A device and method for measuring the minimum equivalent diameter of an irregular hole

Abstract

The present invention discloses a device for measuring the minimum equivalent diameter of an irregular hole. The device includes a measuring workbench, a support frame, a digital depth gauge, a hand sewing needle, an ammeter, a battery, and a syringe. A certain amount of water is repeatedly injected into the broken hole of the target plate to be measured. By measuring the height change of the water surface in the broken hole of the target plate to be measured, the cross-sectional area of ​​the irregular body formed by a certain amount of water in the broken hole of the target plate to be measured is calculated. The cross-sectional equivalent diameter of the irregular body can be calculated by treating the cross-sectional area as a circle. When the water surface height change value in the broken hole of the target plate to be measured is the largest, the cross-sectional area of ​​the irregular body is the smallest, and the equivalent diameter at this time is the minimum equivalent diameter of the broken hole of the target plate to be measured; the device can solve the technical problem of accurately measuring the minimum equivalent diameter of the irregular broken hole of the target plate with large deformation under the conditions of the explosion impact of the shaped charge warhead explosive and the impact of the shaped charge penetrator formed by the charge cap, and quantitatively evaluate the destructive power of the shaped charge warhead, which has important military significance.

Description

Technical Field

[0001] The present application relates to the field of measurement technology, and in particular to a device and a method for measuring the minimum equivalent diameter of an irregular hole, which is suitable for measuring the minimum equivalent diameter of an irregular hole of a certain thickness. Background Art

[0002] In order to effectively improve the destructive power against modern enemy ships, the use of shaped-charge warheads has become an important direction for the development of the torpedo industry on the basis of continuously improving the accuracy of torpedo guidance and the probability of hitting. In addition to the shock waves and bubble pulsations generated by explosives to kill underwater targets, the shaped-charge warhead of a torpedo mainly relies on the shaped-charge penetrator generated after the explosion to carry out penetrating strikes on ships and submarines, forming through holes in the hull of the target ship, causing damage to the hull of the target ship and water ingress, causing severe damage to the ammunition, equipment and personnel inside, and causing it to sink or withdraw from the battle.

[0003] The size and penetration depth of the holes caused by the shaped charge penetrator formed after the explosion of the shaped charge warhead on the target hull or deck of the ship are important parameters for evaluating the destructive power of the shaped charge warhead. The destructive power of the shaped charge warhead is usually carried out by simulated explosion tests on land or underwater, using target plates to simulate the hull or deck of the ship. Since the explosion is an extremely rapid energy release process, a sharp pressure jump occurs in the surrounding medium, and a huge impact load acts on the target plate, causing the target plate to tear or even break, and at the same time, it undergoes large explosion erosion, deformation, and warping, making the shape of the holes on the target plate extremely irregular, resulting in great difficulty in accurately measuring the diameter of the holes in the target plate, which has a great impact on the accurate evaluation of the destructive power of the shaped charge warhead.

[0004] At present, the measurement of the diameter of the hole penetrated by the shaped charge warhead in the target plate is mainly carried out by general measuring instruments such as steel ruler, tape measure, vernier caliper, etc. For irregularly shaped holes, the instrument measures the damage size of the hole in the target plate in different directions for multiple times, and takes the measured average value as the equivalent diameter of the hole. The measurement accuracy of this method is not high, and the measured result is the approximate average equivalent diameter of the hole. In addition, there is also a measurement principle based on the flow comparison method, which detects the flow of water passing through the hole of the target plate under the same initial conditions for a period of time, and compares the flow of water passing through the hole of the standard target plate under the same time conditions. If the two are the same, it can be considered that the flow area of ​​the hole of the target plate under test is equal to the flow area of ​​the standard target plate hole of the same size, that is, the equivalent diameter of the hole of the target plate under test can be obtained. The measuring device used in this method is relatively complex, the system is large, and it is inconvenient to use. The measurement result is the average equivalent diameter of the hole compared with the standard target plate hole. The measurement of the minimum equivalent diameter of irregular holes and the calculation of the lower limit of the equivalent diameter of irregular holes cannot be solved by direct measurement of general instruments and equipment or indirect measurement of flow measurement devices. Therefore, it is necessary to construct a measurement method that is suitable for measuring the minimum equivalent diameter of irregular holes to accurately quantify and evaluate the destructive power of shaped charge warheads. Summary of the invention

