JP4922844B2 - Humidity sensor - Google Patents

Description

  The present invention relates to a humidity sensor, and more particularly to a capacitance type humidity sensor.

  A conventional capacitive humidity sensor has been proposed that utilizes the fact that when a water molecule adheres to a dielectric polymer, the dielectric constant of the polymer increases. For example, as shown in the cross-sectional view of FIG. 6, the polymer film 50 serving as a dielectric layer is sandwiched between a pair of electrodes 51 made of metal, and the ratio of water absorbed in the polymer film 50 to the polymer film 50. Capacitance change due to this change is captured by both electrodes 51, converted into electrical humidity information, and output as a control signal to a subsequent signal processing circuit.

The humidity sensor 52 described above is high because the relative dielectric constant of water is as high as about 80 while the relative dielectric constant of the polymer film is about 3, and the difference between the relative dielectric constants of the polymer film and water is large. A high-sensitivity humidity sensor is realized by attaching water molecules to the molecules (see, for example, Patent Document 1).
Japanese Patent No. 2846948

By the way, in the humidity sensor 52 having the above-described configuration, the dielectric constant of the polymer film 50 is ε, the area of the electrode 51 is S [m ² ], and the distance between the electrodes 51 (layer thickness of the polymer film 50) is d [m]. Then, the capacitance C [F] is expressed by the following formula (1)
C = ε (S / d) (1)
Where C and ε are in a proportional relationship (C∝ε).

  However, when water is absorbed into the polymer film 50, the polymer film 50 expands, and a phenomenon occurs in which the distance d between the electrodes 51 is increased. Then, as the value of the distance d between the electrodes 51 increases from the equation (1), the value of the capacitance C decreases, and the increase in the dielectric constant ε is smaller than the relationship (1). Will work in the direction of.

  Therefore, there is a problem that the expansion of the polymer film reduces the humidity sensitivity and hinders high accuracy of measurement. This problem is a problem common to the capacitive humidity sensor having the above-described configuration.

  Therefore, the present invention was devised in view of the above problems, and the object of the present invention is to suppress humidity expansion of the polymer film due to water absorption, thereby providing high humidity sensitivity and good measurement accuracy. It is to provide a humidity sensor.

  In order to solve the above-mentioned problem, the invention described in claim 1 of the present invention is characterized in that both sides of the first polymer film are sandwiched between a pair of electrodes having a plurality of through holes, A second polymer film is disposed on the opposite side of the polymer film, a stopper is disposed on the opposite side of the second polymer film to the electrode, and the stopper is the first polymer film and the electrode. And a fixing means such that the distance between the stoppers sandwiching the second polymer film does not change even if the expansion force generated by the water absorption of the first polymer film and the second polymer film is received. It is characterized by being given.

  The invention described in claim 2 of the present invention is the frame according to claim 1, wherein the fixing means surrounds the stopper with the first polymer film, the electrode, and the second polymer film. It is characterized by being fixed to the body or being part of the frame.

  The invention described in claim 3 of the present invention is characterized in that, in any one of claims 1 and 2, the stopper has a plurality of through holes.

  Further, in the invention described in claim 4 of the present invention, in any one of claims 1 to 3, the first polymer film and the second polymer film are both formed of the same material. It is characterized by being.

  Moreover, the invention described in claim 5 of the present invention is any one of claims 1 to 4, wherein the film thickness of the first polymer film is the first polymer film, the electrode, and It is equal to or more than the total film thickness of the second polymer film sandwiching the second polymer film.

  The invention described in claim 6 of the present invention is characterized in that, in claim 5, the thicknesses of the second polymer films are equal to each other.

  The humidity sensor of the present invention is a capacitance type humidity sensor using a polymer film as a dielectric, and has a mechanism for suppressing the polymer film from expanding due to water absorption by mechanical stress.

  As a result, humidity sensitivity and measurement accuracy are improved, and it is possible to construct a humidity control system with good controllability by using the humidity sensor of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIG. 1 to FIG. 5 (the same reference numerals are given to the same portions). The embodiments described below are preferable specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. Unless stated to the effect, the present invention is not limited to these embodiments.

  FIG. 1 is a half sectional view of a first embodiment relating to a humidity sensor of the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. In the humidity sensor 1 of the present embodiment, a first polymer film 3 is arranged at the center of a cylindrical frame 2, and a pair of net-like or porous materials that transmit moisture to both sides of the first polymer film 3. Between the electrodes 4a and 4b. The polymer film uses a polyimide-based material.

  From each electrode 4a, 4b, lead wires 5a, 5b connected to each electrode 4a, 4b extend through the frame 2 to the outside, and the first polymer film of each electrode 4a, 4b. On the opposite side to 3, second polymer films 6 a and 6 b made of the same material as the first polymer film 3 are arranged.

  Furthermore, net-like or porous lid bodies 7a and 7b that transmit moisture are arranged on the opposite sides of the respective second polymer films 6a and 6b to the electrodes 4a and 4b, and the lid bodies 7a and 7b are both frame bodies. 2 is fixed.

  That is, the first polymer film 3 is sandwiched between the pair of electrodes 4a and 4b, and the second polymer films 6a and 6b are sandwiched between the electrode 4a and the lid body 7a, and the electrode 4b and the lid body 7b. It has a structure. At this time, since the lid bodies 7a and 7b located on the outermost sides are respectively fixed to the frame body 2, the distance L between the opposite surfaces of the lid bodies 7a and 7b is also fixed. It has become.

  In this case, as shown in FIG. 2, when the film thickness of the first polymer film 3 is d1, and the film thicknesses of the second polymer films 6a and 6b are d2 and d3, the film thicknesses d1, d2, It is preferable that the relationship of d1 = d2 + d3 is established between d3.

  Thereby, when both the first polymer film 3 and the second polymer films 6a and 6b have the same water absorption rate, the expansion force of the first polymer film 3 is set to P1, and the second polymer film 6a. 6b, when the expansion forces of P2 and P3 are P2, P3, the expansion forces P1, P2, and P3 have a relationship of P1 = P2 + P3, and at least the film thickness d1 of the first polymer film 3 hardly changes. On the contrary, it shrinks. Therefore, a humidity sensor with high humidity sensitivity can be realized. Further, the water absorption rate of the second polymer films 6 a and 6 b may be larger than the water absorption rate of the first polymer film 3.

  In addition to the relationship of film thickness d1 = d2 + d3 of each polymer film, the film thicknesses d2 and d3 of the second polymer films 6a and 6b are equal (d2 = d3) so that the relationship of P2 = P3 is established. More preferably.

  As a result, when both the first polymer film 3 and the second polymer films 6a and 6b have the same water absorption, the second polymer film together with the film thickness d1 of the first polymer film 3 is obtained. The film thicknesses d2 and d3 of the films 6a and 6b hardly change, and when the expansion rate of the second polymer films 6a and 6b is large, the film of the first polymer film 3 A humidity sensor with a reduced humidity and a higher humidity sensitivity can be realized.

  Here, how the humidity sensitivity is improved by suppressing the expansion due to water absorption of the first polymer film 3 sandwiched between the pair of electrodes 4a and 4b will be described.

The amount of change in the film thickness d1 of the first polymer film 3 due to water absorption is -Δd1 [m] (the sign indicates the direction in which the film thickness d1 expands due to water absorption), and the amount of change in the capacitance C at that time Is ΔC [F]. From the above equation (1), ΔC = ε (S / d1) · (−Δd1 / d1) = C · (−Δd1 / d1) (2)
When formula (2) is rearranged, (ΔC / C) = (− Δd1 / d1) (3)
It becomes.

Therefore, for example, when the linear expansion coefficient of the first polymer film 3 due to water absorption is 80 ppm /% RH, the linear expansion of the first polymer film 3 is in the range of 0 to 8000 ppm in the humidity range of 0 to 100% RH. Become. Therefore, when the linear expansion of 8000 ppm of the first polymer film 3 at a humidity of 100% RH is substituted into the equation (3),
(−Δd1 / d1) = 8000 ppm = (ΔC / C)
Thus, the amount of change in capacitance (ΔC / C) becomes 8000 ppm, and the capacitance C changes by 0.8% when the humidity is 0% to 100% RH.

  Therefore, the humidity sensor of the present invention can suppress a change in capacitance of about 1% at the maximum by suppressing the change (expansion) of the film thickness in the water absorption state of the first polymer film 3. become. This numerical value does not include the effect of reducing the film thickness of the first polymer film 3.

  The suppression of the capacitance change of about 1% is based on the conventional capacitance considering that the change amount of the capacitance C when the humidity of the conventional capacitance humidity sensor is 100% RH is around 10%. This corresponds to about 10% of the capacity change of the humidity sensor.

  In other words, the humidity sensor of the present invention has an improved humidity sensitivity by about 10% compared to the conventional capacitive humidity sensor.

  3 is a perspective view of a second embodiment of the humidity sensor according to the present invention, and FIG. 4 is a cross-sectional view taken along the line BB of FIG. The humidity sensor 1 according to this embodiment includes a sensor body 8 and a pair of frames 2a and 2b, and the sensor body 8 is inserted into the frames 2a and 2b.

  The sensor body 8 sandwiches both sides of the first polymer film 3 with a pair of net-like or porous electrodes 4a and 4b that transmit moisture, and a lead wire 5a connected from the electrodes 4a and 4b to the electrodes 4a and 4b. 5b extends to the outside of the sensor body 8.

  Each frame 2a, 2b includes an expansion preventing frame 10, 11 having through windows 9a, 9b having a rectangular cross section, between the expansion preventing frame 10 and the electrode 4a of the through window 9a, and between the expansion preventing frame 10 and the electrode 4b. The second polymer films 6 a and 6 b made of the same material as that of the first polymer film 3 are disposed between them.

  Similarly, the second polymer film 6a made of the same material as the first polymer film 3 is provided between the expansion preventing frame 11 and the electrode 4a of the through window 9b and between the expansion preventing frame 11 and the electrode 4b. , 6b are arranged.

  That is, the sensor body 8 is fixed in a state of being sandwiched between the second polymer films 6a and 6b disposed in the through windows 9a and 9b of the respective frames 2a and 2b. At this time, since the outermost surfaces of the second polymer films 6a and 6b are in contact with the expansion preventing frames 10 and 11, respectively, the distance L between the outermost surfaces of the second polymer films 6a and 6b. Is in a fixed state.

  In this case, as in FIG. 3, the first polymer film 3 is d1, and the second polymer films 6a and 6b are d2 and d3. It is preferable that the relationship d1 = d2 + d3 is established among the film thicknesses d1, d2, and d3.

  Thereby, when both the first polymer film 3 and the second polymer films 6a and 6b have the same water absorption rate, the expansion force of the first polymer film 3 is set to P1, and the second polymer film 6a. 6b, the expansion forces P1, P2, and P3 have a relationship of P1 = P2 + P3, and at least the film thickness d1 of the first polymer film 3 hardly changes. Therefore, a humidity sensor with high humidity sensitivity can be realized.

  Further, it is more preferable that the film thicknesses d2 and d3 of the second polymer films 6a and 6b are equal (d2 = d3) together with the relation of d1 = d2 + d3 so that the relation of P2 = P3 is established.

  As a result, when both the first polymer film 3 and the second polymer films 6a and 6b have the same water absorption, the second polymer film together with the film thickness d1 of the first polymer film 3 is obtained. The film thicknesses d2 and d3 of the films 6a and 6b hardly change, and a humidity sensor with higher humidity sensitivity can be realized.

  In Example 1, the first polymer film 3 and the second polymer film 6a, and the first polymer film 3 and the second polymer film 6b are connected to each other via the electrodes 4a and 4b, respectively. Since they face each other over almost the entire surface, the first polymer film 3 and the second polymer film 6a, and the first polymer film 3 and the second polymer film, which face each other across the electrodes 4a and 4b, respectively. The expansion forces P1 and P2 and the expansion forces P1 and P3 at the time of water absorption of 6b act in a plane shape. Therefore, the electrodes 4a and 4b may be made of a material having rigidity and strength enough to be deformed by the minimum expansion force among the expansion forces P1, P2, and P3.

  On the other hand, in the second embodiment, the second polymer films 6a and 6b are partially opposed to the first polymer film 3 via the electrodes 4a and 4b, respectively. Expansion forces P1 and P2 and expansion force P1 at the time of water absorption of the first polymer film 3 and the second polymer film 6a, and the first polymer film 3 and the second polymer film 6b facing each other, P3 partially acts on the first polymer 3. Therefore, the electrodes 4a and 4b are required to be made of a material having rigidity and strength that does not deform even when the maximum expansion force among the expansion forces P1, P2, and P3 is partially applied.

  FIG. 5 is a perspective view of Example 3 according to the humidity sensor of the present invention. The humidity sensor 1 of the present embodiment has a configuration in which the sensor body 8 is compressed and fixed with a clip 12.

  In the sensor body 8, a metal base electrode 14 is disposed on a substrate 13 made of a robust material such as glass, ceramic, Si, etc., a polymer film 15 is disposed on the metal base electrode 14, and the polymer film 15 is further disposed. A net-like or porous metal upper layer electrode 16 that allows moisture to permeate is disposed on the substrate.

  And the sensor main body 8 of the said structure is compression-fixed at two places with the clip 12 which consists of insulating materials, such as engineering plastics. In addition, the arrangement | positioning location of the clip 12 is not restricted to two places, It sets suitably in consideration of the magnitude | size of the sensor main body 8, the magnitude | size of the clip 12, the compression force of the clip 12, etc. FIG.

  In this case, the substrate 13 that indirectly sandwiches the polymer film 15 and the metal upper layer electrode 16 that directly sandwiches the polymer film 15 are materials having rigidity and strength that do not deform even when the maximum expansion force due to water absorption of the polymer film 15 is partially applied. It is necessary to be.

  By adopting such a structure for the humidity sensor, expansion of the polymer film 15 due to water absorption is suppressed, and a humidity sensor with high humidity sensitivity is realized.

  As described above in the first to third embodiments, the humidity sensor of the present invention has a relational expression of the capacitance C, the electrode area S, and the thickness d of the polymer film serving as a dielectric: C = ε ( In S / d), the amount of change in the thickness d of the polymer film was suppressed by suppressing the expansion of the polymer film during water absorption.

  As a result, the humidity sensitivity and measurement accuracy of the humidity sensor based on the capacitance method are improved, and it becomes possible to construct a humidity control system with good controllability by using the humidity sensor of the present invention.

It is a half sectional view of Example 1 relating to the humidity sensor of the present invention. It is AA sectional drawing of FIG. It is a perspective view of Example 2 concerning the humidity sensor of this invention. It is BB sectional drawing of FIG. It is a perspective view of Example 3 concerning the humidity sensor of this invention. It is sectional drawing of the conventional humidity sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Humidity sensor 2 Frame body 2a, 2b Frame body 3 1st polymer film 4a, 4b Electrode 5a, 5b Lead wire 6a, 6b 2nd polymer film 7a, 7b Cover body 8 Sensor main body 9a, 9b Penetrating window 10 Expansion prevention frame 11 Expansion prevention frame 12 Clip 13 Substrate 14 Metal base substrate 15 Polymer film 16 Metal upper layer electrode

Claims (6)

  The both sides of the first polymer film are sandwiched between a pair of electrodes having a plurality of through holes, a second polymer film is disposed on the opposite side of each electrode from the first polymer film, A stopper is disposed on the opposite side of the polymer film to the electrode, and the distance between the stopper sandwiching the first polymer film, the electrode, and the second polymer film is the first polymer film. A humidity sensor characterized in that a fixing means is provided so as not to change even when receiving an expansion force generated by water absorption of the second polymer film and the second polymer film.   The fixing means is characterized in that the stopper is fixed to a frame body surrounding the first polymer film, the electrode, and the second polymer film or a part of the frame body. The humidity sensor according to claim 1.   The humidity sensor according to claim 1, wherein the stopper has a plurality of through holes.   The humidity sensor according to any one of claims 1 to 3, wherein both the first polymer film and the second polymer film are formed of the same material.   The film thickness of the first polymer film is equal to the total film thickness of the second polymer film across the first polymer film, the electrode, and the second polymer film, or It is more than that, The humidity sensor of any one of Claims 1-4 characterized by the above-mentioned.   6. The humidity sensor according to claim 5, wherein the film thicknesses of the second polymer films are equal to each other.

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