CN111051851B

CN111051851B - Particle detection sensor

Info

Publication number: CN111051851B
Application number: CN201880055186.7A
Authority: CN
Inventors: 永谷吉祥; 中川贵司; 川人圭子; 安池则之
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2017-08-29
Filing date: 2018-07-20
Publication date: 2022-12-06
Anticipated expiration: 2038-07-20
Also published as: JP7008252B2; CN111051851A; WO2019044250A1; JPWO2019044250A1; KR102327743B1; KR20200027028A

Abstract

A particle detection sensor (1) for detecting a plurality of particles contained in a measurement object, comprising: a light projecting unit (20) that emits light to the Detection Area (DA); a light receiving unit (30) that receives scattered light of light generated by at least one target particle, which is one of the plurality of particles, when the target particle passes through the detection region (DA); a housing (10) which houses the light projecting section (20) and the light receiving section (30) and has a Detection Area (DA) therein; and a signal processing circuit (50), wherein the signal processing circuit (50) obtains the variation with time of the light receiving intensity of the diffused light received by the light receiving part (30) when a plurality of particles do not pass through the Detection Area (DA), corrects the light receiving intensity of the diffused light according to the obtained variation with time, classifies the object particles into any one of a plurality of particle sizes according to the corrected light receiving intensity of the diffused light, and determines the number of the detected object particles to calculate the mass concentration of the particles contained in the measurement object.

Description

Particle detection sensor

Technical Field

The present invention relates to a particle detection sensor.

Background

Conventionally, a photoelectric particle detection sensor is known which includes a light projecting element and a light receiving element, detects particles floating in a measurement target, and calculates the mass concentration of the particles contained in the measurement target (see, for example, patent document 1). The photoelectric particle detection sensor emits light from a light projecting element to a detection region, and when a particle passes through the detection region, scattered light of the light generated by the passing particle is received by a light receiving element. The size of the particles is determined from 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.

(Prior art documents)

(patent document)

Patent document 1: japanese patent laid-open publication No. 2015-210183

However, according to the above-described conventional technique, when particles adhere to at least one of the light projecting element and the light receiving element, for example, the interior of the particle detection sensor is contaminated, and light that should be emitted to the detection region and scattered light that should be incident on the light receiving element are blocked by the adhering particles and are reduced. Further, there may be a case where light scattered by the attached particles and light that should not be incident on the light receiving element is incident on the light receiving element. In any case, the particle size is erroneously detected, and the detection accuracy is lowered.

Disclosure of Invention

Accordingly, 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 a measurement target with high accuracy.

In order to achieve the above object, a particle detection sensor according to an aspect of the present invention detects a plurality of particles included in a measurement target, and includes: a light projecting section for projecting light to the detection area; a light receiving unit that receives scattered light of the light generated by a target particle when the target particle passes through the detection region, the target particle being at least one of the plurality of particles; a housing that accommodates the light projecting section and the light receiving section and has the detection area therein; and a signal processing circuit that obtains a temporal change amount of a received light intensity of the diffused light received by the light receiving unit when the plurality of particles do not pass through the detection region, corrects the received light intensity of the scattered light based on the obtained temporal change amount, classifies the target particles into any one of a plurality of particle sizes based on the corrected received light intensity of the scattered light, and determines the number of detected target particles to calculate a mass concentration of particles included in the measurement target.

According to the particle detection sensor of the present invention, even in a state where the inside of the particle detection sensor is dirty due to the passage of time, the size of the particles can be detected with high accuracy, and the mass concentration of the particles contained in the measurement object can be calculated with high accuracy.

Drawings

Fig. 1 is a perspective view of a particle detection sensor according to an embodiment.

Fig. 2 is a perspective view of the particle detection sensor according to the embodiment when the cover is opened.

Fig. 3 is a sectional view of a particle detection sensor according to an 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 electric signal output from the light receiving element in the operation shown in fig. 4.

