A fast vacuum leak detection system and method

Abstract

The present invention discloses a rapid vacuum leak detection system, including a vacuum pipe connected to a vacuum pump at one end, the vacuum pipe is provided with a solenoid valve YV1 for controlling the on and off of the vacuum pipe and a pressure sensor for detecting the pressure of the vacuum pipe in sequence, the other end of the vacuum pipe is provided with a solenoid valve YV2 and a solenoid valve YV3 in parallel, the vacuum pipe where the solenoid valve YV2 is located is connected to a first cavity, a solenoid valve YV4, and a detection cavity in sequence until it is connected to the positive phase of a differential pressure sensor; the vacuum pipe where the solenoid valve YV3 is located is connected to a second cavity, a solenoid valve YV5, and a reference cavity in sequence until it is connected to the negative phase of the differential pressure sensor. The present invention also provides a rapid vacuum leak detection method, the detection range of which covers the situation where the contents of the package being inspected are gas, liquid, and a mixture of gas and liquid; and it can be applied to full product online detection of repeated opening and closing of a vacuum system, and can greatly shorten the detection time.

Description

Technical Field

[0001] The present invention relates to the technical field of sealing detection, and in particular to a rapid vacuum leak detection system and method. Background Art

[0002] In the process flow of food and drug production, sealing detection is an indispensable quality inspection link. At present, the sealing detection methods on the market are mainly light inspection, high-voltage discharge detection, and vacuum decay detection. High-voltage discharge detection has high requirements on the physical properties of samples, mainly because the sealed package is not conductive, and the solution contained is conductive. Therefore, for some opaque packages that cannot be inspected by light and whose conductivity does not meet the requirements of high-voltage discharge detection, the vacuum decay method is often used for testing. Although the vacuum decay method is basically applicable to the detection of all sealed products, and is irreplaceable for certain specific packaging structures and materials, the vacuum decay method takes a long time to detect and has high requirements for the sealing of the instrument. Therefore, so far, the vacuum decay method is rarely used for full product sealing detection, and sampling detection is mostly selected.

[0003] The difficulties of the vacuum decay method for full product testing are mainly divided into two points. One is that the vacuum decay method takes a long time to test. This method is usually divided into three stages. In the first stage, the test chamber is vacuumed for judgment. If the preset value cannot be reached, it is judged as a large leak; the second stage is the pressure holding stage. If the reference vacuum degree cannot be reached within the preset time, it is a medium leak; the third stage is the test stage. If the actual vacuum decay rate value is greater than the reference value, it is a small leak. The upper limit of micropores that can be tested by this method is smaller than other methods, but there are many test stages and the long test time has been criticized by the industry. The second is the high requirements for the sealing of the detection system. In fact, in order to detect smaller micropores, the sealing requirements for the back pressure, that is, the detection chamber, are extremely strict. Experiments show that when using a high-sealing chamber to detect 1-micron micropores, its signal-to-noise ratio is almost close to 1, and the data reliability is greatly reduced at this time. Full product testing requires repeated vacuuming and pressure relief of the vacuum chamber, which is basically difficult to meet the sealing requirements for detecting small leaks. More importantly, when testing sealed packages containing liquids, liquid leakage caused by defective products will remain in the vacuum testing chamber, which will seriously affect the repeatability of the vacuum pumping of the chamber, and basically make it impossible to continue testing. Cleaning and drying the chamber will take a lot of time. That is, compared with the testing time of 10 seconds, the drying time of more than 1 minute seriously affects the efficiency of the testing system. Summary of the invention

[0004] In order to solve the above problems, this method starts from the "water hammer" phenomenon that often occurs in liquid pipelines, and judges whether the test sample is leaking by judging whether the "water hammer" effect occurs in the early stage of vacuuming. This method has low requirements for the repeatability of the vacuum degree of the cavity and the sealing of the sealed chamber, and can well solve the problem of full product detection of the vacuum detection method. The "water hammer" phenomenon mainly occurs when the pipeline valve is opened and closed quickly, which will produce an energy shock wave, which is very destructive to the pipeline and valve. The principle is that when the valve is suddenly closed, the liquid near the valve end suddenly stops, and the liquid at the far end has inertia and a certain degree of compressibility. Therefore, the rapid change in flow causes an excessive pressure shock in the pipeline. The force generated by this shock wave back and forth is like a hammer hitting, so it is called water hammer. The rapid closing of the valve generates positive pressure on the pipe wall and the valve, which is called positive water hammer. Similarly, when the valve is opened rapidly, negative pressure is generated on the pipe wall, which is called negative water hammer. The "water hammer" phenomenon also occurs when a sealed package leaks. If there is a leak in a sealed package inside a vacuum chamber that has been evacuated, when the pressure difference between the inside and outside of the leak hole is large enough, the leak channel suddenly opens, generating a negative pressure shock wave that can be captured by the patented device to determine the tightness of the sealed package. Using the "water hammer" principle to detect the tightness of a sealed package is the first case in the field of vacuum leak detection.

[0005] The purpose of the present invention is to provide a fast vacuum leak detection system. The technical solution to achieve the purpose of the present invention is: a fast vacuum leak detection system, including a vacuum pipe connected to a vacuum pump at one end, the vacuum pipe is provided with a solenoid valve YV1 for controlling the on and off of the vacuum pipe and a pressure sensor for detecting the pressure of the vacuum pipe in sequence, the other end of the vacuum pipe is provided with a solenoid valve YV2 and a solenoid valve YV3 in parallel, and also includes a first cavity, a second cavity, a detection cavity with a sample to be detected, a reference cavity with a reference entity, and a differential pressure sensor, the vacuum pipe where the solenoid valve YV2 is located is connected to the first cavity, the solenoid valve YV4, and the detection cavity in sequence until it is connected to the positive phase of the differential pressure sensor; the vacuum pipe where the solenoid valve YV3 is located is connected to the second cavity, the solenoid valve YV5, and the reference cavity in sequence until it is connected to the negative phase of the differential pressure sensor.

[0006] Preferably, the volume of the reference entity is larger than the volume of the sample to be detected.

[0007] The present invention also provides a leak detection method using the rapid vacuum leak detection system, comprising the following steps:

[0008] Step 1: Open solenoid valves YV1, YV2 and YV3, close solenoid valves YV4 and YV5, turn on the vacuum pump, and when the pressure sensor reaches the set threshold, close the solenoid valve YV1 and delay the closure of the vacuum pump;

[0009] Step 2: After a certain period of time, when the pressure values ​​of the first cavity and the second cavity are equal and stable, close the solenoid valve YV2 and the solenoid valve YV3 at the same time; if the pressure sensor cannot maintain stability, the system is shut down and waits for instrument inspection. After the inspection, execute step 1. If the pressure sensor maintains stability, execute the next step;

[0010] Step 3: Open the solenoid valve YV4 and the solenoid valve YV5 at the same time, and start recording the differential pressure sensor data, the data of the differential pressure sensor is the current value, and then perform leakage detection based on the current value.

[0011] Preferably, the current value leakage detection determination method is:

[0012] Step A: If the current value of the differential pressure sensor signal reaches a preset value within a preset time, it is determined to be a leak;

[0013] Step B: If the current value of the differential pressure sensor signal does not reach the preset value within the preset time, then enter the next step to execute the next judgment mode;

[0014] Step C: Enter the pressure growth rate judgment mode and use discrete data for interpolation judgment to determine whether there is a leak.

[0015] As a preferred method, the specific method of using discrete data for interpolation judgment is:

[0016] Step a: exporting the current value data of the differential pressure sensor according to the sampling frequency to form equally spaced discrete data;

[0017] Step b: using the difference method to obtain the first-order and second-order derivatives of the equally spaced discrete data,

[0018] Step c: judge the first-order derivative. If it is less than the preset value 1, it is a leak, and the leak pore radius is large; if it is greater than the preset value 1, enter the second-order derivative judgment stage. If it is less than the preset value 2, it is a leak, and the leak pore radius is small; if the second-order derivative is greater than the preset value 2, it is a good seal.

[0019] Preferably, the extracted data is data after the solenoid valve YV4 and the solenoid valve YV5 are opened for a certain preset time.

[0020] Preferably, solenoid valve YV4 and solenoid valve YV5 are three-way solenoid valves. After the detection is completed, solenoid valve YV4 and solenoid valve YV5 are connected to the vacuum pipeline and opened to release pressure. After the pressure reaches the preset value, the pressure relief is closed and the pipeline connection between solenoid valve YV4 and solenoid valve YV5 is disconnected.

[0021] Preferably, the differential pressure sensor value is detected within a preset time, and when it exceeds a preset value, the detected value is used as a "compensation value" to compensate for the preset value of step A.

[0022] By adopting the above technical scheme, the present invention has the following beneficial effects: (1) This method utilizes the "water hammer" effect to realize the sealing detection of the vacuum system. It does not have high requirements for the repeatability of the background vacuum degree, and does not have high requirements for the sealing of the vacuum system. It is very suitable for online detection of the whole product in which the vacuum system is repeatedly opened and closed.

[0023] (2) This method can realize rapid detection. The medium leakage that cannot be judged in the original vacuum leak detection and pressure maintenance stage can be judged in the vacuum extraction stage of the existing technology, which greatly shortens the judgment time.

[0024] (3) This method can detect the contents of the package being tested, including gas, liquid, and a mixture of gas and liquid. It has a better detection effect on sealed samples containing liquid, and there is no need to clean up the residual liquid. Experimental data show that the "water hammer" effect is more obvious when liquid leaks. The reason is that liquid has greater inertia than gas, and the shock wave generated is more obvious.

[0025] (4) The present invention sets a reference cavity to eliminate the disturbance effect of shock waves on the pressure field, thereby performing universal testing.

[0026] (5) The present invention adopts a compensation value of the detection data and adds it to the preset value, which can eliminate the influence of high air pressure caused by liquid volatilization; it can solve the technical problem of the prior art that due to the possibility of residual liquid in the contaminated detection cavity, the detection cavity is closed after a short pressure relief, which will cause the liquid in the detection cavity to volatilize. At this time, the pressure in the detection cavity is greater than the atmospheric pressure, thereby causing a misjudgment of the differential pressure sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments and in conjunction with the accompanying drawings, wherein

[0028] Figure 1 It is a schematic diagram of the vacuum system of the present invention;

[0029] Figure 2 To detect a leak-free sample, the current of the differential pressure sensor changes with time after the valve is opened;

[0030] Figure 3 Schematic diagram of the data difference between intact samples and leaking samples. DETAILED DESCRIPTION

[0031] Embodiment 1

[0032] Figure 1It is a schematic diagram of a rapid vacuum system, and YV represents a solenoid valve, which is used to control the opening and closing of the vacuum pipe 8. The sample 51 to be tested is placed in the detection chamber 5, and the reference entity 61, which is slightly larger than the sample to be tested, is placed in the reference chamber 6. It is worth pointing out that due to the inevitable slight differences in the volume of the tested samples, and the differential pressure sensor is very sensitive, when the tested sample is leak-proof and the volume is larger than the reference entity, the negative phase pressure of the differential pressure sensor is greater than the positive phase pressure, and no value is displayed, and detection and judgment cannot be performed. Therefore, the volume of the reference entity should be greater than the volume of the tested sample. The straight line is a vacuum pipe. The function of the vacuum pump 1 is to extract the pipeline gas to reach a certain vacuum degree, and the solenoid valve YV1 is used to control the opening and closing of the main pipeline of the vacuum pipeline. A rapid vacuum leak detection system comprises a vacuum pipe 8 connected to a vacuum pump 1 at one end, the vacuum pipe being provided with a solenoid valve YV1 for controlling the on / off of the vacuum pipe and a pressure sensor 2 for detecting the pressure of the vacuum pipe in sequence, a solenoid valve YV2 and a solenoid valve YV3 being provided in parallel at the other end of the vacuum pipe, and further comprising a first cavity 3, a second cavity 4, a detection cavity 5 with a sample to be detected 51 built in, a reference cavity 61 with a reference entity 61 built in, and a differential pressure sensor 7, the vacuum pipe where the solenoid valve YV2 is located being connected to the first cavity, the solenoid valve YV4, and the detection cavity in sequence until being connected to the positive phase of the differential pressure sensor; the vacuum pipe where the solenoid valve YV3 is located being connected to the second cavity, the solenoid valve YV5, and the reference cavity in sequence until being connected to the negative phase of the differential pressure sensor.

[0033] The present invention also provides a leak detection method using the rapid vacuum leak detection system, comprising the following steps:

[0034] Step 1: Open solenoid valves YV1, YV2 and YV3, close solenoid valves YV4 and YV5, turn on the vacuum pump, and when the pressure sensor reaches the set threshold, close the solenoid valve YV1 and delay the closure of the vacuum pump;

[0035] Step 2: After a certain period of time, when the pressure values ​​of the first cavity and the second cavity are equal and stable, close the solenoid valve YV2 and the solenoid valve YV3 at the same time; if the pressure sensor cannot maintain stability, the system is shut down and waits for instrument inspection. After the inspection, execute step 1. If the pressure sensor maintains stability, execute the next step;

[0036] Step 3: Open the solenoid valve YV4 and the solenoid valve YV5 at the same time, and start recording the differential pressure sensor data, the data of the differential pressure sensor is the current value, and then perform leakage detection based on the current value.

[0037] Preferably, the current value leakage detection determination method is:

[0038] Step A: If the current value of the differential pressure sensor signal reaches a preset value within a preset time, it is determined to be a leak;

[0039] Step B: If the current value of the differential pressure sensor signal does not reach the preset value within the preset time, then enter the next step to execute the next judgment mode;

[0040] Step C: Enter the pressure growth rate judgment mode and use discrete data for interpolation judgment to determine whether there is a leak.

[0041] As a preferred method, the specific method of using discrete data for interpolation judgment is:

[0042] Step a: exporting the current value data of the differential pressure sensor according to the sampling frequency to form equally spaced discrete data;

[0043] Step b: using the difference method to obtain the first-order and second-order derivatives of the equally spaced discrete data,

[0044] Step c: judging the first-order derivative, if it is less than the preset value 1, it is a leak, and the leak pore radius is large, the detection cavity is marked as "contaminated";

[0045] If it is greater than the preset value 1, the second-order derivative judgment stage is entered; if it is less than the preset value 2, it is a leak, and the detection cavity is marked as "contaminated" and the leak pore radius is small; if the second-order derivative is greater than the preset value 2, it is well sealed. Regarding preset values ​​1 and 2, theoretically both preset values ​​should be 0, but when actually testing data, the high accuracy of the differential pressure sensor and the high environmental noise will cause the test data to fluctuate. Therefore, according to actual conditions, preset values ​​1 and 2 are often slightly less than 0.

[0046] The data extracted in the present invention are the data after the solenoid valve YV4 and the solenoid valve YV5 are opened for a certain preset time. When the pressure acceleration judgment mode is used to judge the leakage, it is only necessary to perform a simple wind blowing drying and cleaning on the detection cavity, which greatly shortens the drying and cleaning time. The existing technology can only use the wind blowing cleaning method when there is a gas leak, and can only use other complex cleaning methods such as washing when there is a liquid leak. In addition, the previous technology cannot perform liquid leakage detection using online detection; however, since the present invention applies this system, it can directly use the wind blowing drying and cleaning method to clean gas leaks, liquid leaks, and gas-liquid leaks.

[0047] Solenoid valve YV4 and solenoid valve YV5 are three-way solenoid valves. After the detection is completed, solenoid valve YV4 and solenoid valve YV5 are connected to the vacuum pipeline and the pressure relief is opened. After the pressure reaches the preset value, the pressure relief is closed and the pipeline connection of solenoid valve YV4 and solenoid valve YV5 is disconnected.

[0048] Within the preset time, the differential pressure sensor value is detected. If it does not reach the preset value, the "contamination" mark of the original detection cavity is cleared; when it exceeds the preset value, the detected value is used as the "compensation value" to compensate the preset value of step A.

[0049] During the implementation process, the test preparation stage is first entered: the solenoid valves YV4 and VY5 are closed, and the solenoid valves YV1, YV2, and YV3 are opened. When the pressure sensor reaches the preset vacuum value, the solenoid valve YV1 is automatically controlled to close. After the solenoid valve YV1 receives the closing signal of the solenoid valve YV1, the solenoid valves YV2 and YV3 are closed at the same time after a certain preset time delay. The purpose of using multiple solenoid valves is to delay for a certain time so that the gas diffusion in the first cavity and the second cavity is stable and the pressure is equal. The reason for setting the cavity is that the vacuum pump is a slow process. If the vacuum pump is used directly to pump the test cavity and the reference cavity, the pressure gradient generated in the vacuum stage is small, and the "valve" in the "water hammer" effect cannot be opened quickly. The "water hammer" phenomenon is not obvious. In the detection stage, the solenoid valves YV1, YV2, and YV3 remain closed, and the solenoid valves YV4 and YV5 are opened at the same time. Before the solenoid valve is opened, the pressure value in the cavity is significantly lower than the atmospheric pressure, while the pressure in the detection cavity and the reference cavity is atmospheric pressure. After the solenoid valve is opened, the gas flows from the reference cavity and the detection cavity into the second cavity and the first cavity respectively, and the pressure in the reference cavity and the detection cavity drops sharply. The differential pressure sensor detects the pressure difference in one direction, and its positive phase is connected to the detection cavity, and the negative phase is connected to the reference cavity. Considering the leakage judgment process, if there is a leak in the sealed package, the gas in the sealed package overflows, and the pressure in the detection cavity is greater than that in the reference cavity. In the process close to steady state, the pressure in the detection cavity is always greater than that in the reference cavity, and the pressure difference growth rate gradually decreases. At this time, the leakage of the sealed package is mainly judged by judging that the current signal of the differential pressure sensor reaches a certain threshold, that is, the pressure difference between the reference cavity and the detection cavity. When a small amount of liquid overflows from the sealed package, or there is residual liquid in the previous detection cavity, the current threshold of the differential pressure sensor cannot judge the leakage. At this time, the leakage is judged by judging whether the growth rate of the current signal decreases or tends to 0 during the increasing process.

[0050] like Figure 2 As shown, Figure 2 To detect leak-free samples, the current of the differential pressure sensor changes with time after the valve is opened. The current of the differential pressure sensor is proportional to the pressure, and the detection range of the differential pressure sensor is 4 to 20 mA. Figure 2 It can be seen that the time for gas diffusion to stabilize is very short, basically completed within 3 seconds, and the current increase rate during the diffusion process changes from fast to slow, and finally tends to a stable value.

[0051] It is necessary to emphasize the necessity of using a reference cavity for many reasons. First of all, if a reference cavity is not used, the differential pressure sensor needs to be replaced by a pressure sensor, and the measurement accuracy of the pressure sensor is not as high as that of the differential pressure sensor, and the high-precision pressure sensors are mostly segmented, that is, the absolute measurement range is short and universal testing cannot be performed. The cost of pressure sensors is generally higher than that of differential pressure sensors. Secondly, in the process of opening solenoid valves YV4 and YV5, the "positive water hammer" phenomenon will also occur. In order to eliminate the disturbance effect of shock waves on the pressure field, a reference cavity is used to eliminate it.

[0052] Considering that different test samples have different final effects, 10mL oral liquid is used as an example, and pores are pre-made to observe the data difference between intact samples and leaking samples. Figure 3 The following is a 10 mL intact sample of oral solution (see Figure 3 sealed curve), the sample with pore channel in the liquid part (see Figure 3 Liquid curve) and samples with pore channels in the gas part (see Figure 3 The leak1, leak2, and leak3 curves) show the current of the differential pressure sensor after the solenoid valve YV4 and the solenoid valve YV5 are turned on. It can be seen from the figure that the intact sample of this embodiment completes gas diffusion stabilization within 5 seconds and remains at about 5.8mA, the sample with pores in the liquid part is stabilized at about 7.4mA, and the sample with pores in the gas part is stabilized at about 12mA. The leak1, leak2, and leak3 curves indicate the current changes of the samples to be tested with different gas contents (such as oral liquids, which contain different amounts of gas). The leakage of liquid and gas can be judged from the final stable value, and the most obvious one is gas leakage. It can be seen from the test curves of the five samples that the sample pores have a significant slope reduction regardless of whether they are leaking in the air part or in the liquid part. Therefore, leakage can be judged by data processing of the system and method of the present invention.

[0053] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A rapid vacuum leak detection method, characterized in that: The rapid vacuum leak detection method is implemented by a rapid vacuum leak detection system, the rapid vacuum leak detection system comprising a vacuum pipe (8) connected to a vacuum pump (1) at one end, the vacuum pipe being provided with a solenoid valve YV1 for controlling the on / off of the vacuum pipe and a pressure sensor (2) for detecting the pressure of the vacuum pipe in sequence, the other end of the vacuum pipe being provided with a solenoid valve YV2 and a solenoid valve YV3 in parallel, and further comprising a first cavity (3), a second cavity (4), a detection cavity (5) containing a sample to be detected (51), a reference cavity (6) containing a reference entity (61), and a differential pressure sensor (7), the vacuum pipe where the solenoid valve YV2 is located being connected to the first cavity, the solenoid valve YV4, and the detection cavity in sequence until it is connected to the positive phase of the differential pressure sensor; the vacuum pipe where the solenoid valve YV3 is located being connected to the second cavity, the solenoid valve YV5, and the reference cavity in sequence until it is connected to the negative phase of the differential pressure sensor; The rapid vacuum leak detection method comprises the following steps: Step 1: Open solenoid valves YV1, YV2 and YV3, close solenoid valves YV4 and YV5, turn on the vacuum pump, and when the pressure sensor reaches the set threshold, close the solenoid valve YV1 and delay the closure of the vacuum pump; Step 2: After a certain period of time, when the pressure values ​​of the first cavity and the second cavity are equal and stable, close the solenoid valve YV2 and the solenoid valve YV3 at the same time; if the pressure sensor cannot maintain stability, the system is shut down and waits for instrument inspection. After the inspection, execute step 1. If the pressure sensor maintains stability, execute the next step; Step 3: Open the solenoid valve YV4 and the solenoid valve YV5 at the same time, and start recording the differential pressure sensor data, the data of the differential pressure sensor is the current value, and then perform leakage detection according to the current value; The current value leakage detection determination method is: Step A: If the current value of the differential pressure sensor signal reaches a preset value within a preset time, it is determined to be a leak; Step B: If the current value of the differential pressure sensor signal does not reach the preset value within the preset time, then enter the next step to execute the next judgment mode; Step C: Enter the pressure growth rate judgment mode and use discrete data for interpolation judgment to determine whether there is a leak; The specific method of using discrete data for interpolation judgment is: Step a: exporting the current value data of the differential pressure sensor according to the sampling frequency to form equally spaced discrete data; Step b: using the difference method to obtain the first-order and second-order derivatives of the equally spaced discrete data, Step c: judge the first-order derivative. If it is less than the preset value 1, it is leaking, and the leaking pore radius is large; if it is greater than the preset value 1, enter the second-order derivative judgment stage. If it is less than the preset value 2, it is leaking, and the leaking pore radius is small; if the second-order derivative is greater than the preset value 2, it is well sealed, and the preset value 1 and the preset value 2 are less than 0; The volume of the reference entity is greater than the volume of the sample to be detected; The extracted data is the data after the solenoid valve YV4 and the solenoid valve YV5 are opened for a certain preset time.

2. The rapid vacuum leak detection method according to claim 1, characterized in that: Solenoid valve YV4 and solenoid valve YV5 are three-way solenoid valves. After the detection is completed, solenoid valve YV4 and solenoid valve YV5 are connected to the vacuum pipeline and the pressure relief is opened. After the pressure reaches the preset value, the pressure relief is closed and the pipeline connection of solenoid valve YV4 and solenoid valve YV5 is disconnected.

3. The rapid vacuum leak detection method according to claim 2, characterized in that: Within a preset time, the differential pressure sensor value is detected. When it exceeds the preset value, the detected value is used as a "compensation value" to compensate the preset value of step A.

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