RU1816973C - Mass-spectroscopy method of hermetic state testing for working pieces - Google Patents

Abstract

Usage: leak detection technique for highly sensitive tests of leakproofness. The inventive product is sealed, placed in a vacuum chamber, connect one of the resulting volumes (the free volume of the vacuum chamber or the internal volume of the product) with the analyzer mass spectrometric leak detector, and the leakage of the product is judged by comparing the two results of measurements with the accumulation of gas in the volume connected to the mass spectrometric leak detector, with the inlet of the test gas into another volume and without the inlet of the test gas at the same accumulation time, and during laziness sample gas in one of the volumes of pumping is carried out other gases from the scope of this selective pumping means, such as a getter. 1 s.p. f-ly. 3 ill.

Description

The invention relates to a leak detection technique and can be used in highly sensitive testing of products using a mass spectrometric leak detector.

The purpose of the invention is to increase the sensitivity and accuracy of control by reducing the amount of gases other than the test one in the accumulated gases transferred to the analyzer.

Figure 1 shows the dependence of the change in the signal of the analyzer's recording device (o) on time (t) for the case when the recorded signal does not exceed the normalizing value (s) of the selected sensitivity range; figure 2 - when the recorded signal exceeds the normalizing value of the selected range

Sensitivity Fig. 3 is a block diagram of an apparatus for monitoring tightness.

The tightness control device (Fig. H) contains a tight chamber 1 into which the test product 2 is placed with selective pumping means 3, valves 4-9, 17, a test cylinder 10 with helium, a pressure gauge 11 for controlling the test gas pressure, fore-vacuum pump 12, high-vacuum pumping means 13, nitrogen trap 14, mass spectrometric leak detector 15, sorption pump 16.

The tightness control of products is carried out as follows.

The test article 2 is placed in an airtight chamber 1. At the same time, selective means is placed in the airtight chamber 1 or in the test article 2

00

 Yu

4

With

pumping 3. There are no fundamental differences in the location of the selective pumping means 3. This is determined in each case by the convenience of testing. At the same time, the following requirement must be fulfilled: selective pumping means 3 and subsequently injected test gas must be on opposite sides of the shell of the test product 2, and that part of the internal volume of the sealed chamber f in which the selective pumping means 3 is placed must communicate with the analyzer. As a selective pumping means 3, for example, a KNT-18 getter is used, which in our case is located on the tested product.

The test article 2 is evacuated to a pressure of not more than 1.3 10 Pa, after which, without stopping the vacuum operation, the getter 3 is activated in accordance with the instructions for its use. Before the beginning of the accumulation operation, the internal volume of the chamber 1 is vacuumized to a pressure of no more than 1.3 10 Pa, then the 4.9 sealed chamber 1 and the test article 2 are cut off by vacuum evacuation valves, while the chamber of the analyzer of the mass spectrometric leak detector 15 is evacuated. When the sealed chamber 1 and the test article 2 are cut off from the vacuum pumping means, the accumulation time (ti) of the background gases of the test article 2 begins.

The minimum necessary accumulation time is estimated before the start of testing, taking into account the value of the minimum reliable signal of the recording equipment (sensitivity threshold), the price of the division of the scale K of the recording equipment and the value of the allowable leak (flow Q through the leak) of the tested product according to the formula:

1n

to

IOCT.

Q

After the time elapsed immediately before transferring the accumulated gases, the pump gas from the analyzer 15 is stopped (valve 6 is closed), pumping of the remaining gases is continued and the concentration of the test gas in the analyzer is started. At a fixed point in time ti 2: tH, by opening valve 4, the gases accumulated in the test product 2 are transferred to the analyzer 15, and soaking is carried out until a linear

5

0

5

0

5

0

5

0

5

the concentration of the sample gas and determine the difference between the total background concentration of the sample gas and the background concentration of the sample gas of the analyzer (i.e., determine the background Dof value of the tested device from the sample gas during the accumulation time ti) by extrapolating the linear portion of the recorded signal after passing to point in time of the start of re-start.

After that, the background test gas is removed by vacuum pumping the test article 2 to a pressure of not more than 1.3 1SG4 Pa and the internal volume of the pressurized chamber 1 is vacuumized to a pressure of more than 1.3 10 Pa, the test product 2 and the pressurized chamber 1 are stopped evacuating, continuing evacuating the chambers of the analyzer of a mass-spectrometric leak detector 15. vacuum into the internal volume of the sealed chamber 1 test gas is injected from the cylinder 10 to a pressure of 1 CgPa (1 atm) and the countdown time of the test gas accumulation in the test article 2 starts. After expiration At no time t непосредственно immediately before transferring the accumulated gases, the pump gas from the analyzer 15 is stopped (valve 6 is closed), while the remaining gases are pumped out, and the concentration of the test gas in the analyzer is started. At a fixed time ti 1n, by opening valve 4, the gases accumulated in the test article 2 are transferred to the analyzer 15, the samples are held until the concentration of the sample gas increases linearly and the difference between the total concentration of the sample gas a and the background concentration of the sample gas of the analyzer Of is extrapolated the linear portion of the recorded signal after bypassing at the time of the start of bypassing. By the difference in the values of Yes and Daph, the leakage of the tested product is judged.

Claims (1)

The claims 1. The method of mass spectrometric control of the tightness of the product, which consists in the fact that on both sides of the test shell of the product create closed volumes, vacuum the first volume, pump out the analyzer during the accumulation of sample gas in the second volume, stop pumping directly from the sample gas analyzer Before transferring the accumulated gas into it, while continuing to pump out the remaining gases, the concentration of test gas is continuously recorded in the analyzer, the accumulated gas is passed into the analyzer, etc. the shutter speed is set until a linear increase in the background concentration of the sample gas is established, the sample gas is supplied to the first volume, all operations are repeated from pumping the analyzer to the shutter until the linear increase in the total concentration of the sample gas is established, the difference between the total and background concentrations is determined by one and the same instant in the linear portion of the rise of one of the concentrations and extrapolation of the linear section of the rise of a different concentration, characterized in that, in order to increase the sensitivity and accuracy of the control, during the accumulation of the test gas in the second volume, all gases except the test one are pumped out of this volume. 2, The method according to claim 1, characterized in that the pumping of all gases except the test one from the second volume is carried out by selective pumping means in the form of a getter. Figure 1