WO2019044250A1

WO2019044250A1 - Particle detection sensor

Info

Publication number: WO2019044250A1
Application number: PCT/JP2018/027221
Authority: WO
Inventors: 吉祥永谷; 貴司中川; 圭子川人; 則之安池
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2017-08-29
Filing date: 2018-07-20
Publication date: 2019-03-07
Also published as: JPWO2019044250A1; CN111051851A; KR20200027028A; KR102327743B1; CN111051851B; JP7008252B2

Abstract

A particle detection sensor (1) that detects a plurality of particles contained in a subject to be measured is provided with: a light projection unit (20) that outputs light toward a detection region (DA); a light receiving unit (30) which, in the cases where a particle to be detected, i.e., at least one of the particles, passes through the detection region (DA), receives light scattered by the particle; a housing (10), which houses the light projection unit (20) and the light receiving unit (30), and which has the detection region (DA) inside; and a signal processing circuit (50). The signal processing circuit (50) acquires the amount of intensity change of stray light over time, said stray light having been received by the light receiving unit (30) when the particles were not passing through the detection region (DA), then, on the basis of the acquired change amount over time, the signal processing circuit corrects the intensity of the scattering light thus received, and on the basis of corrected intensity of the scattering light thus received, classifies the particle into any one of the groups of a plurality of particle sizes, and identifies the number of detected particles, thereby calculating the mass concentration of the particles contained in the subject to be measured.

Description

Particle detection sensor

The present invention relates to a particle detection sensor.

BACKGROUND Conventionally, there is known a photoelectric particle detection sensor that includes a light emitting element and a light receiving element, detects particles suspended on a measurement target, and calculates a mass concentration of the particles included in the measurement target (for example, patent documents See 1). In the photoelectric particle detection sensor, light is emitted from the light emitting element toward the detection area, and when the particles pass through the detection area, the light receiving element receives scattered light of light by particles passing through. The size of the particles is determined based on the received light intensity of the scattered light, and the mass concentration of the particles contained in the measurement object is calculated from the size and the number of the particles.

JP, 2015-210183, A

However, in the above-mentioned prior art, when the inside of the particle detection sensor is dirty, for example, when the particles adhere to at least one of the light emitting element and the light receiving element, the light should be originally irradiated to the detection area and the light originally enters the light receiving element. The scattered light that is to be blocked by the attached particles is reduced respectively. In addition, light that is scattered by attached particles and that should not be originally incident on the light receiving element may be incident on the light receiving element. In either case, it causes false detection of particle size, and detection accuracy decreases.

Therefore, an object of the present invention is to provide a particle detection sensor capable of detecting the size of particles with high accuracy and calculating the mass concentration of particles contained in the measurement object with high accuracy.

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 a plurality of particles included in a measurement target, and a light projecting unit that emits light toward a detection region A light receiving unit for receiving scattered light of the light by the target particle when the target particle which is at least one of the plurality of particles passes through the detection area; and the light emitting unit and the light receiving unit. And a signal processing circuit, the signal processing circuit receiving light intensity of stray light received by the light receiving unit when the plurality of particles do not pass through the detection region. The temporal change amount of the target particle is acquired, the light reception intensity of the scattered light is corrected based on the acquired temporal change amount, and the target particle is subjected to any of a plurality of particle sizes based on the light reception intensity of the scattered light corrected. Classified into crabs, One, by identifying the number of detected target particles, to calculate the mass concentration of the particles contained in the measurement target.

According to the particle detection sensor according to the present invention, it is possible to accurately detect the size of particles and accurately calculate the mass concentration of particles contained in the measurement object even in a state in which the inside of the particle detection sensor is dirty with time. it can.

FIG. 1 is a perspective view of a particle detection sensor according to an embodiment. FIG. 2 is a perspective view when the lid of the particle detection sensor according to the embodiment is opened. FIG. 3 is a cross-sectional view of the particle detection sensor according to the embodiment. FIG. 4 is an enlarged cross-sectional view for explaining the operation of the particle detection sensor according to the embodiment. FIG. 5 is a diagram showing an electrical signal output from the light receiving element during the operation shown in FIG. FIG. 6 is a view for explaining classification of particles by size by the particle detection sensor according to the embodiment. FIG. 7 is a histogram of particles detected by the particle detection sensor according to the embodiment. FIG. 8 is an enlarged cross-sectional view for explaining an operation when particles adhere to the light emitting unit and the light receiving unit of the particle detection sensor according to the embodiment. FIG. 9 is a diagram showing an electrical signal output from the light receiving element during the operation shown in FIG. FIG. 10 is a diagram showing correction processing of the electric signal shown in FIG. FIG. 11 is a diagram illustrating an example of timing when the particle detection sensor according to the embodiment acquires the amount of change with time. FIG. 12 is a diagram illustrating another example of the timing at which the particle detection sensor according to the embodiment acquires the amount of change with time.

