JP2000155006A - Sensor for crack depth measuring instrument by direct current potential difference method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the operability and to carry out accurate measurement with as little error as possible, in a sensor for a crack depth measuring instrument by a direct current potential difference method for, when a three- dimensional fatigue crack or the like is formed on an object to be inspected, nondestructively measuring its depth. SOLUTION: This sensor is formed of a probe part 9 provided with a one- dimensional proximity terminal formed by arranging four terminals, that is, a pair of current input-output terminals 11 and a pair of potential difference measuring terminals 12 on one straight line on the tip end of a holding part 8. The probe part 9 is provided with marks for positioning 15, by which it can be confirmed that the one-dimensional proximity terminal is orthogonally straddling a crack and that the center between one-dimensional proximity terminals corresponds to the intermediate position of the crack length, and is installed with a light for illumination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a potential difference method for non-destructively evaluating a material by applying a direct current to a conductive test object and measuring a potential difference on the surface of the test object. In particular, the operability of a sensor for a crack depth measuring instrument by the DC potential difference method for non-destructively measuring the depth when a three-dimensional fatigue crack or the like has occurred in the inspection object has been improved.
It is intended to enable accurate measurement with as little error as possible.

[0002]

2. Description of the Related Art Saka et al., One of the present inventors, have advanced and proposed research on a nondestructive inspection method using a potential difference method (Japanese Patent Application Laid-Open No. 2-245649, Japanese Patent Publication No. 5-11575, Japanese Patent Application Laid-Open No. 7-72022). issue). The potential difference method includes an AC method and a DC method, which are called an AC potential difference method and a DC potential difference method, respectively. In the case of high-frequency alternating current, most of the current flows along the surface (skin effect), whereas in direct current, the current flows not only on the surface of the test object but also inside the plate thickness. The flow field is disturbed not only by the surface defects protruding on the surface but also by the buried defects and the back surface defects, so that it is easy to apply to the evaluation, and the defense range is wide. In addition, DC does not generate induced electromotive force unlike AC. Therefore, there is an easy handling that does not cause a problem such as elimination of the induced electromotive force.

[0003] However, in the DC potential difference method, due to the characteristic that the current also flows inside the plate thickness of the inspection object,
Heretofore, there has been a defect that a large change in potential difference is difficult to occur on the surface of the inspection object and the sensitivity is not high. In contrast,
In recent years, a method has been proposed in which a potential difference measuring terminal is placed near a crack, and a terminal where the current input / output terminal and the potential difference measuring terminal are close to each other, that is, a method of evaluating a surface crack using a proximity terminal, is used to input a current away from the potential difference measuring terminal. A significant improvement in measurement sensitivity (higher sensitivity of the DC potential difference method) compared to the conventional method of outputting is realized. Here, increasing the sensitivity of the DC potential difference method means that a smaller current can be evaluated with a smaller current.

[0003]

If the potential difference measuring terminal is a close terminal as described above in order to realize the measurement and evaluation of a crack with extremely high sensitivity, a terminal for measuring the current input / output and the potential difference is used. Can be stored in one small sensor. As a result, in the measurement, the depth of the crack can be accurately measured only by correctly pressing the sensor against the surface of the inspection object. Therefore, based on such knowledge, the present inventor will conduct research and development of a sensor for a crack depth measuring instrument by the DC potential difference method that makes the measurement operation simple and the measurement value is as accurate as possible. Was.

First, as shown in FIG. 9, the measurement of the crack depth by the DC potential difference method using the adjacent terminals needs to be performed under the following conditions. Hereinafter, a method for measuring the depth of a crack formed on a surface of a material as a semi-elliptical vertical crack as shown in FIG.

