JPH0792418B2 - Air leak tester - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air leak tester used for detecting scratches on various hollow specimens.

[0002]

2. Description of the Related Art An air leak tester is provided with an air passage having one end connected to an air pressure source and the other end connected to a hollow specimen. A solenoid valve is provided in this air passage. By opening the solenoid valve, the air pressure source and the specimen are made to communicate with each other to supply air pressure to the specimen, and then the solenoid valve is closed to shut off the specimen and the air pressure source. Then, at the closed position of the solenoid valve, a pressure sensor (pressure detecting means) is used to detect a change in the air pressure of the sample as an electric signal. When the pressure change is large, the sample is damaged and an air leak occurs. It is judged as a thing. The pressure fluctuation appears as a pressure decrease when the air pressure is a compressed air pressure (positive pressure), and as a pressure increase when the air pressure is a vacuum pressure (negative pressure).
By the way, the conventional drive circuit for the solenoid valve controls the solenoid valve by supplying and stopping a constant current. The solenoid valve is, for example, open when it is not supplied with current and closed when it is supplied with current.

[0003]

The solenoid valve does not require a large exciting force to maintain the closed position, but
A large excitation force is required during the switching operation from the open position to the closed position. The current supplied from the drive circuit is determined according to the exciting force required for the switching operation, which causes an excessively large current to be supplied to the solenoid valve in order to maintain the closed position of the solenoid valve. The coil of the solenoid valve generates heat, and this heat greatly affects the air pressure in the air passage and the sample. That is, it becomes a factor of increasing the air pressure. As a result, the fluctuation of the air pressure in the sample cannot be accurately detected, and the accuracy of detecting the air leak is lowered. The amount of heat generated by the solenoid valve varies with each solenoid valve even if the standard is the same, and the degree of increase in internal pressure due to heat generation also varies with each leak tester used and each sample tested. When trying to compensate for heat generation in consideration of these, a complicated compensating circuit is required, and the work required for compensation is also complicated.

[0004]

The present invention has been made in order to solve the above problems, and its gist is to provide an air passage having an air pressure source connected to one end and a hollow specimen connected to the other end. In an air leak tester equipped with a solenoid valve provided in this air passage for communicating and blocking between an air pressure source and a specimen, and a pressure detecting means for detecting a variation in the air pressure of the specimen, a solenoid valve switching operation An air leak tester is provided with a drive circuit that sometimes supplies a high current to the solenoid valve and supplies a low current for holding the position of the solenoid valve after the switching operation.

[0005]

Since a relatively large current is supplied to the solenoid valve during the switching operation of the solenoid valve, this switching operation can be performed reliably. After the switching operation, only the low current necessary for holding the position of the solenoid valve is supplied, so that the heat generation amount of the coil of the solenoid valve can be suppressed to a low level. As a result, the sample pressure increase due to heat generation can be suppressed to a low level, and the sample air leak test can be performed accurately.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows the basic known construction of an air leak tester. The air leak tester includes an air passage 1. A compressed air source 2 (air pressure source) is provided at one end of the air passage 1.
Are connected. The other end of the air passage 1 is branched into two, a hollow specimen A is connected to the end of one branch passage 1a, and a reference container B is connected to the end of the other branch passage 1b. The air passage 1 is provided with a regulator 3 and a two-position three-port solenoid valve 4 for maintaining a constant pressure on the downstream side in this order from the one end to the branch point 1x. This solenoid valve 4 has a branch point 1 when no current is supplied (when it is off).
x is cut off from the regulator 3 and opened to the outside, and the branch point 1x is cut off from the outside and communicated with the regulator 3 when a current is supplied (on).

Two-position two-port solenoid valves 5 and 6 are provided on the pair of branch passages 1a and 1b, respectively. These solenoid valves 5 and 6 are in the open position when current is not supplied (when off) and in the closed position when current is being supplied (on). The air leak tester includes a differential pressure sensor 7 (pressure detection means). The two pressure introduction ports of the differential pressure sensor 7 are connected to the branch passages 1a and 1b on the downstream side of the solenoid valves 5 and 6, respectively, so that the differential pressure between the sample A and the reference container B can be detected. ing.

The air leak tester comprises a drive circuit 10 for the solenoid valves 4, 5, 6 as shown in FIG.
Since the three drive circuits 10 have the same configuration, only one will be illustrated and described. The drive circuit 10 includes a rectifier circuit 11 that rectifies the AC voltage from the AC power supply 20, and a charging circuit 12 that is composed of a resistor 12a and a capacitor 12b and that charges the voltage from the rectifier circuit 11. One end of the capacitor 12b is connected to one end of the coil 30 of the solenoid valve 4 (or the solenoid valves 5 and 6) via the switch 13, and the other end is connected to the coil 30.
Is directly connected to the other end of.

In the above structure, the specimen A and the reference container B are first connected to the air passage 1. The solenoid valves 4, 5 and 6 are off and in the state of FIG. 1, and the sample A and the reference container B are cut off from the compressed air source 2 and opened to the outside. Then, the solenoid valve 4 is turned on to supply a constant air pressure to the specimen A and the reference container B. After that, the electromagnetic valves 5 and 6 are turned on to disconnect the sample A from the reference container B and to disconnect the sample A and the reference container B from the compressed air source 2.
In this state, the differential pressure sensor 7 detects the change in the differential pressure between the sample A and the reference container B. Since it has been confirmed in advance that the reference container B has no damage and no air leak occurs, the internal pressure does not drop from the start of detection. When the sample A is not damaged, the internal pressure does not drop because there is no air leak of the sample A, and therefore the differential pressure is maintained at substantially zero. When the sample A has a scratch, an air leak occurs in the sample A and the internal pressure decreases, so that the differential pressure increases. In a processing circuit (not shown), a calculation is performed based on an electric signal from the differential pressure sensor 7, and when it is determined that the increase in the differential pressure in a certain time exceeds an allowable range, an alarm indicating that the specimen A has a flaw is rejected. Emit. After the test is completed, all the solenoid valves 5, 6 and 7 are turned off, the tested sample A is removed from the air passage 1, a new sample is connected, and the above air leak test is executed again.

Next, the operation of the drive circuit 10 for the solenoid valve 5 will be described as an example. When the switch 13 is off and a main switch (not shown) interposed between the AC power supply 20 and the rectifier circuit 11 is turned on, the rectifier circuit 11 and the resistor 12a are connected to the capacitor 12b as shown in FIG. Charging starts. And the capacitor 12
Charging ends when the voltage of b matches the output voltage V _H of the rectifying circuit 11. After that, the capacitor 12b receives this voltage V
Keep _H. When the switch 13 is off, no current is supplied to the coil 30 and the solenoid valve 5 is in the open position.
In FIG. 3, the time range in which the above-mentioned solenoid valve 5 is in the open position is indicated by a symbol A.

Next, when the switch 13 is turned on, a current is supplied to the coil 30 and the solenoid valve 5 is switched from the open position to the closed position. At this time, a relatively high charging voltage V _H of the capacitor 12b is applied to the coil 30, and a large current corresponding to the exciting force required for the switching operation is supplied by discharging the capacitor 12b. Therefore, the switching operation can be surely executed. In Figure 3,
The time range of this switching operation is shown by the symbol B.

The discharge of the capacitor 12b ends when the voltage V _L is reached. The voltage V _L is the resistance from the rectified voltage V _H 1
The voltage is the voltage after subtracting the voltage drop at 2a, and is maintained constant. The solenoid valve 5 is supplied with a current corresponding to the voltage V _{L, so} that the solenoid valve 5 is maintained in the closed position. Since this supplied current is smaller than the current during the switching operation, the amount of heat generated in the coil 30 can be suppressed to a small value. As a result, when the electromagnetic valve 5 is in the closed position, the influence of the heat generation on the pressure of the sample A can be suppressed to a low level. Therefore, for example, when there is an air leak in the sample A, the inconvenience of supplementing the pressure decrease due to the air leak with the pressure increase due to the heat generation does not occur, and the air leak can be accurately detected. In FIG. 3, a time range in which the closed position of the solenoid valve 5 is held is indicated by a symbol C.

When the switch 13 is turned off after the leak test of one specimen A, the current supply to the coil 30 is stopped and the solenoid valve 5 is switched from the closed position to the open position. At the same time, charging of the capacitor 12b is started, and its voltage rises from V _L to V _H. And
Preparation for the next switching operation of the solenoid valve 5 from the open position to the closed position is completed. Drive circuit 1 for solenoid valve 6
The action of 0 is also the same, and the switching operation from the open position to the closed position of the solenoid valve 6 can be reliably executed, and the influence of the heat generation of the solenoid valve 6 on the internal pressure of the reference container B can be suppressed to a low level. The operation of the drive circuit 10 of the solenoid valve 4 is also the same, so that the switching operation of the solenoid valve 4 can be surely executed, and the influence of the heat generation of the solenoid valve 4 on the internal pressures of the sample A and the reference container B can be kept low. You can

FIG. 4 shows another drive circuit 50. The drive circuit 50 includes a one-shot multivibrator 51, a constant voltage generation circuit 52, and an amplification circuit 53. For example, when switching the solenoid valve from the open position to the closed position, a command signal from a control circuit (not shown)
The one-shot multivibrator 51 outputs a pulse, and the constant voltage generation circuit 52 outputs a constant voltage V _L. The amplification circuit 53 amplifies this pulse and adds a constant voltage V _L to apply a high voltage V _H to the coil 30 of the solenoid valve. As a result, a large current flows through the solenoid valve, and the exciting force required for the switching operation is generated. After the pulse output is completed, the output voltage of the amplifier circuit 53 drops to the level of the constant voltage V _L , and the solenoid valve is supplied with a small current for holding its closed position.
Next, in response to the command signal from the control circuit, the constant voltage generation circuit 52 stops the output of the constant voltage V _L , whereby the solenoid valve performs a switching operation opposite to the above, that is, from the closed position to the open position. The switching operation of is executed. In FIG. 5, reference numeral A'indicates a time range when the solenoid valve is off and is in the open position, reference numeral B'indicates a time range when the solenoid valve is switched from the open position to the closed position, and the reference numeral C ' Indicates the time range in which the solenoid valve holds the closed position.

The present invention is not limited to the above-mentioned embodiment and various modes are possible. For example, the branch passage 1b, the electromagnetic valve 6, and the reference container B in FIG. 1 may be omitted, and the variation in the internal pressure of the sample A may be detected by the differential pressure sensor 7. In this case, the differential pressure sensor 7
One pressure introduction port is open to the atmosphere. Further, a vacuum device may be used as the air pressure source and the air pressure supplied to the sample may be a negative pressure.

[0016]

As described above, in the air leak tester of the present invention, the switching operation of the solenoid valve is reliably executed by supplying a large current, and the heat generation amount is suppressed by the supply of a small current to maintain the position of the solenoid valve. . As a result, the influence of heat generation on the pressure inside the sample can be suppressed, and the air leak test can be performed accurately.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic configuration of an embodiment of an air leak tester of the present invention.

FIG. 2 shows a drive circuit for a solenoid valve.

FIG. 3 is a diagram showing a relationship between a capacitor voltage and time of the drive circuit of FIG.

FIG. 4 is a diagram showing another example of a drive circuit for a solenoid valve.

5 is a diagram showing a relationship between a voltage supplied from the drive circuit of FIG. 4 to a solenoid valve and time.

[Explanation of symbols]

 1 Air Passage 2 Air Pressure Source (Compressed Air Source) 4, 5, 6 Solenoid Valve 7 Pressure Detecting Means (Differential Pressure Sensor) 10, 50 Drive Circuit A Sample

Claims (1)

[Claims] 1. An air passage having an air pressure source connected to one end and a hollow specimen connected to the other end, and a solenoid valve provided in the air passage for communicating and blocking the air pressure source and the specimen. In an air leak tester equipped with pressure detection means for detecting fluctuations in the air pressure of a specimen, a high current is supplied to the solenoid valve during the switching operation of the solenoid valve, and a low current for maintaining the position of the solenoid valve after the switching operation. An air leak tester comprising a drive circuit for supplying the air leak.