Leak inspection method and leak inspection device

Abstract

To provide a leak inspection method and leak inspection device capable of accurately inspecting an air leak in an inspection object in a short time.SOLUTION: A leak inspection method for inspecting an air leak in an inspection object that has an internal space which is depressurized to a prescribed vacuum level and sealed airtightly, includes: a light projection step of projecting excitation light from the outside of the internal space onto a pressure-sensitive paint whose light emission intensity changes due to a change in the oxygen concentration in the internal space; a measurement step of measuring the attenuation speed of the light emission intensity; and a determination step of determining the presence of an air leak when the attenuation speed exceeds a predetermined threshold.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a leak inspection method and a leak inspection device. [Background technology]

[0002] An optical oxygen concentration measurement method is known in which a light-emitting layer that emits light in response to excitation light and an absorbing dye layer whose light absorption spectrum changes depending on the degree of bonding with oxygen molecules, which changes depending on the oxygen concentration, are combined, and the oxygen concentration is measured by detecting the light intensity of output light that changes based on the fact that incident light for causing the light-emitting layer to emit light or emitted light from the light-emitting layer is partially absorbed when passing through the absorbing dye layer (Patent Document 1).

[0003] A pressure field measurement process in which the pressure distribution on the surface of an object in contact with a fluid is optically measured using pressure-sensitive paint, and a velocity field measurement process in which visible particles are dispersed in the fluid to optically measure the spatial behavior of the fluid, are simultaneously performed, and the pressure field and velocity field information for the same event are treated as information correlated in the time direction. A fluid measurement method in which the fluid is acquired by measuring the fluid pressure is also known (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-28650 A [Patent Document 2] JP 2013-79878 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a leak inspection method and leak inspection device capable of inspecting an object to be inspected for air leaks with high accuracy and in a short time. [Means for solving the problem]

[0006] In order to solve the above problem, the leak inspection method according to claim 1 includes: 1. A leak inspection method for inspecting an object for air leaks, the object having an internal space that is depressurized to a predetermined vacuum level and hermetically sealed, comprising: a light projection step of projecting excitation light from outside the internal space onto a pressure-sensitive paint whose luminescence intensity changes with a change in oxygen concentration in the internal space; a measuring step of measuring a decay rate of the luminescence intensity; and a notification step of determining that there is an air leak and notifying the user when the attenuation rate exceeds a predetermined threshold value. It is characterized by:

[0007] The invention described in claim 2 is the leak inspection method described in claim 1, and determining whether or not there is an air leak when the time it takes for the emission intensity, expressed by formula (1), to decrease to 37% of its maximum value at the decay rate is measured. It is characterized by: I(t)=I0×exp(-t / τ) (1) Here, I(t) is the emission intensity at time t, I0 is the emission intensity when the excitation light is extinguished, and τ is the emission lifetime.

[0008] The invention described in claim 3 is the leak inspection method described in claim 1, The excitation light is pulsed and the excitation wavelength of the pressure-sensitive paint includes a wavelength range of 400 nm or more and 700 nm or less. It is characterized by:

[0009] The invention described in claim 4 is a leak inspection method according to any one of claims 1 to 3, The pressure sensitive paint comprises a ruthenium complex. It is characterized by:

[0010] In order to solve the above problem, the leak test device according to claim 5 is A leak inspection device for inspecting an object for air leaks, the object having an internal space that is depressurized to a predetermined vacuum level and hermetically sealed, comprising: an excitation light source that projects excitation light from outside the internal space onto a pressure-sensitive paint whose luminescence intensity changes with a change in oxygen concentration in the internal space; A light receiving means for receiving light emitted from the pressure sensitive paint; a measuring means for measuring a decay rate of the luminous intensity of the received light; and a notification means for notifying the user when the attenuation rate exceeds a predetermined threshold value. It is characterized by:

[0011] The invention described in claim 6 is the leak inspection device described in claim 5, The pressure-sensitive paint is applied onto a white board. It is characterized by:

[0012] The invention described in claim 7 is the leak inspection device described in claim 5 or 6, The pressure sensitive paint comprises a ruthenium complex. It is characterized by: Effect of the Invention

[0013] According to the invention recited in claim 1, an object to be inspected can be inspected for air leaks with high accuracy in a short period of time.

[0014] According to the invention recited in claim 2, air leaks can be detected based on the luminescence lifespan of the pressure-sensitive paint.

[0015] According to the invention as recited in claim 3, air leaks can be detected regardless of the light intensity of the excitation light source or the brightness of the surroundings.

[0016] According to the invention as recited in claim 4, air leaks can be detected at lower cost than with platinum complexes.

[0017] According to the invention as recited in claim 5, the object to be inspected can be inspected for air leaks with high accuracy in a short period of time.

[0018] According to the invention as recited in claim 6, it is possible to improve the reflection of the excitation light source.

[0019] According to the seventh aspect of the invention, air leaks can be detected at lower cost than with platinum complexes. [Brief description of the drawings]

[0020] [Figure 1] 1 is a block diagram showing a functional configuration of a leak inspection device according to an embodiment of the present invention; [Diagram 2] 1 is a schematic diagram showing an example of a leak inspection device according to an embodiment of the present invention; [Diagram 3] FIG. 4 is a flow chart diagrammatically illustrating the flow of a leak inspection according to the present embodiment. [Figure 4] FIG. 1 is a diagram conceptually illustrating attenuation of luminous intensity. [Diagram 5] FIG. 13 is a diagram showing an example of the measurement results of the luminescence lifetime under vacuum and atmospheric pressure. [Figure 6] FIG. 13 is a diagram showing an example of the measurement results of the emission lifetime when the emission intensity of the excitation light source under atmospheric pressure is changed. [Figure 7] FIG. 13 is a diagram showing an example of the measurement results of the emission lifetime when the emission intensity of the excitation light source in a vacuum is changed. [Figure 8] 1 is a schematic cross-sectional view showing a configuration of a water meter as an example of an object to be inspected. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will now be described in more detail with reference to the drawings, showing embodiments and specific examples, but the present invention is not limited to these embodiments and specific examples. In addition, in the following explanation using the drawings, it should be noted that the drawings are schematic and the ratios of the dimensions, etc. may differ from the actual ones, and in order to make it easier to understand, illustrations other than those of parts necessary for the explanation have been appropriately omitted.

[0022] The leak testing method of this embodiment is a leak testing method for testing for air leaks in an object under test having an internal space that is depressurized to a predetermined vacuum level and hermetically sealed, and includes a light projection step of projecting excitation light from outside the internal space onto a pressure-sensitive paint P whose luminescence intensity changes with changes in the oxygen concentration in the internal space, a measurement step of measuring the decay rate of the luminescence intensity, and a determination step of determining that an air leak exists if the decay rate exceeds a predetermined threshold value.

[0023] The leak testing device 1 which implements the leak testing method according to this embodiment includes a light emitting unit 10 which projects excitation light from outside the internal space onto the pressure-sensitive paint P, whose light emission intensity changes with changes in the oxygen concentration in the internal space, a light receiving unit 20 which serves as a light receiving means for receiving the light emitted from the pressure-sensitive paint P, a measuring unit 30 which serves as a measuring means for measuring the decay rate of the light emission intensity of the received light, and a notification unit 40 which serves as a notification means for notifying the user when the decay rate exceeds a predetermined threshold value.

[0024] First, a leak inspection device 1 for carrying out a leak inspection method according to the present embodiment and a water meter 100 as an example of an object to be inspected will be described with reference to the drawings. FIG. 1 is a block diagram showing the functional configuration of a leak testing device 1 according to this embodiment, FIG. 2 is a schematic diagram showing an example of a leak testing device 1 according to this embodiment, and FIG. 8 is a schematic cross-sectional view showing the configuration of a water meter 100 as an example of an object to be tested.

[0025] (Water meter) 8, water meter 100 as an example of the object to be inspected has lower case 110 with inlet 111 and outlet 112 formed at both ends, and inner case 120 is housed within lower case 110. Inner case 120 is provided with a plurality of inlet nozzles 121 and outlet nozzles 122, and impeller support member 123 is erected at the center of the inner bottom of inner case 120. Impeller 124 having magnet M1 at its shaft upper portion is rotatably supported by impeller support member 123.

[0026] An indication unit 130 is provided above the impeller 124 via a gasket G1. The indication unit 130 is composed of a register box 131, a lower base plate 132, an upper base plate 133, a magnet gear 134 to which a magnet M2 is attached, a gear train 135, a pointer (not shown), a number wheel 136, and a glass plate 137 attached via an O-ring S1. The magnet M2 of the magnet gear 134 and the magnet M1 of the impeller 124 face each other across the bottom wall of the register box 131 and are magnetically coupled to each other. The indication unit 130 thus configured is depressurized to a predetermined vacuum level and airtightly sealed. In the leak test device 1 according to this embodiment, the indication unit 130, which is evacuated and sealed with pressure-sensitive paint P applied onto the upper base plate 133, is used as the test object for the leak test.

[0027] (Overall configuration of leak testing device) 1, the leak inspection device 1 for carrying out the leak inspection method according to the present embodiment includes a light emitting unit 10 for projecting excitation light from outside the internal space onto the pressure-sensitive paint P whose light emission intensity changes with changes in the oxygen concentration in the internal space, a light receiving unit 20 as a light receiving means for receiving the light emitted from the pressure-sensitive paint P, a measuring unit 30 as a measuring means for measuring the decay rate of the light emission intensity of the received light, and an alarm unit 40 as an alarm means for notifying the user when the decay rate exceeds a predetermined threshold. In the leak inspection device 1, the processes of the light emitting unit 10, the light receiving unit 20, the measuring unit 30, and the alarm unit 40 are realized by a general computer in which a processor consisting of a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory) executes a predetermined program.

[0028] (Light emitting part) The light emitting section 10 comprises an excitation light source 11 and a driving section 12 that controls the emission of light from the excitation light source 11 . The excitation light source 11 is an LED (light-emitting diode) with an emission wavelength of 400 nm to 700 nm, and emits pulsed light by a driving unit 12. The emission intensity of the excitation light source 11 may be the same as the light intensity emitted by the pressure-sensitive paint P when pressure is applied, and as will be described later, the decay rate of the emission intensity of the pressure-sensitive paint P does not depend on the emission intensity of the excitation light source 11.

[0029] (Light receiving part) The light receiving unit 20 is composed of a photodiode 21 that receives light emitted from the pressure-sensitive paint P, and a trans-impedance amplifier (TIA) 22. When light is irradiated onto the photodiode 21, an electric charge is generated in the photodiode 21 by photoelectric conversion. The amount of electric charge generated depends on the amount of light irradiated onto the photodiode 21. In the light receiving unit 20, the electric charge generated in the photodiode 21 is converted into a voltage signal by the TIA 22.

[0030] (Measurement part) The measurement unit 30 includes an oscilloscope 31, and reads out the voltage signal converted by the TIA 22 to measure the decay rate of the emission intensity of the light received by the photodiode 21. Specifically, the oscilloscope 31 reads out the voltage signal converted by the TIA 22 to obtain a time waveform of the emission intensity from the emission intensity information from the photodiode 21. The measurement unit 30 performs signal processing on the time waveform information of the emission intensity converted into a digital signal from the oscilloscope 31 to calculate the decay rate of the emission intensity of the light received by the photodiode 21.

[0031] The notification unit 40 determines that there is an air leak and issues an alert when the decay rate detected by the measurement unit 30 exceeds a predetermined threshold value Th. It is known that the decay rate of the emission intensity detected from the time waveform information of the emission intensity depends on the number of collisions with oxygen. The relationship between the emission lifetime τ and the emission intensity I(t) at a certain time t is given by Equation (1): I(t)=I0×exp(-t / τ) (1) I0 is the emission intensity (maximum value) when the excitation light is turned off. When t=τ, the emission intensity I(τ) is expressed as follows: The presence or absence of an air leak is determined by measuring the time (decay rate) at which the emission intensity decreases to 37% of its maximum value (I0), where I(τ) = (1 / e)I0 - 0.37I0.

[0032] The notification unit 40 may be configured, for example, with a speaker that notifies information by sound, a vibrator that notifies information by vibration, a lamp that notifies information by lighting or blinking, etc. Alternatively, the notification may be performed by displaying information on a display of a computer that executes the processing of the leak testing device 1. The notification unit 40 is not limited to the example shown here, and may be configured with other mechanisms capable of notifying information, or may be configured with a combination of multiple mechanisms. Furthermore, these notification units 40 may be provided independently of the computer constituting the leak test device 1, and may be controlled by communication.

[0033] (Leak inspection method) The leak inspection method according to this embodiment includes a light projection step of projecting excitation light from outside the internal space onto a pressure-sensitive paint P whose luminescence intensity changes with changes in the oxygen concentration in an internal space that has been reduced in pressure to a predetermined vacuum level and hermetically sealed, a measurement step of measuring the decay rate of the luminescence intensity, and a notification step of determining that an air leak exists and notifying that fact if the decay rate exceeds a predetermined threshold value Th.

[0034] FIG. 3 is a flow chart diagram showing a schematic flow of a leak inspection according to this embodiment. In this embodiment, the indicator unit 130 of the water meter 100 is used as an example of an internal space that is depressurized to a predetermined vacuum level and hermetically sealed, and is used as a test subject for the air leak test. First, the pressure-sensitive paint P is inserted into the indicator unit 130, which is the object to be measured (S101). Examples of the pressure-sensitive paint P include platinum-porphyrin complexes such as PtTFPP and PtOEPP, palladium-porphyrin complexes such as PdTFPP, ruthenium complexes, and polycyclic aromatic hydrocarbons such as pyrene.

[0035] In this embodiment, a ruthenium complex, which is less expensive than a platinum-porphyrin complex, such as a ruthenium-diphenylphosphine complex such as Ru(dpp)3, is applied onto a white plate as the pressure-sensitive paint P. By applying the pressure-sensitive paint P onto a white plate, it is possible to improve the reflection of the excitation light source. The pressure-sensitive paint P is a paint whose luminescence intensity and luminescence lifespan change according to the oxygen partial pressure, and the luminescence intensity slowly decays when it goes out. It is known that the rate at which the luminescence intensity decays depends on the number of collisions with oxygen, and by evaluating the rate at which the luminescence intensity decays, it is possible to determine the level of oxygen partial pressure, i.e., the state of reduced pressure.

[0036] Next, the unit 130 is connected to a vacuum pump and a vacuum is drawn to reduce the pressure inside the unit 130 to a predetermined vacuum level (S102). At this time, it is desirable to connect a pressure gauge to the unit 130 in order to check the reduced pressure state. Then, the excitation light source 11 is caused to emit light, and light is irradiated onto the pressure-sensitive paint P inside the unit 130, which has been depressurized to a predetermined vacuum level (S103). In this embodiment, the excitation light source 11 is an LED (light-emitting diode) with an emission wavelength of 440 nm, and emits light in a pulsed manner with a driving current of 20 A (A: Ampere).

[0037] The excitation light source 11 is caused to emit light, and while irradiating the pressure-sensitive paint P with light, the photodiode 21 of the light receiving unit 20 receives the light emitted from the pressure-sensitive paint P (S104). The photodiode 21 generates an electric charge in proportion to the amount of light received. In the light receiving unit 20, the electric charge generated by the photodiode 21 is converted into a voltage signal by the TIA 22 (S105). The TIA 22 amplifies the charge signal generated by the photodiode 21, converts it into a digital signal by an A / D converter (not shown), and outputs it to the measurement unit 30 as a voltage signal.

[0038] In the measurement unit 30, the voltage signal converted by the TIA 22 is read out by the oscilloscope 31, and the decay rate of the emission intensity of the light received by the photodiode 21 is measured (S106). Specifically, the oscilloscope 31 reads out the voltage converted by the TIA 22, thereby acquiring a time waveform of the emission intensity from the emission intensity information from the photodiode 21. The measurement unit 30 performs signal processing on the time waveform information of the emission intensity converted into a digital signal from the oscilloscope 31, and calculates the decay rate of the emission intensity of the light received by the photodiode 21. That is, when I0 is the emission intensity (maximum value) when the excitation light is extinguished, the time it takes for the emission intensity I to decrease to 37% of the maximum value (I0) is calculated as the decay rate.

[0039] Fig. 4 conceptually illustrates the attenuation of the emission intensity. As shown in Fig. 4, the pressure-sensitive paint P emits light while the excitation light is being irradiated by the excitation light source 11 (excitation light source ON), and attenuates when the excitation light is no longer irradiated. The attenuation rate varies depending on the oxygen partial pressure in the internal space, and the attenuation rate increases as the oxygen partial pressure increases and decreases in a vacuum. In this embodiment, the time it takes for the emission intensity I to decrease to 37% of the maximum value (I0) is calculated as the attenuation rate, and if it is greater than a predetermined threshold value Th, it is determined that there is a certain oxygen partial pressure, i.e., that there is an air leak rather than a vacuum state (S107; Yes).

[0040] If it is determined in step S107 that an air leak exists, the notification unit 40 notifies the fact (S108). If it is determined in step S107 that an air leak does not exist (S107; No), the process returns to step S101, and an air leak test is performed on the next test object. EXAMPLES

[0041] An air leak test was carried out on the indicating unit 130 of the water meter 100 shown in FIG. 8 using the leak test device 1 shown in FIG.

[0042] "Example 1" A ruthenium complex was applied as pressure-sensitive paint P onto the upper base plate 133 of the indicator unit 130, and the time it took for the luminescence intensity to decrease to 37% of its maximum value in a vacuumed state (under vacuum) and in an open valve state (under atmospheric pressure) was measured as the decay rate of the luminescence intensity. As shown in Figure 5, there was a difference in the decay rate of the emission intensity between under vacuum and atmospheric pressure. The decay rate of the emission intensity in vacuum was 1.01 μs, whereas the decay rate of the emission intensity in atmospheric pressure was 0.60 μs. In this way, when the internal space of the indication unit 130 is at atmospheric pressure, the rate of decay of the luminescence intensity is greater than in a vacuum state, and by measuring the change in luminescence lifetime due to oxygen quenching, it is possible to accurately and quickly determine whether or not there is an air leak in the indication unit 130.

[0043] "Example 2" A ruthenium complex was applied as pressure-sensitive paint P onto the upper base plate 133 of the indicator unit 130, and the decay rate of the luminescence intensity was measured in a dark room and a bright room when the device was evacuated (under vacuum) and when the valve was open (under atmospheric pressure).

[0044] 6 shows the results of measuring the decay rate of the emission intensity under atmospheric pressure in a dark room with the emission intensity of the excitation light source 11 changed to 20 A, 40 A, and 80 A (drive current of the drive unit 12) and in a bright room with the emission intensity of the excitation light source 11 set to 40 A. As shown in FIG. 6, even when the emission intensity of the excitation light source 11 was changed to 20 A, 40 A, and 80 A in a dark room, the decay rates of the emission intensity were 0.68 μs, 0.60 μs, and 0.60 μs, respectively, which was not dependent on the emission intensity of the excitation light source 11. Furthermore, when the emission intensity of the excitation light source 11 was set to 40 A in a bright room, the decay rate of the emission intensity was 0.60 μs, which was not dependent on the brightness of the inspection environment.