Below, the particle | grain detection sensor which concerns on embodiment of this invention is demonstrated in detail using drawing. Each embodiment described below shows one specific example of the present invention. Therefore, numerical values, shapes, materials, components, arrangements 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 components in the following embodiments, components that are not described in the independent claims indicating the highest concept of the present invention are described as optional components.

Further, each drawing is a schematic view, and is not necessarily illustrated exactly. Therefore, for example, the scale and the like do not necessarily match in each figure. Further, in each of the drawings, substantially the same configuration is given the same reference numeral, and overlapping description will be omitted or simplified.

Embodiment
The particle detection sensor according to the present embodiment detects the size of particles based on the received light intensity of light scattered by the particles passing through the detection area, and calculates the mass concentration of the particles contained in the measurement target. Particle detection sensor of the formula. The particle detection sensor is a light that should be originally irradiated to the detection area and a scattering that should originally be incident on the light receiving element based on the amount of time-dependent change of the received light intensity of the stray light received when the particles are not passing The variation of the light intensity is estimated and corrected, the particle size is accurately detected based on the corrected scattered light intensity, and the mass concentration of the particles included in the measurement object is calculated.

[Constitution]
First, a particle detection sensor 1 according to the present embodiment will be described using FIGS. 1 to 4.

FIG. 1 is a perspective view of a particle detection sensor 1 according to the present embodiment. FIG. 2 is a perspective view when the lid 13 of the particle detection sensor 1 according to the present embodiment is opened. The lid 13 is opened for the purpose of cleaning the inside of the housing 10, for example, while the particle detection sensor 1 is not operated.

FIG. 3 is a cross-sectional view of the particle detection sensor 1 according to the present embodiment. Specifically, FIG. 3 shows a cross section parallel to the XY plane at substantially the center of the casing 10 of the particle detection sensor 1 in the Z-axis direction.

FIG. 4 is an enlarged sectional view for explaining the operation of the particle detection sensor 1 according to the present embodiment. Specifically, FIG. 4 is an enlarged view of a portion including the detection area DA in the cross section shown in FIG.

The X-axis, the Y-axis, and the Z-axis indicate 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 included in a measurement target. In the present embodiment, the measurement target is a gas such as air (atmosphere). The particles P are fine particles on the order of micrometers suspended in a gas, that is, particulate matter (aerosol). Specifically, the particles P are PM 2.5, suspended particulate matter (SPM: Suspended Particulate Matter), PM 10 and the like.

As shown in FIGS. 1 to 3, the particle detection sensor 1 includes a housing 10, a light projecting unit 20, a light receiving unit 30, a blower mechanism 40, a signal processing circuit 50, and a control circuit 60. Since the signal processing circuit 50 and the control circuit 60 do not appear in the cross section shown in FIG. 3, the signal processing circuit 50 and the control circuit 60 are schematically shown in FIG. The signal processing circuit 50 and the control circuit 60 are attached to, for example, the outer surface of the housing 10 on the opposite side to the lid 13 or the like.

The housing 10 accommodates the light emitting unit 20 and the light receiving unit 30 and has a detection area DA inside. 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 inlet 11 for allowing gas to flow therein, and an outlet 12 for allowing the gas to flow out. As indicated by thick dashed arrows in FIG. 3, a path from the inlet 11 to the outlet 12 in the inside of the housing 10 corresponds to a gas flow path. Although the example in which the flow path of gas is formed in L shape is shown in FIG. 3, it may be formed in linear form which connects the inflow port 11 and the outflow port 12.

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

Inside the housing 10, a light trap structure may be provided to attenuate stray light by multiple reflection. Stray light is light other than the scattered light L2 (see FIG. 4) which is not scattered by the particles P passing through the detection area DA among the light L1 (see FIG. 4) emitted from the light projection unit 20 The light of The light trap structure can also attenuate external light that has entered from the inlet 11 or the outlet 12.

As shown in FIG. 1, the housing 10 has a lid 13 which can be opened and closed. The lid 13 is detachably fixed so as to close an opening 14 (see FIG. 2) provided in the housing 10. The user can open and close the lid 13 as needed.

The opening 14 is a cleaning window for exposing the inside of the housing 10 to the outside when the lid 13 is opened and removing particles adhering to the inside of the housing 10. For example, the user inserts a cleaning rod or the like into the opening 14 to remove particles attached to the lens 22 of the light emitting unit 20, the lens 32 of the light receiving unit 30, and the detection area DA. The size and shape of the lid 13 and the opening 14 are not particularly limited. Although the lid 13 and the opening 14 are provided at positions overlapping with the detection area DA when viewed in the Z-axis direction, the present invention is not limited thereto.

The light projecting unit 20 emits the light L1 toward the detection area DA. As shown in FIGS. 3 and 4, the light projecting unit 20 includes a light emitting 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 emitting element 21 may be a light emitting diode (LED) or an organic electroluminescent (EL) element.

The light L1 emitted by the light emitting 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 driven by DC, but is not limited thereto.

The lens 22 is disposed between the light emitting 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 emitting element 21 on the detection area DA.

When the target particle which is at least one of the plurality of particles P passes through the detection area DA, the light receiving unit 30 receives the scattered light L2 of the light L1 by the target particle. As shown in FIGS. 3 and 4, 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, such as a photodiode, a phototransistor, or a photomultiplier, which converts received light into an electric signal. The light receiving element 31 outputs a current signal according to the light receiving intensity of the received light. The light receiving element 31 is sensitive to the wavelength band of the light L1 emitted by the light emitting element 21.

The light receiving element 31 receives the scattered light L2 of the light L1 by the particles P passing through the detection area DA. Furthermore, the light receiving element 31 receives stray light. Stray light is light that enters the light receiving element 31 when the particle P has not passed through the detection area DA. Specifically, the stray light is light other than the scattered light L2 of the light by the particle P passing through the detection area DA, and corresponds to a noise component. That is, stray light is light which should not be received originally. The stray light includes scattered light L3 (see FIG. 8) and the like by particles attached to the light projecting unit 20.

The light receiving element 31 is arrange | positioned in the position where direct light of light L1 which the light emitting element 21 radiate | emitted does not inject, as shown in FIG. Specifically, the light receiving element 31 is disposed at a position not overlapping the optical axis of the light emitting element 21. The optical axis of the light emitting element 21 corresponds to the path of the light with the strongest intensity among the light L1 emitted by the light emitting element 21. Specifically, the optical axis of the light emitting element 21 corresponds to a straight line connecting the light emitting element 21 and the detection area DA. In the present embodiment, the light receiving element 31 is disposed such that the optical axis of the light receiving element 31 intersects the optical axis of the light emitting 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 condenses the scattered light L2 scattered by the particles P in the detection area DA on the light receiving element 31.

The blower mechanism 40 generates an air flow passing through the detection area DA. The blower mechanism 40 is, for example, a heating element such as a heater, and generates an updraft by heat generation. In the present embodiment, the particle detection sensor 1 is configured such that the positive direction of the Y axis shown in FIGS. 1 to 3 is vertically upward and the negative direction of the Y axis is vertically downward in order to efficiently use the rising air flow. It is used by standing.

The blower mechanism 40 may be a small fan or the like. The blower mechanism 40 is disposed inside the housing 10, but may be disposed outside the housing 10.

The signal processing circuit 50 acquires the temporal change amount of the light reception intensity of the stray light received by the light receiving unit 30 when the plurality of particles P do not pass through the detection area DA. The signal processing circuit 50 corrects the light reception intensity of the scattered light L2 based on the acquired temporal change amount. The signal processing circuit 50 classifies the target particles into any of a plurality of particle sizes based on the corrected light reception intensity of the scattered light L2, and specifies the number of detected target particles to obtain a gas. The mass concentration of the particles P contained is calculated. Specific processing of the signal processing circuit 50 will be described later. The signal processing circuit 50 outputs the calculated mass concentration to an external device as a sensor output value.

The signal processing circuit 50 is realized by, for example, one or more electronic components. For example, the signal processing circuit 50 is realized by an MPU (Micro Processing Unit) or the like.

The control circuit 60 stops the operation of the blower mechanism 40 when the signal processing circuit 50 acquires the temporal change amount. Specifically, the control circuit 60 stops the operation of the blower mechanism 40 at the timing when the signal processing circuit 50 acquires the temporal change amount. The signal processing circuit 50 changes over time based on the received light intensity of the stray light received by the light receiving unit 30 after waiting for a predetermined period until the air flow in the housing 10 becomes sufficiently small after the operation of the blower mechanism 40 is stopped. Get the amount.

The control circuit 60 is realized by, for example, one or more electronic components. For example, the control circuit 60 is realized by an MPU or the like. The control circuit 60 may be realized by the same hardware configuration as the signal processing circuit 50.

[Operation]
Subsequently, the operation of the particle detection sensor 1 will be described using FIGS. 4 and 5.

As shown in FIG. 4, in the particle detection sensor 1, the light emitting element 21 always emits the light L <b> 1 during the operation period. When the particle P passes through the detection area DA, the light receiving element 31 receives the scattered light L2 by the particle P passing through. The particles P passing through are target particles to be detected by the particle detection sensor 1.

FIG. 5 is a diagram showing an electrical signal output from the light receiving element 31 during the operation shown in FIG. In FIG. 5, the horizontal axis is time, and the vertical axis is signal strength.

As shown in FIG. 5, the signal intensity of the electrical signal output from the light receiving element 31 has a substantially constant noise level when particles are not detected. The noise level is generated in the housing 10 and corresponds to the light amount of stray light which may be incident on the light receiving element 31 (hereinafter, simply referred to as “stray light amount”). When the scattered light L2 is incident on the light receiving element 31, a peak S corresponding to the light reception intensity of the scattered light L2 appears in the electric signal.

In the present embodiment, the signal processing circuit 50 classifies the size of the particles P based on the received light intensity of the scattered light L2. Specifically, the signal processing circuit 50 classifies the size of the particles P based on the size of the peak corresponding to the received light intensity of the scattered light L2.

FIG. 6 is a view for explaining classification of each size of particles P by 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 intensity of the electrical signal output from the light receiving element 31, specifically, the intensity of the received light. FIG. 6 shows the relationship between the light reception intensity of the scattered light by the particle P and the size of the particle when the particle P passes through the center of the detection area DA.

When the particle P passes through the detection area DA during the operation period, the scattered light L2 by the particle P passing through is incident on the light receiving element 31. Therefore, the current signal output from the light receiving element 31 has a large signal strength. For example, as shown in FIG. 6, every time the particle P passes through the detection area DA, peaks S1 to S3 of the current signal are detected.

The size of the peak depends on the size of the particle P passing through the detection area DA, that is, the particle P that has generated the scattered light L2. Specifically, as the particle P is larger, the light reception intensity of the scattered light L2 is larger, and the signal intensity is larger. The smaller the particle P, the smaller the received light intensity of the scattered light L2, and the smaller the signal intensity.

The signal processing circuit 50 classifies the particles P by size based on the magnitude of the signal intensity. For example, as shown in FIG. 6, the signal processing circuit 50 classifies the particles P into three sizes of “large particle”, “medium particle” and “small particle” based on the magnitude of the signal intensity. The number of classifications of the particles P is not limited to three, and may be two, or four or more.

In the particle detection sensor 1 according to the present embodiment, in practice, a large number of particles passing through a portion other than the center of the detection area DA are also included. For example, when a large particle passes the end of the detection area DA, the intensity of light received by the light receiving element 31 of the scattered light by the particle decreases. For this reason, despite being large particles, the size of the particles may be misjudged as being "small particles".

The signal processing circuit 50 according to the present embodiment holds, for example, a histogram as shown in FIG. 7 in which the signal intensity is associated with the frequency of particles for each size of particles in order to suppress the erroneous determination. ing. FIG. 7 is a histogram of particles P detected by the particle detection sensor 1 according to the present embodiment. In FIG. 7, the horizontal axis is the signal intensity, and the vertical axis is the frequency of particles per particle size.

As shown in FIG. 7, when the signal strength is high, most of them are large particles. On the other hand, when the signal intensity is small, not only small particles but also large particles and medium particles which pass through a portion other than the center of the detection area DA are included. The signal processing circuit 50 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 electrical signal.

The signal processing circuit 50 counts the number of particles P detected during a predetermined operation period for each size. The signal processing circuit 50 calculates the product of the predetermined average mass and the counted number for each size, and adds the product for each calculated size, so that the particles included in the measurement target during the operation period Calculate the mass concentration of

Subsequently, a case where particles adhere to the light emitting unit 20 and the light receiving unit 30 will be described.

FIG. 8 is an enlarged cross-sectional view for explaining the operation when particles adhere to the light emitting unit 20 and the light receiving unit 30 of the particle detection sensor 1 according to the present embodiment. Similar to FIG. 4, FIG. 8 is an enlarged view of a portion including the detection area DA in the cross section shown in FIG. 3.

As shown in FIG. 8, the particle detection sensor 1 calculates a mass concentration of the particles P in the gas by taking in a gas containing a plurality of particles P into the inside of the housing 10. The particles P taken into the inside of the housing 10 are not all released from the outlet 12, but a part thereof adheres to the inside of the housing 10. As the operation period of the particle detection sensor 1 becomes longer, the amount of particles adhering to the inside of the housing 10 increases and the amount of stray light also increases.

At this time, like the particles P1 and P2 shown in FIG. 8, the particles also adhere to the lens 22 of the light emitting unit 20 and the lens 32 of the light receiving unit 30.

The particles P1 attached to the lens 22 of the light emitting unit 20 may block part of the light emitted from the light emitting element 21. Therefore, the light L1 reaching the detection area DA is attenuated. As the light L1 reaching the detection area DA is attenuated, the scattered light L2 by the particles P passing through the detection area DA is also attenuated. The particles P2 attached to the lens 32 of the light receiving unit 30 may block the scattered light L2 from the particles P. Therefore, the scattered light L2 reaching the light receiving element 31 is attenuated.

Therefore, as shown in FIG. 9, the peak of the electrical signal corresponding to the scattered light L2 has a signal strength smaller than that of the original peak. The original peak is a peak due to the scattered light L2 when no particle is attached to the light emitting unit 20 and the light receiving unit 30 (specifically, in the case shown in FIG. 4).

Here, FIG. 9 is a diagram showing an electrical signal output from the light receiving element 31 during the operation shown in FIG. In FIG. 9, the horizontal axis is time, and the vertical axis is signal strength. In FIG. 9, the broken line represents the signal strength of the original peak.

The particles P1 may scatter part of the light emitted from the light emitting element 21. A part of the scattered light L3 due to the particles P1 may be incident on the light receiving element 31. The particles P1 generally remain attached to the lens 22 unless removed by the cleaning operation. For this reason, a part of the scattered light L3 by the particles P1 always enters the light receiving element 31 as stray light.

Therefore, as shown in FIG. 9, the noise level of the electric signal output from the light receiving element 31, that is, the amount of stray light rises. In FIG. 9, the original noise level is indicated by an alternate long and short dash line.

As described above, when particles adhere to the light emitting unit 20 and the light receiving unit 30, both a decrease in the signal intensity of the scattered light L2 to be detected and an increase in the noise level, that is, the stray light amount occur. The same applies to the case where particles adhere to the detection area DA.

Therefore, in the particle detection sensor 1 according to the present embodiment, the signal processing circuit 50 acquires the temporal change amount of the light reception intensity of the stray light, and corrects the light reception intensity of the scattered light L2 based on the acquired temporal change amount. . The signal processing circuit 50 calculates the mass concentration of the particles P contained in the gas, based on the corrected received light intensity of the scattered light L2.

FIG. 10 is a diagram showing correction processing of the electric signal shown in FIG. In FIG. 10, the horizontal axis is time, and the vertical axis is signal strength. As shown in FIG. 10, the signal processing circuit 50 subtracts the rise amount of the noise level from the signal strength of the peak Sa before correction, and then multiplies the corrected peak by the correction coefficient to generate the original peak Sb. Do. The rise amount of the noise level shown in FIG. 10 corresponds to the time-dependent change amount of the received light intensity of the stray light.

Since the scattered light L3 by these particle | grains increases, so that there are many particle | grains adhering to the light projection part 20 or the light reception part 30, the amount of time-dependent change becomes large. In addition, as the number of particles attached to the light emitting unit 20 or the light receiving unit 30 increases, the light L1 that should originally reach the detection area DA and the scattered light L2 by the particles P passing through the detection area DA decrease. Therefore, the larger the amount of change over time, the larger the amount of decrease in the signal intensity of the original scattered light L2. Also, the smaller the amount of change over time, the smaller the amount of decrease in the signal intensity of the original scattered light L2.

Therefore, the signal processing circuit 50 corrects the peak Sa having a large decrease in signal intensity to the original peak Sb by increasing the correction coefficient as the time-dependent change of the light reception intensity of stray light increases. Further, the signal processing circuit 50 corrects the peak Sa having a small amount of decrease in the signal intensity to the original peak Sb by reducing the correction coefficient as the amount of temporal change in light reception intensity of the stray light decreases.

As described above, in the particle detection sensor 1 according to the present embodiment, the temporal change amount of the light reception intensity of the stray light is acquired, and the light reception intensity of the scattered light L2 is corrected based on the acquired temporal change amount. Thereby, calculation accuracy of mass concentration of particles P can be raised.

Note that the signal processing circuit 50 may correct the light reception intensity of the scattered light not only based on the temporal change amount of the light reception intensity of the stray light but also on the degree of deterioration of the light emitting element 21. For example, when the intensity of the light L1 output from the light emitting element 21 is reduced due to the aged deterioration, the intensity of the scattered light L2 by the particles P is also reduced.

Therefore, the signal processing circuit 50 may acquire the decrease amount of the intensity of the light output from the light emitting element 21 and correct the light reception intensity of the scattered light L2 based on the acquired decrease amount. Specifically, the signal processing circuit 50 corrects the peak with a large decrease in signal intensity to the original peak by increasing the correction coefficient as the decrease in intensity of the light output from the light emitting element 21 is larger. You may The signal processing circuit 50 may correct the peak having a small amount of decrease in signal intensity to the original peak by reducing the correction coefficient as the amount of decrease in intensity of light output from the light emitting element 21 is smaller.

[When to acquire the amount of change over time]
Subsequently, the timing for acquiring the temporal change amount of the light reception intensity of the stray light will be described.

FIG. 11 is a diagram showing an example of timing when the particle detection sensor 1 acquires the amount of change with time in the present embodiment. In FIG. 11, the horizontal axis is the operation time, and the vertical axis is the received light intensity of the stray light (ie, the stray light amount).

As shown in FIG. 11, as the operation time of the particle detection sensor 1 increases, the amount of particles adhering to the inside of the housing 10 increases, and the stray light amount also increases. The operating time and the stray light amount have, for example, a linear relationship.

Therefore, in the present embodiment, the signal processing circuit 50 acquires the amount of change over time each time a predetermined period elapses. In FIG. 11, the timing at which the temporal change amount is acquired is indicated by a broken line. The signal processing circuit 50 corrects the light reception intensity of the scattered light L2 based on the amount of change with time obtained at the timing shown in FIG. Specifically, when acquiring the temporal change amount at the first timing, the signal processing circuit 50 acquires the temporal change amount until the operation time reaches the second timing which is the next acquisition timing. The light reception intensity of the scattered light L2 is corrected based on the temporal change amount. The accuracy of the correction can be enhanced by setting the time from the first timing to the second timing short.

Alternatively, the signal processing circuit 50 may acquire the time-dependent change amount based on the time accumulation value of mass concentration instead of the operation time. FIG. 12 is a diagram showing another example of the timing at which the particle detection sensor 1 according to the present embodiment acquires the amount of change with time. In FIG. 12, the horizontal axis is the time cumulative value of mass concentration, and the vertical axis is the received light intensity of stray light.

The signal processing circuit 50 calculates a time cumulative value of mass concentration. When the mass concentration is calculated, the signal processing circuit 50 stores the calculated value as a time accumulation value in a memory (not shown). The signal processing circuit 50 repeatedly calculates, for example, the mass concentration periodically. Therefore, whenever the mass concentration is calculated, the time accumulation value is read from the memory, and the read time accumulation value and the newly calculated value are added. Do. The signal processing circuit 50 stores the value after the addition in the memory as a new time accumulation value.

As shown in FIG. 12, as the time cumulative value of mass concentration increases, the amount of particles adhering to the inside of the housing 10 increases, and the amount of stray light also increases. The time accumulation value and the stray light amount have, for example, a linear relationship.

Therefore, the signal processing circuit 50 increases the amount of change over time every time the amount of increase from the amount of time accumulation when the calculated amount of time accumulation is obtained immediately before the calculated amount of increase over time reaches a predetermined threshold. You may get it. In FIG. 12, the timing for acquiring the temporal change amount is indicated by a broken line. The signal processing circuit 50 corrects the received light intensity of the scattered light based on the amount of change with time obtained at the timing shown in FIG.

In the present embodiment, as shown in FIGS. 1 and 2, the case 10 is provided with a lid 13 and an opening 14 for removing particles adhering to the inside. When the attached particles are removed, the amount of stray light due to the attached particles is sufficiently reduced.

Therefore, the signal processing circuit 50 further initializes the amount of change over time when the lid 13 is opened and then closed. For example, the lid 13 is opened by the user to clean the interior of the housing 10, and after particles are removed, the lid 13 is closed again. By removing the particles, the amount of stray light is reduced. The signal processing circuit 50 initializes the amount of change over time when the stray light amount (that is, the noise level) decreases to a predetermined threshold value or less based on the electrical signal output from the light receiving element 31.

Alternatively, the particle detection sensor 1 may be provided with an open / close sensor for detecting the open / close of the lid 13. In this case, the signal processing circuit 50 initializes the amount of change over time when the lid 13 is closed based on the output signal output from the open / close sensor. Alternatively, the particle detection sensor 1 may be provided with a user interface such as a physical button for receiving the completion of cleaning from the user.

[Effect, etc.]
As described above, the particle detection sensor 1 according to the present embodiment is a particle detection sensor that detects a plurality of particles P included in the measurement target, and a light projection unit that emits the light L1 toward the detection area DA 20, a light receiving unit 30 for receiving the scattered light L2 of the light L1 by the target particle when the target particle which is at least one of the plurality of particles P passes the detection area DA, the light projecting unit 20, and the light receiving unit And a signal processing circuit 50. The housing 10 has a detection area DA therein. The signal processing circuit 50 acquires the temporal change amount of the light reception intensity of the stray light received by the light receiving unit 30 when the plurality of particles P do not pass through the detection area DA, and based on the acquired temporal change amount, scattered light By correcting the light reception intensity of L2, classifying the target particles into any of a plurality of particle sizes based on the corrected light reception intensity of the scattered light L2, and specifying the number of detected target particles, Calculate the mass concentration of particles contained in the measurement object.

Thereby, the light reception intensity of the scattered light L2 is corrected by taking into consideration the increase amount and the decrease amount of the signal intensity caused by the particles adhering to the inside of the housing 10 by acquiring the temporal change amount of the stray light. be able to. The particle detection sensor 1 calculates the mass concentration based on the corrected received light intensity of the scattered light L2, so that the mass concentration of the particles can be accurately calculated.

Also, for example, the signal processing circuit 50 acquires the temporal change amount each time a predetermined period elapses.

Thereby, since the temporal change amount can be updated regularly, the accuracy of mass concentration calculation can be always maintained high.

In addition, for example, the signal processing circuit 50 further calculates the time accumulation value of the calculated mass concentration, and is an increase amount of the calculated time accumulation value, which is obtained from the time accumulation value when acquiring the last time change amount. The amount of change over time may be acquired each time the amount of increase reaches a predetermined threshold.

Thereby, since the time accumulation value of mass concentration corresponds to the accumulated amount of particles having passed through the inside of the housing 10, update the amount of change over time each time the amount of particles adhering to the inside of the housing 10 increases. Can. Therefore, the particle detection sensor 1 can always maintain high accuracy of calculation of mass concentration.

Further, for example, the housing 10 has a lid 13 which can be opened and closed.

Thereby, the lid 13 can be opened to clean the inside of the housing 10. Since the particles attached to the inside of the housing 10 can be removed, the life of the particle detection sensor 1 can be extended.

Further, for example, when the lid 13 is closed after being opened, the signal processing circuit 50 further initializes the amount of change over time.

As a result, by initializing the temporal change amount, it is possible to enhance the accuracy of the correction of the light reception intensity of the scattered light L2 based on the temporal change amount. Therefore, the particle detection sensor 1 can calculate the mass concentration of particles with high accuracy.

Further, for example, the particle detection sensor 1 further controls the operation of the air blowing mechanism 40 when the air processing mechanism 50 generates an air flow passing through the detection area DA and the signal processing circuit 50 acquires the temporal change amount. And a circuit 60.

Thereby, when acquiring a temporal change amount, it is necessary to cause the light receiving unit 30 to receive stray light, not scattered light L2 by particles passing through the detection area DA. Therefore, when the control circuit 60 stops the operation of the air blowing mechanism 40, the particles P can be prevented from being taken into the inside of the housing 10 from the outside. Therefore, the light receiving unit 30 can easily receive stray light with high accuracy. For this reason, since the particle detection sensor 1 can acquire the temporal change amount with high accuracy, it is possible to calculate the mass concentration with high accuracy.

Also, for example, the light emitting unit 20 has a laser element.

The laser element generally includes a light receiving element, and can detect the intensity of the emitted light L1. Therefore, by detecting the intensity of the light L1 emitted from the laser element, the deterioration of the laser element can be accurately detected. Therefore, the decrease in the light reception intensity of the scattered light L2 based on the deterioration of the light emitting unit 20 can be corrected. Thereby, according to the particle | grain detection sensor 1, the mass concentration of particle | grains can be calculated further accurately.

(Others)
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, although the above embodiment has described the case where the object to be measured is a gas, the present invention is not limited to this. The measurement target may be a liquid. 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 contacting liquid. The waterproof mechanism is, for example, a metal shield member provided to cover the signal processing circuit 50. The shield member is fixed to the housing 10 without a gap, for example, by welding.

Also, for example, the housing 10 may not include the lid 13 and the opening 14. The inlet 11 or the outlet 12 may be used as a cleaning window.

Also, for example, the particle detection sensor 1 may not include the air blowing mechanism 40. For example, the particle detection sensor 1 may be disposed so that the inlet 11 is located on the upstream side of the air flow, and the outlet 12 is located on the downstream side, where the air flow is flowing in a fixed direction.

Also, for example, in the above-described embodiment, although an example in which each of the light emitting unit 20 and the light receiving unit 30 includes a lens is shown, the present invention is not limited to this. For example, at least one of the light emitting unit 20 and the light receiving unit 30 may include a mirror (reflector) instead of a lens.

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

In addition, the present invention can be realized by arbitrarily combining components and functions in each embodiment without departing from the scope of the present invention or embodiments obtained by applying various modifications that those skilled in the art may think to each embodiment. The form is also included in the present invention.

DESCRIPTION OF SYMBOLS 1 Particle detection sensor 10 Case 13 Lid 20 Light projection part 21 Light projection element (laser element)
Reference Signs List 30 light receiving unit 40 air blowing mechanism 50 signal processing circuit 60 control circuit

Claims

A particle detection sensor for detecting a plurality of particles contained in a measurement object, comprising:
A light emitting unit that emits light toward the detection area;
A light receiving unit that receives scattered light of the light by the target particle when the target particle, which is at least one of the plurality of particles, passes through the detection area;
A housing that accommodates the light emitting unit and the light receiving unit and has the detection area inside;
And a signal processing circuit,
The signal processing circuit
Acquiring a temporal change amount of received light intensity of stray light received by the light receiving unit when the plurality of particles do not pass through the detection area;
The light reception intensity of the scattered light is corrected based on the acquired temporal change amount,
The particles included in the measurement target by classifying the target particles into any of a plurality of particle sizes based on the corrected received light intensity of the scattered light and specifying the number of detected target particles. Particle detection sensor that calculates the mass concentration of.
The particle detection sensor according to claim 1, wherein the signal processing circuit acquires the temporal change amount each time a predetermined period elapses.
The signal processing circuit further calculates the time accumulation value of the calculated mass concentration, and is the increase amount of the calculated time accumulation value, and the increase amount from the time accumulation value when the immediately preceding change amount is acquired is The particle detection sensor according to claim 1, wherein the temporal change amount is acquired each time a predetermined threshold is reached.
The particle detection sensor according to any one of claims 1 to 3, wherein the case has a lid that can be opened and closed.
The particle detection sensor according to claim 4, wherein the signal processing circuit further initializes the temporal change amount when the lid is opened and then closed.
Furthermore, a blower mechanism that generates an air flow passing through the detection area;
The particle detection sensor according to any one of claims 1 to 5, further comprising: a control circuit configured to stop the operation of the air blowing mechanism when the signal processing circuit acquires the temporal change amount.
The particle detection sensor according to any one of claims 1 to 6, wherein the light projecting unit has a laser element.