JPH06194257A - Method and device for measuring gas leak of container - Google Patents

Abstract

PURPOSE:To accurately measure the air leakage of different containers to be measured by using the same reference container by measuring a differential pressure between the respective containers at a point of later when the compressed gases in respective containers attains a thermal equilibium state after the container to be measured and the reference container are filled with a compressed gas. CONSTITUTION:After a solenoid valve SV1 is turned on, the valves SV2 and SV3 are simultaneously turned on to supply a compressed air to a reference container MV and a container to be measured WV from a compressed air source S. The pressures in the containers MV and WV raise and at a point when the both reach a supply pressure PS, the filling is completed and the differential pressure becomes zero. Then, when the supply of compressed air is stopped at a point of time tb, the pressure Pm in the container MV gradually drops due to the temperature change of the compressed air, and the pressure Pw of the container WV due to the temperature change of the compressed air and leakage, respectively, thereby generating a differential pressure D. After the differential pressure D shows its peak at a point of time tc, it attains thermal equilibium state at a point of time ts. A differential meter DPS measures the differential pressure D (t) with time elapse caused by only leakage at the point ts or later and calculates a leake ratio q.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for accurately measuring gas leakage of a container (measurement container) by a differential pressure method.

[0002]

2. Description of the Related Art Conventionally, in order to measure air leakage of a container to be measured, a container (balance container) having exactly the same shape and volume as the container to be measured and having no air leakage was manufactured, and the container to be measured was measured. After supplying compressed air to the container and the balance container and filling them so that they have the same pressure,
It is practiced to stop the supply of compressed air and then measure the differential pressure between these vessels.

When the differential pressure is measured, it is possible to estimate the air leakage amount of the measured container from the differential pressure and the volume of the measured container.

[0004]

However, in the above-mentioned conventional method, in order to eliminate the influence of temperature change due to compression or expansion of compressed air, it is necessary to use a balance container having exactly the same shape and volume as the container to be measured. There is.

Therefore, it is necessary to manufacture a balance container corresponding to each different container to be measured, and to connect it by pipe connection, which is troublesome and extremely inconvenient in practical use.

Moreover, in order to perform accurate measurement, the balance container must have no air leakage at all, so it is not easy to manufacture the balance container, and it takes a lot of time and cost to measure the air leakage. Was.

In view of the above problems, it is an object of the present invention to provide a method and an apparatus for accurately measuring air leakage for different containers to be measured by using the same reference container.

[0008]

In order to solve the above-mentioned problems, a method according to the invention of claim 1 is a method for measuring gas leakage of a container to be measured, wherein After the compressed gas is supplied and filled, the supply of the compressed gas is stopped, and the gas leakage is prevented based on the time change of the differential pressure between the compressed gas in each of the containers after the time ts when they reach the thermal equilibrium state. measure.

In the method according to the second aspect of the present invention, the thermal equilibrium time constant when the time ts when the thermal equilibrium state is reached is regarded as the indial response of the first-order lag element in the temperature change of the compressed gas in each container. Calculate based on th.

In the method according to the third aspect of the present invention, the thermal equilibrium time constant thw of the container to be measured is calculated as follows: the thermal equilibrium time constant thm of the reference container, the time ta at which the compressed gas is completely charged, and the time tb at which the supply of the compressed gas is stopped. , As a function of the differential value of the differential pressure at time tc when the differential pressure becomes an extreme value after stopping the supply of the compressed gas and at the time tb.

According to a fourth aspect of the present invention, there is provided a pipe connecting portion for connecting to a container to be measured, a reference container having no leak and a known thermal equilibrium time constant thm, and the reference container and the container to be measured. A compressed gas source for supplying compressed gas,
An opening / closing valve respectively provided between the reference container and the measured container and the compressed gas source, and a throttle valve provided between the reference container and the measured container and each of the opening / closing valves, The differential pressure D between the reference container and the measured container is
And a differential pressure gauge for measuring at least after the time point ts when both the compressed gases in the respective containers reach the thermal equilibrium state.

