JP6228285B1 - Air leak inspection apparatus and method - Google Patents

Abstract

[PROBLEMS] To inspect leaks with accuracy close to that of a conventional air leak detector, easy to handle, and close to that of a helium leak detector. An air leak inspection device that does not break or break down is provided. A vacuum pump 3, an exhaust pipe 4, and a vacuum gauge 6 are provided. A shutoff valve V0 is provided in the exhaust pipe downstream of the vacuum gauge. An exhaust narrow pipe 5 having a diameter smaller than that of the exhaust pipe, branched from the upstream side of the shut-off valve, and connected to the downstream side of the shut-off valve is provided. When the shutoff valve is opened, the object to be inspected is exhausted through the exhaust pipe and the exhaust narrow pipe, and the shutoff valve is closed after the detected pressure of the vacuum gauge reaches the first threshold, the detected pressure of the vacuum gauge is the first If a second threshold value greater than the threshold value is exceeded, it is determined that there is a leak. [Selection] Figure 1

Description

  The present invention relates to an air leak inspection apparatus and method for inspecting the presence or absence of leakage of an object to be inspected such as a vacuum device, a pressurizing device, and a sealing device.

In general, leak inspection includes submerged inspection, inspection using an air leak detector and a helium leak detector. There are two types of air leak detectors: a pressure type and a suction type (negative pressure type). In the pressurization method, the object to be inspected is filled with a detection gas and pressurized, and leakage is inspected by a decrease in pressure. In the suction type, the object to be inspected is evacuated to a vacuum, and leakage is inspected by increasing the pressure. These air leak detectors can inspect for leaks up to about 1 × 10 ⁻⁶ Pa · m ³ / sec. The helium leak detector is for detecting helium leaked by filling the object to be inspected with helium, and can inspect small leaks up to about 1 × 10 ⁻¹⁰ Pa · m ³ / sec.

  Air leak detectors are cheap and easy to handle, but their accuracy is low. The helium leak detector is highly accurate, but is very expensive and has a high running cost because helium gas is used. In addition, because it has precision and dirt-sensitive components such as analysis tubes, high vacuum pumps, liquid nitrogen coolers, etc., inspecting an inspected object with a large amount of leakage or water or oil will result in reduced accuracy or failure. There are problems such as being easy to repair and requiring a lot of labor for repair.

  Patent Document 1 describes a leak inspection apparatus that replaces a submersion type inspection provided with a housing that is in close contact with a portion to be inspected of an object to be inspected. However, since a flow meter is used, accuracy is higher than that of an air leak detector or a helium detector. Is bad.

  In Patent Document 2, before inspecting a small leak by the helium mass spectrometer leak detector, the gas from the inspection unit is drawn into the expansion chamber of the non-helium expansion leak detector, and the pressure in the expansion chamber is measured. An inspection device for inspecting large leaks of parts is described. Although the apparatus of Patent Document 2 can inspect a wide range of leaks, there is a problem that the apparatus is complicated and expensive because there are many pumps.

  In Patent Document 3, in the helium leak inspection method, when helium is present, the heat is taken from the platinum filament of the Pirani vacuum gauge and the measured value of the vacuum pressure changes, and the leak is inspected only by the Pirani vacuum gauge. Things are listed.

  Patent Document 4 describes a helium leak detector using a sniffer probe that traces an object to be inspected and sucks helium gas, and controls the amount of flow into the analysis section of the leak detector with a variable orifice valve.

  However, since the patent document 3 and the patent document 4 also use helium gas, the above-mentioned problem is not solved.

JP 7-146199 A (Patent No. 3390981) Utility Kaihei 5-69653 Japanese Patent Laid-Open No. 5-118949 Japanese Utility Model Publication No. 7-41441

  The present invention has been made in view of such conventional problems, and is less expensive than conventional air leak detectors, is easy to handle, can inspect for leaks with accuracy close to that of a helium leak detector, It is an object of the present invention to provide an air leak inspection apparatus and method in which the accuracy of a test object that has not been sufficiently removed to a level necessary for maintaining the accuracy of the helium leak detector does not deteriorate or fail.

  Since the conventional air leak detector closes the valve immediately after pressurization or suction, it does not appear in the change in pressure except for a large leak due to the influence of adiabatic compression or adiabatic expansion and is hidden. Therefore, the present inventor has obtained knowledge that a leakage amount (leak) larger than the minute flow rate can be detected by switching the exhaust speed from a large flow rate to a minute flow rate without blocking the exhaust path.

