JPS6364734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a leak detector that performs exhaust using a turbo-molecular pump.

A conventional leak detector of this type has a configuration as shown in FIG. That is, by placing the starting end of the vacuum pumping line 3, which is made up of a turbo molecular pump 1 and an auxiliary vacuum pump 2 inserted in series, facing into the test object 4, and operating both the pumps 1 and 2. Then, the inside of the vacuum exhaust system path 3 is 2×10 ^-4 Torr ~
We try to create a high vacuum of 10 ^-9 Torr or ultra-high vacuum. And this vacuum exhaust system path 3
An analyte gas inlet 5a of the mass spectrometer tube 5 is opened on the upstream side of the turbo molecular pump 1. Note that 6 is a vacuum gauge for measuring the pressure of this mass spectrometer tube 5. This vacuum gauge 6 is 2×
It also has a protection function that cuts off the power supply to the filament of the ion source of the mass spectrometer tube 5 when the pressure reaches 10 ^-4 Torr or higher. Further, 7 is a throttle valve inserted near the starting end of the evacuation system 3, and 8 is connected to a part of the evacuation system 3 upstream of the throttle valve 7 via a valve 9. It is a roughing pump.

With such a configuration, a leak test can be performed as follows. That is, first, after performing preliminary evacuation from atmospheric pressure to a pressure range of 1 to ^10-2 Torr using the roughing pump 8, the valve 9 is closed and the throttle valve 7 is opened, and then the probe gas is supplied. A certain amount of helium gas is sprayed onto the crack-shaped leak location on the test piece. Then, due to the pressure difference between the inside and outside of the test object 4, the helium gas leaks into the test object 4 through the leakage point. Then, this helium gas flows into the mass spectrometer tube 5 via the throttle valve 7 and is simultaneously discharged into the atmosphere by the turbo molecular pump 1 and the auxiliary vacuum pump 2. The helium gas that has flowed into the mass spectrometer tube 5 is positively ionized by thermionic bombardment in the ion source together with other gas molecules, and the m/m of ions is determined according to the well-known principle of magnetic field deflection type mass spectrometry. Separated by e (m = atomic mass number of gas, e = amount of charge of ion). That is, the mass spectrometer tube 5 of the helium leak detector is designed so that only helium ions with m/e = 4 reach the ion collector, so the helium ions receive free electrons and return to their original neutral state. Back to molecules. Therefore, in the ion collector, a so-called ion current proportional to the amount of helium ions is obtained, and by measuring this ion current, it is possible to detect the amount of helium gas leaking.

By the way, assuming that the amount of thermionic radiation at the ion source in the mass spectrometer tube 5, that is, the electron current, is constant, the amount of helium ions produced is equal to the amount of helium gas molecules that enter the ion source, that is, the amount of helium gas. Proportional to pressure. Therefore, the specific sensitivity R of the mass spectrometer tube 5 is as follows: R=I/P(A/Torr), where the partial pressure of helium gas is P (Torr) and the ion current is I(A). ...(1) It is expressed by the formula. In addition, the mass spectrometer tube 5
Essentially, it cannot operate unless the pressure is 2×10 ^-4 Torr or less, that is, in a high vacuum region, so it is evacuated to a high vacuum using the turbo molecular pump 1, etc. Assuming that the pumping speed of pump 1 is S (/sec) and the amount of helium gas leaked is Q (Torr /sec), the partial pressure P of helium gas mentioned above is: P=Q/S (Torr) ...(2) It is expressed by the following formula. Therefore, these formulas
As is clear from (1) and (2), if the helium gas leakage amount Q is constant, the smaller the pumping speed S becomes, the more the partial pressure P of helium gas in the mass spectrometer tube 5 increases, causing leakage. The sensitivity as a detector is improved. In other words, the sensitivity of such a leak detector is controlled by the pumping speed S of the turbomolecular pump 1. However, if the evacuation speed S is made too small, the gas emitted from the wall surface constituting the high vacuum space will not be exhausted, and the total pressure in the mass spectrometer tube 5 will increase. Sensitivity cannot be improved by reducing S indefinitely. It is necessary to set the pumping speed to such an extent that the total pressure of the mass spectrometer tube 5 remains in the high vacuum region. Therefore, the sensitivity of the conventional leak detector in which the analyte gas inlet 5a of the mass spectrometer tube 5 is opened on the upstream side of the turbomolecular pump 1 in the evacuation system 3 has a limit in this respect.

The present invention has been made in view of these circumstances, and has a unique configuration in which the gas analyte inlet of the mass spectrometer is opened in the middle of the gas molecule compression system using a turbo molecular pump, thereby achieving dramatic sensitivity. The present invention provides a leak detector that can improve the performance of the leak detector.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. Note that the same parts as in the conventional example shown in FIG. 1 are given the same symbols, and the explanation will be omitted.

In a leak detector comprising a vacuum exhaust line 3 in which a turbo molecular pump 11 and an auxiliary vacuum pump 2 are inserted in series, the turbo molecular pump 11
The gas analyte inlet 5a of the mass spectrometer 5 is opened in the middle of the gas molecule compression system. Specifically, the turbo molecular pump 11 has a motor 22 supported on a base frame 21 as shown in FIG.
is firmly attached. The rotor 23 has a cylindrical shape that surrounds the upper half of the motor 22, and on its outer periphery, a rotor blade group 24 is formed by arranging a large number of rotor blades 24a at equal angular intervals in the circumferential direction. are set up in multiple stages. Further, a cylindrical casing 25 whose lower end is airtightly connected to the base frame 21 and surrounds the rotor 23 is provided, and on the inner periphery of this casing 25, a large number of stator blades 26a are arranged in the circumferential direction. Stator blade groups 26 arranged at angular intervals are provided in multiple stages, located between the rotor blade groups 24, 24, respectively. The upper opening of the casing 25 serves as an intake port 27, and the base frame 21 is provided with an exhaust port 28 that communicates with the auxiliary vacuum pump 2. When the rotor 23 of the turbo molecular pump 11 is rotated at high speed, the gas molecules that enter the intake port 27 due to free movement are struck by the first stage rotor blade 24a and sent to the first stage stator blade 26a. The gas molecules that hit the stator blades 26a and bounced back are struck by the rotor blades 24a of the next stage, and then hit the stator blades 26a of the next stage, so that the incident gas is compressed in each stage. It's getting old. Then, when reaching the exhaust port 27, 1×10 ⁸ of chitsuso gas and 1×10 ⁴ of helium gas
It is compressed to a certain degree. The intermediate part of the casing 25 of the turbomolecular pump 11 constructed in this way, that is, the compression of helium gas is 10 ¹
A through hole 25a is provided in a portion of approximately 10 ³ , and a portion of the stator blade 2 corresponding to the through hole 25a is provided.
6a is removed, and the gas inlet 5a of the mass spectrometer 5 is connected to this through hole 25a.

With such a configuration, a leak test can be performed by the same operation as a conventional leak detector, but according to the present invention, the gas to be analyzed intake port 5a of the mass spectrometer 5 is opened in the middle of the gas molecule compression system by the turbo molecular pump 11 to allow the helium gas with increased pressure to flow into the mass spectrometer 5, so the sensitivity as a leak detector is dramatically improved. It is something that can be done.

Specifically, for example, it will be as follows. That is, the turbo-molecular pump 11 is controlled to a certain extent by the ultimate pressure of the auxiliary vacuum pump 2, and if the ultimate pressure of the auxiliary vacuum pump 2 is 1×10 ^-2 Torr, the inlet port 27 of the turbo-molecular pump 11 compresses the pressure. Since the pressure decreases by the ratio, approximately 1×
The ultimate pressure at total pressure is 10 ^-10 Torr. Therefore, assuming that the gas constituting the total pressure is _N2 , if the analysis gas intake port 5a of the mass spectrometer 5 is opened at the point where the total compression ratio becomes 1/2, the total pressure here is 1
The pressure becomes ×10 ^-6 Torr, which is sufficient for the mass spectrometer 5 to operate. Furthermore, since the compression ratio of helium gas at this point is also 1/2, the pressure of helium gas increases by 10 ² compared to the inlet 27 portion. However,
A comparison of this embodiment with the conventional example shown in FIG. 1 is as follows. That is, the pumping speed S of the turbo molecular pumps 1 and 11 is 100 (/sec), and the leakage amount Q of the test object 4 is 1×10 ^-9 (Torr /
sec), the helium partial pressure P obtained by the 5 parts of the mass spectrometer in the conventional example is 1×10 ^-9 (Torr
/sec)/100(/sec)=1×10 ^-11 (Torr). On the other hand, in the embodiment according to the present invention,
Due to the compression action of the turbomolecular pump 11, the pressure of helium gas flowing into the mass spectrometer 5 increases by ¹⁰² . In other words, in this example, (1×10 ^-11 )×(1×10 ² )=1×10 ^-9 (Torr).
This results in a helium partial pressure P that is 100 times greater.
Therefore, it is possible to obtain a sensitivity 100 times higher than that of conventional methods.

In the above embodiment, a case was explained in which exhaust gas was performed using one turbo-molecular pump, but it goes without saying that the present invention is not limited to this type of pump. As shown in the figure, two turbo molecular pumps 11',
11'' may be connected in series for exhaustion.In this case,
By appropriately selecting the pumping speeds of both turbo-molecular pumps 11', 11'', a pipe line connecting the exhaust port of the turbo-molecular pump 11' at the front stage and the intake port of the turbo-molecular pump 11" at the rear stage is created. The analyte gas intake port 5a of the mass spectrometer 5 may be opened in the middle of the mass spectrometer 29. In the above explanation, the mass spectrometer was explained using a magnetic field deflection method as an embodiment.
There are various types of mass spectrometers such as quadrapol mass spectrometers, and the present invention is applicable to these various mass spectrometers.

[Brief explanation of drawings]

FIG. 1 is a circuit explanatory diagram showing a conventional example. Second
The figure is an explanatory circuit diagram showing one embodiment of the present invention, and FIG. 3 is a front sectional view showing a turbo molecular pump section in the same embodiment. FIG. 4 is a front view showing another embodiment of the present invention. 5...Mass spectrometer, 5a...analyte gas inlet, 11, 11', 11''...turbo molecular pump.

Claims (1)

[Claims] 1. A leak detector that performs evacuation using a turbo-molecular pump, characterized in that an analyte gas inlet of a mass spectrometer is opened in the middle of a gas molecule compression line by the turbo-molecular pump.