JPS5890125A - Measuring method for gas flow rate - Google Patents

Abstract

PURPOSE:To accurately measure the mass flow rate of any kind of gas, by measuring the pressure in a container at a predetermined time interval and successively calculating a mass flow rate. CONSTITUTION:A gas entering through an inlet 36 is controlled by a mass flow controller 30 so as to have a constant flow rate and introduced into a container 31 and then made to flow out from an outlet 37 through a valve 33. In measurement, the valve 33 is closed, and the pressure in the container 31 is successively measured by means of a pressure gauge 32 made of stainless steel at a predetermined time interval (e.g., 0.1sec). Since the volumes of the container 31 and the piping of the measuring circuit are previously set in a memory circuit 38, a mass flow rate is calculated by an arithmetic circuit 34 according to the Boyle-Charles' law and displayed on a display 35. According to this momentary flow rate, the mass flow controller 30 is calibrated and corrected. Upon completion of the measurement, the valve 33 is opened. Thus, the mass flow rate of any kind of gas can be accurately measured.

Description

[Detailed description of the invention] The present invention relates to a method and apparatus for measuring gas flow.

More particularly, the present invention relates to a method and apparatus for calibrating a mass flow controller for controlling the mass flow rate of gas.

In processing in semiconductor manufacturing equipment and analysis equipment, many gases such as oxygen, hydrogen, and nitrogen are used. A surface l* flowmeter using a float, a thermal mass flowmeter that adds a heater to the flow and measures the temperature difference between upstream and downstream to measure mass, and a mass flowmeter that combines a control valve and mass flowmeter to maintain a constant flow rate. A flow controller is used.

In this description, a thermal mass flow controller will be specifically taken as an example.

FIG. 1 is a basic configuration diagram of a thermal mass flow controller.

1 is a pipe through which gas flows, 2 is a gas input port, 3 is a gas output port, 4 is a heater coiled around the outer circumference of the pipe 1, 5 is an upstream coil for gas, 6 is a downstream coil, 7 is a gas control valve, 8 is a resistance detection circuit, 9 is a flow rate setting circuit, 10
is a comparison circuit.

11 is a drive circuit for the control valve 7; 12 is a flow rate indicator; 1
3 is a mass flow meter.

A coil 5.6 is wound around the tube and detects the gas temperature inside the tube as a change in resistance.

The temperature of the gas input from the input port 2 is detected by the upstream coil 5, and the temperature of the gas heated by the heater 4 is detected by the downstream coil 6.

The temperature detected by the upstream coil 5 and the downstream coil 6
This is based on the fact that the difference between the temperature detected at

A resistance detection circuit 8 detects and amplifies the resistance values of the coils 5 and 6.
The flow rate at that time is displayed on the flow rate display 12. This is the mass flow meter 13. on the other hand.

The output of the resistance detection circuit 8 is compared with the flow rate setting circuit 9 in the comparison circuit 1O, and the drive circuit 11 is adjusted so that the set flow rate is achieved.
The control pulp 7 is controlled through.

On the other hand, the reference device used to calibrate this thermal mass flow controller includes a tank method that measures the flow rate of liquid flowing out from a pre-filled tank and compares it with the indicated value of a test flow meter, and a standard device that moves the piston at a constant speed. Although there is a moving piston type gas prover method (3), the soap film prover method is often used for minute flow rates of 1 tA or less.

FIG. 2 is a structural diagram of the soap film prover.

15 is a gas input port, 16 is a thermal mass flow controller to be calibrated, 17 is a glass container, 18 is a glass container 17
19 is the first marked line, 20 is the second
Marked line 21 is the rubber bladder.

22 is soapy water.

