JP2024032149A - thermal flow meter - Google Patents

Abstract

An object of the present invention is to form a protective film on a wiring pattern of a temperature measuring resistor and a heat generating resistor provided on the inner wall of a pipe of a thermal flowmeter by sufficiently covering the step portion. [Solution] This thermal flowmeter includes a first protective film 121 that covers a first wiring 102, a second protective film 122 that covers a second wiring 103, and a third protective film that covers a third wiring 104. 123 and a fourth protective film 124 that covers the fourth wiring 105. The first protective film 121, the second protective film 122, the third protective film 123, and the fourth protective film 124 are formed separately from each other. [Selection diagram] Figure 1

Description

The present invention relates to a thermal flowmeter.

There is a thermal flow rate sensor in which a temperature sensing resistor serving as a temperature sensor and a heat generating resistor serving as a heater are provided on the inner wall of a pipe. When measuring a conductive liquid with this type of thermal flow sensor, it is necessary to insulate and separate the heating resistor and temperature-measuring resistor from the liquid in order to prevent short circuits in the wiring pattern. Furthermore, even if a non-conductive fluid is to be measured, for example, if foreign matter adheres across adjacent wiring patterns and short circuits occur in the current, an abnormal output may occur. For this reason, the wiring pattern is covered with a protective film made of an insulating material such as silicon nitride (Patent Documents 1 and 2).

Japanese Patent Application Publication No. 2002-328053 Japanese Patent Application Publication No. 2009-025099

However, the protective film made of silicon nitride has low thermal conductivity, which is disadvantageous in efficiently transmitting the heat of the heater to the fluid and in accurately measuring the temperature of the fluid. For this reason, the protective film is formed to be thin, and there are areas where the stepped portion cannot be sufficiently covered, which may cause fluid to enter and cause abnormalities.

The present invention has been made in order to solve the above-mentioned problems.The present invention has been made in order to solve the above-mentioned problems. The purpose is to form a protective film.

The thermal flowmeter according to the present invention includes a pipe that transports a fluid to be measured, a first wiring that constitutes a heat generating resistor that is provided on the inner wall of the pipe and heats the fluid, and a pipe that is connected upstream of the heat generating resistor. a second wiring constituting a first resistance temperature detector which is provided on the inner wall of the piping to measure the temperature of the fluid; and a second temperature sensor which is provided on the inner wall of the piping downstream of the heating resistor and which measures the temperature of the fluid. The first wiring is covered with a third wiring that constitutes a resistor, a fourth wiring that constitutes a third resistance temperature detector that measures the temperature of the fluid at an upstream position that is not affected by the heat of the heating resistor. A first protective film, a second protective film that covers the second wiring, a third protective film that covers the third wiring, and a fourth protective film that covers the fourth wiring. The protective film, the third protective film, and the fourth protective film are separated from each other and formed individually.

In one configuration example of the thermal flowmeter described above, the first protective film, the second protective film, the third protective film, and the fourth protective film are made of a material having a thermal conductivity of 10 W/m·K or more. There is.

In one configuration example of the thermal flowmeter, the first protective film, the second protective film, the third protective film, and the fourth protective film are made of alumina.

In one configuration example of a thermal flowmeter, the heating resistor is controlled such that the difference between the temperature of the heating resistor and the temperature measured by the third resistance temperature detector becomes a set temperature difference. The configured control unit and the temperature of the fluid measured by the first resistance temperature detector and the temperature of the fluid measured by the second resistance temperature detector in a state where the heating resistor is controlled by the control unit. and a flow rate calculation unit configured to calculate the flow rate of the fluid from the temperature difference.

As explained above, according to the present invention, since the heat generating resistor and the temperature measuring resistor are individually covered with a highly thermally conductive protective film, there is no need to make the protective film very thin, and the thermal flowmeter A protective film can be formed on the wiring pattern of the temperature measuring resistor and heat generating resistor provided on the inner wall of the pipe by sufficiently covering the stepped portion.

