JPH03202718A - Method and apparatus for measuring gas in minute flow rate - Google Patents

Abstract

PURPOSE:To improve the measuring accuracy of a minute flow rate by measuring the time interval from a time point when a soap liquid film for closing the tip opening of a detecting pipe starts expansion to a time point when the soap liquid film is detected with a soap-liquid- film detecting device, and operating the flow rate of gas based on the measured time. CONSTITUTION:Soap liquid 1 is injected into a soap-liquid storing part 7a up to a specified liquid level L. A purging valve V3 is closed, an atmosphere communicating valve V2 is opened and a test valve V1 is opened. A gas to be measured 5 which is introduced into a detecting pipe 4 through the valve V1 is discharged into atmosphere through the valve V2 under this state. Then, a cylinder device 3 is actuated, and a ring body 2 is lifted out of the liquid 1. Then, a liquid film 1a is attached to a tip opening 4d of the pipe 4. The opening 4d is closed with the film 1a. Then, the valve V2 is closed. At the same time, time counting is started with a CPU device 11. Then the film 1a is expanded by the gas 5. A light signal H which is inputted into a light receiving part 9b from an emitting part 9a is totally reflected from the film 1a. The incident light into the light receiving part 9b is screened. A detected signal S is sent into the device 11 from a fiber amplifier 9c, and time counting is stopped. In the device 11, the flow rate of the gas is operated by using the measured value of the time up to the total reflection.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring a small amount of gas and an improvement in a measuring device.

(Conventional technology) In semiconductor manufacturing equipment and vacuum equipment, the flow rate is 0.
, 01 = 0, 02 It is often necessary to detect or measure a small amount of gas on the order of cc/win.

As a device for measuring the minute flow rate of gas as described above, the inventor of the present invention previously developed a membrane flowmeter as shown in FIG. 3 and disclosed it to the public (Japanese Patent Laid-Open No. 63-222221).

That is, by pulling the ring body 2 immersed in the soap liquid 1 upward through the cylinder 3, a soap liquid film 1a is formed inside the ring body 2, and this is applied to the lower end surface 4a of the detection tube 4.
By contacting and adhering to the lower end opening 4b, the lower end opening 4b is closed.

The soap liquid film 1a that closes the lower end opening 4b of the detection tube 4 is lifted upward in the detection tube 4 by the gas to be measured 5 at a predetermined speed. When this soap liquid film 1a passes through point P and point P2, its passage is detected by the liquid film detection sensor 6a and the liquid film detection sensor 6b,
In the computer 7, the flow rate of the gas to be measured 5 is calculated based on the transit time between the two points P□.22.

However, in the membrane flowmeter of JP-A No. 63-222221, the rate of rise of the soap liquid film 1a varies greatly depending on the degree of wetting of the inner wall surface 4c of the detection tube 4.
When the flow rate of is small and the rising speed of the liquid film 1a is slow, 8
There is a drawback that the constant accuracy deteriorates significantly.

In addition, in order to make the rise of the liquid film 1a smooth, the inner wall surface 4C of the detection tube 4 is pre-wetted with soap solution 1, but this wetting soap solution drips over time. It descends and adheres relatively thickly to the lower end surface 4a of the detection tube 4. Then, when the liquid film 1a formed inside the ring body 2 is attached to the lower end surface 4a of the detection tube 4, the lower end surface 4a
The problem is that the thickness of the soap liquid film 1a that closes the lower end opening 4b changes depending on the accumulation of the wetting soap solution in step a, and as a result, the rising speed of the liquid film 1a changes, causing measurement errors. There is.

