JP2016109629A - Particle measuring apparatus, air cleaner, and particle measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle measuring apparatus etc., that can secure long-period reliability.SOLUTION: A particle measuring apparatus 1 comprises: a particle detection sensor 110 having a light projection element 111 projecting light on a detection region DA and a light receiving element 112 receiving scattered light of light scattered by a particle 2 positioned in the detection region DA; an AD conversion part 161 which generates digital data as a digitized voltage signal by sampling and quantizing a voltage signal indicative of output from the light receiving element 112; and an arithmetic part 162 which computes a particle size after offset processing for subtracting digital data in a second period in which the voltage signal does not include a signal component from digital data in a first period in which the voltage signal includes a signal component corresponding to the particle 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a particle measuring device for measuring particles contained in a gas, an air cleaner provided with the particle measuring device, and a particle measuring 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. For example, particles such as dust, pollen, and smoke floating in the atmosphere can be detected.

  As a particle measuring apparatus 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. (See Patent Document 1).

JP 2001-087613 A

  However, in such a particle measuring apparatus, a long-term performance drift may occur due to a change in temperature characteristics of an analog element included in the particle measuring apparatus due to long-term use or so-called deterioration over time. In this case, for example, it is difficult to ensure the long-term reliability of the particle measuring apparatus, such as high accuracy measurement of the particle diameter of the particles.

  Then, an object of this invention is to provide the particle | grain measuring apparatus etc. which can ensure long-term reliability.

  In order to achieve the above object, a particle measuring apparatus according to an aspect of the present invention is a particle measuring apparatus that measures the particle size of particles contained in a gas, and a light projecting element that projects light onto a detection region; By sampling and quantizing a particle detection sensor having a light receiving element that receives scattered light of light scattered by the particles located in the detection region, and a sensor signal indicating an output from the light receiving element, From the digital data in the first period in which the sensor signal includes a signal component corresponding to the particle, and the sensor signal does not include the signal component A calculation unit that calculates the particle size after performing an offset process for subtracting the digital data in the second period.

  According to the present invention, long-term reliability can be ensured.

It is a block diagram which shows an example of a structure of the particle | grain measuring apparatus which concerns on embodiment. It is a circuit diagram of the analog signal processing part in an embodiment. It is a block diagram of the calculating part in embodiment. In an embodiment, it is a wave form diagram showing an example of a current signal outputted from a photo acceptance unit. It is a wave form diagram which shows an example of the digital data produced | generated in embodiment. It is a wave form diagram which shows an example of the digital data produced | generated in embodiment. It is a wave form diagram which shows an example of the digital data produced | generated in embodiment. It is a flowchart which shows the particle size calculation process which concerns on embodiment. It is a flowchart which shows the detail of the reference voltage acquisition process (S10) shown in FIG. It is a figure which shows each signal in the particle | grain measuring apparatus which concerns on embodiment. It is a block diagram which shows an example of a structure of the particle | grain measuring apparatus which concerns on the modification 1 of embodiment. It is a circuit diagram of the analog signal processing part in the modification 1 of an embodiment. It is a block diagram which shows an example of a structure of the particle | grain measuring apparatus which concerns on the modification 2 of embodiment. It is a circuit diagram of the light projection element in the modification 2 of embodiment. It is a block diagram which shows an example of a structure of the particle | grain measuring apparatus which concerns on the modification 3 of embodiment. It is a block diagram which shows an example of a structure of the calculating part which concerns on the modification 3 of embodiment. It is a figure which shows each signal in the particle | grain measuring apparatus which concerns on the modification 3 of embodiment. It is a block diagram which shows an example of a structure of the particle | grain measuring apparatus which concerns on the modification 4 of embodiment. It is a block diagram which shows an example of a structure of the calculating part which concerns on the modification 4 of embodiment. It is a figure which shows each signal and the temperature of a heating part in the particle | grain measuring apparatus which concerns on the modification 4 of embodiment. It is an external view of an air cleaner.

  Below, the particle | grain measuring apparatus etc. which concern on embodiment of this invention are demonstrated in detail using drawing. 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.

(Embodiment)
[1. Constitution]
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 showing an example of the configuration of the particle measuring apparatus 1 according to the present embodiment.

  As shown in the figure, the particle measuring apparatus 1 includes a particle detection sensor 110, an analog signal processing unit 120, a sensor module 10 including a power supply unit 130, and a general-purpose MPU (Micro Processing Unit) 160, and the atmosphere ( The particle size of the particles contained in the gas is measured.

  Hereinafter, each structure of the particle | grain measuring apparatus 1 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 2 in the detection area DA. The particles 2 contained therein are detected. The light projecting element 111, the light receiving element 112, and the detection area DA are arranged inside the housing 113 so that external light is not irradiated. The light projecting element 111 and the light receiving element 112 are held by the housing 113. Yes. Further, the particle detection sensor 110 in the present embodiment further includes 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 (Light Emitting Diode) 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 this case, the light projecting element 111 may be configured to emit a mixed wave having two or more wavelengths. In the present embodiment, a bullet-type LED that outputs light having 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 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 emitted from the light projecting element 111 passes through the detection area DA via a light projecting lens arranged in front of the light projecting element 111, for example. At this time, if the particle 2 passes through the detection area DA, the light from the light projecting element 111 is scattered by the particle 2.

  The light receiving element 112 is a light receiving unit that receives light scattered from the light projecting element 111 by the particles 2 in the detection area DA. For example, the light receiving element 112 is a photo diode, a photo IC diode, a photo transistor, a photomultiplier tube, or the like. It is an element (photodetector) that receives and converts it into an electrical signal. 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 scattered light from the particles 2 is condensed on the light receiving element 112 by, for example, a light receiving lens disposed between the detection area DA and the light receiving element 112.

  The housing 113 is a member that has a light shielding property and is provided with a particle flow path that is a cylindrical space region through which air (gas) including the particles 2 flows. For example, the housing 113 is black at least on the inner surface so as to absorb stray light. Specifically, the inner surface of the housing 113 has a high light absorptance and reflects light in a specular manner. Note that the reflection on the inner surface of the housing 113 may not be a specular reflection, and a part of the light may be scattered and reflected.

  Here, the stray light is light other than the scattered light by the particles 2. Specifically, the stray light is not scattered by the particles 2 in the detection area DA among the light emitted from the light projecting element 111, and the inside of the housing 113. Traveling light, etc. The stray light also includes external light that has entered the inside of the housing 113 through the particle flow path.

  The housing 113 is formed by, for example, injection molding using a resin material such as ABS resin. At this time, for example, the inner surface of the housing 113 can be made a black surface by using a resin material to which a black pigment or dye is added. Alternatively, the inner surface of the housing 113 can be made black by applying a black paint to the inner surface after injection molding. Further, stray light may be absorbed by performing surface treatment such as embossing on the inner surface of the housing 113.