In FIG. 9, a is a half length of a crack, b is a crack depth, and t is a plate thickness. On the other hand, the proximity terminals are the same as a pair of current input / output terminals 11 and 11, which are arranged on a straight line outside at a predetermined proximity at the tip of the sensor for the crack depth measuring instrument as shown in FIG. Four terminals including a pair of potential difference measuring terminals 12 and 12 disposed inside the straight line are provided. In the following, such a case will be described, but the same applies to the case where the pair of current input / output terminals 11 and 11 are disposed inside and the pair of potential difference measuring terminals 12 and 12 are disposed outside. . While maintaining the configuration as shown in FIG. 9, the proximity terminals are pressed and contacted, a DC current flows from the current input / output terminals 11, 11, and the potential difference V is measured between the two points by the potential difference measuring terminals 12, 12. That is, current input / output is performed between two points having a distance S1 from the crack on a line passing through the middle position of the crack length and perpendicular to the crack surface on the material surface, and performing a current input and output between two points having a distance S2 from the crack. The potential difference V is measured. The proximity terminal is, for example, S1 =
1.5 mm, S2 = 1 mm (Probe A) or / and S1 = 3 mm, S2 = 2.5 mm (Prob
BeB) A proximity terminal or the like is prepared, and measurement is performed using this. Using such a proximity terminal, the potential difference across the crack is measured, and at the same time, the potential difference as a reference is measured on the surface of the inspection object without cracks, and the crack depth is evaluated from the ratio between the two.

An accurate numerical value of the crack depth can be obtained only when the DC potential difference method using the proximity terminal is measured under the condition that the above-mentioned structural relationship is correctly maintained. Therefore, when the sensor for the crack depth measuring device is pressed against the crack, the positioning method is very important, and a high-precision measurement result can be obtained only by accurate positioning. As a result, the sensor for a crack depth measuring instrument according to the present invention is required to display a positioning mark capable of easily performing accurate positioning.

Further, the sensor for a crack depth measuring instrument according to the present invention is provided on a probe portion so that the correct positioning can be performed.
There is a demand for mounting a lighting light and brightly illuminating a crack, a one-dimensional proximity terminal, and a positioning mark so that the crack and the pressed position can be easily visually recognized.

Further, the surface of the object to be inspected is not necessarily a smooth measurement surface, but may be a measurement surface having irregularities. There is a demand for providing a biasing force to the proximity terminal so that the terminal can surely come into contact with such various shapes of the measurement surface.

Furthermore, in order to ensure the contact of the terminals with various measurement surfaces as described above, it is desired that a current for measurement flows for the first time when a predetermined load is applied, and that the measurement operation be started. There is also a request.

It is desired to make the sensor as sensitive as possible by adjusting the distance between adjacent terminals (Probe distance).
There is also a request.

The present invention solves the technical problem based on such a demand, improves the operability thereof, and embodies a sensor for a crack depth measuring instrument by a DC potential difference method capable of performing accurate measurement with as little error as possible. It is intended to facilitate the active use of the potentiometric method.

[0012]

According to the present invention, means for solving the above technical problems are constituted as follows.

The first invention to be patented is a one-dimensional one in which four terminals, a pair of current input / output terminals and a pair of potential difference measurement terminals, are arranged on a straight line at the tip of the grip portion. In the crack depth measuring device sensor provided with a probe portion having a proximity terminal, a one-dimensional proximity terminal straddles the probe portion so as to be orthogonal to the crack, and between the terminals of the one-dimensional proximity terminal. A sensor for a crack depth measuring instrument by a DC potential difference method, wherein a positioning mark for confirming that a center coincides with an intermediate position of a crack length is provided.

In the DC potential difference method using the proximity terminal according to the present invention, the crack and the one-dimensional proximity terminal can obtain an accurate numerical value of the crack depth only when the measurement is performed under the condition that the predetermined configuration relation is correctly maintained. Focusing on the fact that it can be obtained, the crack depth measuring instrument sensor is provided with an accurate positioning mark. The precise positioning mark is the first
Second, the center between the terminals and the middle position of the crack length coincide with each other, and second, the one-dimensional proximity terminal comes to a position straddling so as to be orthogonal to the crack. Must be easily visible and easily accessible.

[0015] A second invention to be patented is a one-dimensional one in which four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, are arranged on a straight line at the tip of the grip portion. In the crack depth measuring device sensor provided with a probe portion having a proximity terminal, a one-dimensional proximity terminal straddles the probe portion so as to be orthogonal to the crack, and between the terminals of the one-dimensional proximity terminal. In addition to providing a positioning mark for confirming that the center coincides with the middle position of the crack length, an illumination light is attached to the probe, so that the crack, the one-dimensional proximity terminal, and the positioning mark can be illuminated. This is a sensor for a crack depth measuring device by a DC potential difference method.

According to the second aspect of the present invention, a positioning mark, a crack, a one-dimensional proximity terminal, and an illuminating light capable of illuminating a portion of the positioning mark are attached to the crack depth measuring sensor so that positioning can be further facilitated. Things.

According to a third aspect of the present invention, a positioning mark is a one-dimensional proximity terminal in which four terminals of a pair of current input / output terminals and a pair of potential difference measuring terminals are arranged on one straight line. 2. A display showing an arrangement direction line, a display showing a crack direction line, and a scale display showing a distance from the arrangement direction line of the one-dimensional proximity terminal along the crack direction line. 2 is a sensor for a crack depth measuring instrument according to the DC potential difference method described in 2.

According to a fourth aspect of the present invention, a one-dimensional structure is provided in which four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, are arranged on a straight line at the tip of the grip portion. In a crack depth measuring instrument sensor provided with a probe portion provided with a proximity terminal, at least a one-dimensional proximity terminal of the probe portion is formed as a transparent body and / or a space portion to visually identify a target crack. 3. A sensor for a crack depth measuring instrument according to the DC potential difference method according to claim 1 or 2, wherein a positioning mark is displayed near the transparent body and / or the space portion so that the crack can be confirmed.

According to a fifth aspect of the present invention, a one-dimensional structure is provided in which four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, are arranged on a straight line at the tip of the grip portion. A crack depth measuring instrument sensor provided with a probe having a proximity terminal, wherein the probe has an illumination line on a line orthogonal to an intermediate position of an arrangement direction line of the one-dimensional proximity terminals provided. A pair of lenses are disposed so as to straddle the arrangement direction line of the one-dimensional proximity terminal, and a spot light in which light from a built-in irradiation light source is focused through an illumination lens is the one-dimensional proximity terminal. A symmetric position straddling the arrangement direction line as a reference, and irradiating the same as two spot lights, and using the spot light as a positioning mark, this is a sensor for a crack depth measuring instrument by a DC potential difference method.

According to a fifth aspect of the present invention, the one-dimensional proximity terminal is set at a predetermined correct position only by adjusting two spot lights to the crack.

According to a sixth aspect of the present invention, a one-dimensional structure is provided in which four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, are arranged on a straight line at the tip of the grip portion. In a sensor for a crack depth measuring instrument provided with a probe having a proximity terminal, a plate-shaped spring member is provided on the one-dimensional proximity terminal, and a load is applied to the plate-shaped spring member or the load is reduced. To reduce the distance between one-dimensional proximity terminals,
A sensor for a crack depth measuring instrument based on a DC potential difference method, comprising an inter-terminal adjustment mechanism capable of performing adjustment such as widening.

According to a seventh aspect of the present invention, a one-dimensional one-dimensional structure is provided in which four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, are arranged on a straight line at the tip of the gripping portion. In the sensor for a crack depth measuring instrument provided with a probe having a proximity terminal, a pressing button of the probe is provided on the grip portion, and a predetermined pressing force is applied to the one-dimensional proximity terminal. A sensor for a crack depth measuring instrument based on a DC potential difference method, wherein a current for measurement is caused to flow.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on illustrated embodiments. When applying fracture mechanics to the evaluation of the soundness of various structures, it is important to nondestructively evaluate the dimensions and shapes of existing cracks. The DC potential difference method has been attracting attention as an effective tool for non-destructive evaluation of cracks. In the DC potential difference method, a total of four terminals of two current input / output terminals and two potential difference measurement terminals are used. However, the DC potential difference method has a disadvantage that a large potential difference is hardly generated on the surface of the inspection object, in other words, the sensitivity is not high. Proximity terminals have been proposed to eliminate the drawbacks of the DC potential difference method and to increase the sensitivity. By taking the form of the proximity terminal, it is possible to accommodate a total of four terminals, two current input / output terminals and two potential difference measurement terminals, in one small sensor. The three-dimensional crack measurement has been simplified by simply pressing it.

