CN108291862B

CN108291862B - Particle detection sensor, dust sensor, smoke sensor, air conditioner, and particle detection method

Info

Publication number: CN108291862B
Application number: CN201780004105.6A
Authority: CN
Inventors: 桐原昌男; 稻叶雄一; 奥村真; 小川纯矢; 野村建太朗; 小原弘士
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2016-01-29
Filing date: 2017-01-13
Publication date: 2020-11-06
Anticipated expiration: 2037-01-13
Also published as: JP6083660B1; CN108291862A; JP2017134038A; WO2017130730A1

Abstract

A particle detection sensor (1) is provided with: a light projecting element (111) that projects light onto the Detection Area (DA); and a light receiving element (121) that receives scattered light of the light from the light projecting element (111) that is generated by the particles (2) that have passed through the Detection Area (DA), and generates an electrical signal that includes a pulse-like waveform corresponding to the particles (2). The particle detection sensor (1) further includes a signal processing unit (20) that amplifies the electric signal and detects the particles (2) using the amplified electric signal. The signal processing unit (20) amplifies the electrical signal at a first amplification factor when the flow of the fluid in the Detection Area (DA) is at a first speed, and amplifies the electrical signal at a second amplification factor different from the first amplification factor when the flow of the fluid is at a second speed different from the first speed.

Description

Particle detection sensor, dust sensor, smoke sensor, air conditioner, and particle detection method

Technical Field

The present invention relates to a particle detection sensor, a dust sensor, a smoke sensor, an air conditioner, and a particle detection method for detecting particles contained in a fluid.

Background

The light scattering type particle detection sensor is a photoelectric type sensor having a light projecting element and a light receiving element, and takes in a fluid to be measured, irradiates light of the light projecting element to the fluid, and detects whether particles are included in the fluid by using scattered light. Such a particle detection sensor can detect particles such as dust, pollen, and smoke floating in the atmosphere, for example.

As a device including such a particle detection sensor, a device is known in which a fluid taken into the device is separated into a main flow path through which coarse particles pass and a branch flow path through which fine particles pass (see, for example, patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-114176

Disclosure of Invention

Problems to be solved by the invention

In such a configuration, both coarse particles and fine particles can be detected by providing a processing circuit having a very large dynamic range. However, the intensity of scattered light generated by coarse particles is very large compared to the intensity of scattered light generated by fine particles. For example, coarse particles having a particle size of 50 μm have an intensity of scattered light about 5 ten thousand times larger than that of fine particles having a particle size of 0.3 μm. Therefore, in order to detect both coarse particles and fine particles, it is necessary to provide a processing circuit having a dynamic range similar to the intensity ratio of these scattered lights. However, it is extremely difficult to realize such a processing circuit from the viewpoint of characteristics of analog elements and the like.

Accordingly, the present invention aims to provide a particle detection sensor and the like: the range of detectable particle size can be widened in dynamic range.

Means for solving the problems

In order to achieve the above object, a particle detection sensor according to an aspect of the present invention is a particle detection sensor for detecting particles contained in a fluid, including: a light projecting element for projecting light to the detection area; a light receiving element that receives scattered light generated by the light from the light projecting element due to the particles passing through the detection region and generates an electric signal including a pulse-like waveform corresponding to the particles; and a signal processing unit that amplifies the electric signal and detects the particle using the amplified electric signal, wherein the signal processing unit amplifies the electric signal at a first amplification factor when a flow velocity of the fluid in the detection region is a first velocity, and amplifies the electric signal at a second amplification factor different from the first amplification factor when the flow velocity of the fluid is a second velocity different from the first velocity.

In addition, the dust sensor and the smoke sensor according to one aspect of the present invention each include the particle detection sensor.

An air conditioning apparatus according to an aspect of the present invention includes the particle detection sensor and the flow velocity generation unit.

A particle detection method according to an aspect of the present invention is a particle detection method for detecting particles contained in a fluid by using a particle detection sensor, the particle detection sensor including: a light projecting element for projecting light to the detection area; and a light receiving element that receives scattered light generated by the light from the light projecting element due to the particles passing through the detection region and generates an electric signal including a pulse-like waveform corresponding to the particles, the particle detection method including: amplifying the electric signal at a first amplification factor when the flow velocity of the fluid in the detection region is a first velocity, and amplifying the electric signal at a second amplification factor different from the first amplification factor when the flow velocity of the fluid is a second velocity different from the first velocity; and detecting the particles using the amplified electric signal.

Effects of the invention

According to the particle detection sensor and the like of the present invention, the range of detectable particle diameters can be widened in a dynamic range.

Drawings

Fig. 1 is a block diagram showing an example of the structure of a particle detection sensor according to an embodiment.

Fig. 2 is a graph showing the intensity of scattered light in time series.

Fig. 3 is a graph showing the peak intensity of a pulse waveform with respect to the particle diameter of the particles.

Fig. 4 is a graph showing an outline of frequency characteristics of the light receiving element gain and the amplifier circuit gain.

Fig. 5A is a graph showing the gain of the light receiving element with respect to the flow rate magnification.

Fig. 5B is a graph showing the gain of the amplifier circuit versus the flow rate magnification.

Fig. 6 is a graph showing the conversion efficiency of the entire particle detection sensor with respect to the flow rate magnification.

Fig. 7 is a timing chart showing the operation of the particle detection sensor.

Fig. 8A is a flowchart showing the operation of the particle detection sensor in the PM2.5 mode.

Fig. 8B is a flowchart showing the operation of the particle detection sensor in the pollen mode.

Fig. 9 is a graph showing the wave height value (peak value) of the electric signal obtained by amplifying the particle diameter.

Fig. 10A is a waveform diagram showing an amplified electric signal in the PM2.5 mode.

Fig. 10B is a waveform diagram showing the amplified electric signal in the pollen mode.

Fig. 11 is a table showing the particle size and the number of particles corresponding to each particle size partition.

Fig. 12 is a block diagram showing an example of the structure of the particle detection sensor according to variation 1 of the embodiment.

Fig. 13 is a block diagram showing an example of the structure of the particle detection sensor according to variation 2 of the embodiment.

Fig. 14 is an external view of an air purifier having a particle detection sensor.

Fig. 15 is an external view of a smoke sensor having a particle detection sensor.

Fig. 16 is an external view of a ventilation fan having a particle detection sensor.

Fig. 17 is an external view of an air conditioner showing a particle detection sensor.

Fig. 18 is a graph showing another example of the outline of the frequency characteristics of the light receiving element gain and the amplifier circuit gain.

Detailed Description

Hereinafter, a particle detection sensor and the like according to an embodiment of the present invention will be described in detail with reference to the drawings. The embodiments described below are each a specific example preferred in the present invention. Therefore, the numerical values, shapes, materials, constituent elements, arrangement and connection of constituent elements, and the order of steps and steps shown in the following embodiments are examples, and do not limit the scope of the present invention. Therefore, among the components of the following embodiments, components not described in the independent claims representing the uppermost concept of the present invention will be described as arbitrary components.

The drawings are schematic drawings, and are not necessarily strictly shown. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted or simplified.

(embodiment mode)

[1. Structure ]

First, the overall structure of the particle detection sensor according to the embodiment of the present invention will be described.

Fig. 1 is a block diagram showing an example of the structure of a particle detection sensor 1 according to the present embodiment.

The particle detection sensor 1 detects particles contained in air floating around the particle detection sensor 1 (hereinafter referred to as "ambient air"). The ambient air contains, for example, fine particles having a particle size of 5 μm or less and coarse particles having a particle size of 20 μm or more. The particle detection sensor 1 operates by switching between a PM2.5 mode in which fine particles corresponding to PM2.5 and the like are detected and a pollen mode in which coarse particles corresponding to pollen and the like are detected.

