Resistance-type humidity sensor

Abstract

Provided is a resistance-type humidity sensor that does not significantly reduce the performance of the humidity sensor even if a heat-shrinkable tube that does not have air permeability is used to prevent an increase in size of a surrounding body. The resistive humidity sensor is provided with an electrically insulating surrounding body (20) comprising a heat-shrinkable tube, and the surrounding body (20) is disposed so as to surround a sensor main body (2) and a facing portion (9Bb) of one lead wire facing the sensor main body together. The surrounding body (20) in the contracted state has a pair of openings (21, 22) at both ends in the direction in which the cylindrical insulating base (3) extends, and is in contact with at least a part of the pair of cap-shaped terminals (7, 7) and a part of an opposing part (9Bb) of the one lead wire so as to have a communication path (23) between the pair of openings.

Description

Resistive humidity sensor Technical Field

[0001] This invention relates to a resistive humidity sensor. Background Technology

[0002] Japanese Patent Application Publication No. 2021-175973 discloses a conventional resistive humidity sensor that is an improvement upon the present invention. This conventional resistive humidity sensor includes: a pair of cap-shaped terminals fitted and fixed to both ends of a cylindrical insulating substrate; a resistive film formed on the surface of the cylindrical insulating substrate and electrically connected to the pair of cap-shaped terminals; a slit formed in the resistive film to divide the resistive film in two; a moisture-sensing film disposed to close the slit and whose resistance value changes according to changes in humidity; a sensor body having a moisture-permeable protective film covering at least the moisture-sensing film to protect it; and a pair of leads connected to the pair of cap-shaped terminals. Furthermore, in FIG. 4, a resistive humidity sensor formed in a state where one of the leads is bent at intervals from the sensor body along the sensor body and parallel to the other lead. Additionally, FIG. 5(D) discloses a structure in which a heat-shrinkable tube with ventilation properties covers the entire circumference of the sensor body. In this resistive humidity sensor, it is possible to prevent excessive current from flowing through, and by appropriately setting the resistance value of the resistive film, the necessity of an external resistor as another component for characteristic adjustment can be eliminated.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-175973, Figures 4 and 5 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In this resistive humidity sensor, there is no need for an external resistor as a component for characteristic adjustment, thus enabling miniaturization. However, even with a protective film, performance degradation occurs if moisture adheres to the protective film of the sensor body or external force is applied during substrate mounting. Furthermore, using a breathable housing to protect the sensor body hinders miniaturization. Additionally, completely covering the sensor body with a breathable heat-shrink tubing not only makes it difficult to prevent external moisture ingress but also obstructs airflow, leading to reduced humidity sensor accuracy.

[0008] The purpose of this invention is to provide a resistive humidity sensor that can use a non-breathable heat shrink tubing to protect the sensor body without significantly reducing its performance as a humidity sensor.

[0009] Solution for solving the problem

[0010] In the resistive humidity sensor of the present invention, the sensor body comprises a cylindrical insulating substrate, a pair of cap-shaped terminals fitted and fixed at both ends of the cylindrical insulating substrate, a resistive film formed on the surface of the cylindrical insulating substrate and electrically connected to the pair of cap-shaped terminals, a slit formed in the resistive film in such a way as to divide the resistive film in two, and a moisture-sensing film disposed in such a way as to close the slit and whose resistance value changes according to the change of humidity. It should be noted that, in this specification, "divided in two" means that the resistive film is divided into two parts, and is not limited to the resistive film being 1 / 2. The moisture-sensing film can theoretically be disposed in such a way as to close the slit, but it can also be disposed in such a way as to completely cover the resistive film and the slit located between the pair of cap-shaped terminals. In addition, a moisture-permeable protective film is provided to at least cover the moisture-sensing film to protect the moisture-sensing film. Furthermore, one of the pair of leads has a bent portion, which is bent so that the one lead is spaced apart from the sensor body and runs along the sensor body and is parallel to the other lead. In particular, this invention includes an electrically insulating enclosure made of heat-shrinkable tubing, which is configured to surround the sensor body and the opposing portion of a lead wire opposite the sensor body. Furthermore, the enclosure in its contracted state has a pair of openings at both ends in the direction extending from the cylindrical insulating substrate, and a communication path between the pair of openings, thus contacting at least a portion of a pair of cap-shaped terminals and a portion of the opposing portion of the lead wire.