[0045] 7 shows the results of measuring the decay rate of the emission intensity under vacuum by changing the emission intensity of the excitation light source 11 to 20 A, 40 A, and 80 A (drive current of the drive unit 12) in a dark room and by setting the emission intensity of the excitation light source 11 to 40 A in a bright room. As shown in FIG. 7, even when the emission intensity of the excitation light source 11 was changed to 20 A, 40 A, and 80 A in a dark room, the decay rates of the emission intensity were 1.05 μs, 1.02 μs, and 0.97 μs, respectively, which was not dependent on the emission intensity of the excitation light source 11. Furthermore, when the emission intensity of the excitation light source 11 was set to 40 A in a bright room, the decay rate of the emission intensity was 0.92 μs, which was not dependent on the brightness of the inspection environment.

[0046] Thus, the result showed that the decay rate of the emission intensity in either vacuum or atmospheric pressure was independent of the emission intensity of the excitation light source 11 and was also independent of the brightness of the inspection environment. This makes it possible to determine the presence or absence of an air leak in the indication unit 130 by measuring the attenuation rate of the emission intensity, regardless of the emission intensity of the excitation light source 11 or the brightness of the inspection environment. In other words, measurement can be performed in a bright room, and air leak inspection of the indication unit 130 can be performed at, for example, the production site of the water meter 100.

[0047] Although the embodiment of the present invention has been described above in detail, the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist of the present invention described in the claims. For example, platinum-porphyrin complexes such as PtTFPP and PtOEPP, which have a longer emission life due to oxygen quenching than ruthenium complexes, may be used as the pressure-sensitive paint P. The excitation light source 11 may be an excitation light source composed of a laser diode with an emission wavelength of 400 nm to 700 nm. [Explanation of symbols]

[0048] 1. Leak inspection device 10 Light-emitting part 11 ... excitation light source, 12 ... driving unit 20... Light receiving section 21 Photodiode, 22 Transimpedance amplifier (TIA) 30...Measuring section 31. Oscilloscope 40. Notification Department 100···Water meter 130...Indication unit 131 register box, 132 lower base plate, 133 upper base plate

Claims

1. 1. A leak inspection method for inspecting an object for air leaks, the object having an internal space that is depressurized to a predetermined vacuum level and hermetically sealed, comprising: a light projection step of projecting excitation light from outside the internal space onto a pressure-sensitive paint whose luminescence intensity changes with a change in oxygen concentration in the internal space; a measuring step of measuring a decay rate of the luminescence intensity; and a notification step of determining that there is an air leak and notifying the user when the attenuation rate exceeds a predetermined threshold value. A leak inspection method comprising:

2. and determining whether or not there is an air leak when the time it takes for the emission intensity, expressed by formula (1), to decrease to 37% of its maximum value at the decay rate is measured.

2. The leak inspection method according to claim 1. I(t)=I ０ ×exp(-t / τ) (1) where I(t) is the emission intensity at time t, I ０ is the emission intensity when the excitation light is extinguished, and τ is the emission lifetime.

3. The excitation light is pulsed and has an excitation wavelength of the pressure-sensitive paint in a wavelength range of 400 nm or more and 700 nm or less.

2. The leak inspection method according to claim 1.

4. The pressure sensitive paint comprises a ruthenium complex.

4. The leak inspection method according to claim 1, wherein the leak inspection method is a method for detecting a leak caused by a leakage current.

5. A leak inspection device for inspecting an object for air leaks, the object having an internal space that is depressurized to a predetermined vacuum level and hermetically sealed, comprising: an excitation light source that projects excitation light from outside the internal space onto a pressure-sensitive paint whose luminescence intensity changes with a change in oxygen concentration in the internal space; A light receiving means for receiving light emitted from the pressure sensitive paint; a measuring means for measuring a decay rate of the luminous intensity of the received light; and a notification means for notifying the user when the attenuation rate exceeds a predetermined threshold value. A leak inspection device characterized by:

6. The pressure-sensitive paint is applied onto a white board.

6. The leak inspection device according to claim 5.

7. The pressure sensitive paint comprises a ruthenium complex.

7. The leak inspection device according to claim 5 or 6.

Images