JP2004093573A - Small potential difference measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a minute potential difference measuring device capable of accurately measuring a minute potential difference by measuring in advance whether a contact state of an individual contact with a sample surface is good or not prior to a potential difference measurement.
SOLUTION: An electrode that is pressed against a sample surface to supply a high-frequency current, and an electrode that can advance and retreat only in the direction of the sample surface and contacts a measurement point near a surface defect at an arbitrary position on the sample surface and has a minute distance between the measurement points. At least a pair of contacts for detecting a potential, a circuit board made of a material having flexibility to be connected to the contacts, and a measuring point based on a detection signal input from the contacts via the circuit board. Measuring means for measuring a minute potential difference occurring between them, contact quality determining means for determining the quality of a contact state between each contact and a sample surface, and a tip of each contact at a measuring point with an equal force. And a pressing mechanism for pressing.
[Selection diagram] Fig. 1

Description

{Circle over (1)} The present invention relates to a minute potential difference measuring device capable of quantitatively measuring a risk of a surface defect such as a crack generated in a large structure developing into a fracture.

In general, structures are difficult to use so that surface defects do not occur on their surface, and small cracks may occur during use, and this crack may develop into fracture depending on the condition .

Conventionally, in order to prevent the development of this fracture in advance, the average stress state has been monitored using a strain gauge or load cell, but it is difficult to quantitatively measure the local risk of the crack itself. And it was not performed until the detection of this risk.

If the amount of current used, the frequency of the current, the position of the current input / output terminal and the potential difference measuring terminal, and the material of the target member are the same, the amount of change in the potential difference and the change in the stress intensity factor due to the load change It has been found that there is a certain proportional relationship with the amount, and a technique for measuring the stress intensity factor of the crack portion has been proposed (Transactions of the Japan Society of Mechanical Engineers, Vol. 56, No. 528, Paper No. 89-0566A). . In this measurement, since the measurement signal is as small as μV, it was necessary to weld the measurement electrode to the surface of the structure in order to prevent noise, and the potential difference could not be measured at an arbitrary position.

However, on the practical side, since there are many places for measuring the potential difference, it is possible to measure the minute potential difference sandwiching the cracks by simply pressing the contact against the surface of the object without welding the contact to the object to be measured. It is desired. In addition, in the measurement of the minute potential difference sandwiching such a crack, there is a demand that all the contacts are pressed against the sample surface with a uniform force so that the potential difference can be measured with a uniform contact resistance. .

However, the measurement surface has slopes and irregularities, and when the measurement surface is inclined, the surface formed by the tip of the contact and the measurement surface are not parallel, some rise, and some make strong contact As a result, it is difficult to make the contact resistance of all the contacts small and uniform, that is, it is difficult to uniformly press all the contacts on the sample surface. Also, even when the measurement surface has irregularities, due to the stroke of each contact, a part will rise and a part will come into strong contact. It was difficult to apply pressure uniformly.

In such a case, since the lock-in amplifier that is the center of the measurement of the minute potential difference is a voltmeter that uses an AC reference current, a minute interval generated between the contacts is measured as a voltage regarded as an air capacitor. In some cases, the measurement of the potential difference may be an incorrect measurement value. Under such circumstances, prior to the potential difference measurement, there is a long-awaited need for a mechanism capable of identifying a measurable contact by measuring the contact state of each contact with the sample surface in advance, or in place of this. Therefore, the appearance of a mechanism capable of correcting the surface formed by the contact tip and the measurement surface in parallel has been expected.

(4) In addition, since the crack on the sample surface is hidden below the sensor unit of the measuring device, there is a problem that it is difficult to accurately position the measurement point sandwiching the crack. Furthermore, when a minute potential difference is measured using a lock-in amplifier, it is necessary to supply a reference current to the surface of the sample, so that there is a problem that an induced magnetic field is generated and a contact or the like easily picks up noise.

The present invention has been made in view of the circumstances described above, and can accurately measure a minute potential difference by measuring in advance whether or not a contact state of an individual contact with a sample surface is good before measuring a potential difference. In addition, it is an object of the present invention to provide a minute potential difference measuring device that enables the measurement camera to be accurately positioned by enabling exchange of an imaging camera and a sensor unit.

Further, another minute potential difference measuring device according to the present invention,
An electrode that is pressed against the sample surface to pass a high-frequency current;
At least one pair of contacts that can advance and retreat only in the sample surface direction, contact a measurement point near a surface defect at an arbitrary position on the sample surface and detect a minute potential between the measurement points,
A circuit board made of a material having flexibility to connect a circuit to the contact,
Measuring means for measuring a small potential difference generated between the measurement points based on a detection signal input from the contact via a circuit board,
Contact quality determination means for determining the quality of the contact state between each contact and the sample surface,
And a pressing mechanism for pressing the tip of each contact to a measurement point with an equal force.

The measurement of the lock-in amplifier alone cannot determine the quality of the contact between the contact and the sample surface, and the measurement of the lock-in amplifier accurately displays the minute potential difference between the measurement points. It was difficult to confirm whether or not. On the other hand, in the present invention, since the contact state can be determined as described above, by reading the information on the contact state, the measured value of the lock-in amplifier accurately displays the minute potential difference between the measurement points. Can be confirmed, and the accuracy of the measurement of the minute potential difference can be improved.

Further, in the minute potential difference measuring device according to the present invention, it is not possible to determine whether the contact state between the contactor and the sample surface is good or not using only the measured value of the conventional lock-in amplifier, It was difficult to confirm whether the value accurately displayed the minute potential difference between the measurement points. On the other hand, in the present invention, since the contact state can be determined as described above, by reading the information on the contact state, the measured value of the lock-in amplifier accurately displays the minute potential difference between the measurement points. Can be confirmed, and the accuracy of the measurement of the minute potential difference can be improved.

Hereinafter, a minute potential difference measuring device according to an embodiment of the present invention will be described with reference to the drawings.
1 to 14 show a minute potential difference measuring device according to the first embodiment. FIG. 1 is a schematic perspective view of the minute potential difference measuring device according to the first embodiment. As shown in FIG. 1, a crack 2 is formed on the sample surface of the DUT 1. A small potential difference measuring device main body 3 is placed and mounted near the crack 2, and an operation pendant 4, a measuring device 5, and a control box 6 are connected to the measuring device main body 3.

The measuring device main body 3 is generally provided with a gate-shaped support member 11 that supports the measuring device main body 3, and below the gate-shaped support member 11, the measurement of the sample surface of the DUT 1 is performed. An attachment plate 12 having a sensor unit 10 for detecting a minute potential between points and an imaging unit 15 for specifying the position of a measurement point is arranged. The mounting plate 12 is configured to be moved and tilted by a moving and tilting mechanism 13 suspended from a gate-shaped support member 11, and the mounting plate 12 is provided below the mounting plate 12. It is configured to be moved by the air cylinder mechanism 14.

Further, as shown in FIGS. 2 and 3, legs 16a extend downward from the mounting plate 12, and the lower end of each leg 16a is connected to the sensor 1 by the sensor unit 10 when measuring a potential difference. An adsorbing mechanism 16 that adsorbs to the DUT 1 is provided so as to absorb a reaction force of the pressing when the pressing is performed. Further, the mounting plate 12 is provided with a lifting mechanism 17 for raising and lowering each leg 16a. Further, as shown in FIG. 3, a pressing air cylinder mechanism 18 for pressing the sensor unit 10 against the DUT 1 when measuring the potential difference is provided on the lower surface of the mounting plate 12.

The moving / tilting mechanism 13 has an xyθ table 19 for moving the mounting plate 12 in the horizontal direction with respect to the gate-shaped support member 17, and makes the mounting plate 12 parallel to the sample surface of the DUT 1. And a tilt correcting mechanism 20 for tilting the mounting plate 12 as described above.

Further, the air cylinder mechanism 14 is supported by a mounting member 21 fixed to the lower surface of the mounting plate 12, as shown in FIG. A first guide rail 22 is fixed to the upper surface of the mounting plate 12, and a second guide rail 23 connected to the piston rod 14 a of the air cylinder mechanism 14 is fixed to a lower part of the moving / tilting mechanism 13. The first and second guide rails 22 and 23 are configured to slide with each other. With such a configuration, when the piston rod 14a of the air cylinder mechanism 14 expands and contracts, the first guide rail 22 and the mounting plate 12 are horizontally moved with respect to the stationary second guide rail 23 and the moving / tilting mechanism 13. Moved in the direction.
Further, in the imaging unit 15, a CCD camera 24 that captures an image of the measurement point and its vicinity in order to specify the position of the measurement point, and an input to the CCD camera 24. And a reflection mirror 26 that reflects an image to be reproduced.

Next, the sensor unit 10 will be described with reference to FIGS.
First, as shown in FIG. 4, the sensor unit 10 has a casing 31 having a rectangular cross section, and a front plate 32 is fixed to the sample surface side of the casing 31. The front plate 32, an opening ₃₃ a1 forming a plurality of _{pairs, 33 a2 ...... 33 an, 33} b1, 33 b2 ...... 33 bn are two rows drilled at a predetermined interval, the openings _{33 a1} , ₃₃ a2 the _{...... 33 an, 33 b1, 33} b2 ...... 33 bn, contacts ₃₄ for measuring the small potential difference _{a1, 34 a2 ...... 34 an,} 34 b1, 34 b2 ...... 34 bn respectively It is slidably inserted in the axial direction.

The contacts 34 _a1 , 34 _a2 ... 34 _an , 34 _b1 , 34 _b2 ... 34 _bn are inserted upward while being in electrical contact with a circuit board 35 made of a flexible material. As shown in FIG. 5, the circuit board 35 is connected to the circuit shown in FIG. 14 by a signal cable 37 connected via a socket to a support member 36 to which the circuit board 35 is fixed. The circuit of FIG. 14 will be described later.

Then, in the housing 31 of the sensor unit 10, the generally-pressing mechanism is provided for pressing the contact _{34 a1 ... 34 an, 34 b1} , the tip of ... _{34 bn} to the measurement point. The pressing mechanism generally includes an air bag 41, a top plate 42 that moves downward due to inflation of the air bag 41, and a guide that moves downward by the top plate 42 and elastically holds each contact. When the guide block 43 is moved downward, the tips of the contacts 34 _{a1 to} 34 _an , 34 _b1 to 34 _bn are pressed to the measurement points on the sample surface 1.

As shown in FIGS. 5 and 6, the guide block 43 of the pressing mechanism is inserted into and guided by the opening 44a of the frame member 44. The frame member 44 is fixed to the support member and also fixed to a fixing block 45 provided in the housing 31. The fixing block 45 is fixed to a lid plate 46 disposed above the airbag 41. 8, 9 and 10, the frame member 44 has an opening 44a extending in the longitudinal direction and through which the guide block 43 is inserted. The guide block 43, as shown in FIGS. 11 and 12, are elongated formed in the longitudinal direction, as inserted through the opening 44a of the frame member 44, contacts _{34 a1 ... 34 an, 34 b1} , guide hole ₄₃ a1 _... 43 for guiding the ... _{34 bn an,} 43 _b1, and a ... _{43 bn.} These guide holes _{43 a1 ... 43 an, 43 b1} , ... 43 Within _bn, as shown in FIG. 6, the spring 48 contacts _{34 a1 ... 34 an, 34 b1} , the ... _{34 bn} urges the sample surface direction Is interposed. Each contact ₃₄ a1 _... 34 due to unevenness of the sample surface 1 _{an, 34 b1,} ... 34 the difference in per _bn is equalized by the spring 48 (the force equalizing means), all contacts ₃₄ a1 ... _{34 an, 34 b1,} ... 34 _bn is biting at a right angle to ensure the surface. Further, as shown in FIG. 6, an end of the circuit board 35 is fixed to the lower surface of the guide block 43, and the top plate 42 is fixed so as to move integrally with the guide block 43. The top plate 42 plays a role of holding down a spring 48. Further, a supply pipe 47 for supplying air is connected to the air bag 41. As shown in FIGS. 4 and 5, an electrode 50 for passing a high-frequency current of about 1 A (100 kHz) to the sample surface 1 is provided at an end of the front plate 32 via an insulating plate 49. Further, as shown in FIGS. 4 and 6, a leg 51 slightly lower than the height of the electrode 50 and the insulating plate 49 is provided at the end of the front plate 32 so that the electrode 50 comes into contact with the sample surface 1 preferentially. Is provided.

Further, the operation pendant 4 is provided with a screen 52 for displaying the crack 2 as shown in FIG. As shown in FIG. 13, the screen 52 includes _an x-axis cursor 53 that divides the columns of the contacts 34 _a1 ... 34 _an , 34 _{b1 ,.} , And the imaging center position mark 55 of the crack 2.

Next, as shown in FIG. 14, a plurality of signals corresponding to the contacts 34 _{a1 to} 34 _an , 34 _{b1 ,.} Line 56 is connected to measuring instrument 5. The measuring device 5 includes a signal selection circuit 60 for selecting a signal line of an arbitrary contact from all the signal lines 56, and a contact quality determination for measuring the quality of a contact state of the signal circuit selected by the signal selection circuit 60. It comprises a circuit 70 and a lock-in amplifier 80 which is the center of measurement of a minute potential difference.

More specifically, the signal selection circuit 60 has a multiplexer 61 to which all the signal lines 56 are connected, and an instruction signal for opening and closing the measurement signal circuit in the multiplexer 61 is transmitted to the control unit via a control signal 62. 6 to the control computer 91. A signal is transmitted from an open circuit in the multiplexer 61 to the lock-in amplifier 80 via the signal line 63 and the gate unit 71.

More specifically, the contact quality judgment circuit 70 switches the signal line 63 from the multiplexer 61 to one of a signal line 78 to a DC resistance meter 72 and a signal line 75 to a lock-in amplifier 80 described later. 71. The DC resistance meter 72 is configured to transmit a signal from a signal line 78 to a contact quality determination unit 73 via a signal line 76. The result of the determination by the contact quality determination unit 73 is transmitted to the control unit 6 via the signal line 77 and displayed on the display unit 92. The gate unit 71 is connected to a control computer 91 of the control unit 6 via a signal line 74.

Next, the operation of the minute potential difference measuring device according to the first embodiment will be described.

As shown in FIGS. 1 to 3, the measuring device main body 3 is placed on the sample surface of the DUT 1, the suction mechanism 16 is contracted, and the measuring device main body 3 is supported by the portal-type support member 11. Next, the crack 2 is imaged by the CCD camera 24, and the movement / tilt mechanism 13 is operated so that the crack 2 is aligned with the y-axis cursor 54 shown in FIG. The air cylinder mechanism 14 is contracted, and the sensor unit 20 is moved right above the crack 2 instead of the CCD camera 24.

Then, the elevating mechanism 17 is extended, and as shown in FIG. 2, in place of the support member 11 supporting the apparatus main body 3, the suction mechanism 16 is held by the suction mechanism 16 in a state where the suction mechanism 16 is adsorbed on the sample surface. 3 is supported and fixed. Thereafter, as shown in FIG. 3, the pressing air cylinder mechanism 18 is extended, and the sensor section 10 is pressed against the sample surface, whereby the electrode 50 is brought into contact with the sample surface and the reference current is supplied. .

Next, as shown in FIGS. 5 and 6, when compressed air is supplied to the airbag 41 through the supply pipe 47 and the airbag 41 is inflated, the total inflation load is arbitrary via the top plate 42. contacts _{34 a1 ... 34 an, 34 b1} , acting on ... _{34 bn.} Each contact ₃₄ due to unevenness of the sample surface _{1 a1 ... 34 an, 34 b1} , the difference in per ... _{34 bn,} is equalized by the spring 48 of the force equalizing means, all contacts ₃₄ a1 _{... 34} an,, 34 _b1, ... _{34 bn} is biting at a right angle to ensure the surface.

Any contacts _{34 a1 ... 34 an, 34 b1} , ... 34 determines the contact quality of _bn, as shown in FIG. 14, is switched from the lock-in amplifier 80 for measuring the gate portion 71 to the contact quality decision circuit 70 Te, contacts ₃₄ a1 _... 34 by the DC resistance meter 72 based on the signal from the flexible circuit board 35 _{an, 34 b1,} ... 34 the contact resistance between _bn and the sample surface is measured, predetermined by the contact quality decision section 73 The magnitude of the measured resistance value with respect to the threshold value is determined. Thereby, if the measured resistance value is smaller than the predetermined threshold value, it is determined that the contact is good.

If the measured resistance value is larger than the predetermined threshold value, it is determined that the contact is poor. In this case, while observing the quality indication on the display unit 92, the inclination correcting mechanism 20 of the moving / tilting mechanism 13 performs the operation. The orientation of the sensor unit 10 is adjusted, and the surface formed by the tips of the contacts 34 _a1 ... 34 _an , 34 _{b1 ,.} In the case of a contact failure, the pressing force from the sensor unit 10 to the sample surface by the pressing air cylinder mechanism 18 is controlled, so that the surface formed by the tips of the contacts 34 _a1 ... 34 _an , 34 _b1 ,. The measurement surface and the contact force may be adjusted.

As described above, in the present embodiment, when the sample surface 1 is inclined or the like, even if the contacts 34 _{a1 to} 34 _an , 34 _{b1 ,.} the correcting mechanism 20, contacts _{34 a1 ... 34 an, 34 b1} , and correct the inclination angle of the tip formed face of ... _{34 bn,} contacts _{34 a1 ... 34 an, 34 b1} , ... 34 bn sample contact state of And the minute potential difference between the measurement points can be accurately measured.

Furthermore, it is not possible to judge the quality of the contact state between the contact and the sample surface using only the measured values of the conventional lock-in amplifier, and the measured values of the lock-in amplifier accurately display the minute potential difference between the measurement points. It was difficult to confirm whether or not. On the other hand, in the present embodiment, since the contact state can be determined as described above, by reading the information on the contact state, the measurement value of the lock-in amplifier 80 accurately displays the minute potential difference between the measurement points. Can be confirmed, and the accuracy of the minute potential difference measurement can be improved.

Further, as a modified example of the first embodiment, a signal is amplified using a chip IC immediately after the flexible circuit board 35 inside the sensor unit 10, and noise or the like coming out of the sensor unit 10 and being placed on the signal line 56 is detected. And the signal can be easily distinguished. Further, an insulating amplifier can be provided at a position coming out of the multiplexer 61. Further, in the first embodiment, the guide block 43 is inserted into the opening 44a of the frame member 44. However, the frame member 44 restricts the vertical movement of the guide block 43 and the contacts _34a1 ... _34an. , 34 _b1 ,... 34 _bn may fall off from the guide block 43. Therefore, the frame member 44 may be omitted, and the guide block 43 may be supported on the flexible circuit board 35 by screws or the like.

Next, a small potential difference measuring device according to the second embodiment will be described with reference to FIGS. The same members as those in the first embodiment are denoted by the same reference numerals.

FIG. 15 is a schematic perspective view of a minute potential difference measuring device according to the second embodiment. The operation pendant 4, the measuring device 5, and the control box 6 are connected to the measuring device main body 3 as in the first embodiment. The measuring device main body 3 is generally provided with a gate-shaped support member 11 for supporting the measuring device main body 3, and a moving / tilting mechanism 13 is hung below the gate-shaped support member 11. A common base 100 for mounting the sensor unit replacement unit 150 or the imaging camera replacement unit 200 is fixed below the moving / tilting mechanism 13.

As in the first embodiment, the detailed description is omitted, but the moving / tilting mechanism 13 is provided with an xyθ table 19 and a tilt correcting mechanism 20, and the portal-type support member 11 is provided with the suction mechanism 16 and the suction mechanism 16. An elevating mechanism 17 is provided.

In the second embodiment, as described above, the sensor unit replacement unit 150 and the imaging camera replacement unit 200 are configured to be detachably replaceable with the common base 100. First, the common base 100 and the sensor unit replacement unit 150 will be described with reference to FIGS.

As shown in FIG. 19, the common base 100 is formed in a flat plate shape and is fixed to the xyθ table 19, and has a frame 101 at one end thereof. The other end of the common base 100 is formed with a female screw hole 102 which is screwed into a thumb screw 152 of an exchange plate 151, which will be described later, and the frame 101 is used to fit a positioning pin 153 of the exchange plate 151. Recess 103 is formed.

On the other hand, in the sensor unit replacement unit 150, a replacement plate 151 that is aligned below the common base 100 is provided, and a frame 199 is provided at one end of the replacement plate 151. A thumb screw 152 screwed into the female screw hole 102 of the base 100 is provided. At the other end of the exchange plate 151, a positioning pin 153 for fitting into the recess 103 is provided.

昇 A lift mechanism 154 is mounted below the exchange plate 151, and the sensor unit 10 is supported by the lift mechanism 154. The sensor unit 10 is moved up and down by the elevating mechanism 154 and pressed against the sample surface during measurement.

As shown in FIG. 20, the imaging camera exchange unit 200 is provided with an exchange plate 151 having a thumb screw 152 and a positioning pin 153, similarly to the sensor unit exchange unit 150. The CCD camera 24 and the reflection mirror 26 are attached to an attachment member 201 provided below the exchange plate 151.

Next, the structure of the sensor unit 10 will be described with reference to FIGS. The same members as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

First, in the present embodiment, the housing of the sensor unit 10 is composed of a metal box 31a that stores each component and a cover 31b of the box 31a. With this configuration, noise caused by the induced magnetic field is cut off, and accurate minute potential difference measurement is performed.

Furthermore, as shown in FIGS. 21 and 22, an insulating block 155 is provided on the side of the housing 31 as a structure of the electrode, and a metal tubular member 156 is housed in the insulating block 155. I have. An electrode rod 157 is slidably housed below the cylindrical member 156, and the electrode rod 157 is urged to press the sample surface by a spring 158 interposed above the cylindrical member 156. Have been. Further, the electrode rod 157 is configured to be energized by a power cable 159 connected thereto, and the power cable 159 is wound by a metal band spirally wound tube 160.

The signal cable 161 connected to the flexible circuit board 35 further includes a signal connector 162 fixed to the circuit board 35 and a signal cable main body 163 connected to the signal connector 162. The signal connector 162 is covered with a metal connector cover 164 having a structure hermetically sealed against an induced magnetic field, and the signal cable main body 163 is covered with a metal band spirally wound tube 165. Therefore, noise caused by the induced magnetic field generated by the frequency of the signal flowing through the signal cable 161 is cut off.

As shown in FIG. 25, the guide block 43 to the top plate 42 is secured to the guide block 43, the contact _{34 a1 ... 34 an, 34 b1} , ... 34 bn is housed is biased by a spring 48 At the same time, an end of the circuit board 35 is attached to the bottom of the guide block 43 by a screw 168. Further, contacts _{34 a1 ... 34 an, 34 b1} , ... 34 bn penetrates the plate-like member 166, which protrudes through the opening 167 in the bottom of the box portion 31a. An opening 167 of the box portion 31a is provided with an insulating member 169, and the contacts _34a1 ... _34an , _34b1 , ... _34bn are slidably provided in the insulating member 160. Further, an insulating sheet 171 is attached to the outside of the bottom and side portions of the box 31a, and an insulating sheet 172 is attached to the inside of the bottom of the box 31a. Note that the leg 51 is also covered with an insulating member.

Next, the operation of the minute potential difference measuring device according to the second embodiment will be described.

First, the position of the crack 2 is imaged by the imaging camera 15. The apparatus main body 3 is placed on the DUT 1, the suction mechanism 16 is driven, the elevating mechanism 17 is contracted, and the apparatus main body 3 is supported by the portal-type support member 11. The exchange plate 151 of the imaging camera exchange unit 200 is mounted on the common base 100, positioning is performed by the positioning pins 153, and the thumb screw 152 is tightened to fix the imaging camera exchange unit 200.

Next, the imaging and centering of the crack 2 by the imaging camera 15 are performed by the CCD camera 24 in the same manner as in the first embodiment.
After the position of the crack 2 is accurately aligned with the display unit 52 by the xyz table 20 using the imaging camera 15, the imaging camera replacement unit 200 is removed, and the sensor unit replacement unit 150 is mounted on the common base 100. Is done. That is, the replacement plate 151 is mounted on the common base 100, the positioning is performed by the positioning pins 153, and the thumb screw 152 is tightened to fix the sensor unit replacement unit 100. Thereafter, similarly to the first embodiment, the minute potential difference between the measurement points sandwiching the crack 2 is measured.

Note that the present invention is not limited to the above-described embodiment, and can be variously modified. For example, the contact element only needs to be pressed uniformly and uniformly, and instead of the airbag 41, a direct acting air cylinder may be used. Although the signal cable is directly connected to the measuring unit 5 in the above-described embodiment, an insulating transformer may be interposed at a position as close as possible to the sensor unit 10 to block noise.

Further, the sensor unit is covered with a metal housing, and each contact is supported by the housing via an insulating member so as to be movable in the axial direction. An insulating member is provided between the sample and the sample surface. With this configuration, noise caused by the induced magnetic field generated by the frequency of the measurement reference current flowing through the contact or the like is cut off, and accurate minute potential difference measurement is performed.

FIG. 2 is a schematic perspective view of the minute potential difference measuring device according to the first embodiment. FIG. 2 is a front view of the minute potential difference measuring device shown in FIG. 1. FIG. 2 is a side view of the minute potential difference measuring device shown in FIG. 1. FIG. 2 is a perspective view of a sensor unit provided in the minute potential difference measuring device shown in FIG. 1. FIG. 5 is a cross-sectional view of the sensor unit shown in FIG. 4. FIG. 5 is a longitudinal sectional view of the sensor unit shown in FIG. 4. FIG. 7 is a perspective view along the line VII-VII in FIG. 6. FIG. 5 is a plan view of a frame member provided in the sensor unit shown in FIG. 4. The arrow view seen from arrow IX of FIG. The arrow view seen from arrow X of FIG. FIG. 5 is a plan view of a guide block provided in the sensor unit shown in FIG. FIG. 12 is a partially cutaway side view of the guide block shown in FIG. 11. FIG. 2 is a front view of a display unit of an operation pendant provided in the minute potential difference measuring device shown in FIG. 1. FIG. 2 is a control circuit block diagram of the minute potential difference measuring device shown in FIG. 1. FIG. 9 is a schematic perspective view of a minute potential difference measuring device according to a second embodiment. FIG. 16 is a front view of the minute potential difference measuring device shown in FIG. 15. FIG. 16 is a plan view of the minute potential difference measuring device shown in FIG. 15. FIG. 16 is one side view of the minute potential difference measuring device shown in FIG. 15. FIG. 16 is another side view of the minute potential difference measuring device shown in FIG. 15. FIG. 16 is a diagram in which an imaging camera exchange unit is mounted on the minute potential difference measuring device shown in FIG. 15. FIG. 16 is a perspective view of a sensor unit mounted on the minute potential difference measuring device shown in FIG. 15. FIG. 22 is a transverse sectional view of the sensor unit shown in FIG. 21. FIG. 22 is a horizontal sectional view of the sensor unit shown in FIG. 21. FIG. 22 is a longitudinal sectional view of the sensor unit shown in FIG. 21. FIG. 22 is a partially enlarged view of a vertical section of the sensor unit shown in FIG. 21. FIG. 22 is a partially cutaway perspective view of a circuit board mounted on the sensor unit shown in FIG. 21.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Measurement object 2 Crack 3 Micro electric potential difference measuring device main body 4 Operation pendant 5 Measurement part (measurement means)
6 control part (control means)
Reference Signs List 10 Sensor unit 20 Tilt correcting mechanism 31 Housing 31a Housing box (made of metal)
31b Case cover (metal)
34 _a1 ... 34 _n1 , 34 _b1 ... 34 _n1 contact 35 Circuit board 41 Air bag (pressing mechanism)
48 spring (pressing mechanism)
50 electrode 60 signal selection circuit (switching means)
70 Contact quality judgment circuit (contact quality judgment means)
71 Gate section (switching means)
72 Resistance meter (contact resistance measuring means)
100 common base (exchange means)
150 Sensor unit exchange unit (exchange means)
156 cylindrical member 157 electrode rod 158 spring 169 insulating member 171 insulating sheet 172 insulating sheet 200 imaging camera replacement unit (replacement means)

Claims (4)

An electrode that is pressed against the sample surface to pass a high-frequency current;
At least one pair of contacts that can advance and retreat only in the sample surface direction, contact a measurement point near a surface defect at an arbitrary position on the sample surface and detect a minute potential between the measurement points,
A circuit board made of a material having flexibility to connect a circuit to the contact,
Measuring means for measuring a small potential difference generated between the measurement points based on a detection signal input from the contact via a circuit board,
Contact quality determination means for determining the quality of the contact state between each contact and the sample surface,
A pressure mechanism that presses the tip of each contact to a measurement point with a uniform force. The measuring means has a contact resistance measuring means for measuring the contact resistance between the contact and the sample surface, and a switching means for switching between the potential difference measuring means and the contact resistance measuring means,
2. The contact quality determination unit according to claim 1, wherein the quality of the contact state between each contact and the sample surface is determined based on the contact resistance value measured by the contact resistance measurement unit. 3. Small potential difference measuring device. 3. The contact quality determining means includes control means for controlling a pressing force of each contact in a pressing mechanism based on a contact resistance value measured by the contact resistance measuring means. The small potential difference measuring device according to 1. It further comprises an inclination correction mechanism for correcting the surface formed by the tips of the contacts in parallel with the sample surface,
The contact quality determining means has a control means for controlling a surface formed by the tip of each contact in the inclination correcting mechanism based on the contact resistance value measured by the contact resistance measuring means. The minute potential difference measuring device according to claim 2.

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