FIG. 1 is a configuration diagram showing the configuration of a thermal flowmeter according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing the relationship between the thickness of the protective film and the temperature difference between the first resistance temperature detector and the second resistance temperature detector.

Hereinafter, a thermal flowmeter according to an embodiment of the present invention will be described with reference to FIG. 1. This thermal flowmeter includes a piping 101 that transports a fluid to be measured, a first wiring 102 , a second wiring 103 , and a third wiring 104 provided on the inner wall of the piping 101 . The first wiring 102, the second wiring 103, the third wiring 104, and the fourth wiring 105 can be made of, for example, Pt.

The first wiring 102 constitutes a heating resistor that heats the fluid to be measured flowing through the piping 101 . The second wiring 103 constitutes a first resistance temperature detector that measures the temperature of the fluid on the upstream side of the heat generating resistor. The third wiring 104 constitutes a second resistance temperature detector that measures the temperature of the fluid downstream of the heating resistor. The fourth wiring 105 constitutes a third resistance temperature detector that measures the temperature of the fluid at an upstream position that is not affected by the heat of the heating resistor. For example, the first wiring 102, the second wiring 103, the third wiring 104, and the fourth wiring 105 are formed on the measurement chip 106.

The control unit 108 controls the temperature of the heating resistor by the first wiring 102 and the temperature of the heating resistor measured by the third resistance temperature detector by the fourth wiring 105 at a position not affected by the heat of the heating resistor, for example, at a position upstream of the heating resistor. The heating resistor is controlled and driven so that the difference between the temperature of the fluid and the temperature of the fluid becomes a preset temperature difference.

The first resistance temperature detector formed by the second wiring 103 measures the temperature of the fluid on the downstream side of the third resistance temperature detector and upstream of the heating resistor. Further, the second resistance temperature detector formed by the third wiring 104 measures the temperature of the fluid on the downstream side of the heating resistor. The flow rate calculation unit 107 calculates the flow rate of the fluid based on the temperature difference between the temperature of the fluid measured by the first resistance temperature detector and the temperature of the fluid measured by the second resistance temperature detector.

As is well known, the heating resistor is driven so that the difference between the temperature of the heating resistor and the temperature of the fluid at a position not affected by the heat of the heating resistor becomes a preset temperature difference. There is a correlation between the temperature difference between the temperature of the fluid upstream of the heating resistor and the temperature of the fluid downstream of the heating resistor and the flow rate of the fluid when the heating resistor is running. Also, this correlation is reproducible for the same fluid/flow rate/temperature. Therefore, as described above, when the heating resistor is controlled by the control unit 108, the difference (temperature difference) between the temperature measured by the first resistance temperature detector and the temperature measured by the second resistance temperature detector Therefore, the flow rate can be calculated by using a predetermined correlation coefficient (constant).

Further, the thermal flowmeter according to the embodiment includes a first protective film 121 that covers the first wiring 102 , a second protective film 122 that covers the second wiring 103 , and a third protective film 122 that covers the third wiring 104 . A protective film 123 and a fourth protective film 124 covering the fourth wiring 105 are provided. The first protective film 121, the second protective film 122, the third protective film 123, and the fourth protective film 124 are formed separately from each other.

The first protective film 121, the second protective film 122, the third protective film 123, and the fourth protective film 124 can be made of a material having higher thermal conductivity than silicon nitride of 10 W/m·K or more. For example, the first protective film 121, the second protective film 122, the third protective film 123, and the fourth protective film 124 can be made of alumina, which is a high thermal conductivity material.

FIG. 2 shows the relationship between the thickness of the protective film and the temperature difference between the first resistance temperature detector and the second resistance temperature detector. The larger the temperature difference between the first resistance temperature detector and the second resistance temperature detector, the higher the sensitivity can be obtained. In FIG. 2, black circles indicate the case where the protective film is made of alumina and has a thickness of 1 μm, black triangles indicate the case where the protective film is made of silicon nitride and has a thickness of 1 μm, and open circles indicate the case where the protective film is made of silicon nitride and has a thickness of 1 μm. The case where the film is made of alumina and has a thickness of 2 μm is shown. Furthermore, the black squares indicate the result of continuously forming a protective film made of alumina over the entire area (entire surface) of the first wiring 102, second wiring 103, third wiring 104, and fourth wiring 105.

