JP2017142142A - Particle detection sensor, portable gas monitor, and particle detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle detection sensor with which it is possible to reduce power consumption without degrading detection accuracy.SOLUTION: A particle detection sensor 1 comprises a light projection element 111, a light receiving element 121, an air flow generation unit 15, a drive control unit 224 for intermittently driving the air flow generation unit 15, and a signal processing unit 20 for processing time-series signals indicating outputs from the light receiving element 121 and thereby calculating the mass concentration of particles included in a fluid. The signal processing unit 20 acquires a reference waveform that is a basis for the case where an air flow in a detection area D is in a steady state, acquires a measurement waveform corresponding to the time-series signals while the drive control unit 224 is intermittently driving the air flow generation unit 15, calculating a mass concentration without making corrections when waveforms pertaining to the reference waveform and the measurement waveform approximately match, and calculating a mass concentration after making corrections when the waveforms do not approximately match.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a particle detection sensor that measures particles contained in a fluid that is a gas or a liquid, a portable gas monitor including the particle detection sensor, and a particle detection method.

  The light scattering particle detection sensor is a photoelectric sensor including a light projecting element and a light receiving element, takes in a gas to be measured, irradiates the light of the light projecting element, and is contained in the gas by the scattered light. It detects the presence or absence of particles. Such a light scattering detection sensor can detect particles such as dust, pollen, and smoke floating in the atmosphere.

  As a device including this type of light scattering particle detection sensor, a device that detects the amount (concentration) of particles per unit volume in the atmosphere using a detection signal from the light scattering particle detection sensor is known. (For example, refer to Patent Document 1).

Japanese Patent No. 4555664

  However, in the configuration of the conventional light scattering particle detection sensor, the power consumption of the heat generating unit and the light projecting element that generate the rising airflow becomes a problem. Further, since the response speed from the start of heat generation of the heat generating portion to the stabilization of the rising airflow is low, there is a problem that it is difficult to reduce power consumption.

  Therefore, an object of the present invention is to provide a particle detection sensor or the like that can reduce power consumption without degrading detection accuracy.

  In order to achieve the above object, a particle detection sensor according to one embodiment of the present invention is a particle detection sensor that detects particles contained in a fluid that is a gas or a liquid, and projects light on a detection region. An element, a light receiving element that receives light scattered by the particles located in the detection region, a flow rate generation unit that generates a flow of the gas or the liquid in the detection region, and an intermittent drive of the flow rate generation unit And a signal processing unit that calculates a mass concentration of the particles contained in the fluid by performing signal processing on a time-series signal indicating an output from the light receiving element, and the signal processing unit. Obtains a reference waveform as a reference when the flow of the gas or the liquid in the detection region is in a steady state, and the drive control unit intermittently drives the flow rate generation unit. Measurement waveform corresponding to the time-series signal is obtained, and when the reference waveform and the measurement waveform substantially match, the mass concentration is calculated without performing correction processing, and the waveform is substantially If they do not match, the correction process is performed to calculate the mass concentration.

  A portable gas monitor according to an aspect of the present invention includes a particle detection sensor described above, a battery for driving the particle detection sensor, and a display that displays the mass concentration calculated by the particle detection sensor. A part.

  In addition, a particle detection method according to one embodiment of the present invention includes a light projecting element that projects light onto a detection region, a light receiving device that receives light scattered by particles located in the detection region, and a gas that is disposed on the detection region. Alternatively, a particle detection method for detecting the particles contained in the fluid that is the gas or the liquid using a particle detection sensor having a flow velocity generation unit that generates a liquid flow, the gas or the gas in the detection region Corresponding to the time-series signal indicating the output from the light receiving element in the step of acquiring a reference waveform as a reference when the liquid flow is in a steady state and the flow velocity generating unit being intermittently driven When the waveform substantially matches between the step of obtaining the measured waveform and the reference waveform and the measured waveform, they are included in the fluid without performing correction processing. Calculating the mass concentration of the serial particles, if the waveform is not substantially match, and calculating the mass concentration by performing the correction process.

  According to the present invention, power consumption can be reduced without degrading detection accuracy.

It is a block diagram which shows an example of a structure of the particle | grain detection sensor which concerns on embodiment. It is a wave form diagram which shows an example of the electric current signal output from a light receiving element. It is a wave form diagram which shows an example of digital data. It is a flowchart which shows operation | movement of a particle | grain detection sensor. It is a flowchart which shows an example of a reference waveform acquisition process. It is a wave form diagram which shows an example of reference waveform data. It is a figure which shows an example of the information which shows reference waveform data. It is a flowchart which shows an example of a measurement waveform acquisition process and a mass concentration calculation process. It is a timing chart which shows an example of the intermittent drive of an airflow generation part and a light projection element. It is a wave form diagram which shows an example of the waveform data obtained in the case of intermittent drive. It is an external view which shows an example of the portable gas monitor which concerns on embodiment.

  Below, the particle | grain detection sensor etc. which concern on embodiment of this invention are demonstrated in detail using drawing. Note that each of the embodiments described below shows a preferred specific example of the present invention. Therefore, numerical values, shapes, materials, components, arrangement and connection forms of components, and steps and order of steps 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, and the overlapping description may be abbreviate | omitted or simplified. Further, in the following, expressions such as substantially coincidence are used. For example, “substantially match” not only means that they completely match, but also means that they substantially match. That is, “substantially” includes an error of about several percent.

(Embodiment)
[1. Constitution]
First, the overall configuration of the particle detection sensor according to the embodiment of the present invention will be described.

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

  The particle detection sensor 1 is mounted on a moving body such as a vehicle and measures the mass concentration of particles contained in air (hereinafter referred to as ambient air) drifting around the particle detection sensor 1. For example, the ambient air includes fine dust, pollen, smoke, PM2.5, and the like particles having a particle size of 10 μm or less, and the particle detection sensor 1 can measure the mass concentration of these particles for each particle size category. Is possible.

  In the following, “mass concentration of particles in fluid” may be simply referred to as “mass concentration”.

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

  Hereinafter, each structure of the particle | grain detection sensor 1 is demonstrated concretely.

[1-1. Sensor unit]
The sensor unit 10 captures the ambient air that is the measurement target of the particle detection sensor 1, irradiates the captured ambient air with light, and outputs a signal (here, a current signal) indicating the light intensity of the scattered light. Type sensor (light scattering type particle detection sensor). That is, the sensor unit 10 outputs a time-series signal corresponding to the particles 2 contained in the captured ambient air.

  Specifically, in the present embodiment, the sensor unit 10 includes a light projecting system 11, a light receiving system 12, a housing 13, and an airflow generating unit 15, and from the inlet 18 to the outlet 19 of the housing 13. A signal corresponding to the scattered light from the particles 2 located in the detection area DA provided in the particle flow path is output. The light projecting system 11, the light receiving system 12, and the detection area DA are accommodated in the housing 13 so that external light is not irradiated.

  The detection area DA is an aerosol detection area (aerosol measurement unit) for detecting particles 2 (aerosol) contained in the gas to be measured, and includes an optical axis P of the light projecting system 11 and an optical axis Q of the light receiving system 12. For example, it is a region of about φ2 mm including the intersection where the two intersect. That is, the detection area DA is a spatial area where a spatial area where the light of the light projecting system 11 is projected and a spatial area for guiding the scattered light generated when the light of the light projecting system 11 hits the particles 2 to the light receiving system 12 overlap. It is.

  The light projecting system 11 includes an optical element that projects light onto the detection area DA. In the present embodiment, the light projecting element 111 and a light projecting element disposed in front of the light projecting element 111 (light projecting side). And a lens 112.

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

  In addition, it becomes easy to detect the particle | grains 2 with a small particle size, so that the wavelength of the light projected from the light projection element 111 is short. Moreover, the light projection control system of the light projecting element 111 is not particularly limited, and the light projected from the light projecting element 111 can be continuous light or pulsed light by DC driving. Moreover, the light intensity of the light projected from the light projecting element 111 may change with time.

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

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

  The light receiving element 121 receives light scattered by the particles 2 located in the detection area DA. Specifically, the light receiving element 121 is a photoelectric conversion element that converts received light into an electrical signal. In this embodiment, the photodiode and the phototransistor are sensitive to the light projected by the light projecting element 111. At least one of the following. That is, the light receiving element 121 outputs a signal (here, a current signal) corresponding to the received light intensity. Note that the light receiving element 121 may include, for example, a photo IC diode or a photomultiplier tube.

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

  The housing 13 is a member having a light shielding property and provided with a particle flow path that is a cylindrical space region through which ambient air (gas) including the particles 2 flows. For example, the housing 13 has a black surface at least on the inner surface so that stray light can be easily attenuated. Specifically, the inner surface of the housing 13 has a high light attenuation rate and reflects light in a specular manner. The reflection on the inner surface of the housing 13 may not be specular reflection, and a part of the light may be scattered and reflected.

  Here, the stray light is light other than the light scattered by the particles 2, and specifically, the light projected by the light projecting element 111 is not scattered by the particles 2 in the detection area DA, and the housing 2 Light traveling in the body 13 or the like. Further, the stray light includes external light that has entered the inside of the housing 13 through the particle flow path.

  The casing 13 is formed by, for example, injection molding using a resin material such as ABS resin. At this time, for example, by forming the housing 13 using a resin material to which a black pigment or dye is added, the inner surface of the housing 13 can be made a black surface and stray light can be attenuated. Alternatively, stray light can be attenuated by applying a black paint to the inner surface of the housing 13 after injection molding, thereby making the inner surface of the housing 13 a black surface. Further, stray light can be attenuated by subjecting the inner surface of the housing 13 to surface treatment such as embossing.

  The casing 13 is provided with the inlet 18 and the outlet 19 as described above. For this reason, the ambient air enters the inside of the housing 13 from the inlet 18, is guided to the detection area DA through the particle flow path, and flows out of the housing 13 from the outlet 19.

  In the present embodiment, the flow direction of the particle flow path (the direction in which gas flows in the particle flow path) is the vertical direction on the paper surface of FIG. 1, but may be the vertical direction on the paper surface of FIG. That is, in the present embodiment, the flow path axis of the particle flow path is set to exist on a plane through which each optical axis of the light projecting system 11 and the light receiving system 12 passes, but is orthogonal to the plane. May be set.

  The airflow generation unit 15 is configured by, for example, a fan (small electric fan), and is a flow rate generation unit that generates an airflow in the particle channel by operating the fan. When the fan is activated, the air velocity in the particle channel gradually increases from a low speed (approximately 0 speed) and becomes constant after a predetermined period. Due to the generation of the airflow by the airflow generation unit 15, the ambient air around the particle detection sensor 1 is drawn into the inside of the housing 13 from the inlet 18, so that a larger amount of air is generated in the sensor unit 10 than when the airflow generation unit 15 is not provided. Particles 2 can be taken up.

  The airflow generation unit 15 is intermittently driven by a drive control unit described later for the purpose of reducing the power consumption of the particle detection sensor 1. However, due to the intermittent drive, a period in which an air flow is generated by the air flow generation unit 15 (air flow generation mode) and a period in which no air flow is generated by the air flow generation unit 15 (air flow disappearance mode) are repeated at a constant cycle. In the airflow generation mode, the particles 2 that pass through the detection area DA are detected. Here, in order for the particle detection sensor 1 to measure the mass concentration of the particles 2 with high accuracy, it is important to generate an airflow at a stable airflow velocity in the airflow generation mode.

  From this point of view, the airflow generation unit 15 is preferably configured by a drive element that has a quick response to a drive signal from the drive control unit, and is configured by a fan, a micropump, a direct current electric motor, or the like. May be included. Also by these, it becomes possible to generate an air flow in the particle flow path at high speed by the drive signal. In addition, the airflow generation part 15 should just be installed in the sensor part 10 so that an airflow may be generated toward the outflow port 19 side from the inflow port 18 side in a particle flow path.

  Moreover, the airflow generation part 15 may be comprised with the heating mechanism. In this case, an air flow is generated in the particle channel by heating the gas around the heating mechanism. Specifically, when the heating mechanism heats the surrounding gas, the heated gas expands and decreases in density, thereby moving upward in the direction opposite to gravity. That is, an upward air flow (upward air flow) is generated by the heating mechanism. When this air flow causes the gas in the particle flow path to flow, an air flow is generated in the particle flow path. In addition, since the airflow generation part 15 which has a heating mechanism generate | occur | produces an updraft, it is preferable to install in the lower part of a particle flow path, as shown in FIG. In addition, when the air flow is generated by the heating mechanism, the period from the start of the air flow generation mode to the stabilization of the air flow speed is longer than the case where the air flow is generated by the fan, the micro pump, or the DC electric motor described above. have. Also from this viewpoint, it is preferable that the airflow generation unit 15 according to the present invention includes a fan, a micropump, a DC electric motor, or the like.

[1-2. Signal processor]
The signal processing unit 20 intermittently drives the airflow generation unit 15 and the light projecting element 111. In addition, the signal processing unit 20 performs signal processing on a time-series signal indicating the output from the light receiving element 121 acquired by the sensor unit 10 by the intermittent driving, so that it is included in the fluid (in the present embodiment, in the gas). The mass concentration of the particles 2 to be obtained is calculated. Specifically, the signal processing unit 20 performs analog signal processing on the signal (current signal in the present embodiment) output from the light receiving element 121, and further performs digital signal processing on the signal after analog signal processing. By performing the processing, the above-described mass concentration is calculated.

  As shown in FIG. 1, the signal processing unit 20 includes an analog signal processing unit 21 that performs analog signal processing and a general-purpose MPU 22 that performs digital signal processing.

  The analog signal processing unit 21 includes an analog circuit. In the present embodiment, the analog signal processing unit 21 performs various analog signal processing on the current signal output from the light receiving element 121 to output a voltage signal based on the current signal. To do. Here, various types of analog signal processing include, 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 the output signal and outputting it. The analog signal processing unit 21 includes an IV conversion unit 211 that performs I / V conversion, and an amplification unit 212 that performs bandpass filter processing and amplification processing.

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

  The IV conversion unit 211 generates a voltage signal corresponding to the current signal by performing I / V conversion on the current signal output from the light receiving element 121. By converting the current signal to the voltage signal in this way, the subsequent signal processing can be facilitated, and the design of the amplifying unit 212 connected to the subsequent stage of the IV converting unit 211 can be facilitated.

  The amplification unit 212 amplifies a predetermined band of the voltage signal generated by the IV conversion unit 211. Specifically, the amplification unit 212 amplifies a frequency component in a predetermined band among frequency components included in the voltage signal with a higher amplification factor than frequency components in other bands. Here, the predetermined band is, for example, a band in which the frequency f1 corresponding to the flow velocity v1 of the gas flowing through the particle flow path of the sensor unit 10 is the center frequency and the bandwidth is fbw. Note that fbw may be a predetermined frequency or a frequency that is appropriately set according to noise of the voltage signal.

  For example, as illustrated in FIG. 1, the amplifying unit 212 includes a band-pass filter 215 that passes a frequency component in a predetermined band among frequency components included in the voltage signal output from the IV conversion unit 211, and a band-pass filter 215. And an amplifier 216 that amplifies the signal composed of the frequency components that have passed through. Note that the connection order of the bandpass filter 215 and the amplifier 216 is not limited to this, and the amplifier 216 may be provided upstream of the bandpass filter 215.

  With such a configuration, the analog signal processing unit 21 outputs an output from the light receiving element 121 and outputs a time-series voltage signal including a pulsed waveform corresponding to the particle 2 located in the detection area DA.

  Here, the pulse-like waveform corresponding to the particle 2 is a sine wave corresponding to the velocity and particle size of the particle 2 passing through the detection area DA, or a waveform similar thereto. However, this is not the case, for example, when the large particle 2 and the small particle 2 pass through the detection area DA at the same timing.

  The general-purpose MPU 22 intermittently drives the airflow generation unit 15 and the light projecting element 111 of the sensor unit 10. The general-purpose MPU 22 is configured by a digital circuit, and the mass concentration of particles contained in the gas flowing in the particle flow path of the sensor unit 10 using the voltage signal output from the analog signal processing unit 21 during the intermittent drive. Is calculated. The general-purpose MPU 22 is realized by, for example, a system LSI that is an integrated circuit, and may be individually made into one chip for each functional block described below, or may be made into one chip so as to include some or all of them. Good.

  The general-purpose MPU 22 is not limited to the system LSI, and may be realized by a dedicated circuit or a general-purpose processor. The general-purpose MPU 22 may use a field programmable gate array (FPGA) 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.

  As shown in FIG. 1, the general-purpose MPU 22 includes an AD conversion unit 221, a calculation unit 222, a storage unit 223, and a drive control unit 224 as functional blocks. The drive control unit 224 drives the airflow generation unit 15 and the light projecting element 111 by outputting a drive signal to the airflow generation unit 15 and the light projection element 111. The general-purpose MPU 22 performs various analyzes on particles contained in the gas flowing in the particle flow path of the sensor unit 10 using the digital data generated by the AD conversion unit 221. The various analyzes are not limited to the mass concentration of the particles, and may include calculation of the particle size of the particles, identification of the particles, and the like.

  Hereinafter, each functional block of the general-purpose MPU 22 will be described in detail.

  The drive control unit 224 intermittently outputs drive signals to the airflow generation unit 15 and the light projecting element 111 for the purpose of reducing the power consumption of the particle detection sensor 1. More specifically, when the driving signal from the drive control unit 224 is switched to an on state (for example, a driving voltage is in a high level state), the airflow generating unit 15 starts generating an airflow to the particle channel, When the state is switched to an off state (for example, a state where the drive voltage is at a low level), the generation of the airflow to the particle channel is stopped. That is, the drive control unit 224 intermittently drives the airflow generation unit 15 by repeatedly turning on and off the drive signal.

  Further, the drive control unit 224 may supply a drive signal to the light projecting element 111 in synchronization with the intermittent drive of the airflow generation unit 15. More specifically, the drive control unit 224 emits a drive signal that causes the light projecting element 111 to emit light when the airflow generation unit 15 is operating and to extinguish the light projecting element 111 when the airflow generation unit 15 is not operating. This is supplied to the element 111. Thereby, since the light projecting element 111 emits light intermittently in conjunction with the intermittent driving of the airflow generation unit 15, the power consumption of the particle detection sensor 1 can be further reduced.

  Further, although not shown in FIG. 1, the drive control unit 224 may supply a drive signal to the analog signal processing unit 21 in synchronization with the intermittent drive of the airflow generation unit 15. More specifically, the drive control unit 224 drives the power supply voltage to the amplifying unit 212 when the airflow generating unit 15 is operating, and stops the power supply voltage to the amplifying unit 212 when the airflow generating unit 15 is not operating. The signal is supplied to the analog signal processing unit 21. Thereby, since the amplification unit 212 operates intermittently in conjunction with the intermittent driving of the airflow generation unit 15, the power consumption of the particle detection sensor 1 can be further reduced.

  The AD conversion unit 221 samples (samples) and quantizes the voltage signal amplified by the amplification unit 212. In other words, the AD conversion unit 221 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 processing unit 21. That is, the AD conversion unit 221 generates time-series digital data based on the current signal output from the light receiving element 121.

  In the present embodiment, the AD conversion unit 221 is an AD conversion module that is built in the general-purpose MPU 22 in advance, and converts the voltage signal input to the analog input terminal of the general-purpose MPU 22 into digital data. For example, the AD conversion unit 221 samples a voltage signal in the range of 0.0 to 5.0 V input to the analog input terminal of the general-purpose MPU 22 at a predetermined sampling period. Thereafter, the AD conversion unit 221 generates the time-series digital data by converting the voltage of the sampled voltage signal into a 10-bit digital value.

  The calculation unit 222 calculates the mass concentration of the particles 2 contained in the gas flowing in the particle flow path of the sensor unit 10 using the digital data generated by the AD conversion unit 221. Details of the processing by the calculation unit 222 will be described later.

  The storage unit 223 stores various types of information for the calculation unit 222 to calculate the mass concentration. The storage unit 223 is realized by a storage device such as a semiconductor memory, and in this embodiment is a memory area that is built in the general-purpose MPU 22 in advance. Note that the storage unit 223 may be provided as a separate storage device from the general-purpose MPU 22. Details of various information stored in the storage unit 223 will be described later.

  Note that the drive control unit 224 may not be included in the general-purpose MPU 22 and may be configured by a processing unit different from the general-purpose MPU 22.

[2. Operation]
Next, the operation of the particle detection sensor 1 will be described.

[2-1. Sensor unit]
First, the operation of the sensor unit 10 will be described.

  When the air flow generation unit 15 is operated, an air flow is generated in the particle flow path in the housing 13. Along with this, particles in the surrounding air enter the inside of the housing 13 from the inlet 18 of the particle flow path, pass through the particle detection area DA, and pass through the outlet 19 of the particle flow path to the housing 13. It is leaked outside. At this time, the light projected from the light projecting system 11 is scattered by the particles 2 located in the detection area DA.

  When the light scattered by the particles 2 enters the light receiving element 121, a current signal corresponding to the amount of light received (the light intensity of the received scattered light) is output by the light receiving element 121.

  FIG. 2 is a waveform diagram showing an example of a current signal output from the light receiving element 121.

  The waveform of the current signal shown in the figure includes four pulse waveforms W1 to W4. Specifically, the waveform of the current signal includes a waveform W1 having a peak value I3, a waveform W2 having a peak value I2, and waveforms W3 and W4 having a peak value I1. Note that a waveform WN due to noise is superimposed on these waveforms W1 to W4.

  The waveforms W1 to W4 correspond to the particles 2 that pass through the detection area DA as the airflow flows through the particle flow paths, and each has a peak value corresponding to the particle size of the corresponding particle 2. Here, each of the waveforms W1 to W3 has only one peak, whereas the waveform W4 has two peaks. That is, each of the waveforms W1 to W3 is a single waveform corresponding to one particle, whereas the waveform W4 is a combined waveform in which two waveforms corresponding to two particles having the same particle diameter are combined.

[2-2. Signal processor]
Next, the operation of the signal processing unit 20 will be described.

  The IV conversion unit 211 generates a voltage signal by converting the current output from the light receiving element 121 into a voltage. That is, the current signal output from the light receiving element 121 is converted into a voltage signal.

  Next, the amplification unit 212 amplifies the voltage signal in a predetermined band.

  After that, the AD conversion unit 221 generates digital data by performing digital conversion (AD conversion) on the voltage signal that is an analog signal amplified by the amplification unit 212. That is, the AD conversion unit 221 generates time-series digital data in which the sensor signal indicating the output from the light receiving system 12 is digitized by sampling and quantization, and outputs the digital data to the calculation unit 222.

  FIG. 3 is a waveform diagram illustrating an example of digital data generated by the AD conversion unit 221. Specifically, FIG. 2 shows a waveform diagram of digital data generated by signal processing of the current signal shown in FIG.

  The digital data shown in the figure is, for example, 10-bit time series digital data. Although the waveform of the digital data is a step-like waveform, in the same figure, it is assumed that the width of the step is very small and is shown by an apparent curve. In the same figure, the digital value of each sample of digital data is converted into a voltage. These matters are the same in the following waveform diagrams.

  As shown in the figure, in the waveform of digital data generated by the AD conversion unit 221, the waveform WN (see FIG. 2) due to noise is filtered and cut, and pulse-like waveforms W1 to W4 corresponding to the respective particles. Is included.

  Using the digital data generated in this way, the calculation unit 222 calculates the mass concentration.

  Here, when the airflow generation unit 15 is intermittently driven, the airflow velocity of the particle flow path is not stable at the start of the airflow generation mode, and a pulsed waveform included in the digital data is generated according to the change in the airflow velocity. It may change and the detection accuracy of mass concentration may deteriorate. For this reason, in the present embodiment, when the airflow velocity is not stable due to the intermittent driving of the airflow generation unit 15, the correction process is performed to calculate the mass concentration, and when the airflow velocity is stable, the correction is performed. The mass concentration is calculated without processing. Thereby, according to the particle | grain detection sensor 1 which concerns on this Embodiment, degradation of a detection precision can be reduced, reducing the power consumption of the particle | grain detection sensor 1. FIG.

  In other words, according to the particle detection sensor 1 according to the present embodiment, low power consumption can be achieved by intermittent driving of the airflow generation unit 15, and the particles are detected and corrected when the airflow in the particle flow path rises. By executing, mass concentration can be calculated with high accuracy and high speed.

[2-3. Particle detection processing]
Hereinafter, as an operation of the particle detection sensor 1, a particle detection process that is a process of calculating a mass concentration by the particle detection sensor 1 will be described. FIG. 4 is a flowchart showing the operation of the particle detection sensor 1.

  First, the signal processing unit 20 acquires a pulse-like reference waveform that serves as a reference when the airflow generation unit 15 is continuously driven and the flow of the airflow in the particle channel is in a steady state (S10). In the present embodiment, when the airflow in the particle channel is in a steady state, the calculation unit 222 acquires a plurality of pulse-shaped waveforms included in the digital data output from the AD conversion unit 221. Thus, a plurality of reference waveforms are acquired.

  Note that the method of acquiring the reference waveform is not limited to this, and for example, a reference waveform predetermined according to the characteristics of the sensor unit 10 or the like may be acquired from the storage unit 23. Further, the number of reference waveforms is not limited to one as long as it is 1 or more, but it is preferable that the number of reference waveforms is large from the viewpoint of accuracy of mass concentration.

  The timing at which the signal processing unit 20 acquires the reference waveform is not particularly limited. For example, the reference waveform is acquired every time the particle detection sensor 1 is activated or every predetermined time (for example, every hour). Also good. In this case, the particle detection sensor 1 can suppress deterioration in detection accuracy due to a change in characteristics over time of the analog elements constituting the analog signal processing unit 21 and the like. Further, for example, the reference waveform may be acquired at the time of quality adjustment of the particle detection sensor 1 before shipment from the factory. In this case, the particle detection sensor 1 does not need to acquire a reference waveform after shipment from the factory, and can reduce the processing load.

  Here, the steady state of the airflow in the particle channel is a state in which the flow rate of the gas flowing in the particle channel is constant as the airflow generator 15 is continuously driven for a predetermined period or longer. is there. The predetermined period is defined according to the airflow driving element of the airflow generation unit 15. For example, when the airflow driving element is a fan, the predetermined period is relatively short and is about several seconds. On the other hand, when the airflow driving element is a heating mechanism, the predetermined period is long and is several minutes or longer.

  Next, the signal processing unit 20 acquires a pulsed measurement waveform included in a time-series signal indicating the output from the light receiving element 121 in a state where the drive control unit 224 is intermittently driving the airflow generation unit 15. (S20). In the present embodiment, the arithmetic unit 222 acquires the pulse waveform included in the digital data output from the AD conversion unit 221, whereby the digital data of the measurement waveform is acquired.

  The timing at which the signal processing unit 20 acquires the measurement waveform is preferably synchronized with the intermittent driving of the airflow generation unit 15 and the timing at which the airflow generation unit 15 is in the on state (airflow generation mode).

  The measurement waveform may be acquired subsequent to the acquisition of the reference waveform, or may be acquired after an arbitrary time has elapsed since the acquisition of the reference waveform.

  The measurement waveform may be acquired at a predetermined interval (for example, every 10 minutes). In this case, the airflow generation unit 15 may not be driven within the predetermined interval (for example, 10 minutes), and the airflow generation unit 15 may be intermittently driven after the predetermined interval has elapsed. That is, the airflow generation unit 15 is intermittently driven only at the timing at which the measurement waveform needs to be acquired. Thereby, since the driving power of the airflow generation unit 15 is not consumed in the idling state where the measurement waveform is not acquired, the power consumption can be further reduced.

  Next, the signal processing unit 20 calculates a mass concentration using the acquired reference waveform and measurement waveform (S30). Specifically, the signal processing unit 20 calculates the mass concentration without performing the correction process when the time widths of the reference waveform and the measurement waveform whose peak values are substantially the same, and the time width is substantially the same. If they do not match, the correction process is performed to calculate the mass concentration.

  Hereinafter, the details of each process included in such a particle detection process will be described.

  First, details of the above-described reference waveform acquisition process (S10) will be described.

  FIG. 5 is a flowchart showing an example of the reference waveform acquisition process (S10) by the particle detection sensor 1.

  First, the drive control unit 224 continuously drives the airflow generation unit 15 (S11). Thereby, after the elapse of a predetermined period from the start of driving, the gas in the particle channel is in a steady state in which the airflow velocity is constant.

  Next, the particle detection sensor 1 introduces the particles 2 into the detection area DA by drawing the ambient air into the particle flow path in the housing 13 (S12).

  Next, the calculation unit 222 acquires waveform data that is a pulse-like waveform included in time-series digital data indicating the output from the light receiving element 121 (S13).

  Next, the calculation unit 222 determines whether or not the acquired waveform data is a single waveform (S14), and in the case of a single waveform (Yes in S14), the waveform data is stored as reference waveform data. It is stored in 223 (S15). On the other hand, if it is not a single waveform (No in S14), the process returns to the waveform data acquisition process (S13) and the subsequent processes are repeated. Specifically, when the waveform data has one peak, the calculation unit 222 determines that the waveform data is a single waveform, and when the waveform data has a plurality of peaks, the waveform data is a single waveform. Judge that it is not.

  By such processing, reference waveform data as shown in FIG. 6 is acquired. FIG. 6 is a waveform diagram showing an example of reference waveform data.

  In the drawing, reference waveform data whose peak values are Vref1, Vref2, and Vref3 (where Vref1 <Vref2 <Vref3 is satisfied) is shown for explanation. The waveform data obtained in the steady state of the airflow is not limited to this, and may have any peak value as long as it is a single waveform. Further, the reference waveform data whose peak values are Vref1, Vref2, and Vref3 respectively correspond to particles 2 having particle diameters D1, D2, and D3 (providing that D1 <D2 <D3 is satisfied).

  As shown in the figure, it can be seen that the reference waveform data of the particle 2 having a larger particle size has a larger time width in each of the plurality of threshold voltages Vth1 to Vth4. For example, focusing on the time width of each reference waveform data at the threshold voltage Vth1, the time width Tref1 of the particle size D1, the time width Tref2 of the particle size D2, and the time width Tref3 of the particle size D3 satisfy Tref1 <Tref2 <Tref3. .

  In the present embodiment, the calculation unit 222 causes the storage unit 223 to store information indicating the acquired reference waveform data. Specifically, the calculation unit 222 causes the storage unit 223 to store the peak value and the time width of each of the plurality of threshold values Vth1 to Vth4 for each acquired reference waveform data as the information.

  The number and interval of the plurality of threshold values Vth1 to Vth4 are not particularly limited, but may be set as appropriate according to the particle size distribution of the measurement target of the particle detection sensor 1, for example.

  FIG. 7 is a diagram illustrating an example of information 223 a indicating reference waveform data stored in the storage unit 223.

  As shown in the figure, the storage unit 223 stores the peak value and the time width of each of the plurality of threshold values Vth1 to Vth4 in association with each other for each reference waveform data shown in FIG. The information stored in the storage unit 223 is not limited to this, and for example, the reference waveform data itself may be stored.

  Next, details of the measurement waveform acquisition process (S20) and the mass concentration calculation process (S30) will be described.

  FIG. 8 is a flowchart illustrating an example of a measurement waveform acquisition process (S20) and a mass concentration calculation process (S30) by the particle detection sensor 1.

  First, the drive controller 224 intermittently drives the airflow generator 15 (S21).

  FIG. 9 is a timing chart illustrating an example of intermittent driving of the airflow generation unit 15 and the light projecting element 111. In FIG. 9, in step S21, the drive signal output by the drive control unit 224 to the airflow generation unit 15 and the light projecting element 111, the light emission intensity of the light projecting element 111, and the airflow velocity in the detection area DA in the particle flow path. , Time changes are shown. The drive signal (drive voltage) output from the drive control unit 224 is an intermittent repetition of an on-state (drive voltage is high level) pulse signal, and intermittent drive by the drive control unit 224 is executed.

  On the other hand, the light projecting element 111 repeats light emission / non-light emission in conjunction with the ON / OFF state of the drive signal. The rise and fall of light emission responds quickly to changes in the drive signal.

  On the other hand, the airflow generation unit 15 starts generating airflow to the particle channel when the drive signal is switched on, and stops generating airflow to the particle channel when the driving signal is switched to the off state. As a result, the rising waveform of the airflow velocity in the detection area DA does not immediately correspond to the rising waveform of the drive signal, and converges to a constant velocity after a predetermined time has elapsed. That is, during the period in which the drive signal is on, the airflow velocity in the detection area DA gradually changes from low speed to high speed.

  Next, in a state where the airflow generation unit 15 is intermittently driven, the particle detection sensor 1 introduces the particles 2 into the detection area DA by drawing the ambient air into the particle flow path in the housing 13 (S22). This process is the same as step S12 described above.

  At this time, a time-series signal including a pulse waveform is output from the light receiving element 121 to the analog signal processing unit 21. Here, the time width of the pulse-like waveform included in the signal output from the light receiving element 121 changes compared to the time width of the pulse-like waveform included in the reference waveform.

  Next, the calculation unit 222 acquires waveform data that is a pulsed waveform included in the time-series digital data indicating the output from the light receiving element 121 (S23).

  FIG. 10 is a waveform diagram showing an example of waveform data obtained when the airflow generation unit 15 is intermittently driven. The figure also shows waveform data obtained from the particles 2 having the same particle diameter when the airflow generator 15 is continuously driven (the airflow is in a steady state).

  As shown in the figure, when the airflow generation unit 15 is intermittently driven (rise state), the time width at an arbitrary threshold value is changed as compared with the case where it is continuously driven (steady state). In addition, the peak value may decrease. Specifically, in the intermittent drive state (rise state), the peak value decreases to Vβ as compared to the continuous drive state (steady state) in which the peak value is Vα and the time width is Tα (however, , Vα> Vβ), and the time width at the threshold value Vth1 varies in the range from Tα to Tβ1 and Tβ2 (where Tα> Tβ2> Tβ1). Note that the magnitude relationship between the time width in the continuous drive state and the time width in the intermittent drive state varies depending on the threshold value for comparing the time widths, and therefore the time width in the continuous drive state is in the intermittent drive state. It may be smaller than the time width.

  Next, the computing unit 222 excludes waveform data having a plurality of peaks from the plurality of acquired waveform data (S31). For example, when acquiring the waveform data as shown in the waveforms W1 to W4 shown in FIG. 3, the calculation unit 222 performs the process by excluding the waveform data of the waveform W4 having two peaks in the subsequent processing. That is, the signal processing unit 20 calculates the mass concentration by excluding the measurement waveform having a plurality of peaks. Hereinafter, the waveform data to be processed is referred to as measurement waveform data.

  Next, the computing unit 222 reads the reference waveform data from the storage unit 223 (S32). In the present embodiment, the calculation unit 222 acquires information indicating the reference waveform data stored in the storage unit 223.

  Thereafter, the calculation unit 222 determines whether there is reference waveform data having a peak value close to the measured waveform data (S33). If there is reference waveform data having a peak value close to the peak value (Yes in S33), the time width of the threshold value (Waveform width) is acquired (S34). Specifically, in the present embodiment, calculation unit 222 determines whether or not there is reference waveform data having a close peak value for each of a plurality of acquired measurement waveform data. For the measurement waveform data having peak values close to the reference waveform data, the time width at each of the plurality of threshold values Vth1 to Vth4 is acquired. In addition, that a peak value is near indicates that a peak value substantially corresponds.

  On the other hand, when there is no reference waveform data whose peak value is close to the measured waveform data (No in S33), the process returns to the waveform data acquisition process (S23) and the subsequent processes are repeated.

  Next, the calculation unit 222 determines whether or not the time width of the measured waveform data matches the time width of the reference waveform data (S35). If these time widths match (Yes in S35), the particle flow It is determined that particles are detected in the steady state of the road airflow, and correction is not performed (S36). That is, in this case, the signal processing unit 20 calculates the mass concentration without performing correction processing. The method for calculating the mass concentration is not particularly limited. For example, the number concentration calculated based on the number of peaks in the measured waveform data acquired within a predetermined time, and the average mass based on the average value of the peaks. Etc. can be calculated.

  On the other hand, when these time widths do not match (No in S35), the calculation unit 222 determines that particles are detected in the transition state of the airflow in the particle flow path, and performs correction (S37). That is, in this case, the signal processing unit 20 performs correction processing to calculate the mass concentration. That is, the calculation unit 222 estimates whether the air flow in the particle channel is in the transition state or the steady state by comparing the time width of the measurement waveform data and the time width of the reference waveform data, and is in the transition state The correction process is performed to calculate the mass concentration. Note that the calculation accuracy improves because the measured waveform data and the reference waveform data are approximated as the duty ratio (on-state period / one cycle) of the drive signal output from the drive control unit 224 increases. The effect of reducing is increased.

  Specifically, in the present embodiment, the signal processing unit 20 uses a plurality of threshold values Vth1 to Vth1 for a reference waveform (here, reference waveform data) and a measurement waveform (here, measured waveform data) whose peak values substantially match. When the time widths of the respective Vth4 are substantially the same, the correction process is not performed. On the other hand, the signal processing unit 20 performs correction processing when the time widths of at least one of the plurality of threshold values Vth1 to Vth4 do not substantially match.

  Note that the criterion for determining whether or not to perform the correction process is not limited to this. For example, the correction process is performed when the time widths substantially match at half or more of the plurality of thresholds, and the correction process is performed in other cases. You don't have to.

  In the correction process, the signal processing unit 20 calculates the mass concentration using the following correction coefficient. As a correction coefficient, when the airflow generation unit 15 is continuously driven and the airflow in the particle channel is in a steady state, the airflow generation unit 15 is intermittently driven and the airflow in the particle channel is in a transition state. Relative to the time width or peak value of the pulse waveform included in the signal (here, voltage signal) indicating the output from the light receiving element 121 when particles having the same particle diameter are introduced into the detection area DA. There is a relationship. For example, the signal processing unit 20 may use a ratio between the peak value in the steady state and the peak value in the transition state as the correction coefficient.

  Alternatively, the correction coefficient may be, for example, a ratio between the time width of the steady state and the time width of the transition state. Further, the correction coefficient is not limited to any ratio between the steady state and the transition state, and may be a difference. Further, the correction coefficient is not limited to one, and a plurality of correction coefficients may be determined. That is, for example, the signal processing unit 20 may perform correction processing using a database in which correction coefficients are stored in association with the peak values of the transition state.

  For example, the signal processing unit 20 calculates the mass concentration in the transition state by multiplying the mass concentration calculated when the steady state is assumed as the correction processing by multiplying the mass concentration calculated by the above correction coefficient. To do. Note that the correction processing method is not limited to this, and for example, the mass concentration in the transition state may be calculated by multiplying each peak value in the transition state by a correction coefficient.

  The correction coefficient may be stored in the storage unit 23, or may be stored in a storage device different from the storage unit 23. Alternatively, the correction coefficient may be included in the code executed when the signal processing unit 20 (the calculation unit 222 in the present embodiment) performs the correction process.

  As described above, the signal processing unit 20 performs correction processing on the acquired measured waveform (here, measured waveform data) and the reference waveform (here, reference waveform data) having a close peak value when the time width is close to the measured waveform. The mass concentration is calculated without performing the correction, and when the time width is not close to the measurement waveform, the correction processing is performed to calculate the mass concentration.

  Steps S21 to S23 are an example of the measurement waveform acquisition process (S20), and steps S31 to S37 are an example of the mass concentration calculation process (S30).

[3. Application example]
The particle detection sensor 1 described above can be applied to a portable gas monitor that monitors (detects) the mass concentration of gas and is portable.

  FIG. 11 is a functional block diagram showing an example of the portable gas monitor 100 according to the present embodiment. As shown in the figure, the portable gas monitor 100 displays the particle detection sensor 1 described above, the battery 3 that supplies driving power to the particle detection sensor 1, and the mass concentration calculated by the particle detection sensor 1. Part 4. The portable gas monitor 100 can monitor the mass concentration of gas in an open space as well as in a closed space by being carried by a person and installed on a moving body.

  According to the particle detection sensor 1 according to the present embodiment, since low power consumption can be realized by intermittent driving of the airflow generation unit 15, a commercial power supply is not used as a drive power supply, for example, a battery with a limited capacity is used as the drive power supply. It becomes possible to do. Thereby, by providing the battery 3 and the display unit 4, a small portable gas monitor can be realized.

[4. Summary]
As described above, the particle detection sensor 1 is a particle detection sensor that detects particles contained in a fluid that is gas or liquid (in this embodiment, gas). The particle detection sensor 1 generates a gas flow in the detection area DA, a light projecting element 111 that projects light onto the detection area DA, a light receiving element 121 that receives light scattered by the particles 2 located in the detection area DA, and the detection area DA. An air flow generation unit 15 to be driven, and a drive control unit 224 that intermittently drives the air flow generation unit 15. In addition, the particle detection sensor 1 includes a signal processing unit 20 that calculates a mass concentration of particles contained in the fluid by performing signal processing on a time-series signal indicating an output from the light receiving element 121. Here, the signal processing unit 20 acquires a reference waveform as a reference when the airflow in the detection area DA is in a steady state, and the drive control unit 224 is intermittently driving the airflow generation unit 15. A measurement waveform corresponding to the signal of the series is acquired, and if the reference waveform and the measurement waveform are approximately the same, the mass concentration is calculated without performing the correction process. If the waveform does not approximately match, the correction process is performed. Go to calculate mass concentration.

  More specifically, the signal processing unit 20 acquires a pulse-shaped reference waveform that is a reference in a steady state, and converts the time-series signal into a state in which the drive control unit 224 is intermittently driven. When the pulse width measurement waveform is acquired and the time widths of the reference waveform and the measurement waveform whose peak values are approximately the same, the mass concentration is calculated without performing correction processing, and the time width is approximately If they do not match, the correction process is performed to calculate the mass concentration.

  Here, when the airflow generation unit 15 is intermittently driven for the purpose of reducing power consumption, the time-series signal changes due to the change in the airflow velocity in the detection area DA as compared with the case of continuous driving. For this reason, the peak value and time width of the measurement waveform change compared to the case of the continuous driving. Therefore, when the time widths of the reference waveform and the measurement waveform whose peak values substantially coincide with each other do not substantially coincide with each other, the particle detection sensor 1 regards that the air velocity in the detection area DA is in the transition (rise) state and performs the correction process. . By the intermittent drive of the airflow generation unit 15 and the correction processing by the signal processing unit 20, it is possible to realize low power consumption and high speed of mass concentration calculation while reducing deterioration in detection accuracy.

  Further, according to the particle detection sensor 1, since low power consumption can be realized by intermittent driving of the air flow generation unit 15, a commercial power source is not required as a driving power source, and for example, a battery can be used as a driving power source. Become. For this reason, the particle detection sensor 1 can be suitable as a small particle detection sensor that can be carried.

  Further, the drive control unit 224 synchronizes with the intermittent driving of the airflow generation unit 15 to cause the light projecting element 111 to emit light when the airflow generation unit 15 is operating, and to quench the light projection element 111 when the airflow generation unit 15 is not operating. . Thereby, since the electric power for making the light projection element 111 light-emit can be reduced, the power consumption of the particle | grain detection sensor 1 can be reduced more.

  Further, the signal processing unit 20 excludes the pulse-shaped measurement waveform having a plurality of peaks and calculates the mass concentration.

  Here, the pulse-like measurement waveform having a plurality of peaks is a combined wave of a plurality of waveforms corresponding to the plurality of particles 2 located in the detection area DA. For this reason, the pulse-shaped measurement waveform having a plurality of peaks has a longer time width than the waveform of one particle, which may cause deterioration in detection accuracy. Therefore, the detection accuracy can be improved by calculating the mass concentration excluding the measurement waveform having a plurality of peaks.

  Further, the signal processing unit 20 does not perform the correction process when the time widths of each of the plurality of threshold values are substantially the same for the reference waveform and the measurement waveform whose peak values are approximately the same, and performs the time for at least one of the plurality of threshold values. If the widths do not substantially match, correction processing is performed.

  Here, when the time widths of the reference waveform and the measurement waveform having substantially the same peak value and different waveform shapes are compared with only one threshold, the time widths may be substantially the same. In this case, the mass concentration is calculated without performing the correction process, and the detection accuracy may be deteriorated. Therefore, for the reference waveform and the measurement waveform having substantially the same peak value, when the time width of at least one of the plurality of threshold values does not substantially match, the detection accuracy can be further reduced by performing the correction process. .

  The signal processing unit 20 is the same as the detection area DA in the correction process when the airflow generation unit 15 is continuously driven and the airflow is in a steady state and when the airflow generation unit 15 is intermittently driven. The mass concentration is calculated using the relative relationship between the time width or peak value of the pulse-like waveform included in the time-series signal when the particle having the particle size is introduced.

  By using such a relative relationship, it is possible to correct the mass concentration when the airflow generation unit 15 is intermittently driven, and to reduce deterioration in detection accuracy.

  The airflow generation unit 15 includes a fan, a micro pump, or a DC electric motor.

  This makes it possible to speed up the rise of the airflow in the particle flow path. For this reason, since the period of the ON state and the period of intermittent drive in the intermittent drive of the airflow generation unit 15 can be shortened, it is possible to realize low power consumption and high speed of mass concentration calculation.

  The portable gas monitor 100 includes the above-described particle detection sensor 1, a battery 3 for driving the particle detection sensor 1, and a display unit 4 that displays a mass concentration calculated by the particle detection sensor 1.

  As a result, the portable gas monitor 100 can realize low power consumption by intermittent driving of the airflow generation unit 15, so that the commercial power source is not used as the driving power source, for example, the battery 3 having a limited capacity is used as the driving power source. It becomes possible. Thereby, the portable small gas monitor is realizable.

  The particle detection method includes a light projecting element 111 that projects light onto the detection area DA, a light receiving element 121 that receives light scattered by the particles 2 located in the detection area DA, and an air flow in the detection area DA. This is a particle detection method for detecting particles contained in a fluid using a particle detection sensor 1 having an air flow generation unit 15 to be performed. In the particle detection method, a step (S10) of acquiring a reference waveform as a reference when the airflow in the detection area DA is in a steady state, and the light-receiving element 121 from the light-receiving element 121 in a state where the airflow generation unit 15 is intermittently driven. Obtaining a measurement waveform corresponding to a time-series signal indicating output (S20). In addition, the particle detection method calculates the mass concentration of particles contained in the fluid without performing a correction process when the waveform is approximately the same for the reference waveform and the measurement waveform, and corrects when the waveform is not approximately the same. A step (S30) of performing processing to calculate a mass concentration.

  Thus, in the particle detection method, when the waveform (time width) does not substantially match the reference waveform and the measurement waveform in the state where the airflow generation unit 15 is intermittently driven, the correction process is performed to calculate the mass concentration. . As a result, it is possible to reduce power consumption and increase the mass concentration calculation while reducing deterioration in detection accuracy.

(Other embodiments)
As described above, the present invention has been described based on the embodiment and the modification. However, the present invention is not limited to the above embodiment and the modification.

  For example, in the above-described embodiment, the signal processing unit 20 compares the time-series measurement waveform represented by the light reception intensity from the light receiving element 121 and the measurement time with the reference waveform, and performs correction processing and mass concentration calculation. However, the processing of the signal processing unit 20 is not limited to this.

  The signal processing unit 20 compares the measurement waveform represented by the received light intensity from the light receiving element 121 and the frequency component corresponding to the received light intensity with the reference waveform, and executes the correction process and the calculation of the mass concentration. Good. Specifically, the signal processing unit 20 acquires reference information indicating a relationship between a frequency component serving as a reference when the airflow is in a steady state and the intensity for each frequency component. On the other hand, by analyzing the frequency of a time-series signal indicating the output from the light receiving element 121 when the drive control unit 224 intermittently drives the airflow generation unit 15, the frequency component included in the signal and each frequency component are analyzed. Measurement information indicating the relationship with intensity is acquired. The reference information and the measurement information are, for example, a reference waveform and a measurement waveform obtained by Fourier-transforming a time-series signal indicating an output from the light receiving element, respectively. Then, when the relative relation of the intensity for each frequency component is substantially constant for the reference information and the measurement information, the calculation unit 222 calculates the mass concentration without performing correction processing, and the relative relation is not substantially constant. In this case, the correction process is performed to calculate the mass concentration.

  That is, the signal processing unit 20 acquires a reference waveform that serves as a reference when the airflow in the detection area DA is in a steady state, and the time series when the drive control unit 224 intermittently drives the airflow generation unit 15. If the reference waveform and the measured waveform are approximately the same, the mass concentration is calculated without performing the correction process. If the waveform does not approximately match, the correction process is performed. To calculate the mass concentration.

  When the airflow generation unit 15 is intermittently driven for the purpose of reducing power consumption, the time-series signal changes as the airflow velocity in the detection area DA varies as compared to the case of continuous driving. For this reason, compared with the case of a continuous drive, the intensity | strength for every frequency component and frequency component contained in the said signal will change. Therefore, regarding the reference information and the measurement information, when the relative relationship of the intensity for each frequency component is not substantially constant, the correction process is performed assuming that the airflow in the detection area DA is in a transition (rise) state. As a result, it is possible to reduce power consumption and increase the mass concentration calculation while reducing deterioration in detection accuracy.

  For example, the particle detection sensor 1 may not include at least one of the IV conversion unit 211, the amplification unit 212, and the AD conversion unit 221. For example, the particle detection sensor 1 does not include the AD conversion unit 221. The calculation unit 222 may calculate the particle size of the particles 2 using the voltage signal output from the amplification unit 212. However, from the following viewpoint, the particle detection sensor 1 preferably includes the AD conversion unit 221.

  That is, when the particle detection sensor 1 does not include the AD converter 221, for example, a peak hold circuit and a plurality of comparators for comparison with a plurality of thresholds are used as a configuration for calculating the peak of the voltage signal in an analog manner. Configuration is conceivable. However, in such a configuration, it takes time to charge and discharge the capacitor in the peak hold circuit, so that it is difficult to detect the peak of the voltage signal at high speed. Furthermore, it is necessary to provide a plurality of comparators as an analog circuit configuration.

  On the other hand, when the particle detection sensor 1 includes the AD conversion unit 221 that is an AD conversion module incorporated in advance in the general-purpose MPU 22, it is possible to detect the peak of the voltage signal at a higher speed than when the above-described peak hold circuit is used. Therefore, the particle size of the particles can be calculated at high speed. Furthermore, since it is not necessary to provide a plurality of comparators as the analog circuit configuration, the analog circuit configuration can be simplified and reduced in cost.

  In the above description, the medium containing particles is gas (air), but it may be a medium other than gas (liquid such as water). That is, the particle detection sensor 1 detects particles contained in a fluid that is a gas or a liquid.

  In the above description, each component in the general-purpose MPU 22 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, some or all of the constituent elements (functions) constituting the general-purpose MPU 22 are part of a microprocessor, ROM, RAM, and the like mounted on various devices (for example, the portable gas monitor 100) including the particle detection sensor 1. It may be realized as.

  Further, the present invention can be realized not only as such a particle detection sensor 1 but also as a method including steps (processing) performed by the particle detection sensor 1.

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

  For example, when the present invention is realized by a program (software), each step is executed by executing the program using hardware resources such as a CPU, a memory, and an input / output circuit of a computer. . That is, each step is executed by the CPU obtaining data from a memory or an input / output circuit or the like, and outputting the calculation result to the memory or the input / output circuit.

  In addition, it is realized by variously conceiving various modifications conceived by those skilled in the art to each embodiment, or by arbitrarily combining the components and functions in each embodiment without departing from the spirit of the present invention. This form is also included in the present invention.

DESCRIPTION OF SYMBOLS 1 Particle detection sensor 2 Particle 3 Battery 4 Display part 15 Airflow generation part (flow velocity generation part)
20 signal processing unit 100 portable gas monitor 111 light projecting element 121 light receiving element 224 drive control unit

Claims (9)

A particle detection sensor for detecting particles contained in a fluid that is a gas or a liquid,
A light projecting element that projects light to the detection region, and a light receiving device that receives light scattered by the particles located in the detection region;
A flow rate generator for generating a flow of the gas or the liquid in the detection region;
A drive controller that intermittently drives the flow velocity generator;
A signal processing unit that calculates a mass concentration of the particles contained in the fluid by processing a time-series signal indicating an output from the light receiving element;
The signal processing unit
Obtain a reference waveform as a reference when the flow of the gas or the liquid in the detection region is in a steady state,
Obtaining a measurement waveform corresponding to the time-series signal when the drive controller is intermittently driving the flow velocity generator;
For the reference waveform and the measurement waveform, when the waveforms are substantially the same, the mass concentration is calculated without performing a correction process. When the waveforms are not substantially the same, the correction process is performed to calculate the mass concentration. Particle detection sensor. The drive control unit
The particle detection according to claim 1, wherein the light projecting element is caused to emit light when the flow speed generating unit is operated, and the light projecting element is quenched when the flow rate generating unit is not operated, in synchronization with the intermittent driving of the flow rate generating unit. Sensor. The signal processing unit
Obtain the pulse-shaped reference waveform as a reference when the steady state,
Obtaining the pulsed measurement waveform included in the time-series signal when the drive control unit is intermittently driven;
When the time widths of the reference waveform and the measurement waveform having substantially the same peak value are substantially the same, the mass concentration is calculated without performing the correction process, and when the time widths are not substantially the same, the correction process is performed. The particle detection sensor according to claim 1, wherein the mass concentration is calculated by performing. The particle detection sensor according to claim 3, wherein the signal processing unit calculates the mass concentration by excluding the pulse-shaped measurement waveform having a plurality of peaks. The signal processing unit does not perform the correction process and does not perform the correction process when the time widths of each of the plurality of threshold values substantially match for the reference waveform and the measurement waveform whose peak values substantially match, and at least one of the plurality of threshold values The particle detection sensor according to claim 3, wherein the correction process is performed when the time widths of the two do not substantially match. In the correction process, the signal processing unit is the same as the detection region when the flow rate generation unit is continuously driven and the flow is in the steady state and when the flow rate generation unit is intermittently driven. The mass concentration is calculated using a relative relationship between a time width or a peak value of a pulse-like waveform included in the time-series signal when a particle having a particle size is introduced. The particle detection sensor according to Item. The particle detection sensor according to claim 1, wherein the flow velocity generation unit includes a fan, a micro pump, or a DC electric motor. The particle detection sensor according to any one of claims 1 to 7,
A battery for driving the particle detection sensor;
A portable gas monitor comprising: a display unit that displays the mass concentration calculated by the particle detection sensor. Particle detection having a light projecting element that projects light onto a detection area, a light receiving element that receives light scattered by particles located in the detection area, and a flow velocity generator that generates a flow of gas or liquid in the detection area A particle detection method for detecting the particles contained in a fluid that is a gas or a liquid using a sensor,
Obtaining a reference waveform as a reference when the flow of the gas or the liquid in the detection region is in a steady state;
Obtaining a measurement waveform corresponding to a time-series signal indicating an output from the light receiving element in a state where the flow velocity generation unit is intermittently driven;
For the reference waveform and the measurement waveform, when the waveforms are substantially the same, the mass concentration of the particles contained in the fluid is calculated without performing the correction process, and when the waveforms are not substantially the same, the correction process is performed. And calculating the mass concentration. A particle detection method.

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