θ ≦ sin ⁻¹ (λ / 4a), and Formula 4 is applied when sin ⁻¹ (λ / 4a) ≦ θ ≦ π / 2a.

In the above equation, λ represents the wavelength of the ultrasonic wave, and a is a length that is ½ of the length of one side of the surface (sending surface) of the heating element layer 13 that vibrates the air as the medium in the sound source unit 1. (That is, the transmission surface of the sound source unit 1 has a square shape with a side of 2a). As is well known, the wavelength λ is represented by the product of the sound speed and the period (pulse width). Therefore, when the sound speed in the monitoring space changes, the wavelength λ changes and the directivity coefficient D ₁ (θ) is changed. Change.

When the directivity coefficient D ₁ (θ) changes, the sound pressure increase coefficient A changes, and the sound pressure P ₂₀ (second ultrasonic wave Sw 2 reflected by the reflecting surfaces 7a and 7b is correspondingly changed. = A · P ₂ ) changes. Here, if the sound pressure increase coefficient after the change is A ′ (≠ A), the sound pressure P ₂₀ ′ of the second ultrasonic wave Sw2 after the change is expressed by P ₂₀ ′ = A ′ · P _2. Therefore, the sound pressure ratio between the first and second ultrasonic waves Sw1 and Sw2 is R ₀ ′ (= P ₂₀ ′ / P ₁₀ ) = A ′ · P ₂ / P ₁₀ , and the initial value R ₀ (= P ₂₀ / P ₁₀ ) = A · P ₂ / P ₁₀ That is, if the directivity coefficient D ₁ (θ) changes, the sound pressure ratio R _S of the first and second ultrasonic waves Sw1 and Sw2 changes regardless of the concentration of suspended particles.

Therefore, the sound pressure ratio correcting means 45 in this embodiment, so as to cancel the fluctuation of the sound pressure ratio R _S due to a change in the sound velocity, it corrects the sound pressure ratio R _S in accordance with a change in sound velocity. Specifically, as shown in FIG. 10, not only the estimation result (attenuation coefficient α) in the attenuation coefficient estimation means 44 but also the measurement result (sound speed) in the sound speed measurement means 47 is input to the sound pressure ratio correction means 45, The variation of the sound pressure decrease rate B ₁ due to the change of the attenuation coefficient α is removed, and the variation (A′−A) of the sound pressure increase coefficient due to the change in the directivity of the ultrasonic wave due to the change of the sound speed is removed. Then, the correction value of the sound pressure ratio R _S in the sound pressure ratio correction means 45 is determined. As a result, the concentration estimation means 41 can estimate the concentration of suspended particles in the monitoring space using the sound pressure ratio R _S in which the variation from the initial value R ₀ caused by the change in sound speed is canceled. A change in directivity due to a change in sound speed does not affect the density estimated by the estimation means 41.

  Therefore, when judging the presence or absence of a fire from the measurement result of the concentration of airborne particles (smoke particles), even if the directivity of the ultrasonic wave may change due to the change in the sound speed of the monitoring space, the influence of the change in directivity By determining whether or not a fire has occurred without receiving a non-fire, there is an advantage that non-fire reports and misreports resulting from the change in directivity can be reduced, and the accuracy of determining the presence or absence of a fire is improved.

The sound pressure ratio correction means 45 corrects the sound pressure ratio R _S in consideration of two factors: a change in the attenuation coefficient α due to a change in the surrounding environment and a change in directivity due to a change in sound speed. Therefore, the correction may be performed using a multiple regression equation relating to correction in which these two elements are integrated. As a result, it is possible to reduce the load on the calculation processing when performing the correction. Note that the multiple regression equation is expressed by a quadratic function of temperature and humidity, for example, assuming that the atmospheric pressure is constant.

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

(Embodiment 3)
The suspended particle measuring system according to the present embodiment is different from the suspended particle measuring system according to the first embodiment in that the signal processing unit 4 includes an atmospheric pressure measuring unit 48 that measures the atmospheric pressure in the monitoring space as illustrated in FIG. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted suitably.

  The atmospheric pressure measurement unit 48 constitutes a parameter acquisition unit together with the temperature measurement unit 46 and the sound velocity measurement unit 47. The attenuation coefficient estimation means 44 estimates the attenuation coefficient α using the temperature and humidity of the monitoring space obtained from the outputs of the temperature measurement means 46 and the sound velocity measurement means 47 and the atmospheric pressure of the monitoring space obtained from the atmospheric pressure measurement means 48 as parameters. . Therefore, there is an advantage that the calculation accuracy of the attenuation coefficient α is higher than that when the attenuation coefficient α is obtained only from the temperature and humidity of the monitoring space.

  By the way, the atmospheric pressure measuring means 48 of the present embodiment measures the atmospheric pressure based on the output of any of the wave receiving elements 3. Here, as shown in FIG. 12, the wave receiving element 3 includes a partition wall 32 ′ that separates the monitoring space from the reference pressure chamber 39a in which the atmospheric pressure is kept constant, and is movable to a part of the partition wall 32 ′. The electrode 33b is arranged. The partition wall 32 ′ forms a pressure receiving portion that receives ultrasonic pressure from the monitoring space side (upper side in FIG. 12). Therefore, the partition wall 32 ′ receives ultrasonic waves from the monitoring space side, thereby fixing the fixed electrode 33a and the movable electrode 33b. And the capacitance between the fixed electrode 33a and the movable electrode 33b changes. In the example of FIG. 12, an insulating film 35 ′, a fixed electrode 33a made of a metal thin film, an insulating layer 39 forming a partition wall 32 ′, and a movable electrode 33b made of a metal thin film are laminated on one surface side of the silicon substrate 31 ′. A configuration in which a hollow reference pressure chamber 39a is formed inside the insulating layer 39 is employed.

  In the wave receiving element 3, a DC bias voltage is applied between the pads 33c and 33c provided on the fixed electrode 33a and the movable electrode 33b, and a minute voltage generated according to the sound pressure of the ultrasonic wave between the pads 33c and 33c. Although the change is taken out as an output, the DC component included in the voltage change corresponds to the difference in atmospheric pressure between the reference pressure chamber 39a and the monitoring space. Therefore, the atmospheric pressure measurement unit 48 is configured to measure the atmospheric pressure in the monitoring space based on the DC component of the voltage change described above.

  According to this configuration, since the atmospheric pressure in the monitoring space is measured using the change in capacitance between the fixed electrode 33a and the movable electrode 33b, which is the output of the wave receiving element 3, the pressure for measuring the atmospheric pressure is measured. There is no need to newly provide a pressure sensor or the like. Therefore, the number of parts of the suspended particle measurement system can be reduced.

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

(Embodiment 4)
As shown in FIG. 13, the floating particle measurement system according to the present embodiment is provided with particle type estimation means 49 for estimating the type of particles floating in the monitoring space in the signal processing unit 4. Different from particle measurement system. 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 indicate the unit change rate of the output frequency and the sound pressure ratio of the sound source unit 1 as shown in FIG. 14 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. “I” in FIG. 14 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. 14 is data when the output frequency is 82 kHz, and FIG. 15 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. 15, 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. 15), the unit change rate (data extracted from the above-mentioned FIG. 14) of the sound pressure ratio at a specific frequency (for example, 82 kHz) for each suspended particle is stored in the storage means 43, and For each ultrasonic wave transmitted from the sound source unit 1, 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 Remembered Particle type estimation means 49 for estimating the type of particles floating in the monitoring space using the relationship data is provided.

Here, in this embodiment, as in the first embodiment, a sound pressure ratio correction unit 45 is provided after the sound pressure ratio calculation unit 40, and the sound pressure ratio R _S calculated by the sound pressure ratio calculation unit 40 is corrected by the sound pressure ratio correction unit 45. Then, it is passed to the particle type estimation means 49. As a result, the particle type estimation means 49 can estimate the type of suspended particles in the monitoring space using the sound pressure ratio R _S from which the variation from the initial value R ₀ caused by the change in the attenuation coefficient α is cancelled. Therefore, the change of the attenuation coefficient α does not affect the estimation result of the particle type estimation unit 49. Here, since the concentration of suspended particles measured by the signal processing unit 4 is used to determine whether or not there is a fire, the concentration estimating means 41 is specified when the particles estimated by the particle type estimating means 49 are smoke particles. The concentration of suspended particles in the monitoring space is estimated based on the amount of change from the initial sound pressure ratio _R0 of the output of the sound pressure ratio calculating means 40 for ultrasonic waves of frequency (for example, 82 kHz). The sound pressure ratio R _S used in the density estimation means 41 is also the corrected sound pressure ratio R _S in which the fluctuation from the initial value R ₀ due to the change in the attenuation coefficient α is canceled by the sound pressure ratio correction means 45. .

Hereinafter, an operation example of the suspended particle measurement system of the present embodiment will be described 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 49 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. 15, white smoke is 0, black smoke is 0.2, and steam is 0.5), and the particle type estimation means 49 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 proceeds to the processing by the concentration estimating means 41 (step S15). In this case, in the case of white smoke, as shown in FIG. 17, the relationship between the concentration of suspended particles measured by a dimming smoke densitometer and the rate of change of the sound pressure ratio is data that can be shown by a straight line. Therefore, the concentration estimation means 41 calculates the ratio of the unit pressure change rate in the storage means 43 with respect to the change rate of the sound pressure ratio with respect to ultrasonic waves of a specific frequency (for example, 82 kHz) for the estimated particle type. When the ratio value is y, it is estimated that the smoke concentration in the monitoring space corresponds to the suspended particle concentration y [% / m] in the evaluation with the dimming smoke densitometer (step S16). The concentration of airborne particles estimated in step S16 is compared with a predetermined threshold (for example, the concentration of airborne particles that is 10% / m in the evaluation with a dimming smoke densitometer), and the airborne particle concentration estimated. 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.

  In the above example, the particle type estimation means 49 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 this embodiment, the concentration estimation unit 41 targets one frequency as the specific frequency, but targets a plurality of frequencies as the specific frequency, and obtains the average value of the concentration of suspended particles estimated for each specific frequency. In this case, the accuracy of estimation of the concentration of suspended particles is improved. The signal processing unit 4 is constituted by a microcomputer, and the particle type estimation means 49 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 of sequentially transmitting three or more types of ultrasonic waves. 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 suspended particle measurement system of the present embodiment described above, the particle type estimation unit 49 uses the sound pressure ratio for each ultrasonic wave transmitted from the sound source unit 1 and the relationship 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 49 are smoke particles, the concentration estimation unit 41 calculates the sound pressure ratio for ultrasonic waves of a specific frequency. Since the concentration of suspended particles in the monitoring space is estimated based on the amount of change from the initial sound pressure ratio, smoke particles and steam are estimated by estimating the type of particles floating in the monitoring space in the particle type estimation means 49. This makes it possible to identify non-fire reports caused by steam and is suitable for use in kitchens and bathrooms. Further, since the white smoke particles and the black smoke particles can be discriminated by the particle type estimating means 49, it is also possible to use for identifying the nature of the fire. In addition, it is possible to distinguish between dust and smoke particles floating when cleaning the room where the suspended particle measurement system is installed or when electrical work is performed on the back of the ceiling, thus reducing non-fire reports caused by dust. It 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). 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 of the first embodiment, and the sound source unit 1 and the receiving element 3 may be provided one by one in combination with the configuration of the second embodiment.

  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 including the control unit 2 and a reception side unit including the wave receiving element 3 and the signal processing unit 4 are configured as separate bodies to constitute a separate suspended particle measurement system. It may be. Further, the sound source unit 1 is not limited to the sound wave generating element having the configuration shown in FIG. 2 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, Incorrect measurement of the concentration of airborne particles caused by insects can be reduced. Here, the control unit 2 periodically transmits ultrasonic waves 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 concentration of suspended particles. Alternatively, in order to estimate the concentration of suspended particles, the frequency of the ultrasonic wave transmitted from the sound source unit 1 may be set to a frequency having an insecticidal effect.

It is a schematic block diagram which shows the structure of Embodiment 1 of this invention. 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 operation | movement same as the above. It is a schematic block diagram which shows the other structure same as the above. It is a wave form diagram which shows operation | movement same as the above. It is the schematic which shows the structure of the principal part same as the above. It is a schematic perspective view which shows the principal part same as the above. It is the schematic which shows operation | movement same as the above. It is a schematic block diagram which shows the structure of Embodiment 2 of this invention. It is a schematic block diagram which shows the structure of Embodiment 3 of this invention. It is a schematic sectional drawing which shows the structure of the receiving element used for the same as the above. It is a schematic block diagram which shows the structure of Embodiment 4 of this invention. It is explanatory drawing which shows the relationship between the output frequency of a sound source part same as the above, and the unit 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 the density | concentration of a suspended particle 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

1 tone generator 2 controller 3 wave receiving element 4 the signal processing section 7a, 7b reflecting surface 40 the sound pressure ratio calculating means 41 concentration estimation means 44 attenuation coefficient estimating means 45 sound pressure ratio correcting means 46 temperature measuring means 47 sound speed measuring means L _1, L ₂ path lengths P ₁₀ , P ₂₀ , P _1S , P _2S Sound pressure R ₀ Sound pressure ratio initial value R _S Sound pressure ratio Sw1, Sw2 Ultrasound