  The detection area DA is an aerosol detection area (aerosol measurement unit) that is an area for detecting particles 2 (aerosol) contained in the gas to be measured, and is a spatial area in which 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 from the light projecting device 111 hits the particle 2 to the light receiving device 112. The detection area DA is set so as to exist in the particle flow path, and the gas to be measured enters the inside of the housing 113 from the inlet 101 of the particle flow path and is detected through the particle flow path. It is guided to the area DA and flows out of the casing 113 from the outlet 102 of the particle flow path.

  In the present embodiment, the flow direction of the particle flow path (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 channel axis of the particle flow channel is set 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. May be set.

  The heating unit 115 heats the atmosphere in order to introduce the atmosphere including the particles 2 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. To do. Specifically, the heating unit 115 is a low-cost heater resistor or the like, and is disposed in the particle channel in the present embodiment. That is, the heating unit 115 heats the atmosphere in the particle channel.

  For example, when the heating unit 115 is a heater resistor, the heater resistor is heated when a voltage is applied to the heater resistor. 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 air in the particle flow path is heated by the heating unit 115, an upward air flow (upward air flow) can be generated.

  Thus, by heating the atmosphere in the particle flow path by the heating unit 115, the measurement target gas (atmosphere) can be easily drawn into the housing 113 (particle flow path). More particles 2 can be taken into the particle detection sensor 110 than when not provided. Therefore, since the amount of the particles 2 per unit volume in the detection area DA included in the particle flow path can be increased, the sensitivity can be increased.

  Moreover, since the heating unit 115 generates an upward air flow, it is preferable to install the heating unit 115 in a lower part of the particle channel 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 the particles 2 contained in the atmosphere.

[1-2. Configuration of signal processor]
Next, the configuration of the signal processing unit (analog signal processing unit 120 and general-purpose MPU 160) that performs signal processing on the current signal output from the particle detection sensor 110 and calculates the particle size of the particle 2 will be described. The signal processing unit converts the current signal, which is an analog signal, into a voltage signal and performs signal processing by analog means (circuit), and a voltage signal that is signal-processed by the analog signal processing unit 120 And a general-purpose MPU 160 that calculates the particle size of the particles 2 using digital data generated by digitizing the. Hereinafter, each component of the signal processing unit will be described in detail.

[1-2-1. 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 122 and an amplification unit 123. In the present embodiment, analog signal processing unit 120 further includes a switch 121. Hereinafter, each configuration of the analog signal processing unit 120 will be described in detail with reference to FIG.

  FIG. 2 is a circuit diagram of the analog signal processing unit 120 in the present embodiment. In the figure, only the first-stage amplifier is shown as the amplifying unit 123. However, an amplifier may be further arranged after the amplifier, or a band-pass filter independent of the amplifier may be arranged. Absent.

[1-2-1-1. switch]
The switch 121 is, for example, a transistor that is arranged in a signal path of an output signal (current signal) from the light receiving element 112 of the particle detection sensor 110 and is turned on and off according to a control signal output from a control unit 163 described later. . In the present embodiment, as shown in FIG. 2, the switch 121 is provided between the light receiving element 112 and a resistance element R11 of the IV conversion unit 122 described later in the signal path of the output signal from the light receiving element 112. For example, it is turned on when the control signal is high and turned off when it is low.

[1-2-1-2. IV conversion unit]
The IV converter 122 converts the current output from the light receiving element 112 into a voltage (IV conversion). That is, the IV conversion unit 122 converts the current signal output from the particle detection sensor 110 into a voltage signal. By converting to the voltage signal in this way, the subsequent signal processing is facilitated, and the design of the amplifying unit 123 connected to the subsequent stage of the IV converting unit 122 is facilitated.

  Specifically, as illustrated in FIG. 2, the IV conversion unit 122 includes a resistance element R <b> 11 that converts an output signal from the light receiving element 112 from a current signal to a voltage signal. When the current output from the light receiving element 112 flows through the resistance element R11, a voltage corresponding to the current is generated at both ends of the resistance element R11. As a result, the current signal from the light receiving element 112 is converted into a voltage signal and input to the amplifying unit 123.

[1-2-1-3. Amplification section]
The amplification unit 123 amplifies a predetermined band of the voltage signal converted by the IV conversion unit 122. 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 in which the frequency f1 corresponding to the flow velocity v1 of the atmosphere flowing in the particle flow path of the particle detection sensor 110 is the center frequency and the bandwidth is fbw. Note that fbw may be a predetermined frequency, or may be a frequency that is appropriately set according to the noise floor of the voltage signal. In other words, the amplification unit 123 amplifies the voltage signal converted by the IV conversion unit 122 and converts it to a voltage signal including a pulse waveform corresponding to the particle.

  Here, the pulse waveform corresponding to the particle 2 is a sine wave corresponding to the velocity of the particle 2 passing through the detection area DA, the particle size of the particle 2, or a similar waveform. This pulse waveform generally corresponds to each one of the particles 2. 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.

  For example, as illustrated in FIG. 1, the amplifying unit 123 includes a bandpass filter that passes a frequency component in a predetermined band among frequency components included in the voltage signal output from the IV conversion unit 122, and a bandpass filter. And an amplifier for amplifying a signal composed of the passed frequency component. Note that the connection order of the band-pass filter and the amplifier is not limited to this, and the amplifier may be provided upstream of the band-pass filter.

  Specifically, as illustrated in FIG. 2, the amplifying unit 123 includes an operational amplifier OP21, a capacitive element C21 arranged in series on the input side of the operational amplifier OP21, a resistive element R21 arranged in parallel, and the operational amplifier OP21. Capacitance element C22 and resistance element R22 arranged in series in the feedback loop, and resistance element R23 arranged in parallel in the feedback loop. The amplification unit 123 amplifies the voltage signal input from the IV conversion unit 122 with a predetermined band and amplification gain determined by the resistance values of the resistance elements R21 to R23 and the capacitance values of the capacitance elements C21 and C22. And output.

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

[1-3. 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.

  As shown in FIG. 1, such a general-purpose MPU 160 includes an AD conversion unit 161 and a calculation unit 162, and uses digital data generated by the AD conversion unit 161 in the particle flow path of the particle detection sensor 110. Various analyzes can be performed on particles contained in the flowing atmosphere. The various analyzes include, for example, calculation of the particle diameter of the particle or identification of the particle. In the present embodiment, general-purpose MPU 160 further includes a control unit 163. Hereinafter, each configuration of the general-purpose MPU 160 will be described in detail.

[1-3-1. AD conversion unit]
The AD conversion unit 161 samples (samples) and quantizes the voltage signal amplified by the amplification unit 123. 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.