Furthermore, the soap liquid film 1a once formed inside the ring body 2 is attached to the lower end surface 4a of the detection tube 4, and the lower end opening 4b is closed with the soap liquid film 1a. There is a problem in that it is difficult to stably and reliably attach the liquid film 1a to the lower end surface 4a of the detection tube 4, and the liquid film 1a often breaks.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems in conventional membrane flowmeters, namely (a) When the gas flow rate becomes small, the wetness of the inner wall surface of the detection tube and the lower end surface of the detection tube are reduced. The rate of rise of the liquid film varies greatly depending on the level of accumulation of the wetting soap solution, which significantly deteriorates measurement accuracy. (2) It is difficult to always accurately close the lower end opening of the detection tube with the soap film, and This system aims to solve problems such as the trouble of flow rate detection due to breakage of the liquid film, and allows for easy and highly accurate flow measurement even at minute fluid flow rates, as well as the ability to measure the required amount of soap liquid film. Formation and attachment can be performed easily and reliably.

The object of the present invention is to provide a method and apparatus for measuring a small amount of gas, which makes it possible to significantly improve measurement accuracy and measurement efficiency.

(Means for Solving the Problems) The present device invention comprises a main body case 7 in which a soap solution 1 is stored; an upper end opening 4d thereof protrudes into the main body case 7 above the liquid level of the soap solution 1; The detection tube 4 is arranged at least; The soap solution film adhering device 8 is configured to close the upper end opening 4d of the detection tube 4 with the soap solution film 1a; The soap solution film expanded by the gas to be measured 5; a soap liquid film detection device 9 for detecting the arrival of the liquid 1a at a certain position; the detection tube 4;
A ventilation control bag that controls the atmosphere communication valve v2 that communicates the interior with the atmosphere and the purge valve v3 that supplies purge gas into the detection tube 4! 1o: Measuring the time from the start of expansion of the soap film 1a that closes the tip opening 4d of the detection tube 4 to the detection of the soap film 1a by the soap film detection device 9;
The basic configuration of the invention includes a CPU device that calculates the gas flow rate from the measurement time.

Further, in the present method invention, after opening the atmosphere communication valve v2 to communicate the inside of the detection tube 4 to the atmosphere, the ring body 2 immersed in the soap solution 1 is pulled upward with the detection tube 4 inserted therein. The upper end opening 4d of the detection tube 4 is closed with a soap liquid film 1a,
Thereafter, the atmospheric communication valve v2 is closed to inflate the soap liquid film 1a that closes the upper end opening 4d with the gas to be measured 5, and the time when the soap liquid film 1a starts to expand is measured;
Further, by reflecting the optical signal H by the expanded soap liquid film 1a, the reaching of the soap liquid film 1a to a certain position is detected, and the arrival of the soap liquid film 1a to a certain position from the start of expansion of the soap liquid film 1a is detected. The basic configuration of the invention is to measure the time until the arrival is detected and calculate the flow rate of the gas to be measured 5 from the measured time.

(Function) By opening the atmosphere communication valve v2, the inside of the detection tube 4 is brought into communication with the atmosphere.

In this state, when the ring body 2 is pulled up from inside the soap solution l with the detection tube 4 inserted, a soap solution film 1a is first formed between the outer wall surface of the detection tube 4 and the ring body 2, and then, When the ring body 2 comes to the position of the upper end opening 4d of the detection tube 4, the opening 4d is closed by the liquid film 1a.

Thereafter, when the atmosphere communication valve V2 is closed, the inside of the detection tube 4 is pressurized by the gas 5, and the soap liquid film 1a expands.

When the upper part of the expanded soap liquid film 1a reaches a certain position, the optical signal S is reflected by the liquid film 1a, and the light receiving part 9
Light incidence on b is blocked. As a result, arrival of the liquid film 1a at a certain position is detected.

Further, by measuring the time from the start of expansion of the liquid film 1a to detection, the gas flow rate is determined from the time using the time-flow rate characteristic measured in advance, or
The five gas flow rates are determined from the measured time and the calculated value of the internal volume of the expanded liquid film.

(Example) Hereinafter, embodiments of the present invention will be described based on the drawings.

Fig. 1 is a partial cross-sectional view of the overall configuration of the microflow gas measuring device according to the present invention, and parts in Fig. 1 that are the same as those in Fig. 3 are given the same reference numerals. ing.

