JPS6315133A - Method for checking vacuum leak - Google Patents

Abstract

PURPOSE:To detect a vacuum leak, by a method wherein a pressure change ratio is calculated from an exhaust volume, an exhaust speed, pressure at an exhaust start point and pressure at an exhaust final point during the exhaust process of a vacuum system and the estimated pressure after an arbitrary time obtained from the pressure change ratio is compared with measured pressure obtained when the vacuum system is exhausted for the same time. CONSTITUTION:Valves 2, 6, 7 are closed to start the driving of a vacuum pump 3. When the pressure of the vacuum pump 3 measured on the suction side thereof by a vacuum gauge 5 lowers to predetermined pressure, the main valve 2 is opened. This point of time comes to the exhaust start point of time of a vacuum container 1. A pressure change ratio is calculated from the pressure of the vacuum container 1 at this time and pressure after an arbitrary time at the first time is estimated while pressure after evacuation is performed for the same time is measured. Then, the estimated pressure is compared with the measured pressure and, when the difference between both of them is larger than a threshold value, it is judged that there exists a vacuum leak so that an alarm is emitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a vacuum leak check method for checking the airtightness of the entire vacuum system.

(Prior Art) As is well known, a leak check is to pressurize or depressurize a vacuum container to be examined and check whether gas actually blows out from the container or enters the container. Many of the conventionally used methods are called a pressurized leaving method, a vacuum leaving method, a probe gas method, and the like.

However, the pressurized leaving method is a method in which a vacuum container is left sealed under pressure for a certain period of time to see if there is a drop in pressure.
The vacuum leaving method is based on the same principle as the pressurizing leaving method, and is a method in which a vacuum container is left sealed under reduced pressure for a certain period of time, and the presence or absence of pressure rise is observed.

On the other hand, the probe gas method uses a special gas, such as helium gas, to detect gas ejecting or entering through a leak point.This gas is called a probe gas. A typical detector using this probe gas method is a helium leak detector.

(Problems to be Solved by the Invention) Of the leak check methods described above, the pressurized leaving method and the vacuum leaving method do not allow for the determination of whether the initial pressure or the width of leaving for a certain period of time is within an allowable range. It must be made. Further, in the probe gas method, an expensive leak detector is provided separately from the vacuum device used in the system to be inspected, and inspection work must still be performed manually. therefore,
The leak check work became complicated, took a long time, and required expensive J2 equipment.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to detect vacuum leaks by automatically monitoring pressure changes during the evacuation process of the vacuum system, without requiring equipment or time solely for leak checking. The purpose is to provide a checking method.

[Structure of the invention] (Means and effects for solving the problems) The present invention has the following features:
During the evacuation process of a vacuum system consisting of a vacuum container and evacuation equipment, the rate of pressure change is determined from the pumping volume, pumping speed, starting point pressure, and ending point pressure, and is obtained from this rate of pressure change. By comparing the estimated pressure after a given time with the measured pressure after evacuation for the same time and detecting a vacuum leak from this difference, there is no need for equipment or time just to detect vacuum leaks, and This detection work is also made easier.

(Example) Hereinafter, an example of the vacuum leak check method of the present invention will be described with reference to the drawings. First, the principle of the present invention will be explained.

Generally, the temporal change in pressure when the internal volume V is evacuated by a vacuum pump with an evacuation speed S is given by the following equation.

Here, Qo: Gas leakage and amount of gas generated in the vacuum container po: Ultimate pressure of the vacuum pump However, in reality, it is necessary to perform the following correction to this equation (1).

(1) Correction of pumping speed S by conduit conductance 3-p3eff Here, 5eff: Effective pumping speed C: Conduit conductance (2) Internal volume ■ for gas in internal volume V and gas staying on the inner surface Correction of V-+KV Here, K: Correction coefficient (3) Correction by gas release from the container wall (provided that p is 10-31orr or less) Qo -)Q Q=qA Here, Q: No leakage Total gas release amount q: Gas release amount per unit area A: Container inner surface area From the above, the actual pressure change over time is limited to the case where there is no leakage, and is expressed by the following equation (2a): (2tl) can be obtained from the equation.

(1) KVdJ2 when pressure p is 1O-21orr or more
=-8eff (p-po) -<2a>t (2) When the pressure p is 10-3 TOrr or less, it is equal to V =-
3eff <o-po>10qA・<2b)t In other words, from equations (2a) and (2b), the rate of change in pressure when there is no leakage is K, V, 5eff,
po.

(It can be said that this is a value that can be estimated based on the value of 1, A.

Therefore, by comparing the measured pressure value and the estimated pressure value, it is possible to detect a leak depending on the degree of the difference.

Next, a vacuum system related to an embodiment of the present invention will be explained. In FIG. 1, a vacuum container 1 is evacuated by a vacuum pump 3 with a main valve 2 open, and the internal pressure is measured by a vacuum gauge 4.

The suction side pressure of the vacuum pump 3 is also measured by the vacuum gauge 5. The leak valve 6.7 is provided to introduce N2 gas when the vacuum container 1 and the vacuum pump 3 are returned to atmospheric pressure (vented).

Further, a signal input/output device 8 and a controller 9 are provided for controlling the vacuum system and detecting vacuum leaks. This controller 9 is provided with a CPU and a memory, performs calculations according to the above-mentioned equations (2a) and (2b), and issues a vacuum leak indication and alarm on the display 10 via the input/output device 8.

In addition, from the vacuum gauge 4 (or other detector not shown),
A pressure signal from the vacuum container 1 is input to the input/output device 8 .

Next, the operation of evacuation of such a vacuum system from the atmospheric pressure state will be explained. First, valve 2, leak valves 6 and 7 are closed, and vacuum pump 3 is started. When the suction side pressure of the vacuum pump 3 measured by the vacuum gauge 5 drops to a predetermined pressure, the main valve 2 is opened. This point is the point in time when evacuation of the target vacuum container 1 is started.

Therefore, the pressure Pci of the vacuum vessel 1 at this time is read, the rate of pressure change dp/dt is determined from the above equation (2a), and the pressure Pi (estimated pressure) after the first arbitrary time ts is estimated. On the other hand, the pressure P (measured pressure) after evacuation is performed for the same time ts is measured. Then, this pressure P and pressure PC1 are compared, and the difference is a threshold value (thresholc).
l) When the difference is smaller than dPIim, it is determined that there is no vacuum leak, and when the difference is larger than the threshold value dl)Iim, it is determined that there is a vacuum leak and an alarm is issued. In this case, a single vacuum leak will not immediately cause an alarm, but will occur several times (
An alarm may be issued when a vacuum leak is determined (3 to 5 times) consecutively, and the value of dplim is set to about three times the estimated pressure Pi, taking into account errors.

When it is determined that there is no vacuum leak, pressure estimation and comparison 1 determination are performed in the same manner at every time ts, and vacuum leak detection is repeated until the end of evacuation. Here, if the pressure at the end of exhaust is 10-3 Torr or less, the above (2b)
Vacuum leak detection is performed in the same manner based on the formula.

FIG. 2 shows a flowchart of the above-mentioned operation, and the third
The figure shows temporal changes in the estimated pressure (indicated by a broken line) and the measured pressure (indicated by a solid line) during the above-mentioned exhaust process. Both figures show an example in which a vacuum leak alarm is issued when a vacuum leak is determined three times in a row.

Therefore, with the above configuration, vacuum leaks can be detected during the evacuation process without requiring a special leak detector.

In the above-mentioned embodiment, evacuation was performed using one stage of the vacuum pump, but for high vacuum evacuation, it is customary to use a multi-stage configuration of vacuum pumps. Even in this case, the vacuum pumps at each stage are operated in series depending on the pressure range, so if we focus only on the main exhaust pump and apply the constants in equation (2a) or equation (2b) above, good.

[Effects of the Invention] Since the present invention is configured as described above, the following effects can be obtained.

(1) Leakage can be detected without using a special leak detector.

(2) Time and effort are not required just to detect leaks.

(3) Leakage can be detected not only in the vacuum container but also in the exhaust system including the vacuum pump, valves, piping, etc.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a vacuum system related to an embodiment of the vacuum leak check method of the present invention, FIG. 2 is a flowchart showing the operation of an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the presence or absence of vacuum leakage and pressure change during the evacuation process. 1...Vacuum container 3...Vacuum pump 4.5...Vacuum gauge 8...Input/output device 9...Controller representative Patent attorney Noriyuki Chika Yudo Hirofumi Mitsumata Figure 1 Figure 2

Claims (1)

[Claims] During the evacuation process of a vacuum system consisting of a vacuum container and evacuation equipment, the rate of pressure change is calculated from the pumping volume, pumping speed, starting point pressure, and ending point pressure. A vacuum leak check method characterized by comparing an estimated pressure after a period of time with a measured pressure after evacuation for the same period of time, and detecting a vacuum leak from this difference.