As shown in the figure, the particle detection sensor 1 includes a sensor unit 10 and a signal processing unit 20, and detects particles included in the ambient air taken into the particle detection sensor 1 based on the scattered light of the particles 2 located in the detection area DA from the sensor unit 10. The particle detection sensor 1 further includes a power supply unit 30 that supplies power to each component included in the particle detection sensor 1. The power supply unit 30 is configured by, for example, a regulator or the like that converts a voltage supplied from the outside of the particle detection sensor 1 into a desired voltage.

Hereinafter, each configuration of the particle detection sensor 1 will be specifically described.

[1-1. sensor part ]

The sensor unit 10 is a photoelectric sensor (light scattering type particle detection sensor) that takes in ambient air that is a measurement target of the particle detection sensor 1, irradiates the taken-in ambient air with light, and outputs an electric signal (here, a current signal) indicating the intensity of the scattered light. In other words, the sensor unit 10 outputs a time-series electric signal corresponding to the particles 2 included in the captured ambient air.

Specifically, in the present embodiment, the sensor unit 10 includes the light projecting system 11, the light receiving system 12, the housing 13, and the heater 15, and outputs an electric signal according to scattered light from the particles 2 (located in the detection area DA) passing through the detection area DA of the particle flow path provided from the inlet 18 to the outlet 19 of the housing 13. The light projecting system 11, the light receiving system 12, and the detection area DA are housed in the case 13 so as not to be irradiated with external light.

The detection region DA is a suspended particle detection region (suspended particle measurement section) for detecting particles 2 (suspended particles) contained in the gas to be measured, and is a region of, for example, approximately 2mm, which includes an intersection point where the optical axis P of the light projection system 11 intersects the optical axis Q of the light reception system 12. In other words, the detection area DA is a spatial area in which a spatial area on which light of the light projecting system 11 is projected and a spatial area for guiding scattered light generated by the light of the light projecting system 11 hitting the particle 2 to the light receiving system 12 overlap each other.

The light projection system 11 is composed of optical elements that project light to the detection area DA, and in the present embodiment, includes a light projection element 111 and a light projection lens 112 disposed in front of (on the light projection side of) the light projection element 111.

The Light projecting element 111 is a solid-state Light Emitting element such as an LED (Light Emitting Diode) or a semiconductor laser that projects Light to the detection area DA. The light projecting element 111 projects light having a predetermined wavelength such as infrared light, blue light, green light, red light, or ultraviolet light, or may project a mixed wave of 2 or more wavelengths. In the present embodiment, in consideration of the intensity of light (scattered light intensity) of the particles 2, a bullet-type LED that projects light having a wavelength of 400nm to 1000nm, for example, is used as the light projecting element 111.

Further, the shorter the wavelength of the light projected from the light projection element 111, the more easily the particles 2 having a small particle diameter are detected. The light projection control method of the light projection element 111 is not particularly limited, and the light projected from the light projection element 111 may be continuous light or pulsed light by DC driving. Further, the light intensity of the light projected from the light projection element 111 may be changed with time.

The light projecting lens 112 is disposed in front of the light projecting element 111 on the optical axis P of the light projecting system 11, and is configured to move the light projected from the light projecting element 111 toward the detection area DA. For example, the light projecting lens 112 is a condensing lens that condenses the light projected from the light projecting element 111 onto the detection area DA, and is formed of a transparent resin such as PC (Polycarbonate) or glass. In other words, the light projected from the light projecting element 111 reaches the detection area DA via the light projecting lens 112. At this time, when the particle 2 is located in the detection area DA, the light from the light projecting element 111 is scattered by the particle 2.

Fig. 2 is a graph showing the intensity of scattered light (scattered light intensity) in time series.

The pulse-like waveform included in the waveform shown in the figure corresponds to the scattered light generated by the particles 2 passing through the detection area DA. In other words, the peak intensity of the pulse-like waveform corresponds to the particle 2 passing through the detection area DA.

Fig. 3 is a graph showing the peak intensity of the pulse waveform with respect to the particle diameter of the particles 2. In the figure, the intensity of the scattered light is shown when the intensity of the scattered light when the particle 2 does not pass through the detection region DA is taken as a reference value 0.

The larger the particle diameter of the particles 2 passing through the detection area DA, the more scattered light is generated. Therefore, as shown in the figure, the larger the particle diameter of the particles 2, the larger the peak intensity of the pulse waveform. For example, the peak intensity of a pulse waveform of coarse particles having a particle size of 30 μm is about 400 times that of fine particles having a particle size of 2 μm.

Here, the pulse-like waveform is a sine wave corresponding to the flow velocity, particle diameter, and the like of the ambient air passing through the detection area DA, or a waveform similar thereto. The frequency of the pulse-like waveform is determined by 2 factors: (i) the size of the detection area DA (optical focal area diameter), and (ii) the velocity (i.e., flow velocity) of the particles 2 passing through the detection area DA. Therefore, the frequency of the pulse-like waveform corresponds to the flow velocity of the fluid (or the ambient air) passing through the detection area DA, and the frequency is higher as the flow velocity is higher. In other words, the greater the flow velocity, the higher the frequency of scattered light.

The light receiving system 12 is composed of an optical element that receives light from the detection area DA, and in the present embodiment, includes a light receiving element 121 and a light receiving lens 122 disposed in front of the light receiving element 121 (on the light incident side). When the particle 2 is located in the detection area DA, light (scattered light) scattered by the particle 2 is received by the light receiving system 12.

The light receiving element 121 receives scattered light generated by the light from the light projecting element 111 due to the particles 2 passing through the detection area DA, and generates an electric signal including a pulse-like waveform corresponding to the particles 2. In the present embodiment, the light receiving element 121 converts the received scattered light with a frequency-dependent conversion efficiency to generate the electric signal. The conversion efficiency of the light receiving element 121 will be described later.

The light receiving element 121 is a photoelectric conversion element that converts received scattered light into an electric signal, and in the present embodiment, includes at least one of a photodiode and a phototransistor that have sensitivity to light projected by the light projecting element 111. In other words, the light receiving element 121 outputs an electric signal (current signal in this case) according to the intensity of received light. The light receiving element 121 may include, for example, a photo IC diode or a photomultiplier tube.

The light receiving lens 122 is disposed between the detection area DA and the light receiving element 121, and is configured to condense scattered light generated by the particles 2 located in the detection area DA to the light receiving element 121. For example, the light receiving lens 122 is a condensing lens that condenses light scattered by the particles 2 located in the detection area DA to the light receiving element 121, and is formed of the same material as the light projecting lens 112.

The housing 13 has a light-shielding property, and is a member provided with a particle flow path which is a cylindrical space region where peripheral air including the particles 2 flows. For example, the housing 13 has a black surface at least on the inner surface to easily attenuate stray light. Specifically, the inner surface of the housing 13 has a high light attenuation ratio and reflects light specularly. The reflection on the inner surface of the housing 13 may be not specular reflection, but may be scattered reflection of a part of the light.

Here, the stray light is light other than light scattered by the particles 2, specifically, light that travels inside the housing 13 without being scattered by the particles 2 in the detection area DA, among light received by the light projecting element 111. The stray light also includes external light entering the inside of the housing 13 through the particle flow path.

The housing 13 is formed by injection molding using a resin material such as ABS resin. In this case, for example, the case 13 is formed using a resin material to which a black pigment or dye is added, and the inner surface of the case 13 is made black, whereby stray light can be attenuated. Alternatively, stray light can be attenuated by applying black paint to the inner surface of the case 13 after injection molding and setting the inner surface of the case 13 as a black surface. Further, the stray light can be attenuated by performing surface treatment such as embossing on the inner surface of the housing 13.