  That is, the AD conversion unit 161 generates digital data that is a digitized voltage signal by sampling and quantizing a voltage signal (sensor signal) indicating an output from the light receiving element 112.

  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 digital data. 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 set for analog input in the general-purpose MPU 160 at a predetermined sampling period, and the sampled voltage signal Is converted into a 10-bit digital value to generate digital data.

  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. Further, the number of bits of digital data generated by the AD conversion unit 161 is not limited to the above example, and may be, for example, 8 bits or 12 bits.

[1-3-2. Calculation unit]
The calculation unit 162 calculates the particle size of the particles 2 included 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. Specifically, the calculation unit 162 calculates the voltage signal from the digital data in the first period in which the voltage signal (sensor signal) input to the AD conversion unit 161 includes a pulse waveform (signal component) corresponding to the particle 2. After passing through an offset process for subtracting digital data in the second period not including the pulse waveform, the particle size is calculated.

  In the present embodiment, the arithmetic unit 162 is digital data in a first period in which the voltage signal input to the AD converter 161 when the switch 121 is turned on includes a pulse waveform corresponding to the particle 2 in the offset process. From the fact that the switch 121 is turned off, the digital data in the second period in which the voltage signal does not include the pulse waveform is subtracted.

  That is, in this embodiment, the first period is a period during which the switch 121 is on, and the second period is a period during which the switch 121 is off.

  Hereinafter, each component of the calculating part 162 is demonstrated in detail, referring FIG.

  FIG. 3 is a block diagram of the calculation unit 162 in the present embodiment. As shown in the figure, the calculation unit 162 includes a switching unit 212, a holding unit 213, a subtracting unit 214, and a particle size estimating unit 215.

  The switching unit 212 outputs the digital data generated by the AD conversion unit 161 to the holding unit 213 according to the control signal output from the control unit 163, or outputs the digital data to the subtraction unit 214. Specifically, when the control signal indicates that the switch 121 is on (for example, when the control signal is high), the switching unit 212 outputs the digital data to the subtraction unit 214. On the other hand, when the control signal indicates that the switch 121 is off (for example, when the control signal is low), the digital data is output to the holding unit 213 and held.

  The holding unit 213 is, for example, a memory that holds the digital data output from the switching unit 212.

  The subtraction unit 214 subtracts the digital data held in the holding unit 213 from the digital data output from the switching unit 212 and outputs the subtraction result to the particle size estimation unit 215. Here, both the digital data input from the switching unit 212 and the digital data held in the holding unit 213 are time-series digital values. For example, the subtracting unit 214 subtracts the average value obtained by averaging the digital values of the digital data held in the holding unit 213 from the digital value of each sample of the digital data input from the switching unit 212, and subtracts each sample. The resulting digital value is output to the particle size estimation unit 215. Thus, in this embodiment, subtraction is performed by digital signal processing.

  Here, when subtraction is performed by analog signal processing, a configuration using an operational amplifier or the like can be considered as the configuration of the subtraction circuit. However, with such a configuration, the subtraction result may vary from a long-term viewpoint due to the long-term performance drift of the subtraction circuit itself. In addition, the analog circuit configuration may be complicated. Therefore, by performing subtraction by digital signal processing, accurate subtraction processing can be ensured over a long period of time, and the analog circuit configuration can be simplified and reduced in cost.

  The particle size estimation unit 215 estimates (calculates) the particle size of the particle 2 using time-series digital data that is a digital value of the subtraction result output from the subtraction unit 214.

[1-3-3. Control unit]
The control unit 163 generates a control signal indicating ON / OFF of the switch 121 and outputs the control signal to the switch 121 and the calculation unit 162. In the present embodiment, control unit 163 switches on and off of switch 121 alternately at predetermined time intervals.

[1-4. Power supply part]
The power supply unit 130 supplies power to the components (particle detection sensor 110 and analog signal processing unit 120) other than the power supply unit 130 among the configurations included in the sensor module 10. The power supply unit 130 is configured by, for example, a regulator that converts a voltage supplied from the outside of the sensor module 10 into a desired voltage.

  Heretofore, the configuration of the particle measuring apparatus 1 according to the present embodiment has been described.

[2. Operation]
Next, the operation of the particle measuring apparatus 1 will be described.

[2-1. Operation of particle detection sensor]
First, the detection operation of the particle 2 by the particle detection sensor 110 will be described.

  When air is heated by the heating unit 115, an ascending air current is generated in the particle channel in the housing 113. Accordingly, particles in the atmosphere enter the inside of the casing 113 from the inlet 101 of the particle flow path, pass through the particle detection area DA, and flow out of the casing 113 from the outlet 102 of the particle flow path. Is done.

  The light emitted from the light projecting element 111 is scattered by the particles 2 when the particles 2 in the detection area DA are present.

  Thereafter, when scattered light (part of the scattered light) scattered from the particles 2 is received by the light receiving element 112, a current signal corresponding to the amount of light received from the light receiving element 112 (light intensity of the received scattered light) is generated. Is output.

  FIG. 4 is a waveform diagram showing an example of a current signal output from the light receiving element 112.

  The waveform shown in the figure includes a waveform indicating the intensity of scattered light of four particles. More specifically, the waveform includes a waveform W1 having a peak value (also referred to as “peak value”) I1, a waveform W2 having a peak value I2, a waveform W3 having a peak value I3, and a peak value I4. And a waveform W4. A waveform WN due to noise is superimposed on these waveforms W1 to W4.

  Here, the larger the particle diameter of the particle 2 located in the detection area DA, the greater the light intensity of the scattered light from the particle 2. Therefore, the current signal output from the light receiving element 112 is a signal whose peak value increases as the particle size of the particle 2 increases.

  Moreover, each peak of the light intensity of the scattered light corresponds to each of the particles 2 that move together when the airflow flows through the particle flow path. Therefore, each peak value of the current signal output from the light receiving element 112 is a value corresponding to the particle size of the corresponding particle 2.

  By such an operation, the particle detection sensor 110 can detect the particles 2 contained in the gas.

[2-2. Operation of signal processor]
Next, signal processing by the signal processing unit (analog signal processing unit 120 and general-purpose MPU 160) will be described. Here, description will be made assuming that the switch 121 is on.

  First, the IV conversion unit 122 generates a voltage signal by converting the current output from the light receiving element 112 into a voltage. That is, the current signal output from the light receiving element 112 is converted into a voltage signal.

  Next, the amplifying unit 123 amplifies the voltage signal in a predetermined band.

  Thereafter, the AD conversion unit 161 generates digital data by performing digital conversion (AD conversion) on the voltage signal, which is an analog signal amplified by the amplification unit 123. That is, the AD conversion unit 161 generates time-series digital data including a pulse waveform corresponding to the particle 2 by sampling and quantization.

