JP5092161B2 - Alcohol concentration sensor - Google Patents

Description

  The present invention relates to an alcohol concentration sensor, and more particularly to an alcohol concentration sensor for a direct fuel cell.

  A direct fuel cell is being developed for installation in portable electronic devices. In direct alcohol fuel cells, it is necessary to always control the alcohol concentration to be about 10 to 20% in order to prevent crossover, which is a phenomenon in which alcohol as fuel permeates the electrolyte membrane and leaks to the air electrode side. . In other words, when the alcohol concentration decreases with power generation, it is necessary to detect it and open the storage tank valve to add high-concentration alcohol. For this reason, when the direct alcohol fuel cell is mounted on a portable electronic device, it is essential to measure the concentration of alcohol in the aqueous fuel solution, and there is a demand for downsizing and cost reduction of the sensor element.

As a conventional method for measuring the alcohol concentration in a solution, a method using a refractive index, a method using a crystal resonator (for example, see Patent Document 1), and a method using an ultrasonic transmission speed (for example, a patent). A method using a difference in infrared absorption (see, for example, Patent Documents 3 to 5) is known.
JP-A-6-18394 JP 11-23541 A JP 2006-292474 A Japanese Patent Laid-Open No. 5-223733 Japanese Patent Laid-Open No. 1-112137

  The method using the refractive index is a method in which a small amount of a test solution is collected and the alcohol concentration is measured with a refractometer, and is the most accurate method, but continuous measurement is difficult.

  In a method using a crystal resonator (see, for example, Patent Document 1), the resonance frequency of the crystal resonator immersed in the test solution changes depending on the density or viscosity of the test solution surrounding the crystal resonator. It is a method that uses to do. This method has the disadvantages that it requires specialized technology for processing the quartz crystal part, is difficult to produce easily, and the measurement part also requires a high precision and an expensive one.

  A method using the transmission speed of ultrasonic waves (see, for example, Patent Document 2) is a method using the fact that the transmission speed of ultrasonic waves in a liquid differs depending on the composition of the liquid. This method has a disadvantage that the ultrasonic oscillation / reception element and the measurement circuit are special and expensive.

  A method that uses the difference in infrared absorption (see, for example, Patent Documents 3 to 5) is a method that uses the difference in infrared absorption between water and methanol. In this method, since the infrared absorption of methanol is in the region of several micrometers, the optical element in that wavelength region becomes expensive, and the electronic circuit for measurement also has a drawback of requiring high accuracy.

  Therefore, an object of the present invention is to provide a small and low-priced alcohol concentration sensor that can be used in a direct fuel cell for mounting on a portable electronic device.

The alcohol concentration sensor according to the present invention is in contact with an alcohol aqueous solution, scatters light that passes through the alcohol aqueous solution, scatters light, irradiates light to the light scatterer, and transmits or reflects the light scatterer. A light intensity detecting means for detecting the intensity of the light , wherein the light scattering means is a light-transmitting porous glass powder sintered body that is irradiated from the light irradiation means to the light scattering means; A feature is that light is propagated by repetitively refracting and reflecting at the interface between the light scattering means and the aqueous alcohol solution, and a part of the light reaches the light intensity detecting means .

  According to the alcohol concentration sensor of the present invention, it utilizes the fact that the refractive index of the alcohol aqueous solution is slightly different depending on the alcohol concentration, and the light scattering means in contact with the alcohol aqueous solution is irradiated with light and transmitted through the light scattering means. The intensity of the reflected light is detected. Even if the refractive index of the alcohol aqueous solution is a slight difference, the intensity of the transmitted or reflected light appears as a large difference, so that the alcohol is accurately based on the intensity of the transmitted or reflected light in spite of a very simple configuration. The concentration can be calculated.

  Therefore, it is possible to provide a small and low-priced alcohol concentration sensor that can be used in a direct fuel cell for mounting on a portable electronic device.

  Hereinafter, embodiments of the alcohol concentration sensor of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows the configuration of an alcohol concentration sensor in this embodiment. Reference numeral 1 denotes a flow path through which an aqueous alcohol solution to be measured flows, and a scatterer 2 as a light scattering means is disposed inside the flow path 1. In addition, outside the flow path 1, light irradiation means 3 for irradiating light to the scatterer 2 so as to sandwich both sides of the scatterer 2, and light intensity detection means 4 for detecting the intensity of light transmitted through the scatterer 2. Is arranged. Further, in order to supply the alcohol solution to the flow path 1, a pump (not shown) is provided connected to the flow path 1.

  The flow path 1 is comprised from the transparent glass tube, for example. When this flow path 1 is formed of a glass tube, in order to increase the detection accuracy in the light intensity detection means 4, the portions facing the light irradiation means 3 and the light intensity detection means 4 are flat glass tubes, that is, face each other. It is preferable to use a glass tube made of a glass plate having two parallel surfaces. Note that a glass tube whose two surfaces are not flat may be used, but in that case, the light intensity incident from the light irradiation means 3 and the light intensity detection means 4 are detected by the influence of the curved surface. The intensity of light decreases, and the detection accuracy in the light intensity detection means 4 decreases.

  The scatterer 2 is composed of a transparent glass powder sintered body as a porous body having translucency. When the scatterer 2 is composed of a glass powder sintered body, for example, a glass particle having a particle diameter of 10 to 100 μm that is baked and hardened to such an extent that the pores are not crushed can be used. Depending on the situation, it can be changed appropriately. In the case of using a commercially available glass powder sintered body, for example, one used for a glass filter can be processed and used.

  The light irradiation means 3 and the light intensity detection means 4 may be separately configured by using a light emitting diode, a phototransistor, or the like, but can be integrally configured by, for example, a transmissive photo interrupter. By using a photo interrupter, the alcohol concentration sensor can be easily downsized. The photo interrupter is an electronic component that is composed of a light emitting unit corresponding to the light irradiating unit 3 and a light receiving unit corresponding to the light intensity detecting unit 4, and is used to determine the presence or absence and position of an object. The light receiving unit is configured to face the light receiving unit, and the light from the light emitting unit is detected by the light receiving unit. As the light emitting element of the light emitting unit, an infrared light emitting diode is preferably used as a measure against disturbance light. A phototransistor or a photo IC is used as the light receiving element of the light receiving unit. The alcohol concentration sensor of the present embodiment can be configured by arranging a portion where the scatterer 2 of the flow path 1 is provided between the light-emitting portion and the light-receiving portion of the photo interrupter.

FIG. 2 shows an example of an electric circuit of the alcohol concentration sensor in the present embodiment. A constant current power source 6 is connected to the light emitting diode 5 of the light irradiating means 3 so that light of a certain intensity is irradiated. Further, a resistor 8 and a constant voltage power source 9 are connected in series to the phototransistor 7 of the light intensity detection means 4. Since the output voltage V _out across the resistor 8 changes according to the change in the current of the phototransistor 7, that is, the intensity of light detected by the phototransistor 7, the scatterer 2 is detected by detecting the output voltage _Vout. The intensity of the light transmitted through can be measured.

  Next, the operation of the alcohol concentration sensor of this embodiment will be described.

  When an aqueous alcohol solution as a measurement target is supplied to the flow channel 1 by a pump (not shown), the aqueous alcohol solution flows inside the scatterer 2 disposed in the flow channel 1. The light irradiated to the scatterer 2 from the light irradiating means 3 is repeatedly refracted and reflected repeatedly at the interface between the scatterer 2 and the alcohol aqueous solution, and a part of the light passes through the scatterer 2 and the light intensity on the opposite side. The detection means 4 is reached. The greater the difference in refractive index between the alcohol aqueous solution and the scatterer 2, the greater the amount of light that is refracted, reflected and scattered at the interface between the scatterer 2 and the alcohol aqueous solution, so the intensity of the light reaching the light intensity detecting means 4 Decrease. That is, the intensity of the light reaching the light intensity detecting means 4 changes corresponding to the change in the refractive index of the alcohol aqueous solution. Therefore, the alcohol concentration of the alcohol aqueous solution can be obtained by measuring the intensity of the light reaching the light intensity detecting means 4 based on the fact that the refractive index of the alcohol aqueous solution varies depending on the alcohol concentration.

  Table 1 shows refractive indexes of water, methanol, ethanol, typical transparent materials that can be used as materials for formic acid, acetaldehyde, and by-products of power generation of the direct fuel cell, and the scatterer 2.

  Next, actual measurement examples will be described.

A methanol aqueous solution was used as the alcohol aqueous solution, and the methanol concentration was changed stepwise from 0% to 100% every 10% by mass to measure the response characteristics of the output voltage V _out . The result is shown in FIG. It was confirmed that the output voltage responded promptly according to the change in methanol concentration.

  Based on this result, the relationship between methanol concentration and output voltage is summarized in FIG. FIG. 6 shows the relationship between the methanol concentration measured with a refractometer and the refractive index. The output voltage curve shown in FIG. 4 and the refractive index curve shown in FIG. 6 have similar shapes, and it was confirmed that the output voltage changes according to the change in the refractive index of the aqueous methanol solution. When the methanol concentration was changed from 10% by mass to 20% by mass, the output voltage showed a change of 91 mV. Therefore, it was confirmed that a change in the concentration of methanol of about 0.1% by mass can be detected sufficiently.

  As a comparative example, when the same measurement was performed without providing the scatterer 2, the change in the output voltage was 35 mV, which was a smaller value than in the case of the present example.

  Further, when the alcohol concentration sensor of this embodiment is used for a direct fuel cell, the influence of by-products during power generation becomes a problem. Therefore, the influence of formic acid considered as a by-product during power generation of the direct fuel cell was examined.

  In a 20% by mass methanol solution, the formic acid concentration dependency on the output voltage was measured by changing the formic acid concentration stepwise from 0.1% by mass (1000 ppm) to 1% by mass (10000 ppm). The result is shown in FIG. Until the formic acid concentration was 0.1% by mass, there was almost no change in the output voltage, and there was almost no influence of formic acid, and it was confirmed that it could be used without any problem as an alcohol sensor for a direct fuel cell. When the formic acid concentration was 1% by mass, an increase in output voltage was observed. However, in an actual direct fuel cell, such a high concentration of formic acid cannot be generated. Don't be.

  As described above, the alcohol concentration sensor of the present embodiment includes the scatterer 2 that contacts the aqueous alcohol solution and scatters the light that passes through the aqueous alcohol solution, the light irradiation means 3 that irradiates the scatterer 2 with light, and the scattering. Light intensity detecting means 4 for detecting the intensity of light transmitted through the body 2 is provided. According to the alcohol concentration sensor of the present embodiment, the fact that the refractive index of the alcohol aqueous solution is slightly different depending on the alcohol concentration is utilized, and the scatterer 2 in contact with the alcohol aqueous solution is irradiated with light and transmitted through the scatterer 2. The intensity of the light is detected. Even if the refractive index of the alcohol aqueous solution is a slight difference, the intensity of the transmitted light appears as a large difference, so that the alcohol concentration is accurately calculated based on the intensity of the transmitted light, despite an extremely simple configuration. be able to. Therefore, it is possible to provide a small and low-priced alcohol concentration sensor that can be used in a direct fuel cell for mounting on a portable electronic device.

  Further, since the scatterer 2 is a porous body having translucency, the light irradiated from the light irradiating means 3 is refracted at the interface between the aqueous alcohol solution and the scatterer 2 before passing through the scatterer 2. The number of reflections can be extremely increased, and as a result, the alcohol concentration can be accurately calculated.

  In addition, since the scatterer 2 is a glass powder sintered body, it is easy to obtain materials for forming the scatterer 2, and the manufacture of the scatterer 2 is easy, so an alcohol concentration sensor is provided at a low price. can do.

  Further, by attaching the alcohol concentration sensor of this embodiment to the fuel supply flow path of the direct type fuel cell, it becomes possible to keep the alcohol concentration constant while constantly monitoring the alcohol concentration in the supplied fuel. . In other words, when alcohol is consumed due to the progress of power generation and the concentration decreases, it is detected and the valve of the storage tank containing high concentration alcohol is opened, and when the target concentration is reached, the valve is closed. The alcohol concentration can be kept within a certain range.

  The alcohol concentration sensor of the present embodiment can be used not only for direct fuel cells but also for fuel cells using alcohol as fuel and internal combustion engines in general.

  FIG. 7 shows the configuration of the alcohol concentration sensor in this embodiment. In addition, the same code | symbol is attached | subjected to the part similar to Example 1, and the detailed description is abbreviate | omitted.

  In the present embodiment, the arrangement of the light irradiation means 3 and the light intensity detection means 4 is different from that in the first embodiment. Outside the flow path 1, light irradiation means 3 for irradiating the scatterer 2 with light and light intensity detection means 4 for detecting the intensity of the light reflected from the scatterer 2 are arranged on one side of the scatterer 2. Yes.

  When the flow path 1 is formed of a glass tube, it is preferable to use a glass tube having a flat portion facing the light irradiation means 3 and the light intensity detection means 4 in order to increase the detection accuracy of the light intensity detection means 4. . Note that a glass tube having a non-flat portion may be used. In this case, the intensity of light incident from the light irradiation means 3 and the light detected by the light intensity detection means 4 are affected by the curved surface. The intensity decreases, and the detection accuracy in the light intensity detection means 4 decreases.

  The light irradiation means 3 and the light intensity detection means 4 may be separately configured using light emitting diodes, phototransistors, or the like. For example, the light irradiation means 3 and the light intensity detection means 4 can be integrally configured by a reflective photo interrupter, that is, a photo reflector. . By using a photo reflector, the alcohol concentration sensor can be easily downsized. The photo reflector is an electronic component that is composed of a light emitting unit corresponding to the light irradiating unit 3 and a light receiving unit corresponding to the light intensity detecting unit 4, and is used to determine the presence or absence and position of an object. The light receiving unit is arranged adjacent to each other in the same direction, and is configured such that light from the light emitting unit is applied to the object and the reflected light is detected by the light receiving unit.

The electric circuit in the present embodiment can be configured in the same manner as in the first embodiment. In this embodiment, the intensity of light reflected from the scatterer 2 can be measured by detecting the output voltage _Vout .

  Next, the operation of the alcohol concentration sensor of this embodiment will be described.

  The light irradiated to the scatterer 2 from the light irradiating means 3 advances in a repetitive manner by refraction and reflection at the interface between the scatterer 2 and the alcohol aqueous solution, and a part of the light is reflected from the scatterer 2 and the light intensity detecting means 4. To reach. The greater the difference in refractive index between the alcohol aqueous solution and the scatterer 2, the greater the amount of light that is refracted, reflected and scattered at the interface between the scatterer 2 and the alcohol aqueous solution, so the intensity of the light reaching the light intensity detecting means 4 Will increase. Therefore, the alcohol concentration of the alcohol aqueous solution can be obtained by measuring the intensity of the light reaching the light intensity detecting means 4 based on the fact that the refractive index of the alcohol aqueous solution varies depending on the alcohol concentration.

  Next, actual measurement examples will be described.

An aqueous methanol solution was used as the alcohol aqueous solution, and the output voltage _Vout was measured by changing the methanol concentration stepwise from 0% to 100% every 10% by mass. The relationship between the methanol concentration and the output voltage is summarized in FIG. It was confirmed that the output voltage changed according to the change in the refractive index of the aqueous methanol solution. The alcohol concentration sensor of the present embodiment has a smaller output voltage than that of the first embodiment, but the light irradiation means 3 and the light intensity detection means 4 can be integrally formed on one side of the flow path 1 and thus can be easily downsized. Has the advantage of being.

  As described above, the alcohol concentration sensor of the present embodiment includes the scatterer 2 that contacts the aqueous alcohol solution and scatters the light that passes through the aqueous alcohol solution, the light irradiation means 3 that irradiates the scatterer 2 with light, and the scattering. A light intensity detecting means 4 for detecting the intensity of light reflected from the body 2 is provided. According to the alcohol concentration sensor of the present embodiment, the fact that the refractive index of the alcohol aqueous solution is slightly different depending on the alcohol concentration is utilized. Light is applied to the scatterer 2 in contact with the alcohol aqueous solution, and the scatterer 2 is reflected. The intensity of the light is detected. Even if the refractive index of the aqueous alcohol solution is a slight difference, the intensity of the reflected light appears as a large difference, so that the alcohol concentration is accurately calculated based on the intensity of the reflected light, despite the extremely simple configuration. be able to.

  In addition, this invention is not limited to said each Example, A various deformation | transformation implementation is possible.

  For example, as the material of the scatterer 2, various transparent plastics can be used in addition to glass. Further, not only the powder sintered body but also a chip-like, plate-like, or rod-like material can be used. In the case of a plate shape, the refraction and reflection of light can be adjusted by adjusting the angle of the plate with respect to the optical path. Furthermore, the scatterer 2 can be substituted by making the inner surface of the flow channel 1 rough, for example, ground glass.

  In addition to infrared light emitting diodes, visible light emitting diodes such as red and blue and laser diodes can be used as the light emitting elements of the light irradiation means 3.

It is a schematic diagram which shows the structure of the alcohol concentration sensor in Example 1 of this invention. It is a circuit diagram which shows an example of an electric circuit same as the above. It is a graph which shows the response characteristic of an output voltage same as the above. It is a graph which shows the relationship between methanol concentration and an output voltage same as the above. It is a graph which shows the formic acid density | concentration dependence to an output voltage same as the above. It is a graph which shows the relationship between methanol concentration and refractive index. It is a schematic diagram which shows the structure of the alcohol concentration sensor in Example 2 of this invention. It is a graph which shows the relationship between methanol concentration and an output voltage same as the above.

2 Scatterer (light scattering means)
3 Light irradiation means 4 Light intensity detection means

Claims (1)

A light scattering means for scattering light passing through the alcohol aqueous solution in contact with the alcohol aqueous solution, a light irradiation means for irradiating the light scattering means with light, and a light intensity for detecting the intensity of the light transmitted or reflected by the light scattering means The light scattering means is a porous glass powder sintered body having translucency, and the light emitted from the light irradiation means to the light scattering means is the light scattering means and alcohol. An alcohol concentration sensor configured to repeatedly refract and reflect at an interface of an aqueous solution in a multiplex manner so that a part thereof reaches the light intensity detecting means .

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