JP2015210184A - Particle measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle measuring apparatus capable of precisely measuring grain size of fine particles.SOLUTION: A particle measuring apparatus 100 includes: a light projection element 111; a particle flow pass 33 for allowing the atmospheric air containing particles to flow therethrough; a light receiving element 112 that receives scattered light of light from the light projection element 111 which is scattered by the particles in the particle flow pass 33; a heating part 115 that heats a part of the atmospheric air with a current flowing thereon to generate an air flow in the particle flow pass 33; a temperature sensor 180 that measures the atmosphere temperature; a current adjustment section 170 that adjusts the current to flow on the heating part 115 based on the atmosphere temperature measured by the temperature sensor 180; a IV conversion section 121 that converts the voltage signal current output from the light receiving element 112; an amplifier 122 that amplifies the voltage signal and converts the same into a voltage signal which includes a pulse waveform corresponding to the particles; and a calculation unit 162 that calculates the grain size of the particles based on the voltage signal including the pulse waveform.

Description

  The present invention relates to a particle measuring apparatus.

  The light scattering particle measuring device is a particle measuring device having a photoelectric particle detection sensor provided with a light projecting element and a light receiving element, takes in a gas to be measured and irradiates the light of the light projecting element to the gas, The presence / absence and particle size of particles contained in the gas are detected by the scattered light. For example, particles such as dust, pollen, and smoke floating in the atmosphere can be detected.

  As this type of light scattering type particle detection sensor, a sensor provided with a light trap at a position facing a light projecting element or a light receiving element is known in order to reduce the generation of stray light (see, for example, Patent Document 1). .

Japanese Patent Laid-Open No. 11-248629

  In recent years, there has been a demand for further enhancement of the sensitivity of particle detection sensors in order to detect fine particles having a smaller particle diameter. For example, a large amount of particles are taken into the particle detection sensor by generating an air flow using a fan or heater resistance. It is considered to increase the sensitivity.

  However, simply providing a fan or heater resistor cannot keep the airflow velocity constant, and the measurement accuracy such as particle size varies.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a particle measuring apparatus capable of measuring the particle diameter of fine particles with high accuracy.

  In order to achieve the above object, an aspect of the particle measuring apparatus according to the present invention includes a light projecting element, a particle flow path for flowing an atmosphere containing particles, and the light projecting element by the particles in the particle flow path. A light-receiving element that receives scattered light, a heating unit that heats a part of the atmosphere by an electric current to generate an air flow in the particle flow path, a temperature sensor that measures an outside air temperature, and the temperature sensor Based on the measured outside air temperature, a current adjustment unit that adjusts the current flowing through the heating unit, an IV conversion unit that converts the current output from the light receiving element into a voltage signal, amplifies the voltage signal, and An amplification unit that converts a voltage signal into a voltage signal including a pulse waveform corresponding to the particles, and an arithmetic unit that calculates the particle size of the particles based on the voltage signal including the pulse waveform are provided. .

  Moreover, in one aspect of the particle measuring apparatus according to the present invention, when the outside air temperature measured by the temperature sensor is higher than a reference temperature, the current adjusting unit increases a current flowing through the heating unit to be larger than a predetermined value. When the outside air temperature is lower than the reference temperature, the current flowing through the heating unit may be smaller than the predetermined value.

  Moreover, in one aspect of the particle measuring apparatus according to the present invention, the current adjustment unit is caused to flow through the heating unit so that a temperature difference between the outside air temperature measured by the temperature sensor and the temperature of the heating unit is constant. The current may be adjusted.

  In the aspect of the particle measuring apparatus according to the present invention, the heating unit may be a resistance element.

  In one aspect of the particle measuring apparatus according to the present invention, the particle measuring apparatus further includes an AD conversion unit that samples and quantizes the voltage signal including the pulse waveform, and the arithmetic unit is sampled and quantized by the AD conversion unit. The particle size of the particles may be calculated based on the voltage signal.

  According to the present invention, it is possible to measure the particle size and the like of fine particles with high accuracy.

It is a block diagram which shows an example of a structure of the particle | grain measuring apparatus which concerns on embodiment. It is sectional drawing for demonstrating operation | movement of the particle | grain detection sensor in case the particle | grains do not exist in air | atmosphere. It is sectional drawing for demonstrating operation | movement of the particle | grain detection sensor in case the particle | grains with a small particle diameter exist in air | atmosphere. It is sectional drawing for demonstrating operation | movement of the particle | grain detection sensor in case the particle | grains with a large particle diameter exist in air | atmosphere. It is a graph which shows the time dependence of the light intensity detected with a light receiving element. It is a figure explaining an example of the particle size measuring method using analog data. It is a figure explaining the subject of the particle measuring device concerning a comparative example. It is an operation | movement flowchart explaining the flow velocity control of the particle flow path in the particle | grain measuring apparatus which concerns on embodiment. It is a graph showing the relationship between a temperature difference and an airflow speed.