  Finally, the calculation unit 162 calculates the particle size of the particle 2 by executing a particle size calculation process to be described later using the digital data generated by the AD conversion unit 161.

[2-3. Particle size calculation processing (particle measurement method)]
Hereinafter, the particle size calculation process (particle measurement method) by the calculation unit 162 will be described.

[2-3-1. Effects of long-term performance drift]
Here, in the particle measuring apparatus 1, long-term performance drift may occur due to temperature characteristics and aging deterioration in the analog element included in the particle measuring apparatus 1. Since this long-term performance drift is a fluctuation with a large time constant (for example, 7 years), there is little influence on the particle size measurement and the like from a short-term viewpoint. However, from the long-term viewpoint, the measurement of the particle size becomes difficult, which greatly affects the reliability.

  5A to 5C are waveform diagrams illustrating examples of digital data generated by the AD conversion unit 161, respectively. These digital data include pulse waveforms W1 to W4 corresponding to each of the particles 2. Specifically, FIG. 5A shows a case where the long-term performance drift of the particle measuring apparatus 1 has not occurred, FIG. 5B shows a case where the long-term performance drift has progressed more than FIG. 5A, and FIG. The case where the said long-term performance drift advanced is shown.

  These figures show digital data when four particles 2 pass through the detection area DA of the particle detection sensor 110 under the same conditions. The digital data shown in these figures is, for example, 10-bit time series digital data. Although the waveform of the digital data is a step-like waveform, in these figures, it is assumed that the width of the step is very small and is shown by an apparent curve. In these figures, for convenience of explanation, the digital value of each sample of the digital data is shown converted into a voltage.

  As shown in these drawings, in the particle measuring apparatus 1, the digital data reference voltages (offset voltages) Voffset1, Voffset2, and Voffset3 vary as the long-term performance drift progresses. Specifically, Voffset1 (= 0) <Voffset2 (= 0 + α1) <Voffset3 (= 0 + α2).

  Here, the reference voltage of digital data is a voltage of a DC component (DC offset voltage) of the digital data, and is a voltage generated regardless of the pulse waveform corresponding to the particle 2. That is, the reference voltage of the digital data is a voltage that is always generated even when the particle 2 does not exist in the detection area DA.

  The fluctuation of the reference voltage is caused by the long-term performance drift of the analog element due to the above-described temperature characteristics and aging deterioration, and in particular, the fluctuation of the offset voltage of the analog signal processing unit 120 due to the long-term performance drift.

  In addition, the pulse waveforms W1 to W4 also vary as the reference voltage varies. That is, the peak values of the pulse waveforms W1 to W4 vary with the variation of the reference voltage. Thereby, even if it is the pulse waveform W1 corresponding to the same particle size, the value of a peak will be V11 <V21 <V31. Similarly, for other pulse waveforms Wk (where k = 2, 3, 4) corresponding to the same particle size, the peak value is V1k <V2k <V3k.

  Thus, due to the long-term performance drift, different peak values are obtained even with the same particle size. Therefore, when the particle size is obtained using the peak value, there is a problem that the estimation accuracy of the particle size deteriorates.

[2-3-2. Particle size calculation processing that suppresses the effects of long-term performance drift]
Therefore, the calculation unit 162 according to the present embodiment executes the particle size calculation process as follows in order to suppress the influence due to the long-term performance drift. That is, the calculation unit 162 calculates the voltage signal from the digital data in the first period in which the voltage signal (sensor signal) input to the AD conversion unit 161 includes a pulse waveform (signal component) corresponding to the particle 2. After the offset processing for subtracting the digital data in the second period that does not include the particle size, the particle size is calculated.

  Hereinafter, the particle size calculation process (particle measurement method) by the calculation unit 162 will be described in detail with reference to FIGS. FIG. 6 is a flowchart showing the particle size calculation process according to the present embodiment. FIG. 7 is a flowchart showing details of the reference voltage acquisition process (S10) shown in FIG. FIG. 8 is a diagram showing each signal in the particle measuring apparatus 1 according to the present embodiment. Specifically, FIG. 8 shows waveforms of a control signal output from the control unit 163, a current signal input to the IV conversion unit 122, and a voltage signal input to the AD conversion unit 161. .

  As illustrated in FIG. 6, first, the calculation unit 162 acquires digital data in a state where the voltage signal (sensor signal) input to the AD conversion unit 161 does not include a pulse waveform corresponding to the particle 2 (S10: Standard acquisition step). Thereby, the calculating part 162 acquires the digital value which shows the reference voltage influenced by a long-term performance drift.

  Specifically, as shown in FIGS. 7 and 8, when the control signal becomes low at time T11, the switch 121 is turned off (S11). Thereby, after time T11, the current signal input to the IV conversion unit 122 is a signal that does not include the pulse waveform corresponding to the particle 2 indicated by the broken line in the drawing. Therefore, the voltage signal input to the AD conversion unit 161 is a signal including the offset voltage of the analog signal processing unit 120 without including the pulse waveform corresponding to the particle 2.

  Then, the switching unit 212 outputs and holds the digital data generated by the AD conversion unit 161 to the holding unit 213 when the control signal becomes low after time T11 (S12).

  Thereafter, when the control signal becomes high at time T12, the switch 121 is turned on (S13). Thereby, after time T12, the current signal input to the IV conversion unit 122 is a signal including a pulse waveform corresponding to the particle 2 located in the detection area DA. Therefore, the voltage signal input to the AD conversion unit 161 is a signal including both the pulse waveform corresponding to the particle 2 and the offset voltage of the analog signal processing unit 120.

  By such a reference voltage acquisition process (S10), the holding unit 213 is a digital data obtained by digitizing the voltage signal input to the AD conversion unit 161 at times T11 to T12, and a pulse corresponding to the particle 2 Digital data including the offset voltage of the analog signal processing unit 120 is held without including the waveform.

  After the reference voltage acquisition process (S10), the calculation unit 162 acquires digital data in a state where the voltage signal input to the AD conversion unit 161 includes a pulse waveform corresponding to the particle 2 (S20: signal acquisition step). This is because the voltage signal input to the AD converter 161 after time T12 includes the pulse waveform corresponding to the particle 2 and the offset voltage of the analog signal processor 120 because the switch 121 is turned on at time T12. This is because it becomes a signal.

  Specifically, the switching unit 212 outputs the digital data generated by the AD conversion unit 161 to the subtraction unit 214 when the control signal is high after time T12.

  And the calculating part 162 calculates the particle size of the particle | grains 2 after performing the offset process which subtracts the digital data acquired by the reference voltage acquisition process (S10) from the digital data acquired by the signal acquisition process (S20). (S30: Particle size calculation step).