Therefore, a device for measuring a three-dimensional crack by the DC potential difference method has been newly developed. FIG. 7 is a perspective view showing an example of the entire configuration of the three-dimensional crack measuring apparatus using the DC potential difference method. The illustrated three-dimensional crack measuring device includes a sensor 1 for a crack depth measuring instrument having a proximity terminal, a stabilized DC power supply 2, a digital multimeter 3, a GP-IB adapter 4, a personal computer 5, and a carrier case 6. I have.

As shown in FIG. 8, the arrangement of the proximity terminals provided in the crack depth measuring device sensor 1 is a one-dimensional proximity terminal in which four terminals are arranged in a straight line.
FIG. 9 shows a method of measuring a semi-elliptical surface crack by the proximity terminal. In the illustrated embodiment, S1 = 1.5
mm, S2 = 1 mm (Probe A)
Two types of sensors having proximity terminals of 1 = 3 mm and S2 = 2.5 mm (Probe B) were used. A DC current of 1 A was supplied to the DC input / output terminal of the sensor. The potential difference measured by the potential difference measuring terminal of the sensor was taken into a digital multimeter, A / D converted, and transferred to a personal computer via a GP-IB adapter. The personal computer incorporates software for calculating the depth of a three-dimensional surface crack using a calibration relational expression.

The present invention is a sensor for a crack depth measuring instrument in a three-dimensional crack measuring device according to the DC potential difference method as described above. With the development of the sensor for the crack depth measuring device, it has become possible to easily and non-destructively measure and evaluate the depth of a three-dimensional crack, which has been considered difficult particularly, by the DC potential difference method. . Therefore, the practicality of the sensor for the crack depth measuring device has been dramatically improved.

<Embodiment 1> FIG. 1 is a perspective view showing a first embodiment of a sensor for a crack depth measuring instrument according to the present invention, and FIG. 2 is a perspective view showing a crack according to the first embodiment shown in FIG. FIG. 3 is a side view of the sensor for a depth measuring instrument, and FIG. 3 is a plan view (a) and a front view (b) of the sensor for a crack depth measuring instrument according to the first embodiment shown in FIG.

The sensor for the crack depth measuring instrument comprises a prismatic grip portion 8 and a probe 9 provided at the tip thereof. The probe 9 is bifurcated, and a transparent body is inserted in the middle of the probe, and a one-dimensional proximity terminal 10 is provided therein. The one-dimensional proximity terminal 10 includes a pair of current input / output terminals 11 and 11 and a pair of potential difference measurement terminals 12 and 12.
Are arranged on one straight line.
In the following, the same applies to the case where the pair of current input / output terminals 11 and 11 are provided inside and the pair of potential difference measuring terminals 12 and 12 are provided outside.

The terminal space of at least the one-dimensional proximity terminal 10 of the probe 9 is formed as a transparent body 13 and / or a space 13a so that the crack 14 can be visually confirmed. A positioning mark 15 is displayed on the transparent body 13. The positioning mark 15 can confirm that the one-dimensional proximity terminal 10 straddles so as to be orthogonal to the crack 14 and that the center between the terminals of the one-dimensional proximity terminal 10 matches the middle position of the crack length. is there. A specific positioning mark 15 is a line in the arrangement direction of the one-dimensional proximity terminal 10 in which four terminals of a pair of current input / output terminals 11 and 11 and a pair of potential difference measurement terminals 12 and 12 are arranged on one straight line. , A display 17 indicating a crack direction line, and a scale display 18 indicating a distance from the arrangement direction line of the one-dimensional proximity terminals 10 along the crack direction line. In the drawing, reference numeral 7 denotes an illumination light, which can illuminate the crack 14, the one-dimensional proximity terminal 10, and the positioning mark 15. In addition, 19 in the figure is a pressing button portion provided on the grip portion, and when the pressing button portion is pressed, a pressing force is applied to the one-dimensional proximity terminal 10 and contact with the inspection object becomes reliable, In addition, the configuration may be such that the current for measurement starts to flow when the pressing force exceeds a predetermined value.

Further, a plate-like spring member 20 is connected to the one-dimensional proximity terminal 10, and the distance between the one-dimensional proximity terminals 10 can be reduced by applying a load to the plate-like spring member 20 or reducing the load. In addition, an inter-terminal adjustment mechanism 21 is provided so as to enable adjustment such as widening.

<Embodiment 2> FIG. 4 is a plan view (a) and a front view (b) showing a second embodiment of the sensor for a crack depth measuring instrument according to the present invention. This embodiment is similar to the first embodiment in that it has a prism-shaped gripping portion 8 and a probe 9 provided at the tip thereof.
And the basic configuration is the same. Further, a portion of the transparent body 13 and a space 13a corresponding to the crack are formed in the terminal interval portion of the one-dimensional proximity terminal 10. Therefore, the crack 14 can be easily visually confirmed. Also, the display of the positioning mark 15 is different. A specific positioning mark 15 of the present embodiment is a one-dimensional proximity terminal 1 in which four terminals of a pair of current input / output terminals 11 and a pair of potential difference measuring terminals 12 and 12 are arranged on one straight line.
A display 16 indicating an array direction line of 0, two displays 17 indicating a crack direction line along the space 13a, and a distance from the array direction line of the one-dimensional proximity terminal 10 along the crack direction line display 17 Is provided. In the case of the present embodiment, since the positioning marks 15 are displayed in a rich manner, the illumination light 7 may not be provided.

<Embodiment 3> FIG. 5 is a plan view (a) and a front view (b) showing a third embodiment of a sensor for a crack depth measuring instrument according to the present invention, and FIG. FIG. 6A is a side view showing a third embodiment of the sensor for a crack depth measuring instrument shown in FIG. This embodiment comprises a cylindrical grip portion 8 and a probe 9 provided at the tip thereof. A pair of current input / output terminals 11 and 11 are provided at the tip of the probe 9.
And a one-dimensional proximity terminal 10 in which four terminals of a pair of potential difference measuring terminals 12 and 12 are arranged on one straight line.
A pair of illumination lenses 23 are arranged on a line orthogonal to the line in the arrangement direction of the one-dimensional proximity terminals 10 so as to straddle the arrangement direction line of the one-dimensional proximity terminals. Then, the spot light 22, 22 in which the light from the built-in irradiation light source is focused through the illumination lenses 23, 23, is transmitted to the one-dimensional proximity terminal 10.
Are illuminated as two spot lights 22 at a symmetrical position straddling the arrangement direction line as a reference, and this is used as a positioning mark.

[0033]

According to the present invention, a sensor for a crack depth measuring instrument by the DC potential difference method for non-destructively measuring the depth when a three-dimensional fatigue crack or the like occurs in an object to be inspected is provided. The operability is improved by enabling positioning and reliable contact, thereby enabling accurate measurement without error. Specifically, each invention has the following effects.

According to a first aspect of the present invention, in the sensor for a crack depth measuring instrument, a one-dimensional proximity terminal straddles the probe so as to be orthogonal to the crack, and the center between the terminals of the one-dimensional proximity terminal is a crack length. By providing a positioning mark that can confirm that the crack depth coincides with the middle position, it is easy to correctly position when pressing the crack depth measurement sensor on the inspection object, so that the crack depth can be easily adjusted. Measurement can be performed with high accuracy and errors are reduced.

According to a second aspect of the present invention, a positioning mark and an illuminating light are provided on a sensor for a crack depth measuring instrument, and the crack and the positioning mark are raised by illumination to make the positioning operation easier.

According to the third aspect of the present invention, a specific display having necessary requirements is specified as a positioning mark of a sensor for a crack depth measuring instrument. Appropriate positioning of the crack depth measuring sensor can be easily performed according to the positioning marks.

According to a fourth aspect of the present invention, the terminal gap portion of the one-dimensional proximity terminal is formed as a transparent body and / or a space so that the target crack can be visually confirmed, and at the vicinity of the transparent body and / or the space. Since the positioning mark is displayed, high-precision positioning can be easily performed.

According to a fifth aspect of the present invention, the spot light can be radiated as two spot lights to a symmetrical position straddling the arrangement direction line of the one-dimensional proximity terminals as a reference, and this is not used as a positioning mark. The one-dimensional proximity terminal can be set at a predetermined correct position only by adjusting the spot light to the crack.

According to the sixth aspect of the present invention, an inter-terminal adjustment mechanism is provided which can adjust the distance between the one-dimensional proximity terminals to be narrower or wider, so that a single probe can be changed to various probe needles. .

According to the seventh aspect of the present invention, the holding button is provided with a contact button for the probe, and a current for measurement is applied when a predetermined pressing force is applied to the one-dimensional proximity terminal. , Even if the surface of the test object has irregularities, press the pressing button part to ensure that the terminals can be in contact with the shape of the measurement surface, and when a predetermined load is applied, The current was made to flow so that there was no waste of electricity.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a sensor for a crack depth measuring instrument according to the present invention.

FIG. 2 is a side view of the sensor for a crack depth measuring instrument according to the embodiment shown in FIG.

FIG. 3 is a plan view (a) and a front view (b) of the sensor for a crack depth measuring instrument according to the embodiment shown in FIG.

FIG. 4 is a plan view (a) and a front view (b) showing another embodiment of the sensor for a crack depth measuring instrument according to the present invention.

FIG. 5 is a plan view (a) and a front view (b) showing another embodiment of the sensor for a crack depth measuring instrument according to the present invention.

6 is a side view (a) and a front view (b) showing another embodiment of the crack depth measuring device sensor according to the embodiment shown in FIG.

FIG. 7 is a perspective view showing an example of the overall configuration of a three-dimensional crack measuring apparatus using a DC potential difference method.

FIG. 8 is an enlarged schematic view of a main part showing an example of an arrangement state of one-dimensional proximity terminals of a sensor for a crack depth measuring instrument.

FIG. 9 is an explanatory diagram showing a method for measuring a semi-elliptical surface crack by a proximity terminal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sensor for crack depth measuring device 2 ... DC stabilized power supply 3 ... Digital multimeter 4 ... DP-IB adapter 5 ... Personal computer 6 ... Carrier case 7 ... Lighting light 8 ... Grip section 9 ... Styling section 10 ... One-dimensional proximity terminal 11 ... Current input / output terminal 12 ... Potential difference measurement terminal 13 ... Space 14 ... Crack 15 ... Positioning mark 16 ... Display indicating the arrangement direction line 17 Display indicating the crack direction line 18 ... Scale display 19 ... Press button Part 20: plate-shaped spring member 21: inter-terminal adjustment mechanism 22: spot light 23: illumination lens

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Mitsuhiro Mikami, 1-4-11 Matsugaoka, Iwanuma City, Miyagi Prefecture (72) Mitsumasa Toyokawa 7-6 Ishizuka, Koriyama, Kakuyama, Sendai-shi, Miyagi Pref. F term in the machine (reference) 2F063 AA15 BB02 BD07 BD20 CA40 DA02 EA20 EB18 EB23 EB30 FA10 ZA01 2G060 AA20 AE01 AE40 AF02 AF09 AG04 AG11 EA01 EB03 EB05 EB06 GA01 HA01 HC10 2G061 BA20 CA01 CB01 CB01 CC10

Claims (7)

[Claims] 1. A probe having a one-dimensional proximity terminal in which four terminals, a pair of current input / output terminals and a pair of potential difference measurement terminals, are arranged on a straight line at a tip end of a grip portion. In the crack depth measuring device sensor provided, a one-dimensional proximity terminal straddles the probe so as to be orthogonal to the crack,
And a positioning mark for confirming that the center between the terminals of the one-dimensional proximity terminal coincides with the middle position of the crack length. A sensor for a crack depth measuring instrument by a DC potential difference method. 2. A probe having a one-dimensional proximity terminal having four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, arranged on a straight line at a tip of a grip portion. In the crack depth measuring device sensor provided, a one-dimensional proximity terminal straddles the probe so as to be orthogonal to the crack,
In addition to providing a positioning mark for confirming that the center between the terminals of the one-dimensional proximity terminal coincides with the middle position of the crack length, an illumination light is attached to the probe, and the crack and the one-dimensional proximity terminal are positioned. A sensor for a crack depth measuring instrument based on a DC potential difference method, wherein a mark portion can be illuminated. 3. A display in which a positioning mark indicates an arrangement direction line of a one-dimensional proximity terminal in which four terminals of a pair of current input / output terminals and a pair of potential difference measurement terminals are arranged on a straight line. 3. A crack according to the DC potential difference method according to claim 1 or 2, wherein the indication indicates a direction line and a scale indication indicating a distance from the arrangement direction line of the one-dimensional proximity terminals along the crack direction line. Sensor for depth measuring instrument. 4. A probe portion provided with a one-dimensional proximity terminal in which four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, are arranged on a straight line at the tip of the grip portion. In the sensor for a crack depth measuring instrument provided, at least the one-dimensional proximity terminal of the probe portion has a transparent body and / or
3. The direct current according to claim 1, wherein the target crack is visually recognized as a space, and a positioning mark is displayed near the transparent body and / or the space. Sensor for crack depth measuring device by potentiometric method. 5. A probe having a one-dimensional proximity terminal in which four terminals, a pair of current input / output terminals and a pair of potential difference measurement terminals, are arranged on a straight line at a tip end of a grip portion. In the crack depth measuring instrument sensor provided, a pair of illumination lenses are arranged on a line orthogonal to an intermediate position of an arrangement direction line of the one-dimensional proximity terminals provided on the probe, and the one-dimensional proximity terminal is provided. Arranged so as to straddle the arrangement direction line, the spot light in which the light from the built-in irradiation light source is focused through the illumination lens, straddles with reference to the arrangement direction line of the one-dimensional proximity terminal. 2 at symmetrical position
A sensor for a crack depth measuring instrument by a DC potential difference method, which can be radiated as a spot light of a point and used as a positioning mark. 6. A probe having a one-dimensional proximity terminal in which four terminals, a pair of current input / output terminals and a pair of potential difference measuring terminals, are arranged on a straight line at the tip of the grip portion. In the crack depth measuring device sensor provided, a plate-like spring member is provided on the one-dimensional proximity terminal, and a distance between the one-dimensional proximity terminals is reduced by applying a load to the plate-like spring member or reducing the load. A sensor for a crack depth measuring instrument by a DC potential difference method, comprising an inter-terminal adjusting mechanism capable of adjusting the width and width of the crack. 7. A probe portion provided with a one-dimensional proximity terminal in which four terminals of a pair of current input / output terminals and a pair of potential difference measuring terminals are arranged on a straight line at a grip portion and a tip portion thereof. In the sensor for a crack depth measuring instrument provided with, a pressing button portion of the probe portion is provided in the gripping portion, and a current for measurement flows when a predetermined or more pressing force is applied to the one-dimensional proximity terminal. A sensor for a crack depth measuring instrument by a DC potential difference method, characterized in that: