Strain gauge transducer

Abstract

To realize a strain gauge type converter that measures a physical quantity, such as a pressure, by converting the same into an electric signal by using a strain gauge and can start measurement rapidly after installation and can be managed easily at low cost.SOLUTION: A pressure gauge 1 as a strain gauge type converter includes a casing 10 having a strain element 14 deformed according to force received from the outside, a strain gauge 16 disposed on the strain element 14, a conductor 21 that is connected to the strain gauge 16 and is withdrawn to the outside of the casing 10 through an aperture 19 provided in the casing 10, a coating material 24 that covers the conductor 21, is adhered to the casing 10 in one end, and has a gap 25 between the conductor 21 and itself, a conductor 41 for supplying an output signal to an external device, and a board 31 having circuits connected to the conductor 21 and the conductor 41, respectively, and an airway continuous from the inside of the casing 10 to the other end of the coating material 24 through the gap 25 is formed.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a strain gauge transducer that uses a strain gauge to convert a physical quantity such as pressure into an electrical signal for measurement. [Background technology]

[0002] 2. Description of the Related Art Conventionally, strain gauge transducers have been known that use strain gauges to convert physical quantities such as pressure into electrical signals for measurement. Strain gauges have the property that their electrical resistivity changes when subjected to force, and the minute change in output electrical signal caused by this change in resistivity can be extracted by amplifying it using a bridge circuit or amplifier.For example, by attaching a strain gauge to a strain-generating body that generates strain when subjected to pressure and recording the change in the output electrical signal, it is possible to measure the pressure applied to the strain-generating body.

[0003] Strain gauges can be broadly divided into metal (foil) strain gauges and semiconductor strain gauges, and pressure meters and pore water pressure meters that use either of these strain gauges have traditionally been manufactured and sold as strain gauge transducers. In addition to these, strain gauge transducers are also used as devices for measuring pressure and stress, such as soil pressure gauges, water pressure gauges, and load cells. These pressure gauges and other instruments are used in experiments using scaled-down models of actual structures, conducted in a wide range of fields, including shipbuilding, railways, construction, disaster prevention structures, and natural disasters (tsunami wave pressure, earthquake shaking, and strong wind pressure), and are making a significant contribution to the development of technologies necessary for the development of social infrastructure and research related to human safety. As the above-mentioned pressure gauge, for example, the one described in Patent Document 1 is known. Furthermore, a pressure gauge used in the medical field is known, for example, as described in Patent Document 2. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-346042 [Patent Document 2] Japanese Patent Application Publication No. 7-275211 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, some of the above-mentioned strain gauge-based transducers are designed for use underwater, with the strain gauge and strain element housed in a sealed case. However, such strain gauge-based transducers, particularly sensitive devices capable of detecting slight pressures, have the problem that they take a very long time, sometimes as long as a day, from installation at the measurement location until they reach a stable state where measurements can be made. This is thought to be because the output (electrical resistivity) of a strain gauge is easily affected by changes in the surrounding environment, such as temperature, and when the housing is sealed, the environment outside the housing is not quickly reflected inside the housing, and the environment around the strain gauge inside the housing continues to change slowly for a long period of time.

[0006] However, when considering use underwater, a configuration in which an opening is provided in the housing itself to allow direct ventilation between the housing and the outside through that opening is difficult to adopt, as water can easily seep in through the opening, which can cause a short circuit in the circuit. This problem becomes particularly pronounced when semiconductor strain gauges, which are highly accurate and sensitive to changes in force, are used.

[0007] To address this problem, it is conceivable to provide an opening in the case in which the strain gauge is placed and connect a ventilation hose to the opening, thereby enabling ventilation between the inside of the case and the outside air through the ventilation hose, as described in Patent Document 2. It is also conceivable to provide such a ventilation hose inside the jacket of the cable used to extract signals from the strain gauge. However, providing a ventilation hose separate from the cable would complicate the structure, making it undesirable in terms of cost and handling, and simply providing a ventilation path inside the cable jacket would increase the cable's thickness and stiffness, making it difficult to handle.

[0008] The present invention aims to solve these problems and provide a strain gauge type transducer that uses a strain gauge to convert a physical quantity such as pressure into an electrical signal for measurement, that can start measuring quickly after installation, and that is easy to handle. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the strain gauge type transducer of the present invention comprises a housing having a strain element that deforms in response to an external force, a strain gauge arranged on the strain element, a first conducting wire connected to the strain gauge and drawn out to the outside of the housing through a through hole provided in the housing, a covering material that covers the first conducting wire, one end of which is in close contact with the housing and has a gap between it and the first conducting wire, a second conducting wire for supplying an output signal to an external device, and circuits connected to the first conducting wire and the second conducting wire, and a first air passage is formed that passes through the gap and continues from the inside of the housing to the other end of the first covering material.

[0010] Such a strain gauge type transducer preferably includes a housing member for housing the circuit, which is provided so as to be in close contact with the other end of the first covering material, and the first air passage extends from the inside of the housing through the gap to the inside of the housing member and comes into contact with the outside air at an opening formed in the surface of the housing member. Furthermore, it is preferable to provide a water-repellent material on the outer surface of the container member around the opening. Alternatively, a water-repellent material that is both water-repellent and breathable may be provided to cover the opening.

[0011] Furthermore, the strain gauge type transducer preferably has a second air passage formed along the second conducting wire, and a continuous air passage including the first air passage and the second air passage is formed from the inside of the housing through the other end of the first covering material to near the end of the second conducting wire opposite the circuit, and the cross-sectional area of ​​the second air passage is smaller than the cross-sectional area of ​​the gap. Furthermore, it is preferable that a housing member for housing the circuit is provided so as to be in close contact with the other end of the first covering material, and that the first air passage and the second air passage are connected through the inside of the housing member.

[0012] Furthermore, the invention described above can be embodied in any manner, not just the described manner, such as a method for measuring a physical quantity such as pressure using a strain gauge-based transducer, a system including a strain gauge-based transducer and its peripheral devices, or components that constitute a strain gauge-based transducer. [Effects of the Invention]

[0013] According to the present invention as described above, it is possible to realize a strain gauge type transducer that uses a strain gauge to convert a physical quantity such as pressure into an electrical signal for measurement, which can start measurement quickly after installation and is easy to handle. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing a schematic configuration of a pressure gauge which is a first embodiment of the strain gauge based transducer of the present invention. [Figure 2] FIG. 2 is a schematic plan view of the pressure gauge shown in FIG. [Figure 3] Figures 3A and 3B are schematic cross-sectional views taken along lines AA and BB, respectively, showing cross sections of cables 20 and 40 included in the pressure gauge of Figure 2. Figure 3C is a schematic cross-sectional view showing a state of cable 20 different from that shown in Figure 3A. [Figure 4]Fig. 4A is a schematic cross-sectional view taken along line CC of the pressure gauge shown in Fig. 2. Fig. 4B is a schematic end view showing the configuration of the end face of the cable relay tube 30 of Fig. 4A as viewed from the arrow D side. [Figure 5] 5A and 5B are cross-sectional views corresponding to FIG. 3A, each showing a cross section of a comparative cable. [Figure 6] Fig. 6A is a schematic cross-sectional view corresponding to a part of Fig. 4A, showing the configuration of a pressure gauge according to a second embodiment of the present invention. Fig. 6B is a schematic end view showing the configuration of the end face of the cable relay tube 30 of Fig. 6A, as seen from the side indicated by arrow E. [Figure 7] FIG. 7 is a schematic end view corresponding to FIG. 6B, showing the configuration of a modified example of the second embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view showing the configuration of a pressure gauge according to a third embodiment of the present invention, corresponding to FIG. 6A and showing the configuration up to a connector 50. [Figure 9] FIG. 9 is a schematic cross-sectional view corresponding to FIG. 3B, showing a cross section of the cable 40 included in the pressure gauge of FIG. [Figure 10] 10A and 10B are schematic cross-sectional views corresponding to FIG. 9, each showing a cross section of a cable 40 used in a modification of the third embodiment. [Figure 11] FIG. 11 is a cross-sectional view corresponding to FIG. 4A, showing the configuration of a first modified example of the present invention. [Figure 12] 12A and 12B are cross-sectional views corresponding to FIG. 4A, showing the configurations of second and third modified examples of the present invention, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0015] [First embodiment: Figs. 1 to 4B] An embodiment of the present invention will be described with reference to the drawings. First, the outline of the configuration of a pressure gauge 1, which is a first embodiment of a strain gauge based transducer of the present invention, will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a perspective view showing a schematic configuration of the pressure gauge 1. Fig. 2 is a schematic plan view of the pressure gauge 1.

[0016] As shown in Figures 1 and 2, the pressure gauge 1 comprises a housing 10 having a protrusion 15 protruding from the side of a substantially cylindrical body, a coated cable 20, a cable relay tube 30, a cable 40, and a connector 50. As will be described later with reference to Figure 4, the housing 10 is made up of a diaphragm 11, a frame 12, a back cover 13, and a protrusion 15, and has a built-in strain gauge 16, functioning as a sensing unit that detects pressure. The configuration of the housing 10 and its interior may be similar to that of a conventional pressure gauge.

[0017] The cable 20 is a cable in which a conductor for extracting an electrical signal output from the strain gauge 16 in response to pressure applied to the housing 10 is covered for insulation and waterproofing. The cable relay tube 30 is an approximately cylindrical housing member that contains a substrate 31 (see Figure 4A) that controls the pressure gauge 1 and serves as an interface with external control equipment that acquires and records the pressure measurement results from the pressure gauge 1. The connector 50 is a connector for connecting the pressure gauge 1 to an external control device to input and output signals and data. The cable 40 is a cable for electrically connecting the board 31 in the cable relay tube 30 and the connector 50.

[0018] One of the distinctive features of the pressure gauge 1 described above is the structure of the ventilation path formed through the inside of the cable 20 to allow ventilation between the inside and outside of the housing 10. This will be described next with reference to Figures 3A to 4B.

[0019] First, FIG. 3A shows a schematic cross section of cable 20 taken along line AA in FIG. As shown in FIG. 3A, cable 20 includes four conductors 21a-21d (hereinafter, the reference numeral "21" will be used when there is no need to distinguish between individual conductors). These are each a first conductor and function as two pairs of input and output wires for strain gauge 16 (see FIG. 4A). The surface of each of conductors 21a-21d is covered with insulating covering material 22 to prevent short-circuiting with other conductors. Each of conductors 21a-21d including insulating covering material 22 may be twisted together. In addition, a protective layer 23 made of paper, metal foil, shielded wire, or the like is provided around insulating covering material 22 to bundle the four conductors and shield them from surrounding magnetic fields.

[0020] Various cables, each consisting of multiple conductors bundled together and shielded after being individually insulated, are commercially available for transmitting multiple electrical signals. While FIG. 3A shows a certain space in the center surrounded by the insulating coatings 22 enveloping the four conductors 21, and the space appears to be filled with a protective layer 23, this is a schematic illustration for clarity. In reality, particularly in thin cables or cables with four twisted conductors 21, there is almost no space in the center surrounded by the insulating coatings 22. Therefore, even if the protective layer 23 were not present in this center, it would not be expected to function similarly to the gap 25 described below. This also applies to the cross sections of various cables shown in FIG. 3B and subsequent figures.

