RU2295710C1 - Method of testing pressure tightness - Google Patents

Abstract

FIELD: testing engineering.

SUBSTANCE: method comprises setting article in the pressure-tight testing chamber, measuring the background concentration of test gas inside it, recording the background value in the additional chamber, and balancing this value with that of the background concentration of test gas in the testing chamber. The article is filled with the test gas and is allowed to stand for a given time. The pressure tightness is judged by the comparison of concentration of the test gas in the chamber with the background concentration. The value of pressure-tightness is determined from the equation presented.

EFFECT: enhanced precision.

1 dwg

Description

The invention relates to the field of testing equipment, in particular for testing products for leaks, and can find application in those areas of technology where high demands are placed on the reliability of products.

There is a known method of leak testing, in which the product is enclosed in a closed shell, the product is filled with control gas, the control gas is accumulated in the volume of the shell, its concentration is measured using a leak detector, and the tightness is judged by the rate of change in the concentration of the control gas in the closed shell (ed. USSR No. 214851, published on March 29, 68).

The disadvantage of this method is the relatively low reliability of the measurement caused by the presence of a control gas in the atmosphere.

There is also a known method of tightness control, in which the product is placed in the chamber, filled with control gas, the background concentration of the control gas in the chamber is measured, and the tightness is judged by the change in the concentration of the control gas in the chamber compared to the background (Vacuum technique. Reference edited by C. C. Frolova et al. M., Mechanical Engineering, 1992, p. 455).

After filling the product with control gas, it is impossible to determine its background value, and the comparison is carried out with the background signal until the product is filled, and the background signal changes over time.

Closest to the proposed technical solution is a method of testing products for leaks by ed. St. USSR No. 1132160 (publ. 30.12.84 g.), Which consists in the fact that the product is placed in a chamber, the background concentration of the control gas is measured in it, then the product is filled with control gas, and simultaneously the background concentration of the gas is different from the control, and the background concentration of the control gas in the chamber after filling the product is judged by the gas concentration that is different from the control, by the ratio between the measured concentrations in time, the tightness is judged by the change in the concentration of the control gas in the chamber compared to the background oh.

The presence of an additional leak detector that registers a gas concentration other than the control also increases the measurement error, since it is likely a change in its concentration and a change in the reactivity of leak detectors during the exposure time.

The aim of the invention is to increase the accuracy and reliability of the results of the tightness control by eliminating the influence of the background of the control gas.

This goal is achieved by the fact that in the method of tightness control the product is placed in a sealed test chamber, the background concentration of the control gas is measured in it, then the cavity of the product is filled with control gas and held for a certain time. The tightness is judged by the change in the concentration of the control gas in the chamber compared to the background. An additional chamber is used, and before filling the product with control gas, the background content of the control gas in the test and additional chambers is recorded and equalized. After exposure of the product, the background value is recorded in the additional chamber, and the leakage is calculated by the ratio:

where Q _And - leakage of the product, g / s;

C _K - the value of the reference concentration of the control gas, g / l;

V _And - free volume of the test chamber, l;

α _And - leak detector response to the concentration of the control gas in the test chamber, μA;

α _Ф - leak detector response to the background content of the control gas in the additional chamber, μA;

α _K - leak detector response to the reference concentration of the control gas, μA;

t _And is the accumulation time of the control gas in the test chamber, sec.

Distinctive features of the proposed method from similar ones is the registration of the background gas concentration of the control gas not only in the test chamber, but also in the additional chamber used, and the background value in both chambers is equalized. This allows you to reduce the effect of changes in the background of the control gas or the reactivity of the leak detector during the test on the result of determining leakage.

The proposed method is illustrated in the drawing, which shows a diagram of a device for implementing the technology of tightness control.

The diagram shows: 1 - product, 2 - test chamber, 3 - probe of the leak detector, 4 - leak detector, 5 - additional camera; 6 - nozzles with plugs for introducing the probe, 7 - pneumatic console for supplying control gas, 8 - capacity with a reference concentration, B1 ... B6 - valves.

The method is as follows.

The product 1 is placed in the test chamber 2. Using the probe 3 of the leak detector 4, the background concentration of the control gas in the test 2 and additional 5 chambers is recorded and its value is equalized, for example, by purging with neutral gas, after which the chambers are sealed.

Then, the test gas is supplied to the product 1 under test pressure and maintained for a certain time t _И necessary for the accumulation of the control gas in the chamber 2. The signal α _{Ф of the} leak detector 3 is recorded in the additional chamber 5, then the response of this leak detector to the content of the control gas from the leakage of the product 1 in the test chamber 2 - α _And .

The response of α _{To the} leak detector 4 to the reference concentration is determined by one of the existing methods, for example, a calibrated leak or a container with a pre-prepared concentration of the control gas can be applied.

The leakage of the product is evaluated by the ratio (1).

The proposed method has been tested in practice when conducting leak testing of butt joints of a high-voltage SF6 circuit breaker. The internal cavities of the circuit breaker were filled with sulfur hexafluoride SF ₆ (SF6 gas), used both as an extinguishing medium and as a control gas. For registration, a TP-3 plasma leak detector was used. Around the controlled butt joint a sealed closed volume was created (test chamber), the free volume was V _И = 15 l. The leak detector readings for the background content in a closed volume and in an additional chamber were 10 μA, so no purging was carried out. The additional chamber was sealed. The accumulation of control gas in a closed volume was carried out for 4 hours. During the accumulation period, the background content of SF6 gas increased at the test site due to technological operations with other switches. The leak detector was switched on before measurement after accumulation. The potentiometer for compensating the background signal, the measuring device of the leak detector was installed in its initial position - α _f '= 10 μA. Then, the response of the leak detector in the closed volume of the butt joint and the additional chamber was determined, while the response of the leak detector, respectively, was α _И = 12 μA, α _Ф = 7 μA. The response to the reference concentration is α _K = 40 μA. The value of the reference concentration in this case was C _K = 1 · 10 ^-8 g / L.

In this case, if the leakage of the product is calculated without taking into account the change in the concentration of the control gas during the test time, then the leakage of the product will be determined by the ratio:

where α _Ф '= 10 μA is the response of the leak detector to the background content of the control gas recorded before the test.

Then the leakage calculated by the relation (2) will be:

If in the calculation we take for the background content of the test gas the leak detector response to the initial background content stored in the additional chamber at the test site - 7 μA, then the leakage from the butt joint calculated according to relation (1) will be:

Thus, without taking into account the initial background content of the control gas, the result of leakage of the control gas from the butt joint is 2.5 times less than the actual value. Taking into account the influence of the background content of the control gas at the test site allowed to increase the reliability of the tests.

The method has increased reliability and accuracy of determining leaks, because a possible change in the background content of the control gas or a change in the reactivity of the leak detector during the accumulation process does not affect the accuracy of the leak test results.

Claims (1)

The method of tightness control, namely, that the product is placed in a sealed test chamber, the background concentration of the control gas in the chamber is measured, the cavity of the product is filled with control gas and held for a certain time, and the tightness is judged by the change in the concentration of the control gas in the chamber compared to the background, characterized in that it uses an additional chamber, and before filling the product with control gas, the background content of the control gas is recorded and equalized in the test nd and additional chambers, after holding the product, the background value is recorded in the additional chamber, and the leakage is calculated by the ratio:

where Q _and - leakage of the product, g / s; C _to - the value of the reference concentration of the control gas, g / l; V _and - free volume of the test chamber, l; α _and - leak detector response to the concentration of the control gas in the test chamber, μA; α _f - leak detector response to the background content of the control gas in the additional chamber, μA; α _to - leak detector response to the reference concentration of the control gas, αA; t _and - time of accumulation of the control gas in the test chamber, sec.