Claims (5)

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 the sound source unit and the receiving unit based on the output of the receiving element. A signal processing unit for measuring the concentration of suspended particles existing in the monitoring space between the sound wave element and the signal processing part propagates from the sound source part to the wave receiving element through propagation paths having different path lengths in the monitoring space. A sound pressure ratio calculating means for calculating a sound pressure ratio between a plurality of sound waves, a concentration estimating means for estimating the concentration of suspended particles in the monitoring space based on the sound pressure ratio calculated by the sound pressure ratio calculating means, and no suspended particles An attenuation coefficient estimating means for estimating the attenuation coefficient of the sound wave absorption attenuation in the monitoring space in a state, and a variation of the sound pressure ratio due to the change of the attenuation coefficient based on the attenuation coefficient estimated by the attenuation coefficient estimating means. To remove the sound pressure ratio A sound pressure ratio correcting means positive for, the sound speed measuring means for determining the speed of sound in the monitored space possess,
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 source unit and the receiving element is provided on each reflecting surface. Each reflecting surface is formed of a concave curved surface that is curved to collect sound waves from the sound source unit, and the sound pressure ratio calculating means reflects and reflects the sound waves directly propagated from the sound source unit to the receiving element. The sound pressure ratio between the sound wave reflected by the surface and propagated to the receiving element is calculated, and the sound pressure ratio correcting means is based on the sound speed obtained by the sound speed measuring means, and is caused by the change in the sound speed. A suspended particle measurement system , wherein the sound pressure ratio is corrected so as to remove the fluctuation of the sound pressure ratio .   The signal processing unit includes parameter acquisition means for measuring at least one of temperature, humidity, and atmospheric pressure in the monitoring space as a parameter, and the attenuation coefficient estimation means estimates the attenuation coefficient using the parameter. The suspended particle measuring system according to claim 1. 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 the sound source unit and the receiving unit based on the output of the receiving element. A signal processing unit for measuring the concentration of suspended particles existing in the monitoring space between the sound wave element and the signal processing part propagates from the sound source part to the wave receiving element through propagation paths having different path lengths in the monitoring space. A sound pressure ratio calculating means for calculating a sound pressure ratio between a plurality of sound waves, a concentration estimating means for estimating the concentration of suspended particles in the monitoring space based on the sound pressure ratio calculated by the sound pressure ratio calculating means, and no suspended particles An attenuation coefficient estimating means for estimating the attenuation coefficient of the sound wave absorption attenuation in the monitoring space in a state, and a variation of the sound pressure ratio due to the change of the attenuation coefficient based on the attenuation coefficient estimated by the attenuation coefficient estimating means. To remove the sound pressure ratio A sound pressure ratio correcting means positive for, and a parameter acquisition means for measuring at least one as a parameter of temperature and humidity and atmospheric pressure in the monitoring space,
The attenuation coefficient estimation means estimates the attenuation coefficient using the parameter,
The wave receiving element includes a fixed electrode and a movable electrode arranged opposite to each other, a partition wall that separates the monitoring space from a reference pressure chamber in which air pressure is kept constant, and the movable electrode is a part of the partition wall From the capacitive receiving element in which the distance between the movable electrode and the fixed electrode changes as the partition wall receives sound waves from the monitoring space side and the capacitance between the movable electrode and the fixed electrode changes. Thus, the parameter acquisition unit includes an atmospheric pressure measurement unit that measures the atmospheric pressure of the monitoring space based on the change in the capacitance . The parameter acquisition means includes a temperature measurement means for measuring the temperature of the monitoring space, and a sound speed measurement means for obtaining a sound speed of the monitoring space, and the attenuation coefficient estimation means includes a temperature measured by the temperature measurement means, The suspended particle measuring system according to claim 2 or 3 , wherein the temperature and the humidity calculated from the sound velocity obtained by the sound velocity measuring means are used as the parameter . The sound speed measuring means transmits a difference in path lengths of the propagation paths for a plurality of sound waves to be calculated for the sound pressure ratio in the sound pressure ratio calculating means, and the sound waves propagate from the sound source unit to the wave receiving element. suspended particle measuring system according to any one of claims 1, 2, 4, characterized in that to calculate the speed of sound divided by the time difference required for being.

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