  Specifically, the subtraction unit 214 subtracts the digital data held in the holding unit 213 from the digital data output from the switching unit 212 in the offset process, and outputs the subtraction result to the particle size estimation unit 215. After the offset process, the particle size estimation unit 215 estimates (calculates) the particle size of the particle 2 using the subtraction result output from the subtraction unit 214.

  Here, the digital data output from the switching unit 212 includes a pulse waveform corresponding to the particle 2 and an offset voltage of the analog signal processing unit 120. On the other hand, the digital data held in the holding unit 213 includes the offset voltage of the analog signal processing unit 120 without including the pulse waveform corresponding to the particle 2.

  Therefore, the subtraction result by the subtraction unit 214 is digital data that includes a pulse waveform corresponding to the particle 2 and does not include the offset voltage of the analog signal processing unit 120. Therefore, the particle size estimation unit 215 can estimate the particle size while suppressing a decrease in estimation accuracy due to fluctuations in the offset voltage of the analog signal processing unit 120. That is, long-term reliability of the estimation accuracy of the particle diameter can be ensured.

  Specifically, the particle size estimation unit 215 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 particle size estimation unit 215 obtains a peak value of the digital data using the time-series digital data output from the subtraction unit 214, and calculates the particle size of the particles using the obtained peak value.

  By the particle size calculation process described above, the calculation unit 162 can accurately measure the particle size of the particles 2 even when the long-term performance drift has advanced.

  That is, in the example shown in FIGS. 5A to 5C, V11 = V21−α1 = V31−α2 holds for the pulse waveform W1 corresponding to the same particle size. Similarly, V1k = V2k−α1 = V3k−α2 holds for other pulse waveforms Wk (where k = 2, 3, 4) corresponding to the same particle size. Therefore, it is possible to estimate the particle size while suppressing the influence of fluctuations in the reference voltages Voffset1, Voffset2, and Voffset3 due to long-term performance drift.

  Here, the method for detecting the peak value is arbitrary. For example, when the digital value continuously decreases in a predetermined number of samples compared to the digital value of the sample to be determined, The digital value of the sample may be detected as the peak value. Further, the digital value of the sample to be determined may be detected as the peak value when the digital value of the immediately following sample is lower than a predetermined value as compared with the digital value of the sample to be determined. In addition, when the digital value of the determination target sample is larger than the digital value of the preceding and succeeding samples, the number of samples to be compared with the determination target sample may be one or more, and may be plural.

  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 particle size estimation unit 215 can also calculate the number (amount) of particles in the atmosphere introduced into the particle detection sensor 110.

  The particle size estimation unit 215 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 particle size estimation unit 215 has a plurality of threshold values (for example, 10 levels of threshold values Vth1 to Vth10) for calculating the particle size of the particles, and the digital data output from the subtraction unit 214 is the plurality of threshold values. A peak search may be performed when the threshold value is larger than the lowest threshold value (for example, Vth1). In other words, the particle size estimation unit 215 may start the peak search when the digital data exceeds the minimum threshold value.

  As described above, the particle size estimation unit 215 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. it can. 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, various misdetections caused by the particle size estimation unit 215 calculating the noise peak can be reduced. Note that various misdetections include, for example, misdetection of the particle diameter of particles and misdetection of the number of particles.

  The particle size estimation unit 215 may detect digital data peaks asynchronously. That is, the detection of the peak of the digital data by the particle size estimation unit 215 is not limited to the predetermined time interval but may be an arbitrary time interval. Thereby, even when a plurality of particles having different particle diameters are successively introduced into the detection area DA, the particle diameter of each of the plurality of particles can be calculated.

  As a result, the phase at which the peak of the pulse waveform included in the digital data appears may change. However, by detecting the peak of digital data asynchronously, each peak can be detected even when the phase in which the peak appears changes. Therefore, since the peak can be detected with high accuracy, the particle size of each particle can be calculated with high accuracy.

  In this embodiment, operation part 162 acquires the reference voltage of digital data regularly. Thereby, the long-term reliability of the estimation accuracy of the particle diameter can be further ensured.

  That is, as shown in FIG. 8, the control signal is alternately switched between high and low at a predetermined time interval. That is, the control unit 163 alternately switches on and off the switch 121 at predetermined time intervals.

  In other words, the calculation unit 162 is a second period in which the voltage signal (sensor signal) input to the AD conversion unit 161 does not include a pulse waveform corresponding to the particle 2 in a period repeated at a predetermined timing. In the example shown, the digital data in the period is updated every time T11 to T12 and time T13 to T14. And the digital in the 1st period (in the example shown in FIG. 8, time T12-T13, time T14-T15, etc.) in which the voltage signal (sensor signal) input into AD conversion part 161 contains the pulse waveform according to particle 2 The particle diameter is calculated after an offset process for subtracting the updated digital data from the data.

  For example, the arithmetic unit 162 updates the digital data held in the holding unit 213 every second period, and in the first period after the second period, the holding unit starts from the digital data input from the AD conversion unit 161. An offset process for subtracting the digital data held in 213 is executed.

[3. Effect]
As described above, the particle measuring apparatus 1 according to the embodiment of the present invention is a scattered light of light scattered by the light projecting element 111 that projects light to the detection area DA and the particles 2 that are positioned in the detection area DA. Sampling and quantizing a particle detection sensor 110 having a light receiving element 112 that receives light and a sensor signal indicating an output from the light receiving element 112 (in this embodiment, a voltage signal input to the AD converter 161). The AD converter 161 that generates digital data that is a digitized sensor signal, and the sensor signal has a pulse waveform from the digital data in the first period in which the sensor signal includes a pulse waveform (signal component) corresponding to the particle 2 And a calculation unit 162 that calculates the particle size after performing an offset process for subtracting digital data in the second period that does not include.

  Thereby, the subtraction result in the calculating part 162 becomes digital data including the pulse waveform corresponding to the particle 2 and not including the reference voltage of the sensor signal. Therefore, since it is possible to estimate the particle size while suppressing a decrease in estimation accuracy due to fluctuations in the reference voltage of the sensor signal, it is possible to ensure long-term reliability of the particle size estimation accuracy.

  The particle measuring apparatus 1 further includes a switch 121 arranged in a signal path of an output signal from the light receiving element 112 (in this embodiment, a current signal), and performs sensor signal processing on the output signal. An analog signal processing unit 120 that generates a signal and outputs the signal to the AD conversion unit 161 is provided. The calculation unit 162 is a digital signal in a first period in which the sensor signal includes a pulse waveform when the switch 121 is turned on in the offset processing. The digital data in the second period in which the sensor signal does not include a pulse waveform is subtracted from the data because the switch 121 is turned off.

