JP6739360B2 - Carbon dioxide sensor - Google Patents

Description

The present invention relates to a carbon dioxide sensor.

In recent years, there has been an increasing demand for carbon dioxide sensors for monitoring carbon dioxide with low power consumption in buildings, offices, agricultural fields, industrial fields, and the like.

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

JP, 2014-6128, A (claim 12)

However, in the carbon dioxide sensor described in Patent Document 1, the impedance value may change significantly even if the carbon dioxide concentration does not change, and the reliability of the measured value of the carbon dioxide concentration is low. There was room for improvement.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a carbon dioxide sensor that can improve the reliability of the measured value of the carbon dioxide concentration.

The present inventor has conducted repeated studies on the cause of the above problems in the carbon dioxide sensor described in Patent Document 1. 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 present inventor has found that the ionic liquid contained in the detection unit is affected by a change in the moisture content in the detection unit due to a change in the external humidity and the influence of a change in the outside temperature. I wondered if it was because the impedance value of was changed. Then, as a result of further intensive research, the present inventor has found that the above-mentioned problems can be solved by heating the detection part with a heater, and has completed the present invention.

That is, the present invention is a carbon dioxide sensor for measuring the concentration of carbon dioxide based on the change in the impedance of the detection unit by detecting carbon dioxide, the substrate supporting the detection unit, the contact with the detection unit Provided with a pair of electrodes for measuring the 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 an ionic liquid that changes.

According to the carbon dioxide sensor of the present invention, the detection unit is heated by the heater device. At this time, when 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 water 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 kept in a state of having a low water content. Therefore, it is possible to sufficiently suppress the change in the impedance value of the detection unit due to the change in humidity. Further, according to the carbon dioxide sensor of the present invention, by heating the detection unit with the heater device, it is possible to keep the temperature of the detection unit constant even when the outside air temperature changes. Therefore, it is possible to sufficiently suppress the change in the impedance of the detection unit due to the change in the outside air temperature. 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 above carbon dioxide sensor, it is preferable that the detection unit further includes a gelling agent.

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

In the above carbon dioxide sensor, it is preferable that the substrate is a glass substrate or a silicon substrate whose surface is covered with an oxide film.

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

According to the present invention, a carbon dioxide sensor that can improve the reliability of the measured value of the carbon dioxide concentration is provided.

It is a top view showing one embodiment of a carbon dioxide sensor of the present invention. FIG. 2 is a sectional end view taken along line II-II of FIG. 1. 5 is a graph showing the relationship between the measured impedance ratio and humidity for the carbon dioxide sensor of Example 1. 7 is a graph showing the relationship between the impedance ratio and humidity measured for the carbon dioxide sensor of Comparative Example 1. 5 is a graph showing the relationship between the impedance ratio and the carbon dioxide concentration measured for the carbon dioxide sensor of Example 1. 7 is a graph showing the relationship between the impedance ratio measured for the carbon dioxide sensor of Comparative Example 1 and the carbon dioxide concentration. 3 is a graph showing the relationship between the impedance ratio measured for the carbon dioxide sensor of Example 1 and the outside air temperature. 7 is a graph showing the relationship between the impedance ratio measured for the carbon dioxide sensor of Comparative Example 1 and the outside air temperature.

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

As shown in FIG. 1, the carbon dioxide sensor 100 measures the concentration of carbon dioxide based on the change in impedance of the detection unit 20 due to the detection of carbon dioxide. The carbon dioxide sensor 100 heats the substrate 10 that supports the detection unit 20, the pair of electrodes 31 and 32 that is provided in contact with the detection unit 20 and that measures the impedance in the detection unit 20, and the detection unit 20. Heater device 40, a temperature measuring device 50 for measuring the temperature of the detection part 20, and a heating amount of a heating part 44 in the heater device 40 is adjusted based on the temperature of the detection part 20 measured by the temperature measuring device 50. And a control device 60 that controls the temperature of the detection unit 20. In the present embodiment, the pair of electrodes 31, 32 is provided between the one surface 10 a of the substrate 10 and the detection unit 20. Further, in the present embodiment, the heater device 40 has the heater device main body 41 having the heat generating portion 44 for heating the detection portion 20, and the heater device main body 41 includes the detection portion 20 and the substrate 10. It is arranged to 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 heater 40 heats the detection unit 20. At this time, the temperature of the detection unit 20 is measured by the temperature measurement device 50, and the heat generation amount of the heat generation unit 44 in the heater device 40 is adjusted by the control device 60 based on the measured temperature, and the temperature of the detection unit 20 is adjusted. For example, when the temperature is controlled to 70 to 120° C., even if the ionic liquid in the detection unit 20 absorbs water in the air, the water in the ionic liquid contained in the detection unit 20 can be evaporated and removed. It will be possible. That is, the detection unit 20 can be in a state of having a low water content. Therefore, the change in the impedance value of the detection unit 20 due to the change in humidity can be sufficiently 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. Therefore, even when the outside air temperature changes, the temperature of the detection unit 20 can be kept constant. Therefore, the change in the impedance of the detection unit 20 due to the change in the outside temperature can be sufficiently suppressed. Therefore, according to the carbon dioxide sensor 100, 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 20.

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

<Substrate>
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. Above all, 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, non-alkali glass, quartz glass, or the like can be used.

<Detection unit>
The detection unit 20 includes the ionic liquid, as described above.

(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 an ionic liquid 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 Bromide (OMIM-Br) etc. are mentioned. These may 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 easily occurs, so that the carbon dioxide sensor 100 is used in an environment in which the carbon dioxide concentration is likely to change. Also can increase the reliability of the carbon dioxide concentration value.

From the viewpoint of shape retention, 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. 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 or may not further contain a gelling agent in addition to the ionic liquid, but it is preferable that the detecting unit 20 further contains a gelling agent. In this case, since the detection unit 20 is gelled, the fluidity of the detection unit 20 is reduced, and 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, and examples of the gelling agent include vinylidene fluoride/hexafluoropropylene copolymer. And so on.

<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 forming 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 laminated body of a plurality of layers made of different conductive materials. The shapes of the electrodes 31 and 32 are not particularly limited, and examples of the shape of the electrodes 31 and 32 include a circular shape, a square shape, and a comb tooth shape. Above all, it is preferable that the electrodes 31 and 32 have a comb-teeth shape because the detection sensitivity to carbon dioxide is high even when the electrodes 31 and 32 are minute electrodes. When the electrodes 31 and 32 have a comb-teeth shape, the electrode 31 is connected to, for example, the main body 31a, the teeth 31b extending from the main body 31a, the main body 31a, and the connection provided outside the detection unit 20. It has a terminal portion 31c. Similarly, the electrode 32 has, for example, a main body portion 32a, a tooth portion 32b extending from the main body portion 32a, and a connection terminal portion 32c connected to the main body portion 32a and provided outside the detection portion 20.

<Heater device>
The heater device 40 may be any device that has 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 the heater device body 41 having a heat generating portion 44 and the heater device body 41 as shown in FIGS. It has a voltage application device 42 for applying a voltage to the device body 41. The heater device body 41 includes a support body 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 body 43 and 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 heats the heat generating portion 44 by applying a voltage between the connection terminals 45 a and 45 b by the voltage applying device 42, and heats the detection portion 20 via the substrate 10.

The support 43 is not particularly limited as long as it can support the heat generating portion 44, but examples of the support 43 include a glass substrate, a silicon substrate, an alumina substrate, and a metal substrate having good thermal conductivity, and a silicone. A laminated substrate obtained by forming an insulating layer such as a layer or an alumina layer can be given.

<Temperature measuring device>
The temperature measuring device 50 may be any device as long as it 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 one that controls the temperature of the detection unit 20 by adjusting the heat generation amount of 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, the moisture is more likely to be evaporated from the detection unit 20, and the influence of the 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 body 41 of the heater device 40 is arranged so as to indirectly heat the detection unit 20 via the substrate 10. However, the heater device body 41 does not include the detection unit 20. It may be arranged to heat 20 directly.

Further, although the heater device main body 41 has the support 43, the support 43 does not necessarily have to be provided. In this case, the heating element 44 is provided, for example, on the surface of the substrate 10 opposite to the detection unit 20.

Further, 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 do not necessarily have to be provided between the detection unit 20 and the substrate 10. Absent. For example, when the detection unit 20 contains a gelling agent and the detection unit 20 is gelated and the shape of the detection unit 20 is maintained, the electrodes 31 and 32 are, for example, the substrate 10 of the detection unit 20 and the substrate 10. It may be provided on the opposite surface.

Further, in the above-described embodiment, the carbon dioxide sensor 100 adjusts the heat generation amount of 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. Although the control device 60 is provided, the control device 60 can be omitted. Even in this case, the operator can manually control the heat generation amount in the heat generating portion 44 of the heater device 40 based on the temperature measured by the temperature measuring device 50. Alternatively, it is possible to make the temperature of the detection unit 20 constant only by applying a constant voltage to the heat generating unit 44 of the heater device 40. This is because the temperature of the heat generating part 44 does not rise indefinitely even if voltage is continuously applied to the heater device 40, and there is a temperature at which heating and heat dissipation are in equilibrium in the heat generating part 44, which is an object to be heated. Is. Therefore, there is a correlation between the power consumption of the heater device 40 and the reached temperature of the heat generating portion 44 of the heater device 40. If the voltage of the heater device 40 is kept constant, the temperature of the heat generating portion 44 becomes the temperature corresponding to the voltage. Become.

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

(Example 1)
First, as the support body 43, a glass substrate of 30 mm×30 mm×1 mm (thickness) was prepared, and a platinum heater was formed on the glass substrate. At this time, the platinum heater was formed to have the meandering heating portion 44 and the connection terminals 45a and 45b provided at both ends thereof by photolithography after forming the platinum layer by the 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, as the substrate 10, a substrate made of quartz glass having a size of 18 mm×18 mm×0.15 mm was prepared. Then, on the one surface 10a of the substrate 10, a Pt layer having a thickness of 500 nm is formed by a sputtering device (manufactured by ULVAC, Inc., product name “SH-350H”) to form a metal layer. A pair of comb-teeth-shaped electrodes 31 and 32 were formed by performing photolithography. At this time, the comb-teeth-shaped electrode 31 is formed so as to have a main body portion 31a, a tooth portion 31b, and a connection terminal 31c, the number of the tooth portions 31b is set to 15, and an interval between adjacent tooth portions 31b is set. Was 100 μm. Similarly, the comb-teeth-shaped electrode 32 is formed so as to have a main body portion 32a, a tooth portion 32b, and a connection terminal 32c, the number of the tooth portions 32b is 15, and the interval between the adjacent tooth portions 32b is set. Was 100 μm. Thus, a substrate with electrodes was produced.

Next, the substrate 10 of the substrates with electrodes and the heater device 40 were bonded using an adhesive (manufactured by Fujikura Kasei Co., Ltd., trade name “Dotite”). At this time, the heater device body 41 of the heater device 40 is bonded to the substrate 10 with the heat generating portion 44 facing the substrate 10. Further, 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, the structure was obtained.

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

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

The 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 attached to the substrate 10.

<Comparison of reliability of measured values of carbon dioxide concentration>
Between the carbon dioxide sensor of Example 1 and the carbon dioxide sensor of Comparative Example 1 obtained as described above, the change of the impedance ratio of the detection unit 20 to the change of humidity, the change of the impedance ratio of the detection unit 20 to the carbon dioxide concentration, Also, the reliability of the measured value of the carbon dioxide concentration was compared by examining and comparing the change of the impedance ratio of the detection unit 20 with respect to the change of the outside air temperature.

Specifically, in the carbon dioxide sensor of Example 1, while applying a constant voltage to the heater device 40 so that the temperature of the detection unit 20 becomes 90° C., the outside air temperature (° C.), the humidity (%RH) ) And the carbon dioxide concentration (volume ppm) were changed with the passage of time, the impedance Z (Ω) of the detection unit 20 was measured. 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 FIGS. 3, 5 and 7. In the carbon dioxide sensor of the first embodiment, Z ₀ has a carbon dioxide concentration of 787 volume ppm and a relative humidity of 56.% when voltage is applied to the heater device 40 so that the temperature of the detection unit 20 becomes 90° C. This is the impedance value of the detection unit 20 measured under the environment of 287% RH.

On the other hand, regarding 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) were changed with the elapse of 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 FIGS. 4, 6 and 8. In addition, Z ₀ is a value different from Z _{0 of} Example 1, and 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 volume ppm, and the relative humidity is It is the value of the impedance of the detection unit 20 measured under the environment of 64.601% RH.

Then, in the carbon dioxide sensor of Comparative Example 1, as shown in FIG. 4, when the relative humidity was drastically decreased after 327 seconds from the start of measurement, 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, after the relative humidity was drastically reduced 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, although the carbon dioxide concentration was drastically reduced after 336 seconds from the start of measurement, the carbon dioxide concentration was made almost constant, The impedance ratio (Z/Z ₀ ) changed greatly. On the other hand, in the carbon dioxide sensor of Example 1, as shown in FIG. 5, when the carbon dioxide concentration was drastically decreased after 318 seconds from the start of measurement and then the carbon dioxide concentration was made almost constant, 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. 8, when the outside air temperature is drastically reduced after 312 seconds have elapsed from the start of measurement, 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 was drastically changed after 306 seconds from the start of measurement, the impedance ratio ( The variation of Z/Z ₀ ) was sufficiently smaller than that of Comparative Example 1.

As described above, in the carbon dioxide sensor of Example 1, the variation of the impedance ratio (Z/Z ₀ ) is considerably smaller than that of the carbon dioxide sensor of Comparative Example 1 even if the outside air temperature and the humidity change. It was Further, in the carbon dioxide sensor of Example 1, it was found that the variation of the impedance ratio (Z/Z ₀ ) was considerably smaller than that of the carbon dioxide sensor of Comparative Example 1 if the carbon dioxide concentration was substantially constant.

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

Reference numeral 10... Substrate 20... Detectors 31, 32... Electrode 40... Heater device 100... Carbon dioxide sensor

Claims (3)

A carbon dioxide sensor that measures the concentration of carbon dioxide based on the change in impedance of the detection unit due to the detection of carbon dioxide,
A substrate supporting the detection unit,
A pair of electrodes provided in contact with the detection unit, for measuring impedance in the detection unit,
A heater device for heating the detection unit,
A carbon dioxide sensor, wherein the detection unit includes an ionic liquid that changes the impedance value of the detection unit according to the 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 a glass substrate or a silicon substrate whose surface is covered with an oxide film.

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