Fig. 6 is a diagram for explaining classification of the size of each particle in 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 according to the embodiment are attached to the light-emitting portion and the light-receiving portion of the particle detection sensor.

Fig. 9 is a diagram showing an electric signal output from the light receiving element in the operation shown in fig. 8.

Fig. 10 is a diagram illustrating correction processing of the electric signal illustrated in fig. 8.

Fig. 11 is a diagram showing an example of the timing at which the particle detection sensor according to the embodiment obtains the amount of change with time.

Fig. 12 is a diagram showing another example of the timing at which the particle detection sensor according to the embodiment obtains the amount of change with time.

Detailed Description

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

Each drawing is a schematic diagram, and is not necessarily a strictly illustrated drawing. Therefore, for example, the scale or the like in each drawing does not necessarily coincide. In the drawings, the same reference numerals are given to the same components, and redundant description is omitted or simplified.

(embodiment mode)

The particle detection sensor according to the present embodiment is a photoelectric particle detection sensor that detects the size of particles based on the received light intensity of scattered light of light generated by the particles passing through a detection region, and calculates the mass concentration of the particles included in a measurement target. The particle detection sensor estimates and corrects a variation in intensity of light that should be originally irradiated to the detection region and a variation in intensity of scattered light that should be originally incident on the light receiving element, based on a change with time in the received light intensity of the scattered light received when the particle does not pass through the detection region, detects the size of the particle with high accuracy based on the corrected scattered light intensity, and calculates the mass concentration of the particle included in the measurement object.

[ Structure ]

First, the particle detection sensor 1 according to the present embodiment will be described with reference to fig. 1 to 4.

Fig. 1 is a perspective view of a particle detection sensor according to the present embodiment. Fig. 2 is a perspective view of the particle detection sensor 1 according to the present embodiment when the cover 13 is opened. The cover 13 is opened, for example, for the purpose of cleaning the inside of the housing 10 during a period in which the particle detection sensor 1 is not operated.

Fig. 3 is a 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 housing 10 of the particle detection sensor 1 in the Z axis direction.

Fig. 4 is an enlarged cross-sectional view for explaining the operation of the particle detection sensor 1 according to the present embodiment. Specifically, fig. 4 shows an enlargement, and fig. 3 shows a section including the detection area DA.

Further, the X-axis, Y-axis, and Z-axis show three axes of a three-dimensional orthogonal coordinate system. The X-axis direction and the Y-axis direction are directions along two sides of the housing 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 of micron order floating in the gas, that is, particulate matter (aerosol). Specifically, the particles P include PM2.5, suspended Particulate Matter (SPM), PM10, and the like.

As shown in fig. 1 to 3, the particle detection sensor 1 includes a housing 10, a light projecting section 20, a light receiving section 30, an air blowing mechanism 40, a signal processing circuit 50, and a control circuit 60. In the cross section shown in fig. 3, the signal processing circuit 50 and the control circuit 60 are not shown, and therefore, the signal processing circuit 50 and the control circuit 60 are schematically shown in fig. 3. The signal processing circuit 50 and the control circuit 60 are mounted on, for example, the outer surface of the casing 10 and the surface opposite to the cover 13.

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

Specifically, as shown in fig. 1, the casing 10 includes an inlet 11 through which gas flows into the casing, and an outlet 12 through which the gas flows out. As indicated by thick broken line arrows in fig. 3, a path from the inlet 11 to the outlet 12 corresponds to a gas flow path inside the casing 10. Although fig. 3 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, a light-shielding property, and suppresses the incidence of external light, which 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 formed by combining a plurality of members formed by injection molding. The light projecting section 20 and the light receiving section 30 are fixed at predetermined positions in the housing 10 by being sandwiched between these members.

An optical trap structure that attenuates diffused light by reflecting it multiple times may be provided inside the housing 10. The diffused light is light that is not scattered by the particles P passing through the detection area DA, that is, light other than the scattered light L2 (see fig. 4), among the light L1 (see fig. 4) emitted from the light emitter 20. The optical trap structure can attenuate external light entering the interior from the inlet 11 or the outlet 12.

