JP2000162084A - Method and apparatus for inspection of leak - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute the inspection of a leak in a short time and precisely even when a temperature environment is changed by a method wherein a differential-pressure change value which corresponds to a true leak amount is estimated and computed so as to be found for every object, to be inspected, by using a specific expression and the existence of the leak is judged on the basis of whether its computed result is large or small. SOLUTION: A differential-pressure-change measuring means 40 is constituted of a reset-signal generator 44 or the like which applies a gas pressure to an object 20, to be inspected, and to a reference tank 21 and which gives a reset signal to an automatic zero reset-type amplifier 31 at unit time intervals. Differential-pressure change values a1, a2, a3 per unit time which are detected by the differential-pressure-change measuring means 40 are sent to a computing and control device 43 via a sample-and- hold circuit 41 and an A/D converter 42, The differential-pressure change values a1, a2, a3 as measured values which are input from an input port 43D are substituted into an expression by a computing means 43C-2, and a differential-pressure change value C in a state that a drift is removed is calculated. Then, the differential-pressure change value C is compared with a set value by a comparison and judgment means 43C-3, and the existence of a leak is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leakage inspection method for inspecting the presence or absence of leakage of various containers and the like, and a leakage inspection apparatus which operates using the leakage inspection method.

[0002]

2. Description of the Related Art Conventionally, products or parts which are required to have no leakage in use are inspected sequentially in a production process line, and the inspection data is compared with a set standard to determine whether the products or parts are good or bad. Is determined. FIG. 3 is a block diagram showing a general configuration of this type of leakage inspection device. A flow tube 10 connected to an output side of a pneumatic pressure source 11 has a three-way electromagnetic valve via a pressure regulating valve 12 and a three-way electromagnetic valve 14. The outlets of the valve 14 are connected to branch paths 15A and 15B, respectively. A pressure gauge 13 for setting an inspection pressure is connected between an outlet side of the pressure regulating valve 12 and an inlet side of the three-way solenoid valve 14.

[0003] The branch path 15A is connected to the conduit 1 via an electromagnetic valve 16.
At the other end of the conduit 18 is provided a connection jig 24 to which an object 20 to be inspected for leakage can be connected. The inspection objects 20 are sequentially connected by the connection jig 24 so that the inspection can be performed. On the other hand, the branch path 15B is connected to one end of a conduit 19 via an electromagnetic valve 17, and the other end of the conduit 19 is connected to a reference tank 21. At the outlet side of the solenoid valves 16 and 17, conduits 18A and 19A are branched off and taken out, and a differential pressure detector 22 is mounted between their ends.

The output signal of the differential pressure detector 22 is supplied to a comparator 32 via an auto-zero reset type amplifier 31 so that the comparator 32 can compare with a reference value of a reference signal value setting unit 33. The test object 20 is attached to the end of the conduit 18, the reference tank 21 having no leakage is attached to the conduit 19, the space between a and b of the three-way solenoid valve 14 is closed, the pressure regulating valve 12 is opened, and the pressure gauge 13 is opened. Is adjusted so that a predetermined air pressure from the air pressure source 11 is obtained. The solenoid valves 16 and 17 are opened, the three-way solenoid valve 14 is opened between a and b, and the set constant air pressure is applied to the branch passages 15A and 15A.
B, and supplies the specimen 20 and the reference tank 21 through the conduits 18 and 19, respectively.

After a predetermined time has passed and the pressures in the test object 20 and the reference tank 21 have stabilized, the solenoid valves 16 and 17
Is closed. Further, after a predetermined stabilization time, the differential pressure detector 2
The output signal of the auto-zero reset type amplifier 31 connected to 2 is read. When the test object 20 is completely airtight and has no leakage, the output signal from the amplifier 31 becomes ideally zero after a certain detection time. When a leak exists in the test object 20, an output signal that gradually decreases when the internal pressure is a positive pressure and gradually increases when the internal pressure is a negative pressure is obtained, and the output signal within a certain detection time is negative or positive. The value is almost proportional to the leakage amount.

[0006] The reference differential pressure value provided from the reference signal setting unit 33 and the output value of the amplifier 31 are compared by a comparator 32, and whether or not the output signal exceeds the reference differential pressure value indicates whether the product is good or bad. An output 35 is obtained. In this general leak inspection device, the reference tank 21 is
Even if a sample having exactly the same shape as 0 and having no leakage is used, it is mainly affected by the temperature difference between the test object 20 and the reference tank 21. If the shapes of the test object 20 and the reference tank 21 are different, when the gas is pressurized, a gas temperature difference occurs in a process in which the gas temperature rise due to adiabatic change becomes equal to the temperature of the test object 20 and the reference tank 21. However, the output signal does not ideally become zero. That is, even if there is no leakage of the test object 20, the output signal during the certain detection time does not become an ideal zero state and usually shows a differential pressure value comparable to a positive or negative leakage amount. It is. The differential pressure value equivalent to this leakage amount is generally called a drift amount.

This situation will be described with reference to FIG. A curve A shown in FIG. 4 indicates a drift amount, a curve B indicates a leak amount, and a curve C indicates a differential pressure value substantially detected by the differential pressure detector 22 obtained by adding the leak amount to the drift amount. As can be seen from FIG. 4, most of the differential pressure value indicated by the curve C is the drift amount, and the differential pressure value corresponding to the leakage amount is small. This differential pressure value (curve C)
As a method of taking out only the leakage amount from the differential pressure value generated by the drift, the rate of increase approaches zero over time, whereas the differential pressure value generated by the leakage amount It also exhibits a phenomenon of rising at a constant rate of increase.

Focusing on this point, in the leak inspection apparatus having the configuration shown in FIG. 3, the output of the auto-zero reset type amplifier 31 is forced for a certain time (timing after the rate of increase of the drift amount approaches 0) TIM1. Reset to zero,
After the zero reset, the gain is increased to amplify the detection signal of the differential pressure detector 22 to obtain an output signal SD (curve D),
The output signal SD is supplied to a comparator 32, and the output signal SD generated after a predetermined time is compared with a reference value by the comparator 32.
If the output signal SD exceeds the reference value at the point in time when the predetermined time has elapsed, it is determined that the output signal SD is defective.

According to this detection method, the inspection is started after the rate of increase of the drift amount approaches zero, and therefore, there is a disadvantage that the inspection time required for one inspection object is increased. In order to solve this drawback, a leak inspection method as shown in FIG. 5 has been proposed. This inspection method is in the calibration mode,
The differential pressure generation value generated in the differential pressure detector 22 is reset to zero at regular intervals by, for example, an auto zero reset type amplifier 31 shown in an auto zero reset type amplifier 31 shown in FIG. This is repeated until is converged to a constant value. When the differential pressure change value per unit time converges to a constant value, the converged differential pressure change value Db is obtained. This differential pressure change value Db indicates a true differential pressure value per unit time generated by the amount of leakage. Therefore, by obtaining Da−Db = D1 by subtracting Db from the first differential pressure change value Da, the difference value D1 can be regarded as a drift value due to disturbance such as temperature.

Therefore, by storing the value D1 as a drift correction value, the drift correction value D1 is then subtracted from the first differential pressure generation value immediately after the pressurized gas is applied to the test object 20. Thus, a differential pressure value corresponding to the true leak amount of each test object 20 can be obtained.

[0011]

In the calibration method shown in FIG. 5, it is possible to perform a correct leak test only in a temperature environment (air temperature, temperature of the inspection object 20) in which the calibration mode is executed. However, in the temperature range, the calibration mode is executed each time the temperature of the test object 20 deviates from the condition of the calibration mode for obtaining the drift correction value D1, and the drift correction value D1 is set.
There is a drawback that has to be sought again.

An object of the present invention is to propose a leakage inspection method and a leakage inspection apparatus using the leakage inspection method, which can continue to execute an accurate leakage inspection in a short time regardless of how the temperature environment changes. is there.

[0013]

In the present invention, a differential pressure change per unit time is measured a plurality of times in a short time immediately after the pressurized gas is applied in the process of inspecting each test object. A differential pressure change value corresponding to a true leak amount corresponding to the convergence value Db shown in FIG. 5 is obtained from the plurality of actually measured values by performing a predictive calculation for each of the test objects. The present invention proposes a leakage inspection method and apparatus characterized by determining the presence / absence.

Therefore, according to the present invention, it is equivalent to executing the calibration mode shown in FIG. 5 for each test object in a short time. , The correct drift correction can be performed, so that the advantage that the accurate leakage inspection can be continuously performed is obtained.

