JP2018112510A - Carbon dioxide sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon dioxide sensor that offers improved reliability of carbon dioxide concentration measurements.SOLUTION: A carbon dioxide sensor measures carbon dioxide concentration based on impedance of a detection unit that changes when carbon dioxide is detected, and comprises a substrate supporting the detection unit, a pair of electrodes which is disposed in contact with the detection unit to measure impedance of the detection unit, and a heater unit for heating the detection unit which contains an ionic liquid that causes the impedance of the detection unit to vary in accordance with carbon dioxide concentration.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carbon dioxide sensor.

  In recent years, there has been an increasing demand for carbon dioxide sensors that monitor carbon dioxide with low power consumption in buildings, offices, agriculture, and industrial fields.

  As such a carbon dioxide sensor capable of monitoring carbon dioxide with low power consumption, an ionic liquid type carbon dioxide sensor is known (for example, see Patent Document 1 below). In this ionic liquid type carbon dioxide sensor, a detection unit including an ionic liquid whose impedance changes depending on the concentration of carbon dioxide is used, and the concentration of carbon dioxide is determined based on a change in impedance measured for the detection unit. The

JP 2014-6128 A (Claim 12)

  However, in the carbon dioxide sensor described in Patent Document 1, the impedance value may change greatly even though the carbon dioxide concentration has not changed. There was room for improvement.

  This invention is made | formed in view of the said situation, and it aims at providing the carbon dioxide sensor which can improve the reliability of the measured value of a carbon dioxide concentration.

  This inventor repeated research about the cause which the said subject arises in the carbon dioxide sensor of the said patent document 1. FIG. As a result, the present inventor has found that even if the carbon dioxide concentration is constant, the impedance value of the detection unit changes greatly due to changes in humidity and outside air temperature. For this reason, the inventor believes that the ionic liquid contained in the detection unit is affected by fluctuations in the moisture content in the detection unit due to changes in external humidity and the influence of changes in the outside air temperature. I thought that the impedance value was changed. As a result of further earnest research, the present inventor has found that the above-mentioned problem can be solved by heating the detection unit with a heater, and has completed the present invention.

  That is, the present invention is a carbon dioxide sensor that measures the concentration of carbon dioxide based on a change in impedance of the detection unit by detecting carbon dioxide, and is in contact with a substrate that supports the detection unit and the detection unit Provided with a pair of electrodes for measuring impedance in the detection unit, and a heater device for heating the detection unit, the detection unit impedance value of the detection unit according to the carbon dioxide concentration It is a carbon dioxide sensor containing the ionic liquid which changes.

  According to the carbon dioxide sensor of the present invention, the detection unit is heated by the heater device. At this time, if the temperature of the detection unit is set to, for example, 70 to 120 ° C., even if the ionic liquid in the detection unit absorbs moisture in the air, the water in the ionic liquid contained in the detection unit is evaporated. Can be removed. That is, the detection unit can be held in a state where the water content is low. For this reason, the change of the impedance value of the detection part by the change of humidity can fully be suppressed. Further, according to the carbon dioxide sensor of the present invention, the temperature of the detection unit can be kept constant even when the outside air temperature changes by heating the detection unit with the heater device. For this reason, the change of the impedance of the detection part by the change of external temperature can fully be suppressed. Therefore, according to the carbon dioxide sensor of the present invention, it is possible to improve the reliability of the measured value of the carbon dioxide concentration measured based on the impedance value of the detection unit.

  In the carbon dioxide sensor, the detection unit preferably further includes a gelling agent.

  In this case, since the detection unit is gelled, the fluidity of the detection unit is lowered, and the movement of the detection unit is sufficiently suppressed.

  In the carbon dioxide sensor, the substrate is preferably composed of a glass substrate or a silicon substrate whose surface is covered with an oxide film.

  In this case, since the thermal conductivity of the substrate is good, the heat from the heater device can be efficiently transmitted to the detection unit.