[0012]

The gas leakage of the containers to be measured is performed by using the same reference container, supplying compressed gas to these containers to fill them and stopping the supply of compressed gas, Both are measured based on the time change of the differential pressure after the time ts when the thermal equilibrium state is reached.

The temperature change of the compressed gas in each container is regarded as the indial response of the first-order lag element, and the time ts is obtained based on the thermal equilibrium time constant th. The thermal equilibrium time constant thw of the measured container is obtained as a function of the thermal equilibrium time constant thm, the time points ta, tb, tc, and the differential value of the differential pressure at the time point tb.

[0014]

1 is a circuit diagram showing the configuration of a measuring apparatus 1 according to the present invention. In FIG. 1, the measuring device 1 includes a compressed air source PS, a filter FT, a pressure adjusting valve RV, solenoid valves SV1 to SV3, throttle valves SE1 to SE2, a reference container (master container) MV, a differential pressure gauge DPS, and a recorder RE. Measured container W
It is composed of a pipe connection portion 21 for connecting V and the like.

The reference container MV is commonly used for all the measured containers WV and has no leakage.
The thermal equilibrium time constant thm is known. Thermal equilibrium time constant thm
Will be described later.

The differential pressure gauge DPS is for measuring a minute differential pressure D (t) between the reference container MV and the measured container WV. The recorder RE records the differential pressure D (t) on the memory. The recorded time change of the differential pressure D (t) is processed by a microcomputer or the like.

The compressed air source PS is for supplying compressed air to the reference container MV and the measured container WV, and is adjusted to an appropriate pressure by the pressure adjusting valve RV.
The solenoid valves SV1 to SV3 are for controlling the supply and stop of compressed air to the reference container MV or the container to be measured WV. When the solenoid valves SV2 and 3 are closed, the solenoid valves SV1 to WV are supplied to these containers MV and WV. The air flow is completely cut off.

The throttle valves SE1 and SE2 adjust the flow rates of the compressed air to the reference container MV and the measured container WV so that the differential pressure between the containers MV and WV is not generated as much as possible when the compressed air is supplied. It is for Therefore, the throttle valve SE on the measured container WV side
Reference numeral 2 denotes a variable diaphragm, which is adjusted according to the volume of the container WV to be measured.

FIG. 2 is a diagram showing the operation timing of each device when the measurement device 1 measures the air leakage.
In FIG. 2, the vertical scales of the pressure Pm (t) in the reference container MV and the pressure Pw (t) in the measured container WV are equal to each other, and the vertical scale of the differential pressure D (t) is The scale has been expanded.

When the solenoid valve SV1 is turned on and then the solenoid valves SV2 and 3 are turned on at the same time, the supply of compressed air to the reference container MV and the measured container WV is started. The supply start time point to = 0.
As a result, the compressed air flows through the throttle valves SE1 and SE2 into the respective containers MV and WV, and the respective pressures P
m (t) and Pw (t) rise.

During this period, the differential pressure D (t) is generated, but at the time ta when both the pressures Pm (t) and Pw (t) reach the supply pressure Ps, that is, the filling into both the containers MV and WV is completed. At that time, the differential pressure D (t) becomes zero.

At a subsequent time point tb, the solenoid valves SV2, 3 are turned off, and the supply of compressed air to both the containers MV, WV is stopped. Then, the pressure Pm (t) and Pw (t) in the reference container MV decrease due to the temperature change of the compressed air and the temperature change and leakage of the compressed air in the measured container WV, respectively. A differential pressure D (t) is generated. At this time, at time tc, the first peak of the differential pressure D (t) occurs. After that, the differential pressure D (t) once becomes 0, the positive and negative are reversed, and gradually increases.

The compressed air in both vessels MV and WV is at time t.
At s, a thermal equilibrium state is reached, and thereafter, the differential pressure D (t) changes only due to the leakage of the measured container WV. After an appropriate time has passed from the time point ts, the solenoid valve SV1 is off and the solenoid valve SV2,
3 is turned on, and the compressed air in both containers MV and WV is discharged. Then, the solenoid valves SV2, 3 are turned off, and the measurement of the differential pressure D (t) is completed.

Based on the time change of the differential pressure D (t) thus measured after time ts, the container W to be measured is measured.
The leak rate q of V can be obtained. That is, the leakage rate q
Is the ratio of air leaked per unit time to the amount of air in the measured container WV, and is calculated by the following equation (1).

Q = [1 / Po] · dD (t) / dt (t = ts) (1) As described above, in the measurement using the measuring device 1, the shape and volume of the measured container WV, etc. Irrespective of the fact, that is, even when various containers WV to be measured are replaced, the same reference container M
V is used and the reference container MV is not replaced. Instead, in order to eliminate the influence of the temperature change of the compressed air due to the difference in shape and volume of the containers MV and WV, the differential pressure D after the time ts when the thermal equilibrium state is reached.
The leak rate q is obtained based on the time change of (t).

The waveform of the differential pressure D (t) shown in FIG.
When the thermal equilibrium time constant thw of the measured container WV is smaller than the thermal equilibrium time constant thm of the reference container MV (thw ≦ th
m), but FIG. 3 shows the opposite case (thw> t).
It is a figure which shows the example of the waveform of the differential pressure D (t) of (hm).

Next, a method for obtaining the time ts at which the thermal equilibrium state is reached will be described. First, the inventor of the present invention approximated the temperature change of the compressed air in the container due to heat transfer through the wall of the container as the indial response of the first-order lag element. Then, the temperature T (t) of the compressed air in the container
Is expressed by the following equation (2) using the time constant th.

T (t) = To + [T (0) −To] · e ^{−t / th} (2) where To is the ambient temperature of the container T (0) is the temperature of the container at t = 0, and It was discovered that the thermal equilibrium time constant of the compressed air in the container can be defined as the time constant th of the equation (2), and it was confirmed experimentally.

The thermal equilibrium time constant thw of the compressed air in the container to be measured WV is obtained as follows. First, the constant (heat transfer constant) H relating to the heat transfer property of the container is defined as H = f (Sh, ht, V) (3). Here, Sh represents the heat transfer area of the container, V represents the volume, and ht represents the heat transfer coefficient. This (3)
The heat transfer constant Hm of the reference container MV is experimentally obtained based on the equation.

Theoretically, the relational expression of th = f (H, ρo, ρ) (4) holds between the thermal equilibrium time constant th and the heat transfer constant H. Further, between the compressed air pressure P in the container and the temperature T, the relational expression P = R · ρ · T (5) holds. Where R is the gas constant of air,
ρo is the density of the atmosphere, ρ is the density of the compressed air in the container,
Represent each.

More specifically, the relationship between the thermal equilibrium time constant thm and the heat transfer constant Hm is expressed by the following equation (6). thm = (ρm / ρo) · (1 / Hm) (6) Here, ρm is obtained by the following equation (7).

[0032]

[Equation 1]

Now, the reference container M at time (time) t
Regarding the differential pressure D (t) between V and the measured container WV, D (t) = Pm (t) −Pw (t) = f [t, Hm, thw, ρo, ρm, Tm (0) , Ρ
w, Tw (0), ...] (8) A logical expression is obtained. By using this formula (8) to derive, the following formula (9), which is a calculation formula for the thermal equilibrium time constant thw, is obtained.

[0034]

[Equation 2]

Here, ta, tb, tc are obtained from the graph of the measured differential pressure D (t), and dD (t) / dt is obtained by the numerical differentiation of the differential pressure D (t) at the time point tb. Further, the heat transfer constant Hm of the reference container MV is experimentally obtained.

Therefore, the graph of the differential pressure D (t) is obtained by properly adjusting the switching timing of the solenoid valves SV1 to SV1 of the measuring device 1, and the thermal equilibrium of the measured container WV is obtained by using the above equation (9). The time constant thw is estimated.

When the thermal equilibrium time constant thw of the compressed air in the container to be measured WV is obtained in this way, the time point ts can be obtained from this as follows. That is, since the time point ts is the thermal equilibrium time of the compressed air in the container, the time point ts is obtained by the following equation (10).

Ts = tb-th · ln [x (ts)] (10) In this equation (10), the effect of heat transfer at time t is evaluated by x (t). x (ts) can be regarded as a constant (= 10 ⁻⁷ ).

Therefore, the time point ts is as follows: ts = tb + 16.1 · thw (11) The above equation (9) changes the heat transfer constant Hm to the thermal equilibrium time constant thm to obtain the following (12). It can be expressed as an expression.

[0040]

[Equation 3]

This equation (12) is derived from the following equation (13).

[0042]

[Equation 4]

However, in the equation (13),

[0044]

[Equation 5]

[0045]

[Equation 6]

Where κ is the specific heat ratio, Po is the atmospheric pressure,
Ps represents the supply pressure, respectively. As described above, in calculating the leak rate q by the differential pressure method, the influence of the temperature change of the compressed air cannot be ignored, but in principle, the temperature change of the compressed air in the container can be quantified by a theoretical formula. If it is possible to evaluate it, it is possible to solve the problem. Further, if the thermal equilibrium time constant th of the compressed air in the container is given and further various parameters representing the initial state of the compressed air in the container and the environment outside the container are given, a theoretical formula expressing the temperature change of the compressed air in the container is given. Is required.

However, since the thermal equilibrium time constant th is governed by the heat transfer property of the container, etc., the measured container W to be inspected
The thermal equilibrium time constant thw for V is an undetermined constant before the measurement of the leakage rate q.

Therefore, in the measuring method using the above-described measuring device 1, the thermal equilibrium time constant thw is estimated by the differential pressure method at the stage of filling compressed air and thermal equilibrium during the measurement of the differential pressure D (t). It was decided.

Thermal equilibrium time constant thw estimated in this way
From the time point ts, the time point ts is obtained from the differential pressure D
Since the leakage rate q is obtained based on the time change of (t),
Even if the same reference container MV is used, the leak rate q can be accurately measured without being affected by the temperature change due to the difference from the measured container WV.

Therefore, it is not necessary to manufacture a reference container MV corresponding to each different container to be measured WV or to attach it by pipe connection, and the work for measurement becomes extremely simple. Moreover, since it is only necessary to manufacture one reference container MV without air leakage, it is possible to significantly reduce time and cost.

When the volumes of the reference container MV and the measured container WV are significantly different, the switching timings of the solenoid valves SV1 to SV1 to SV3 at each stage such as filling, equilibrium, and measurement in the whole process of measurement may be changed.
Overpressure that is considerably larger than the measurement range of the differential pressure gauge DPS may occur during measurement. However, by adjusting the throttle valve SE2, it is possible to adjust the time until completion of filling of each to be substantially the same, and prevent the differential pressure D (t) from becoming too large.

That is, the differential pressure D (t) is determined by the measured container WV.
In addition to the air leak, the measured container WV and the reference container M
It also occurs due to the volume difference from V and the effect of temperature change. It is known that the differential pressure D (t) before the time point ta shown in FIG. 2 is generated by the former and the differential pressure D (t) after the time point ta is generated by the latter.

Among these, the differential pressure D (t) before the time point ta is reduced by adjusting the throttle valve SE2. As for the differential pressure D (t) after the time point ta, its extreme value [D (tc)] and the thermal equilibrium state, that is, the value of the differential pressure D (t) after the time point ts is a function of the time point tb. By adjusting the time point tb according to the switching timing of the solenoid valves SV1 to SV3, it is possible to eliminate or reduce the overpressure.

The heat transfer constant Hm of the reference container MV is
The pressure Pm (t) of the air inside the reference container from the time point tb is experimentally measured and is obtained by the least square method using the following equation.

[0055]

[Equation 7]

However, in the pressurizing process before the time point ta, the heat transfer coefficient thm of the container wall becomes considerably larger than in the case other than the pressurizing process due to the influence of the vortex flow of the air in the container, and the reference container MV The heat transfer constant Hm of is expected to be considerably larger than that obtained by the above method. Therefore, it is necessary to experimentally obtain only the value of the heat transfer constant Hm in the pressurizing step using the following equation.

[0057]

[Equation 8]

In the above embodiment, the solenoid valves SV1 to SV1 to 3 are used to open and close the flow paths of the container to be measured WV and the reference container MV, but various valves other than this can be used. The throttle valve SE1 may be variable. In addition, the configuration of the measuring device 1 can be variously changed in accordance with the gist of the present invention. INDUSTRIAL APPLICABILITY The present invention can be applied to measurement of gas leakage of various containers in various industries such as the automobile industry, the valve industry, the medical device industry, the electrical equipment industry, and the like.

[0059]

According to the present invention, it is possible to accurately measure air leakage for different containers to be measured by using the same reference container.

According to the second or third aspect of the invention, the time ts can be obtained in the leak measurement, and the fact that the thermal equilibrium state has been reached can be known earlier and the measurement can be performed in a short time.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a measuring device according to the present invention.

FIG. 2 is a diagram showing an operation timing of each device when an air leak is measured by a measuring device.

FIG. 3 is a diagram showing an example of a waveform of a differential pressure when the thermal equilibrium time constant of the reference container is smaller than the thermal equilibrium time constant of the measured container.

[Explanation of symbols]

 1 Measuring device 21 Piping connection part WV Measured container MV Reference container th, thw, thm Thermal equilibrium time constant ta, tb, tc, ts time point D (t) Differential pressure PS Compressed air source (compressed gas source) SV1 to 3 Solenoid valve (Open / close valve) SE1-2 throttle valve DPS differential pressure gauge

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 13, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012]

The gas leakage of the containers to be measured is performed by using the same reference container, supplying compressed gas to these containers to fill them and stopping the supply of compressed gas, The measurement is performed based on the time change of the differential pressure after the time ts when both reach the thermal equilibrium state.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction content]

However, since the thermal equilibrium time constant th is governed by the heat transfer property of the container, etc., the measured container W to be inspected
The thermal equilibrium time constant thw for V is an unknown constant before the measurement of the leakage rate q.

[Procedure amendment]

[Submission date] December 13, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

Claims (4)

[Claims] 1. A method for measuring gas leakage in a container to be measured, which comprises supplying compressed gas to a container to be measured and a reference container, filling the compressed gas, and then stopping the supply of the compressed gas. A method for measuring gas leakage in a container, which comprises measuring gas leakage based on the time change of the differential pressure between the compressed gas and the time point (ts) after reaching a thermal equilibrium state. 2. The time point (ts) when the thermal equilibrium state is reached,
The thermal equilibrium time constant (t when the temperature change of the compressed gas in each container is regarded as the indial response of the first-order lag element)
The method for measuring gas leakage in a container according to claim 1, wherein the method is based on h). 3. A thermal equilibrium time constant (thw) of the container to be measured.
The thermal equilibrium time constant (thm) of the reference container, the time point (ta) when the compressed gas was completely filled, the time point (tb) when the supply of the compressed gas was stopped, and the differential pressure became the extreme value after the supply of the compressed gas was stopped. 3. The method for measuring gas leakage of a container according to claim 2, wherein the differential value of the differential pressure at the time point (tc) and the time point (tb) is obtained as a function. 4. A pipe connecting portion for connecting to a container to be measured, a reference container having no leakage and a known thermal equilibrium time constant (thm), and for supplying compressed gas to the reference container and the container to be measured. A compressed gas source, and an on-off valve provided between the reference container and the measured container and the compressed gas source, and between the reference container and the measured container and each of the on-off valves. A throttle valve, and a differential pressure gauge for measuring the differential pressure D between the reference container and the measured container at least after the time point (ts) when the compressed gas in each container has reached a thermal equilibrium state. An apparatus for measuring gas leakage in a container, comprising: