JP2011095022A - Particle sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particle sensor which discriminates the particle sizes of fine particles, using an inexpensive device, regardless of the concentration of particles. <P>SOLUTION: The particle sensor is equipped with an emitter A and first and second light detectors S1 and S2, producing light detection output signals corresponding to the scattered light of the particles in a measuring area B, based on the LED light emitted from the emitter. The first light detector S1 is arranged behind the measuring area B, positioned in front of the irradiation direction of the LED light from the emitter, and the second light detector S2 is arranged in front of the measuring area B, positioned in front of the irradiation direction of the LED light from the emitter, and the particle sensor is also equipped with a means 1 for calculating the ratio of the light detection output signals by the first and second light detectors and means 2 and 3 for calculating the particle size of the particles from the ratio of the light detection output signals. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a particle sensor that detects fine particles, and more particularly to a particle sensor that can identify the size of particles.

  Conventionally, light is emitted to particles floating in the atmosphere or liquid, and the intensity of the light (scattered light) scattered by the irradiated light hitting the particles is converted into voltage by the light receiving element and output. Particle sensors that detect suspended particles from their values and identify their sizes are widely known. As these conventional particle sensors, for example, a dust detection device (Patent Document 1) of an air cleaner that detects and operates dust for general household use, or detection of pollen particles floating in the air causing hay fever is used. A pollen sensor (Patent Document 2) and the like are known. In addition, a particle sensor based on the above principle is also used in a particle counter for managing an aseptic and dust-free environment in a clean room, a particle size distribution measuring device for measuring the particle size of powder, and the like.

  However, the conventional particle sensor for measuring the particle size of suspended particles is intended to measure the particle size of one particle from the detected scattered light intensity. In this method, a count loss occurs when the particle concentration at which a certain number of particles simultaneously pass through the measurement area is large. As a result, there is a problem that the counting is over and the detection is not accurate. As this cause, multiple scattering between particles occurs. In order to accurately determine the size of the particles, various means such as using a filter and a complicated device have been used. Thus, in the measurement when the particle concentration is high, there is a problem that the conventionally known method easily causes counting loss and takes a lot of time and effort.

Japanese Patent Laid-Open No. 5-126717 JP-A-2005-283152

  The present invention has been made on the basis of the above-described circumstances, and it is possible to easily identify the particle size of fine particles with an inexpensive apparatus that does not cause a count loss regardless of the particle concentration (darkness). An object of the present invention is to provide a particle sensor that can be used.

  The particle sensor of the present invention includes a light emitting unit, and a first light receiving unit and a second light receiving unit that generate a light reception output signal in accordance with scattered light of particles in a measurement area based on LED light emitted from the light emitting unit. The first light receiving part is behind the measurement area located in front of the irradiation direction of the LED light from the light emitting part, and the second light receiving part is ahead of the measurement area located in front of the irradiation direction of the LED light from the light emitting part. And a means for calculating a ratio of light reception output signals by the first light receiving section and the second light receiving section, and a means for calculating the particle diameter of the particles from the ratio of the light reception output signals. .

  From the output voltage ratio of the first light receiving part and the second light receiving part, the ratio of the back scattered light scattered backward and the forward scattered light scattered forward from the measurement area located in front of the irradiation direction of the LED light is calculated. Detect. From this value, it is possible to identify the particle size (size) of the particle without causing a count loss regardless of the particle concentration, and the particle size can be identified with an inexpensive apparatus. In addition, the first light receiving unit and the second light receiving unit are preferably arranged in directions of 45 ° and 135 ° from the center of the measurement area with respect to the irradiation direction of the LED light from the LED light emitting unit. The output voltage ratio can be acquired efficiently and stably. The particle size to be identified is preferably about 0.5 to 5 μm, and it is particularly preferable to use blue light for particle size identification of fine particles of 1 μm or less.

It is a top view which shows the structural example of the experimental apparatus used as the foundation of this invention. It is a graph showing the light-receiving ratio of each light-receiving part channel by irradiating infrared light to a particle group having a large / medium / small particle diameter of 0.5 μm. It is a graph showing the light-receiving ratio of each light-receiving part channel by irradiating infrared light to a particle group having a particle size of 5 μm of high / medium / small concentration. It is a graph which shows the output voltage of each light-receiving part channel at the time of taking light-receiving part channel 1-19 on a horizontal axis and irradiating blue light to three types of particle groups of 0.5, 5, and 30 micrometers. (A) is a 30 μm particle group, (b) is a 5 μm particle group, (c) is a 0.5 μm particle group when irradiated with infrared light, green light, and blue light, respectively. It is a graph which shows the output voltage of. It is a graph which shows the sensitivity of each channel about channels 6-8. It is a graph which shows the relationship of the output voltage and voltage ratio of channel 1 and channel 7. It is a graph which shows the output voltage ratio of the channel 1 at the time of irradiating a 0.5 micrometer particle group and a 5 micrometer particle group with infrared light, green light, and blue light. It is a top view which shows the structural example of the particle | grain sensor of one Example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 9. In addition, in each figure, the same code | symbol is attached | subjected and demonstrated to the same or equivalent member or element.

  As shown in FIG. 1, the inventor of the present invention has an LED light emitting part A and a measurement area B positioned in front of the direction x irradiated with LED light and a center C that is the center point of the measurement area B in a circle. An apparatus was prepared in which channels 1-19, which are 19 light receiving portions, were arranged around measurement area B at intervals of 15 ° as the center. The sample particle group arranged in the measurement area B was irradiated with LED light, and the scattered light intensity of almost the entire circumference was measured by the channel 1-19. In the sample particle group, a large number of particles of a specific size are attached to a transparent adhesive tape and fixed in the vicinity of the center C.

Specifically, in an environment where a large number of particles having the same particle size are different (high density / medium / small), the type (wavelength) of LED light is changed, and infrared light, green light, blue light is changed. The amount of light received by each channel 1-19 was measured. In this experimental example, as an example, the high concentration is 336 particles / 0.30 mm ² , the particle density is 296 particles / 0.30 mm ² , and the low concentration is 192 particles / 0.30 mm ^2. It is.

  FIG. 2 irradiates a group of particles having a large / medium / small particle size of 0.5 μm with infrared light, and FIG. 3 irradiates a group of particles having a large / medium / small particle size of 5 μm with infrared light. It is a graph showing the light reception ratio of each channel, where the total voltage value of each channel 1-19 is 100. The channel 8-11 is excluded from the measurement target of the light reception ratio for the reason described later.

  From these graphs, the light receiving ratio decreases in the channel 1 to the channel 4 where the angle from the center C of the LED light emitting part A and the measurement area B is 45 ° to 90 ° with respect to the irradiation direction x of the LED light, and the angle is It shows that the light reception ratio increases in channel 5 to channel 8 which is 105 ° to 150 °. From these graphs of FIGS. 2 and 3, it can be seen that the light reception ratio is independent of the particle concentration, but is substantially constant in each channel 1-19, and varies greatly depending on the particle diameter. These two phenomena are not limited to the infrared light of the LED light shown in FIGS. 2 and 3, but are not shown here, but are commonly seen regardless of the type (wavelength) of the LED light. This inventor was able to confirm by experiment.

  FIG. 4 is a graph in which the horizontal axis represents each channel of the light receiving unit and the vertical axis represents the output voltage of each channel. A blue LED is used for the light emitting part, and the particle diameters of the particles are three types of 0.5, 5, and 30 μm, each having a large concentration. When using a short wavelength LED such as blue light, the backscattered light (light irradiated by the LED hits the particle and scatters back from the vicinity of the center C in the irradiation direction) becomes large, which is noticeable with small diameter particles. The result was obtained. It can be seen that the output voltage of channel 1 increases significantly as the particle size decreases.

  5A, 5B, and 5C are graphs in which the horizontal axis represents the light receiving unit 1-8 channel and the vertical axis represents the output voltage of each channel. The particle diameters were (a) 30 μm, (b) 5 μm, and (c) 0.5 μm, each having a large concentration, and the LED light was acquired for three types of infrared light, green light, and blue light. As the particle size decreases, the backscattered light (light scattered backward from the center C, that is, the output voltage of the channel 1-3) increases, and the forward scattered light (light scattered forward from the center C, that is, the channel 5). It can be seen that the output voltage (−8) tends to decrease. The output power increases as the particle size decreases, and this tendency is particularly strong in blue with a short wavelength. In particular, this relationship is significant when the particle size (b) is 5 μm- (c) 0.5 μm. As described above, there is no relation to the concentration of the particles.

  Moreover, as the type of LED light, the above-mentioned tendency becomes most remarkable with blue light having a short wavelength (about 430 nm), followed by green light (about 525 nm), and finally the order of short wavelength of infrared light (about 850 nm). I understand that Note that the channel 9-11 is a position where the light is blocked by the particles, and the position where the influence of the direct irradiation of the LED irradiation light is the largest, so it is determined that the channel 9-11 is not suitable for acquiring scattered light data. Acquisition is omitted. In addition, the channel 8 is also considered to be unstable due to the influence of the light emitted from the light emitting unit LED in addition to the forward scattered light.

  Therefore, the above-mentioned tendency can be detected most stably and remarkably in the channel 1-3 receiving the backscattered light, and the channel 1 in the channel 5-8 receiving the forward scattered light. Moreover, when measuring output voltage using LED of a different wavelength in the same environment, it turns out that the value of output voltage differs with the kind of LED.

FIG. 6 shows which channel among channels 4 to 8 is most suitable for light reception with respect to channel 1. The light emitting unit LED in this figure is blue, and the “sensitivity” on the vertical axis in the figure is defined as follows.
When the output voltage of channel X when the particle size of the measurement target particle is D is VcX (D) and the output voltage of channel 1 is Vc1 (D),
Sensitivity = (Vc1 (0.5μm) / VcX (0.5μm)) / (Vc1 (5μm) / VcX (5μm))
However, channel X is 5-8.

  When this value is large, it becomes easy to identify a particle diameter of 0.5 to 5 μm. It can be seen from FIG. 6 that channel 7 is the best. The sensitivity of channel 8 is negative because when the particle size is small or when an LED with a short wavelength is used as the light emitting part, the forward scattered light decreases and the output voltage may become negative. . From these, it can be seen that a blue LED is effective in detecting a minute particle size of about 0.5 μm as the type of LED light. Thus, channel 7 is most desirable for combination with channel 1.

  FIG. 7 is a graph showing the relationship between the output voltages of channel 7 and channel 1. The LED is blue light, and the particle size is 0.5 μm for the x mark and 5 μm for the Δ mark. The measurement data at the three locations for the two types of particle sizes show the difference in concentration, but when the concentration is large and the particle size is 0.5 μm, the voltage ratio of channel 1 / channel 7 is 3.40. When the particle diameter is 5 μm, the voltage ratio of channel 1 / channel 7 is 0.35.

  This means that when the particle size is 0.5 μm, the backscattered light (output voltage of channel 1) is larger and the forward scattered light (output voltage of channel 7) is smaller than the particle size of 5 μm. Therefore, the particle diameter can be identified from the output voltage ratio between the back scattered light and the forward scattered light.

  As shown in FIG. 7, the absolute values of the output voltages of the channel 1 and the channel 7 are different between the large, medium, and small concentrations, but the voltage ratio that is the ratio does not change and has a substantially constant slope. Therefore, by calculating the output voltage ratio (Ch1 / Ch7), it is possible to identify the particle size without being affected by the counting loss regardless of the concentration.

  FIG. 8 is a graph showing the relationship between the LED type and the channel 1 / channel 7 voltage ratio. That is, for the infrared light, green light, and blue light, the respective voltage ratios of channel 1 / channel 7 having a particle size of 0.5 μm and a particle size of 5 μm are shown. Therefore, the particle size can be identified by referring to the graph of FIG. 8 as a data table from the relationship between the LED type and the voltage ratio of channel 1 / channel 7.

  FIG. 9 shows the main part of the particle sensor of one embodiment of the present invention. For example, a fluid such as air flows in a cylindrical container D in a direction perpendicular to the paper surface. The central portion of the container D is set as a measurement area B, and the particle size of particles P floating in the measurement area B is set as an identification target. To do.

  This particle sensor is composed of a light emitting unit A composed of LED light emitting elements and a PD (photodiode) that generates a light reception output signal in accordance with scattered light of particles in a measurement area B based on LED light emitted from the light emitting unit A. The first light receiving unit S1 and the second light receiving unit S2 are provided. The first light receiving unit S1 is in a position where it can detect backscattered light (light that the LED light scatters backward by irradiating the suspended particles), and is backward from the measurement area B in the LED light irradiation direction (from the y-line). The second light receiving unit S2 is disposed at the light emitting unit A side, and the second light receiving unit S2 is a position where the forward scattered light (light that the LED light irradiates the suspended particles and scatters forward) can be detected. (In the drawing, on the right side of the figure) in front of the.

  For this reason, the first light receiving unit S1 generates an output voltage due to the backscattered light, and the second light receiving unit S2 generates an output voltage due to the forward scattered light. Here, the first light receiving unit S1 and the second light receiving unit S2 are in directions of 45 ° and 135 ° from the center C of the measurement area B with respect to the irradiation direction (x direction) of the LED light from the light emitting unit A. It is preferable to arrange.

  The reason is that by arranging the first light receiving part S1 in the direction of 45 ° from the center C of the measurement area B, it can be output at a place where the backscattered light becomes large. This is because by arranging the second light receiving unit S2 in the direction of 135 ° from the center C, the forward scattered light becomes large, and there is a good proportional relationship with the entire scattered light, so that data can be stably acquired. These can be clearly seen from the experimental results.

The particle sensor of the present invention includes means 1 for calculating the ratio of the light reception output signals from the first light receiving unit S1 and the second light receiving unit S2 whose arrangement positions are specified in this way. That is, the output values of the back scattered light and the forward scattered light in the two light receiving units S1 and S2 are used to obtain the ratio L of the following received light output signal. Then, a means 3 for identifying the particle size of the particles P in the measurement area B is provided by referring to the data table 2 from the ratio of the received light output signals (ratio of back / forward scattered light).
L (voltage ratio) = Vs1 (S1 output value (backscattered light)) / Vs2 (S2 output value (forward scattered light))

  Regarding the LED used in the light emitting section A, referring to FIG. 8, the voltage ratio at a particle size of 5 μm hardly changes depending on the type of LED. However, a fine particle having a particle diameter of 0.5 μm is preferable because, as shown in FIG. 8, an LED having a short wavelength such as blue light has a large voltage ratio and is easily identified.

  The voltage ratio of the particle group having a particle diameter of 0.5 to 5 μm is considered to fall between the voltage ratios shown in the graph of FIG. Therefore, it is considered that the identification of the particle diameter is more advantageous for the LED having a short wavelength, and the particle diameter of 0.5 to 5 μm is obtained by referring to the data table shown in FIG. Can be identified.

  Therefore, it is possible to identify the particle size (size) of suspended particles in the atmosphere or liquid from the output voltage ratio of the light receiving unit S1 and the light receiving unit S2, regardless of the concentration, without causing a count loss. The particle size can be identified with an inexpensive device. The particle size that can be measured is preferably about 0.5 to 5 μm (such as smoke). For example, the particle size of pollen is about 30 μm, and the particle size of house dust is about 5 μm or more. It is considered particularly suitable for detecting the particle size of fine particles having a size.

  In addition, although the example using a cylindrical container was demonstrated in the said Example, of course, other shapes may be sufficient. Moreover, although the example of particle diameter identification of the floating particle | grains in air | atmosphere or a liquid was demonstrated, you may affix by attaching a sample particle | grain to a transparent tape as demonstrated in the experiment example.

  Further, the first light receiving unit S1 and the second light receiving unit S2 are arranged in directions of 45 ° and 135 ° from the center C of the measurement area B with respect to the irradiation direction (x direction) of the LED light from the light emitting unit A. However, the same effect can be obtained with the channel 13 and the channel 19 that are diagonally opposite to the S1 and S2. A combination of channel 7 and channel 19 is also possible. As described above, it is needless to say that the output voltage generated by the back scattered light and the forward scattered light may be disposed at a place where the output voltage is generated efficiently and stably.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

  The present invention can discriminate the particle size (size) of a large number of particles without causing counting loss regardless of the particle concentration, and is about 0.5 to 5 μm with an inexpensive apparatus. The fine particle size can be identified. Therefore, it can be suitably used for identifying the particle diameter of fine particles.

Claims (4)

A light-emitting unit, and a first light-receiving unit and a second light-receiving unit that generate a light-receiving output signal according to the scattered light of the particles in the measurement area based on the LED light emitted from the light-emitting unit,
The first light receiving unit is behind the measurement area positioned in front of the irradiation direction of the LED light from the light emitting unit, and the second light receiving unit is ahead of the measurement area positioned in front of the irradiation direction of the LED light from the light emitting unit. Arranged,
A particle sensor comprising: means for calculating a ratio of light reception output signals by the first light receiving part and the second light receiving part; and means for calculating the particle diameter of the particles from the ratio of the light reception output signals.   The first light receiving part and the second light receiving part are arranged in directions of 45 ° and 135 ° from the center of the measurement area with respect to the irradiation direction of the LED light from the LED light emitting part. Particle sensor.   The particle sensor according to claim 1, wherein blue light is used for the LED light emitting unit.   The particle sensor according to claim 1, wherein the particle diameter is about 0.5 to 5 μm.

Images