  ADVANTAGE OF THE INVENTION According to this invention, the carbon dioxide sensor which can improve the reliability of the measured value of a carbon dioxide concentration is provided.

It is a top view which shows one Embodiment of the carbon dioxide sensor of this invention. It is a cut surface end view along the II-II line of FIG. It is a graph which shows the relationship between the impedance ratio measured about the carbon dioxide sensor of Example 1, and humidity. It is a graph which shows the relationship between the impedance ratio measured about the carbon dioxide sensor of the comparative example 1, and humidity. It is a graph which shows the relationship between the impedance ratio measured about the carbon dioxide sensor of Example 1, and a carbon dioxide concentration. It is a graph which shows the relationship between the impedance ratio measured about the carbon dioxide sensor of the comparative example 1, and a carbon dioxide concentration. It is a graph which shows the relationship between the impedance ratio measured about the carbon dioxide sensor of Example 1, and external temperature. It is a graph which shows the relationship between the impedance ratio measured about the carbon dioxide sensor of the comparative example 1, and external temperature.

  Hereinafter, embodiments of the carbon dioxide sensor of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG. 1 is a plan view showing an embodiment of the carbon dioxide sensor of the present invention, and FIG. 2 is a cross-sectional end view taken along the line II-II in FIG.

  As shown in FIG. 1, the carbon dioxide sensor 100 measures the concentration of carbon dioxide based on a change in impedance of the detection unit 20 by detecting carbon dioxide. The carbon dioxide sensor 100 is provided in contact with the substrate 10 that supports the detection unit 20, the detection unit 20, and heats the detection unit 20 with a pair of electrodes 31 and 32 for measuring impedance in the detection unit 20. Heater device 40, temperature measuring device 50 for measuring the temperature of detection unit 20, and the amount of heat generated by heating unit 44 in heater device 40 based on the temperature of detection unit 20 measured by temperature measurement device 50. And a control device 60 for controlling the temperature of the detection unit 20. In the present embodiment, the pair of electrodes 31 and 32 are provided between the one surface 10 a of the substrate 10 and the detection unit 20. In the present embodiment, the heater device 40 includes a heater device main body 41 having a heat generating portion 44 for heating the detection unit 20, and the heater device main body 41 connects the detection unit 20 to the substrate 10. It arrange | positions so that it may heat indirectly through.

  The detection unit 20 includes an ionic liquid that changes the impedance value of the detection unit 20 according to the carbon dioxide concentration.

  According to the carbon dioxide sensor 100, the detection unit 20 is heated by the heater device 40. At this time, the temperature of the detection unit 20 is measured by the temperature measurement device 50, and the amount of heat generated by the heat generation unit 44 in the heater device 40 is adjusted by the control device 60 based on the measured temperature. For example, when the temperature is controlled to 70 to 120 ° C., even if the ionic liquid in the detection unit 20 absorbs moisture in the air, the moisture in the ionic liquid contained in the detection unit 20 can be evaporated and removed. It becomes possible. That is, the detection part 20 can be made into a state with little moisture content. For this reason, the change of the impedance value of the detection part 20 by the change of humidity can fully be suppressed. Further, according to the carbon dioxide sensor 100, the temperature of the detection unit 20 can be maintained at a constant temperature by heating the detection unit 20 with the heater device 40. For this reason, even when the outside air temperature changes, the temperature of the detection unit 20 can be kept constant. For this reason, the change of the impedance of the detection part 20 by the change of external temperature can fully be suppressed. Therefore, according to the carbon dioxide sensor 100, the reliability of the measured value of the carbon dioxide concentration measured based on the impedance value of the detection unit 20 can be improved.

  Next, each of the substrate 10, the detection unit 20, the pair of electrodes 31 and 32, the heater device 40, the temperature measurement device 50, and the control device 60 described above will be described in detail.

