JPH06300600A - Mass flowmeter - Google Patents

Abstract

PURPOSE:To measure a flow rate extending from a large flow to a small flow without lowering accuracy by providing the device consisting of a main pipe line and a measuring pipe line, and providing a means to change flow ratio of the main pipe line to the measuring pipe line. CONSTITUTION:The measuring device is constituted of a main pipe line 2 letting flow fluid, and a measuring pipe line 3 branched from the pipe line 2 and letting flow fluid. The outer circumference of the measuring pipe line 3 is wound with a heating resistor 31 in the upstream and a heating resistor 32 ;in the downstream and a mass flow flowing in the measuring pipe line 3 is measured by means of the resistors 31, 32. Fluid flowing in the inlet 4 of a mass flowmeter 1 is separated to the main pipe line 2 and the measuring pipe line 3, and made together in the vicinity of the outlet 5 again. A valve 21 is provided in the main pipe line 2, the valve 21 is moved right and left by the action of an actuator 22 so as to open/close the main pipe line 2, and flow ratio of the main pipe line 2 to the measuring pipe line 3 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter used in a mass flow controller.

[0002]

2. Description of the Related Art Some mass flow controllers for measuring the mass flow rate of a fluid have a valve for controlling the flow rate before or after a mass flow meter. In this mass flowmeter, there is a main pipeline and a measurement pipeline parallel to the main pipeline. The measuring conduit is a thin metal pipe, and a heating resistor is attached upstream and downstream on the outer circumference. This mass flowmeter utilizes the temperature change of the resistor due to the heat of the upstream and downstream heat generating resistors being dissipated by the fluid, and changes the voltage at the intermediate point or keeps the temperature constant. It has been practiced to supply electric power to the fluid and measure the mass of the fluid based on the magnitude of the electric power. Normally, the metal pipe used for this measuring pipe has an inner diameter of about 0.5 mm, so the outlet pressure of this pipe is 0 torr and the differential pressure is 20 torr.
_{When 2} is flowed, it is about 5cc / min. When using a pipe made of SUS316L material, the range where the linearity between the flow rate and the measured voltage can be secured is about 5 cc / min. Therefore, the main pipeline is placed parallel to the measurement pipeline, and its cross-sectional area is set to 100 times the measurement pipeline, etc., and the measured mass flow rate of the fluid flowing through the measurement pipeline is 10 times.
It is assumed that 0 times as much fluid has flowed through the mass flow meter. Full scale of mass flowmeter is 1SCCM, 10SCCM, 50SCCM, 100S
In the case of each of CCM and 10SLM, the flow rate of the main pipeline is set to 0, 2, 10, 20, 200 times that of the measurement pipeline, and a mass flowmeter suitable for the measured flow rate is used. ing.

[0003]

Since the measurement accuracy of the mass flow meter and the control error of the mass flow controller are what% of the full-scale flow rate, a small flow rate is measured using a large flow meter. Is not a virtue. Assuming a measurement error of ± 2% with a full scale 1SLM flowmeter, the flow error is ± 20 SCCM. When measuring the flow rate of 10 SCCM with this flow meter, it becomes 10 ± 20 SCCM and it is completely useless.
An object of the present invention is to provide a mass flow meter that can measure from a large flow rate to a small flow rate without lowering the accuracy. Further, when this mass flowmeter is used in a mass flow controller capable of controlling from a large flow rate to a small flow rate, even if the digit of the control flow rate changes, the control accuracy can be provided.

[0004]

The mass flowmeter of the present invention comprises:
A main conduit for flowing the fluid, a measuring conduit for branching the main conduit to allow the fluid to flow, and measuring the mass flow rate of the fluid, and a means for changing the flow rate ratio between the main conduit and the measuring conduit. It is characterized by having. In the practice of the invention,
The ratio of the flow area of the main pipeline / the flow area of the measuring pipeline is 0, 9,
I want something that can be changed to 99,999.

[0005]

[Operation] A movable valve such as a solenoid valve or a piezoelectric element drive valve should be inserted in the main pipeline, and the flow passage area ratio of the main pipeline / measurement pipeline should be 999 when it is fully open and 0 when it is fully closed. You can By setting in this way, the flow rate in the measurement line can be reduced to 1
In case of SCCM, if the main pipeline is fully opened, 999SCC will appear in the main pipeline.
Since M flows, the total flow rate is 1 SLM, 1 SCCM when fully closed, and 10 SCCM and 100 SCCM in the middle. It is possible to accurately measure each of these flow rates.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is a mass flowmeter of the present invention, 2 is a main conduit, and 3 is a measuring conduit. The measurement pipe line 3 is made of a metal pipe, and a heating resistor 31 is wound on the upstream side of the outer circumference and a heating resistor 32 is wound on the downstream side. The mass flow rate flowing in the measuring conduit 3 is measured by the heating resistors 31 and 32 on the upstream side and the downstream side. The fluid entering from the inlet 4 of the mass flowmeter 1 is divided into the main conduit 2 and the measuring conduit 3 and flows together again near the outlet 5. A valve 21 is provided in the main pipeline, and the valve 22 moves left and right by the action of an actuator 22 to open and close the main pipeline to control the flow rate ratio between the main pipeline and the measurement pipeline.
It is also possible to move the valve 21 to the right to fully close the main flow path 2.
21 can move to the left and fully open. A desired flow rate ratio can be obtained by controlling any position between them.

[0007]

As described above, it is possible to change the flow rate ratio of the fluid in the main pipeline and the measurement pipeline. Therefore, the mass flow rate can be measured from the large flow rate to the small flow rate without lowering the accuracy.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating an outline of a mass flowmeter of the present invention.

[Explanation of symbols]

 1 ... Mass flowmeter 2 ... Main pipeline 3 ... Measuring pipeline 4 ... Inlet 5 ... Exit 21 ... Valve 22 ... Actuator 31, 32 ... Heating resistor

Claims (1)

[Claims] 1. A main pipeline for flowing a fluid, and a measurement pipeline for branching the main pipeline to flow the fluid and measuring a mass flow rate of the fluid, the main pipeline and the fluid of the measurement pipeline A mass flowmeter characterized by having a means for changing a flow rate ratio.