As described above, the casing 13 is provided with the inlet 18 and the outlet 19. Therefore, the ambient air enters the inside of the casing 13 through the inlet 18, is introduced into the detection region DA through the particle flow path, and flows out of the casing 13 through the outlet 19.

In the present embodiment, the flow direction of the particle flow path (the direction in which the gas flows through the particle flow path) is the vertical direction on the paper surface of fig. 1, but may be the vertical direction on the paper surface of fig. 1. In other words, in the present embodiment, the flow path axis of the particle flow path is set so that the optical axes of the light projecting system 11 and the light receiving system 12 pass through and exist on a plane, and may be set so as to be orthogonal to the plane.

The heater 15 is a flow velocity generating portion that causes a fluid (or ambient air) in the detection area DA to flow. In the present embodiment, the heater 15 generates the gas flow by heating the gas around the heater 15 and flowing the gas in the particle flow path. Specifically, when the surrounding gas is heated by the heater 15, the heated gas expands to decrease its density and moves upward in the opposite direction to the gravity. In other words, the heater 15 generates an upward airflow (updraft). The gas flow is generated in the particle flow path by the gas flow of the particle flow path. As a result, since the ambient air of the particle detection sensor 1 is introduced into the casing 13 through the inlet 18, more particles 2 can be taken into the sensor portion 10 than in the case where the heater 15 is not provided.

The heater 15 switches the flow of the fluid in the detection region DA between the first speed v1 and the second speed v2 by switching the amount of current supplied. The second speed v2 is a speed different from the first speed v1, and in the present embodiment, the second speed v2 is greater than the first speed v1 (e.g., 0.069m/s), specifically, a speed that is about 30 times the first speed v1 (e.g., 2.12 m/s).

Specifically, the heater 15 is controlled by a flow rate control unit 224 described later, and energization is performed based on a control signal indicating the amount of current input from the flow rate control unit 224. Thereby, the heater 15 generates an air flow at the first speed v1 in the PM2.5 mode and at the second speed v2 in the pollen mode.

The heater 15 generates an updraft, and is therefore disposed below the detection area DA as shown in fig. 1 in the present embodiment.

The sensor unit 10 configured as described above generates an ascending air current at the first velocity v1 or the second velocity v2 in the particle flow path in the casing 13 by heating with the heater 15. Accordingly, the particles in the ambient air enter the casing 13 through the inlet 18 of the particle flow path, pass through the particle detection region DA at the first velocity v1 or the second velocity v2, and flow out of the casing 13 through the outlet 19 of the particle flow path. At this time, the particles 2 in the detection area DA scatter the light projected from the light projection system 11, and the light receiving element 121 outputs an electric signal (or a current signal) including a pulse-like waveform corresponding to the particles 2.

In other words, the light receiving element 121 outputs an electric signal including a pulse-like waveform having a larger peak value and a larger flow velocity and a higher frequency as the particle diameter of the particle 2 is larger.

[1-2. Signal processing section ]

The signal processing unit 20 amplifies the electric signal output from the light receiving element 121, and detects particles using the amplified electric signal. Specifically, when the flow of the fluid in the detection region DA is at the first velocity v1 (in the PM2.5 mode), the signal processing section 20 amplifies the electric signal at the first amplification factor G1. On the other hand, when the flow of the fluid in the detection region DA is at the second velocity v2 (in the pollen mode) different from the first velocity v1, the signal processing section 20 amplifies the electric signal at the second amplification factor G2 different from the first amplification factor G1.

Specifically, when the second speed v2 is greater than the first speed v1, the signal processing section 20 amplifies the electric signal at a second amplification factor G2 that is smaller than the first amplification factor G1. Here, in the present embodiment, as described above, the second speed v2 is greater than the first speed v 1. Therefore, the signal processing unit 20 amplifies the electric signal at the second amplification factor G2 smaller than the first amplification factor G1 in the pollen mode.

The signal processing unit 20 performs analog signal processing such as amplification processing on the electric signal output from the light receiving element 121, and further performs digital signal processing on the signal after the analog signal processing, thereby performing various analyses on particles in the fluid. The various analyses are, for example, to obtain the mass concentration or particle size of particles in the fluid, or to determine the classification of the particles.

As shown in fig. 1, the signal processing unit 20 includes an analog signal processing unit 21 that performs analog signal processing, and a general-purpose MPU22 that performs digital signal processing.

The analog signal processing unit 21 is configured by an analog circuit, and in the present embodiment, various analog signal processes are performed on the current signal output from the light receiving element 121, thereby outputting a voltage signal based on the current signal. Here, the various analog signal processes are, for example, an I/V conversion for converting a current (I) into a voltage (V), a band-pass filtering process for passing an input signal through a desired frequency band, and an amplification process for amplifying and outputting the input signal. The analog signal processing section 21 includes an IV conversion circuit 211 that performs I/V conversion and an amplification circuit 212 that performs amplification processing.

The analog signal processing unit 21 is not limited to the respective processes illustrated here, and may be configured to further perform other signal processing (for example, high-pass filtering, low-pass filtering, attenuation processing, and the like).

The IV conversion circuit 211 generates a voltage signal corresponding to the current signal output from the light receiving element 121 by I/V conversion of the current signal. In this way, by converting the current signal into a voltage signal, the subsequent signal processing can be simplified, and the design of the amplifier circuit 212 connected to the subsequent stage of the IV conversion circuit 211 can be simplified.

The amplifier circuit 212 amplifies an electric signal (or a voltage signal) with a frequency-dependent amplification factor. For example, the amplifier circuit 212 includes a band pass filter for passing a frequency component having a predetermined bandwidth included in the frequency component of the voltage signal output from the IV conversion circuit 211, and an amplifier element for amplifying a signal composed of the frequency component passed through the band pass filter. The amplification factor of the amplifier circuit 212 will be described later.

The analog signal processing unit 21 configured as described above displays the output from the light receiving element 121 and outputs an electric signal including a pulse-like waveform corresponding to the particle 2 located in the detection area DA.

The general-purpose MPU22 is configured with a digital circuit, and detects particles contained in the fluid in the detection area DA using the electric signal output from the analog signal processing unit 21. The general-purpose MPU22 is realized by, for example, a system LSI which is an integrated circuit, and may be a single chip for each of the functional blocks described below, or may be a single chip including a part or all of the functional blocks.

The general-purpose MPU22 is not limited to a system LSI, and may be implemented by a dedicated circuit or a general-purpose processor. The general-purpose MPU22 may be an FPGA (field programmable Gate Array) that can be programmed after LSI manufacture, or a reconfigurable processor that can reconfigure connection and setting of circuit units inside LSI.

As shown in fig. 1, the general-purpose MPU22 includes, as functional blocks, an AD conversion unit 221, an arithmetic unit 222, and a flow rate control unit 224.

The AD converter 221 samples (samples) and quantizes the voltage signal amplified by the amplifier circuit 212. In other words, the AD converter 221 performs AD (Analog to Digital) conversion on the Analog voltage signal output from the Analog signal processor 21, thereby generating time-series Digital data corresponding to the voltage signal. In other words, the AD converter 221 generates time-series digital data based on the current signal output from the light-receiving element 121.

In the present embodiment, the AD converter 221 is an AD conversion module incorporated in advance in the general-purpose MPU22, and converts a voltage signal input to the analog input terminal of the general-purpose MPU22 into digital data. For example, the AD converter 221 samples a voltage signal of 0.0 to 5.0V inputted to the analog input terminal of the general-purpose MPU22 at a predetermined sampling period. Then, the AD converter 221 converts the voltage of the sampled voltage signal into a 10-bit digital value, thereby generating the time-series digital data.