[0015]

FIG. 1 shows an outline of a leakage inspection method according to the present invention. In the figure, a curve A1 indicates a differential pressure generation characteristic curve A1 ^' detected by the differential pressure detector 22 when an object to be inspected without leakage is detected by the differential pressure detector 22 when an inspected object to be leaked is inspected. 5 shows the obtained differential pressure generation characteristic curve.

According to the present invention, a plurality of differential pressure change values per unit time a1, a2, a3, or a1 ', a2', for each differential pressure generation characteristic curve A1 or A1 'generated for each test object.
a3 'is measured, and the measured values a1, a2, a3, or a
The convergence value C1 or C1 'at the time when a sufficient time has elapsed is calculated by predictive calculation using 1'a2' and a3 '. The convergence value C1 or C1 ′ is a differential pressure change value per unit time due to a true leak that is not affected by temperature. Therefore, if the presence or absence of a leak is determined based on the magnitude of the differential pressure change value C1 or C1 ', the presence or absence of a leak that is not affected by disturbance such as temperature can be determined.

In order to measure the differential pressure change value per unit time, the change of the differential pressure generation characteristic curve A1 or A1 'may be detected at unit time intervals. For this purpose, for example, a reset signal may be given to the auto-zero reset type amplifier at equal time intervals, the differential pressure detection value may be reset at equal time intervals, and the differential pressure value immediately before the reset may be sampled and stored. .

Differential pressure change values a1, a2, per unit time
The attenuation curve B1 or B1 'is predicted by actually measuring a3 or a1'a2' and a3 '. This decay curve B
1, B1 'is obtained by calculation to obtain the differential pressure change value C1 or C1 per unit time at the time when a sufficient time has elapsed.
1 ′ can be calculated. Hereinafter, a method of predicting the attenuation curve B1 or B1 ′ and calculating the differential pressure change value C1 or C1 ′ per unit time when a sufficient time has elapsed will be described.

The temperature of the gas confined in the test object 20 (see FIG. 2 or FIG. 3) goes through a process of gradually becoming equal to the surface temperature in the test object 20 according to Newton's law of cooling. In the differential pressure type leak inspection device, the flow rate Q leaked to the atmosphere per unit time is represented by: Q = (V _E / Po) × (dp / dt) (1)

Here, V _E is the equivalent internal volume of the test object 20 (the internal volume on the test object 20 side viewed from the leak test apparatus), and P
o is the atmospheric pressure, and p is the differential pressure change value at the time of detecting the differential pressure. From Newton's law of cooling, dp / dt is: dp / dt = Ae- ^kt + C (2) where A is a proportional constant, K is a constant related to the speed of decay, and C is the differential pressure change value to be obtained. It is a change in pressure difference per unit time due to leakage, and is assumed to be constant at all times during the inspection.

In order to solve the equation (2), t = T1, t = 2T
The differential pressure change value per unit time of Expression (2) at each time of 1, t = 3T1 is actually measured. This is defined as a1 or a1 'for T1, a2 or a2', 3T for 2T1.
If a3 or a3 'is set at 1, the equation (2) is described below (only the attenuation curve B will be described below). ^A1 = Ae- ^kT1 + C (3) a2 = Ae- ^2kT1 + C ... ^.. (4) a3 = Ae ^−3kT1 + C (5) When the differential pressure change value C is obtained from the equations (4), (5) and (6), C = a1− (a2−a3) / [{(A2-a3) / (a1-a2)}-{(a2-a3) ² / (a1-a2) ² }] (6) Inside the object 20 according to the equation (6) The differential pressure change value C per unit time when the gas temperature converges to a constant value can be obtained. That is, the differential pressure change value C1 or C1 'per unit time generated only by leakage can be obtained. Therefore, the presence or absence of leakage can be determined based on whether the differential pressure change value C is smaller or larger than the boundary value R between the presence and absence of leakage.

As is apparent from equation (2), to solve equation (2), three parameters A, K, and C must be determined. Therefore, since the unknown number is 3, actual measurement is required at least three times. Therefore, in this embodiment, a1, a
2 shows an example in which three measurements of a3 are performed. The three actual measurements may be performed by providing an operation for supplying a reset signal to the auto-zero reset type amplifier 31 and a sampling means for reading the output value of the auto-zero reset type amplifier 31 immediately before supplying the reset signal.

FIG. 2 shows an embodiment of a leakage inspection apparatus employing the leakage inspection method according to the present invention described with reference to FIG. Parts corresponding to those in FIG. 3 are denoted by the same reference numerals. In FIG. 2, the configuration different from that in FIG. 3 is a configuration subsequent to the auto-zero reset type amplifier 31, so that only the different configuration will be described here. The leak inspection apparatus according to the present invention includes a reset signal generator 44 for giving a reset signal to the auto zero reset type amplifier 31 at unit time intervals immediately after gas pressure is applied to the test object 20 and the reference tank 21; an auto zero reset type amplifier 31; Differential pressure change measuring means 4
0 and a sample and hold circuit 41 for sampling the differential pressure change values a1, a2 and a3 per unit time detected by the differential pressure change measuring means 40,
The differential pressure change values a1, a2 and a3 per unit time sampled and held by the sample and hold circuit 41 are AD
An operation of obtaining the AD converter 42 to be converted and the differential pressure change values a1, a2, and a3 AD-converted by the AD converter 42 and calculating the differential pressure change value C according to the above equation (6). It is characterized by a configuration in which a control device 43 is provided.

The arithmetic and control unit 43 can be constituted by a computer system. As is well known, the computer system is a central processing unit 43A.
, ROM 43B, RAM 43C, input port 43
D and an output port 43E. RAM4
3C stores an actually measured value storage unit 43C that stores the actually measured differential pressure change values a1, a2, and a3 input from the input port 43D.
-1 and the actual measurement values a1, a2, and a3 are substituted into the equation (6) to calculate a differential pressure change value C in a state where the drift is removed, and the operation means 43C-2.
And a comparison / decision unit 43C-3 for comparing the differential pressure change value C calculated in the above with a set value to determine the presence or absence of leakage.

That is, each of these measured value storage units 43C-
1, the calculating means 43C-2 and the comparing / determining means 43C-3
The differential pressure change values a1, a2, and a are actually measured by executing the program in accordance with an instruction from the central processing unit 43A.
3, the calculation of the expression (6), and the comparison / determination operation are executed.

The RAM 43C is further provided with control means 43C-4 for controlling the sample hold circuit 41 and the reset signal generator 44. The control means 43C-4 controls the sample hold circuit 41 and the reset signal generator 44. The sampling operation and the reset operation are executed under the control of the output port 43E. In the execution example shown in FIG. 2, the case where various programs are stored in the RAM 43C has been described.
And can be freely selected.

In the leakage inspection method according to the present invention described with reference to FIG. 1, the differential pressure change value C obtained by the equation (6) is compared with a set value as it is to determine whether or not leakage has occurred. , The differential pressure change value C calculated using the equation (6)
It is conceivable that a difference C-Cn = Co occurs between the difference and the pressure difference change value Cn actually measured over time. The fact that the difference value C−Cn = Co does not become 0 means that the prediction calculation of the equation (6) includes an error.

By calculating the error Co of the prediction operation once, the difference between the differential pressure change value C calculated every time and C-Co is determined, thereby removing the error associated with the prediction operation. . That is, a certain test object 2
In the state where 0 is connected, a1, a2, and a3 are actually measured as usual, and the differential pressure change value C predicted by the calculating means 43C-2 is calculated. While the differential pressure change value C is calculated, the test object 2
0, the auto-zero reset type amplifier 31 is reset when a sufficient time has passed and the temperature of the air inside the device under test 20 becomes equal to the temperature of the inner wall of the device under test 20, and the unit time The differential pressure change value Cn obtained by reading the differential pressure change value Cn after elapse and calculating the differential pressure change value Cn is obtained.
Is subtracted from C to obtain C-Cn = Co, an error associated with the prediction operation can be removed by subtracting Co from the differential pressure change value C obtained by the prediction operation each time another test object 20 is inspected. . However, it can be easily understood that the error Co is a very small value and is not a correction that must be always executed because it is not an error having a nature that greatly fluctuates due to disturbance.

In the above description, the positive pressure is applied from the pneumatic pressure source 11 to the test object 20 and the reference tank 21. However, the present invention is not limited to the positive pressure and can be applied to a negative pressure. The negative pressure refers to a state in which a certain amount of air remains in the test object 20 and the reference tank 21 instead of a complete vacuum.

[0030]

As described above, according to the present invention, the differential pressure change values a1, a2, and a3 per unit time are measured at equal time intervals for each of the test objects 20, and the actual measured values a1, a
Since the damping characteristic of the differential pressure change value per unit time is predicted from 2 and a3, and the differential pressure change value C at the time when a sufficient time has passed by the prediction calculation is obtained, the differential pressure change value C obtained by this calculation is It can be seen that any test object 20 can be regarded as a value corresponding to only the true leakage amount, which is free from the influence of disturbance such as temperature at each test time.

Therefore, by using the leak inspection method according to the present invention, even if the temperature of the device under test 20 changes greatly for each device under test 20, the influence of the drift due to the temperature is removed and the presence or absence of correct leakage is determined. Can be determined. Further, even if the temperature changes or the drift amount changes with the change in the temperature, the change in the drift amount can be removed.

The time interval for actually measuring the differential pressure change values a1, a2, a3 can be an extremely short time interval of, for example, about 0.5 to 1 second, so that the time for actually measuring the differential pressure change values a1, a2, a3 is sufficient. Is short. Therefore, the time required to inspect one test object 20 is short, and the advantage that a high-speed test can be realized is obtained. Therefore, the correct leak inspection can be performed at high speed without any adjustment at all times, and the effect is extremely large for practical use.

[Brief description of the drawings]

FIG. 1 is a graph for explaining a leak inspection method according to the present invention.

FIG. 2 is a block diagram for explaining an actual measurement example of a leakage inspection apparatus to which the leakage inspection method according to the present invention is applied.

FIG. 3 is a block diagram for explaining a configuration of a conventional leakage inspection device.

FIG. 4 is a graph for explaining a conventional leak inspection method.

FIG. 5 is a graph for explaining a method for removing drift due to disturbance such as temperature in a conventional leak inspection apparatus.

[Explanation of symbols]

a1, a2, a3 Actual measured value representing the differential pressure change value per unit time C1 Differential pressure change value obtained by predictive calculation B1 Decay curve T1 Unit time 31 Auto-zero reset type amplifier 41 Sample hold circuit 42 AD converter 43 Operation control device 43C-1 Measured value storage device 43C-2 Operation means 43C-3 Comparison judgment means 44 Reset signal generator

Claims (3)

[Claims] 1. A positive or negative gas pressure is applied to an object to be inspected and a reference tank, and leakage of the object to be inspected depends on whether or not a predetermined differential pressure or more is generated between the two after a lapse of a predetermined time. In the leak inspection method for determining whether or not there is, a plurality of differential pressure change values per unit time are obtained at a unit time interval from the time when gas pressure is applied to the test object and the reference tank, and the plurality of differential pressure change values are determined. , A differential pressure change value C per unit time corresponding to the amount of leakage at the time when a sufficiently long time has elapsed is calculated by a prediction calculation formula, and whether or not leakage is present or the magnitude of leakage is determined based on whether the calculated value is a predetermined value or more. A leakage inspection method characterized by determining the following. 2. The leak inspection method according to claim 1, wherein
A1, a2, a are the differential pressure change values per unit time to be measured.
The differential pressure change value C per unit time at the time when a sufficient time has elapsed using the three values is C = a1- (a2-a3) / [／ (a2-a3) / (a
1-a2)｝-｛(a2-a3) ² / (a1-a
2) A leakage inspection method, wherein the calculation is performed using a prediction operation expression of ² ｝]. 3. A. A gas pressure is applied to the test object and the reference tank from an air pressure source, and a differential pressure value generated between the two at the time of application of the gas pressure is measured by a differential pressure detector, and the differential pressure value exceeds a specified value. B. A leakage inspection apparatus that detects that the inspection has been performed and determines that the inspection object has leakage. Immediately after the application of the gas pressure, a differential pressure change measuring unit that measures an increase amount of the differential pressure value detected by the differential pressure detector at unit time intervals, and detects a differential pressure change value per unit time at a plurality of timings. C. B. sampling means for taking in a plurality of differential pressure change values per unit time measured by the differential pressure change measuring means; A plurality of differential pressure change values taken in by this sampling means are calculated as C = a1- (a2-a3) / [｛(a2-a3) / (a
1-a2)｝-｛(a2-a3) ² / (a1-a2)
² ｝], and an arithmetic means for calculating by substituting And a comparing and judging means for comparing the value C calculated by the calculating means with a set value and judging the presence or absence of a leak.