[0011] The technique of using non-breathable heat-shrink tubing to enclose electronic components is employed, for example, in the surge-absorbing element disclosed in Utility Model Registration No. 2573087. In this technique, the surge-absorbing element is enclosed within the heat-shrink tubing with one of a pair of leads bent at a distance from the element body and parallel to the other lead, including the bent portion of the lead terminals. Since the surge-absorbing element does not need to detect atmospheric humidity like a humidity sensor, there is no problem in enclosing it within the heat-shrink tubing. Furthermore, in the fuse resistor described in Patent No. 4373539, a resistive element with axial leads and a fuse element with axial leads are placed side-by-side in contact, and the junction of the leads of these two elements is enclosed within a heat-shrink tubing enclosure. The purpose of heat shrink tubing is to apply pressure to two elements and to minimize the opening of the heat shrink tubing enclosure located outside the junction of the leads of the two elements, so that heat is stored inside the enclosure. Thus, existing technology utilizes heat shrink tubing when electrical components are enclosed within the enclosure, but it does not consider using non-breathable heat shrink tubing for the enclosure of a humidity sensor that needs to actively contact external gas. Therefore, as an existing technology for covering a humidity sensor with an enclosure, as described in Japanese Utility Model Application Publication No. 56-114452, a technique is proposed whereby, in order to allow the humidity sensor element to contact external gas, a bag-like body made of a breathable film such as polypropylene with multiple air bubbles is used to surround the humidity sensor element, which has leads with bends. However, in the technology described in this publication, since sufficient space is ensured between the bag-like body made of the film such as polypropylene with multiple air bubbles and the humidity sensor, a large bag-like body would hinder the miniaturization of the overall shape and size of the sensor.

[0012] This invention utilizes a non-breathable heat-shrinkable tube, which would be considered unusable by those skilled in the art in the prior art, as the enclosure for a humidity sensor element. As previously described, in this invention, the electrically insulating enclosure, constructed from a non-breathable heat-shrinkable tube, has a pair of openings at both ends extending in the direction of the cylindrical insulating substrate, and a connecting passage between the pair of openings, and contacts at least a portion of a pair of cap-shaped terminals and a portion of the opposing portion of a lead. With this structure, the pair of cap-shaped terminals and a portion of the opposing portion of the lead become spacers separating the space between the heat-shrinkable tube and the moisture-sensing film. Furthermore, the pair of leads are spaced apart and arranged side by side, thereby preventing the opening area of ​​one opening from decreasing. In addition, a required amount of moisture-containing air is introduced into the interior of the enclosure through the connecting passage formed between the pair of openings. As a result, a sufficient amount of space for humidity detection can be formed inside the enclosure formed from the non-breathable heat-shrinkable tube, around the protective film covering the moisture-sensing film, and an amount of external gas required for humidity detection can be introduced into the interior of the enclosure through the connecting passage with openings at both ends. Furthermore, since the protective film is surrounded by an enclosure made of a non-ventilated heat-shrinkable tube, the possibility of moisture adhering to the protective film is greatly reduced, thus preventing performance degradation caused by moisture adhesion. Therefore, according to the present invention, a resistive humidity sensor can be provided that does not significantly degrade the performance of the humidity sensor even when using a non-ventilated heat-shrinkable tube to prevent the enclosure from becoming too large.

[0013] It should be noted that at least a portion of the bent portion of a lead wire may or may not be exposed to the outside from another opening of the enclosure formed by the heat-shrink tubing. If the enclosure is short, at least a portion of the bent portion of a lead wire will be exposed to the outside from the other opening of the enclosure; if the enclosure is long, the bent portion of a lead wire will not be exposed to the outside from the other opening of the enclosure. If the bent portion of a lead wire is exposed to the other opening, the opening area of ​​the other opening of the connecting path can be reliably prevented from decreasing.

[0014] The heat shrink tubing, which is not breathable, is preferably made of polyolefin, silicone rubber, or similar materials. Furthermore, the gap between the enclosure and the protective film is typically approximately 0.1 mm to 2.0 mm, and the gap between the enclosure and a portion of the opposite part of the lead is approximately 2.5 mm to 7.5 mm. If these values ​​are within the aforementioned range, humidified air required for humidity measurement can be reliably introduced into the interior of the enclosure. It should be noted that these values ​​will naturally vary depending on whether the sensor body is miniaturized or enlarged. Attached Figure Description

[0015] In Figure 1, (A) is a front view of the resistive humidity sensor of the first embodiment, (B) is a front view of the resistive humidity sensor obtained by cutting the enclosure body made of a heat shrink tube that does not have ventilation, which will be described later, and (C) is a top view of the resistive humidity sensor.

[0016] In Figure 2, (A) is a view showing the cap-shaped terminal as a transparent component during the manufacturing process of the resistive humidity sensor of the first embodiment, (B) is a view after the leads are welded to both sides of the cap-shaped terminal and a moisture-sensing film, a protective film and a resin coating layer are applied, and (C) is a schematic cross-sectional view showing the structure of the moisture-sensing film forming part of the resistive humidity sensor of this embodiment.

[0017] Figure 3 is a front view of a resistive humidity sensor obtained by cutting through the enclosure made of heat shrink tubing according to the second embodiment.

[0018] Figure 4 is a graph showing the average (arithmetic mean) of the humidity measurements of various test specimens (three of each) when the humidity of the precision humidity chamber was reduced from 50% to 30%.

[0019] Figure 5 is a graph showing the average (arithmetic mean) of the humidity measurements of various test specimens (three of each) when the humidity of the precision humidity chamber was increased from 50% to 90%.

[0020] Figure 6 is a graph showing the actual experimental data. Detailed Implementation

[0021] Hereinafter, the first embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG1(A) is a front view of the resistive humidity sensor 1 of this embodiment, FIG1(B) is a front view of the resistive humidity sensor 1 obtained by taking the enclosure 20, which is composed of a non-breathable heat shrink tube described later, as a longitudinal section, and FIG1(C) is a top view of the resistive humidity sensor 1. The resistive humidity sensor 1 includes a pair of leads 9A, 9B extending from both ends of the sensor body 2, which will be described in detail later, and a cylindrical electrically insulating enclosure 20 composed of a non-breathable heat shrink tube. One of the leads 9B has a bend 9Ba, which is bent such that one lead 9B is spaced apart from the sensor body 2 and runs parallel to the other lead 9A.

[0022] The enclosure 20 is configured to surround the sensor body 2 and the opposing portion 9Bb of a lead 9B opposite to the sensor body 2. In its contracted state, the enclosure 20 has a pair of openings 21 and 22 at both ends in the direction extending from the cylindrical insulating substrate 3 (described later) of the sensor body 2, and a connecting passage 23 is formed between the openings 21 and 22. A pair of leads 9A and 9B extend outwards from one of the openings 21 of the enclosure 20 in a parallel arrangement, and a bent portion 9Ba of one lead 9B protrudes outwards from the other opening 22. It should be noted that the lead 9B has a bent portion 9Bc, which is adjacent to a portion of the opposing portion 9Bb and located on the free end side of the lead 9B, bending outwards to act as a stop relative to the enclosure 20.

[0023] The sensor body 2 will be described in detail based on Figures 2(A) to (C). Figure 2(A) shows the cap-shaped terminals 7, 7 as transparent components during the manufacturing process. Figure 2(B) shows the cap-shaped terminals 7, 7 after the leads 9A, 9B are welded to both sides and the moisture-sensing film 13, protective film 15, and resin coating layer 19 are applied. Figure 2(C) is a schematic diagram showing the structure of the moisture-sensing film forming part of the resistive humidity sensor 1. The sensor body 2 of the resistive humidity sensor 1 in the intermediate state shown in Figure 2(A) has a cylindrical insulating substrate 3 made of ceramic material and a resistive film 5 formed on most of the outer peripheral surface of the cylindrical insulating substrate 3. The resistive film 5 is formed of a resistive material, which includes conductive substances such as ruthenium oxide, metal, metal oxide, and carbon, which do not migrate. A pair of metal cap-shaped terminals 7, 7 are fitted into both ends of the cylindrical insulating substrate 3 in contact with the resistive film 5. These two cap-shaped terminals 7 and 7 are formed by plating Cu and Sn onto the surface of an iron cap-shaped body, respectively. The cap-shaped terminal 7 includes: an opening 7A for fitting into a cylindrical insulating substrate 3; an annular end face 7B; a cylindrical portion 7C continuous with the annular end face 7B and facing the outer periphery of the end of the cylindrical insulating substrate 3; and a bent portion 7D facing the end face 3A of the end of the cylindrical insulating substrate 3. Furthermore, an annular slit 11 covering the entire circumference of the resistive film 5 is formed in a manner that divides the resistive film 5 in two. It should be noted that the shape of the cap-shaped terminals 7 and 7 is not limited to having the bent portion 7D as in this embodiment; they may also have a shape that runs along the end face of the cylindrical insulating substrate 3 without the bent portion 7D.