As shown in fig. 1, the housing 10 has a lid 13 that can be opened and closed freely. The cover 13 is detachably fixed to close an opening 14 (see fig. 2) provided in the housing 10. The user or the like can open and close the lid 13 as necessary.

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 adhering to the lens 22 of the light projecting section 20, the lens 32 of the light receiving section 30, and the detection area DA. The size and shape of the lid 13 and the opening 14 are not particularly limited. The cover 13 and the opening 14 are provided at positions overlapping the detection area DA when viewed from the Z-axis direction, but the present invention is not limited thereto.

The light emitter 20 emits light L1 toward the detection area DA. As shown in fig. 3 and 4, the light projecting section 20 includes a light projecting element 21 and a lens 22.

The light projecting element 21 is, for example, a solid-state light emitting element, specifically, a laser element such as a semiconductor laser. Alternatively, the Light projecting element 21 may be a Light Emitting Diode (LED) or an organic EL (electroluminescent) 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 of the peak of the light L1 may be a narrow band such as 50nm or less, for example. The light L1 is continuous light or pulsating light generated 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 on the detection area DA.

When a target particle, which is at least one of the plurality of particles P, passes through the detection region DA, the light receiving unit 30 receives scattered light L2 of light L1 generated by the target particle. As shown in fig. 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 that converts received light into an electrical signal, such as a photodiode, a phototransistor, or a photomultiplier tube. The light receiving element 31 outputs a current signal corresponding to the received light intensity. The light receiving element 31 has sensitivity in the wavelength band of the light L1 emitted from the light projecting element 21.

The light receiving element 31 receives scattered light L2 of the light L1 generated by the particles P passing through the detection area DA. Further, the light receiving element 31 receives the diffused light. The diffused light is light that is incident on the light receiving element 31 when the particles P do not pass through the detection area DA. Specifically, the diffused light is light other than the scattered light L2 of the light generated by the particles P passing through the detection region DA, and corresponds to a noise component. That is, diffuse light is light that should not be accepted. The diffused light includes scattered light L3 (see fig. 8) generated by particles adhering to the light emitter 20, and the like.

As shown in fig. 3, 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 is not incident. Specifically, the light receiving element 31 is disposed at a position not overlapping the optical axis of the light projecting element 21. The optical axis of the light projecting element 21 corresponds to a path of light having the strongest 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 disposed such 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 condenses the scattered light L2 scattered by the particles P in the detection area DA on the light receiving element 31.

The air blowing mechanism 40 generates an air flow passing through the detection area DA. The air blowing mechanism 40 is a heating element such as a heater, for example, and generates an ascending air current due to heat generation. In order to efficiently utilize the ascending air current, in the present embodiment, the particle detection sensor 1 is used in a standing state such that the positive direction of the Y axis is vertically upward and the negative direction of the Y axis is vertically downward as shown in fig. 1 to 3.

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

The signal processing circuit 50 obtains the temporal change amount of the received light intensity of the diffused light received by the light receiving section 30 when the plurality of particles P do not pass through the detection region DA. The signal processing circuit 50 corrects the received light intensity of the scattered light L2 based on the obtained temporal change amount. The signal processing circuit 50 classifies the target particles into any one of a plurality of particle sizes based on the corrected received light intensity of the scattered light L2, and determines the number of detected target particles, thereby calculating the mass concentration of the particles P contained in the gas. The specific processing of the signal processing circuit 50 will be described later. The signal processing circuit 50 outputs the calculated mass density to an external device as a sensor output value.

The signal processing circuit 50 is implemented 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 air blowing mechanism 40 when the signal processing circuit 50 obtains the amount of change over time. Specifically, the control circuit 60 stops the operation of the air blowing mechanism 40 at the timing when the signal processing circuit 50 obtains the amount of change with time. The signal processing circuit 50 obtains the amount of change over time from the received light intensity of the diffused light of the light received by the light receiving unit 30 after a predetermined period of time has elapsed since the operation of the air blowing mechanism 40 was stopped until the air flow in the casing 10 became sufficiently small.

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

[ work ]

Next, the operation of the particle detection sensor 1 will be described with reference to fig. 4 and 5.

As shown in fig. 4, in the particle detection sensor 1, the light projection element 21 constantly emits the light L1 during the operation. When the particles P pass through the detection area DA, the scattered light L2 generated by the particles P passing through is received by the light receiving element 31. The particles P passing through are target particles to be detected by the particle detection sensor 1.

Fig. 5 is a diagram showing an electric signal output from the light receiving element 31 in the operation shown in fig. 4. In fig. 5, the horizontal axis represents time, and the vertical axis represents signal intensity.

As shown in fig. 5, the signal intensity of the electric signal output from the light receiving element 31 is at a substantially constant noise level when no particle is detected. The noise level corresponds to the amount of diffused light generated in the housing 10 and allowed to enter the light receiving element 31 (hereinafter, simply referred to as "diffused light amount"). When the scattered light L2 enters the light receiving element 31, a peak S corresponding to the received light intensity of the scattered light L2 appears in the electrical 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 diagram for explaining classification of the size of each particle P in 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 electric signal output from the light-receiving element 31, specifically, the intensity of received light. Fig. 6 shows a relationship between the received light intensity of the scattered light generated by the particle P and the size of the particle when the particle P passes through the center of the detection region DA.

When the particle P passes through the detection region DA during the operation period, the scattered light L2 generated by the passing particle P enters the light receiving element 31. Therefore, the current signal output from the light receiving element 31 has a large signal intensity. For example, as shown in fig. 6, the peaks S1 to S3 of the current signal are detected every time the particles P pass through the detection area DA.

The size of the peak depends on the size of the particle P passing through the detection region DA, that is, the particle P in which the scattered light L2 is generated. Specifically, the larger the particle P, the larger the received light intensity of the scattered light L2, and the larger the signal intensity. The smaller the particle P is, the smaller the received light intensity of the scattered light L2 becomes, and the smaller the signal intensity becomes.

The signal processing circuit 50 classifies the particles P for each size according to 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 particles", "medium particles", and "small particles" according to the magnitude of the signal intensity. The number of classes of the particles P is not limited to three, and may be two, or four or more.

The particle detection sensor 1 according to the present embodiment also includes a large number of particles that actually 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 intensity of the scattered light generated by the particle received by the light receiving element 31 is small. Therefore, even if the particle is large, the size of the particle is erroneously determined as "small particle".

In order to suppress such a determination error, the signal processing circuit 50 according to the present embodiment holds a histogram in which the signal intensity is associated with the frequency of particles of each size, as shown in fig. 7, for example. Fig. 7 is a histogram of the particles P 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 frequency of particles of each size.

As shown in fig. 7, in the case where the signal intensity is large, most of them are large particles. On the other hand, when the signal intensity is small, large particles and medium particles passing through the portion other than the center of the detection area DA are included in addition to the small particles. The signal processing circuit 50 refers to the histogram shown in fig. 7 based on the peak intensity of the electric signal, and estimates the size of the particle P corresponding to the peak.

The signal processing circuit 50 counts the number of particles P detected in a predetermined operation period for each size. The signal processing circuit 50 calculates products of the predetermined average mass and the counted number for each size, and adds the calculated products for each size to calculate the mass concentration of the particles included in the measurement object during the operation period.

Next, the case where particles are attached to the light projecting section 20 and the light receiving section 30 will be described.

Fig. 8 is an enlarged cross-sectional view for explaining an operation when particles according to the present embodiment are attached to the light emitter 20 and the light receiver 30 of the particle detection sensor 1. Fig. 8 is an enlarged view of the portion including the detection area DA in the cross section shown in fig. 3, as in fig. 4.

As shown in fig. 8, the particle detection sensor 1 captures a gas containing a plurality of particles P inside the housing 10, thereby calculating the mass concentration of the particles P in the gas. The particles P captured inside the casing 10 are not all discharged from the outlet 12, but a part of the particles P adhere to the inside of the casing 10. The longer the operation period of the particle detection sensor 1 is, the more the amount of particles adhering to the inside of the housing 10 increases, and the amount of diffused 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 projecting section 20 and the lens 32 of the light receiving section 30.

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

Therefore, as shown in fig. 9, the peak value of the electric signal corresponding to the scattered light L2 has a signal intensity lower than the original peak value. The original peak is a peak based on the scattered light L2 in the case where particles are not attached to the light emitter 20 and the light receiver 30 (specifically, the case shown in fig. 4).

Here, fig. 9 is a diagram showing an electric signal output from the light receiving element 31 in the operation shown in fig. 8. In fig. 9, the horizontal axis represents time, and the vertical axis represents signal strength. In fig. 9, the signal intensity of the original peak is shown by a broken line.

Further, the particle P1 may scatter a part of the light emitted from the light-emitting element 21. In some cases, a part of the scattered light L3 generated by the particles P1 enters the light receiving element 31. The particles P1 are normally attached to the lens 22 as long as they are not removed by the cleaning operation. Therefore, a part of the scattered light L3 generated by the particles P1 is constantly incident on the light receiving element 31 as diffused 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 diffused light increases. In fig. 9, the original noise level is shown by a chain line.

As described above, when particles adhere to the light projecting section 20 and the light receiving section 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 amount of diffused light occur. The same applies to the case where particles are attached to the detection area DA.

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

Fig. 10 is a diagram illustrating correction processing of the electric signal illustrated in fig. 8. In fig. 10, the horizontal axis represents time, and the vertical axis represents signal strength. As shown in fig. 10, the signal processing circuit 50 subtracts the rise amount of the noise level from the signal intensity of the peak Sa before correction, and multiplies the subtracted peak by a correction coefficient to generate the original peak Sb. The rise amount of the noise level shown in fig. 10 corresponds to the change amount of the received light intensity of the diffused light with time.

The more particles are adhered to the light projecting part 20 or the light receiving part 30, the more the scattered light L3 generated by the particles increases, and thus the amount of change with time becomes large. As the number of particles adhering to the light emitter 20 or the light receiver 30 increases, the amount of light L1 that should reach the detection area DA and the amount of scattered light L2 generated 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 scattered light L2, which is inherent. Further, the smaller the change with time, the smaller the amount of decrease in the signal intensity of the scattered light L2, which is inherent.

Therefore, the signal processing circuit 50 increases the correction coefficient as the change amount of the received light intensity of the diffused light with time increases, and corrects the peak Sa having a large decrease amount of the signal intensity to the original peak Sb. The signal processing circuit 50 decreases the correction coefficient as the change amount of the received light intensity of the diffused light with time decreases, and corrects the peak Sa, which is a small decrease in the signal intensity, to the original peak Sb.

As described above, the particle detection sensor 1 according to the present embodiment obtains the temporal change amount of the received light intensity of the scattered light, and corrects the received light intensity of the scattered light L2 based on the obtained temporal change amount. This can improve the accuracy of calculating the mass concentration of the particles P.

The signal processing circuit 50 may correct the received light intensity of the scattered light according to the degree of deterioration of the light projecting element 21, in addition to the temporal change amount of the received light intensity of the scattered light. For example, when the intensity of the light L1 output from the light projecting element 21 decreases due to aging degradation, the intensity of the scattered light L2 generated by the particles P also decreases.

Therefore, the signal processing circuit 50 may obtain the amount of decrease in the intensity of the light output from the light projecting element 21, and correct the received light intensity of the scattered light L2 based on the obtained amount of decrease. Specifically, the signal processing circuit 50 may correct the peak having a large decrease in the signal intensity to the original peak by increasing the correction coefficient as the decrease in the intensity of the light output from the light projecting element 21 increases. The signal processing circuit 50 may correct the peak having a small decrease in signal intensity to the original peak by decreasing the correction coefficient as the decrease in intensity of the light output from the light projecting element 21 decreases.

[ timing for obtaining amount of change with time ]

Next, the timing of obtaining the temporal change amount of the received light intensity of the diffused light will be described.

Fig. 11 is a diagram showing an example of the timing at which the particle detection sensor 1 according to the present embodiment obtains the amount of change with time. In fig. 11, the horizontal axis represents the operating time, and the vertical axis represents the received light intensity of the diffused light (i.e., the amount of diffused light).

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

Therefore, in the present embodiment, the signal processing circuit 50 obtains the amount of change over time every time a predetermined period elapses. In fig. 11, the timing of obtaining the amount of change over time is shown by a broken line. The signal processing circuit 50 corrects the received light intensity of the scattered light L2 based on the change with time obtained at the timing shown in fig. 11. Specifically, when the temporal change amount is obtained at the first timing, the signal processing circuit 50 corrects the received light intensity of the scattered light L2 based on the temporal change amount obtained at the first timing until the operating time reaches the second timing, which is the next obtaining timing. The time from the first timing to the second timing is set short, so that the accuracy of correction can be improved.

Alternatively, the signal processing circuit 50 may obtain the time-dependent change amount from the time-integrated value of the mass concentration, not from the operating time. Fig. 12 is a diagram showing another example of the timing at which the particle detection sensor 1 according to the present embodiment obtains the amount of change with time. In fig. 12, the horizontal axis represents the time accumulation value of the mass density, and the vertical axis represents the received light intensity of the diffused light.

The signal processing circuit 50 calculates a time integration value of the mass concentration. When calculating the mass density, the signal processing circuit 50 stores the calculated value in a memory (not shown) as a time accumulation value. The signal processing circuit 50 periodically repeats the calculation of the mass density, for example, and therefore, each time the mass density is calculated, reads out the time integration value from the memory and adds the read time integration value to the calculated new value. The signal processing circuit 50 stores the added value as a new time accumulation value in the memory.

As shown in fig. 12, the larger the time accumulation value of the mass concentration is, the more the amount of particles attached to the inside of the housing 10 increases, and the amount of diffused light also increases. The time integration value and the amount of diffused light have, for example, a linear relationship.

Therefore, the signal processing circuit 50 may obtain the amount of change over time each time the calculated amount of increase in the time-integrated value, that is, the amount of increase from the time-integrated value at which the immediately preceding amount of change over time was obtained reaches a predetermined threshold value. In fig. 12, the timing of obtaining the amount of change with time is shown by a broken line. The signal processing circuit 50 corrects the received light intensity of the scattered light based on the change with time obtained at the timing shown in fig. 12.

In the present embodiment, as shown in fig. 1 and 2, the case 10 is provided with a cover 13 and an opening 14 for removing particles adhering to the inside of the case 10. When the adhered particles are removed, the amount of diffused light due to the adhered particles is sufficiently small.

Therefore, the signal processing circuit 50 initializes the amount of change with time when the cover 13 is closed after being opened. For example, after the inside of the housing 10 is cleaned by the user opening the cover 13 and removing particles, the cover 13 is closed again. The particles are removed, and thereby the amount of diffused light is reduced. The signal processing circuit 50 initializes the amount of change with time when the amount of diffused light (i.e., the noise level) decreases to a predetermined threshold value or less based on the electric signal output from the light receiving element 31.

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

[ Effect and the like ]

As described above, the particle detection sensor 1 according to the present embodiment is a particle detection sensor for detecting a plurality of particles P included in a measurement target, and includes: a light projecting unit 20 that emits light L1 toward the detection area DA; a light receiving unit 30 that receives scattered light L2 of light L1 generated by at least one of the plurality of particles P when the particle passes through the detection region DA; a housing 10 which houses the light projecting section 20 and the light receiving section 30 and has a detection area DA therein; and a signal processing circuit 50. The signal processing circuit 50 obtains the change with time of the light reception intensity of the diffused light received by the light receiving unit 30 when the plurality of particles P do not pass through the detection region DA, detects the light reception intensity of the scattered light L2 from the obtained change with time, classifies the target particles into any one of a plurality of particle sizes from the corrected light reception intensity of the scattered light L2, and determines the number of the detected target particles to calculate the mass concentration of the particles included in the measurement target.

Accordingly, the amount of change over time in the diffused light is obtained, and the received light intensity of the scattered light L2 can be corrected in consideration of the amount of increase and decrease in the signal intensity due to the particles adhering to the inside of the housing 10. The particle detection sensor 1 calculates the mass concentration from the light reception intensity of the corrected scattered light L2, and therefore can calculate the mass concentration of particles with high accuracy.

For example, the signal processing circuit 50 obtains the amount of change over time every time a predetermined period elapses.

Accordingly, the amount of change over time can be periodically updated, and therefore, high accuracy in calculating the mass concentration can be constantly maintained.

For example, the signal processing circuit 50 may further calculate a time-integrated value of the calculated mass density, and may obtain the amount of change over time each time an increase in the calculated time-integrated value, that is, an increase from the time-integrated value at which the immediately preceding amount of change over time was obtained reaches a predetermined threshold value.

Accordingly, since the time accumulation value of the mass concentration corresponds to the accumulation amount of the particles passing through the inside of the housing 10, the change amount with time can be updated every time the amount of the particles adhering to the inside of the housing 10 increases. Therefore, the particle detection sensor 1 can constantly maintain high accuracy of calculation of the mass concentration.

The housing 10 has, for example, a lid 13 that can be opened and closed freely.

Accordingly, the inside of the housing 10 can be cleaned by opening the cover 13. Since particles adhering to the inside of the case 10 can be removed, the life of the particle detection sensor 1 can be extended.

Further, for example, when the signal processing circuit 50 is closed after the cover 13 is opened, the amount of change with time is initialized.

Accordingly, the temporal change amount is initialized, and the accuracy of correction of the received light intensity of the scattered light L2 based on the temporal change amount can be improved. Therefore, the particle detection sensor 1 can calculate the mass concentration of the particles with high accuracy.

For example, the particle detection sensor 1 further includes: an air blowing mechanism 40 that generates an air flow passing through the detection area DA; and a control circuit 60 for stopping the operation of the air blowing mechanism 40 when the signal processing circuit 50 obtains the variation with time.

Accordingly, when the change amount with time is obtained, it is necessary to receive the diffused light in the light receiving unit 30 without receiving the scattered light L2 generated by the particles passing through the detection region DA. Therefore, the control circuit 60 can stop the operation of the air blowing mechanism 40, and can suppress the particles P from being captured from the outside into the casing 10. Therefore, the light receiving unit 30 can easily receive the diffused light with high accuracy. Therefore, the particle detection sensor 1 can accurately obtain the amount of change over time, and thus can accurately calculate the mass concentration.

The light projecting section 20 includes, for example, a laser element.

In general, a laser element includes a light receiving element and is capable of detecting the intensity of the emitted light L1. Therefore, the intensity of the light L1 emitted from the laser element is detected, and the deterioration of the laser element can be detected with high accuracy. Therefore, a decrease in the received light intensity of the scattered light L2 due to deterioration of the light projecting unit 20 can be corrected. Accordingly, according to the particle detection sensor 1, the mass concentration of the particles can be calculated with higher accuracy.

(others)

Although the particle detection sensor according to the present invention has been described above with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments.

For example, in the above embodiment, the case where the measurement target is a gas is described, but the present invention is not limited thereto. The measurement object may be a liquid. The particle detection sensor 1 detects particles contained in a liquid such as water, and calculates a mass concentration. In this case, the particle detection sensor 1 has a waterproof mechanism for preventing the signal processing circuit 50 mounted on the outer surface of the housing 10 from coming into contact with the liquid. The waterproof mechanism is, for example, a metal-made sealing member provided to cover the signal processing circuit 50. The sealing member is fixed to the housing 10 without a gap by, for example, welding.

For example, the case 10 may not have the cover 13 and the opening 14. The inlet 11 or the outlet 12 may be used as a cleaning window.

For example, the particle detection sensor 1 may not include the air blowing mechanism 40. For example, the particle detection sensor 1 is disposed in a portion where the airflow flows in a certain direction, with the inlet 11 located on the upstream side of the airflow and the outlet 12 located on the downstream side.

For example, although the above embodiment shows an example in which the light projecting unit 20 and the light receiving unit 30 are each provided with a lens, the present invention is not limited to this. For example, at least one of the light projecting section 20 and the light receiving section 30 may be provided with a mirror (reflector) instead of the lens.

The particle detection sensor 1 is mounted on various home appliances such as an air conditioner, an air cleaner, and a ventilation fan. Various home appliances may control their operations in accordance with the mass concentration of the particles detected by the particle detection sensor 1. For example, the air cleaner may be configured to increase the operation intensity (specifically, the air cleaning power) when the mass concentration of the particles is greater than a predetermined threshold value.

The present invention also includes an embodiment obtained by implementing various modifications of the embodiments, and an embodiment obtained by arbitrarily combining the constituent elements and functions of the embodiments without departing from the scope of the present invention.

Description of the symbols

1. Particle detection sensor

10. Shell body

13. Cover

20. Light projecting part

21. Light projecting element (laser element)

30. Light receiving part

40. Air supply mechanism

50. Signal processing circuit

60. Control circuit

Claims

1. A particle detection sensor for detecting a plurality of particles included in a measurement object, the particle detection sensor comprising:

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

a light receiving unit that receives scattered light of the light generated by the target particle when the target particle passes through the detection region, and outputs an electric signal including a peak corresponding to a received light intensity of the received scattered light, the target particle being at least one of the plurality of particles;

a housing that accommodates the light projecting section and the light receiving section and has the detection region therein; and

a signal processing circuit for processing the signal received from the signal receiving circuit,

the signal processing circuit is provided with a signal processing circuit,

obtaining a change with time in received light intensity of the diffused light received by the light receiving section when the plurality of particles do not pass through the detection region,

after subtracting the obtained amount of change over time from the signal intensity of the peak value, multiplying the subtracted peak value by a correction coefficient, thereby correcting the signal intensity of the peak value, wherein the larger the obtained amount of change over time, the larger the value of the correction coefficient,

the target particles are classified into any one of a plurality of particle sizes based on the corrected signal intensity of the peak, and the mass concentration of the particles included in the measurement target is calculated by determining the number of the detected target particles.

2. The particle detection sensor of claim 1,

the signal processing circuit obtains the temporal change amount every time a predetermined period elapses.

3. The particle detection sensor as in claim 1,

the signal processing circuit further calculates a time-integrated value of the calculated mass concentration, and obtains the amount of change over time each time an increase in the calculated time-integrated value, that is, an increase from the time-integrated value at which the amount of change over time immediately before was obtained reaches a predetermined threshold value.

4. A particle detection sensor as in any one of claims 1 to 3,

the housing has a lid that can be opened and closed freely.

5. The particle detection sensor as in claim 4,

the signal processing circuit initializes the time-dependent change amount in a case where the cover is closed after being opened.

6. A particle detection sensor as in any one of claims 1 to 3,

the particle detection sensor further includes:

an air supply mechanism for generating an air flow passing through the detection area; and

and a control circuit that stops the operation of the air blowing mechanism when the signal processing circuit obtains the temporal change amount.

7. A particle detection sensor as in any one of claims 1 to 3,

the light projecting section has a laser element.