Based on the above knowledge, the air leak inspection apparatus according to the present invention is:
A vacuum pump, an exhaust pipe having one end connected to the object to be inspected and the other end connected to the vacuum pump, and a vacuum gauge connected to the exhaust pipe and detecting the pressure in the object to be inspected, An air leak inspection apparatus that inspects the presence or absence of leakage of the inspection object by increasing the detection pressure of the vacuum gauge after the inspection object is evacuated by a vacuum pump,
A shut-off valve is provided downstream of the vacuum gauge of the exhaust pipe,
The exhaust pipe has a smaller diameter, branches from the upstream side of the shut-off valve, and is provided with an exhaust thin pipe connected to the downstream side of the shut-off valve,
When the shut-off valve is closed and the shut-off valve is closed after the detected pressure of the vacuum gauge reaches the first threshold after the shut-off valve is opened and the inspection object is exhausted through the exhaust pipe and the exhaust narrow pipe. A control unit is provided that determines that there is a leak when the pressure detected by the meter exceeds a second threshold value greater than the first threshold value.

  When the object to be inspected is evacuated with the exhaust pipe and the exhaust narrow pipe, and the pressure of the vacuum gauge reaches the first threshold value, the shut-off valve is closed, and the exhaust continues only with the exhaust thin pipe. The flow rate exhausted by the exhaust thin tube depends on the conductance and the pressure on both sides of the exhaust thin tube. If there is a leak in the inspection object and the leak amount is larger than the exhaust speed of the exhaust thin tube, the pressure of the exhaust tube rises. If the amount of leakage is small, the exhaust pipe is exhausted, so the pressure in the exhaust pipe does not increase. If the pressure of the vacuum gauge is larger than the second threshold, it can be judged that there is a leak, and if it is smaller than the second threshold, it is judged that there is no leak.

  The exhaust thin tubes are preferably composed of a plurality of exhaust thin tubes having different conductances connected in parallel, and each of the plurality of exhaust thin tubes is connected to the downstream side of the shutoff valve via an on-off valve. In this case, the combined conductance of the exhaust pipe can be changed stepwise by selecting an on-off valve.

It is preferable to further have a clean gas introduction part for introducing clean gas into the object to be inspected via the exhaust pipe. When the object to be inspected was evacuated by the vacuum pump, the temperature decreased due to adiabatic expansion, and then the pressure was increased by being heated by the surrounding air, but once the object to be inspected was exhausted to 100 Pa or less, 100, By introducing a clean gas such as nitrogen (N ₂ ) up to 000 to 110,000 Pa, the influence of water, oil, and adiabatic expansion phenomenon can be reduced. That is, by introducing clean gas, adiabatic compression is caused to heat the object to be inspected, and water and oil are evaporated and exhausted.

The vacuum pump is preferably a medium vacuum region pump having an ultimate pressure of 0.1 to 100 Pa. In the present invention, since a small amount of leakage is exhausted through the exhaust thin tube, a rotary pump having an ultimate pressure of about 0.1 to 100 Pa may be used, which is expensive and can reach a vacuum degree of 10 ⁻² Pa or less like a helium leak detector. There is no need to use a mechanical booster pump or diffusion pump.

An air leak inspection method according to the present invention includes:
Exhaust the object to be inspected with an exhaust pipe connected to the object to be inspected and an exhaust narrow pipe having a diameter smaller than that of the exhaust pipe,
After the pressure of the object to be inspected reaches a first threshold after a predetermined time, the exhaust pipe is stopped and exhausted only by the exhaust narrow pipe,
When the pressure of the object to be inspected exceeds a second threshold value greater than the first threshold value, it is determined that there is a leak.

  It is preferable that after the exhaust through the exhaust pipe is stopped, a clean gas is introduced into the object to be inspected through the exhaust pipe.

  According to the present invention, a small leak amount of the object to be inspected is released by an exhaust thin tube that is thinner than the exhaust pipe. A vacuum pump can be used. For this reason, the price of the air leak detector is less than or equal to that of the conventional air leak detector, it is easy to handle, and the leak can be inspected with an accuracy close to that of a helium leak detector. It has the effect that it does not break down.

1 is a system diagram of an air leak inspection apparatus according to a first embodiment of the present invention. The figure which shows the time change of the detection pressure by the air leak test | inspection apparatus of FIG. The flowchart which shows operation | movement of the air leak test | inspection apparatus of FIG. The systematic diagram of the air leak test | inspection apparatus which concerns on 2nd Embodiment of this invention. The figure which shows the time change of the detection pressure by the air leak test | inspection apparatus of FIG. 5 is a flowchart showing the operation of the air leak inspection apparatus of FIG. The flowchart following FIG. The systematic diagram of the air leak test | inspection apparatus which concerns on 3rd Embodiment of this invention. The figure which shows the time change of the detection pressure by the air leak test | inspection apparatus of FIG. The flowchart which shows operation | movement of the air leak test | inspection apparatus of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 shows an air leak inspection apparatus 1a according to a first embodiment of the present invention. The air leak inspection apparatus 1 a is for inspecting a leak of the object 2 to be inspected, and includes a vacuum pump 3, an exhaust pipe 4, an exhaust thin tube 5, a vacuum gauge 6, and a control unit 7.

  The inspected object 2 is an inspection target of an air leak inspection. In the present invention, various devices such as vacuum equipment having a vacuum exhausted space such as a thermos bottle or a vacuum jacket, a pressure equipment having a pressure space such as a pressure vessel, a sealing equipment having an airtight or liquid tight sealing portion, etc. It can be the subject of inspection. FIG. 1 shows a vacuum vessel to which a tip tube 2b communicating with a space 2a to be evacuated is connected.

The vacuum pump 3 may be a rotary pump that can evacuate the device under test 2 to a vacuum of about 4 × 10 ⁻¹ Pa (3 × 10 ⁻³ Torr), and does not require a mechanical booster pump or a diffusion pump.

The exhaust pipe 4 is made of a stainless steel pipe and has an inner diameter of 10 to 100 mm. The inner diameter of the exhaust pipe 4 may be selected according to the exhaust volume of the device 2 to be inspected, but is 20 to 25 mm when the exhaust capacity is 1 liter. One end of the exhaust pipe 4 is connected to the tip pipe 2 b of the device under test 2, and the other end is connected to the vacuum pump 3. Hereinafter, when the object to be inspected 2 is exhausted by the vacuum pump 3 through the exhaust pipe 4, the inspected object side in the exhaust direction of the exhaust pipe 4 is referred to as “upstream side”, and the vacuum pump side is referred to as “downstream side”. A filter 8 is provided on the upstream side of the exhaust pipe 4, and a shut-off valve V0 is provided on the downstream side. A first branch pipe 4a is provided downstream from the filter 8, and a second branch pipe 4b is provided downstream from the shutoff valve V0. On the upstream side of the shutoff valve V0 of the exhaust pipe 4, a clean gas is introduced into the exhaust pipe 4, that is, the inspection object 2 by introducing, for example, nitrogen (N ₂ ), carbon dioxide gas (CO ₂ ), argon (Ar) or the like as a clean gas. A gas introduction part 9 is provided.

  The exhaust thin tube 5 is made of a stainless steel tube or a copper tube, is narrower than the exhaust tube 4, and has an inner diameter of 1 to 6 mm. One end of the exhaust thin tube 5 is connected to the first branch pipe 4 a of the exhaust pipe 4, and the other end is connected to the second branch pipe 4 b of the exhaust pipe 4 via the on-off valve V. The exhaust narrow pipe 5 may be directly connected to the exhaust pipe 4 without providing the first branch pipe 4a and the second branch pipe 4b.

  As the vacuum gauge 6, a Pirani vacuum gauge or a thermocouple vacuum gauge can be adopted, but a Pirani vacuum gauge is preferable. The Pirani gauge obtains the pressure from the change in the resistance value of the platinum wire that has been deprived of heat by the collision of gas molecules. The sensor unit 6 a of the vacuum gauge 6 is connected to the vicinity of the first branch pipe 4 a on the downstream side of the filter 8. The main body 6b of the vacuum gauge 6 detects and displays the pressure (degree of vacuum) in the exhaust pipe 4, that is, the object to be inspected 2, and outputs a digital value of the detected pressure to the control unit 7 described later.

  The control unit 7 controls the opening and closing of the shutoff valve V0 and the on-off valve V based on the detected pressure output from the vacuum gauge 6 by sequence control, determines whether or not the inspection object 2 has leaked, and displays the display unit. 10 indicates whether or not there is a leak.

Here, a method of selecting the diameter D and the length L of the exhaust thin tube 5 will be described. Exhaust resistance occurs when gas flows through the pipe during exhaust, and in order to show the ease of pipe flow, the inverse of the exhaust resistance is taken and this is called conductance. When the conductance is C [m ³ / s] and the pressures at both ends of the pipe are P ₁ [Pa] and P ₀ [Pa], the flow rate Q [Pa · m ³ / s] is expressed by Equation 1.

(Equation 1)
_{Q = C (P 1 -P 0} )

Assuming that the gas flow in the pipe is a viscous flow region, P = (P ₁ + P ₀ ) / 2 [Pa], the pipe diameter (inner diameter) is D [m], and the pipe length is L [m]. And long pipe conductance C [m ³ / s] is expressed by Equation 2 (Hirohiko Senda, “Theoretical calculation of vacuum evacuation in viscous flow region and its application”, January 2010, SEI Technical Review, No. 176 Issue, page 2).

(Equation 2)
C = 1349D ⁴ P / L

  Assuming that the flow rate Q is an allowable leakage amount of the object 2 to be inspected, the pressures P1 and P2 at both ends of the exhaust thin tube 5 are assumed according to the situation, and the diameter D of the exhaust thin tube 5 is fixed, The length L of the thin tube 5 can be determined. Further, when the length L of the exhaust thin tube 5 is fixed, the diameter D of the exhaust thin tube 5 can be determined. When the diameter D of the exhaust thin tube 5 and the length L of the pipe are fixed, the allowable leakage amount Q can be determined.

For example, assuming that the pressures P1 and P2 at both ends of the exhaust thin tube 5 are 10 Pa and 1 Pa, respectively, and the exhaust thin tube 5 has an outer diameter of 4 mm, a wall thickness of 0.45 mm, and a length of 50 cm,
P = (10 + 1) /2=5.5 [Pa]
D = (4-0.45 × 2) × 10 ⁻³ = 3.1 × 10 ⁻³ [m]
L = 0.5 [m]
Therefore, the conductance C and the flow rate Q are as follows.
C = 1349 × (3.1 × 10 ⁻³ ) ⁴ × 5.5 / 0.5
= 1.370 × 10 ⁻⁶ [m ³ / s]
Q = 1.370 × 10 ⁻⁶ × (10−1)
= 12.33 × 10 ⁻⁶ [Pa · m ³ / s]

In this case, the presence or absence of a leak can be inspected based on the flow rate Q = 12.33 × 10 ⁻⁶ [Pa · m ³ / s]. That is, in the present invention, if there is an amount of leakage exceeding the flow rate Q of the exhaust thin tube 5, an increase in the pressure P2 (decrease in the degree of vacuum) on the inspection object 2 side of the exhaust thin tube 5 is observed, and the inspection object 2 leaks. It can be judged that there is (leakage). On the contrary, if there is a leakage amount equal to or less than the flow rate Q, the exhaust gas is exhausted through the exhaust thin tube 5, so there is no increase in the pressure P2 (decrease in the degree of vacuum) on the inspection object 2 side of the exhaust thin tube 5. 2 can be determined to have no leak.

  Next, the operation of the air leak inspection apparatus 1b of the first embodiment will be described based on the pressure change diagram of FIG. 2 and the flowchart of FIG. In the following description and drawings, the opening of the shut-off valve V0 and the on-off valve V is indicated by “◯”, and the closing is indicated by “x”.

In FIG. 3, both the shut-off valve V0 and the on-off valve V are opened in step 101, and the vacuum pump 3 is driven in step 102. As a result, the air in the space 2 a of the device under test 2 is exhausted to the outside from the vacuum pump 3 through the exhaust pipe 4 and the exhaust thin pipe 5. Therefore, as shown in FIG. 2, the pressure detected by the vacuum gauge 6 decreases. In step 103, it is determined whether t1 seconds (for example, 24 seconds) have elapsed since the vacuum pump 3 was driven. If not, exhausting by the vacuum pump 3 is continued. If t1 seconds have elapsed, the pressure P1 of the vacuum gauge 6 is read in step 104. In step 105, it is determined whether or not the pressure P1 is equal to or lower than a predetermined first threshold value Pth1. In this embodiment, the first threshold value Pth1 is 4 × 10 ⁻¹ Pa (3 × 10 ⁻³ Torr). When the pressure P1 exceeds the first threshold value Pth1 as indicated by a two-dot chain line in FIG. 2, it is considered that the exhaust is insufficient due to leakage (leakage) of the inspection object 2, and there is a leak at step 106. It is determined that (leak level: L1). If the pressure P1 is equal to or lower than the first threshold value Pth1, there is no significant leakage and exhaust is sufficiently performed. Therefore, in step 107, the shutoff valve V0 is closed and the on-off valve V is kept open. When the shut-off valve V0 is closed at the time t1, it is cooled by the adiabatic expansion inside the object 2 to be inspected, but since it is heated by the surrounding air and the water and the oil part in the space 2a of the object 2 are evaporated, As shown in FIG. 2, the detected pressure of the vacuum gauge 6 increases for a while (ta).

  Exhaust by the exhaust pipe 4 is stopped by shutting off the shut-off valve V0, but since the on-off valve V is open, exhaust by the exhaust narrow pipe 5 continues. However, since the conductance of the exhaust pipe 5 is smaller than the conductance of the exhaust pipe 4, the flow rate is limited. When the pressure P1 is reached and the shut-off valve V0 is closed, if there is no leak in the object 2 to be inspected, there is no flow in the exhaust thin tube 5, and the vacuum gauge 6 is set as indicated by a two-dot chain line y in FIG. The degree of vacuum to be detected is maintained at P1 + α. If there is a leak in the inspection object 2 and the leak amount is less than or equal to the allowable flow rate of the exhaust thin tube 5, the leak amount is exhausted from the vacuum pump 3 through the exhaust thin tube 5. The change is small. Further, if there is a leak in the inspection object 2 and the leakage amount is not less than the allowable flow rate of the exhaust thin tube 5, the leakage amount does not pass through the exhaust thin tube 5, so that the pressure in the inspection object 2 and the exhaust pipe 4 is reduced. As a result of the large change, the pressure detected by the vacuum gauge 6 increases.

  Therefore, in step 108, it is determined whether t2 seconds (tb (tb> ta) since closing the shutoff valve V0) has elapsed since the vacuum pump 3 was driven. If t2 seconds have elapsed, the pressure P2 of the vacuum gauge 6 is read in step 109. In step 110, it is determined whether or not the pressure P2 is equal to or less than a predetermined second threshold value Pth2. As indicated by a two-dot chain line z in FIG. 2, when the pressure P2 exceeds the second threshold value Pth2, the pressure increases due to leakage of the object 2 to be inspected, and the degree of vacuum is considered to be worse. In step 111, it is determined that there is a leak (leak level: L2). When the pressure P2 is less than or equal to the second threshold value Pth2, it is determined in step 112 that the leak (leakage) of the device under test 2 is less than the allowable value, it is determined that there is no leak, and the inspection is terminated.

  If there is no exhaust narrow tube as in the past, after closing the exhaust pipe shutoff valve, regardless of the size of the leak, if there is a leak, the pressure detected by the vacuum gauge will rise, so the allowable leak However, it is determined that there is a leak. However, in the present invention, when the leak amount is equal to or less than the allowable leak by the exhaust narrow tube 5, the leak amount is exhausted from the exhaust narrow tube 5, so that the detected pressure of the vacuum gauge 6 does not increase and it is determined that there is no leak. Therefore, compared with a conventional leak inspection apparatus that has been determined to be defective even if there is an allowable leak, the leak inspection apparatus according to the present invention can determine that the allowable leak or less is a non-defective product. High inspection accuracy.

When water or oil adheres to the space 2a of the inspection object 2, as shown by a dotted line in FIG. 2, the inspection object 2 is once exhausted to 100 Pa or less by the vacuum pump 3, and then the clean gas is introduced. The unit 9 is operated to introduce clean gas such as nitrogen (N ₂ ), carbon dioxide gas (CO ₂ ), argon (Ar), etc. into the object 2 to be inspected 2 through the exhaust pipe 4 to 100,000 to 110,000 Pa. can do. By introducing clean gas, the object to be inspected 2 is heated by adiabatic compression, and water and oil are evaporated and discharged. As a result, an increase in pressure due to the influence of adiabatic expansion after reaching the pressure P1 can be reduced. it can.

Second Embodiment
FIG. 4 shows an air leak inspection apparatus 1b according to the second embodiment of the present invention. This air leak inspection apparatus 1b has the same configuration as the air leak inspection apparatus 1a of the first embodiment except that a plurality of exhaust thin tubes 5a, 5b, and 5c are connected in parallel with the exhaust pipe 4, and therefore corresponding parts Are denoted by the same reference numerals and description thereof is omitted.

  The first, second, and third exhaust tubules 5a, 5b, and 5c of the air leak inspection apparatus 1b of the second embodiment have a length L1, a length L2, and a length L3, respectively, and the diameters are all the same. (L1> L2> L3). One end of the first narrow exhaust pipe 5a is connected to the first branch pipe 4a, and the other end is connected to the second branch pipe 4b via the first on-off valve V1 and the pipe 4c, and communicates with the exhaust pipe 4. Similarly, one end of the second exhaust narrow pipe 5b is connected to the first branch pipe 4a, and the other end is connected to the second branch pipe 4b via the second on-off valve V2 and the pipe 4d, and communicates with the exhaust pipe 4. ing. One end of the third exhaust narrow pipe 5c is connected to the first branch pipe 4a, and the other end is connected to the second branch pipe 4b via the third on-off valve V3 and the pipe 4e and communicates with the exhaust pipe 4.

In the second embodiment, the first, second, and third exhaust valves 5a, 5b, and 5c are appropriately combined by opening and closing the first, second, and third on-off valves V1, V2, and V3. The combined conductance of the second and third exhaust tubules 5a, 5b, and 5c can be changed to increase the leak level. When the exhaust resistances of the exhaust thin tubes 5a, 5b, and 5c are R1, R2, and R3, the combined exhaust resistance R and the conductance C of the exhaust thin tubes 5a, 5b, and 5c connected in parallel are expressed by the following equation (3).
(Equation 3)
1 / R = 1 / R1 + 1 / R2 + 1 / R3
C = C1 + C2 + C3

  First, when the leakage amount is larger than the flow rate of the combination of the exhaust thin tubes 5a, 5b, and 5c having the largest combined conductance C, there is a leakage, and when the leakage amount is small, the exhaust gas is exhausted through the exhaust thin tubes 5a, 5b, and 5c. Next, the leak of the device under test 2 can be inspected for each level of the leak amount by decreasing the synthetic conductance C step by step and determining the presence or absence of the leak.

The diameter and length of the first exhaust thin tube 5a are D1 and L1, the diameter and length of the second exhaust thin tube 5b are D2 and L2, and the diameter and length of the third exhaust thin tube 5c are D3 and L3, and D1 = D2 = If D3 and L1> L2> L3, then C1 <C2 <C3. Therefore, the first on-off valve V1, the second on-off valve V2, and the third on-off valve V3 are closed in the order shown in Table 1.

  Next, the operation of the air leak inspection apparatus 1b of the second embodiment will be described based on the pressure change diagram of FIG. 5 and the flowcharts of FIGS.

  In FIG. 6, in step 201, the shutoff valve V0, the first on-off valve V1, the second on-off valve V2, and the third on-off valve V3 are all opened, and in step 202, the vacuum pump 3 is driven. Thereby, the air in the space 2a of the device under test 2 is exhausted from the vacuum pump 3 to the outside through the exhaust pipe 4 and the first, second, and third exhaust thin tubes 5a, 5b, and 5c. Therefore, as shown in FIG. 5, the pressure detected by the vacuum gauge 6 decreases. In step 203, it is determined whether t1 seconds have elapsed since the vacuum pump 3 was driven. If not, exhausting by the vacuum pump 3 is continued. If t1 seconds have elapsed, in step 204, the pressure P1 of the vacuum gauge 6 is read. In step 105, it is determined whether or not the pressure P1 is equal to or lower than a predetermined first threshold value Pth1. If the pressure P1 exceeds the first threshold value Pth1, it is determined in step 206 that there is a leak (leak level: L1).

  If the pressure P1 is less than or equal to the first threshold value Pth1, in step 207, the shutoff valve V0 is closed, and the first on-off valve V1, the second on-off valve V2, and the third on-off valve V3 are kept open. In step 208, it is determined whether t2 seconds (tb (tb> ta) since closing of the shutoff valve V0) has elapsed since the vacuum pump 3 was driven. If not, the process waits for t2 seconds. If elapses, the pressure P2 of the vacuum gauge 6 is read in step 209. In step 210, it is determined whether or not the pressure P2 is equal to or lower than a predetermined second threshold value Pth2. If the pressure P2 exceeds the second threshold value Pth2, it is determined in step 211 that there is a leak (leak level: L2).

  If the pressure P2 is less than or equal to the first threshold value Pth2 in step 210, in step 212 and subsequent steps, one of the first on-off valve V1, the second on-off valve V2, and the third on-off valve V3 is closed, and the exhaust thin tubes 5a, 5b, The conductance of 5c is reduced stepwise, the pressure of the vacuum gauge 6 is read after t3 seconds (tc (tc> tb> ta) after closing the shutoff valve V0) after the vacuum pump 3 is driven, Compared with the threshold value Pth3, the same steps are repeated until a leak occurs. Note that the pressure may be reduced by driving the vacuum pump 3 each time the first on-off valve V1, the second on-off valve V2, and the third on-off valve V3 are switched.

  Even if the first on-off valve V1 is opened, the second on-off valve V2 and the third on-off valve V3 are closed at step 237 in FIG. 7 to minimize the conductance, the pressure P8 is equal to or lower than the eighth threshold value Pth8 at step 240. In this case, it is determined in step 242 that the leak (leakage) of the device under test 2 is below an allowable level, it is determined that there is no leak, and the inspection is terminated.

As in the first embodiment, when water or oil adheres to the inspection object 2, the inspection object 2 is once evacuated to 100 Pa or less by the vacuum pump 3, and then the clean gas introduction unit 9 is used. Thus, a clean gas such as nitrogen (N ₂ ), carbon dioxide (CO ₂ ), argon (Ar) or the like can be introduced into the device under test 2.

<Third Embodiment>
FIG. 1 shows an air leak inspection apparatus 1c according to a third embodiment of the present invention. Since this air leak inspection apparatus 1c has the same configuration as the air leak inspection apparatus 1b of the second embodiment except that the control unit 7 is provided with the level setting unit 11, the corresponding parts are denoted by the same reference numerals. The description is omitted.

  In the air leak inspection apparatus 1c of the third embodiment, the level setting unit 11 allows the user to set the leak level in advance, and the first, second, and third on-off valves V1, V2 are set according to the set leak level. The combined conductance C of the exhaust thin tubes 5a, 5b, 5c is changed in accordance with the set leak level by appropriately combining the first, second, and third exhaust thin tubes 5a, 5b, 5c by opening and closing V3. The leak can be inspected at the set leak level. In addition, the inspection result based on the set leak level can be viewed, the leak level can be changed, and the inspection can be performed again.

  Next, the operation of the air leak inspection apparatus 1c of the third embodiment will be described based on the pressure change diagram of FIG. 9 and the flowchart of FIG.

  First, in step 301, the leak level set by the level setting unit 11 is read. In step 302, the shutoff valve V0, the first on-off valve V1, the second on-off valve V2, and the third on-off valve V3 are all opened, and in step 303, the vacuum pump 2 is driven. In step 304, it is determined whether t1 seconds have elapsed since the vacuum pump 3 was driven. If not, exhausting by the vacuum pump 3 is continued. If t1 seconds have elapsed, the pressure P1 of the vacuum gauge 6 is read in step 305. In step 306, it is determined whether or not the pressure P1 is equal to or lower than a predetermined first threshold value Pth1. If the pressure P1 exceeds the first threshold value Pth1, it is determined in step 307 that there is a leak (leak level: L1).

  If the pressure P1 is less than or equal to the first threshold value Pth1, in step 308, the first on-off valve V1, the second on-off valve V2, and the third on-off valve V3 are opened / closed according to the leak level set by the level setter 1. In step 309, it is determined whether ts seconds have elapsed since the vacuum pump 3 was driven. If not, exhausting by the vacuum pump 3 is continued. If ts seconds have elapsed, the pressure Ps of the vacuum gauge 6 is read in step 310. In step 311, it is determined whether or not the pressure Ps is equal to or lower than a predetermined first threshold value Pths. If the pressure Ps exceeds the first threshold value Pths, it is determined in step 312 that there is a leak (leak level: Ls (set leak level)). If the pressure Ps is equal to or lower than the first threshold value Pths, it is determined in step S313 that there is no leak. In step 314, it is determined whether there is a change in the leak level. If there is a change in the leak level, the leak level is read in step 315, the process returns to step 308, and the same steps are repeated. If there is no change in the leak level, the process ends.

As in the first embodiment, when water or oil adheres to the inspection object 2, the inspection object 2 is once evacuated to 100 Pa or less by the vacuum pump 3, and then the clean gas introduction unit 9 is used. Thus, a clean gas such as nitrogen (N ₂ ), carbon dioxide (CO ₂ ), argon (Ar) or the like can be introduced into the device under test 2.

  The present invention is not limited to the embodiments described above, and can be modified within the scope of the invention described in the claims. For example, in FIG. 1, FIG. 4, and FIG. 8, an on-off valve is provided between the tip tube 2b and the filter 8, and the downstream side of the on-off valve is evacuated to keep the path clean even when the inspection is stopped. You may do it.

DESCRIPTION OF SYMBOLS 1a, 1b, 1c ... Air leak test | inspection apparatus 2 ... Inspected object 2a ... Space 2b ... Tip pipe 3 ... Vacuum pump 4 ... Exhaust pipe 4a ... First branch pipe 4b ... Second branch pipe 4c ... Piping 4d ... Piping 4e ... Piping DESCRIPTION OF SYMBOLS 5 ... Exhaust thin tube 5a ... 1st exhaust thin tube 5b ... 2nd exhaust thin tube 5c ... 3rd exhaust thin tube 6 ... Vacuum gauge 7 ... Control part 8 ... Filter 9 ... Clean gas introduction part 10 ... Display part 11 ... Level setting part V0 ... Shutoff valve V ... Open / close valve V1 ... First open / close valve V2 ... Second open / close valve V3 ... Third open / close valve

Claims (6)

A vacuum pump, an exhaust pipe having one end connected to the object to be inspected and the other end connected to the vacuum pump, and a vacuum gauge connected to the exhaust pipe and detecting the pressure in the object to be inspected, An air leak inspection apparatus that inspects the presence or absence of leakage of the inspection object by increasing the detection pressure of the vacuum gauge after the inspection object is evacuated by a vacuum pump,
A shut-off valve is provided downstream of the vacuum gauge of the exhaust pipe,
The exhaust pipe has a smaller diameter, branches from the upstream side of the shut-off valve, and is provided with an exhaust thin pipe connected to the downstream side of the shut-off valve,
When the shut-off valve is closed and the shut-off valve is closed after the detected pressure of the vacuum gauge reaches the first threshold after the shut-off valve is opened and the inspection object is exhausted through the exhaust pipe and the exhaust narrow pipe. An air leak inspection apparatus, comprising: a control unit that determines that there is a leak when a pressure detected by a meter exceeds a second threshold value that is greater than the first threshold value.   The exhaust thin pipe is composed of a plurality of exhaust thin pipes having different conductances connected in parallel, and the plurality of exhaust thin pipes are connected to the downstream side of the shut-off valve via open / close valves, respectively. The air leak inspection apparatus according to 1.   The air leak inspection apparatus according to claim 1, further comprising a clean gas introduction unit for introducing clean gas into the object to be inspected via the exhaust pipe.   The air leak inspection apparatus according to any one of claims 1 to 3, wherein the vacuum pump is a medium vacuum region pump having an ultimate pressure of 0.1 to 100 Pa. Exhaust the object to be inspected with an exhaust pipe connected to the object to be inspected and an exhaust narrow pipe having a diameter smaller than that of the exhaust pipe,
After the pressure of the object to be inspected reaches a first threshold after a predetermined time, the exhaust pipe is stopped and exhausted only by the exhaust narrow pipe,
An air leak inspection method for determining that there is a leak when the pressure of the object to be inspected exceeds a second threshold value greater than the first threshold value.   6. The air leak inspection method according to claim 5, wherein after the exhaust through the exhaust pipe is stopped, a clean gas is introduced into the object to be inspected through the exhaust pipe.

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