  Here, the fluctuation of the reference voltage of the sensor signal is caused by a long-term performance drift of the analog element due to temperature characteristics and aging deterioration, and in particular, caused by a fluctuation of the offset voltage of the analog signal processing unit 120 due to the long-term performance drift. It is. Therefore, by turning off the switch 121 arranged in the signal path of the output signal from the light receiving element 112, it is possible to accurately measure the variation in the offset voltage of the analog signal processing unit 120. Long-term reliability can be further secured.

  Specifically, the analog signal processing unit 120 includes an IV conversion unit 122 having a resistance element R11 that converts an output signal from the light receiving element 112 from a current signal to a voltage signal. The signal path of the output signal is disposed between the light receiving element 112 and the resistance element R11.

  Thereby, it is possible to estimate the particle size while suppressing a decrease in estimation accuracy due to a change in the reference voltage of the sensor signal due to the impedance of the resistance element 11.

  In addition, the calculation unit 162 updates the digital data in the second period for each second period that is a period repeated at a predetermined timing and the sensor signal does not include a pulse waveform corresponding to the particle 2, and in the offset process The updated digital data is subtracted from the digital data in the first period in which the sensor signal does not include the pulse waveform.

  Thereby, since the digital data of the reference voltage of the sensor signal is periodically updated and subtracted from the digital data including the pulse waveform corresponding to the particle 2, long-term reliability of the particle size estimation accuracy can be further ensured.

(Modification 1)
Next, Modification 1 of the embodiment of the present invention will be described. In the above embodiment, the switch 121 is disposed between the light receiving element 112 and the resistance element R11 of the IV conversion unit 122 described later in the signal path of the output signal from the light receiving element 112. However, the switch 121 only needs to be disposed in the signal path of the output signal from the light receiving element 112, and is disposed in the path of the voltage signal converted by the IV conversion unit 122 in this modification.

  FIG. 9 is a block diagram showing an example of the configuration of the particle measuring apparatus 1A according to this modification. A particle measuring apparatus 1A shown in the figure includes a sensor module 10A including an analog signal processing unit 120A described later. FIG. 10 is a circuit diagram of the analog signal processing unit 120A in the present modification. In FIG. 10, only the first-stage amplifier is shown as the amplifying unit 123, as in FIG. 2. However, an amplifier may be arranged after the amplifier, or a band-pass filter independent of the amplifier may be arranged. It may be done.

  As shown in these drawings, the switch 121 is disposed between the IV conversion unit 122 and the amplification unit 123.

  Even with the particle measuring apparatus 1A configured as described above, the same effects as those of the above-described embodiment can be obtained.

(Modification 2)
Next, a second modification of the embodiment of the present invention will be described. Compared to the above embodiment, in the present modification, the calculation unit 162 uses the light projecting element from the digital data including the pulse waveform corresponding to the particle 2 by the light projecting element projecting in the offset process. Is different in that the digital data not including the pulse waveform is subtracted by quenching.

  FIG. 11 is a block diagram showing an example of the configuration of the particle measuring apparatus 1B according to this modification. The particle measuring apparatus 1B shown in the figure includes a sensor module 10B including an analog signal processing unit 120B described later.

  As shown in the figure, the analog signal processing unit 120B in this modification example does not have the switch 121 as compared with the analog signal processing unit 120 in the above embodiment. In addition, the control unit 163B included in the general-purpose MPU 160B in this modification outputs a control signal to the light projecting element 111B as compared with the control unit 163 in the above embodiment.

  FIG. 12 is a circuit diagram of the light projecting element 111B in the present modification.

  As shown in the figure, the light projecting element 111B in the present modification includes a light emitting diode 151, a resistance element R103 and a switch 152 connected in series with the light emitting diode 151.

  The switch 152 is, for example, a transistor that is turned on and off according to a control signal output from the control unit 163. For example, the switch 152 is turned on when the control signal is high and turned off when the control signal is low.

  Thereby, the light emitting diode 151 emits and extinguishes according to the control signal. That is, the light projecting element 111B in the present modification is controlled to project and extinguish by the control unit 163B.

  Here, when the light projecting element 111B projects, the current signal output from the light receiving element 112 includes a pulse waveform corresponding to the particle 2. On the other hand, when the light projecting element 111B is extinguished, the light intensity received by the light receiving element 112 is substantially zero because there is no light scattered by the particles 2. Therefore, the current signal output from the light receiving element 112 does not include a pulse waveform corresponding to the particle 2.

  That is, the voltage signal (sensor signal) input to the AD conversion unit 161 includes the pulse waveform corresponding to the particle 2 and the reference voltage when the light projecting element 111B is projecting, and the light projecting element 111B When the light is extinguished, the reference voltage is included without including the pulse waveform corresponding to the particle 2.

  Therefore, in the particle measuring apparatus 1B according to the present modification, the calculation unit 162 determines that the voltage signal input to the AD conversion unit 161 corresponds to the particle 2 because the light projecting element 111B is projecting in the offset process. From the digital data in the first period including the pulse waveform (signal component), the digital signal in the second period in which the voltage signal input to the AD conversion unit 161 due to the light emitting element 111B being extinguished does not include the signal component. Is subtracted. Then, after such an offset process, the particle size is calculated.

  Even the particle measuring apparatus 1B configured as described above can achieve the same effects as those of the above-described embodiment.

  Here, the variation in the reference voltage of the voltage signal input to the AD conversion unit 161 described in the embodiment is caused not only by the variation in the offset voltage of the analog signal processing unit 120B but also in the light receiving element 112. It is also caused by dark current over time (eg, increase).

  Therefore, in this modification, the dark current generated in the light receiving element 112 is obtained by subtracting the digital data in the period in which the light projecting element 111B is extinguished from the digital data in the period in which the light projecting element 111B is projecting. It is possible to estimate the particle size while suppressing a decrease in estimation accuracy due to the change with time. Therefore, the long-term reliability of the estimation accuracy of the particle size can be further secured.

(Modification 3)
Next, a third modification of the embodiment of the present invention will be described. Compared with the above-described embodiment, in this modification, the calculation unit is digital data including a pulse waveform corresponding to the particle 2 because a predetermined period has elapsed since the particle measuring device was started in the offset process. The difference is that the digital data not including the pulse waveform is subtracted because the predetermined period has not elapsed.

  FIG. 13 is a block diagram showing an example of the configuration of a particle measuring apparatus 1C according to this modification. The particle measuring apparatus 1C shown in the figure includes a sensor module 10C in which the light projecting element 111 is not controlled to emit light as compared with the sensor module 10B shown in FIG. FIG. 14 is a block diagram illustrating an example of the configuration of the calculation unit 162C according to the present modification.

  As shown in these drawings, the general-purpose MPU 160C in this modification example does not include the control unit 163 and includes the calculation unit 162C instead of the calculation unit, as compared with the general-purpose MPUs in the above-described embodiment and modification examples 1 and 2. . The calculation unit 162C further includes an activation determination unit 211C as compared with the calculation unit 162 in the above embodiment.