The arithmetic unit 222 detects particles contained in the fluid in the detection region DA using the digital data generated by the AD conversion unit 221. In the present embodiment, the calculation unit 222 switches the processing based on a signal indicating the mode of the particle detection sensor 1 input from the flow rate control unit 224. The signal indicating the mode of the particle detection sensor 1 may not be input from the flow rate control unit 224, and may be input from, for example, a mode switching unit (not shown) different from the flow rate control unit 224.

The flow rate controller 224 controls the heater 15 to switch the flow of the fluid in the detection region DA between the first speed v1 and the second speed v 2. In the present embodiment, the flow rate control unit 224 outputs a control signal indicating the amount of current to be supplied to the heater 15. Specifically, in the PM2.5 mode, the flow rate controller 224 outputs a control signal indicating a predetermined first current amount, thereby generating a flow of the fluid at the first speed v1 in the heater 15. In the pollen mode, the flow rate controller 224 outputs a control signal indicating a predetermined second current amount larger than the first current amount, thereby generating a flow of the fluid at the second speed v2 in the heater 15.

The signal processing unit 20 configured as described above can detect fine particles by amplifying the electric signal at the first amplification factor G1 in the PM2.5 mode, and can detect coarse particles by amplifying the electric signal at the second amplification factor G2 in the pollen mode. In other words, the particle diameter range to be the detection target can be switched by changing the magnification according to the flow of the fluid in the detection region DA.

[1-3. light-receiving element gain, Circuit gain ]

In the particle detection sensor 1 of the present embodiment, since the amplification factor of the signal processing unit 20 is switched between the PM2.5 mode and the pollen mode, the amplifier circuit 212 amplifies the electric signal at an amplification factor having frequency dependency. In the present embodiment, the light receiving element 121 also converts the received scattered light into an electric signal with a frequency-dependent conversion efficiency.

Next, the conversion efficiency of the light receiving element 121 and the amplification factor of the amplifier circuit 212 will be described. In the following, the term flow rate magnification is used with reference to the first speed v 1. For example, the flow rate magnification of 1 refers to a flow rate equal to the first speed v1, and the flow rate magnification of 30 refers to a flow rate 30 times the first speed v1 (i.e., the second speed v 2).

Fig. 4 is a graph showing an outline of frequency characteristics of the conversion efficiency (light receiving element gain) of the light receiving element 121 and the amplification factor (amplification circuit gain) of the amplification circuit 212. In the figure, the frequency characteristic of the gain of the light receiving element and the frequency characteristic of the gain of the amplifier circuit are shown by the same curve, but they may be different from each other. This point is also the same in the subsequent graphs showing the frequency characteristics.

As shown in the figure, the light receiving element 121 and the amplifier circuit 212 each have frequency characteristics such that the gain decreases as the frequency increases.

Specifically, the higher the frequency of the scattered light received by the light receiving element 121 is, the lower the conversion efficiency is, the higher the frequency of the scattered light is, the higher the conversion efficiency is, the electrical signal is. In other words, the scattered light received by the light receiving element 121 is converted into an electric signal with a smaller conversion efficiency as the frequency of the pulse-like waveform is higher.

In addition, the amplification circuit 212 amplifies the electric signal at a smaller amplification factor as the frequency is higher than the frequency of the electric signal at the flow rate magnification of 1. In other words, the electric signal output from the light receiving element 121 is amplified at a smaller amplification factor as the frequency of the pulse waveform included in the electric signal is higher.

Therefore, the conversion efficiency of the light receiving element 121 and the amplification factor of the amplification circuit 212 at the relative flow rate magnification are as shown in fig. 5A and 5B. Fig. 5A is a graph showing the conversion efficiency (light-receiving element gain) of the light-receiving element 121 with respect to the flow rate magnification. Fig. 5B is a graph showing the amplification factor (amplification circuit gain) of the amplification circuit 212 with respect to the flow rate magnification.

As shown in fig. 5A, the light receiving element 121 converts the received scattered light into an electrical signal at a first conversion efficiency H1 when the flow rate magnification is 1 (in the PM2.5 mode). On the other hand, the light receiving element 121 converts the received scattered light into an electric signal at a second conversion efficiency H2 smaller than the first conversion efficiency H1 when the flow rate magnification is 30 (in the pollen mode).

As shown in fig. 5B, the amplifier circuit 212 amplifies the input electric signal at the first amplification factor G1 when the flow rate is 1 (in the PM2.5 mode). On the other hand, the amplifier circuit 212 amplifies the input electric signal at a second amplification factor G2 smaller than the first amplification factor G1 when the flow rate magnification is 30 (in the pollen mode).

Thus, in the present embodiment, by increasing the flow rate magnification, the conversion efficiency of the light receiving element 121 is reduced without performing control for switching the conversion efficiency. Further, by increasing the flow rate magnification, the amplification factor of the amplification circuit 212 is reduced without performing control for switching the amplification factor.

Therefore, the conversion efficiency of the entire particle detection sensor 1 (i.e., the circuit gain combining the conversion efficiency H of the light receiving element 121 and the amplification factor G of the amplification circuit 212) is as shown in fig. 6.

Fig. 6 is a graph showing the conversion efficiency of the entire particle detection sensor 1 with respect to the flow rate magnification. That is, the graph shows the conversion efficiency from the scattered light to the amplified electric signal with a relative flow rate magnification.

As shown in the figure, the particle detection sensor 1 of the present embodiment converts scattered light scattered by the particles 2 into an electric signal at a gain of H1 × G1 at a flow rate magnification of 1 (at the time of the PM2.5 mode). On the other hand, the particle detection sensor 1 converts the scattered light scattered by the particles 2 into an electric signal at a gain of H2 × G2 (for example, 1/450 times of H1 × G1) at a flow rate magnification of 30 (at the time of the pollen mode). In other words, in the present embodiment, the circuit gain is switched by switching the flow rate magnification. Specifically, by increasing the flow rate magnification, the circuit gain becomes extremely small.

[2. action ]

Next, the operation (particle detection method) of the particle detection sensor 1 will be described.

Fig. 7 is a timing chart showing the operation of the particle detection sensor 1.

As shown in the figure, in the particle detection sensor 1, the flow of the fluid in the detection region DA is switched between the PM2.5 mode at the first speed v1 and the pollen mode at the second speed v2 at predetermined intervals.

The timing of switching between the PM2.5 mode and the pollen mode in the particle detection sensor 1 is not limited to this, and may be switched by a user operation or when a predetermined condition is satisfied, for example. For example, the predetermined condition is a case where no particles are detected for a certain period (for example, 30 seconds) in the pollen mode. The period of the PM2.5 mode may be different from the period of the pollen mode, and for example, the period of the PM2.5 mode may be 55 minutes and the period of the pollen mode may be 5 minutes.

Fig. 8A and 8B are flowcharts showing the operation of the particle detection sensor 1. Specifically, fig. 8A is a flowchart showing the operation of the particle detection sensor 1 in the PM2.5 mode. Fig. 8B is a flowchart showing the operation of the particle detection sensor 1 in the pollen mode.

As shown in fig. 8A, in the PM2.5 mode, the heater 15 sets the flow of the fluid in the detection area DA to the first velocity v1, whereby the ambient air of the particle detection sensor 1 is introduced into the particle flow path within the housing 13 and the particles are introduced into the detection area DA at the first velocity v1 (S11). In other words, the particles 2 pass the detection area DA at the first velocity v 1.