  Below, the particle | grain measuring apparatus which concerns on embodiment of this invention is demonstrated in detail using drawing. Note that each of the embodiments described below shows a preferred specific example of the present invention. Therefore, the numerical values, shapes, materials, components, component arrangements, connection forms, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims showing the highest concept of the present invention are described as optional constituent elements.

  Each figure is a mimetic diagram and is not necessarily illustrated strictly. Moreover, in each figure, the same code | symbol is attached | subjected about the same structural member.

(Embodiment)
[1. Overall configuration of particle measuring apparatus]
First, the whole structure of the particle | grain measuring apparatus which concerns on embodiment of this invention is demonstrated.

  FIG. 1 is a block diagram illustrating an example of a configuration of a particle measuring apparatus according to an embodiment.

  As shown in the figure, the particle measuring apparatus 100 includes a particle detection sensor 110, an analog signal processing unit 120, a power supply unit 130, a current adjustment unit 170, and a temperature sensor 180, and a general-purpose MPU (Micro Processing Unit). 160), and the particle size of particles contained in the atmosphere is measured.

  Hereinafter, each structure of the particle | grain measuring apparatus 100 is demonstrated concretely.

[1-1. Configuration of particle detection sensor]
The particle detection sensor 110 is a photoelectric sensor including a light projecting element 111 and a light receiving element 112, and the light receiving element 112 receives scattered light of light from the light projecting element 111 due to particles in the detection area DA. The particle | grains contained in are detected. The particle detection sensor 110 in the present embodiment further includes a reflector 114 having a reflecting surface and a heating unit 115 that heats the atmosphere.

  The light projecting element 111 is a light source (light emitting unit) that emits light of a predetermined wavelength, and is, for example, a solid light emitting element such as an LED or a semiconductor laser. As the light projecting element 111, a light emitting element that emits infrared light, blue light, green light, red light, or ultraviolet light can be used.

  In addition, it becomes easy to detect a particle | grain with a small particle size, so that the light emission wavelength of the light projection element 111 is short. The light emission control method of the light projecting element 111 is not particularly limited, and the light emitted from the light projecting element 111 can be continuous light or pulsed light by DC driving. Moreover, the magnitude | size of the output of the light projection element 111 may be changing temporally.

  The light receiving element 112 is a light receiving unit that receives light, and is an element (photodetector) that receives light and converts it into an electrical signal, such as a photodiode, a photo IC diode, a phototransistor, or a photomultiplier tube. Specifically, the light receiving element 112 generates a current signal as an electrical signal. That is, the light receiving element 112 outputs a current signal corresponding to the received light intensity.

  The light projecting element 111 and the light receiving element 112 are operated by the power supplied from the power supply unit 130.

  As shown in FIG. 1, the light projecting element 111 and the light receiving element 112 are arranged in a housing 113. The housing 113 holds the light projecting element 111 and the light receiving element 112. In the present embodiment, the light projecting element 111 and the light receiving element 112 are arranged in the housing 113 so that their optical axes intersect each other.

  The casing 113 is provided with a particle flow path 33 that is a cylindrical space region through which air (gas) containing particles flows.

  The detection area DA is an aerosol detection area (aerosol measurement unit) that is an area for detecting particles (aerosol) contained in the gas to be measured. The detection area DA is projected with a space area where light from the light projecting element 111 is projected. This is a spatial region that overlaps the spatial region for guiding the scattered light generated when the light of the optical device 111 hits the particles to the light receiving device 112. Further, the detection area DA is arranged so as to exist in the particle flow path 33, and the gas to be measured is guided to the detection area DA through the particle flow path 33.

  In the present embodiment, the flow channel direction of the particle flow channel 33 (the direction in which the gas to be measured flows) is the vertical direction on the paper surface of FIG. 1, but may be the vertical direction on the paper surface of FIG. That is, in the present embodiment, the flow path axis of the particle flow path 33 is arranged so as to exist on a plane through which each optical axis of the light projecting element 111 and the light receiving element 112 passes, but is orthogonal to the plane. It may be arranged as follows.

  The reflector 114 (reflecting plate) is a reflecting member that reflects scattered light of the light projecting element 111 due to particles in the detection area DA and guides the scattered light to the light receiving element 112. In the present embodiment, the reflector 114 reflects the scattered light of the particles and collects it on the light receiving element 112. More specifically, the reflector 114 reflects the scattered light of the particles toward the light receiving element 112.

  As shown in FIG. 1, the reflector 114 is provided in the light receiving region 32 in the present embodiment. Specifically, the reflector 114 is a condensing mirror provided along the inner surface of the housing 113 in the light receiving region 32, and the inner surface which is a reflecting surface is a curved surface. As shown in FIG. 1, the inner surface of the reflector 114 is a part of the rotation surface of the spheroid. That is, the reflector 114 is an elliptical mirror in which the shape of the inner surface (reflective surface) forms a part of the spheroid, and the cross-sectional shape of the inner surface of the reflector 114 is a part of the ellipse.

  As the reflector 114, the base member itself may be made of a reflective material such as metal so that the surface of the base member itself becomes a reflective surface, or a reflective film that becomes a reflective surface on the surface of a resin or metal base member May be formed.

As the reflection film, a metal reflection film such as aluminum, gold, silver or copper, a mirror reflection film, a dielectric multilayer film, or the like can be used. As the reflective film, a film having a low absorptance and a high reflectance is preferable. Moreover, you may use as a reflecting film what laminated | stacked the thin film thinner than the said aluminum film on the surface of the aluminum film formed by vapor deposition. As the thin film laminated on the aluminum film, for example, an MgF film, a SiO ₂ film, a SiO film, an AlN film, an alumina film, an enhanced reflection film, or the like is used. Thus, by laminating these thin films on the aluminum film, it is possible to suppress deterioration (corrosion and the like) of the aluminum film and improve optical characteristics by optical amplification.

  The heating unit 115 heats the atmosphere in order to introduce the atmosphere containing particles into the detection area DA, and functions as an airflow generation device that generates an airflow for promoting the flow of the gas flowing in the particle flow path. . Specifically, the heating unit 115 is, for example, a resistance element such as a heater resistor, and is disposed in the vicinity of the inlet of the particle channel in the present embodiment.

  For example, when the heating unit 115 is a heater resistance, the heater resistance is heated when a current is supplied from the current adjustment unit 170 to the heater resistance. As a result, the atmosphere around the heater resistor is heated to decrease the density, and moves upward in the direction opposite to gravity. That is, when the heating unit 115 heats the atmosphere near the inlet of the particle flow path, an upward air flow (upward air flow) can be generated. Note that the temperature of the heater resistance increases as the current supplied from the current adjustment unit 170 increases. Moreover, the speed of the rising air flow increases as the temperature difference between the lower end near the inlet of the particle channel where the heating unit 115 is installed and the upper end near the outlet of the particle channel increases. Accordingly, for example, when the temperature outside the particle detection sensor 110 is constant, the speed of the updraft increases as the current supplied from the current adjustment unit 170 increases.

  In this way, by heating a part of the atmosphere near the particle flow path by the heating unit 115, the gas (atmosphere) to be measured can be easily drawn into the housing 113 (particle flow path). Thereby, compared with the case where the heating part 115 is not provided, many particles can be taken into the particle detection sensor 110. Therefore, since the amount of particles per unit volume in the detection area DA included in the particle flow path can be increased, the sensitivity can be increased.

  Further, since the heating unit 115 generates an upward air flow, it is preferable to install the heating unit 115 in a lower portion of the particle channel 33 as shown in FIG. Even when the heating unit 115 is not operating, the atmosphere can pass through the particle flow path. That is, even when the heating unit 115 is not operating, it is possible to detect particles contained in the atmosphere.

[1-2. Operation of particle detection sensor]
Next, the operation of the particle detection sensor 110 in this embodiment will be described with reference to FIGS. 2A, 2B, 2C, and 3. FIG.

  2A to 2C show the operation of the particle detection sensor when there are no particles in the atmosphere, when particles with a small particle diameter exist in the atmosphere, and when particles with a large particle diameter exist in the atmosphere, respectively. It is sectional drawing for demonstrating. FIG. 3 is a graph showing a pulse waveform of the light intensity detected by the light receiving element 112 in the state shown in FIGS. 2A to 2C.

  When the heating unit 115 is operated to generate an air flow in the particle flow path, the air is drawn into the particle detection sensor 110 from the air introduction hole 35, and the air is guided to the detection area DA via the particle flow path. .

  In this case, as shown in FIG. 2A, when there is no particle (aerosol) in the atmosphere introduced into the particle detection sensor 110, that is, when the particle does not flow into the detection area DA, the light is emitted from the light projecting element 111. Since the light passes straight through the detection area DA, light scattered by particles is not generated. Therefore, in this case, basically, there is no reaction of the light receiving element 112, so that it can be seen that there are no particles in the atmosphere introduced into the particle detection sensor 110.

  In this case, light traveling straight through the detection area DA may be reflected in the housing 113 and enter the light receiving element 112 as stray light. However, in this case, the light intensity detected by the light receiving element 112 is smaller than when the particles are present in the detection area DA. Therefore, it can be seen that there are no particles in the atmosphere introduced into the particle detection sensor 110.