<Board>
As the substrate 10, a silicon substrate, a sapphire substrate, a glass substrate, an alumina substrate, a SiC substrate, a silicon substrate whose surface is covered with an oxide film, or the like can be used. Among them, a glass substrate or a silicon substrate whose surface is covered with an oxide film is preferable because it has good thermal conductivity and can efficiently transfer heat from the heater device 40 to the detection unit 20.

  As the glass used as the insulating substrate, alkali-free glass, quartz glass, or the like can be used.

<Detector>
As described above, the detection unit 20 includes an ionic liquid.

(Ionic liquid)
The ionic liquid is not particularly limited as long as it changes the impedance value of the detection unit 20 according to the carbon dioxide concentration. Examples of such ionic liquids include 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF ₄ ), 1-ethyl-3-methylimidazolium tetrafluorosilicate (EMIM-SiF ₄ ), 1 - butyl-3-methylimidazolium tetrafluoroborate _(BMIM-BF 4), 1- butyl-3-methylimidazolium hexafluorophosphate _{(BMIM-PF 6), 1} -n- octyl-3-methylimidazolium Examples include bromide (OMIM-Br). These can be used alone or in combination of two or more. Among them, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF ₄ ) or 1-ethyl-3-3-methylimidazolium tetrafluorosilicate (EMIM-SiF ₄ ) is particularly preferable. In this case, not only the ionic liquid easily absorbs carbon dioxide, but also desorption of carbon dioxide from the ionic liquid occurs easily, so the carbon dioxide sensor 100 is used in an environment where the carbon dioxide concentration tends to fluctuate. In addition, the reliability of the carbon dioxide concentration value can be further increased.

  The detection unit 20 is preferably surrounded by an annular outflow prevention unit (not shown) protruding from the one surface 10a of the substrate 10 from the viewpoint of shape retention. In this case, even if the one surface 10a of the substrate 10 is inclined with respect to the horizontal plane, the movement of the detection unit 20 is prevented by the outflow prevention unit.

  The detection unit 20 may further include a gelling agent in addition to the ionic liquid, or may not include the gelling agent, but preferably further includes a gelling agent. In this case, since the detection unit 20 is gelled, the fluidity of the detection unit 20 is reduced, and thus the movement of the detection unit 20 is sufficiently suppressed. The gelling agent is not particularly limited as long as it can be gelled without changing the impedance characteristics of the ionic liquid. Examples of the gelling agent include vinylidene fluoride / hexafluoropropylene copolymer. Etc.

<Electrode>
The electrodes 31 and 32 are not particularly limited as long as they are made of a conductive material. Examples of the conductive material that constitutes the electrodes 31 and 32 include gold, silver, an aluminum alloy, titanium, and platinum. The electrodes 31 and 32 may be a single layer made of the above conductive material, or may be a laminate of a plurality of layers made of different conductive materials. The shape of the electrodes 31 and 32 is not particularly limited, and examples of the shape of the electrodes 31 and 32 include a circular shape, a square shape, and a comb shape. Especially, it is preferable that the shape of the electrodes 31 and 32 is a comb-tooth shape, since the detection sensitivity with respect to a carbon dioxide is high even if the electrodes 31 and 32 are microelectrodes. When the shape of the electrodes 31 and 32 is a comb-tooth shape, the electrode 31 is connected to, for example, the main body 31 a, the tooth 31 b extending from the main body 31 a, and the main body 31 a and provided outside the detection unit 20. Terminal portion 31c. Similarly, the electrode 32 includes, for example, a main body part 32a, a tooth part 32b extending from the main body part 32a, and a connection terminal part 32c connected to the main body part 32a and provided outside the detection unit 20.