[0005] In order to solve the technical problem of accurately measuring the minimum equivalent diameter of irregular holes in a target plate with large deformation after being impacted by the explosive of a shaped charge warhead and penetrated by the shaped charge penetrator formed by the charge liner, and quantitatively evaluate the destructive power of the shaped charge warhead, the present invention provides a device and a method for measuring the minimum equivalent diameter of irregular holes, which adopt the following technical solutions:

[0006] The embodiment of the present invention provides a device for measuring the minimum equivalent diameter of an irregular hole, the device comprising: a measuring workbench, a support frame, a digital depth gauge, a hand sewing needle, an ammeter, a battery and a syringe;

[0007] The measuring workbench is made of conductive material and is used to place the target plate with holes to be measured. The contact gap between the cut target plate to be measured and the measuring workbench is sealed with a waterproof material.

[0008] The support frame is made of conductive material, fixed to the measuring workbench, and insulated from the measuring workbench;

[0009] One pole of the ammeter is connected and fixed to the measuring workbench, and the other pole is connected and fixed to the supporting frame;

[0010] The battery is used to provide current in the working circuit of the ammeter;

[0011] The hand sewing needle is fixed to the end of the measuring needle of the digital depth gauge, and the digital depth gauge with the hand sewing needle is fixed to the crossbeam of the support frame, and the metal part of the digital depth gauge is conductive with the metal part of the crossbeam of the support frame;

[0012] The injector is used for quantitatively injecting water into the holes of the target plate.

[0013] In some embodiments, when the device is used, the measuring workbench is in a horizontal state to ensure that the target plate to be measured is placed stably.

[0014] In some embodiments, the support frame is fixed in a manner including bolt connection, welding or clamping.

[0015] In some embodiments, the cross-sectional area of ​​the needle head of the hand-sewing needle is smaller than the cross-sectional area of ​​the measuring needle of the digital depth gauge.

[0016] In some embodiments, the digital depth gauge has a zeroing function so as to determine a water surface height reference before measurement.

[0017] In some embodiments, the quantitative water injection function of the syringe is achieved by precisely controlling the pushing force and speed of the syringe.

[0018] In some embodiments, the measurement principle includes:

[0019] Repeatedly inject a certain amount of water into the broken hole of the target plate to be tested, and calculate the cross-sectional area of ​​the irregular body formed by a certain amount of water in the broken hole of the target plate to be tested by measuring the height change of the water surface in the broken hole of the target plate to be tested. The cross-sectional equivalent diameter of the irregular body can be calculated by treating the cross-sectional area as a circle.

[0020] When the change value of the water surface height in the hole of the target plate being measured is the largest, the cross-sectional area of ​​the irregular body is the smallest, and the equivalent diameter at this time is the minimum equivalent diameter of the hole of the target plate being measured.

[0021] An embodiment of the present invention provides a measurement method using the device for measuring the minimum equivalent diameter of an irregular hole described in any of the above embodiments, characterized in that the method comprises:

[0022] Step 1, placing the target plate to be measured on the measuring workbench and sealing the contact gap with waterproof material;

[0023] Step 2, fix the support frame on the measuring workbench and ensure insulation;

[0024] Step 3, fix the hand sewing needle on the end of the digital depth gauge probe, and fix the digital depth gauge on the crossbeam of the support frame to ensure verticality and good conductivity;

[0025] Step 4, connect one pole of the ammeter to the support frame, and the other pole to the measuring workbench via the battery;

[0026] Step 5, injecting a certain amount of water close to the lower edge of the hole in the target plate to be tested;

[0027] Step 6, start the power of the digital depth gauge, and slowly lower the probe until the needle of the hand sewing needle touches the water surface;

[0028] Step 7, clear the digital depth gauge;

[0029] Step 8. Lift the measuring needle upward until the needle tip of the hand sewing needle is out of the water, tighten the locking screw of the digital depth gauge, and wipe the moisture off the hand sewing needle with a dry cotton cloth;

[0030] Step 9, inject a certain amount of water into the hole of the target plate to be tested using a syringe;

[0031] Step 10, loosen the locking screw, lower the probe again until the needle tip touches the water surface, and calculate the height difference of the water surface; calculate the height difference of the water surface

[0032] Step 11, repeat steps 8 to 10 to ensure that the amount of water injected each time remains unchanged;

[0033] Step 12, inject water until it reaches the upper edge of the hole;

[0034] Step 13, counting the water surface height change difference to obtain the maximum value Hmax;

[0035] Step 14, calculating the minimum cross-sectional area Smin of the hole in the target plate to be tested by formula (1);

[0036] V=S min ×H max ………………………………(1)

[0037] Where:

[0038] V——Volume of injected water, ml (or 1000mm 3 );

[0039] S min ——Minimum cross-sectional area of ​​the hole in the target plate to be tested, mm 2 ;

[0040] H max ——The maximum value of water surface change height, mm;

[0041] Step 15, calculating the minimum equivalent diameter D of the hole in the target plate to be tested by formula (2);

[0042] S min =0.25×π×D 2 ………………………………(2)

[0043] Where:

[0044] S min ——Minimum cross-sectional area of ​​the hole in the target plate to be tested, mm 2 ;

[0045] D is the minimum equivalent diameter of the hole in the target plate being tested, mm.

[0046] The beneficial effects of the above embodiments include:

[0047] The present invention proposes a device for measuring the minimum equivalent diameter of irregular holes, which can solve the technical problem of accurately measuring the minimum equivalent diameter of irregular holes in a large deformed target plate after being impacted by the explosive of a shaped charge warhead and the penetration of a shaped charge penetrator formed by a charge liner, and quantitatively evaluate the destructive power of a shaped charge warhead. The device and method can also be used to measure the minimum equivalent diameter of irregular holes of similar structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings illustrate generally, by way of example and not limitation, various embodiments discussed herein.

[0049] Figure 1 The present invention is a schematic diagram of the structure of a device for measuring the minimum equivalent diameter of an irregular hole according to an embodiment of the present invention.

[0050] Explanation of symbols:

[0051] 1- measuring workbench; 2- supporting frame; 3- digital depth gauge; 4- ammeter; 5- battery; 6- target plate to be measured; 7- hand sewing needle. DETAILED DESCRIPTION

[0052] In order to enable a more detailed understanding of the features and technical contents of the embodiments of the present application, the implementation of the embodiments of the present application is described in detail below in conjunction with the accompanying drawings. The attached drawings are for reference only and are not used to limit the embodiments of the present application.

[0053] In the embodiments of the present application, it should be noted that, unless otherwise specified and limited, the term "connection" should be understood in a broad sense. For example, it can be an electrical connection or a connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0054] It should be noted that the terms "first\second\third" involved in the embodiments of the present application are only used to distinguish similar objects, and do not represent a specific order for the objects. It is understandable that the specific order or sequence of "first\second\third" can be interchanged where permitted. It should be understood that the objects distinguished by "first\second\third" can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0055] The overall structure of the device for measuring the minimum equivalent diameter of irregular holes is as follows: Figure 1 As shown, a device for measuring the minimum equivalent diameter of an irregular hole in an embodiment of the present application includes: a measuring workbench 1, a support frame 2, a digital depth gauge 3, an ammeter 4, a battery 5, a hand-sewing needle 7 and a syringe.

[0056] The measuring workbench 1 and the support frame 2 are both made of conductive materials and are insulated from each other. The positive and negative poles of the ammeter 4 are respectively connected to the contact points on the support frame 2 and the measuring workbench 1, and the battery 5 is connected in series between the positive and negative poles. The ammeter 4 is a 2.5-level 0.6A3A pointer-type ammeter, and the battery 5 is a No. 1 dry cell. The digital depth gauge 3 and the support frame 2 are well conductive and firmly fixed. The end of the measuring needle of the digital depth gauge 3 and the hand-sewing needle 7 are well conductive and firmly fixed. The syringe is a 20ml plastic syringe syringe. Here, the conductive material can be metal or non-metal, as long as it can provide good conductivity and meet the structural strength of the workbench and the bracket.

[0057] Place the cut target plate 6 with irregular holes on the measuring workbench 1, and seal the contact gap between the target plate 6 and the measuring workbench 1 with waterproof sealant; fix the support frame 2 on the measuring workbench 1 near the target plate 6; fix the hand sewing needle 7 on the end of the probe of the digital depth gauge 3, and the cross-sectional area of ​​the needle of the hand sewing needle 7 is smaller than the cross-sectional area of ​​the probe of the digital depth gauge 3, so as to reduce the contact area with the water surface during measurement and improve the test accuracy. Fix the digital depth gauge 3 with the hand sewing needle on the crossbeam of the support frame 2, so that the probe of the digital depth gauge 3 is in a vertical state with the crossbeam of the support frame 2; connect and fix one pole of the ammeter 4 on the support frame 2, and connect the other pole to the battery 5 and then connect and fix it on the measuring workbench 1; inject a certain amount of water into the cavity formed by the target plate 6 and the measuring workbench 1, and stop injecting water when the water surface approaches the lower edge of the hole of the target plate 6; turn on the power switch of the ammeter 4, and start the power by pressing the switch key of the digital depth gauge 3. Slowly lower the probe of the digital depth gauge 3 until the needle of the hand-sewn needle 7 on the probe touches the water surface in the hole of the target plate 6 to be measured. At this time, the positive and negative electrodes of the ammeter 4 are connected, and the pointer of the ammeter 4 swings; tighten the locking screw of the digital depth gauge 3, and press the reset button (the reading of the digital depth gauge 3 is 0). Here, the digital depth gauge 3 has a reset function so that the water surface height reference can be determined before measurement. Then loosen the locking screw, lift the measuring needle of the digital depth gauge 3 upwards, and wipe off the moisture on the hand-sewn needle 7 with a dry cotton cloth; use a syringe to draw 20 ml of water and inject it into the hole of the target plate 6 to be measured; slowly lower the measuring needle of the digital depth gauge 3, and when the hand-sewn needle 7 on the measuring needle touches the water surface in the hole of the target plate 6 to be measured, tighten the locking screw of the digital depth gauge 3, record the reading on the digital depth gauge 3 at this time, and calculate the difference with the last recorded reading, and take the absolute value as H1; loosen the locking screw, lift the measuring needle of the digital depth gauge 3 upwards, and wipe off the moisture on the hand-sewn needle 7 with a dry cotton cloth. Use a syringe to inject 20 ml of water into the hole of the target plate 6 to be measured, slowly lower the probe of the digital depth gauge 3, and when the hand-sewn needle 7 on the probe touches the water surface in the hole of the target plate 6 to be measured, tighten the locking screw of the digital depth gauge 3, record the reading on the digital depth gauge 3 at this time, and calculate the difference with the reading recorded last time, and take the absolute value as H2; loosen the locking screw, lift the probe of the digital depth gauge 3 upwards, and wipe the water on the hand-sewn needle 7 with a dry cotton cloth; repeat this operation to obtain the height H3, H4, H5...H of the water surface rising when 20 ml of water is injected. n , find out H1~H n The maximum value in is denoted as H max ; Through the formula V = S min ×H max Calculate the maximum water surface height change H max When 20 ml of water is spread in the hole of the target plate 6 to form an irregular cross-sectional area, this area is the minimum area S of the hole of the target plate 6 to be tested.min ; Through the formula S min =0.25×π×D 2 Calculate the minimum equivalent diameter of the hole in the target plate 6 being tested.

[0058] In order to solve the technical problem of accurately measuring the minimum equivalent diameter of irregular holes in a target plate with large deformation after being impacted by the explosive of a shaped charge warhead and penetrated by the shaped charge penetrator formed by the charge liner, and quantitatively evaluate the destructive power of the shaped charge warhead, the present invention provides a device for measuring the minimum equivalent diameter of irregular holes, which adopts the following technical solutions:

[0059] A device for measuring the minimum equivalent diameter of an irregular hole is mainly composed of a measuring workbench, a support frame, a digital depth gauge, a hand sewing needle, an ammeter, a battery, and a syringe. The measuring principle is to repeatedly inject a certain amount of water into the broken hole of the target plate to be measured, and by measuring the height change of the water surface in the broken hole of the target plate to be measured, calculate the cross-sectional area of ​​the irregular body formed by a certain amount of water in the broken hole of the target plate to be measured. The cross section is regarded as a circle, and the cross-sectional equivalent diameter of the irregular body can be calculated. The smaller the amount of water injected at one time, the more times of measurement are required, and the higher the measurement accuracy.

[0060] When measuring, the operation steps are as follows:

[0061] 1) Place the target plate with irregular holes on a horizontal conductive measuring workbench, and seal the contact gap between the target plate and the measuring workbench with waterproof material (Note: For target plates with large deformation and warping, it is allowed to process the material around the holes of the target plate by cutting and turning, and only retain the local structure of the target plate including the holes, and then seal the target plate and the measuring workbench);

[0062] 2) Fix the support frame on the measuring workbench near the target plate to be measured, and make sure that the support frame and the measuring workbench are insulated;

[0063] 3) Fix the hand-sewing needle on the end of the digital depth gauge probe, and fix the digital depth gauge with the hand-sewing needle on the crossbeam of the support frame, so that the digital depth gauge probe and the crossbeam of the support frame are in a vertical state, and pay attention to the good conductivity between the metal part of the digital depth gauge and the metal part of the crossbeam of the support frame;

[0064] 4) Connect one pole of the ammeter to the support frame and the other pole to the measuring workbench. Make sure that the two poles of the ammeter are well conductive to the support frame and the measuring workbench respectively.

[0065] 5) Inject a certain amount of water into the cavity formed by the target plate and the measuring workbench until the water surface approaches the lower edge of the hole in the target plate to be measured, and stop injecting water;

[0066] 6) Turn on the power switch of the ammeter, and press the switch of the digital depth gauge to start the power supply. Slowly lower the probe of the digital depth gauge, and when the needle tip of the hand-sewing needle on the probe touches the water surface in the hole of the target plate being measured, the positive and negative poles of the ammeter are connected, the ammeter pointer swings, or its buzzer sounds. Here, you can determine that the needle tip of the hand-sewing needle touches the water surface by observing the swing of the ammeter pointer or the sound of the buzzer;

[0067] 7) Tighten the locking screw of the digital depth gauge and press the reset button.

[0068] 8) Lift the measuring needle upward until the needle tip of the hand sewing needle is out of the water, tighten the locking screw of the digital depth gauge, and wipe the moisture off the hand sewing needle with a dry cotton cloth;

[0069] 9) Use a syringe to suck a certain amount of water and inject it into the hole of the target plate to be tested;

[0070] 10) Loosen the locking screw and lower the probe again until the needle tip touches the water surface, and calculate the height difference of the water surface change; when the needle on the probe touches the water surface in the hole of the target plate to be measured, tighten the locking screw of the digital depth gauge, record the reading on the digital depth gauge at this time, and calculate the difference with the last recorded reading to take the absolute value;

[0071] 11) Repeat the above steps 8) to 10), and make sure that the amount of water injected into the hole of the target plate remains constant each time;

[0072] 12) When the water injected by the syringe reaches the upper edge of the hole in the target plate to be tested, stop injecting water;

[0073] 13) Count the difference in water surface height during the above operations and obtain the maximum value H max ;

[0074] 14) When the maximum value of the water surface height change is calculated by formula (1), a certain amount of water is distributed in the hole of the target plate to form an irregular cross-sectional area. This area is the minimum area S of the hole of the target plate to be measured. min ;

[0075] V=S min ×H max ………………………………(1)

[0076] Where:

[0077] V——Volume of injected water, ml (or 1000mm 3 );

[0078] S min ——Minimum cross-sectional area of ​​the hole in the target plate to be tested, mm 2 ;

[0079] Hmax ——The maximum value of water surface change height, mm.

[0080] 15) The minimum equivalent diameter of the hole in the target plate is calculated by formula (2).

[0081] S min =0.25×π×D 2 ………………………………(2)

[0082] Where:

[0083] S min ——Minimum cross-sectional area of ​​the hole in the target plate to be tested, mm 2 ;

[0084] D is the minimum equivalent diameter of the hole in the target plate being tested, mm.

[0085] The present invention proposes a device for measuring the minimum equivalent diameter of irregular holes, which can solve the technical problem of accurately measuring the minimum equivalent diameter of irregular holes in a large deformed target plate after being impacted by the explosive of a shaped charge warhead and the penetration of a shaped charge penetrator formed by a charge liner, and quantitatively evaluate the destructive power of a shaped charge warhead. The device and method can also be used to measure the minimum equivalent diameter of irregular holes of similar structures.

[0086] The technical solutions described in the embodiments of the present application can be combined arbitrarily without conflict.

[0087] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A device for measuring the minimum equivalent diameter of an irregular hole, characterized in that: The device comprises: a measuring workbench, a support frame, a digital depth gauge, a hand sewing needle, an ammeter, a battery and a syringe; The measuring workbench is made of conductive material and is used to place the target plate with holes to be measured. The contact gap between the cut target plate to be measured and the measuring workbench is sealed with a waterproof material. The support frame is made of conductive material, fixed to the measuring workbench, and insulated from the measuring workbench; One pole of the ammeter is connected and fixed to the measuring workbench, and the other pole is connected and fixed to the supporting frame; The battery is used to provide current in the working circuit of the ammeter; The hand sewing needle is fixed to the end of the measuring needle of the digital depth gauge, and the digital depth gauge with the hand sewing needle is fixed to the crossbeam of the support frame, and the metal part of the digital depth gauge is conductive with the metal part of the crossbeam of the support frame; The injector is used for quantitatively injecting water into the holes of the target plate.

2. The device for measuring the minimum equivalent diameter of an irregular hole according to claim 1, characterized in that: When the device is used, the measuring workbench is in a horizontal state to ensure that the target plate to be measured is placed stably.

3. The device for measuring the minimum equivalent diameter of an irregular hole according to claim 1, characterized in that: The support frame is fixed in a manner including bolt connection, welding or clamping.

4. The device for measuring the minimum equivalent diameter of an irregular hole according to claim 1, characterized in that: The cross-sectional area of ​​the needle head of the hand-sewing needle is smaller than the cross-sectional area of ​​the measuring needle of the digital depth gauge.

5. The device for measuring the minimum equivalent diameter of an irregular hole according to claim 1, characterized in that: The digital depth gauge has a zeroing function so as to determine the water surface height reference before measurement.

6. The device for measuring the minimum equivalent diameter of an irregular hole according to claim 1, characterized in that: The quantitative water injection function of the syringe is achieved by accurately controlling the pushing force and speed of the syringe.

7. The device for measuring the minimum equivalent diameter of an irregular hole according to claim 1, characterized in that: The measurement principles include: Repeatedly inject a certain amount of water into the broken hole of the target plate to be tested, and calculate the cross-sectional area of ​​the irregular body formed by a certain amount of water in the broken hole of the target plate to be tested by measuring the height change of the water surface in the broken hole of the target plate to be tested. The cross-sectional equivalent diameter of the irregular body can be calculated by treating the cross-sectional area as a circle. When the change value of the water surface height in the hole of the target plate being measured is the largest, the cross-sectional area of ​​the irregular body is the smallest, and the equivalent diameter at this time is the minimum equivalent diameter of the hole of the target plate being measured.

8. A method for measuring the minimum equivalent diameter of an irregular hole using the device for measuring the minimum equivalent diameter of an irregular hole according to any one of claims 1 to 7, characterized in that: The method comprises: Step 1, placing the target plate to be measured on the measuring workbench and sealing the contact gap with waterproof material; Step 2, fix the support frame on the measuring workbench and ensure insulation; Step 3, fix the hand sewing needle on the end of the digital depth gauge probe, and fix the digital depth gauge on the crossbeam of the support frame to ensure verticality and good conductivity; Step 4, connect one pole of the ammeter to the support frame, and the other pole to the measuring workbench via the battery; Step 5, injecting a certain amount of water close to the lower edge of the hole in the target plate to be tested; Step 6, start the power of the digital depth gauge, and slowly lower the probe until the needle of the hand sewing needle touches the water surface; Step 7, clear the digital depth gauge; Step 8. Lift the measuring needle upward until the needle tip of the hand sewing needle is out of the water, tighten the locking screw of the digital depth gauge, and wipe the moisture off the hand sewing needle with a dry cotton cloth; Step 9, inject a certain amount of water into the hole of the target plate to be tested using a syringe; Step 10, loosen the locking screw, lower the probe again until the needle tip of the hand sewing needle touches the water surface, and calculate the height difference of the water surface change; The water surface calculates the height difference of the water surface change in step 11, and repeats steps 8 to 10 to ensure that the amount of water injected each time remains unchanged; Step 12, inject water until it reaches the upper edge of the hole; Step 13, counting the water surface height change difference to obtain the maximum value Hmax; Step 14, calculating the minimum cross-sectional area Smin of the hole in the target plate to be tested by formula (1); V=S min ×H max ………………………………(1) Where: V——Volume of injected water, ml (or 1000mm 3 ); S min ——Minimum cross-sectional area of ​​the hole in the target plate to be tested, mm 2 ; H max ——The maximum value of water surface change height, mm; Step 15, calculating the minimum equivalent diameter D of the hole in the target plate to be tested by formula (2); S min =0.25×π×D 2 ……………………………(2) Where: S min ——Minimum cross-sectional area of ​​the hole in the target plate to be tested, mm 2 ; D is the minimum equivalent diameter of the hole in the target plate being tested, mm.

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