  In addition, as shown in FIG. 2B, when there is a particle (aerosol) P1 having a small particle size in the atmosphere introduced into the particle detection sensor 110, that is, when a particle P1 having a small particle size flows into the detection area DA. The light of the light projecting element 111 strikes the particle P1 existing in the detection area DA and is scattered, and the scattered light is reflected directly or by the reflector 114 and enters the light receiving element 112.

  Specifically, in this case, scattered light having a light intensity as indicated by “particle size: small” in FIG. Here, as described above, the light receiving element 112 outputs a current signal corresponding to the received light intensity. Therefore, in this case, the current signal output from the light receiving element 112 is relatively small. Thereby, it can be seen that particles having a small particle diameter exist in the atmosphere introduced into the particle detection sensor 110.

  In addition, as shown in FIG. 2C, when particles (aerosol) P2 having a large particle size exist in the atmosphere introduced into the particle detection sensor 110, that is, when particles P2 having a large particle size flow into the detection area DA. The light of the light projecting element 111 strikes the particles P2 existing in the detection area DA and is scattered, and the scattered light is reflected directly or by the reflector 114 and enters the light receiving element 112.

  Specifically, in this case, scattered light having a light intensity as indicated by “particle size: large” in FIG. Therefore, in this case, the current signal output from the light receiving element 112 is relatively large. Thus, it can be seen that particles P2 having a large particle size exist in the atmosphere introduced into the particle detection sensor 110.

  In this way, the particle detection sensor 110 can detect whether or not particles are included in the atmosphere introduced into the particle detection sensor 110 (the presence or absence of particles). That is, particles in the atmosphere can be detected. Further, when particles are included in the atmosphere, a current signal corresponding to the particle size of the particles is output.

[1-3. Configuration of analog signal processor]
The analog signal processing unit 120 performs various signal processing on the current signal output from the particle detection sensor 110 to output an analog voltage signal based on the current signal. Here, various signal processing includes, for example, I / V conversion for converting current (I) into voltage (V), bandpass filter processing for passing a desired frequency band of an input signal, and input. Amplification processing for amplifying and outputting the received signal.

  The analog signal processing unit 120 is not limited to the processes exemplified here, and may perform other signal processing (for example, high-pass filter processing, low-pass filter processing, attenuation processing, and the like).

  As illustrated in FIG. 1, the analog signal processing unit 120 includes an IV conversion unit 121 and an amplification unit 122.

[1-3-1. IV conversion unit]
The IV converter 121 converts the current output from the light receiving element 112 into a voltage (IV conversion). That is, the IV conversion unit 121 converts the current signal output from the particle detection sensor 110 into a voltage signal. By converting the voltage signal in this way, the design of the amplifying unit 122 connected to the subsequent stage of the IV converting unit 121 is facilitated.

[1-3-2. Amplification unit]
The amplification unit 122 amplifies a predetermined band of the voltage signal converted by the IV conversion unit 121. Specifically, a frequency component in a predetermined band among frequency components included in the voltage signal is amplified with a higher amplification factor than frequency components in other bands. Here, the predetermined band is, for example, a band where the frequency f1 corresponding to the flow velocity v1 of the atmosphere flowing in the particle flow path 33 of the particle detection sensor 110 is the center frequency and the bandwidth is fbw. Note that fbw may be a predetermined frequency or a frequency that is appropriately adjusted according to the noise floor of the voltage signal. In other words, the amplification unit 122 amplifies the voltage signal converted by the IV conversion unit 121 and converts it to a voltage signal including a pulse waveform corresponding to the particle.

  For example, as illustrated in FIG. 1, the amplifying unit 122 includes a band-pass filter 122 a that passes a frequency component in a predetermined band among frequency components included in the voltage signal output from the IV conversion unit 121, and a band-pass filter. And an amplifier 122b that amplifies a signal composed of frequency components that have passed through 122a. Note that the connection order of the bandpass filter 122a and the amplifier 122b is not limited to this, and the amplifier 122b may be provided upstream of the bandpass filter 122a.

  With such a configuration, the analog signal processing unit 120 outputs a voltage signal based on the current signal output from the particle detection sensor 110.

[1-4. Power supply part]
The power supply unit 130 supplies power to the components (particle detection sensor 110, analog signal processing unit 120, current adjustment unit 170, and temperature sensor 180) other than the power supply unit 130 among the configurations included in the sensor module 150. To do. The power supply unit 130 includes, for example, a regulator that converts a voltage supplied from the outside of the sensor module 150 into a desired voltage.

[1-5. Temperature sensor]
The temperature sensor 180 is a sensor that measures the outside air temperature. For example, the temperature sensor 180 is installed in the air outlet that is the outer surface of the housing 113 or the upper end of the particle channel 33, and outputs measurement data to the current adjustment unit 170.

[1-6. Current adjustment unit]
The current adjustment unit 170 adjusts the current flowing through the heating unit 115 based on the outside air temperature measured by the temperature sensor 180. More specifically, the current adjustment unit 170 adjusts the current flowing through the heating unit 115 so that the temperature difference between the outside air temperature measured by the temperature sensor 180 and the temperature of the heating unit 115 is constant. Details of the current adjustment operation of the current adjustment unit 170 will be described later.

[2. General-purpose MPU configuration]
The general-purpose MPU 160 uses the analog voltage signal output from the analog signal processing unit 120 to calculate the particle size of particles contained in the atmosphere flowing in the particle flow path of the particle detection sensor 110. This general-purpose MPU 160 is realized by, for example, a system LSI that is an integrated circuit, and may be individually made into one chip for each configuration described below, or may be made into one chip so as to include some or all of them. .

  The general-purpose MPU 160 is not limited to the system LSI, and may be realized by a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

  Such a general-purpose MPU 160 includes an AD conversion unit 161 and a calculation unit 162, as shown in FIG. The calculation unit 162 can perform various analyzes on particles contained in the atmosphere flowing in the particle flow path of the particle detection sensor 110 using the digital data generated by the AD conversion unit 161. The various analyzes include, for example, calculation of the particle diameter of the particle or identification of the particle.

  Note that in the particle measuring apparatus 100 according to the present embodiment, the AD conversion unit 161 is not an essential component, and the calculation unit 162 calculates the particle size and the like of the particles using the analog data output from the amplification unit 122. May be. Hereinafter, each configuration of the general-purpose MPU 160 will be described.

[2-1. AD converter]
The AD conversion unit 161 samples (samples) and quantizes the voltage signal amplified by the amplification unit 122. In other words, the AD converter 161 generates time-series digital data corresponding to the voltage signal by performing AD (Analog to Digital) conversion on the analog voltage signal output from the analog signal processor 120. That is, the AD conversion unit 161 generates time-series digital data based on the current signal output from the particle detection sensor 110.

  Specifically, the AD conversion unit 161 is an AD conversion module incorporated in advance in the general-purpose MPU 160, and converts a voltage signal input to an analog input terminal of the general-purpose MPU 160 into a digital signal. For example, the AD conversion unit 161 samples a voltage signal in a range of 0.0 to 5.0 V input to a terminal arranged for analog input in the general-purpose MPU 160 at a predetermined sampling period, and the sampled voltage signal Is converted to a 10-bit digital value.

  The range of the voltage input to the analog input terminal of the general-purpose MPU 160 is not limited to the above example. For example, the maximum value of the input voltage is a voltage specified from the outside of the general-purpose MPU 160 (eg, 3.3 V). It may be. The number of bits of the digital value generated by the AD conversion unit 161 is not limited to the above example, and may be 8 bits or 12 bits, for example.

[2-2. Calculation unit]
The calculation unit 162 calculates the particle size of particles contained in the atmosphere flowing in the particle flow path 33 of the particle detection sensor 110 using the digital data generated by the AD conversion unit 161.

  Here, the calculation process of the particle diameter of the particle | grains by the calculating part 162 is demonstrated.

  As described above, the current signal output from the particle detection sensor 110 is a signal corresponding to the particle size of particles contained in the atmosphere flowing in the particle flow path 33 of the particle detection sensor 110. Therefore, the digital data input from the AD conversion unit 161 to the calculation unit 162 also has a size corresponding to the particle size of the particles. Specifically, since the current signal increases as the particle size of the particle increases, the digital data also increases as the particle size of the particle increases.

  Therefore, the arithmetic unit 162 detects the peak of the time-series digital data, and calculates the particle size of the particle using the detected peak value. That is, the arithmetic unit 162 obtains the peak value of the digital data using the time-series digital data that is the voltage signal sampled and quantized by the AD converter 161, and uses the obtained peak value to determine the particle size of the particles. Calculate the diameter.

  Further, each of the peaks of the current signal output from the particle detection sensor 110, that is, each peak of the light intensity of the scattered light by the particles corresponds to each of the particles. Therefore, the calculation unit 162 can also calculate the number (amount) of particles in the atmosphere introduced into the particle detection sensor 110.

  In addition, the calculation unit 162 may always perform the above-described calculation (peak search) for detecting the peak of the digital data or only when a predetermined condition is satisfied.

  For example, the calculation unit 162 has a plurality of threshold values (for example, ten levels of threshold values Vth1 to Vth10) for calculating the particle size of the particles, and the digital data generated by the AD conversion unit 161 has the plurality of threshold values. A peak search may be performed when it is larger than the lowest threshold (for example, Vth1). In other words, the arithmetic unit 162 may start the peak search when the digital data exceeds the minimum threshold value.

  As described above, the calculation unit 162 can reduce the calculation amount (processing amount) by performing the peak search only when a predetermined condition is satisfied, as compared with the case of performing the constant peak search. That is, the particle size of the particles can be calculated without using a high-performance device as the general-purpose MPU 160.

  Here, the lowest threshold value among the plurality of threshold values for calculating the particle size of the particles may be a value larger than a digital value corresponding to the noise floor of the voltage signal input to the AD conversion unit 161.

  Thereby, the various misdetections which arise when the calculating part 162 calculates the peak of a noise can be reduced. Note that various misdetections include, for example, misdetection of the particle diameter of particles and misdetection of the number of particles.

  In addition, in the particle measuring apparatus 100 according to the present embodiment, when the AD conversion unit 161 is not provided, the calculation unit 162 can calculate the particle size of the particles using the analog data output from the amplification unit 122. Is possible.

  FIG. 4 is a diagram for explaining an example of a particle size measuring method using analog data. In this case, the general-purpose MPU has, for example, a comparator. The comparator compares the voltage signal output from the analog signal processing unit 120 with a predetermined threshold voltage Vth, and outputs a high level voltage when the voltage of the voltage signal is equal to or lower than the threshold voltage Vth. On the other hand, the comparator outputs a low level voltage when the voltage of the voltage signal is larger than the threshold voltage Vth.

  For example, when a particle P1 having a small particle size as shown in FIG. 2B is in the detection area DA, the voltage signal is a graph as shown by “particle size: small” in FIG. Further, when the particle P2 having a large particle size as shown in FIG. 2C is in the detection area DA, the voltage signal becomes a graph as shown by “particle size: large” in FIG. At this time, the period during which the output of the comparator is at the low level voltage is when the particle P2 having a larger particle diameter is in the detection area DA than when the particle P1 having a smaller particle diameter is in the detection area DA (period Pa) (period). Pb) is longer.

  Therefore, the period during which the output of the comparator is at the low level voltage becomes longer as the particle size of the particles located in the detection area DA becomes larger.

  Therefore, by calculating the period from the analog data, the particle size of the particles existing in the detection area DA can be estimated. That is, the calculation unit 162 calculates the particle size of the particles by obtaining the pulse width of the signal corresponding to the voltage signal converted by the amplification unit 122.

[3. Highly accurate measurement of particle size]
Here, it will be described that the particle measuring apparatus 100 according to the present embodiment can measure the particle size of particles contained in the atmosphere with high accuracy. First, the problem of the particle measuring apparatus according to the comparative example will be described.

  FIG. 5 is a diagram for explaining the problem of the particle measuring apparatus according to the comparative example. More specifically, FIG. 5A schematically shows the state of the particle detection sensor 110 when the gas flow rate is small (gas is slow). FIG. 5B schematically shows the state of the particle detection sensor 110 when the gas flow rate is large (the gas is fast). FIG. 5C shows a voltage signal output from the analog signal processing unit 120 in the state shown in FIGS. FIGS. 5A and 5B show the state of scattered light by particles having the same particle diameter.

  As shown to (a) of the figure, when the flow velocity of the gas introduced into the particle detection sensor 110 is small, the period during which the scattered light from the particle P3 is received by the light receiving element 112 becomes long.

  On the other hand, as shown in FIG. 5B, when the flow velocity of the gas introduced into the particle detection sensor 110 is small, the period in which the scattered light from the particle P3 is received by the light receiving element 112 is shortened.

  Therefore, even if the particle diameters of the particles existing in the detection area DA are substantially the same, if the flow velocities are different from each other, the waveform of the voltage signal output from the analog signal processing unit 120 may be different from each other. .

  Specifically, as shown in (c) of the figure, the voltage signal when the flow velocity of the gas introduced into the particle detection sensor 110 is small is higher than the voltage signal when the flow velocity is large. Are the same and appear over a long period of time. In other words, the voltage signal when the flow rate is small has a waveform with the same peak voltage and a large half width as compared with the voltage signal when the flow rate is large.

  When the voltage signal shown in (c) of FIG. 5 is output from the analog signal processing unit to the general-purpose MPU, the general-purpose MPU has the same signal size even if the particles have the same particle size. The period during which the voltage is greater than the threshold voltage Vth varies. As a result, due to the difference in the air velocity, the calculated value of the particle size varies, causing a problem that the accuracy of particle size measurement is reduced.

  The above-described problem is not limited to the case where the general-purpose MPU processes an analog voltage signal, and may occur even when the analog voltage signal is processed as a digital voltage signal obtained by AD conversion. For example, when a peak value is calculated from an AD-converted digital voltage signal, it is assumed that the peak value including an error is calibrated with a pulse width depending on the accuracy of the AD converter and the number of bits.

  On the other hand, in the particle measuring apparatus 100 according to the present embodiment, (1) the temperature sensor 180 measures the outside air temperature, and (2) the current adjusting unit 170 is based on the outside air temperature measured by the temperature sensor 180. The current flowing through the heating unit 115 is adjusted, and (3) the adjustment current flows through the heating unit 115 to heat a part of the atmosphere to generate an air flow at a constant speed in the particle channel 33. More specifically, the particle measuring apparatus 100 adjusts the air velocity of the particle flow path 33 as follows.

  FIG. 6 is an operation flowchart for explaining flow velocity control of the particle flow path in the particle measuring apparatus according to the embodiment.

  First, the temperature sensor 180 measures the outside air temperature (S10).

  Next, the current adjustment unit 170 acquires measurement data of the outside air temperature measured by the temperature sensor 180, and compares the acquired outside air temperature Ta with the reference temperature Tr (S20).

  In step S20, when the outside air temperature Ta is higher than the reference temperature Tr (Y in S20), the current adjustment unit 170 increases the current value supplied to the heating unit 115 from a predetermined value (S30). Here, the predetermined value is, for example, a current value that the current adjustment unit 170 is currently supplying to the heating unit 115.

  When the outside air temperature Ta is not higher than the reference temperature Tr (N in S20) and when the outside air temperature Ta is lower than the reference temperature Tr (Y in S40), the current adjustment unit 170 supplies the heating unit 115. The current value to be reduced is reduced from a predetermined value (S50).

  By executing steps S10 to S50 described above continuously or periodically, the temperature difference between the outside air temperature and the temperature of the heating unit 115 can be kept constant even when the outside air temperature varies.

  The airflow velocity in the particle flow path 33 changes due to the temperature difference. According to the configuration and operation of the particle measuring apparatus 100, the current supplied from the current adjustment unit 170 to the heating unit 115 can be adjusted by the output of the temperature sensor 180, and the temperature difference can be kept constant. That is, the airflow velocity can be kept constant even when the outside air temperature varies. As a result, the voltage signal output from the sensor module 150 can be prevented from fluctuating due to the external environment, so that the particle size and the like of the fine particles can be measured with high accuracy.

  In the airflow velocity control described above, a case where the temperature difference and the airflow velocity are not uniquely determined is assumed.

  FIG. 7 is a graph showing the relationship between the temperature difference and the airflow velocity. In the figure, the horizontal axis represents the temperature difference ΔT between the temperature of the heating unit 115 and the outside air temperature, and the vertical axis represents the air flow velocity in the particle channel 33. The graph of the figure shows that the airflow velocity increases as the temperature difference ΔT increases, but also shows that the temperature difference dependency of the airflow velocity varies depending on the outside air temperature. For example, the temperature difference dependency of the air velocity to be applied differs between a warm region (outside temperature A) and a cold region (outside temperature B). Therefore, it is preferable that the current adjustment unit 170 holds a plurality of temperature difference dependency data of airflow speeds to be referred to according to the assumed outside air temperature. This makes it possible to measure the particle size of the fine particles with higher accuracy.

[4. Summary]
As described above, the particle measuring apparatus 100 according to the present embodiment heats a part of the atmosphere by flowing the light projecting element 111, the particle flow path 33, the light receiving element 112, and the particle flow path 33. A heating unit 115 that generates an air current, a temperature sensor 180 that measures the outside air temperature, a current adjusting unit 170 that adjusts a current flowing through the heating unit 115 based on the outside air temperature, and a current output from the light receiving element 112 as a voltage. Based on the IV converter 121 for converting the signal, the amplifier 122 for amplifying the voltage signal and converting it to a voltage signal including a pulse waveform corresponding to the particle, and the voltage signal including the pulse waveform, the particle size of the particle And a calculation unit 162 that calculates

  According to this, the current supplied from the current sensor 170 to the heating unit 115 is adjusted by the output of the temperature sensor 180, and the temperature difference between the outside air temperature and the temperature of the heating unit 115 can be kept constant. Therefore, it is possible to suppress the voltage signal output from the sensor module 150 from fluctuating due to the external environment, and the arithmetic unit 162 measures the particle size of the fine particles with high accuracy based on the voltage signal including the pulse waveform. It becomes possible.

  In addition, when the outside air temperature measured by the temperature sensor 180 is higher than the reference temperature, the current adjustment unit 170 makes the current flowing through the heating unit 115 larger than a predetermined value, and when the outside air temperature is lower than the reference temperature, the heating unit 115. The current flowing in the battery may be smaller than a predetermined value. That is, the current adjustment unit 170 may adjust the current flowing through the heating unit 115 so that the temperature difference between the outside air temperature measured by the temperature sensor 180 and the temperature of the heating unit 115 is constant.

  Thereby, even if the outside air temperature varies, the temperature difference between the outside air temperature and the temperature of the heating unit 115 can be kept constant.

  Further, the heating unit 115 may be a resistance element.

  This makes it possible to heat part of the atmosphere near the particle flow path 33. Therefore, a large number of particles can be taken into the particle detection sensor 110 with a small and simplified structure. Therefore, since the amount of particles per unit volume in the detection area DA included in the particle flow path can be increased, the sensitivity can be increased.

  Furthermore, the AD converter 161 that samples and quantizes the voltage signal including the pulse waveform is provided, and the arithmetic unit 162 is based on the voltage signal sampled and quantized by the AD converter 161 to determine the particle size of the particles. May be calculated.

  As a result, the voltage signal including the pulse waveform can be digitally converted with high accuracy.

  Note that, even when the voltage calculation unit 162 acquires the voltage signal including the pulse waveform as analog data, the current adjustment unit 170 and the temperature sensor 180 described above suppress the fluctuation of the voltage signal due to the external environment. Therefore, by obtaining the pulse width of the voltage signal including the pulse waveform, the particle diameter of the fine particles can be measured with high accuracy.

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

  In the above description, the medium containing particles is the atmosphere (air), but may be a medium other than the atmosphere (liquid such as water).

  The configuration of the particle detection sensor 110 is not limited to the configuration described above, and includes at least a light projecting device and a light receiving device, and the light receiving device receives scattered light of the light projecting device due to particles in the detection area DA. Thus, particles contained in the atmosphere may be detected. Even with such a configuration, the particle measuring apparatus including the particle detection sensor can accurately measure the particle size of particles contained in the gas.

  For example, in the above-described embodiment, the reflector is a spheroid or a part of a rotating parabola, but is not limited thereto, and may be a part of a conic-curved rotator. In this case, the conic curve may be selected from an ellipse, a parabola and a hyperbola rather than a circle. That is, the reflector is preferably a part of a spheroid, a parabola, or a hyperbola rather than a sphere. When the reflector is a sphere, if diffuse reflection is used like an integrating sphere, scattered light is reflected many times (multiple reflection) and attenuated, so that light does not enter the light receiving element 112 much. For example, in the case of a sphere, only about 1/100 is received compared to the case of a spheroid.

  The configuration of the amplifying unit is not limited to the configuration described above, and at least the voltage signal output from the IV conversion unit 121 may be amplified in a predetermined band. That is, the amplification unit may not include the band pass filter 122a, and may include a high pass filter, a low pass filter, or the like. Further, the amplifier 122b may be a single stage or a plurality of stages.

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

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

33 Particle flow path 100 Particle measuring device 111 Light projecting element 112 Light receiving element 115 Heating unit 121 IV conversion unit 122 Amplification unit 161 AD conversion unit 162 Calculation unit 170 Current adjustment unit 180 Temperature sensor

Claims (5)

A light emitting element;
A particle flow path for flowing air containing particles;
A light receiving element for receiving scattered light of the light projecting element by the particles in the particle flow path;
A heating unit that heats a part of the atmosphere by causing an electric current to flow and generates an air flow in the particle channel;
A temperature sensor that measures the outside temperature;
Based on the outside air temperature measured by the temperature sensor, a current adjustment unit that adjusts the current flowing through the heating unit;
An IV converter that converts the current output from the light receiving element into a voltage signal;
An amplifying unit for amplifying the voltage signal and converting the voltage signal into a voltage signal including a pulse waveform corresponding to the particles;
A particle measuring apparatus comprising: a calculation unit that calculates the particle size of the particles based on a voltage signal including the pulse waveform. When the outside air temperature measured by the temperature sensor is higher than a reference temperature, the current adjusting unit makes a current flowing through the heating unit larger than a predetermined value, and when the outside air temperature is lower than the reference temperature, the heating unit The particle measuring apparatus according to claim 1, wherein a current flowing through the first electrode is made smaller than the predetermined value. The particle measurement according to claim 1, wherein the current adjustment unit adjusts a current flowing through the heating unit such that a temperature difference between an outside air temperature measured by the temperature sensor and a temperature of the heating unit is constant. apparatus. The particle measuring apparatus according to claim 1, wherein the heating unit is a resistance element. further,
An AD conversion unit that samples and quantizes the voltage signal including the pulse waveform,
The particle measuring apparatus according to claim 1, wherein the calculation unit calculates a particle size of the particles based on the voltage signal sampled and quantized by the AD conversion unit.

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