  For example, the activation determination unit 211C detects the activation of the particle measuring device 1C by an increase in the power supply voltage supplied from the power supply unit 130 to the general-purpose MPU 160C, and indicates that the predetermined period has elapsed when a predetermined period has elapsed since the detection. A control signal is output to the switching unit 212. For example, the activation determination unit 211C sets the control signal to low when a predetermined period has not elapsed since the activation of the particle measuring apparatus 1C. On the other hand, when a predetermined period has elapsed since the start of the particle measuring apparatus 1C, the control signal is set to high. When the particle measuring apparatus 1C is not activated, the control signal is low because there is no power supply voltage supplied to the general-purpose MPU 160C.

  As a result, the switching unit 212 outputs and holds the digital data when the predetermined period has not elapsed since the activation of the particle measuring apparatus 1C to the holding unit 213, and the digital data after the predetermined time has passed to the subtracting unit 214. Output.

  FIG. 15 is a diagram illustrating each signal in the particle measuring apparatus 1C according to the present modification. Specifically, the figure shows the waveform of the power supply voltage of the particle measuring apparatus 1C, the current signal input to the IV conversion unit 122, and the voltage signal input to the AD conversion unit 161.

  In the example of the figure, the activation determination unit 211C switches the control signal output to the switching unit 212 from low to high at a time T32 when a predetermined period has elapsed from the time T31 when the particle measuring device 1C was activated.

  Here, it is difficult for the particle measuring apparatus 1 </ b> C to easily draw the gas (atmosphere) to be measured into the particle flow path at times T <b> 31 to T <b> 32 immediately after the activation of the particle measuring apparatus 1. Therefore, at times T31 to T32, the current signal output from the light receiving element 112 is unlikely to include a pulse waveform corresponding to the particle 2, and the pulse waveform is likely to be included in the current signal after time T32.

  That is, the voltage signal (sensor signal) input to the AD converter 161 includes a pulse waveform corresponding to the particle 2 and a reference voltage when a predetermined period has elapsed since the particle measuring apparatus 1C is activated, When the period has not elapsed, the reference voltage is included without including the pulse waveform corresponding to the particle 2.

  Therefore, in the particle measuring apparatus 1C according to the present modification, the calculation unit 162C has passed a predetermined period (a period from time T31 to time T32 in the example of FIG. 15) after the particle measuring apparatus 1C is activated in the offset process. As a result, the voltage signal input to the AD converter 161 has passed from the digital data in the first period including the pulse waveform (signal component) corresponding to the particle 2 from the start of the particle measuring apparatus 1C. The voltage signal input to the AD converter 161 subtracts the digital data in the second period that does not include the pulse waveform. Then, after such an offset process, the particle size is calculated.

  Even with the particle measuring apparatus 1 </ b> C configured as described above, the same effects as those of the above-described embodiment can be obtained.

  Further, according to this modification, the calculation unit 162C subtracts digital data within a predetermined period after the particle measuring apparatus 1C is activated in the offset process. That is, the offset process can be executed using the digital data immediately after the activation of the particle measuring apparatus 1C. Therefore, it is possible to suppress a decrease in estimation accuracy due to a change in characteristics due to the installation state of the particle measuring apparatus 1C and the usage environment.

  Furthermore, since a voltage signal that does not include a pulse waveform corresponding to the particle 2 may be measured immediately after the activation of the particle measuring device 1C, the signal processing speed decreases after a predetermined period has elapsed since the particle measuring device 1C is activated. It becomes difficult to cause.

(Modification 4)
Next, a fourth modification of the embodiment of the present invention will be described. Compared to the above-described embodiment, in this modification, the calculation unit is a digital including a pulse waveform corresponding to the particles 2 because the heating temperature by the heating unit 115 reaches a predetermined stable temperature in the offset processing. The difference is that digital data not including the pulse waveform is subtracted from the data because the heating temperature does not reach the stable temperature.

  FIG. 16 is a block diagram showing an example of the configuration of a particle measuring apparatus 1D according to this modification. FIG. 17 is a block diagram illustrating an example of the configuration of the calculation unit 162D according to the present modification.

  As shown in these drawings, the general-purpose MPU 160D in this modification example does not include the control unit 163 and includes a calculation unit 162D instead of the calculation unit 162, as compared with the general-purpose MPU 160 in the above embodiment. The calculation unit 162D further includes a temperature determination unit 211D as compared with the calculation unit 162 in the above embodiment.

  For example, the temperature determination unit 211D measures the temperature of the heating unit 115, and when the measured temperature reaches a predetermined stable temperature, outputs a control signal indicating that the stable temperature has been reached to the switching unit 212. For example, when the temperature of the heating unit 115 has not reached the stable temperature, the temperature determination unit 211D sets the control signal to low. On the other hand, when the temperature of the heating unit 115 reaches the stable temperature, the control signal is set to high. When the particle measuring device 1D is not activated, the control signal is low because there is no power supply voltage supplied to the general-purpose MPU 160D.

  Thereby, the switching unit 212 outputs and holds the digital data when the temperature of the heating unit 115 does not reach the stable temperature to the holding unit 213 and holds the digital data when the temperature reaches the stable temperature. To 214.

  FIG. 18 is a diagram illustrating each signal and the temperature of the heating unit 115 in the particle measuring apparatus 1D according to the present modification. Specifically, in the figure, the waveform of the power supply voltage of the particle measuring apparatus 1D, the temperature of the heating unit 115, the current signal input to the IV conversion unit 122, and the voltage signal input to the AD conversion unit 161 are shown. It is shown.

  In the example of the figure, the temperature determination unit 211D switches the control signal output to the switching unit 212 from low to high at time T42 when the temperature of the heating unit 115 reaches the stable temperature. The stable temperature may be any temperature as long as the gas (atmosphere) to be measured can be drawn into the particle channel at a desired flow rate, and the temperature of the heating unit may not be constant.

  Here, it is difficult for the particle measuring apparatus 1D to draw the measurement target gas (atmosphere) at a desired flow rate into the particle channel at times T41 to T42 when the temperature of the heating unit 115 does not reach the stable temperature. is there. That is, at the times T41 to T42, the detection target particle 2 is unlikely to pass through the detection area DA. Therefore, at times T41 to T42, the current signal output from the light receiving element 112 does not easily include a pulse waveform corresponding to the particle 2, and the pulse waveform is likely to be included in the current signal after time T42.

  That is, when the temperature of the heating unit 115 reaches the stable temperature, the voltage signal (sensor signal) input to the AD conversion unit 161 includes the pulse waveform corresponding to the particle 2 and the reference voltage, and the temperature When the temperature does not reach the stable temperature, the reference voltage is included without including the pulse waveform corresponding to the particle 2.