[0024] In the examples shown in Figures 2(B) and (C), a moisture-sensitive membrane 13, whose resistance value changes according to humidity, is formed by sealing the slit 11. The moisture-sensitive membrane 13 is formed as follows: a mixture of a moisture-sensitive polymer, such as that disclosed in Japanese Patent Application Publication No. 2003-4685, and an additive polymer such as polyvinyl alcohol that increases the adhesion and water resistance of the moisture-sensitive polymer to the cylindrical insulating substrate 3, is applied to fill the slit 11 and overlaps with the resistive membrane 5, and then the coating is dried and cured. In this example, a protective film 15 is further formed covering a portion of the resistive membrane 5 between a pair of cap-shaped terminals 7, 7 and the moisture-sensitive membrane 13. In this embodiment, the same polymer material as the basic polymer material used to form the moisture-sensitive membrane 13 is used as the protective film 15. The protective film 15 is permeable to prevent moisture, dust, etc., from directly adhering to the moisture-sensitive membrane 13.

[0025] The moisture-sensing membrane 13 can theoretically be provided by blocking the slit 11, and the protective film 15 can be provided by covering the moisture-sensing membrane 13. However, the moisture-sensing membrane 13 can also be provided by completely covering the resistive film 5 and the slit 11 located between the pair of cap-shaped terminals 7, 7. It should be noted that when the moisture-sensing membrane 13 covers the resistive film 5, it is preferable that the moisture-sensing membrane 13 does not contact the pair of cap-shaped terminals 7, 7. In this way, since the smaller the size, the lower the adhesion of the moisture-sensing membrane 13 to the resistive film 5, the increased adhesion area of ​​the moisture-sensing membrane 13 can effectively prevent the moisture-sensing membrane 13 from peeling off. In addition, when the protective film 15 is formed on the moisture-sensing membrane 13, the protective film 15 is also preferably formed in a way that does not contact the pair of cap-shaped terminals 7, 7.

[0026] In this embodiment, a pair of leads 9A and 9B are welded to a pair of cap-shaped terminals 7, 7. Furthermore, a portion of the cap-shaped terminals 7, 7 and the leads 9A and 9B are covered by resin coating layers 19, 19 formed by applying an insulating resin coating made of epoxy resin. During the application process of the moisture-sensitive film 13 and the protective film 15, the resin coating layers 19, 19 prevent corrosion of the cap-shaped terminals 7, 7 and the leads 9A and 9B when they come into contact with the moisture-sensitive film 13 and the protective film 15. Additionally, they suppress the reaction, precipitation, and abnormal characteristics of ions in the moisture-sensitive film.

[0027] It should be noted that, to represent the dimensions of the test sample of the above embodiment, the length L1 between the ends of the pair of cap-shaped terminals 7, 7 is approximately 5.8 mm, the length between the openings 7A, 7A of the pair of cap-shaped terminals 7, 7 is approximately 2.8 mm, the length L2 of the cylindrical insulating substrate 3 is approximately 5.5 mm, the diameter D is approximately 1.5 mm, and the width of the slit is 0.13 ± 0.1 mm. Furthermore, the resistance value of the resistive humidity sensor 1 is preferably around 1 kΩ to 1000 kΩ based on the balance with the surrounding circuitry.

[0028] Furthermore, the lengths of leads 9A and 9B are each 5 mm. Additionally, as shown in Figures 1(B) and (C), the length of the enclosure 20 and the length L3 of the connecting path 23 formed between the pair of openings 21 and 22 are approximately 7 mm, and the width W of the openings 21 and 22 is approximately 3 mm. In this embodiment, the enclosure 20 contacts at least a portion of a pair of cap-shaped terminals and a portion of the opposing portion of one lead. As a result, a portion of the pair of cap-shaped terminals 7, 7 and a portion of the opposing portion 9Bb of lead 9B become spacers separating the enclosure 20 (made of heat-shrink tubing) from the moisture-sensitive film 13 or the protective film 15. In this embodiment, the gap size g1 between the enclosure 20 and the protective film 15 is approximately 0.2 mm, and the gap size g2 between the enclosure 20 and a portion of the opposing portion 9Bb of lead 9B is approximately 2.5 mm. Furthermore, in this embodiment, the opening area of ​​one opening 21 is prevented from decreasing by having the ends of a pair of leads 9A and 9B spaced apart side by side. Additionally, the opening area of ​​the other opening 22 is prevented from decreasing by having the bent portion 9Ba of one lead 9B protruding from the other opening 22. As a result, sufficient space for humidity detection can be formed inside the enclosure 20 formed of a non-ventilated heat-shrinkable tube, around the protective film 15 covering the moisture-sensing film 13. Moreover, the amount of external gas required for humidity detection can be introduced into the enclosure 20 through the connecting passage 23 with openings at both ends. Furthermore, since the protective film 15 is surrounded by the enclosure 20 made of a non-ventilated heat-shrinkable tube, the possibility of moisture adhering to the protective film 15 is greatly reduced, preventing performance degradation.

[0029] It should be noted that, through experiments, it has been confirmed that the preferred size range of the gap dimension g1 between the enclosure 20 and the protective film 15 is approximately 0.1 mm to 2 mm, and the preferred size range of the gap dimension g2 between the enclosure 20 and a portion of the opposing portion 9Bb of the lead 9B is approximately 2.5 mm to 7.5 mm. The lower limit of these two ranges is a value that will not substantially reduce the humidity detection accuracy, and the upper limit of these two ranges is a range that will not excessively increase the overall size of the sensor body 2 in practical applications.

[0030] Figure 3 is a front view showing the enclosure 20', which is made of a non-ventilated heat-shrinkable tube, as a longitudinal section in the resistive humidity sensor 1' of the second embodiment of the present invention. The resistive humidity sensor 1' of this embodiment differs from the resistive humidity sensor 1 of the first embodiment of Figure 1 in the length of the cylindrical electrically insulating enclosure 20'. Other aspects are the same as the structure of each part of the resistive humidity sensor 1 of the first embodiment, therefore, the symbols marked with ' are added to the symbols marked in Figure 3. In this embodiment, as shown in Figure 3, the enclosure 20' has a length such that the bend 9'Ba of a lead 9'B does not protrude to the outside from the opening 22' of one end 20'a. In this embodiment, the other end 20'b of the enclosure 20' extends to the vicinity of the bend 9'Bc of the lead 9'B. As a result, the length L'3 of the connecting path 23' of the resistive humidity sensor 1' of the second embodiment is longer than the length L3 of the connecting path 23 of the resistive humidity sensor 1 of the first embodiment shown in Figure 1. Specifically, the length L'3 of the connecting path 23' is 0.9cm, but this length will not have a significant impact on the accuracy of humidity detection.

[0031] The specific dimensional values ​​of the first and second embodiments described above are examples, and will naturally change depending on further miniaturization or enlargement of the sensor body. Therefore, the present invention is not limited to the specific dimensional values ​​of the above embodiments.

[0032] Figures 4 and 5 show the performance test results for the following cases: using the enclosure 20 as in the first embodiment (tube enclosure A), not using the enclosure 20 (no enclosure B), closing the upper opening 22 of the enclosure 20 (tube enclosure + sealing C), and using adhesive tape instead of the enclosure, resulting in no opening in the vertical direction (overall enclosure D). Three of each of the four test specimens were prepared for the test. After confirming that all four sensors used as test specimens detected a humidity of 60%, they were placed in a precision humidity chamber. Figure 4 is a graph showing the average (arithmetic mean) of the humidity measurements of each test specimen (three of each type) when the humidity of the precision humidity chamber was reduced from 50% to 30%. Figure 5 is a graph showing the average (arithmetic mean) of the humidity measurements of each test specimen (three of each type) when the humidity of the precision humidity chamber was increased from 50% to 90%. Figure 6 shows the actual test data. In this experiment, the resistance (humidity) was measured from the moment the test piece was placed in the precision humidity bath until 10 minutes later when the resistance value changed significantly.

[0033] The test specimens using the enclosure 20 (tube covering A) as in the first embodiment and those without the enclosure 20 (no enclosure B) showed humidity levels close to those in the precision humidity chamber after 10 minutes. In contrast, the test specimens with the upper opening 22 of the enclosure 20 blocked (tube covering + sealing C) and those using adhesive tape instead of the enclosure without openings in the vertical direction (overall enclosure D) showed poor responsiveness, failing to reach the same level as the test specimens without the enclosure (B) and with the enclosure (A) even after 10 minutes. Based on these results, it was determined that measuring humidity through ventilation via the connecting path 23 formed inside the enclosure 20 is effective. Furthermore, the test specimens with a slightly increased length of the enclosure 20', as in the second embodiment shown in Figure 3, also yielded the same results as the first embodiment.

[0034] Industrial applicability

[0035] According to the present invention, a resistive humidity sensor can be provided that does not significantly reduce the performance of the humidity sensor even when a non-ventilable heat-shrinkable tube is used to prevent the encapsulation of the enclosure.

[0036] Explanation of reference numerals in the attached figures

[0037] 1.1' Resistive Humidity Sensor

[0038] 2, 2´ Sensor body

[0039] 21, 22, 21', 22' Openings

[0040] 23, 23' connecting path

[0041] 3. Cylindrical insulating substrate

[0042] 5. Resistive film

[0043] 7 cap terminal

[0044] 9A and 9B leads

[0045] 11. Slit

[0046] 13 Moisture Sensing Film

[0047] 15 Protective film

[0048] 19 Resin Coating Layer

[0049] 20, 20' bounding body

Claims

1. A resistive humidity sensor comprising: a sensor body having a cylindrical insulating substrate, a pair of cap-shaped terminals fitted and fixed at both ends of the cylindrical insulating substrate, a resistive film formed on the surface of the cylindrical insulating substrate and electrically connected to the pair of cap-shaped terminals, a slit formed in the resistive film to divide the resistive film in two, a moisture-sensing film disposed to close the slit and whose resistance value changes according to changes in humidity, and a moisture-permeable protective film at least covering the moisture-sensing film to protect the moisture-sensing film; and a pair of leads connected to the pair of cap-shaped terminals, one of the leads having a bent portion, the bent portion being bent such that the one lead is spaced apart from the sensor body and runs parallel to the other lead along the sensor body, wherein... The resistive humidity sensor includes an electrically insulating enclosure made of a non-breathable heat-shrinkable tube, the enclosure being configured to surround the sensor body and the opposing portion of the lead wire opposite the sensor body, the enclosure having a pair of openings at both ends in the direction extending from the cylindrical insulating substrate and a communication path between the pair of openings, and contacting at least a portion of the pair of cap-shaped terminals and a portion of the opposing portion of the lead wire.

2. The resistive humidity sensor according to claim 1, wherein, The ends of the pair of leads extend outward from one of the openings of the enclosure in a spaced-apart arrangement, and at least a portion of the bend of the lead is exposed outward from the other opening of the pair of openings.

3. The resistive humidity sensor according to claim 1, wherein, The enclosure has a length such that the ends of the pair of leads extend outward from one of the openings in a spaced-apart arrangement and that the bend of one lead does not protrude outward from the other of the openings.

4. The resistive humidity sensor according to claim 1, wherein, The heat shrink tubing is a heat shrink tubing made of polyolefin or fluoropolymer.

5. The resistive humidity sensor according to claim 1, wherein, The resistive film is formed of a resistive material, which includes conductive substances such as ruthenium oxide, metals, metal oxides, and carbon that do not migrate.

6. The resistive humidity sensor according to claim 2, wherein, The gap between the enclosure and the protective film is approximately 0.1 mm to 2 mm, and the gap between the enclosure and a portion of the opposite part of the lead is approximately 2.5 mm to 7.5 mm.

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