When gas is input through the input port 15, the gas is controlled by the mass flow controller 16, and a constant flow rate of the gas flows through the glass tube 18 and flows out into the atmosphere. When the rubber bag 21 is squeezed, bubbles of soapy water 22 reach the bottom surface of the glass tube 18 and the glass tube 1
A soap film is formed on the glass tube 1 along the gas flow.
Rise 8. The time it takes for the soap film to reach the second marked line 20 from the first marked line 19 is measured, and the flow rate is calculated from the volume between them.

In the case of this method, it is difficult to create only one clear soap film, and it is necessary to squeeze the rubber bag 21 many times.

Oh, if you try to measure a flow rate of 5t15+ or more (/l), the diameter of the glass tube 18 will become larger and 1
This method not only makes it more difficult to create a soap film, but also causes fluctuations in each soap film, which significantly deteriorates measurement accuracy.

There is a flaw in that it cannot be measured.

Furthermore, in the case of the 9-soap film prover method, there is a defect in that the flow rate cannot be calculated until after the 9-soap film reaches the second marked line 20 from the first marked line 19.

The present invention (d) is a novel invention that eliminates the above defects, and its objectives are (1) to provide a method and apparatus for measuring gas flow rate with high accuracy.

(2) To provide a method and apparatus for dry gas flow measurement.

(3) To provide a flow rate measurement method and device capable of measuring from minute flow rates to large flow rates.

(4) Propose a method and device for measuring flow rate that does not change over time (5) to offer.

(5) To provide a flow rate measurement method and device that can automate flow 1 calibration.

(6) To provide a flow rate measurement method and device that are capable of successively calculating flow rates.

(7) To provide a method and device for measuring a flow rate that can repeatedly and quickly measure pressure, which comprises a container, a pressure measuring means, and a timing means, and measures the pressure inside the container at predetermined time intervals. This is achieved by doing.

The present invention will be explained in detail below with reference to the drawings.

FIG. 3 is a configuration diagram of a flow rate measuring device according to the present invention.

29 is a flow rate measuring device, 30 is a thermal mass flow controller to be calibrated, 31 is a container, and 32 is a pressure gauge.

33 is a pulp, 34 is an arithmetic control circuit, and 35 is a display.

36 is a gas input port, 37 is a gas outlet, 38 is a volume storage circuit of the container 31, 39 is a timing circuit, and 40 is a flow rate indicator of the mass flow controller 30.

Gas is input from the input port 36 and controlled to have a constant flow rate by the mass 70 controller (6) to the container 31.
Pressure is introduced. Before starting measurement, valve 33 is open and outlet 3 is closed.
It will be leaked from 7.

At the start of measurement, the valve 33 is closed, the pressure P1 in the container 31 at that time is read with the pressure gauge 32, the timing circuit 39 is activated, and the pressure Pz in the container 31 is read again with the pressure gauge 32 after a certain period of time.
Read.

If the volume of the container 31 is ■, then according to Boyle-Charles' law, PV = nRT, where T: absolute temperature, R: gas constant.

By using a container whose volume does not change during constant operation, c, =
, v, f4P80. ■ However, T: temperature at the time of measurement, Ps: standard pressure.

Ts; temperature in standard state n+: number of moles of gas in the container nz during PH measurement;
Number of moles of gas in the container at the time of Pz measurement T=x TB , p
6 W 1 atm. Therefore, the volume of the container 31 is measured in advance and stored in the volume storage circuit 3.
If set to 8, the pressures P1 and P7 at the start and end of measurement. The mass flow rate Q can be obtained by measuring the time t between the two.

This mass flow rate is calculated by the arithmetic control circuit 34 and displayed on the display 35.

For example, if the time t is o, 1 second, the pressure force P2 is applied at intervals of 0.1 seconds.
By successively measuring the instantaneous flow rate, it becomes possible to successively calculate the instantaneous flow rate and display it on the display 35.

Since the instantaneous flow rate is successively displayed on the indicator 40 of the mass flow controller, there is an effect that the calibration + YtlA adjustment of the mass flow controller becomes easier.

When the measurement is completed, the valve 33 is opened to allow the gas in the container 31 to flow out from the outlet 37.

Furthermore, it goes without saying that it is also possible to calculate not only the sequential flow rate but also the average flow rate for one hour T from the pressure P1 at the start of measurement, the pressure P2 at the end, and the total time T from the formula (2).

v In this embodiment, if a volume-coupled stainless steel diaphragm type absolute pressure measurement pressure gauge is used as the pressure gauge 32, it can be used even with corrosive gases, and it can also be used for highly accurate pressure measurement with an error of 0.1 inch or less. is possible.

The volume set in the volume memory circuit 38 includes not only the volume of the container 31 but also the piping volume in the valve 33 trench and the pressure gauge 32.
1 by including the piping volume from the control valve of the mass flow controller 30 to the container 31.
This makes it possible to measure high flow rates.

Now, the total volume V including the volume of the container 31 and piping is 1.2 t.
If the measurement time is 30 seconds, the absolute pressure inside the container 31 before the start of the measurement is 1 atm, and the absolute pressure inside the container 31 at the end of the measurement is 2 atm, then the average flow rate for 30 seconds. From 2〇, Q = (2-1)Xl, 2X - 0 (9) Q = 2. , it becomes 1 minute.

As is clear from the above description, according to the present invention, the flow range can be easily changed by changing the volume (2).

In addition, according to the present invention, there are no mechanically moving parts and there is no need to use glass tubes, so it is robust and durable.
Furthermore, if the valve 33 is opened, the pressure inside the container 31 immediately becomes atmospheric pressure.

Another advantage is that repeated tests can be carried out quickly.

Container 31. If stainless steel or vinyl chloride is used as the piping material, all parts in contact with the gas will be corrosion resistant, making it possible to measure both water-soluble and highly corrosive gases.

However, the flow measurement device of the present invention is a dry type.

Highly accurate measurement is possible without causing flow rate errors due to dirt or the like.

Furthermore, in the above explanation, the case where the mass flow controller is a thermal type has been described, but the present invention is not limited to this (10), and it is clear that the present invention can be implemented with any flowmeter that measures mass. be.

As explained above, according to the present invention, since the flow rate can be measured sequentially using the container, the pressure measuring means, and the timing means, it is possible to accurately measure the mass flow rate of all gases.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of a thermal mass flow controller, FIG. 2 is a configuration diagram of a soap film prover, and FIG. 3 is a configuration diagram of a flow rate measuring device according to the present invention. 1 is a pipe through which gas flows, 2, 15.36 is a gas input port,
3 is a gas output port, 4 is a heater, 5 is an upstream coil, 6
is the downstream coil, and 7 is the control pulp. 8 is a resistance detection circuit, 9 is a flow rate setting circuit, 10 is a comparison circuit, 11 is a drive circuit, 12 is a flow rate indicator, 13 is a mass flow meter, 16.30 is a thermal mass flow controller, 17
is a glass container, and 18 is a glass tube. 19 is a first marked line, 20 is a second marked line, 21 is rubber glue, 22 is soap water, 29 is a flow rate measuring device, 31 is a container, 3
2-piece pressure gauge, 33 is a valve, 34 is an arithmetic control circuit, 35
37 is a gas outlet, 38 is a volume storage circuit,
39 is a timing circuit, and 40 is a flow rate indicator. Patent applicant Representative of Sigma Technology Industry Co., Ltd. Kami 1) Kunbai I Ritsai 2 Figure 9 + 3 Figure

Claims (1)

[Claims] 1. A flow rate measuring method comprising a container, a pressure measuring means, and a time measuring means, and successively calculating the mass flow rate of gas by measuring the pressure inside the container at predetermined time intervals. 2. A gas flow rate measuring device comprising a container, a pressure measuring means, a timing means, a means for storing the volume of the container, and an arithmetic control means, and is configured to continuously calculate a flow rate.