JP2018169205A - Protection structure of strain gauge, method for mounting strain gauge, and specimen - Google Patents

Abstract

To provide a protection structure of a strain gauge which can appropriately protect a strain gauge stuck to a specimen, a method for mounting a strain gauge, and a specimen.SOLUTION: A protection structure 14 is a structure for protecting a strain gauge 12 having a sensor part 20 stuck to a specimen 10 and a lead wire 22 connected to the sensor part 20. The protection structure 14 has a first protective layer 40 and a second protective layer 42. The first protective layer 40 is provided on the surface of the specimen 10, is formed of a vinyl chloride resin, and covers the periphery of at least the sensor part 20 out of the surfaces of the sensor part 20 and the specimen 10 and a predetermined region including at least a connection part with the sensor part 20 in the lead wire 22. The second protective layer 42 is formed on the first protective layer 40, and is formed from a silicon resin.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a strain gauge protective structure, a strain gauge mounting method, and a test body.

  Conventionally, tests using strain gauges have been performed under various environments. When a test using a strain gauge is performed in a special environment such as a wet environment, it is necessary to protect the strain gauge in order to stabilize the output. Therefore, conventionally, a method for protecting the strain gauge has been proposed.

  For example, Patent Literature 1 discloses a strain gauge mounting method for measuring strain generated in a measured part in high-temperature, high-pressure water. In the method disclosed in Patent Document 1, an epoxy-based material is coated as a first-layer coating material on a top surface of a strain gauge attached to a measured portion, and a butyl rubber-based material is coated as a second-layer coating material. A silicon-based material or a Teflon (registered trademark) -based material is coated as a layer coating material.

  In Patent Document 1, by coating the strain gauge as described above, contact between the strain gauge fine wire (electrical resistor) and the contacted part can be prevented even in high temperature and high pressure water. It is described that the disturbance of 0 and the change of 0 point can be reduced.

JP 2001-228035 A

  By the way, there is a demand for conducting a test using a strain gauge even in a severe environment such as a wet hydrogen sulfide environment. Therefore, the present inventors tried to perform the test by attaching the strain gauge to the test piece by the conventional attachment method as described above.

  However, it has been found that when a strain gauge is attached to a test piece by the conventional attachment method as described above, it is difficult to perform an appropriate test under a severe environment such as a wet hydrogen sulfide environment. Specifically, it was found that the coating material corroded in a short time and the strain gauge could not be properly protected. Further, it has been found that the coating material may be peeled off when the deformation amount of the portion (measurement portion) to which the strain gauge is attached increases. Again, the strain gauge cannot be properly protected.

  The present invention has been made to solve such a problem, and provides a strain gauge protective structure, a strain gauge mounting method, and a test body, which can appropriately protect a strain gauge attached to a test piece. The purpose is to provide.

  The present inventors have made various studies on a configuration that can appropriately protect a strain gauge even in a severe corrosive environment such as a wet hydrogen sulfide environment. As a result, it was found that the adhesion, water resistance, chemical resistance and corrosion resistance of the protective layer can be sufficiently secured by forming a protective layer made of vinyl chloride resin as a layer for protecting the strain gauge. Furthermore, it was found that deterioration of the protective layer made of vinyl chloride resin can be sufficiently suppressed by providing a layer made of silicon resin as a layer for protecting the protective layer made of vinyl chloride resin. As a result, it was found that even in a severe corrosive environment, the protective layer can be sufficiently prevented from peeling off and the strain gauge can be protected appropriately.

  The present invention has been made on the basis of the above findings, and the gist thereof is the following strain gauge protective structure, strain gauge mounting method, and test body.

(1) A protective structure for protecting a strain gauge having a sensor unit affixed to a test piece and a lead wire connected to the sensor unit,
Provided on the surface of the test piece, formed from a vinyl chloride resin, and the sensor part, at least the sensor part of the surface of the test piece, and at least a connection part of the lead wire with the sensor part A first protective layer covering a predetermined region including:
A strain gauge protection structure comprising: a second protection layer formed of a silicon resin provided on the first protection layer.

(2) The strain gauge protective structure according to (1), further including a protective tube made of a fluororesin in which the lead wire passes through the inside and one end is embedded in the second protective layer.