Next, the signal processing unit 20 amplifies the electric signal at the first amplification factor G1 (S12). Specifically, the light receiving element 121 converts the scattered light into an electric signal at the first conversion efficiency H1, and the amplifier circuit 212 amplifies the converted electric signal at the first amplification factor G1.

Then, the signal processing unit 20 detects the particles using the amplified electric signal (S13). The details of the detection process (S13) will be described later.

On the other hand, as shown in fig. 8B, in the pollen mode, the heater 15 sets the flow of the fluid in the detection area DA to the second velocity v2, whereby the ambient air of the particle detection sensor 1 is introduced into the particle flow path within the housing 13 and the particles are introduced into the detection area DA at the second velocity v2 (S21). In other words, the particles 2 pass the detection area DA at the second velocity v 2.

Next, the signal processing section 20 amplifies the electric signal at the second amplification factor G2 (S22). Specifically, the light receiving element 121 converts the scattered light into an electric signal at the second conversion efficiency H2, and the amplifier circuit 212 amplifies the converted electric signal at the second amplification factor G2.

Then, the signal processing unit 20 detects the particles using the amplified electric signal (S23). The details of the detection process (S23) will be described later.

In the particle detection sensor 1 of the present embodiment operating in this manner, the electric signal after the amplification process (after S21 in fig. 8B) becomes less saturated in the pollen mode. In order to make this point easier to understand, a particle detection sensor of a comparative example of the present embodiment will be described.

The particle detection sensor of the comparative example is basically the same as the particle detection sensor 1 of the present embodiment, but the flow velocity of the detection area DA is not switched, and is always the first velocity v 1.

Fig. 9 is a graph showing the wave height value of the electric signal after amplification with respect to the particle diameter.

As shown in the figure, in the comparative example, when the scattered light increases due to an increase in the particle diameter (in this case, 2 μm or more), the amplified electric signal reaches the saturation region. In other words, in the comparative example, when coarse particles such as pollen are introduced, the peak of the pulse waveform included in the amplified electric signal is limited. This is mainly due to, for example, saturation of analog elements constituting the analog signal processing unit. Therefore, in this case, the peak of the pulse waveform does not depend on the particle diameter, and therefore, it becomes difficult to detect coarse particles.

In contrast, in the present embodiment, when the flow rate magnification of the fluid in the detection area DA is large (in the pollen mode), the circuit gain is extremely small. Therefore, as shown in the figure, when the flow velocity magnification of the fluid is large, even if scattered light of large intensity is generated by the coarse particles, the amplified electric signal hardly reaches the saturation region. In other words, in the present embodiment, even if the coarse particles are introduced, the peak value of the pulse waveform included in the amplified electric signal is not easily limited. In this way, the peak of the pulse waveform depends on the particle diameter, and therefore, coarse particles can be detected.

Further, for example, when the flow velocity of the fluid in the detection area DA is always the second velocity v2, another problem arises that the peak value of the pulse-like waveform corresponding to the fine particles becomes extremely small, and the fine particles cannot be detected.

In contrast, in the present embodiment, when the flow rate magnification of the fluid is small (in the PM2.5 mode), the circuit gain does not decrease. Therefore, the fine particles can be detected while suppressing the decrease in the peak value of the pulse waveform corresponding to the fine particles.

As described above, in the present embodiment, the particle diameter range of the detection target can be switched by changing the flow rate magnification of the fluid. This enables detection of both coarse particles and fine particles, and enables a wide dynamic range of a detectable particle size range.

Next, details of the detection process (S13 in fig. 8A and S23 in fig. 8B) will be described.

Fig. 10A is a waveform diagram showing an amplified electric signal in the PM2.5 mode. Fig. 10B is a waveform diagram showing the amplified electric signal in the pollen mode.

The signal processing unit 20 measures the number of particles belonging to each of the plurality of peak value divisions divided by the peak threshold value, using the peak value of each of the plurality of pulse-like waveforms included in the amplified electric signal as shown in these figures. In the present embodiment, the signal processing unit 20 measures the number of particles in a predetermined period (for example, every 6 seconds). The period during which the signal processing unit 20 measures the number of particles is not limited to this.

For example, in the signal processing unit 20, the arithmetic unit 222 extracts the peak value using time-series digital data generated by AD-converting the electric signal by the AD converter 221. The arithmetic unit 222 determines which of the plurality of peak value divisions each extracted peak value belongs to, and counts the number of peak values (i.e., the number of particles) belonging to each of the plurality of peak value divisions.

The wave height threshold defines the boundary of the wave height value division, and in the present embodiment, 2 wave height value divisions BS1 and BS2 are divided by 2 wave height thresholds Vth1 and Vth 2. The number and interval of the plurality of threshold values are not particularly limited, and may be set as appropriate according to the particle size distribution of the measurement target of the particle detection sensor 1, for example.

For example, the signal processing unit 20 measures 4 particles belonging to the wave height value division BS1 and 1 particle belonging to the wave height value division BS2 with respect to the electric signal shown in fig. 10A. For example, the signal processing unit 20 measures 3 particles belonging to the wave height value section BS1 and 2 particles belonging to the wave height value section BS2 with respect to the electric signal shown in fig. 10B.

Next, the signal processing unit 20 obtains the numbers of particles belonging to the plurality of particle size divisions partitioned by the plurality of particle size thresholds, respectively, using the measured numbers of particles belonging to the plurality of peak value divisions BS1 and BS2, respectively.

As shown in the figure, in the present embodiment, the number of particles belonging to each of the 4 particle size divisions BP1 to BP4 is obtained. The 4 particle size divisions BP1 to BP4 are defined in the following manner.

The above-mentioned wave height thresholds Vth1 and Vth2 correspond to different particle sizes in the PM2.5 mode and the pollen mode. As is clear from fig. 9, the same peak value corresponds to different particle diameters in the PM2.5 mode and the pollen mode. In the present embodiment, the wave height threshold Vth1 corresponds to a particle size of 1 μm in the PM2.5 mode and corresponds to a particle size of 20 μm in the pollen mode. The wave height threshold Vth2 corresponds to a particle size of 2 μm in the PM2.5 mode and 30 μm in the pollen mode.

In other words, the plurality of particle size thresholds include a first particle size threshold corresponding to the first velocity v1 and the wave height threshold, and a second particle size threshold corresponding to the second velocity v2 and the wave height threshold. That is, in the present embodiment, the first particle size threshold values are 1 μm and 2 μm particle size threshold values corresponding to the wave height threshold values Vth1 and Vth2 in the PM2.5 mode in this order. In the present embodiment, the second particle size threshold is a particle size threshold 20 μm and 30 μm corresponding to the wave height threshold Vth1 and Vth2 in this order in the pollen mode.

Therefore, in the present embodiment, 4 particle size divisions BP1 to BP4 are defined by 4 particle size thresholds 1 μm, 2 μm, 20 μm, and 30 μm.

For example, in the signal processing unit 20, the arithmetic unit 222 calculates the number of particles per particle size division using a signal indicating a mode from the flow rate control unit 224. Specifically, when the signal from the flow rate controller 224 indicates the PM2.5 mode, the arithmetic unit 222 acquires the number of particles measured in the wave height partition BS1 as the number of particles belonging to the particle size partition BP1, and acquires the number of particles measured in the wave height partition BS2 as the number of particles belonging to the particle size partition BP 2. On the other hand, when the signal from the flow rate controller 224 indicates the pollen mode, the arithmetic unit 222 acquires the number of particles measured in the wave height partition BS1 as the number of particles belonging to the particle size partition BP3, and acquires the number of particles measured in the wave height partition BS2 as the number of particles belonging to the particle size partition BP 4.

By this processing, the signal processing unit 20 can detect particles for both fine particles corresponding to PM2.5 and the like and coarse particles corresponding to pollen and the like.

In the PM2.5 mode, for example, the signal processing unit 20 may calculate the mass concentration of the particles in the fluid for a predetermined period of time for each measured particle count. The method for calculating the mass concentration is not particularly limited, and can be calculated from the number of particles belonging to an arbitrary particle size range and the reference mass of the particles belonging to the particle size range, for example.

[3. summary ]

As described above, the particle detection sensor 1 of the present embodiment is a particle detection sensor that detects particles contained in a fluid (in the air in the present embodiment). The particle detection sensor 1 includes: a light projecting element 111 that projects light to the detection area DA; and a light receiving element 121 that receives scattered light generated by the light from the light projecting element 111 due to the particles 2 passing through the detection area DA, and generates an electric signal including a pulse-like waveform corresponding to the particles 2. Further, the particle detection sensor 1 includes a signal processing section 20 that amplifies the electric signal and detects the particles 2 using the amplified electric signal. The signal processing unit 20 amplifies the electric signal at a first amplification factor G1 when the flow of the fluid in the detection region DA is at a first velocity v1, and amplifies the electric signal at a second amplification factor G2 different from the first amplification factor G1 when the flow of the fluid is at a second velocity v2 different from the first velocity v 1.

In this way, the range of particle diameters to be detected can be switched by changing the magnification in accordance with the flow of the fluid in the detection region DA. In other words, particles can be detected over a wide particle size range of a first particle size range (0.3 μm to 2.5 μm in fig. 9) detectable at the first velocity v1 and a second particle size range (2.5 μm to 50 μm in fig. 9) detectable at the second velocity v2 of the flow of the combined fluid. Therefore, the detectable particle size range can be widened in dynamic range.

Further, according to the present embodiment, the signal processing section 20 amplifies the electric signal at the second amplification factor G2 smaller than the first amplification factor G1 when the second speed v2 is greater than the first speed v 1.

When the second speed v2 is higher than the first speed v1 as described above, the number of particles 2 passing through the detection area DA increases. Therefore, coarse particles having a smaller number of floating particles than fine particles easily pass through the detection region DA. Therefore, at this time, by amplifying the electric signal at the second amplification factor G2 smaller than the first amplification factor G1, the coarse particles can be detected while suppressing saturation of the amplified electric signal. Therefore, coarse particles can be detected relatively easily.

Further, according to the present embodiment, the faster the flow of the fluid, the higher the frequency of the pulse-like waveform. The signal processing unit 20 further includes an amplifier circuit 212 that amplifies the electric signal at an amplification factor having frequency dependency.

By changing the flow of the fluid, the amplification factor of the signal processing unit 20 is switched by the characteristics of the amplifier circuit 212. In other words, the amplification factor of the signal processing unit 20 can be automatically switched without performing control for switching the amplification factor of the signal processing unit 20 according to the flow of the fluid. Therefore, the operation of the particle detection sensor 1 can be simplified, and the range of detectable particle diameters can be widened in a dynamic range.

Specifically, according to the present embodiment, the amplification circuit 212 amplifies the electric signal at a smaller amplification factor as the frequency is higher.

Here, the faster the flow of the fluid, the easier it is for particles having larger particle sizes to pass through the detection area DA. Therefore, the higher the frequency (i.e., the faster the fluid flows), the smaller the amplification factor, and the saturation of the amplified electrical signal can be suppressed. Therefore, larger coarse particles can be detected.

Further, according to the present embodiment, the faster the flow of the fluid, the higher the frequency of scattering light. The light receiving element 121 also converts the received scattered light with a frequency-dependent conversion efficiency to generate an electric signal.

As described above, since the conversion efficiency of the light receiving element 121 has frequency dependency, the conversion efficiency of the light receiving element 121 is automatically switched according to the flow of the fluid. Therefore, in the case of switching the flow of the fluid, the conversion efficiency from the scattered light to the amplified electric signal can be largely switched as compared with the case where the conversion efficiency of the light receiving element 121 is substantially constant. In other words, the particle size range to be detected can be largely switched. Therefore, the detectable particle size range can be further widened in dynamic range.

Specifically, according to the present embodiment, the light receiving element 121 performs conversion with a conversion efficiency that decreases as the frequency increases.

Here, the faster the flow of the fluid, the easier it is for particles having larger particle sizes to pass through the detection area DA. Therefore, as the frequency increases (that is, as the flow of the fluid increases), the scattered light is converted into an electric signal with a smaller conversion efficiency, and thereby saturation of the electric signal amplified by the signal processing unit 20 can be suppressed. Therefore, larger coarse particles can be detected.

Further, according to the present embodiment, the signal processing unit 20 measures the number of particles belonging to each of the plurality of wave height value divisions BS1 and BS2 divided by the wave height threshold values Vth1 and Vth2, using the wave height value of each of the plurality of pulse-like waveforms included in the amplified electric signal. Further, the signal processing unit 20 obtains the number of particles belonging to each of the plurality of particle size divisions BP1 to BP4 by using the measured number of particles belonging to each of the plurality of wave height value divisions BS1 and BS2, and the plurality of particle size divisions BP1 to BP4 are divided by a plurality of particle size thresholds including a first particle size threshold corresponding to the first velocity v1 and the wave height thresholds Vth1 and Vth2 and a second particle size threshold corresponding to the second velocity v2 and the wave height thresholds Vth1 and Vth 2.

Further, according to the present embodiment, the particle detection sensor 1 further has a flow velocity generating portion that causes the fluid in the detection area DA to flow.

Thereby, the flow of the fluid in the detection area DA is easily adjusted.

Specifically, according to the present embodiment, the flow velocity generation section is the heater 15 provided below the detection area DA.

In this way, the flow velocity generating portion is the heater 15, and thus the structure of the flow velocity generating portion can be simplified. Further, since the heater 15 generates an updraft, the flow of the fluid in the detection area DA can be effectively switched by being provided below the detection area DA.

Here, according to the present embodiment, the heater 15 switches the flow of the fluid at the first speed v1 and the second speed v2 by switching the amount of current to be supplied.

Since the flow of the fluid is switched by switching the amount of current in this manner, the flow of the fluid can be switched with a simplified configuration.

Further, the particle detection method of the present embodiment is a particle detection method of detecting particles 2 contained in a fluid using the particle detection sensor 1. Here, the particle detection sensor 1 has: a light projecting element 111 that projects light to the detection area DA; and a light receiving element 121 that receives scattered light generated by the light from the light projecting element 111 due to the particles passing through the detection area DA and generates an electric signal including a pulse-like waveform corresponding to the particles 2. The particle detection method comprises the following steps: a step of amplifying the electric signal at a first amplification rate G1 when the flow of the fluid in the detection region DA is a first velocity v1, and amplifying the electric signal at a second amplification rate G2 different from the first amplification rate G1 when the flow of the fluid is a second velocity v2 different from the first velocity v1 (S12 of fig. 8A and S22 of fig. 8B); and a step of detecting particles using the amplified electric signal (S13 of fig. 8A and S23 of fig. 8B).

In this manner, the particle detection method can switch the particle diameter range to be detected by changing the magnification according to the flow of the fluid in the detection area DA. In other words, particles can be detected over a wide particle size range of a detectable first particle size range at a first velocity v1 and a detectable second particle size range at a second velocity v2 of the combined fluid flow. Therefore, the detectable particle size range can be widened in dynamic range.

