WO2019167485A1 - Particle detecting sensor - Google Patents

Abstract

This particle detecting sensor (1) detects particles contained in a fluid of interest, and is provided with: a light projecting unit (20) which emits light (L1) toward a detection area (DA); a light receiving unit (30) which has light-receiving sensitivity with respect to the light emitted by the light projecting unit (20), and which generates and outputs an electrical signal by performing photoelectric conversion of scattered light (L2) originating from the light (L1), caused by a particle passing through the detection area (DA); a signal processing circuit (50) which, on the basis of the electrical signal, calculates a first mass concentration of a first particle category including a first particle, and a second mass concentration of a second particle category including the first particle and a second particle larger than the first particle; and a correcting circuit (60) which estimates the number of second particles on the basis of the number of first particles, and corrects the second mass concentration on the basis of the estimated number of particles.

Description

Particle detection sensor

The present invention relates to a particle detection sensor.

Conventionally, a photoelectric particle detection sensor that includes a light projecting element and a light receiving element, detects particles floating in the air, and calculates the particle size of the detected particles is known (see, for example, Patent Document 1). ).

Japanese Patent Laid-Open No. 2015-210183

In the photoelectric particle detection sensor, the mass concentration for each particle size classification can be calculated from the particle size and the number of particles. At this time, in order to calculate the mass concentration with sufficient accuracy, a certain number of particles or more must be acquired. However, in general, as the particle size increases, the number of particles floating in the atmosphere decreases. For this reason, there exists a problem that the measurement precision of the mass concentration of a large particle size division deteriorates.

Therefore, an object of the present invention is to provide a particle detection sensor that can accurately measure the mass concentration of a plurality of particle size categories.

In order to achieve the above object, a particle detection sensor according to an aspect of the present invention is a particle detection sensor that detects particles contained in a target fluid, and a light projecting unit that emits light toward a detection region; A light receiving unit that has light receiving sensitivity with respect to light emitted from the light projecting unit, and generates and outputs an electric signal by photoelectrically converting the scattered light of the light from the particles passing through the detection region; and the electric signal The first mass concentration of the first particle size segment containing the first particles, and the second mass concentration of the second particle size segment containing the first particles and second particles larger than the first particles, And a correction circuit that estimates the number of the second particles based on the number of the first particles and corrects the second mass concentration based on the estimated number of particles. .

The particle detection sensor according to the present invention can accurately measure the mass concentration of a plurality of particle size categories.

FIG. 1 is a perspective view of a particle detection sensor according to an embodiment. FIG. 2 is a cross-sectional view of the particle detection sensor according to the embodiment. FIG. 3 is an enlarged cross-sectional view for explaining the operation of the particle detection sensor according to the embodiment. FIG. 4 is a diagram illustrating an example of a signal processing circuit of the particle detection sensor according to the embodiment. FIG. 5 is a diagram illustrating an electric signal output from the light receiving element of the particle detection sensor according to the embodiment, and a signal during a period in which the number of fine particles is measured. FIG. 6 is a diagram illustrating an electric signal output from the light receiving element of the particle detection sensor according to the embodiment and a signal during a period in which the number of coarse particles is measured. FIG. 7 is a histogram of particles detected by the particle detection sensor according to the embodiment. FIG. 8 is a diagram showing the concentration distribution of each particle size of PM2.5 and PM10. FIG. 9 is a diagram illustrating an example of adjusting the measurement period of the number of coarse particles as a first example of the operation of the particle detection sensor according to the embodiment. FIG. 10 is a diagram illustrating an example of adjusting the number of cycles for averaging in the calculation of the mass concentration as a second example of the operation of the particle detection sensor according to the embodiment. FIG. 11 is a diagram illustrating an adjustment example of the guidance amount of the target fluid as a third example of the operation of the particle detection sensor according to the embodiment.

Hereinafter, the particle detection sensor according to the embodiment of the present invention will be described in detail with reference to the drawings. Each of the embodiments described below shows a specific example of the present invention. Therefore, numerical values, shapes, materials, components, arrangement and connection forms of components, steps, order of steps, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. Therefore, among the constituent elements in the following embodiments, constituent elements not described in the independent claims are described as arbitrary constituent elements.

Each figure is a schematic diagram and is not necessarily shown strictly. Therefore, for example, the scales and the like do not necessarily match in each drawing. Moreover, in each figure, the same code | symbol is attached | subjected about the substantially same structure, The overlapping description is abbreviate | omitted or simplified.

(Embodiment)
[Constitution]
First, a particle detection sensor 1 according to an embodiment will be described with reference to FIGS.

FIG. 1 is a perspective view of a particle detection sensor 1 according to the present embodiment. FIG. 2 is a cross-sectional view of the particle detection sensor 1 according to the present embodiment. Specifically, FIG. 2 shows a cross section parallel to the XY plane at the approximate center in the Z-axis direction of the housing 10 of the particle detection sensor 1. FIG. 3 is an enlarged cross-sectional view for explaining the operation of the particle detection sensor 1 according to the present embodiment. Specifically, FIG. 3 shows an enlarged portion including the detection area DA in the cross section shown in FIG.

In addition, the X axis, the Y axis, and the Z axis indicate the three axes of the three-dimensional orthogonal coordinate system. The X-axis direction and the Y-axis direction are directions along two sides of the casing 10 having a substantially flat rectangular parallelepiped shape. The Z-axis direction corresponds to the thickness direction of the housing 10.

The particle detection sensor 1 is a photoelectric particle detection sensor that detects a plurality of particles P contained in a target fluid. In the present embodiment, the target fluid is a gas such as air (atmosphere). The particles P are micrometer-order fine particles floating in a gas, that is, particulate matter (aerosol). Specifically, the particles P are PM2.5, suspended particulate matter (SPM: Suspended な ど Particulate Matter), PM10, and the like.

As shown in FIG. 1, the particle detection sensor 1 includes a housing 10. As shown in FIG. 2, the particle detection sensor 1 includes a light projecting unit 20, a light receiving unit 30, a guidance device 40, a signal processing circuit 50, and a correction circuit 60.

Since the signal processing circuit 50 and the correction circuit 60 do not appear in the cross section shown in FIG. 2, the signal processing circuit 50 and the correction circuit 60 are schematically shown in FIG. The signal processing circuit 50 and the correction circuit 60 are attached to, for example, the outer surface of the housing 10 and the surface opposite to the surface on which the inflow port 11 and the outflow port 12 are provided.

The housing 10 accommodates the light projecting unit 20 and the light receiving unit 30 and has a detection area DA therein. The housing 10 forms a gas flow path including a plurality of particles P. The detection area DA is located on the gas flow path.

Specifically, as shown in FIG. 1, the housing 10 has an inflow port 11 through which a gas flows in and an outflow port 12 through which the gas that flows in flows out. As indicated by the thick broken line arrows in FIG. 2, the path from the inlet 11 to the outlet 12 inside the housing 10 corresponds to a gas flow path. Although FIG. 2 shows an example in which the gas flow path is formed in an L shape, the gas flow path may be formed in a straight line connecting the inlet 11 and the outlet 12. .

The housing 10 has, for example, light shielding properties, and suppresses external light that causes noise from entering the light receiving unit 30 and the detection area DA. The housing 10 is formed by injection molding using, for example, a black resin material. Specifically, the housing 10 is configured by combining a plurality of parts formed by injection molding. The light projecting unit 20 and the light receiving unit 30 are sandwiched between the plurality of components and fixed at predetermined positions in the housing 10.

An optical trap structure that attenuates stray light by multiple reflection may be provided inside the housing 10. The stray light is light other than the light L1 emitted from the light projecting unit 20 (see FIG. 3) that is not scattered by the particles P passing through the detection area DA, that is, the scattered light L2 (see FIG. 3). Light. The light trap structure can also attenuate external light incident on the inside from the inlet 11 or the outlet 12.

The light projecting unit 20 emits light L1 toward the detection area DA. As shown in FIGS. 2 and 3, the light projecting unit 20 includes a light projecting element 21 and a lens 22.

The light projecting element 21 is, for example, a solid light emitting element, and specifically a laser element such as a semiconductor laser. Alternatively, the light projecting element 21 may be a light emitting diode (LED: Light Emitting Diode) or an organic EL (Electroluminescence) element.

The light L1 emitted from the light projecting element 21 is light having a peak at a predetermined wavelength such as infrared light, ultraviolet light, blue light, green light, or red light. The half width at the peak of the light L1 may be a narrow band such as 50 nm or less. The light L1 is continuous light or pulsed light by DC driving, but is not limited thereto.

The lens 22 is disposed between the light projecting element 21 and the detection area DA. The lens 22 is, for example, a condensing lens, and efficiently condenses the light L1 emitted from the light projecting element 21 in the detection area DA.

The light receiving unit 30 has light receiving sensitivity with respect to the light emitted from the light projecting unit 20, and generates and outputs an electrical signal by photoelectrically converting the scattered light L2 of the light L1 from the particles P passing through the detection area DA. To do. As shown in FIGS. 2 and 3, the light receiving unit 30 includes a light receiving element 31 and a lens 32.

The light receiving element 31 is a photoelectric conversion element that converts received light into an electrical signal, such as a photodiode, a phototransistor, or a photomultiplier tube. The light receiving element 31 outputs an electrical signal corresponding to the received light intensity of the received light. The light receiving element 31 has sensitivity in the wavelength band of the light L1 emitted from the light projecting element 21.

As shown in FIG. 2, the light receiving element 31 is disposed at a position where the direct light of the light L1 emitted from the light projecting element 21 does not enter. Specifically, the light receiving element 31 is disposed at a position that does not overlap the optical axis of the light projecting element 21. The optical axis of the light projecting element 21 corresponds to the path of light having the highest intensity among the light L1 emitted from the light projecting element 21. Specifically, the optical axis of the light projecting element 21 corresponds to a straight line connecting the light projecting element 21 and the detection area DA. In the present embodiment, the light receiving element 31 is arranged so that the optical axis of the light receiving element 31 intersects the optical axis of the light projecting element 21 in the detection area DA.

The lens 32 is disposed between the light receiving element 31 and the detection area DA. The lens 32 efficiently collects the scattered light L2 scattered by the particles P in the detection area DA on the light receiving element 31.

The guiding device 40 is a device that guides the target fluid toward the detection area DA. Specifically, the guidance device 40 is a blower mechanism that generates an airflow that passes through the detection area DA. The induction device 40 is, for example, a heating element such as a heater, and generates an upward airflow due to heat generation. In order to efficiently use the updraft, in the present embodiment, the particle detection sensor 1 is arranged so that the positive direction of the Y axis shown in FIGS. 1 and 2 is vertically upward and the negative direction of the Y axis is vertically downward. Is used.

The guiding device 40 may be a small fan or the like. The guide device 40 is disposed inside the housing 10, but may be disposed outside the housing 10.

The signal processing circuit 50 calculates the mass concentration for each particle size category based on the electrical signal output from the light receiving unit 30. Specifically, the signal processing circuit 50 includes, based on the electrical signal, the first mass concentration of the first particle size section including the first particles, the first particles, and the second particles larger than the first particles. And the second mass concentration of the second particle size classification.

The first particles are specifically fine particles, and are particles having a particle size of, for example, 2.5 μm or less. In the present embodiment, the first particle size division is a small particle size division such as PM2.5, for example, and the first mass concentration is the mass concentration of PM2.5.

Specifically, the second particles are coarse particles having a particle size larger than that of the fine particles, and the particle size is, for example, 10 μm or less. In the present embodiment, the second particle size classification is a large particle size classification such as PM10, and the second mass concentration is the mass concentration of PM10. The second particle size classification may be SPM, and the second mass concentration may be the mass concentration of SPM.

The signal processing circuit 50 measures the number of particles and the particle size based on the magnitude of the peak value of the electrical signal output from the light receiving unit 30, and calculates the mass concentration for each particle size category based on the measurement result. Specifically, the signal processing circuit 50 estimates the particle size of the detected particle by comparing the peak value of the electrical signal with one or more threshold values that are predetermined to correspond to the particle size. .

In the present embodiment, the signal processing circuit 50 calculates the mass concentration of PM2.5 based on the first signal for the first period of the electrical signal, and the second signal for the second period of the electrical signal. Based on the above, the mass concentration of PM10 is calculated. The first period is, for example, a measurement period of the number of fine particles included in PM2.5 (hereinafter referred to as PM2.5 particle number). The second period is a period different from the first period, for example, a measurement period of the number of coarse particles contained in PM10 (hereinafter referred to as PM10 particle number).

That is, in the particle detection sensor 1 according to the present embodiment, measurement of the number of PM2.5 particles and measurement of the number of PM10 particles are performed in a time division manner. Specifically, the signal processing circuit 50 measures the number of particles for each particle size category by dividing and calculating the electric signal output from the light receiving unit 30 at predetermined intervals.

At this time, the signal processing circuit 50 varies the amplification factor (gain) of the electric signal output from the light receiving element 31 according to the particle size classification of the measurement target. Specifically, as shown in FIG. 4, the signal processing circuit 50 includes two amplifiers 51 and 52 and a switch 53.

FIG. 4 is a diagram showing a configuration of the signal processing circuit 50 according to the present embodiment. As shown in FIG. 4, the signal processing circuit 50 further includes three resistors 54 to 56 and an arithmetic circuit 57. The signal processing circuit 50 has a multistage configuration of two amplifiers 51.

Each of the amplifiers 51 and 52 is, for example, an operational amplifier. The light receiving element 31 is connected between the positive input terminal and the negative input terminal of the amplifier 51. The output terminal of the amplifier 51 is connected to the negative input terminal via the resistor 54. The output terminal of the amplifier 51 is further connected to the positive input terminal of the amplifier 52.

The negative input terminal of the amplifier 52 is grounded via a resistor 55. The output terminal of the amplifier 52 is connected to the negative input terminal via the resistor 56. The output terminal of the amplifier 52 is connected to the arithmetic circuit 57.

The switch 53 is provided in parallel with the resistor 56, that is, between the output terminal and the negative input terminal of the amplifier 52. By making the switch 53 conductive (ON), the output terminal and the negative input terminal of the amplifier 52 are short-circuited, so that amplification by the amplifier 52 is not performed. When the switch 53 is turned on, amplification by only the amplifier 51 is performed. In this way, the amplification factor of the electric signal can be varied by turning on / off the switch 53.

Specifically, the signal processing circuit 50 increases the amplification factor by turning off the switch 53 in the first period in which the number of PM2.5 particles is measured. For example, when the magnitude of the photocurrent output from the light receiving element 31 is I and the voltage of the output signal of the amplifier 52 is Vout, Vout when the switch 53 is turned off is expressed by the following equation (1). The

(1) Vout = Z ₁ × (1 + Z ₃ / Z ₂ ) × I

Z ₁ to Z ₃ are resistance values of the resistors 54 to 56, respectively. The amplification factor is represented by Z ₁ × (1 + Z ₃ / Z ₂ ).

When measuring the number of PM2.5 particles, since the particles that reflect the light from the light projecting element 21 are microparticles, the scattered light L2 due to the particles becomes weak. For this reason, the photocurrent output from the light receiving element 31 is reduced. Therefore, the voltage of the output signal can be increased by turning off the switch 53 and increasing the amplification factor. Thereby, the comparison between the peak value and the threshold value is facilitated, and the particle diameter can be estimated with high accuracy.

In addition, the signal processing circuit 50 reduces the amplification factor by turning on the switch 53 in the second period in which the number of PM10 particles is measured. Vout when the switch 53 is turned on is expressed by the following equation (2).

(2) Vout = Z ₁ × I

When measuring the number of PM10 particles, since the particles that reflect the light from the light projecting element 21 are coarse particles, the scattered light L2 becomes stronger than the fine particles. For this reason, the photocurrent output from the light receiving element 31 also increases. Therefore, the switch 53 may be turned on to reduce the amplification factor.

Thus, by varying the amplification factor according to the size of the particle to be measured, the range that Vout can take can be made equal regardless of the size of the particle to be measured. Thereby, it is possible to easily compare the peak value and the threshold value in the arithmetic circuit 57 in the subsequent stage.

In the present embodiment, the arithmetic circuit 57 calculates the particle size of the particles based on the peak maximum value (hereinafter referred to as the peak value) appearing in the electric signal for the first period for measuring the number of PM2.5 particles. Estimate and classify into one of multiple sub-categories. The sub-section of PM2.5 is a plurality of sub-sections in which the particle size section corresponding to PM2.5 is divided by one or more threshold values.

FIG. 5 is a diagram showing a first signal in the first period in which the number of PM2.5 particles is measured, which is an electrical signal output from the light receiving element 31 of the particle detection sensor 1 according to the present embodiment. In FIG. 5, the horizontal axis represents time, and the vertical axis represents the signal strength of the electric signal. In the present embodiment, since the electric signal output from the light receiving element 31 is converted into the voltage Vout, the vertical axis corresponds to the voltage value.

For example, as shown in FIG. 5, PM2.5 is divided into four sub-sections by four threshold values 1 to 4. Specifically, PM2.5 is, for example, a first subsection of 1.0 μm or more, a second subsection of less than 1.0 μm and 0.5 μm or more, and a third subsection of less than 0.5 μm and 0.3 μm or more. A section and a fourth sub-section smaller than 0.3 μm are included. The threshold value 4 is a threshold value for removing a noise component.

FIG. 5 shows an example in which five peaks S1 to S5 appear. Each of the peaks S1 to S5 corresponds to a change in an electric signal that appears when the light receiving element 31 receives scattered light L2 due to particles that have passed through the detection area DA. The arithmetic circuit 57 classifies the particles into any one of the first subsection to the fourth subsection of PM2.5 by comparing each peak value of the peaks S1 to S5 with the threshold value.

For example, since the peak value of peak S1 is smaller than threshold value 2 and greater than or equal to threshold value 3, the particles corresponding to peak S1 are classified into the third sub-section. Similarly, since the peak value of the peak S2 is smaller than the threshold 3 and greater than or equal to the threshold 4, the particles corresponding to the peak S2 are classified into the fourth subsection. Since the peak value of the peak S3 is smaller than the threshold value 1 and greater than or equal to the threshold value 2, the particles corresponding to the peak S3 are classified into the second sub-section. Since the peak value of each of the peaks S4 and S5 is greater than or equal to the threshold value 1, particles corresponding to each of the peaks S4 and S5 are classified into the first sub-section.

The same applies to PM10. Specifically, the arithmetic circuit 57 estimates the particle size of the particle based on the peak maximum value (peak value) appearing in the electric signal for the second period in which the number of PM10 particles is measured, Classify either. The sub-section of PM10 is a plurality of sub-sections in which the particle size section corresponding to PM10 is divided by one or more threshold values.

FIG. 6 is a diagram illustrating a second signal in the second period in which the number of PM10 particles is measured, which is an electric signal output from the light receiving element 31 of the particle detection sensor 1 according to the present embodiment. In FIG. 6, the horizontal axis represents time, and the vertical axis represents the signal strength of the electric signal. In the present embodiment, since the electric signal output from the light receiving element 31 is converted into the voltage Vout, the vertical axis corresponds to the voltage value.

For example, as shown in FIG. 6, the PM 10 is divided into four sub-sections by four threshold values A to D. Specifically, the PM 10 includes, for example, a first subsection smaller than 10 μm and 5 μm or more, a second subsection smaller than 5 μm and 2.5 μm or more, a third subsection smaller than 2.5 μm and 1.0 μm or more, and A fourth subsection smaller than 1.0 μm is included.

FIG. 6 shows an example in which five peaks Sa to Se appear. Each of the peaks Sa to Se corresponds to a change in an electrical signal that appears when the light receiving element 31 receives scattered light L2 due to particles that have passed through the detection area DA. The arithmetic circuit 57 classifies the particles into any one of the first sub-section to the fourth sub-section of the PM 10 by comparing each peak value of the peaks Sa to Se with a threshold value. The specific process is the same as in PM2.5.

Note that the number of at least one sub-section of PM2.5 and PM10 is not limited to four, and may be two or three, or five. Alternatively, the number of subsections may be one. That is, at least one of PM2.5 and PM10 may not be divided into a plurality of sub-sections.

Note that the particle detection sensor 1 according to the present embodiment actually includes many particles that pass through a portion other than the center of the detection area DA. For example, when a large particle passes through the end of the detection area DA, the light receiving intensity of the scattered light from the particle by the light receiving element 31 decreases. For this reason, although it is a large particle, the size of the particle may be erroneously determined as “small”.

In order to suppress the erroneous determination, the arithmetic circuit 57 according to the present embodiment, for example, as shown in FIG. 7, a histogram in which signal intensity (voltage value) is associated with the frequency of particles for each particle size. Is stored in memory. FIG. 7 is a histogram of particles detected by the particle detection sensor 1 according to the present embodiment. In FIG. 7, the horizontal axis represents signal intensity, and the vertical axis represents the frequency of particles for each particle size.

As shown in FIG. 7, when the signal intensity is large, most of them are particles having a large particle size. On the other hand, when the signal intensity is small, not only particles having a small particle size but also particles having a large particle size and medium particles passing through a portion other than the center of the detection area DA are included. The arithmetic circuit 57 estimates the size of the particle P corresponding to the peak by referring to the histogram shown in FIG. 7 based on the peak intensity of the electric signal.

The arithmetic circuit 57 counts the number of particles P detected during a certain operation period for each sub-section. The arithmetic circuit 57 calculates a product of a predetermined average mass and the counted number for each sub-section, and adds the calculated product for each sub-section, thereby obtaining a mass concentration of PM2.5 and PM10. Each mass concentration is calculated.

The arithmetic circuit 57 is realized by one or more electronic components including a comparator, for example. For example, the arithmetic circuit 57 may be realized by an MPU (Micro Processing Unit) or the like. The processing performed by the arithmetic circuit 57 may be realized by hardware or may be realized by software executed by a processor.

The correction circuit 60 estimates the number of particles of the second particle included in the second particle size category based on the number of particles of the first particle included in the first particle size category, and the second particle based on the estimated number of particles. Correct the mass concentration of the diameter category. Specifically, the correction circuit 60 estimates the number of coarse particles contained in PM10 based on the number of fine particles contained in PM2.5. The correction circuit 60 corrects the mass concentration of PM10 based on the estimated number of coarse particles.

In the present embodiment, the number of fine particles is the number of particles included in the sub-section having the maximum particle size among the plurality of sub-sections into which PM2.5 is divided. For example, the number of fine particles in the example shown in FIG. 5 is the number of particles included in the fourth subsection having a particle size of 1.0 μm or more.

The correction circuit 60 estimates the number of coarse particles based on the content ratio of the number of particles included in the fourth subsection. The content rate corresponds to the ratio of the number of particles included in the fourth subsection to the total number of particles corresponding to PM2.5.

In this embodiment, the correction circuit 60 roughly performs two corrections. The two corrections are a first correction for correcting the mass concentration of PM10 calculated by the signal processing circuit 50 and a second correction for adjusting the method for measuring the number of PM10 particles. Details of each correction process will be described later.

The correction circuit 60 is realized by one or more electronic components, for example. For example, the correction circuit 60 may be realized by an MPU or the like. The operation performed by the correction circuit 60 may be realized by hardware or may be realized by software executed by a processor.

[Correction process]
Below, the correction process which the correction circuit 60 performs is demonstrated.

First, the first correction for correcting the mass concentration of PM10 will be described with reference to FIG. FIG. 8 is a diagram showing the concentration distribution of each particle size of PM2.5 and PM10. In FIG. 8, the horizontal axis represents the particle size [μm], and the vertical axis represents the mass concentration.

As shown in FIG. 8, there are overlapping portions (shaded portions) in the concentration distribution of PM2.5 and the concentration distribution of PM10. An overlapping part is a part corresponded to the 4th subsection of PM2.5, for example.

There is a correlation between the concentration distribution of PM2.5 and the concentration distribution of PM10. Therefore, the number of coarse particles contained in PM10 can be estimated based on the content ratio of the number of fine particles contained in the fourth sub-section corresponding to the overlapping portion. For example, the correction circuit 60 includes a memory that stores correspondence information indicating a correspondence relationship between the content rate and the number of coarse particles. The correction circuit 60 reads the correspondence information from the memory and refers to the read correspondence information to estimate coarse particles based on the content ratio of the number of fine particles.

The correction circuit 60 corrects the mass concentration of PM10 calculated by the arithmetic circuit 57 based on the estimated number of coarse particles. For example, the correction circuit 60 corrects when a difference of a predetermined value or more occurs between the mass concentration based on the estimated number of particles and the mass concentration calculated based on the measurement result of the number of PM10 particles (that is, the actually measured number). The circuit 60 averages the estimation result and the actual measurement result, and outputs the result as a correction value of the mass concentration of PM10. The correction value may not be an average of the estimation result and the actual measurement result, and may be a weighted addition value obtained by strongly weighting the estimation result, for example.

Further, correspondence information that associates the estimated number of coarse particles with the correction value of the mass concentration may be stored in the memory. The correction circuit 60 may read out the correspondence information from the memory and refer to the read correspondence information to determine and output a correction value for the mass concentration from the estimated number of particles. The correspondence information can be generated in advance by, for example, obtaining an estimated value based on the number of PM2.5 particles in an environment where the mass concentration of PM10 is known.

Next, details of the second correction for the particle count measurement method will be described.

<Correction of measurement period (first example)>
First, a first example of correction for the particle count measurement process will be described with reference to FIG.

FIG. 9 is a diagram illustrating an example of adjustment of the measurement period of the number of coarse particles as a first example of correction of the particle detection sensor 1 according to the present embodiment. The correction circuit 60 changes the length of the second period, which is the measurement period of the number of PM10 particles, based on the estimated number of coarse particles.

In the particle detection sensor 1 according to the present embodiment, as shown in FIG. 9, the measurement of the number of fine particles, the measurement of the number of coarse particles, the calculation of the mass concentration of PM2.5, and the PM10 The calculation of the mass concentration is performed in this order. Measurement of the number of fine particles corresponds to the first period for calculating the mass concentration of PM2.5. Measurement of the number of coarse particles corresponds to a second period for calculating the mass concentration of PM10.

In this embodiment, as shown in FIG. 9, the correction circuit 60 makes the second period longer when the estimated number of particles is smaller than when the estimated number of particles is large. This makes it easy to secure a certain number or more of coarse particles to be detected (detection number), so that the number of coarse particles can be measured with high accuracy, and the mass concentration of PM10 can be calculated with high accuracy. .

In addition, when the estimated number of particles is large, it is possible to ensure a detection number of coarse particles of a certain number or more without lengthening the second period. Therefore, the number of coarse particles can be measured with high accuracy, and the mass concentration of PM10 can be calculated with high accuracy. Moreover, the time required from the measurement of the number of particles to the calculation of the mass concentration can be shortened.

<Correction of number of averaging cycles (second example)>
Next, a second example of correction for the particle count measurement process will be described with reference to FIG.

FIG. 10 is a diagram showing an example of adjusting the number of cycles for averaging in the calculation of mass concentration as a second example of correction of the particle detection sensor 1 according to the present embodiment. The correction circuit 60 changes the number of averaging cycles when calculating the mass concentration of PM10 based on the estimated number of coarse particles.

In the particle detection sensor 1 according to the present embodiment, as shown in FIG. 10, the measurement of the number of fine particles, the measurement of the number of coarse particles, the calculation of the mass concentration of PM2.5, and the PM10 The calculation of mass concentration is one cycle, and this cycle is repeated a plurality of times. The mass concentration is calculated by averaging the mass concentration calculated for each cycle for a plurality of times.

Specifically, the arithmetic circuit 57 repeats the process of calculating the mass concentration of PM10 a predetermined number of times based on the electrical signal (second signal) obtained during the measurement period of the coarse particles, and the obtained mass for the predetermined number of times. By averaging the concentration, the mass concentration of PM10 is calculated. The correction circuit 60 changes the number of cycles that is the number of times of averaging.

In the present embodiment, as shown in FIG. 10, the correction circuit 60 increases the number of cycles when the estimated number of particles is small than when the estimated number of particles is large. For example, FIG. 10 shows an example in which the number of cycles is 3 when the estimated number of particles is large, whereas the number of cycles is 6 when the estimated number of particles is small. Yes. Note that specific numerical examples of the number of cycles are not limited to these.

This makes it easy to ensure the number of detected coarse particles (number of detections) above a certain number under the assumption of averaging, so that the number of coarse particles can be accurately measured, and the mass concentration of PM10 can be accurately measured. It can be calculated well.

Note that the calculation circuit 57 is the same for the mass concentration of PM2.5. At this time, the number of cycles for averaging may be the same or different between PM2.5 and PM10. For example, the number of cycles in the case of PM2.5 may always be constant regardless of the estimated number of particles.

<Induction amount correction (third example)>
Next, a third example of correction for the particle count measurement process will be described with reference to FIG.

FIG. 11 is a diagram illustrating an adjustment example of the guidance amount of the target fluid as a third example of the correction of the particle detection sensor 1 according to the present embodiment. The correction circuit 60 changes the guidance amount of the target fluid that is guided by the guidance device 40 within the second period, which is the coarse particle measurement period.

In the present embodiment, the guidance device 40 is a blower mechanism for taking gas into the housing 10. For this reason, the correction circuit 60 changes the intake air amount as the induction amount. For example, when the induction device 40 is a resistance element and uses an upward air flow due to heat generation, the correction circuit 60 adjusts the amount of heat generated by adjusting the current flowing through the resistance element. For example, the correction circuit 60 can increase the amount of intake air by increasing the amount of heat generated by increasing the amount of heat generated by flowing a large amount of current.

As shown in FIG. 11, the correction circuit 60 increases the intake amount when the estimated number of particles is small than when the estimated number of particles is large. Thereby, since the quantity of the gas taken in by one measurement increases, the number of particles contained in gas can also be increased. Therefore, it is possible to secure a detection number of coarse particles of a certain number or more. Therefore, the number of coarse particles can be measured with high accuracy, and the mass concentration of PM10 can be calculated with high accuracy.

In the second correction of the PM10 particle count measurement method, all of the first to third examples described above may be performed, or only one may be performed. In addition, both the second correction of the PM10 particle number measurement method and the first correction of the mass concentration of PM10 may be performed, or only one of them may be performed.

[Effects, etc.]
As described above, the particle detection sensor 1 according to the present embodiment is a particle detection sensor that detects particles contained in a target fluid, and includes a light projecting unit 20 that emits light toward the detection area DA, and a light projecting unit. A light receiving unit 30 that has light receiving sensitivity with respect to the light L1 emitted from the light unit 20, and that generates and outputs an electrical signal by photoelectrically converting the scattered light L2 of the light passing through the detection area DA. . The particle detection sensor 1 further includes a first mass concentration (for example, a mass concentration of PM2.5) of the first particle size classification in which the fine particles are included based on the electrical signal, the fine particles and the coarser than the fine particles. The signal processing circuit 50 that calculates the second mass concentration (for example, the mass concentration of PM10) of the second particle size classification in which the particles are included, and the number of coarse particles are estimated based on the number of fine particles, and estimated And a correction circuit 60 for correcting the second mass concentration based on the number of particles obtained.

This makes it possible to easily measure the number of particles of a certain number or more and estimate the number of coarse particles based on the number of fine particles measured with high accuracy, thus increasing the accuracy of estimating the number of coarse particles. According to the present embodiment, since the mass concentration of PM10 is corrected based on the estimation result, the measurement accuracy of the mass concentration of PM10 is also improved. Therefore, not only PM2.5 but also the mass concentration of PM10 can be accurately measured. Thus, according to particle detection sensor 1 concerning this embodiment, the mass concentration of a plurality of particle size divisions can be measured with high accuracy.

Further, for example, the number of fine particles is the number of particles included in the sub-section having the maximum particle size among the plurality of sub-sections obtained by dividing the first particle size section. The correction circuit 60 estimates the number of coarse particles based on the content of the number of fine particles.

Thereby, since there is a correlation between the content ratio of the number of particles in the sub-section of the maximum particle size of PM2.5 and the number of coarse particles contained in PM10, the particles of coarse particles are based on the correlation. The number can be estimated with high accuracy. Since the estimation accuracy of the number of coarse particles is increased, the measurement accuracy of the mass concentration of PM10 is also increased. Therefore, not only PM2.5 but also the mass concentration of PM10 can be accurately measured.

Further, for example, the signal processing circuit 50 calculates the mass concentration of PM2.5 based on the first signal for the first period of the electric signal, and for the second period different from the first period of the electric signal. Based on the second signal, the mass concentration of PM10 is calculated.

Thereby, the mass concentration of PM2.5 and the mass concentration of PM10 can be calculated in time series. Since the actual measurement value of the mass concentration of PM10 is obtained, the accuracy of correction is improved. Therefore, not only PM2.5 but also the mass concentration of PM10 can be accurately measured.

For example, the correction circuit 60 corrects the mass concentration of PM10 calculated based on the second signal based on the estimated number of particles as correction.

Thereby, since the calculation result of the mass concentration of PM10 is corrected, the mass concentration of PM10 can be accurately measured.

Also, for example, the correction circuit 60 changes the length of the coarse particle measurement period based on the estimated number of particles as a correction.

This makes it possible to lengthen the time required for measuring coarse particles, so that it is easy to secure a certain number of coarse particles or more. Therefore, not only PM2.5 but also the mass concentration of PM10 can be accurately measured.

Further, for example, the signal processing circuit 50 repeats the process of calculating the mass concentration of PM10 based on the second signal a predetermined number of times, and averages the obtained mass concentration for the predetermined number of times, thereby obtaining the mass concentration of PM10. calculate. The correction circuit 60 changes the number of repetitions (that is, the number of cycles) as correction.

This makes it possible to lengthen the averaging cycle when calculating the mass concentration of PM10, so that it is easy to secure a certain number of coarse particles. Therefore, not only PM2.5 but also the mass concentration of PM10 can be accurately measured.

For example, the particle detection sensor 1 further includes a guidance device 40 that guides the target fluid toward the detection area DA. The correction circuit 60 changes the induction amount of the target fluid induced by the induction device 40 within the second period as correction.

This increases the amount of gas induced when measuring the number of coarse particles, so that it is easy to secure a certain number of coarse particles or more. Therefore, not only PM2.5 but also the mass concentration of PM10 can be accurately measured.

(Other)
As mentioned above, although the particle | grain detection sensor which concerns on this invention was demonstrated based on said embodiment, this invention is not limited to said embodiment.

For example, in the above embodiment, the case where the target fluid is a gas has been described. However, the present invention is not limited to this. The target fluid may be a liquid such as water. The particle detection sensor 1 detects particles contained in a liquid such as water and calculates a mass concentration. At this time, the particle detection sensor 1 has a waterproof mechanism that prevents the signal processing circuit 50 attached to the outer surface of the housing 10 from coming into contact with the liquid. The waterproof mechanism is, for example, a metal shield member provided so as to cover the signal processing circuit 50. The shield member is fixed to the housing 10 without a gap by, for example, welding.

Further, for example, the particle detection sensor 1 does not need to measure the number of PM10 particles. Specifically, the signal processing circuit 50 may perform measurement of fine particles, calculation of the mass concentration of PM2.5, and calculation of the mass concentration of PM10 in this order. In the calculation of the mass concentration of PM10, the mass concentration of PM10 may be calculated using the number of coarse particles estimated based on the content rate of the number of fine particles contained in PM2.5.

Further, for example, the correction circuit 60 may estimate the number of coarse particles based on the total number of fine particles contained in PM2.5 instead of the subclass of the maximum particle size of PM2.5.

For example, the particle detection sensor 1 may not include the guidance device 40. For example, the particle detection sensor 1 may be arranged in a place where the airflow is flowing in a certain direction so that the inlet 11 is located upstream of the airflow and the outlet 12 is located downstream.

Further, for example, in the above-described embodiment, the example in which each of the light projecting unit 20 and the light receiving unit 30 includes a lens is shown, but the present invention is not limited thereto. For example, at least one of the light projecting unit 20 and the light receiving unit 30 may include a mirror (reflector) instead of the lens.

In addition, the particle | grain detection sensor 1 is mounted in various household appliances, such as an air conditioner, an air cleaner, and a ventilation fan, for example. Various home appliances may control the operation according to the mass concentration of the particles detected by the particle detection sensor 1. For example, the air cleaner may increase the operating strength (specifically, the air purifying power) when the mass concentration of the particles is larger than a predetermined threshold.

In addition, the embodiment can be realized by arbitrarily combining the components and functions in each embodiment without departing from the scope of the present invention, or a form obtained by subjecting each embodiment to various modifications conceived by those skilled in the art. Forms are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 Particle detection sensor 20 Light projection part 30 Light reception part 40 Guidance device 50 Signal processing circuit 60 Correction circuit DA Detection area | region L1 Light L2 Scattered light

Claims (7)

A particle detection sensor for detecting particles contained in a target fluid,
A light projecting unit that emits light toward the detection region;
A light receiving unit that has light receiving sensitivity with respect to the light emitted from the light projecting unit, and generates and outputs an electrical signal by photoelectrically converting the scattered light of the light from the particles passing through the detection region;
Based on the electrical signal, the first mass concentration of the first particle size segment including the first particles and the second mass of the second particle size segment including the first particles and second particles larger than the first particles. A signal processing circuit for calculating the mass concentration;
A particle detection sensor comprising: a correction circuit that estimates the number of particles of the second particle based on the number of particles of the first particle and corrects the second mass concentration based on the estimated number of particles. The number of particles of the first particle is the number of particles included in the sub-section of the maximum particle size among the plurality of sub-sections into which the first particle size section is divided
The particle detection sensor according to claim 1, wherein the correction circuit estimates the number of particles of the second particle based on a content ratio of the number of particles of the first particle. The signal processing circuit includes:
Based on the first signal for the first period of the electrical signal, the first mass concentration is calculated,
The particle detection sensor according to claim 1, wherein the second mass concentration is calculated based on a second signal for a second period different from the first period in the electrical signal. The particle detection sensor according to claim 3, wherein the correction circuit corrects the second mass concentration calculated based on the second signal based on the estimated number of particles as the correction. The particle detection sensor according to claim 3, wherein the correction circuit changes the length of the second period based on the estimated number of particles as the correction. The signal processing circuit calculates the second mass concentration by repeating the process of calculating the second mass concentration based on the second signal a predetermined number of times and averaging the obtained mass concentrations for the predetermined number of times. And
The particle detection sensor according to claim 3, wherein the correction circuit changes the predetermined number of times as the correction. And a guidance device for guiding the target fluid toward the detection region,
The particle detection sensor according to claim 3, wherein the correction circuit changes, as the correction, an induced amount of the target fluid that is induced by the guidance device within the second period.

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