(3) The strain gauge protective structure according to (2), wherein the first protective layer covers at least a region of the lead wire from a connection portion with the sensor portion to the inside of the protective tube.

(4) The lead wire includes a first lead portion having one end connected to the sensor portion and covering the surface of the test piece, and a second lead rising from the other end of the first lead portion and passing through the protective tube. Including
The first protective layer includes a surface protective part formed on the surface of the test piece so as to cover the sensor part and the first lead part, and the surface so as to cover at least a part of the second lead part. The protective structure of the strain gauge according to (2) or (3), further including an extended protective part extending from the protective part into the protective tube.

(5) It further comprises a protective tape made of a fluororesin wound around the extension protection part so as to cover the extension protection part,
The strain gauge according to (4), wherein the protective tape is wound around the extended protective portion from a position outside the protective tube to a position inside the protective tube in the axial direction of the protective tube. Protection structure.

(6) The strain gauge protective structure according to any one of (2) to (5), wherein the second protective layer is formed so as to enter the protective tube from the one end of the protective tube.

(7) The strain gauge protective structure according to any one of (1) to (6), wherein the test piece is a fatigue test piece made of a steel material.

(8) The strain gauge protective structure according to any one of (1) to (7), wherein the test piece is a tensile fatigue test piece.

(9) The test piece is cracked so that a crack develops in a progress direction intersecting the plate thickness direction and the tensile direction by applying a force in a predetermined tensile direction orthogonal to the plate thickness direction. A rectangular parallelepiped CT test piece formed with a notch for generation,
The sensor part is affixed to a central part in the tensile direction on the surface of the CT test piece on the side of the development direction when viewed from the notch,
The second protective layer is formed so as to cover at least a surface to which the sensor unit is attached,
The portion of the second protective layer formed on the surface to which the sensor unit is attached is such that the central portion in the tension direction is recessed toward the sensor unit when viewed from the plate thickness direction. The strain gage protective structure according to any one of (1) to (8), which is formed.

(10) The first protective layer and the second protective layer are formed at least on two surfaces of the CT test piece that are parallel to each other in the plate thickness direction,
When the region where the first protective layer and the second protective layer are not formed on each of the two surfaces is an uncovered region, the center of the uncovered region in the tensile direction when viewed from the plate thickness direction. The strain gauge protective structure according to (9), wherein the first protective layer and the second protective layer are provided so that the portion is convex toward the sensor portion.

(11) An attachment method for attaching a strain gauge having a sensor part and a lead wire connected to the sensor part to a test piece,
Attaching the sensor part to the surface of the test piece;
A step of forming the protective structure according to any one of (1) to (10) above, and a strain gauge mounting method.

(12) a test piece;
A strain gauge having a sensor part affixed to the test piece and a lead wire connected to the sensor part;
A test body comprising the protective structure according to any one of (1) to (10) above.

  According to the present invention, it is possible to appropriately protect the strain gauge attached to the test piece.

FIG. 1 is a schematic view showing a test body according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. FIG. 3 is a schematic view showing a test body according to another embodiment of the present invention.

  Hereinafter, a strain gauge protection structure, a strain gauge mounting method, and a test body according to an embodiment of the present invention will be described with reference to the drawings. In the following, first, a test body provided with a protective structure according to an embodiment of the present invention will be described.

(Configuration of specimen)
FIG. 1 is a schematic view showing a test body 100 according to an embodiment of the present invention, (a) is a front view showing the test body 100, and (b) is a plan view showing the test body 100. is there. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. FIG. 1A is a view of the specimen 100 viewed from the thickness direction of the test piece 10 to be described later.

  1 and 2, a test body 100 includes a rectangular parallelepiped test piece 10, a strain gauge 12, and a protective structure 14 according to an embodiment of the present invention. The test piece 10 is made of, for example, a steel material. For example, a fatigue test piece is used as the test piece 10. The test body 100 is used in, for example, a fatigue test in a wet hydrogen sulfide environment.

  In the present embodiment, the test piece 10 is a known CT (Compact Tention) test piece used as a tensile fatigue test piece, and has a notch 10a. The notch 10a is formed so that a crack propagates in the direction of propagation intersecting the plate thickness direction and the tensile direction by applying a force to the test piece 10 in the tensile direction orthogonal to the plate thickness direction. It is a notch for crack initiation. The notch 10a is formed in the central portion of the test piece 10 in the tensile direction. Since the test piece 10 is a known CT test piece as described above, a detailed description of the test piece 10 is omitted.

  The strain gauge 12 includes a sensor unit 20 and a lead wire 22 connected to the sensor unit 20. Since various well-known strain gauges can be used as the strain gauge 12, a detailed description thereof is omitted, but the sensor unit 20 includes, for example, a base part and a resistor (metal foil) provided on the base. The lead wire 22 is a conductor made of a copper wire, for example, and is electrically connected to the resistor. Although not shown, the lead wire 22 may have a covering tube that covers the conductor.

  The sensor part 20 is affixed to the center part in the tensile direction on the surface 10b (hereinafter referred to as the affixing surface 10b) of the test piece 10 as viewed from the notch 10a. That is, in the tensile fatigue test using the test body 100 according to the present embodiment, the back gauge method is used.

  The lead wire 22 has one end connected to the sensor unit 20 and covering the surface of the test piece 10, and a second lead rising from the other end of the first lead portion 22a and passing through a protective tube 44 described later. Part 22b.

  In the present embodiment, the second lead portion 22b extends through the protection tube 44 and is connected to a detector (not shown). With such a configuration, a change in electrical resistance generated in the resistor of the sensor unit 20 can be detected by the detector.

  With reference to FIGS. 1 and 2, the protective structure 14 includes a first protective layer 40, a second protective layer 42, a protective tube 44, and a protective tape 46.

  The first protective layer 40 is formed from a vinyl chloride resin. In the present embodiment, the first protective layer 40 has shrinkability and peelability. The first protective layer 40 is formed, for example, by applying a coating containing a vinyl chloride resin and a toluene solvent to the surface of the test piece 10 once or a plurality of times. As a coating material for forming the first protective layer 40, for example, Melcoat (registered trademark) manufactured by Washin Chemical Industry Co., Ltd. can be used. For example, the number of coatings is preferably 3 or more. For example, the first protective layer 40 preferably has a thickness of 0.3 mm or more.

  The first protective layer 40 is formed so as to cover a predetermined region including at least the periphery of the sensor unit 20 on the surface of the sensor unit 20 and the test piece 10 and at least a connection part of the lead wire 22 with the sensor unit 20. The In the present embodiment, the first protective layer 40 is formed so as to cover at least a region of the lead wire 22 from the connecting portion with the sensor unit 20 to the inside of the protective tube 44.

  In the present embodiment, the first protective layer 40 includes at least a part of the surface protective part 40a formed on the surface of the test piece 10 so as to cover the sensor part 20 and the first lead part 22a, and the second lead part 22b. And an extended protective part 40b extending from the surface protective part 40a to the inside of the protective tube 44 so as to cover it.

  With reference to FIG. 1 and FIG. 2, the 1st protective layer 40 is four surfaces 10c, 10d, 10e, 10f connected to the whole surface of the bonding surface 10b and four sides of the bonding surface 10b among the test pieces 10. It is formed so as to cover each part.

  The second protective layer 42 is made of silicon resin and is formed on the first protective layer 40. The second protective layer 42 is formed so as to cover at least the pasting surface 10b. In the present embodiment, like the first protective layer 40, the second protective layer 42 is formed so as to cover the entire surface of the sticking surface 10b and a part of each of the four surfaces 10c, 10d, 10e, 10f. The second protective layer 42 is formed so as to enter the protective tube 44 from one end 44 a of the protective tube 44. The hardness of the second protective layer 42 is preferably, for example, 30 or less in durometer A hardness.

In the present embodiment, the portion of the second protective layer 42 formed on the pasting surface 10 b is such that the central portion in the tensile direction is recessed toward the sensor unit 20 when viewed from the plate thickness direction of the test piece 10. And has a recess 42a. When the test body 100 is used in a wet hydrogen sulfide environment, the thickness d (thickness in the crack propagation direction) of the second protective layer 42 in the recess 42a is preferably set as appropriate according to the hydrogen sulfide partial pressure. Specifically, the thickness d (unit: mm) satisfies the relationship of the following formula (i) when the hydrogen sulfide partial pressure p (unit: atm) is greater than 0 and 0.5 or less. When the hydrogen sulfide partial pressure p (unit: atm) is greater than 0.5 and 1.0 or less, it is preferable to satisfy the relationship of the following formula (ii).
d ≧ 25p + 7.5, (0 <p ≦ 0.5) (i)
d ≧ 20, (0.5 <p ≦ 1.0) (ii)

  As described above, the first protective layer 40 and the second protective layer 42 are formed on the two surfaces 10c and 10d of the test piece 10 that are parallel to each other in the plate thickness direction. Referring to FIG. 1A, a region where the first protective layer 40 and the second protective layer 42 are not formed on the two surfaces 10 c and 10 d is referred to as an uncovered region 16. In the present embodiment, when the test body 100 is viewed from the thickness direction of the test piece 10, the first protective layer is formed such that the central portion of the uncovered region 16 in the tension direction is convex toward the sensor unit 20. 40 and a second protective layer 42 are provided.

  The protective tube 44 is made of a fluororesin. Specifically, the protective tube 44 is made of, for example, Teflon (registered trademark). In the present embodiment, the protective tube 44 has a cylindrical shape. One end 44 a of the protective tube 44 is embedded in the second protective layer 42. In this embodiment, when the test is performed in a corrosive environment (wet hydrogen sulfide environment), the test piece 10 is placed in the corrosive environment, and at least the other end 44b of the protective tube 44 is not in the corrosive environment. The protective tube 44 is formed with a sufficient length so that it can be placed underneath. Thereby, the lead wire 22 in the protection tube 44 can be appropriately protected from a corrosive environment.

  The protective tape 46 is made of a fluororesin. Specifically, the protective tape 46 is made of, for example, Teflon (registered trademark). The protective tape 46 is wound around the extension protection part 40b so as to cover the outer peripheral surface of the extension protection part 40b. In the present embodiment, the protective tape 46 is wound around the extended protective portion 40 b from the position outside the one end 44 a of the protective tube 44 to the position inside the protective tube 44 in the axial direction of the protective tube 44. .

(Strain gauge mounting method)
Hereinafter, a method for attaching the strain gauge in the above-described test body 100 will be briefly described. In the attachment method according to the present embodiment, first, the sensor unit 20 is attached to the surface of the test piece 10 (attachment surface 10b) using an adhesive. Further, a part of the lead wire 22 is attached to a predetermined region on the surface of the test piece 10 using an adhesive. Thereafter, the protective structure 14 described above is formed. Specifically, the first protective layer 40 described above is formed on the surface of the test piece 10, and then the protective tape 46 is wound around the extended protective portion 40 b of the first protective layer 40. Next, the second protective layer 42 is formed on the first protective layer 40. At this time, the protection tube 44 is the second so that at least a part of the extension protection part 40b is located in the protection tube 44 and the protection tape 46 is located inside the one end 44a in the radial direction of the protection tube 44. Embedded in the protective layer 42.

(Function and effect)
In the test body 100 according to the present embodiment, as described above, the first protective layer 40 that protects the strain gauge 12 is formed of a vinyl chloride resin, so that the adhesion and water resistance of the first protective layer 40 are increased. In addition, chemical resistance and corrosion resistance can be sufficiently secured. Furthermore, by protecting the first protective layer 40 with the second protective layer 42 made of silicon resin, deterioration of the first protective layer 40 can be sufficiently suppressed. As a result, even when the test body 100 is used in a severe corrosive environment such as a wet hydrogen sulfide environment, the first protective layer 40 can be sufficiently prevented from being peeled off from the test piece 10, and the strain gauge 12 is appropriately protected. can do.

  In the test body 100 according to this embodiment, one end 44 a of a protective tube 44 made of a fluororesin is embedded in the second protective layer 42, and the lead wire 22 is provided so as to pass inside the protective tube 44. Thereby, even when using the test body 100 in a severe corrosive environment, deterioration of the lead wire 22 can be suppressed.

  In the test body 100 according to the present embodiment, the first protective layer 40 is formed so as to cover at least a region of the lead wire 22 from the connection portion with the sensor unit 20 to the inside of the protective tube 44. More specifically, the first protective layer 40 includes at least a part of the surface protective part 40a formed on the surface of the test piece 10 so as to cover the sensor part 20 and the first lead part 22a, and the second lead part 22b. And an extended protective portion 40b extending from the surface protective portion 40a to the inside of the protective tube 44. With such a configuration, the lead wire 22 can be appropriately protected by the first protective layer 40 and the protective tube 44.

  In the test body 100 according to the present embodiment, the protective tape 46 made of a fluororesin is wound around the extended protective portion 40b from a position outside the one end 44a of the protective tube 44 to a position inside the protective tube 44. Yes. Thereby, even if the 2nd protective layer 42 corrodes in the vicinity of the end 44a of the protective tube 44, it can prevent that the lead wire 22 is exposed to a corrosive environment.

  In the test body 100 according to the present embodiment, the second protective layer 42 is formed so as to enter the protective tube 44 from one end 44 a of the protective tube 44. Thereby, the one end 44 a of the protective tube 44 can be closed by the second protective layer 42. As a result, exposure of the lead wire 22 to a corrosive environment can be sufficiently suppressed, and deterioration of the lead wire 22 in the protective tube 44 can be sufficiently suppressed.

  In the test body 100 according to this embodiment, a recess 42 a is formed in the second protective layer 42. By forming the second protective layer 42 in such a shape, the first protective layer 40 and the second protective layer 42 are peeled off when the test piece 10 is deformed so that the notch 10a is opened in the tensile test. Can be sufficiently suppressed. Thereby, the first protective layer 40 can be sufficiently protected by the second protective layer 42.

  In the test body 100 according to the present embodiment, the first protection is performed such that the central portion of the uncovered region 16 in the tension direction is convex toward the sensor unit 20 when viewed from the thickness direction of the test piece 10. A layer 40 and a second protective layer 42 are provided. Thereby, when a crack progresses from the notch 10a, the crack can be prevented from reaching the region where the first protective layer 40 and the second protective layer 42 are formed in a short time. Thereby, it can prevent that a clearance gap produces between the test piece 10 and the 1st protective layer 40 or between the test piece 10 and the 2nd protective layer 42 for a short time after the start of a fatigue test. As a result, the first protective layer 40 and the second protective layer 42 can protect the strain gauge 12 for a sufficient time.

(Modification)
In the test body 100 described above, the lead wire 22 may be provided with a coated tube made of a fluororesin. In this case, the deterioration of the lead wire 22 can be sufficiently suppressed without providing the protective tube 44.

  In the test body 100 described above, one or more other layers may be provided between the first protective layer 40 and the second protective layer 42, and one or more other layers may be provided on the second protective layer 42. Also good.

(Other embodiments)
In the above-described embodiment, the case where a CT test piece is used as the test piece 10 has been described. However, the test piece provided with the protective structure is not limited to the CT test piece. Although a detailed description is omitted, for example, the protective structure 14 may be provided on the rod-shaped test piece 50 as in the test body 200 shown in FIG. In this case, the sensor unit 20 of the strain gauge 12 is attached to one gripping part 50 a of the bar-shaped test piece 50. More specifically, the sensor part 20 is affixed on parts other than the part (for example, threaded part) fixed to the tensile testing machine among the grip parts 50a. Moreover, the 1st protective layer 40 and the 2nd protective layer 42 are provided so that a part of outer peripheral surface of the holding part 50a and a part of outer peripheral surface of the shoulder part 50b may be covered. In addition, the diameter of the grip part 50a is larger than the diameter of the parallel part 50c. For this reason, when the sensor part 20 is affixed to the grip part 50a, the measured value of distortion becomes smaller than when the sensor part 20 is affixed to the parallel part 50c. In this regard, the distortion of the parallel portion 50c can be obtained by correcting the measured distortion.

  In the example of FIG. 3, the first protective layer 40 and the second protective layer 42 are also formed on the shoulder 50b. However, when the sensor unit 20 can be sufficiently protected from the corrosive environment, the first protective layer is formed. 40 and the second protective layer 42 may be formed only on the grip portion 50a. In the example of FIG. 3, the first protective layer 40 and the second protective layer 42 are formed so as to cover the entire periphery of the grip portion 50 a, but when the sensor unit 20 can be sufficiently protected from the corrosive environment. The first protective layer 40 and the second protective layer 42 may not cover the entire periphery of the grip portion 50a. Moreover, although detailed description is abbreviate | omitted, you may provide the protective structure 14 in a plate-shaped test piece. In this case, similarly to the test body 200 shown in FIG. 3, the first protective layer 40 and the second protective layer 42 are attached so that the sensor unit 20 is attached to the grip portion of the plate-shaped test piece and covers the sensor unit 20. Is formed.

  As described above, according to the present invention, it is possible to appropriately protect the strain gauge attached to the test piece. Therefore, the present invention can be suitably used when performing a fatigue test in a severe corrosive environment such as a wet hydrogen sulfide environment.

DESCRIPTION OF SYMBOLS 10 Test piece 10a Notch 12 Strain gauge 14 Protection structure 16 Uncovered area | region 20 Sensor part 22 Lead wire 22a 1st lead part 22b 2nd lead part 40 1st protective layer 42 2nd protective layer 100,200 Test body

Claims (12)

A protective structure for protecting a strain gauge having a sensor unit affixed to a test piece and a lead wire connected to the sensor unit,
Provided on the surface of the test piece, formed from a vinyl chloride resin, and the sensor part, at least the sensor part of the surface of the test piece, and at least a connection part of the lead wire with the sensor part A first protective layer covering a predetermined region including:
A strain gauge protection structure comprising: a second protection layer formed of a silicon resin provided on the first protection layer.   2. The strain gauge protection structure according to claim 1, further comprising a protection tube made of a fluororesin in which the lead wire passes inside and one end is embedded in the second protection layer.   3. The strain gauge protective structure according to claim 2, wherein the first protective layer covers at least a region of the lead wire from a connection portion with the sensor portion to the inside of the protective tube. The lead wire includes a first lead portion having one end connected to the sensor portion and covering the surface of the test piece, and a second lead portion rising from the other end of the first lead portion and passing through the protective tube. Including
The first protective layer includes a surface protective part formed on the surface of the test piece so as to cover the sensor part and the first lead part, and the surface so as to cover at least a part of the second lead part. The protection structure of the strain gauge of Claim 2 or 3 including the extended protection part extended from the protection part to the inside of the protection tube. Further comprising a protective tape made of a fluororesin wound around the extension protection part so as to cover the extension protection part,
5. The strain gauge according to claim 4, wherein the protection tape is wound around the extension protection portion from a position outside the protection tube to a position inside the protection tube in the axial direction of the protection tube. Protective structure.   The strain gauge protection structure according to claim 2, wherein the second protection layer is formed so as to enter the protection tube from the one end of the protection tube.   The protective structure for a strain gauge according to claim 1, wherein the test piece is a fatigue test piece made of a steel material.   The strain gauge protection structure according to claim 1, wherein the test piece is a tensile fatigue test piece. The test piece is used for crack generation so that a crack develops in a progress direction crossing the plate thickness direction and the tensile direction by applying a force in a predetermined tensile direction orthogonal to the plate thickness direction. It is a rectangular parallelepiped CT specimen with a notch,
The sensor part is affixed to a central part in the tensile direction on the surface of the CT test piece on the side of the development direction when viewed from the notch,
The second protective layer is formed so as to cover at least a surface to which the sensor unit is attached,
The portion of the second protective layer formed on the surface to which the sensor unit is attached is such that the central portion in the tension direction is recessed toward the sensor unit when viewed from the plate thickness direction. The protective structure of the strain gauge in any one of Claim 1 to 8 currently formed. The first protective layer and the second protective layer are at least formed on two surfaces of the CT test piece that are parallel to each other in the plate thickness direction,
When the region where the first protective layer and the second protective layer are not formed on each of the two surfaces is an uncovered region, the center of the uncovered region in the tensile direction when viewed from the plate thickness direction. The strain gauge protective structure according to claim 9, wherein the first protective layer and the second protective layer are provided so that the portion is convex toward the sensor portion. An attachment method for attaching a strain gauge having a sensor part and a lead wire connected to the sensor part to a test piece,
Attaching the sensor part to the surface of the test piece;
A step of forming the protective structure according to any one of claims 1 to 10, and a method for attaching a strain gauge. A specimen,
A strain gauge having a sensor part affixed to the test piece and a lead wire connected to the sensor part;
A test body comprising the protective structure according to claim 1.

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