<Heater device>
The heater device 40 only needs to have a heat generating portion 44 that can heat the detecting portion 20. Examples of the heater device 40 include a platinum heater, a ceramic heater, and a bare heating element. When the heater device 40 is composed of a platinum heater, the heater device 40 is connected to a heater device main body 41 having a heat generating portion 44 and a heater device main body 41 as shown in FIGS. 1 and 2, for example. And a voltage applying device 42 that applies a voltage to the device main body 41. The heater device main body 41 includes a support 43 that supports the heat generating portion 44 on the support surface 43 a, and connection terminals 45 a and 45 b that are provided on the support surface 43 a of the support 43 and are connected to both ends of the heat generating portion 44. Have The voltage application device 42 connects the connection terminal 45a and the connection terminal 45b. The heater device 40 causes the heat generating portion 44 to generate heat by applying a voltage between the connection terminals 45 a and 45 b by the voltage applying device 42, and heats the detecting portion 20 through the substrate 10.

  The support body 43 is not particularly limited as long as it can support the heat generating portion 44. As the support body 43, for example, a glass substrate, a silicon substrate, an alumina substrate, and a metal substrate having a good thermal conductivity may be used. Examples thereof include a laminated substrate obtained by forming an insulating layer such as a layer or an alumina layer.

<Temperature measuring device>
The temperature measuring device 50 may be any device that can measure the temperature of the detection unit 20. Examples of the temperature measuring device 50 include a thermocouple and a platinum resistor.

<Control device>
The control device 60 may be any device that controls the temperature of the detection unit 20 by adjusting the amount of heat generated by the heat generation unit 44 in the heater device 40 based on the temperature of the detection unit 20 measured by the temperature measurement device 50.

  The control target temperature in the control device 60 may be a temperature of 70 to 120 ° C., but is preferably a temperature of 8100 to 120 ° C. In this case, moisture easily evaporates from the detection unit 20 and the influence of moisture on the impedance value can be sufficiently reduced, so that the reliability of the measured value of the carbon dioxide concentration can be further improved.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the heater device main body 41 of the heater device 40 is disposed so as to indirectly heat the detection unit 20 via the substrate 10. It may be arranged to heat 20 directly.

  In addition, the heater device main body 41 includes the support body 43, but the support body 43 may not necessarily be included. In this case, the heating element 44 is provided, for example, on the surface of the substrate 10 opposite to the detection unit 20.

  In the above embodiment, the electrodes 31 and 32 are provided between the detection unit 20 and the substrate 10, but the electrodes 31 and 32 are not necessarily provided between the detection unit 20 and the substrate 10. Absent. For example, when the detection unit 20 includes a gelling agent and the detection unit 20 is gelled and the shape of the detection unit 20 is maintained, the electrodes 31 and 32 are connected to the substrate 10 of the detection unit 20, for example. It may be provided on the opposite surface.

  Furthermore, in the above embodiment, the carbon dioxide sensor 100 adjusts the amount of heat generated by the heat generating unit 44 in the heater device 40 based on the temperature of the detecting unit 20 measured by the temperature measuring device 50, and controls the temperature of the detecting unit 20. However, the control device 60 can be omitted. Even in this case, the worker can manually control the amount of heat generated in the heat generating portion 44 of the heater device 40 based on the temperature measured by the temperature measuring device 50. Alternatively, the temperature of the detection unit 20 can be made constant by simply applying a constant voltage to the heat generation unit 44 of the heater device 40. This is because even if the voltage is continuously applied to the heater device 40, the temperature of the heat generating portion 44 does not rise infinitely, and there is a temperature at which heating and heat dissipation are balanced in the heat generating portion 44 that is a heating object. It is. Therefore, there is a correlation between the power consumption of the heater device 40 and the reached temperature of the heat generating unit 44 of the heater device 40. If the voltage of the heater device 40 is constant, the temperature of the heat generating unit 44 is the temperature corresponding to the voltage. Become.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Example 1
First, a 30 mm × 30 mm × 1 mm (thickness) glass substrate was prepared as the support 43, and a platinum heater was formed on the glass substrate. At this time, the platinum heater was formed so as to have a meandering heat generating portion 44 and connection terminals 45a and 45b provided at both ends thereof by photolithography after forming a platinum layer using a sputtering method. Thus, the heater device main body 41 was formed. Subsequently, the connection terminals 45a and 45b were connected by a voltage application device 42 (manufactured by Matsusada Precision Co., Ltd., product name “PLE-18-2”). Thus, the heater device 40 was produced.

  Next, a substrate made of quartz glass of 18 mm × 18 mm × 0.15 mm was prepared as the substrate 10. Then, after forming a metal layer by forming a Pt layer having a thickness of 500 nm on one surface 10a of the substrate 10 by a sputtering apparatus (product name “SH-350H” manufactured by ULVAC, Inc.), A pair of comb-like electrodes 31 and 32 was formed by performing photolithography. At this time, the comb-like electrode 31 is formed so as to have a main body part 31a, a tooth part 31b, and a connection terminal 31c, and the number of the tooth parts 31b is 15, and the interval between adjacent tooth parts 31b. Was 100 μm. Similarly, the comb-like electrode 32 is formed so as to have a main body portion 32a, a tooth portion 32b, and a connection terminal 32c, and the number of the tooth portions 32b is 15, and the interval between adjacent tooth portions 32b. Was 100 μm. Thus, a substrate with an electrode was produced.

  Next, the board | substrate 10 and the heater apparatus 40 of the board | substrates with an electrode were adhere | attached using the adhesive agent (made by Fujikura Kasei company, brand name "Dotite"). At this time, the heater device main body 41 of the heater device 40 is bonded to the substrate 10 with the heat generating portion 44 facing the substrate 10 side. At this time, the heat generating portion 44 is arranged between the substrate 10 and the support body 43 so that the connection terminals 45a and 45b are exposed. Thus, a structure was obtained.

Next, the structure was placed so that one surface 10a of the substrate 10 was horizontal, and ionic liquid was dropped on the comb-shaped electrodes 31 and 32 in the structure. At this time, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF ₄ ) was used as the ionic liquid. Thus, the detection unit 2 was formed.

  Finally, a thermocouple (manufactured by ASONE, product name “1-3963-01”) as the temperature measuring device 50 was attached to the detection unit 20.

  A carbon dioxide sensor was produced as described above.

(Comparative Example 1)
A carbon dioxide sensor was produced in the same manner as in Example 1 except that the heater device 40 was not adhered to the substrate 10.

<Reliability comparison of measured values of carbon dioxide concentration>
Between the carbon dioxide sensor of Example 1 and Comparative Example 1 obtained as described above, a change in the impedance ratio of the detection unit 20 with respect to a change in humidity, a change in the impedance ratio of the detection unit 20 with respect to the carbon dioxide concentration, And the reliability of the measured value of a carbon dioxide concentration was compared by investigating and comparing the change of the impedance ratio of the detection part 20 with respect to the change of external temperature.

Specifically, for the carbon dioxide sensor of Example 1, the outside temperature (° C.) and humidity (% RH) were applied while applying a constant voltage to the heater device 40 so that the temperature of the detection unit 20 would be 90 ° C. ) And the carbon dioxide concentration (volume ppm) were measured for the impedance Z (Ω) of the detection unit 20 when it was changed with the elapsed time. The change in the impedance ratio of the detection portion 20 with respect to changes in humidity _(Z / Z _0), the change in impedance ratio detection section 20 for the carbon dioxide concentration _(Z / Z _0), and the detection unit 20 to a change in outside air temperature The change in the impedance ratio (Z / Z ₀ ) was investigated. The results are shown in FIG. 3, FIG. 5 and FIG. Z ₀ is the carbon dioxide sensor of the first embodiment, in which the carbon dioxide concentration is 787 ppm by volume and the relative humidity is 56.degree. It is the impedance value of the detection unit 20 measured in an environment of 287% RH.

