SU1640566A1 - Method of calibration of leak detector - Google Patents

Abstract

The invention relates to the monitoring of the leaktightness of products and allows to increase the productivity and efficiency of the calibration of gas analyzing leak detectors. The accumulation chamber is filled with test gas to a predetermined partial pressure. The number of sample gas molecules in the accumulation chamber is determined. A test gas is introduced into the carrier gas stream and, under thermostatic conditions, the signal from the concentration of the test gas is measured by a leaking fluid. The calibration characteristic is determined taking into account the proportionality of the ratio of the values of the concentration signals to the number of molecules of the test gas. 1 ill., 1 tab.

Description

This invention relates to the field of leak testing products.

The purpose of the invention is to increase the productivity and efficiency of calibration of gas analytical leak detectors.

The drawing shows a diagram of the installation for the calibration of gas analytical leak detectors.

The installation includes a unit 1 for the preparation of the sample gas and carrier gas. The test gas line is connected to the internal cavity of the leak-proof product 2 (or its layout), which is located in the storage chamber 3, cut off from the environment by means of a clamping cuff 4. The test gas line is also connected through valve 5 to fitting 6 two-position 7, to which the carrier gas lines (to fitting 8) are connected to valve 9 (to fittings 10 and 11), to accumulation chamber 3 (to fittings 12 and 10), to detector 13 via inductive resistance

14 (to fitting 15), which serves to delay the arrival of the input signal detector.

The detector is a sensing element that converts the input effect of the measuring circuit 16 into a proportional signal. The measuring schema is connected in series with the automatic installation mechanism 17, a recorder 18 and an integrator 19. The installation is controlled using a programmable controller 20. To bring the temperature to a constant valve 5.9 and the detector 13 are placed in a thermostat 21.

The method is carried out as follows.

In the initial position, by signals to, ti, t2, ta, the carrier gas with a constant flow passes through valve 7 through line 8-15 through resistance 14 to detector 13, and a conventional zero signal is recorded on a recorder 18. Test gas under pressure test fills the internal cavity

WITH

Ј

about

(I

about. about

product 2 and in the case of depressurization penetrates through defects into the accumulation chamber 3, spreading through the switching channels. By the signal ti, the gas pressure in the accumulation chamber 3 is brought to atmospheric by connecting the latter with the environment when the valve 4 is opened. By the signal t2-to, the channels of the valve 7 are switched and the carrier gas through channel 8-12 pushes the accumulated gas over time (to -ta) test the amount of test gas from the accumulation chamber 3 to the channel fa and then through resistance 14 to the detector 13. The integrator 19 outputs a signal proportional to the total area Si distributed as a result of the diffusion blurring NI of the molecules of the test gas.

In the calibration mode, to obtain a signal S proportional to the number N of sample gas, in the accumulation chamber 3, instead of the product, its tight layout is placed and a signal t0t2 tits is sent. The flow sections of the switching channels are selected in such a way that the test gas passes through the accumulation chamber 3 and the channels 12-10 and 6-1J to the atmosphere through valve 9. According to the tb signal, the pressure of the test gas in the accumulation chamber 3 becomes equal to atmospheric and when the tato signal is given, the gas the carrier, as in the previous analysis, pushes all N molecules of the test gas to the detector 13. The integrator 19 outputs the signal S.

Thus, in the linear part of the static characteristic of the detector, the ratios of the received signals are proportional to the amounts of sample gas molecules, i.e. NI Si N S

This ratio is valid at constant pressures and temperatures, which imposes restrictions on the flow rate of the carrier gas on some detectors. For example, for an ionization cross section detector with 100% linearity of static characteristics, the space velocity should not exceed 2–3 ml / min. The linearity of the flame ionization detector is not affected by the change in the flow rate of the carrier gas. From the ratio obtained, it follows that

Si

It is important that for a given detector a number of N molecules (and, therefore,

signal S) in the volume V of accumulation chamber 3

is a constant value because

p, n-p-when P, T const, n const.

Hence the N const.

By knowing the number of NJ molecules in the sample gas, other parameters for monitoring tightness can be determined.

It is known that molecular consumption

dNi

dt

or NI

 / QM

idt

to

for the final time At (tcrV2), the molecular flow rate is NI / At. Used as a key parameter in leak detection, the continuum flux Qn is associated with the molecular flow rate by

The table lists the NJ coupling formulas for various modes and types of leaks with defect parameters.

Legend: g, S - equivalent radius and area of a cylindrical defect; h, d — equivalent width and height of a gap defect: I — extent of the defect; t, a is the mass and diameter of the sample gas molecule; y, q2 are molecular densities on both sides of the defect;

2

p 0.94 cr (m + n2) 5 + 141.76 g;

0.94 (h + (5) d a2 (ni + ri2) + 4.24h.

According to the table, you can determine the characteristic dimensions of the leak, the value of Nj and the parameters of the test gas,

The proposed method allows to increase the performance and speed of the calibration operation of gas analytical leak detectors.

Claims (1)

Invention Formula A method for calibrating a gas-leakage leak detector according to the concentration of the test gas, which consists in filling the accumulation chamber with a test gas to a predetermined partial pressure, characterized in that, in order to increase productivity and efficiency, in the accumulation chamber the amount of test gas molecules is pulsed The sample gas from the accumulation chamber to the carrier gas stream is measured using a leak detector, the signal from the concentration of the test gas under thermostatting conditions, and the calibration characteristic is determined eating out with allowance for the proportionality ratio values concentration count signal sample gas molecules.