JP2000250633A - Fluid mass flow rate controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid mass flow rate controller which never causes the clogging at a flow rate detection part, has high heat resistance and can control even a large flow rate with high accuracy. SOLUTION: A fluid mass flow rate controller 1 consists of an ultrasonic flowmeter 3 which measures the flow rate of gas flowing in a gas pipe 2, a flow rate control valve 4 which controls the flow rate of gas flowing in the pipe 2 and a valve drive control circuit 5 which compares the mass flow rate measured by the flowmeter 3 with the mass flow rate of the target gas and controls the opening degree of the valve 4 to secure the coincidence between both mass flow rates. In such a constitution, the clogging is never caused at a flow rate detection part with high heat resistance, being different from the case where a thermal flow rate sensor is used. In addition, even a large flow rate can be controlled with high accuracy and the pressure loss of a gas flow is never caused at the flow rate detection part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow controller used for controlling a flow rate of a material gas, a reaction gas, and the like supplied to a reaction chamber in an optical fiber manufacturing process, a semiconductor manufacturing process, and the like.

[0002]

2. Description of the Related Art In an optical fiber manufacturing process, a semiconductor manufacturing process, or the like, a fluid such as a reaction gas must be supplied to a reaction chamber or the like at a constant mass flow rate. For this purpose, a thermal mass flow controller is used. FIG. 2 shows a schematic configuration of a conventional thermal mass flow controller.

As shown in FIG. 1, a conventional mass flow controller 10 includes a thermal mass flow sensor 12 disposed in a gas supply pipe 11, a flow control valve 13 for opening and closing the gas supply pipe 11, and a valve 13. And a valve drive control circuit 14 for controlling the opening and closing of the valve. The valve drive control circuit 14 detects the flow rate of the gas flowing through the gas supply pipe 11, and controls the opening of Is adjusted.

In the thermal mass flow sensor 12, the resistance values of two resistance wires attached to the shunt tube 15 connected to the gas supply tube 11 change according to the mass flow rate of the gas flowing through the shunt tube 15. The detected heat transfer amount is detected as a change in electrical resistance.

The gas supply pipe 11 is provided with a portion 16 commonly called a bypass in order to adjust the ratio of the flow to the distribution pipe 15. The pressure loss of the bypass 16 is reduced by the size of the full scale of the flow meter. Adjustment is performed, and even if the size of the full scale changes, the flow rate diverted to the diversion pipe 15 is substantially constant.

[0006]

However, the conventional flow controller has the following problems to be solved.
That is, a thin distribution pipe is connected to the gas supply pipe, and a part of the gas flow flowing through the gas supply pipe is led to the flow rate detection part. Since it is necessary to flow gas through a thin branch pipe,
Depending on the type of gas, clogging may occur in such a thin tube portion. In particular, when controlling the flow rate of a gas in which dust, foreign matter and the like are mixed, clogging is likely to occur in such a thin tube portion.

In order to avoid the influence of the ambient temperature change, the operating temperature of the thermal type flow sensor is usually 30 ° C. or more higher than the ambient temperature, that is, the gas temperature.
There is a problem that it is not suitable for controlling the flow rate of a high-temperature gas. For example, a thermal mass flow meter is not suitable for measuring the flow rate of a gas having a temperature exceeding about 100 degrees Celsius. For this reason, for example, in order to obtain a reactive gas depending on the type of gas, as in the case of an optical fiber manufacturing process, the liquid material must be vaporized at a high temperature of about 150 degrees Celsius. Gas flow measurement and flow control cannot be performed.

In addition, when the gas flow rate is large, for example, when the gas flow rate is about 500 liters / minute or more, there is a problem that the flow rate control cannot be performed accurately.

An object of the present invention is to propose a mass flow controller capable of solving such a problem of the conventional mass flow controller.

[0010]

In order to solve the above-mentioned problems, a fluid mass flow controller according to the present invention measures a fluid flow pipe through which a fluid to be controlled flows and a flow rate of the fluid flowing through the fluid flow pipe. Ultrasonic flow meter, a pressure sensor and a temperature sensor for knowing the density of the fluid, a flow control valve for adjusting the flow rate of the fluid flowing through the fluid flow pipe, and based on the measurement value of the ultrasonic flow meter, Valve drive control means for controlling the opening of the flow control valve so that the mass flow rate of the fluid flowing through the fluid flow pipe becomes the target mass flow rate.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a fluid flow controller for adjusting a mass flow rate of a gas to which the present invention is applied will be described below with reference to FIG.

The fluid mass flow controller 1 of the present embodiment adjusts a gas pipe 2, an ultrasonic flow meter 3 for measuring a gas flow flowing through the gas pipe 2, and a gas flow flowing through the gas pipe 2. A flow control valve 4 for controlling the opening of the flow control valve 4 so that the flow rate of gas flowing through the gas pipe 2 coincides with a target value;
An input unit 6 is provided.

The ultrasonic flowmeter 3 includes a pair of transducers 31 and 32 attached to the gas pipe 2 and a thermometer 33 and a thermometer 33 attached to know the density of the fluid, which measure the temperature and pressure of the gas flow, respectively. A pressure gauge 34 and a flow rate calculation circuit 35 for calculating a gas mass flow rate flowing through the gas pipe 2 based on the ultrasonic waves received by the transducers 31 and 32 and the measured temperature and pressure are provided.

The transducers 31 and 32 are mounted at positions capable of receiving ultrasonic waves emitted from the respective transducers. In this example, as shown in the figure, the arrangement relation capable of receiving the reflected waves reflected by the inner peripheral wall of the gas pipe is provided. It has become. Of course, a pair of transducers may be arranged to face each other so that ultrasonic waves can be directly transmitted and received.

In the flow rate calculating circuit 35, the transducers 31, 3
Based on the ultrasonic waves received in 2, the flow velocity of the gas flow is calculated by the propagation velocity difference method or the Doppler method, and the volume flow rate of the gas is obtained based on the calculated gas flow. Further, the density of the fluid is calculated based on the detected temperature and pressure, and the volume of the gas is converted into a mass flow rate in that state.

The valve drive control circuit 5 includes a comparison / control unit 5
1 and a valve driver 52. The comparison / control unit 51 compares the mass flow rate of the gas calculated by the flow rate calculation circuit 35 with the mass flow rate of the target gas, and sets the mass flow rate of the gas to the target flow rate. The opening degree of the flow control valve 4 is adjusted via the valve driver 52 so as to match the mass flow rate of the gas.

The target mass flow rate of the gas may be set, for example, by operating a flow rate setting key or a flow rate setting dial 61 arranged on the display / input section 6, or a higher-level controller ( (Not shown). Various information including the measured gas mass flow rate is displayed on the display screen 62 of the display / input unit 6.

When the flow rate is small, an electromagnetic or piezoelectric proportional valve is used as the flow control valve 4.
When the flow rate is large, it is desirable to use a pilot valve using an electromagnetic valve or an electropneumatic valve.

[0019]

As described above, since the fluid mass flow controller of the present invention employs an ultrasonic flow meter as the fluid mass flow meter, there is no thin tube portion such as a diversion tube unlike the conventional controller. . Therefore, it is possible to control the flow rate of the gas in which foreign matter such as dust is mixed. In addition, since the heat resistance is high, it is possible to control the flow rate of the high-temperature gas. Furthermore, since there is no mechanism commonly called a bypass, no pressure loss occurs. In addition to this, even when the flow rate is large, the flow rate control can be accurately performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a schematic configuration of a main part of a fluid flow controller to which the present invention is applied.

FIG. 2 is a schematic configuration diagram showing a conventional flow controller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fluid flow controller 2 Gas pipe 3 Ultrasonic flow meter 31, 32 Transmitter / receiver 33 Thermometer 34 Pressure gauge 35 Flow rate operation circuit 4 Flow rate adjustment valve 5 Valve drive control circuit 51 Comparison / control unit 52 Valve driver 6 Display / input unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F030 CA03 CC11 CD15 CE02 CE04 CE22 CE27 CF05 CF08 CF20 2F031 AC01 AD10 AF10 2F035 DA07 DA09 DA12 DA14 5H307 AA02 BB01 DD01 DD17 EE02 EE07 EE12 FF05 FF12 FF15 GG15 HH04

Claims (1)

[Claims] 1. A fluid flow pipe for flowing a fluid to be controlled, an ultrasonic flowmeter for measuring a flow rate of the fluid flowing in the fluid flow pipe, a pressure sensor and a temperature sensor for knowing a density of the fluid, and the fluid A flow control valve for adjusting a fluid mass flow rate flowing through the flow pipe; and an opening of the flow rate control valve such that the fluid mass flow rate flowing through the fluid supply pipe becomes a target flow rate based on a measurement value of the ultrasonic flowmeter. And a valve drive control means for controlling the degree.