(modification 1)

In the above embodiment, the signal processing unit 20 has the amplifier circuit 212 that amplifies the electric signal at an amplification factor having frequency dependency, and thereby the amplification factor is set to be different between the PM2.5 mode and the pollen mode. However, the amplification factor is not limited to the configuration in which the signal processing unit is made different between the PM2.5 mode and the pollen mode, and a plurality of amplification circuits having different amplification factors may be provided in parallel, for example. Therefore, the particle detection sensor configured as described above will be described below as modification 1 of the embodiment.

Fig. 12 is a block diagram showing an example of the configuration of a particle detection sensor 1A according to modification 1 of the embodiment.

As shown in the drawing, in the present modification, the signal processing section 20A includes a first amplifier circuit 212A that amplifies an electric signal at a first amplification factor G1, and a second amplifier circuit 212B that amplifies an electric signal at a second amplification factor G2.

The first amplifier circuit 212A and the second amplifier circuit 212B have smaller frequency dependence of the amplification factor than the amplifier circuit 212 in the embodiment, and have substantially constant amplification factors over a wide bandwidth. For example, the amplification factor of the first amplification circuit 212A is the first amplification factor G1 in both the case of the frequency when the flow rate magnification is 1 and the case of the frequency when the flow rate magnification is 30. On the other hand, the amplification factor of the second amplification circuit 212B is the second amplification factor G2 in both the case of the frequency when the flow rate magnification is 1 and the case of the frequency when the flow rate magnification is 30.

In the mode of the particle detection sensor 1A, either one of the first amplification circuit 212A and the second amplification circuit 212B selectively amplifies the electric signal. Specifically, when the particle detection sensor 1A is in the PM2.5 mode, the first amplification circuit 212A amplifies the electric signal, and when the particle detection sensor 1A is in the pollen mode, the second amplification circuit 212B amplifies the electric signal.

Even in the particle detection sensor 1A configured as described above, similarly to the above embodiment, the magnification can be changed according to the flow of the fluid in the detection area DA, thereby switching the particle diameter range to be detected. Therefore, the detectable particle size range can be widened in dynamic range.

In the present modification, the signal processing unit 20A includes a first amplifier circuit 212A that amplifies the electric signal at a first amplification factor G1 and a second amplifier circuit 212B that amplifies the electric signal at a second amplification factor G2.

Accordingly, even when the difference between the first speed v1 and the second speed v2 is small, the difference between the first magnification G1 and the second magnification G2 can be secured large, and therefore the detectable particle size range can be widened in the dynamic range.

(modification 2)

In the above embodiment, the particle detection sensor 1 includes the heater 15 as a flow velocity generating portion for causing the fluid in the detection area DA to flow. However, the particle detection sensor may not have a flow velocity generating unit such as the heater 15, and may be configured to generate a flow (air flow) of the fluid in the detection area DA by a flow velocity generating unit such as a fan (small electric fan) provided outside. Therefore, the particle detection sensor configured as described above will be described below as modification 2 of the embodiment.

Fig. 13 is a block diagram showing an example of the configuration of a particle detection sensor 1B according to modification 2 of the embodiment.

As shown in the drawing, in the particle detection sensor 1B of the present modification, the heater 15 is not provided, and the air flow is generated in the detection area DA by the external fan 15B, as compared with the particle detection sensor 1 of the embodiment.

The fan 15B is provided in, for example, an air conditioning apparatus (for example, an air cleaner, an air conditioner, or the like) on which the particle detection sensor 1B is mounted. The airflow generated by the fan 15B is branched into a main flow of the airflow used for air conditioning as an air conditioner and a branch flow introduced into the particle detection sensor 1B. In this manner, the gas flow introduced into the particle detection sensor 1B generates a gas flow in the detection area DA.

The fan 15B switches the speed of the generated airflow, for example, based on a signal indicating the mode of the particle detection sensor 1 from the flow rate control unit 224. Specifically, when the signal indicating the PM2.5 mode is output from the flow rate control unit 224, the airflow is generated so that the flow of the airflow in the detection area DA becomes the first speed v 1. On the other hand, when the signal indicating the pollen mode is output from the flow rate control unit 224, the airflow is generated so that the flow in the detection area DA becomes the second speed v 2.

Even in the particle detection sensor 1B configured as described above, similarly to the above embodiment, the magnification can be changed according to the flow of the fluid in the detection area DA, and the particle diameter range to be detected can be further switched. Therefore, the detectable particle size range can be widened in dynamic range.

(modification 3)

The particle detection sensor described in the above embodiment and

modifications

1 and 2 can be applied to various devices. Therefore, an example of application of the particle detection sensor will be described below as modification 3 of the embodiment.

Fig. 14 is an external view of an air purifier having a particle detection sensor. Fig. 15 is an external view of a smoke sensor having a particle detection sensor. Fig. 16 is an external view of a ventilation fan having a particle detection sensor. Fig. 17 is an external view of an air conditioner having a particle detection sensor.

According to these devices, the particle detection sensor having a detectable particle diameter range and realizing a wide dynamic range can switch the operation according to more detected particles classified into fine particles and coarse particles, for example. The device to which the particle detection sensor described in the above embodiment and

modifications

1 and 2 can be applied is not limited to the above-described article, and may be, for example, a dust sensor.

(other modification example)

The present invention has been described above based on the embodiments and the modifications, but the present invention is not limited to the embodiments and the modifications described above.

For example, in the above description, the signal processing section is configured to amplify the electrical signal at the first amplification factor G1 when the flow of the fluid in the detection region DA is the first velocity v1, and amplify the electrical signal at the second amplification factor G2 when the flow of the fluid is the second velocity v 2. However, the signal processing unit may switch 3 or more different amplification factors according to the flow (flow velocity) of 3 or more fluids, and further amplify the electric signal. This makes it possible to further widen the dynamic range of the detectable particle size range.

In the above description, the second speed v2 is set to be higher than the first speed v 1. However, if the light-receiving element 121 and the amplifier circuit have the frequency characteristics shown in fig. 18, for example, the second speed v2 may be different from the first speed v1, or may be smaller than the first speed v 1. In other words, the flow of fluid in the detection area DA may be slower in the PM2.5 mode than in the pollen mode.

Fig. 18 is a graph showing an outline of another example of the frequency characteristics of the conversion efficiency (light receiving element gain) of the light receiving element 121 and the amplification factor (amplification circuit gain) of the amplification circuit. As shown in the figure, each of the light receiving element 121 and the amplifier circuit has frequency characteristics in which the gain is highest at a frequency corresponding to the flow velocity magnification of 1.

In such a configuration, the detection of coarse particles requires a little time as compared with the above embodiment, but the magnification can be changed according to the flow of the fluid in the detection area DA, thereby switching the particle size range to be detected. Therefore, as in the above embodiment, the detectable particle size range can be widened in the dynamic range.

The light receiving elements 121 and the amplifier circuit are not limited to the example shown in fig. 18, and may have frequency characteristics such that the gain decreases as the frequency decreases, for example.

In the above description, the light receiving element 121 converts the received scattered light into an electrical signal with a frequency-dependent conversion efficiency. However, the conversion efficiency of the light receiving element 121 may be substantially constant over a wide bandwidth from the frequency corresponding to the first speed v1 to the frequency corresponding to the second speed v 2.

In the above description, the signal processing unit is configured to acquire the number of particles belonging to each of the plurality of particle size divisions. However, the signal processing unit may not acquire the number of particles, and may detect the presence or absence of particles belonging to each of the plurality of particle size divisions, for example.

In the above-described embodiment and

modifications

1 and 2, the particle detection sensor is provided with the heater 15. However, the particle detection sensor may have a flow velocity generating portion such as a fan instead of the heater 15.

In the above-described embodiment and

modifications

1 and 2, the heater 15 is provided below the detection area DA. However, the position where the heater 15 is provided is not limited to this, and any position may be used as long as the heater 15 can generate an air flow in the detection area DA. For example, the heater 15 may be provided in the particle flow path or above or below an arbitrary position in the particle flow path.

In the above-described embodiment and

modifications

1 and 2, the heater 15 switches the flow of the fluid in the detection region DA between the first speed v1 and the second speed v2 by switching the amount of current to be supplied. However, the method of switching the first speed v1 and the second speed v2 is not limited to this, and for example, the first speed v1 and the second speed v2 may also be switched by switching the heater 15 on and off.

In the above description, the second speed v2 is set to be about 30 times the first speed v1, but is not limited thereto. For example, a still further wide dynamic range of the detectable particle size range can be achieved by setting the second speed v2 to be larger. However, if the second speed v2 is too large, a particle size range that cannot be detected at both the first speed v1 and the second speed v2 may occur. Therefore, the second speed v2 is preferably a speed that takes these things into consideration.

For example, the particle detection sensor may not include the AD converter 221, and the arithmetic unit 222 may detect the particles 2 using an analog voltage signal amplified by an amplifier circuit. However, from the following viewpoint, the particle detection sensor preferably has an AD conversion unit 221.

That is, when the particle detection sensor does not include the AD converter 221, a configuration in which a peak hold circuit and a plurality of comparators for comparing with a plurality of thresholds are used as a configuration for detecting the peak value of the analog voltage signal is conceivable. However, in such a configuration, it takes time to charge and discharge the capacitor in the peak hold circuit, and it is difficult to detect the peak of the voltage signal at high speed. Further, as an analog circuit configuration, it is necessary to have a plurality of comparators.

In contrast, when the particle detection sensor includes the AD converter 221, the peak value of the voltage signal can be detected at a higher speed than when the peak hold circuit is used. Therefore, detection omission of particles can be suppressed. Further, since it is not necessary to provide a plurality of comparators as the analog circuit configuration, simplification and cost reduction of the analog circuit configuration can be achieved.

In the above description, the medium containing the particles is a gas (air), but may be a medium other than a gas (a liquid such as water). In other words, the particle detection sensor detects particles contained in a fluid that is a gas or a liquid.

In the above description, each component in the general-purpose MPU22 may be implemented by dedicated hardware or by executing a software program suitable for each component. Each component may be realized by reading a software program recorded in a recording medium such as a hard disk or a semiconductor memory by a program execution unit such as a CPU or a processor.

A part or all of the components (functions) constituting the general-purpose MPU22 may be implemented as a part of a microprocessor, a ROM, a RAM, or the like mounted on various devices (for example, an air cleaner) having a particle detection sensor.

Further, the present invention can be realized not only as a particle detection sensor as described above but also as a method including steps (processes) performed by the particle detection sensor.

For example, these steps may also be performed by a computer (computer system). The present invention can realize the steps included in these methods as a program for causing a computer to execute the methods. The present invention can be realized as a non-transitory computer-readable recording medium such as a CD-ROM on which the program is recorded.

For example, when the present invention is implemented as a program (software), the program is executed by using hardware resources such as a CPU, a memory, and an input/output circuit of a computer, and the steps are executed. In other words, each step is executed by, for example, the CPU acquiring data from the memory, the input/output circuit, or the like, performing an operation, and outputting the operation result to the memory, the input/output circuit, or the like.

In addition, the present invention includes an embodiment obtained by implementing various modifications that can be conceived by those skilled in the art of the embodiments, and an embodiment obtained by arbitrarily combining the components and functions of the embodiments without departing from the scope of the present invention.

Description of the reference numerals

1. 1A, 1B particle detection sensor

2 granules

15 Heater (flow rate generation part)

15B Fan (flow rate generation part)

20. 20A signal processing unit

111 light projecting element

121 light receiving element

212 amplifier circuit

212A first amplifier circuit

212B second amplification circuit.

Claims

1. A particle detection sensor that detects particles contained in a fluid, the particle detection sensor characterized by comprising:

a light projecting element for projecting light to the detection area;

a light receiving element that receives scattered light generated by the light from the light projecting element due to the particles passing through the detection region and generates an electric signal including a pulse-like waveform corresponding to the particles; and

a signal processing unit for amplifying the electric signal and detecting the particle by using the amplified electric signal,

the signal processing unit amplifies the electric signal at a first amplification factor when the flow velocity of the fluid in the detection region is a first velocity, and amplifies the electric signal at a second amplification factor different from the first amplification factor when the flow velocity of the fluid is a second velocity different from the first velocity.

2. The particle detection sensor of claim 1, wherein:

the signal processing unit amplifies the electric signal at the second amplification factor smaller than the first amplification factor when the second speed is higher than the first speed.

3. The particle detection sensor according to claim 1 or 2, wherein:

the faster the flow rate of the fluid the higher the frequency of the pulse-like waveform,

the signal processing section has an amplification circuit that amplifies the electric signal with an amplification factor having frequency dependency.

4. The particle detection sensor of claim 3, wherein:

the amplification circuit amplifies the electric signal at a smaller amplification factor as the frequency amplification factor is higher.

5. The particle detection sensor according to claim 1 or 2, wherein:

the signal processing section includes:

a first amplification circuit that amplifies the electric signal at the first amplification rate; and

a second amplification circuit that amplifies the electrical signal at the second amplification rate.

6. The particle detection sensor according to claim 1 or 2, wherein:

the faster the flow velocity of the fluid the higher the frequency of the scattered light,

the light receiving element generates the electric signal by converting the received scattered light with a frequency-dependent conversion efficiency.

7. The particle detection sensor of claim 6, wherein:

the light receiving element performs conversion with a conversion efficiency that decreases with increasing frequency.

8. The particle detection sensor according to claim 1 or 2, wherein:

the signal processing unit measures the number of particles belonging to each of a plurality of wave height value divisions divided by a wave height threshold value using a wave height value of each of a plurality of pulse-like waveforms included in the amplified electric signal,

the method includes obtaining the number of particles belonging to each of a plurality of particle size divisions, which are divided by a plurality of particle size thresholds including a first particle size threshold corresponding to the first velocity and the wave height threshold, and a second particle size threshold corresponding to the second velocity and the wave height threshold, using the measured number of particles belonging to each of the plurality of wave height value divisions.

9. The particle detection sensor according to claim 1 or 2, wherein:

and a flow rate generating section that causes the fluid in the detection region to flow.

10. The particle detection sensor of claim 9, wherein:

the flow rate generating section is a heater disposed below the detection region.

11. The particle detection sensor of claim 10, wherein:

the heater switches the flow rate of the fluid at the first speed and the second speed by switching the amount of current energized.

12. A dust sensor, characterized by:

a particle detection sensor having the particle detection sensor according to any one of claims 1 to 11.

13. A smoke sensor, comprising:

14. An air conditioning apparatus, comprising:

a particle detection sensor as claimed in any one of claims 1 to 8; and

a flow velocity generating section that causes the fluid in the detection region to flow.

15. A particle detection method for detecting particles contained in a fluid using a particle detection sensor having: a light projecting element for projecting light to the detection area; and a light receiving element that receives scattered light generated by the particles passing through the detection region by the light from the light projecting element and generates an electric signal including a pulse-like waveform corresponding to the particles, the particle detection method including:

amplifying the electric signal at a first amplification factor when the flow velocity of the fluid in the detection region is a first velocity, and amplifying the electric signal at a second amplification factor different from the first amplification factor when the flow velocity of the fluid is a second velocity different from the first velocity; and

detecting the particles using the amplified electrical signal.