The microflow gas measuring device of the present invention includes a main body case 7 in which a soap film is stored, a detection tube 4 whose upper end opening protrudes upward from the liquid level of the soap film, and a detection tube 4. A soap film adhering device 8 for closing the upper end opening 4d with a liquid film 1a of the soap solution 1, a soap film detection device [9] for detecting when the soap film 1a reaches a certain position, and an atmosphere communication valve v
a ventilation control device 10 that controls the ventilation inside the detection tube 4 through the purge valve v3 and a CPU that calculates the flow rate of the gas to be measured 5 based on the signal S from the soap film detection device 9, etc.
It is formed from a device 11 and the like.

The main body case 7 is a box in which a reservoir 7a for the soap solution 1 is formed, and is provided with an air vent lower b, a soap solution replenishment lower 0, and the like. Further, an insertion hole 7d for the detection tube 4 is bored in the center of the bottom of the main body case 7;
The detection tube 4 is inserted into the tube from below, and is fixed in an airtight manner so as to be vertically adjustable, with its upper end opening 4d protruding above the soap liquid level. In FIG. 1, 12 is a nut for fixing the detection tube, and 13 is an O-ring.

The side wall of the detection tube 4 is provided with an inlet 14 for the gas to be measured 5, a communication port 15 to the atmosphere, and a supply port 16 for the purge gas 17. 5 through the supply hole 7e, the atmosphere communication hole 7f, and the supply hole 7g of the purge gas 16, test valve V□ and atmosphere communication valve v2, respectively.
, purge valve V.

The soap film adhering device H8 includes a ring body 2 that moves up and down with the upper end of the detection tube 4 inserted therethrough;
a cylinder device 3 that drives the cylinder in the vertical direction; and a cylinder control valve V4 that controls the supply of working fluid to the cylinder device 3.
It is formed from etc.

By operating the cylinder 3 and pulling up the ring body 2 that has descended into the soap liquid 1, a soap liquid film 1a is first formed between the outer wall surface of the detection tube 4 and the ring body 2, and then the ring body 2 is pulled upward from the upper end of the detection tube 4, the liquid film 1a is attached to the upper end opening 4d of the detection tube 4, and the upper end opening 4d is opened and closed by the soap liquid film 1a.

The soap liquid film detection device 9 includes an optical fiber type light emitting section 9.
a, a light receiving section 9b, a fiber amplifier 90, and the like. That is, the optical signal H output from the amplifier 9c is returned to the amplifier 9c through the optical fiber 9d, the radiation section 9a, the light receiving section 9b, and the optical fiber 9e.
The soap liquid film 1a at the tip opening 4d of the detection tube 4 expands, enters the optical path of the optical signal H, and the optical signal H is totally reflected by the liquid film 1a. Reaching the position is detected.

The ventilation control device 10 includes a test valve v1 for the gas to be measured 5, an atmosphere communication valve v2, a purge valve ■3, and a cylinder control valve V4.
The opening and closing of each valve V□ to ■ is performed in accordance with the order described later.

As will be described later, the CPU device determines whether the gas 5 It is of course possible to use a microcomputer or the like.

Next, a method for measuring a microflow amount of gas using the microflow measurement device shown in FIG. 1 will be described.

First, the soap solution 1 is poured into the soap solution storage section 7a in the main body case 7.
Inject the liquid and hold the liquid level in place,
The distance G between the upper end of the detection tube 4 and the center H' of the optical signal path of the soap film detection device 9 is adjusted to a predetermined value.

Note that the distance G is appropriately selected depending on the flow rate level of the gas to be measured 5, and when the flow rate is relatively large, the distance G is also selected to be thick.

Next, the cylinder device 3 is operated to move the ring body 2 up and down to wet the outer wall surface and the upper end surface of the pre-crimped detection tube 4 with the soap liquid film 1a.

During measurement, as shown in the time chart in Figure 2,
First, close the purge valve ■, open the atmosphere communication valve v2, and open the test valve V.
□ is opened, and the gas to be measured 5 introduced into the detection tube 4 through the test valve □ is released into the atmosphere through the atmosphere communication valve v2.

Next, the cylinder device is operated to pull the ring body 2 immersed into the soap liquid film upwards. As a result, the liquid film 1a formed between the tongue body 2 and the detection tube 4 is attached to the tip opening 4d of the detection tube 4, and the tip opening 4d of the detection tube 4 is attached to the soap liquid film 1.
It is in a state of being blocked by a. At this time, gas 5 is being supplied into the detection tube 4 through the test valve ■□.
Since the atmosphere communication valve v2 is open, the soap liquid film 1a that closes the tip opening 4d of the detection tube 4 is maintained in a substantially flat state. If the atmospheric communication valve V2 is not provided, even if the test valve V1 is closed, if the soap liquid film 1a is applied to the upper end opening 4d of the detection tube 4, the gas inside the ventilation tube 4 will expand. This causes the liquid film 1a to start expanding, making it difficult to accurately measure the flow rate.

When the tip opening 4d of the detection tube 4 is blocked by the soap liquid film 1a, the atmosphere communication valve v2 is closed, and at the same time, time measurement is started using the timer or the CPU device 11.

When the atmosphere communication valve (2) is closed, the soap liquid film 1a starts to expand due to the gas to be measured 5. The soap liquid film 1a expands and the upper part of the film surface becomes the optical path center H' of the soap liquid film detection device 9.
When reaching the vicinity of , the optical signal H that has been incident on the light receiving section 9b from the emitting section 9a is totally reflected by the liquid film 1a, and the light entering the light receiving section 9b is blocked. As a result, the detection signal S is sent from the fiber amplifier 9c to the CPU equipment engineer 1,
The time measurement that started at the same time as the atmospheric communication valve (2) is closed is stopped.

The CPU device subsequently calculates the gas flow rate using the measured value of the time from the closing of the atmosphere communication valve 2 to the total reflection of the optical signal H by the soap liquid film 1a, and displays the gas flow rate on a display (not shown). As well as being displayed, operations such as recording are performed as appropriate.

Note that the relationship between the measured time value and the gas flow rate can be measured in advance, and if the distance MG between the tip of the detection tube 4 and the center H' of the optical path is constant, the relationship between the measured value of the time and the gas flow rate can be measured in advance. There is an almost inversely proportional relationship between the time required for this and the gas flow rate.

In this embodiment, the gas flow rate is calculated from the relationship between the measurement time and the flow rate determined in advance, but the CPU calculates the internal volume of the expanded liquid film 1a from the height of the expanded liquid film.
Attire! 11, and the flow rate of the gas 5 may be calculated from the calculated value of the internal volume and the measured time.

The soap film detection bag! 9 is activated, the purge valve V is opened for a short time after a predetermined period of time has elapsed, and the soap solution adhering to the inner wall surface of the tip opening 4d of the detection tube 4 is removed.

Note that if the purge operation is not performed, the soap solution dripping due to the tearing of the liquid film will flow into the upper end opening 4 of the detection tube 4.
As a result, the thickness of the soap liquid film 1a formed on the opening 4d by the ring body 2 may change, or the soap liquid film 1a may be formed again by the attached soap liquid. This will result in measurement errors and measurement troubles.

When the operation of the purge valve V3 is completed, the ring body 2 is lowered into the soap solution l by the cylinder control valve v4, and the atmosphere communication valve v2 is opened to complete one measurement of the gas flow rate.

By repeating the above-described metering operation at predetermined intervals, the flow rate of the gas 5 is measured.

(Effects of the Invention) In the present invention, while expanding the soap liquid film 1a formed at the tip opening 4d of the detection tube 4 toward the atmosphere,
The optical signal H is totally reflected by the expanded soap liquid film 1a,
By this, it is configured to detect that the soap solution 11i 1 a has reached a certain position. As a result, the soap liquid film 1a is not affected by the condition of the inner wall surface of the detection tube 4 unlike the previous membrane placement needle, and is always expanded under constant external conditions. Arrival at a certain position is detected extremely accurately, greatly improving the accuracy of measuring microflows.

Also, by pulling the ring body 2 immersed in the soap solution l upward with the detection tube 4 inserted inside it,
Since the upper end opening 4d of the detection tube 4 is configured to be closed by the liquid film 1a, the upper end opening 4d of the detection tube 4 can be closed by the liquid film extremely reliably, unlike the case of the conventional membrane placement needle. There are no problems such as breakage of the liquid film.

Furthermore, the inside of the detection tube 4 blocked by the liquid film 1a is communicated with the atmosphere via the atmosphere communication valve V2, and the expansion of the soap liquid film 1a before the measurement is started is completely prevented. The accuracy of measuring the flow rate is improved, and the measurement itself can be performed smoothly and with high efficiency.

As mentioned above, the present invention has excellent practical utility.

[Brief explanation of drawings]

FIG. 1 is a partially longitudinally sectional view of the overall configuration of a microflow measuring device according to the present invention. FIG. 2 is an explanatory diagram showing the operating state of each device in measuring a minute flow rate using the apparatus of the present invention. FIG. 3 is an explanatory diagram of a conventional membrane placement needle. ■ Soap solution 1a Soap solution film 2 Ring body 3 Cylinder device 4 Detection tube 4d Upper end opening 5 Gas to be measured 7 Body case 8 Soap solution film deposition device Soap solution film detection device Ventilation control device CPU device Optical signal Center of optical signal path Distance test valve Atmospheric communication valve Purge valve Cylinder control well

Claims (5)

[Claims] (1) Main case (7) with soap solution (1) stored inside
and; a detection tube (4) disposed in the main body case (7) with its upper end opening (4d) protruding above the liquid level (L) of the soap solution (1); Top opening (4d)
a soap film adhering device (8), which is configured to block the soap film (1a) with a soap film (1a); a soap film that detects when the soap film (1a) expanded by the gas to be measured (5) reaches a certain position Ventilation control that controls the liquid film detection device (9); an atmosphere communication valve V_2 that communicates the inside of the detection tube (4) with the atmosphere; and a purge valve V_3 that supplies purge gas into the detection tube (4). The device (10) and the tip opening of the detection tube (4) (
A CPU that measures the time from the start of expansion of the soap film (1a) that blocks the soap film (1a) to the detection of the soap film (1a) by the soap film detection device (9), and calculates the gas flow rate from the measured time. A microflow rate gas measuring device comprising the device (11). (2) A ring body (2) in which the soap film deposition device (8) is movably arranged in the vertical direction with the detection tube (4) inserted therethrough.
and; the ring body (2) is mixed with a soap solution (1) and a detection tube (4).
Cylinder device (3) that moves between the
The microflow rate gas measuring device according to claim 1, which is formed by: (3) The soap film detection device (9) is formed by an optical signal (S) emitting part (9a) and light receiving part (9b) arranged oppositely; and an optical fiber amplifier (9c). The microflow gas measuring device according to claim (1). (4) After opening the atmosphere communication valve (V_2) and communicating the inside of the detection tube (4) with the atmosphere, the ring body (2) is soaked in the soap solution (1) with the detection tube (4) inserted. ) upward and cover the upper end opening (4d) of the detection tube (4) with the soap liquid film (1a
), and then the atmospheric communication valve (V_2) is closed and the upper end opening (4d) is closed by the gas to be measured (5).
), the soap liquid film (1a) that blocks the soap liquid film (1a) is expanded, the time when the soap liquid film (1a) starts to expand is measured, and the optical signal (H) is reflected by the expanded soap liquid film (1a). Detecting the arrival of the soap liquid film (1a) at a certain position, and measuring the time from the start of expansion of the soap liquid film (1a) to the detection of arrival of the soap liquid film (1a) at a certain position, A method for measuring a minute amount of gas, characterized in that the flow rate of the gas to be measured (5) is calculated from the measured time. (5) From the distance (G) between the tip opening (4d) of the detection tube (4) and the detection point of the expanded soap liquid film (1a) to the expanded liquid film (1a).
5. The method for measuring a minute amount of gas according to claim 4, wherein the internal volume of the gas 1a) is calculated, and the flow rate of the gas to be measured (5) is determined from the calculated value and the measurement time.