[0021] The cable 20 has a covering 24 provided on the outside of the protective layer 23 described above, with a layered gap 25 provided between the conductors 21 and the covering 24. Assuming that part of the cable 20 will be submerged in water, the covering 24 is preferably made of a waterproof material such as polyvinyl chloride (PVC). The waterproofness referred to here is sufficient if it is sufficient to prevent liquid water from entering the interior at the depth at which the pressure gauge 1 is expected to be used. Furthermore, gap 25 only needs to be large enough to form a continuous air passage (first air passage) from housing 10, to which one end of cable 20 is in close contact, to cable relay tube 30, to which the other end is connected, even if cable 20 is bent or folded along the way. From the viewpoint of ensuring an air passage, covering material 24 preferably has a strength large enough to maintain its inner diameter without being crushed by water pressure or its own weight.

[0022] Such a cable 20 can be produced at low cost by inserting a commercially available input / output power cable into a commercially available PVC tube having an inner diameter larger than the outer diameter of the power cable. For example, cable 20 can be formed by using a PVC tube with an outer diameter of 2.4 mm and a wall thickness of 0.4 mm as covering material 24 and inserting an input / output power cable with an outer diameter (R12 in FIG. 3A) of approximately 1.45 mm, which is approximately 0.15 mm smaller than the inner diameter (R11 in FIG. 3A) of covering material 24, into the PVC tube. Even with this configuration, even taking into account manufacturing tolerances for covering material 24, approximately 15 to 20% of the internal space of covering material 24, as viewed in a cross section perpendicular to the longitudinal direction, is secured as an air passage. Sufficient ventilation is possible with this size and air passage ratio. However, the size, shape, material, air passage ratio, etc. described here are merely examples and are not required.

[0023] 3A shows an example in which gap 25 is formed with a roughly uniform width around protective layer 23. However, in reality, as shown in FIG. 3C, it is thought that in many cases conductor 21 including protective layer 23 is located in an uneven position inside coating material 24 or partially comes into contact with coating material 24. Even with such an arrangement, there is no problem with the functionality of cable 20.

[0024] If there is no structure to support the input / output power cable within the tube, such as when the input / output power cable is simply inserted into a PVC tube as described above, the positional relationship between the input / output power cable (protective layer 23) and the tube (coating material 24) in the cross sections of Figures 3A and 3C will naturally change if cable 20 is moved. However, even if such a change occurs, it will not affect the operation of pressure gauge 1.

[0025] FIG. 3B is a schematic cross-sectional view of cable 40 taken along line BB in FIG. 3B, cable 40 includes four conductors 41a to 41d, an insulating coating material 42, and a protective layer 43, which are similar to conductors 21a to 21d, insulating coating material 22, and protective layer 23 of cable 20. That is, a commercially available input / output power cable that is inserted into coating material 24 of cable 20 can be used as cable 40. Conductors 41a to 41d each correspond to a second conductor. In the pressure gauge 1, it is assumed that the section from the cable relay tube 30 to the connector 50 will not be submerged in water, so the cable 40 is not waterproof. However, if waterproofing is required, it may be provided as appropriate.

[0026] Next, FIG. 4A shows a schematic cross section of the pressure gauge 1 taken along line CC in FIG. As shown in Fig. 4A, housing 10 has a structure in which diaphragm 11 is provided on the upper side of a substantially cylindrical frame 12, and back cover 13 is fitted from the lower side of the figure. In addition, a flexure element 14 is fixed inside frame 12. Flexure element 14 is a component that generates an amount of distortion in response to an external force with high linearity to the external force received. A shaft 17 is provided near the center of the diaphragm 11 to transmit the pressure received by the diaphragm 11 to the flexure element 14, which is also fixed to this shaft 17. A strain gauge 16 is provided on each side of the flexure element 14. Here, two strain gauges 16 are provided, one on each side of the flexure element 14, but the number is not limited to this. A pair of conductors 21, one for input and one for output, is connected to the strain gauge 16 on each side.

[0027] Furthermore, a through hole 19 and a hollow protrusion 15 are provided on the side surface of the frame 12, and the through hole 19, a space 18 inside the housing 10, and a space 15a inside the protrusion 15 form a continuous ventilation path. The conducting wire 21 is drawn out to the outside of the housing 10 through the through hole 19 and the space 15a. The protrusion 15 can be formed by fixing a brass or stainless steel pipe to the inside of the through-hole 19 by adhesive, welding, or the like.

[0028] Furthermore, one end (on the left side in the drawing) of the covering material 24 of the cable 20 is fitted onto and adhered to the outer periphery of the protrusion 15, and the inner periphery of the covering material 24 is fixed so as to be in close contact with the outer periphery of the protrusion 15. Therefore, even if the housing 10 is placed in water, water will not enter the housing 10 through the space 15a. This close contact and fixation may be achieved by means other than adhesion. The conductor 21 including the insulating covering material 22 and the protective layer 23 is drawn into the space 15a. The protective layer 23 is peeled off near the through-hole 19, and two conductors 21a to 21d are drawn out above and below the strain generating element 14 and connected to the strain gauges 16, respectively.

[0029] The other end of the covering material 24 of the cable 20 is adhered to one end (on the left side in the figure) of the cable relay tube 30 and is fixed so as to be in close contact with the end. More specifically, a thin-walled portion 35 having a larger inner diameter than the other portions is formed at the end of the cable relay tube 30 on the cable 20 side, and the other end of the covering material 24 is adhered to the inner circumferential surface of the thin-walled portion 35 and to a step portion 35a at the end of the thin-walled portion 35. This ensures a sufficient adhesive area between the covering material 24 and the cable relay tube 30, improving strength and waterproofing.

[0030] At the other end of the covering material 24, the protective layer 23 is stripped away to expose the conductors 21a to 21d, which are connected at the connection portion 32 to terminals of a circuit provided on the substrate 31 inside the cable relay tube 30. The substrate 31 is fixed to the cable relay tube 30 by a support member not shown in Fig. 4A, and a space 34 is secured around the substrate 31. At the connection portion 33, the conductor 41 of the cable 40 extending toward the connector 50 is connected to a terminal of a circuit provided on the substrate 31.

[0031] Here, FIG. 4B shows the end face of the cable relay tube 30 as seen from the side indicated by the arrow D in FIG. 4A. As shown in Fig. 4B, the surface of the cable relay tube 30 on the right side in Fig. 4A has an opening 30a that is open to the outside even when the cable 40 is connected. The area inside the dashed line 30c corresponds to the space 34 inside the cable relay tube 30, and the opening 30a is provided in a part of the inside of the dashed line 30c where the cable 40 does not pass. The remaining part, a support part 30b, supports the cable 40. The hatched area in Fig. 4B is the range where the cable 40 is located.

[0032] Additionally, a water-repellent layer 36 made of a water-repellent material is formed around the opening 30a. The water-repellent layer 36 can be formed by any method, such as by adhering a thin layer or plate of water-repellent material or by applying a water-repellent material. The degree of water repellency can be set according to the desired waterproof performance.

[0033] In the pressure gauge 1 having the above configuration, when pressure is applied to the diaphragm 11 from the direction of arrow P in Figures 1 and 4A, the diaphragm 11 deforms in response to the pressure, and a force corresponding to the deformation is transmitted to the strain element 14 through the shaft 17, causing the strain element 14 to deform. The resistance value of the strain gauge 16 changes in response to the deformation of the strain element 14.

[0034] On the other hand, when a predetermined control signal from an external control device is input to the board 31 through the connector 50 and the cable 40, the board 31 provides an input signal to the strain gauge 16 through the cable 20. A Wheatstone bridge circuit is formed by the circuit on the board 31, the conductors 21, and the strain gauge 16, and the resistance value of the strain gauge 16 can be determined by measuring the voltage or current of the output signal returned from the strain gauge 16 in response to the input signal. This can also be converted to determine the pressure being applied to the diaphragm 11. The circuit on the board 31 can output an output signal indicating this pressure value to the external control device through the cable 40 and the connector 50.

[0035] In the pressure gauge 1, one end of the covering material 24 is fixed to the protrusion 15, and the other end is fixed in close contact with the cable relay tube 30, thereby forming an air passage extending from the space 18 inside the housing 10 through the through hole 19 and the gap 25 inside the cable 20 to the space 34 inside the cable relay tube 30, generally in the range indicated by the arrow R in Fig. 2. This air passage is in contact with the outside air at the opening 30a of the cable relay tube 30.

[0036] When an environmental change other than pressure, such as a temperature change, occurs around the housing 10, this ventilation path quickly balances the effects of the environmental change that also occurs within the space 18 with the outside, preventing the environmental change in the space 18 from occurring slowly over a long period of time. This allows the resistance value of the strain gauge 16, and therefore the baseline of the pressure measurement value, to quickly stabilize. Considering this, the ventilation path including the gap 25 does not need to be so breathable that the air inside the space 18 is quickly exchanged with the outside air; it is sufficient if it is a continuous path that allows a certain degree of air movement.

[0037] In the pressure gauge 1, the housing 10 is sealed except for the through-hole 19, and the covering material 24 is waterproof, with one end thereof in close contact with the housing 10 (the protrusion 15), so that even if the housing 10 or the cable 20 is submerged in water, water will not enter this air passage from the outside.

[0038] Furthermore, by providing the water-repellent layer 36, even when the pressure gauge 1 is used near water and there is a possibility that water may splash onto the cable relay tube 30, it is possible to prevent water droplets adhering to the outer periphery of the cable relay tube 30 from entering the interior through the opening 30a. This is because the water-repellent layer 36 repels water droplets flowing along the outer periphery of the cable relay tube 30, preventing them from reaching the opening 30a. In other words, the water-repellent layer 36 reduces the risk of water entering the cable relay tube 30 even when the opening 30a is provided as an outlet for the ventilation path, and the waterproofness of the pressure gauge 1 can be improved.

[0039] Note that if the pressure gauge 1 is not intended to be used underwater and, for example, dustproofing is sufficient, then the covering material 24 does not need to be waterproof. From the standpoint of preventing dust from entering the space 18, it is also undesirable to provide an opening in the outer wall of the housing 10 that directly (closely) connects the space 18 to the outside, and therefore the ventilation path described above is fully useful.

[0040] Next, some comparative examples of the pressure gauge 1 of the first embodiment described above will be described. 5A and 5B are cross-sectional views corresponding to FIG. 3A, showing cross sections of cables provided at positions corresponding to cable 20 in different comparative examples. These comparative examples are common to the pressure gauge 1 of the first embodiment described above, except for the configuration of the cable connecting the housing 10 and the cable relay tube 30. Therefore, the same reference numerals are used. However, the cable shown in FIGS. 5A and 5B does not have a gap like cable 20, and therefore has a configuration in which the entire cable is pulled into the housing 10 through space 15a inside protrusion 15, similar to the case of the modified example described later using FIG. 12A.

[0041] First, cable 40′ shown in Fig. 5A is configured such that a coating material 44 made of the same material as coating material 24 is provided around the cable shown in Fig. 3B, with no gaps provided inside coating material 44. In cables used for general purposes, gaps are usually not intentionally provided to prevent the intrusion of foreign matter, enhance structural stability, etc. However, when using such a cable 40', it is not possible to form an air passage inside the covering material 44, and therefore it is not possible to obtain the effect of quickly stabilizing the baseline of the pressure measurement value as in the above-mentioned embodiment.

[0042] Next, cable 80 shown in Fig. 5B is different from cable 40' in Fig. 5A in that a hollow spacer 82 is added inside protective layer 43, thereby providing an air layer 85 inside covering material 44. Using such cable 80 makes it possible to form an air passage between space 18 in housing 10 and the outside air through air layer 85. However, if an attempt is made to form an air passage large enough to allow a sufficient amount of air to stabilise the baseline in a short period of time, the diameter of protective layer 43, which is the effective diameter of the conductor bundle, increases compared to cable 20 shown in Fig. 3A, making cable 80 stiffer and more difficult to handle.

[0043] 3A, the diameter of cable 80 is thicker than that of cable 20. Furthermore, since the entire cable 80 must be passed through space 15a inside protrusion 15, a thick protrusion 15 is required, which hinders the miniaturization of housing 10. Furthermore, the cable shown in FIG. 5B has a different configuration from the general one, and therefore is more expensive. Considering these points, it can be said that by using cable 20 as shown in FIG. 3A, it is possible to construct a pressure gauge 1 having a small housing 10 that is low cost and easy to handle, compared to when using cable 80 as shown in FIG. 5B.

[0044] Generally, if the height of the housing 10 of the pressure gauge 1 is smaller than the outer diameter of the cable, the cable will interfere with the water flow, adversely affecting measurement and hindering miniaturization. However, by using the cable 20 with a PVC tube with an outer diameter of 2.4 mm as the covering material 24, as described above, the housing can be easily miniaturized to a thickness (height) of about 3 mm. The diameter of the housing can also be miniaturized to about 6 mm.

[0045] That is, the configuration with an air passage as in the embodiment described above is particularly useful when constructing a small strain gauge-based transducer. For example, the configuration described in this embodiment is particularly effective when constructing a strain gauge-based transducer with a housing 10 having a diameter of 50 mm or less and a thickness of 20 mm or less. The diameters of the cables and tubes should be determined so that the outer diameter of the cable 20 does not exceed the thickness of the housing 10 and so that an air passage with a sufficient cross-sectional area can be formed inside the covering material 24.

[0046] Furthermore, by providing an air passage through gap 25, the baseline can be stabilized quickly, and therefore, the baseline can be stabilized in a realistic amount of time, even without using a highly stable and expensive strain gauge. Generally, when a highly sensitive semiconductor strain gauge is used, the baseline stability is poor, but with the configuration using cable 20 described above, the baseline can be stabilized in a short time, even when an inexpensive bulk semiconductor strain gauge is used.

[0047] In an experiment conducted by the inventors, for example, in a pressure gauge configured with a small housing, when the comparative example cable 40' of Figure 5A was used, it took about 7 hours for the baseline to stabilize. However, by replacing the cable with cable 20 having gap 25, the time required for the baseline to stabilize could be reduced to 3 to 4 hours. Of course, it is not essential to use a semiconductor strain gauge, and any other gauge such as a metal foil strain gauge can be used. As such, according to the pressure gauge 1 of the above-described embodiment, it is believed that multi-point measurements can be realized inexpensively using a stable, fast, and small pressure gauge, and the measurement results are believed to be able to make a significant contribution to the development of social infrastructure and the safety of human life.

[0048] The pressure gauge 1 described above also provides other effects, which will be explained next. First, in the pressure gauge 1, the housing 10 is provided with the protrusion 15, and the covering material 24 is attached to the protrusion 15 so as to cover the outer periphery of the protrusion 15. This makes it easy to process the covering material 24 for adhesion, and there are few restrictions on the material and size of the parts.

[0049] For example, as will be described later with reference to Figure 12A, even in a structure in which covering material 24 is inserted into space 15a of protrusion 15, it is possible to form an air passage including gap 25 by tightly adhering covering material 24 and protrusion 15. However, when considering things like ensuring gap 25 inside space 15a without crushing covering material 24, such a structure imposes restrictions on the selection of materials and sizes and requires more precise processing, leading to increased costs.

[0050] Furthermore, in the pressure gauge 1, both ends of the covering material 24 are fixed in a sufficiently spread state, so even if the covering material 24 is made flexible, the risk of the covering material 24 collapsing and blocking the air passage can be reduced. While it is desirable for the cable 20 to be flexibly deformable, the cable relay tube 30 is a member that is not expected to deform and is normally provided when constructing the pressure gauge 1. By using this cable relay tube 30 as a member that supports the covering material 24, there is no need to provide a special member for supporting the covering material 24 on the side opposite the housing 10 in an expanded state, which reduces the number of parts and cuts costs.

[0051] Furthermore, even when it is assumed that the housing 10 will be used submerged in water, unless the control device connected to the connector 50 is also operated underwater, it is generally assumed that the cable relay tube 30 will not be submerged in water but will be placed in the air. This is because, while the housing 10 can be placed at a desired position underwater by making the cable 20 longer, there is generally no benefit to placing the cable relay tube 30 at a position far from the control device (or the connector 50) at the expense of waterproofing the cable relay tube 30.

[0052] In this case, it can be said that it is sufficient for the air passage continuing from the space 18 inside the housing 10 to continue up to the position of the cable relay tube 30. In the pressure gauge 1, the air passage is configured to be in contact with the outside air at the opening 30a of the cable relay tube 30, so the cable relay tube 30 can also function as a member for securing the end of the air passage (the end opposite the housing 10), which also makes it possible to prevent an increase in the number of parts.

[0053] Furthermore, if an outlet where the ventilation path comes into contact with the outside air is provided before the cable 40, as in the case of the cable relay tube 30, there is no need to provide an ventilation path in the cable 40 (for example, the gap 25 as in the cable 20). Therefore, the cable 40 can be made relatively thin, and there are a wide range of options for structure and material. This allows the cable 40 near the connector 50 that connects to an external device to be designed with an emphasis on ease of handling.

[0054] For example, when multiple pressure gauges are connected to a single control device to control each pressure gauge and process its detection signals, many cables will be wired around the control device, and ease of handling is a major requirement. Providing an outlet for the ventilation path to come into contact with the outside air, for example, in the cable relay tube 30, before the cable 40, is useful for meeting this requirement while ensuring a stable baseline.

[0055] [Second embodiment: Figs. 6A to 7] Next, a pressure gauge 1, which is a second embodiment of the strain gauge based transducer of the present invention, and several modified examples thereof will be described with reference to FIGS. 6A to 7. FIG. The second embodiment differs from the first embodiment in the positions of the opening 30a and the water-repellent material in the cable relay tube 30, and in the structure of the connection between the covering material 24 and the cable relay tube 30. Therefore, these points will be mainly described, and descriptions of other parts will be omitted. Also, the same reference numerals will be used for parts corresponding to those in the first embodiment. Note that these two points can be applied independently as modifications to the first embodiment.

[0056] Fig. 6A is a schematic cross-sectional view corresponding to a part of Fig. 4A, showing the configuration of the pressure gauge 1 of the second embodiment, and showing only the portion in the vicinity of the cable relay tube 30. Fig. 6B is a schematic end view showing the configuration of the end face of the cable relay tube 30 of Fig. 6A, as seen from the side of arrow E. As shown in Fig. 6A, in the pressure gauge 1 of the second embodiment, the opening 30a is provided near the end of the side surface of the cable relay tube 30 that is closer to the cable 40. The cross-sectional shape of the opening 30a is circular, as shown in Fig. 6B. As in the first embodiment, a water-repellent layer 36 made of a water-repellent material is provided around the opening 30a. 6B, the opening 30a is shown enlarged for clarity, but in reality, a smaller opening can provide sufficient ventilation. This also applies to FIG. 7, which will be described later.

[0057] Even when the opening 30a and the water-repellent layer 36 are provided at the positions and in the shapes shown in FIGS. 6A and 6B, the effects of forming an air passage and improving waterproofness can be obtained, similar to the first embodiment. It is preferable that the cross section of opening 30a has a highly symmetrical shape, such as a circle or a regular polygonal shape close to a circle, because this effectively prevents water droplets from entering opening 30a with water-repellent layer 36. Furthermore, if housing 10 is expected to be placed underwater, the cable 20 side will be closest to the water, so from the perspective of waterproofing, it is preferable to provide opening 30a on the side closer to cable 40 rather than on the cable 20 side. However, the location and shape of opening 30a are not limited to these.

[0058] 6A, in the pressure gauge 1 of the second embodiment, the end of the cable relay tube 30 on the cable 20 side is formed with a thin-walled portion 37 that has a smaller outer diameter than the other portions, and the other end of the covering material 24 is bonded to the outer circumferential surface of the thin-walled portion 37 and to a step portion 37a at the end of the thin-walled portion 37. Even with this structure, as in the case of the thin-walled portion 35 of the first embodiment, a sufficient adhesive area can be secured between the covering material 24 and the cable relay tube 30, thereby improving strength and waterproofness.

[0059] Next, a modified example of the second embodiment will be described. This modified example differs from the second embodiment in that the configuration and arrangement of the water-repellent material are as shown in Fig. 7. 7 shows an example in which the portion overlapping the opening 30a is meshed to provide breathability and is provided to cover the opening 30a. The portion surrounding the opening 30a does not need to be meshed, so breathability is not required.

[0060] By providing such a water-repellent material, it is possible to prevent water droplets from flying directly onto the opening 30a and water droplets that cannot be completely prevented by the surrounding water-repellent material from penetrating into the opening 30a, thereby further improving waterproofing compared to the configuration shown in Figure 6B. The breathability of the water-repellent material 38 need only be sufficient to ensure ventilation between the ventilation path and the outside air to a degree sufficient to stabilize the baseline. It is not necessary for the material to have openings visible to the naked eye, as with mesh. Furthermore, the water-repellent material covering the opening 30a may be provided inside the opening 30a or on the inner peripheral surface of the cable relay tube 30, rather than on the outer peripheral surface of the cable relay tube 30.

[0061] [Third embodiment: Figs. 8 to 10B] Next, a pressure gauge 1, which is a third embodiment of the strain gauge based transducer of the present invention, and several modified examples thereof will be described with reference to Figs. 8 to 10B. The third embodiment differs from the first embodiment in that the cable relay tube 30 does not have an opening 30a, but has an air passage extending from the space 18 inside the housing 10 to the vicinity of the end of the cable 40 on the connector 50 side. Therefore, only these points will be described, and descriptions of other parts will be omitted. Also, the same reference numerals will be used for parts corresponding to those in the first embodiment.

[0062] Fig. 8 is a schematic cross-sectional view corresponding to Fig. 4A showing the configuration of a pressure gauge 1 of a third embodiment, illustrating a portion from the vicinity of the cable relay tube 30 to a connector 50 not shown in Fig. 4A. Fig. 9 is a schematic cross-sectional view corresponding to Fig. 3B showing a cross section of a cable 40 provided in the pressure gauge of Fig. 8. 8, in the pressure gauge 1 of the third embodiment, the cable relay tube 30 does not have an opening 30a, and the cable relay tube 30 is sealed. The joints between the cables 20 and 40 are also sealed by adhesive or the like to at least prevent water droplets from entering inside.

[0063] 9, cable 40 is provided with a coating material 44 similar to that of cable 20, and a layered gap 45 is provided between conductor wires 41 and coating material 44 along conductor wires 41. However, the difference between the inner diameter (R21 in FIG. 9) of coating material 44 in cable 40 and the outer diameter (R22 in FIG. 9) of protective layer 43 is smaller than the difference between the inner diameter (R11 in FIG. 3A) of coating material 24 in cable 20 and the outer diameter (R12 in FIG. 3A) of protective layer 23. Therefore, the cross-sectional area of ​​the air passage (second air passage) formed in gap 45 in a cross section perpendicular to the cable longitudinal direction is smaller than the corresponding cross-sectional area of ​​the air passage formed in gap 25.

[0064] 8, the connector 50 includes an exterior 51, connector pins 52, and a support member 53. The connector pins 52 are pins for connecting to an interface of an external device. The support member 53 is a member for supporting the connector pins 52 and includes terminals for connecting the conductors 41 to the connector pins 52. The cable 40 is fixed to the connector 50 by attaching a tubular protective material 54 to the end of the cable 40 that is to be connected to the connector 50 and inserting the protective material 54 into the connector 50. Each conductor 41 of the cable 40 is connected to a terminal on the support member 53.

[0065] At this time, gap 45 in cable 40 is opened inside sheath 51. And, because a gap is provided between sheath 51 and support member 53, ventilation is possible between gap 45 and the outside air through this gap. Even when connector 50 is connected to an external device, sheath 51 and the external device are not usually in close contact with each other, so similar ventilation is possible.

[0066] With the above configuration, the pressure gauge 1 forms a series of air passages that extend from the space 18 inside the housing 10 through the through hole 19, the first air passage formed by the gap 25 inside the cable 20, the space 34 inside the cable relay tube 30, and the second air passage formed by the gap 45 inside the cable 40, continuing to the connector 50 and only coming into contact with the outside air at the connector 50.

[0067] As in the first embodiment, this ventilation path allows the influence of environmental changes occurring in the space 18 inside the housing 10 to be quickly balanced with the outside, and the baseline to be quickly stabilized. Furthermore, in the configuration of the third embodiment, the cable relay tube 30 can be sealed, and therefore the waterproofing of the cable relay tube 30 can be made extremely high.

[0068] 8, the second ventilation path formed by gap 45 is not continued to the inside of connector 50, but rather covering material 44 is set to a length just before connector 50, and the second ventilation path continues to the vicinity of the connector 50 side end (the end opposite substrate 31) of conductor 41, where it is exposed to the outside air. However, from the viewpoint of structural robustness, the configuration in which covering material 44 is fixed to connector 50 as shown in FIG. 8 is preferable.

[0069] If an air passage with a certain cross-sectional area can be secured within cable 20 in contact with housing 10, the effects of environmental changes other than pressure, such as temperature changes, that occur in space 18 inside housing 10 can be mitigated by achieving equilibrium with the air in the air passage, which has a much larger volume than space 18. This equilibrium must ultimately be achieved with the outside air as well, but even if the ventilation between the air passage within cable 20 and the outside air and the resulting equilibrium occur slowly, the impact on the baseline of measurement by pressure gauge 1 is not significant.

[0070] For this reason, the third embodiment employs such a configuration, since the effect of quickly stabilizing the baseline can be obtained to a considerable extent even if the cross-sectional area of ​​the ventilation path provided in the cable 40 is small. This makes it possible to reduce the thickness of the cable 40 extending to the connector 50, achieving both high waterproofing and ease of handling near the connector 50.

[0071] The thickness of the cable 40 in the third embodiment is slightly thicker than in the configurations of the first and second embodiments, but if high waterproofing is important not only in the housing 10 and cable 20 parts but also in the part up to the vicinity of the connector 50 including the cable relay tube 30, the configuration of the third embodiment is also quite meaningful.

[0072] If it is only necessary to make the cable easier to route near the connector 50, it is possible to use a cable in which the cross-sectional area of ​​the air passage is changed at a position other than the cable relay tube 30, and the air passage is narrowed only near the connector 50, thereby making the cable thinner overall. However, a cable whose cross-sectional shape varies depending on the longitudinal position is difficult to manufacture and difficult to accommodate changes in length. Therefore, it is preferable to use a configuration in which the cable used is changed before and after the cable relay tube 30 where the cable is temporarily interrupted, as shown in Figure 8.

[0073] Next, a modified example of the third embodiment will be described. In this modified example, the configuration of the cable 40 differs from that of the third embodiment. 10A and 10B show a cross section of a cable 40 that can be used in place of that shown in FIG.

[0074] 10A shows an example in which a hollow spacer 47 is added inside protective layer 43, thereby providing an air layer 46 inside covering material 44. When this cable 40 is used, the end of air layer 46 on the cable relay tube 30 side is exposed to space 34 inside cable relay tube 30, and the end of air layer 46 on the connector 50 side is exposed to the outside air, thereby forming an air passage that passes through air layer 46 from space 34 to near connector 50.

[0075] As described above, the cross-sectional area of ​​the air passage within cable 40 may be small, and therefore, unlike the comparative example described with reference to Fig. 5B, the required air passage within cable 40 can be formed without significantly increasing the thickness or stiffness of cable 40 even when spacer 47 is used. Note that it is not essential to provide spacer 47 and air layer 46 inside covering material 44, and it is also possible to provide them outside.

[0076] Fig. 10B shows an example in which conductor wires 41a-41d are loosely arranged inside coating material 44, thereby forming a small amount of void space around them. In cable 40 of Fig. 10B, a protective layer 48 made of, for example, a fibrous material is formed around insulating coating material 42, and the protective layer 48 is not densely packed but contains a certain amount of void space.

[0077] When using a cable 40 such as that shown in Figure 10B, the end of the protective layer 48 on the cable relay tube 30 side is exposed to the space 34 inside the cable relay tube 30, and the end of the protective layer 48 on the connector 50 side is exposed to the outside air, thereby forming an air passage that passes through the gap inside the protective layer 48 from the space 34 to near the connector 50. It is conceivable that an air passage having the minimum required level of breathability within the cable 40 may be formed through an air gap of this size.

[0078] [Modification: Figures 11 to 12B] Next, a further modification applicable to each of the above-described embodiments will be described. First, in each of the embodiments described so far, the protrusions 15 and the through holes 19 are provided on the side surfaces of the frame 12, but the protrusions 15 and the through holes 19 may be provided in other parts of the housing 10. Fig. 11 is a cross-sectional view corresponding to Fig. 4A, showing the configuration of the pressure gauge 1 when the protrusion 15 and the through-hole 19 are provided near the center of the back cover 13. In Fig. 11, only the cable 20 near the housing 10 is shown, but the configuration of parts not shown in Fig. 11, such as the cable relay tube 30 and the connector 50, is the same as in Fig. 4A etc.

[0079] In this way, even when the protrusion 15 and the through-hole 19 are provided on a part of the housing 10 other than the side surface of the frame 12, the formation of an air passage that continues from the space 18 inside the housing 10 through the through-hole 19 and the gap 25 inside the cable 20 to the space 34 inside the cable relay tube 30, or further to the vicinity of the connector 50, can be performed in the same way as in the case of Fig. 4A etc. Therefore, the baseline can also be quickly stabilized.

[0080] Furthermore, the contact portion between the covering material 24 and the protrusion 15 (housing 10) does not necessarily have to have the structure shown in FIG. 4A or FIG. 6A. 12A, the entire cable 20 including the covering material 24 may be passed through the inside of the protrusion 15 and guided into the housing 10. In this case, the covering material 24 and the protrusion 15 are adhered to each other by adhesive or the like to prevent water, dust, and the like from entering between them.

[0081] 12B, an adapter 61 may be provided at the end of the covering material 24, and the adapter may be coupled to the protrusion 15. In this case, not only the covering material 24 but also the adapter 61 functions as a covering material that covers the periphery of the conductor 21. The adhesion between the adapter 61 and the protrusion 15 may be ensured by any known means. Furthermore, it is not essential to provide the protrusion 15, and a configuration is also conceivable in which the covering material 24 or the adapter 61 is directly adhered or bonded to the outer side wall of the housing 10, thereby tightly adhering the covering material to the housing.

[0082] Even with these configurations, a sufficient air passage can be formed through the gap 25 provided between the covering material 24 and the conductor 21 (and the insulating covering material 22 and protective layer 23 outside it). However, when the number of parts and ease of manufacturing are taken into consideration, the configuration of Figure 4A is preferable to the configurations of Figures 12A and 12B.

[0083] 4A or 6A, it is not essential to provide the thin-walled portion 35 or 37 at the contact portion between the covering material 24 and the cable relay tube 30. As shown in FIGS. 12A and 12B, the end of the covering material 24 and the end of the cable relay tube 30 may be fixed together by adhesive or the like.

[0084] In the above embodiment, the strain gauge transducer is configured as a pressure meter, but the present invention is not limited to this. The present invention can be applied to any device that has a function to measure physical quantities such as applied pressure, including devices called by names according to the object to be measured, such as earth pressure meters, water pressure meters, load meters, and pore water pressure meters.

[0085] This concludes the description of the embodiment, but in this invention, the specific shape, material, size, etc. of the entire strain gauge based transducer or its components, and the measurement method using the strain gauge based transducer are not limited to those described in the embodiment. The features of the above-described embodiments and modifications may be combined to the extent that they are consistent, or only some of the features may be extracted and implemented. [Explanation of symbols]

[0086] 1...pressure gauge, 10...casing, 11...diaphragm, 12...frame, 13...back cover, 14...flexible body, 15...projection, 15a...space, 16...strain gauge, 17...shaft, 18...space, 19...through hole, 20, 40, 40', 80...cable, 21a to 21d, 41a to 41d...conductor, 22, 42...insulating coating material, 23, 43, 48...protective layer, 24, 44...coating material, 25...gap, 30...cable relay tube, 30a...opening, 30b...supporting portion, 31...substrate, 32, 33...connecting portion, 34...space, 35, 37...thin portion, 35a, 37a...step portion, 36...water-repellent layer, 46, 85...air layer, 47, 82...spacer, 50...connector

Claims

1. A housing having a strain-generating body that deforms in response to external force; a strain gauge disposed on the strain generating body; a first conducting wire connected to the strain gauge and drawn out to the outside of the housing through a through hole provided in the housing; a covering material that covers the first conducting wire, one end of the covering material being in close contact with the housing and having a gap between the covering material and the first conducting wire; a second conductor for providing an output signal to an external device; a circuit connected to the first conducting wire and the second conducting wire, a first air passage is formed that passes through the gap and continues from the inside of the housing to the other end of the first covering material; The device further includes a housing member that houses the circuit and is provided so as to be in close contact with the other end of the first covering material, the first ventilation path is continuous from the interior of the housing through the gap to the interior of the housing member and is in contact with outside air at an opening formed in a surface of the housing member, A strain gauge type transducer characterized in that a water-repellent material having water repellency is provided around the opening on the outer surface of the housing member.

2. A housing having a strain body that deforms in response to external force; a strain gauge disposed on the strain generating body; a first conducting wire connected to the strain gauge and drawn out to the outside of the housing through a through hole provided in the housing; a covering material that covers the first conducting wire, one end of the covering material being in close contact with the housing and having a gap between the covering material and the first conducting wire; a second conductor for providing an output signal to an external device; a circuit connected to the first conducting wire and the second conducting wire, a first air passage is formed that passes through the gap and continues from the inside of the housing to the other end of the first covering material; The device further includes a housing member that houses the circuit and is provided so as to be in close contact with the other end of the first covering material, the first ventilation path is continuous from the interior of the housing through the gap to the interior of the housing member and is in contact with outside air at an opening formed in a surface of the housing member, A strain gauge type transducer characterized in that a water-repellent material having both water repellency and breathability is provided so as to cover the opening.

3. A housing having a strain body that deforms in response to external force; a strain gauge disposed on the strain generating body; a first conducting wire connected to the strain gauge and drawn out to the outside of the housing through a through hole provided in the housing; a covering material that covers the first conducting wire, one end of the covering material being in close contact with the housing and having a gap between the covering material and the first conducting wire; a second conductor for providing an output signal to an external device; a circuit connected to the first conducting wire and the second conducting wire, a first air passage is formed that passes through the gap and continues from the inside of the housing to the other end of the first covering material; a second air passage formed along the second conducting wire; a continuous air passage is formed, the continuous air passage including the first air passage and the second air passage, extending from the inside of the housing through the other end of the first covering material to a vicinity of an end of the second conducting wire opposite to the circuit, A strain gauge type transducer, wherein the cross-sectional area of ​​the second air passage is smaller than the cross-sectional area of ​​the gap.

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