  Therefore, in the particle measuring apparatus 1D according to the present modification, the calculation unit 162D has the voltage signal input to the AD conversion unit 161 when the heating temperature by the heating unit 115 reaches a predetermined stable temperature in the offset process. From the digital data in the first period including the pulse waveform (signal component) corresponding to the particle 2, the voltage signal input to the AD converter 161 because the heating temperature has not reached the stable temperature is the pulse waveform. The digital data in the second period not including is subtracted. Then, after such an offset process, the particle size is calculated.

  Even the particle measuring apparatus 1D configured as described above can achieve the same effects as those of the above-described embodiment.

(Other variations)
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, the particle measurement device may not include at least one of the IV conversion unit 122 and the amplification unit 123. For example, the particle measurement device does not include the amplification unit 123, and the calculation unit 162 is connected to the IV conversion unit 122. The particle size of the particles 2 may be calculated using the output voltage signal.

  In the above description, the voltage signal (the voltage signal output from the amplifying unit 123) input to the AD conversion unit 161 as a sensor signal indicating the output from the light receiving element 112 has been described as an example. However, the sensor signal may be a voltage signal output from the IV conversion unit 122 or a current signal output from the light receiving element 112.

  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).

  Further, the configuration of the particle detection sensor is not limited to the configuration described above, and includes at least a light projecting element 111 and a light receiving element 112, and the light receiving element emits scattered light of the light projecting element due to particles in the detection area DA. What is necessary is just to detect the particle | grains contained in air | atmosphere by just receiving light. Even with such a configuration, the particle measuring apparatus including the particle detection sensor can measure the particle size of particles contained in the gas.

  The configuration of the amplification unit is not limited to the configuration described above, and at least the voltage signal output from the IV conversion unit 122 may be amplified in a predetermined band. That is, the amplifying unit may not include a band pass filter, and may include a high pass filter or a low pass filter. Further, the amplifier 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 present invention can be realized not only as the particle measuring apparatus described in the above embodiment and modifications, but also as an air cleaner provided with the particle measuring apparatus shown in FIG. 19, for example. In this case, some or all of the components (functions) constituting the general-purpose MPU 160 described above may be realized as a part of a microprocessor, ROM, RAM, or the like mounted on the air cleaner.

  Further, the present invention can be realized not only as such a particle measuring apparatus, but also as a particle measuring method using a characteristic process performed by the particle measuring apparatus as a step.

  Further, the present invention is realized as a program for causing a computer to execute characteristic processing included in the particle measurement method, or a computer-readable non-transitory recording medium on which the program is recorded, such as a flexible disk or a hard disk , CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray (registered trademark) Disc), or a semiconductor memory. Needless to say, such a program can be distributed via a recording medium such as a CD-ROM and a transmission medium such as the Internet.

  In addition, any form obtained by subjecting each embodiment and modification to various modifications conceived by those skilled in the art, and any combination of the components and functions in each embodiment without departing from the spirit of the present disclosure Implemented forms are also included in the present disclosure.

1, 1A, 1B, 1C, 1D Particle measuring device 2 Particle 110 Particle detection sensor 111, 111B Light projecting element 112 Light receiving element 121 Switch 122 IV conversion unit 123 Amplification unit 161 AD conversion unit 162, 162C, 162D Calculation unit DA Detection area

Claims (9)

A particle measuring device for measuring the particle size of particles contained in a gas,
A particle detection sensor having a light projecting element that projects light to a detection region, and a light receiving element that receives scattered light of light scattered by the particles located in the detection region;
An AD converter that generates digital data that is the sensor signal digitized by sampling and quantizing the sensor signal indicating the output from the light receiving element;
After the sensor signal undergoes an offset process for subtracting the digital data in a second period in which the sensor signal does not include the signal component from the digital data in a first period in which the sensor signal includes a signal component corresponding to the particle, the grain A particle measuring apparatus comprising a calculation unit that calculates a diameter. The particle measuring apparatus further includes a switch disposed in a signal path of an output signal from the light receiving element, generates the sensor signal by performing analog signal processing on the output signal, and outputs the sensor signal to the AD conversion unit An analog signal processing unit
In the offset processing, the arithmetic unit is configured to detect the sensor signal when the switch is turned off from the digital data in the first period when the sensor signal includes the signal component when the switch is turned on. The particle measuring apparatus according to claim 1, wherein the digital data in the second period that does not include the signal component is subtracted. The analog signal processing unit includes an IV conversion unit including a resistance element that converts an output signal from the light receiving element from a current signal to a voltage signal,
The particle measuring apparatus according to claim 2, wherein the switch is disposed between the light receiving element and the resistance element in a signal path of an output signal from the light receiving element. In the offset processing, the light emitting element is extinguished from the digital data in the first period in which the sensor signal includes the signal component because the light projecting element emits light in the offset processing. The particle measuring apparatus according to claim 1, wherein the digital data in the second period in which the sensor signal does not include the signal component is subtracted. In the offset processing, the calculation unit determines that the sensor signal includes the signal component from the digital data in the first period when a predetermined period has elapsed since the particle measuring apparatus is started. The particle measurement according to any one of claims 1 to 4, wherein the digital signal in the second period in which the sensor signal does not include the signal component is subtracted because the predetermined period has not elapsed since the activation of apparatus. The particle measuring apparatus further includes a heating unit that generates an air flow in the detection region by heating a part of the gas,
In the offset process, the arithmetic unit is configured to calculate the heating temperature from the digital data in the first period in which the sensor signal includes the signal component because the heating temperature by the heating unit has reached a predetermined stable temperature. The particle | grain measuring apparatus of any one of Claims 1-4 by which the said digital signal in the said 2nd period when the said sensor signal does not contain the said signal component is subtracted by not having reached the said stable temperature. The arithmetic unit updates the digital data in the second period every second period repeated at a predetermined timing, and in the offset process, in the second period after the update from the digital data in the first period The particle measuring apparatus according to claim 1, wherein the digital data is subtracted.   An air cleaner provided with the particle | grain measuring apparatus of any one of Claims 1-7. A light projecting element that projects light onto a detection region, a particle detection sensor having a light receiving device that receives scattered light scattered by particles located in the detection region, and a sensor that indicates an output from the light receiving device This is a particle measurement method for measuring the particle size of the particles contained in a gas using an AD converter that generates digital data that is the digitized sensor signal by sampling and quantizing the signal. And
A reference acquisition step of acquiring the digital data in a state in which the sensor signal does not include a signal component corresponding to the particles;
A signal acquisition step of acquiring the digital data in a state where the sensor signal includes the signal component;
A particle size measurement method comprising: a particle size calculation step of calculating the particle size after performing an offset process for subtracting the digital data acquired in the reference acquisition step from the digital data acquired in the signal acquisition step.

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