JP2024146326A - Gas flow rate adjustment mechanism - Google Patents

Abstract

[Problem] With a thermal conduction type sensor, when the gas flow rate in the piping increases, the temperature drop of the sensor's measuring element becomes large, making it difficult to perform proper measurements. [Solution] A gas flow rate adjustment mechanism is provided, which comprises a measuring section that measures the physical quantity of the gas to be measured, a main flow path pipe through which the gas to be measured flows, an introduction pipe that branches off from the main flow path pipe and introduces the fluid to be measured into the measuring section, and a gas introduction amount control plate that is installed from inside the introduction pipe to inside the main flow path pipe and can move in the vertical direction parallel to the introduction pipe to increase or decrease the flow area of the flow path cross section of the main flow path pipe, thereby controlling the flow rate of the fluid to be measured introduced into the measuring section. [Selected Figure] Figure 1B

Description

The present invention relates to a mechanism for adjusting the gas flow rate to a thermal conductivity sensor.

Sensors that use thermal conduction perform measurements by measuring the temperature change caused by a heated sensing element when gas flows near the sensing element. In recent years, micromachining technology that uses semiconductor processing techniques has made it possible to miniaturize sensing elements, and these sensors are used in gas sensors and humidity sensors.

For example, JP 2008-233057 A (Patent Document 1) discloses a thermal conduction sensor that has high sensitivity, high accuracy, and an expanded measurement range for measuring physical quantities such as the degree of vacuum and the flow rate of gas or liquid, and a thermal conduction measurement device that uses the sensor.

Patent Publication 2008-233057

Thermal conduction sensors use miniaturized detection elements, so when the flow rate of gas flowing near the detection element is greater than expected in the design, the temperature change in the detection element becomes large, making accurate measurements impossible. For example, thermal conduction gas sensors are often used to detect flammable gases such as hydrogen, and it is desirable for the gas to exist in a natural diffusion state near the thermal conduction gas sensor.

Therefore, a mechanism is needed to adjust the gas flow rate from the piping to the thermal conductivity sensor so that the thermal conductivity sensor can operate properly.

In order to achieve the above object, the gas flow rate adjustment mechanism described in claim 1 of the present invention is characterized by comprising a measurement unit that measures the physical quantity of the gas to be measured, a main flow path tube through which the gas to be measured flows, an inlet tube that branches off from the main flow path tube and introduces the fluid to be measured into the measurement unit, and a gas introduction amount control plate that is installed from inside the inlet tube to inside the main flow path tube and moves in the vertical direction parallel to the inlet tube, increasing or decreasing the flow path area of the flow path cross section of the main flow path tube, thereby controlling the flow rate of the fluid to be measured introduced into the measurement unit.

The gas flow rate adjustment mechanism described in claim 2 of the present invention is characterized in that a portion of the mechanism is movable to increase or decrease the flow area of the main flow path pipe.

The gas flow rate adjustment mechanism described in claim 3 of the present invention is characterized by having a flow path hole for reducing pressure loss of the fluid in the main flow path pipe.

The present invention provides a gas flow rate adjustment mechanism that enables a thermal conduction sensor that measures a physical quantity related to a gas to operate according to its design value, even when a large flow rate of gas is flowing through a pipe.

FIG. 1 is a side view of an embodiment of the present invention; Conceptual diagram of the internal structure of an embodiment of the present invention. Simulation results of flow rate change due to gas inlet control plate Variation 1 Variation 2

Below, embodiments of the present invention are explained using the drawings. Note that the present invention is not limited to these embodiments, and can be implemented in various forms without departing from the spirit of the present invention.

In this embodiment, we will explain an embodiment in which a thermal conduction gas sensor is used to analyze gas in a pipe. In this embodiment, we will explain a configuration in which gas is introduced from the pipe from the left side of the figure, passes through the sensor, and leaves the pipe to the right side.

Figure 1A is a side view of this embodiment. Specifically, it is a conceptual diagram when viewed from a plane parallel to the direction in which gas flows in the main flow path pipe and the inlet pipe. There are a measurement unit 101 having a gas sensor and a control board for the gas sensor, an inlet pipe 102 having a measurement gas inlet pipe that introduces gas flowing from the piping into the measurement unit 101 and a measurement gas outlet pipe from which gas that has passed through the measurement unit 101 is discharged, a main flow path pipe 103 that branches the gas flowing from the piping into gas that flows from the gas inlet pipe to the measurement unit and gas that passes through without flowing to the measurement unit, an inlet port 104 through which gas from the piping enters, and an outlet port 105 through which both the main flow path pipe 103 and the gas that has passed through the measurement unit return to the piping. The inlet port 104 and the outlet port 105 may be directly connected to the piping or may be connected via a bypass pipe.

The measuring section 101 and the inlet pipe 102, the inlet pipe 102 and the main flow path pipe 103, and the main flow path pipe and the inlet 104 and outlet 105 are connected via joints or the like to ensure airtightness.

Figure 1B is a conceptual diagram showing the internal structure by cutting a part of Figure 1A. Specifically, it is a cross section of the center of the measurement section, the introduction tube, and the main flow tube. The same symbols as in Figure 1A indicate the same things. The gas entering from the introduction port 104 is obstructed by the gas introduction amount control plate 106 and heads toward the measurement gas introduction port 107. The gas that reaches the measurement gas introduction port 107 enters the measurement chamber 108. The measurement chamber 108 contains a sensor 109, and the gas that passes through the sensor passes through the measurement gas discharge tube 110 and returns to the main flow tube 102 from the discharge port 105.

Figure 2 shows the results of a simulation of the effect of the gas introduction amount control plate of the present invention, under the condition that "when each pipe is connected to a φ3/4" T-shaped joint, 1 L/min of air is introduced from the bottom to the top in the figure."

The upper part of the table shows the state of the gas introduction amount control plate. In FIG. 1B, the gas introduction control plate 106 is viewed from the direction a. The lower part of the table shows the measurement gas introduction pipe and the measurement gas discharge pipe installed in the introduction pipe. In FIG. 1B, the introduction pipe 102 is viewed from the direction b. As in FIG. 1, the gas enters from the left side of the figure, travels from the measurement gas introduction pipe to the measurement section, and the gas that passes through the measurement section exits the measurement gas discharge pipe and travels to the piping from the right side of the figure, so the left side is the measurement gas introduction pipe and the right side is the measurement gas discharge pipe. (A) shows a state without the gas introduction amount control plate. (B) to (D) show states in which a rectangular gas introduction amount control plate is installed between the measurement gas introduction pipe and the measurement gas discharge pipe, and the width of the gas introduction amount control plate is changed. The dotted line in FIG. 2 shows the gas introduction amount control plate.

The darker the color inside the measurement gas inlet tube and measurement gas outlet tube, and the darker the color inside the gas introduction amount control plate, the greater the flow rate of the gas inside the tube. As in (A), without the gas introduction amount control plate, there is almost no flow rate. As the width of the gas introduction amount control plate increases in (B), (C), and (D), the flow rate of gas toward the measurement gas inlet tube increases. The higher the flow rate, the more gas flows into the measurement gas inlet tube.

Figure 3 shows a modified example of the gas introduction amount control plate. The gas introduction control plate 106 is viewed from the direction a in Figure 1B. In both figures, the shaded circle represents the area through which gas passes in the main flow path tube. The white part represents the area where the flow is obstructed by the gas introduction amount control plate. The gas introduction amount control plate is composed of a combination of a fixed part 301 and a variable part 302. The dotted part represents the part that is not visible from the direction a in Figure 1B due to the movement of the variable part 302. (A) shows a rectangular opening in the fixed part, and the size of the area obstructing the flow is adjusted by moving the rectangular plate of the variable part to open the rectangular opening. (A-1) shows the state where the opening is maximized, and (A-2) shows the state where the opening is closed. (B) shows the fixed part in the middle, with the variable parts on both sides, which adjust the area of the area obstructing the flow. (B-1) shows the state where the area obstructing the flow is maximized, and (B-2) shows the state where the area obstructing the flow is minimized. (C) shows a configuration in which the opening is made circular compared to (A), and (D) shows a configuration in which the plate shape of the change section is made trapezoidal compared to (A). In this invention, the objective is to flow the required flow rate of gas into the measurement section of the thermal conduction sensor, so the gas introduction amount control plate is configured so as not to completely block the piping in the main flow passage pipe. Therefore, a configuration like (D) can also be applied.

By moving the gas introduction amount control plate in this way, it is possible to change the cross-sectional area of the main flow path pipe, and adjust the gas flow rate to the introduction pipe. In the present invention, the gas introduction amount control plate is adjusted so that appropriate measurement values are obtained based on the diameter of the pipe and the gas flow rate, and the settings of the gas introduction amount control plate are not changed while the sensor is in operation. In this way, if an abnormal measurement value occurs while the sensor is in use, it is possible to detect the abnormality.

FIG. 4 shows a modified example of the method of attaching the measuring part to the pipe. As in FIG. 1, the figure is viewed from a direction perpendicular to the direction of gas flow. The direction of gas flow is indicated by the arrow in the figure. The measuring part 401, the introduction pipe 402, the gas introduction amount control plate 403, and the main flow pipe 404 are shown in simplified form. The gas in the pipe flows from left to right in the figure, as in the other embodiments. (A) is effective when there is little space to install the measuring part by arranging the measuring part 401 at an angle to the main flow pipe. In addition, by bending the tip of the gas introduction amount control plate and bringing it closer to perpendicular to the pipe, the effect of obstructing the gas flow is enhanced more than when the gas introduction amount control plate is straight. (B) is an example in which the measuring part is arranged downward with respect to the main flow pipe, and is effective when the density of the gas to be measured is high.

Measurement unit 101
Inlet pipe 102
Main body flow path pipe 103
Inlet 104
Outlet 105
Gas introduction amount control plate 106
Measurement gas inlet 107
Measurement chamber 108
Sensor 109
Measurement gas outlet pipe 110

Claims (3)

A measurement unit that measures a physical quantity of a measurement target gas;
a main flow passage pipe through which a gas to be measured flows;
an introduction pipe that branches off from the main flow path pipe and introduces the fluid to be measured into the measurement section;
a gas introduction amount control plate that is installed from inside the introduction pipe to inside the main flow passage pipe and moves in a vertical direction parallel to the introduction pipe to increase or decrease the flow passage area of the flow passage cross section of the main flow passage pipe and control the flow rate of the measurement target fluid introduced into the measurement section;
A gas flow rate adjustment mechanism consisting of: The gas flow rate adjustment mechanism according to claim 1, in which the gas introduction amount control plate is partially movable to increase or decrease the flow area of the main flow path pipe. 3. The gas flow rate adjusting mechanism according to claim 1, wherein the gas introduction amount control panel has a flow passage hole for reducing a pressure loss of a fluid in a main flow passage pipe.

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