On the other hand, for the carbon dioxide sensor of Comparative Example 1, the impedance when the outside air temperature (° C.), the humidity (% RH), and the carbon dioxide concentration (volume ppm) are changed with the elapsed time without heating the detection unit 20. The ratio (Z / Z ₀ ) was determined. The change in the impedance ratio of the detection portion 20 with respect to changes in humidity _(Z / Z _0), the change in impedance ratio detection section 20 for the carbon dioxide concentration _(Z / Z _0), and the detection unit 20 to a change in outside air temperature The change in the impedance ratio (Z / Z ₀ ) was investigated. The results are shown in FIG. 4, FIG. 6 and FIG. Z ₀ is a value different from Z _{0 of} Example 1. In the carbon dioxide sensor of Comparative Example 1, the temperature of the detection unit 20 is 25.898 ° C., the carbon dioxide concentration is 821 vol ppm, and the relative humidity is It is the impedance value of the detection unit 20 measured in an environment of 64.601% RH.

In the carbon dioxide sensor of Comparative Example 1, as shown in FIG. 4, when the relative humidity is drastically decreased after 327 seconds from the start of measurement and then the relative humidity is greatly changed, the impedance ratio (Z / Z ₀ ) also fluctuated greatly. On the other hand, in the carbon dioxide sensor of Example 1, as shown in FIG. 3, even after the relative humidity is drastically decreased after 309 seconds from the start of measurement, the impedance ratio ( The variation of Z / Z ₀ ) was sufficiently smaller than that of Comparative Example 1.

Further, in the carbon dioxide sensor of Comparative Example 1, as shown in FIG. 6, after 336 seconds passed from the start of measurement, the carbon dioxide concentration was drastically decreased and then the carbon dioxide concentration was made substantially constant. The impedance ratio (Z / Z ₀ ) varied greatly. On the other hand, in the carbon dioxide sensor of Example 1, as shown in FIG. 5, when the carbon dioxide concentration is made substantially constant after 318 seconds from the start of measurement and the carbon dioxide concentration is lowered rapidly, the impedance ratio is The variation of (Z / Z ₀ ) was sufficiently small as compared with Comparative Example 1.

Furthermore, in the carbon dioxide sensor of Comparative Example 1, as shown in FIG. 8, when the outside air temperature is drastically decreased after 312 seconds from the start of measurement, and the outside air temperature is greatly changed, the impedance ratio (Z / Z ₀ ) also fluctuated greatly. On the other hand, in the carbon dioxide sensor of Example 1, as shown in FIG. 7, even if the outside air temperature is drastically lowered after 306 seconds from the start of measurement, The variation of Z / Z ₀ ) was sufficiently smaller than that of Comparative Example 1.

Thus, in the carbon dioxide sensor of Example 1, even when the outside air temperature and humidity change, the impedance ratio (Z / Z ₀ ) variation is considerably smaller than that of the carbon dioxide sensor of Comparative Example 1. It was. Further, the carbon dioxide sensor of Example 1, the variation of the long substantially constant carbon dioxide concentration impedance ratio (Z / Z _0), as compared to the carbon dioxide sensor of Comparative Example 1 was found to be quite small.

  From the above, according to the carbon dioxide sensor of the present invention, it was confirmed that the reliability of the measured value of the carbon dioxide concentration can be improved.

DESCRIPTION OF SYMBOLS 10 ... Board | substrate 20 ... Detection part 31, 32 ... Electrode 40 ... Heater apparatus 100 ... Carbon dioxide sensor

Claims (3)

A carbon dioxide sensor that measures the concentration of carbon dioxide based on a change in impedance of a detection unit by detecting carbon dioxide,
A substrate that supports the detection unit;
A pair of electrodes provided in contact with the detector, for measuring impedance in the detector;
A heater device for heating the detection unit,
The carbon dioxide sensor in which the said detection part contains the ionic liquid which changes the impedance value of the said detection part according to a carbon dioxide concentration.   The carbon dioxide sensor according to claim 1, wherein the detection unit further includes a gelling agent.   The carbon dioxide sensor according to claim 1 or 2, wherein the substrate is formed of a glass substrate or a silicon substrate whose surface is covered with an oxide film.

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