Compared to a thickness of 1 μm, even when the thickness is 2 μm, the change in temperature difference between the first resistance temperature detector and the second resistance temperature detector is small, and alumina is formed to be twice as thick as SiN. Sensitivity can also be maintained. As described above, according to the embodiment, since the protective film can be formed thicker, the coverage of the stepped portion can be further improved.

By the way, as shown in the results shown in the black squares, it can be seen that when a protective film made of alumina is formed over the entire surface, the temperature difference between the first resistance temperature detector and the second resistance temperature detector decreases significantly. . This means that the heat from the heating resistor is easily conducted to the first, second, and third resistance temperature detectors through the protective film made of alumina, which has a high thermal conductivity. This is because it becomes impossible to accurately measure the temperature difference in the fluid.

In contrast, according to the embodiment, the first protective film 121 covers the first wiring 102, the second protective film 122 covers the second wiring 103, and the third protective film covers the third wiring 104. 123 and the fourth protective film 124 that covers the fourth wiring 105 are formed separately from each other and separately, so that the heat from the heat generating resistor passes through the protective film to the first temperature sensing resistor and the fourth protective film 124. There is no longer any conduction to the second resistance temperature detector and the third resistance temperature detector. Further, according to the embodiment, since it is not necessary to make the protective film very thin, it is possible to prevent the fluid to be measured from penetrating the protective film and reaching the heat generating resistor or the temperature measuring resistor.

As explained above, according to the present invention, since the heat generating resistor and the temperature measuring resistor are individually covered with a highly thermally conductive protective film, there is no need to make the protective film very thin, and the thermal flow rate It becomes possible to form a protective film on the wiring pattern of the temperature measuring resistor and heating resistor provided on the inner wall of the pipe of the meter, sufficiently covering the step portion.

It should be noted that the present invention is not limited to the embodiments described above, and many modifications and combinations can be made within the technical idea of the present invention by those having ordinary knowledge in this field. That is clear.

DESCRIPTION OF SYMBOLS 101... Piping, 102... First wiring, 103... Second wiring, 104... Third wiring, 105... Fourth wiring, 106... Measuring chip, 107... Flow rate calculation part, 108... Control part, 121... First protective film , 122... second protective film, 123... third protective film, 124... fourth protective film.

Claims (4)

Piping that transports the fluid to be measured;
a first wiring constituting a heating resistor that is provided on an inner wall of the piping and heats the fluid;
a second wiring constituting a first resistance temperature detector that is provided on the inner wall of the piping upstream of the heating resistor and measures the temperature of the fluid;
a third wiring constituting a second temperature sensing resistor that is provided on the inner wall of the piping downstream of the heating resistor and measures the temperature of the fluid;
a fourth wiring constituting a third resistance temperature detector that measures the temperature of the fluid at a position on the upstream side that is not affected by heat of the heating resistor;
a first protective film covering the first wiring;
a second protective film covering the second wiring;
a third protective film covering the third wiring; and a fourth protective film covering the fourth wiring,
The first protective film, the second protective film, the third protective film, and the fourth protective film are separated from each other and formed individually. A thermal flowmeter. The thermal flowmeter according to claim 1,
The first protective film, the second protective film, the third protective film, and the fourth protective film are made of a material having a thermal conductivity of 10 W/m·K or more. type flow meter. The thermal flowmeter according to claim 2,
A thermal flow meter, wherein the first protective film, the second protective film, the third protective film, and the fourth protective film are made of alumina. The thermal flowmeter according to any one of claims 1 to 3,
a control unit configured to control the heat generating resistor so that the difference between the temperature of the heat generating resistor and the temperature measured by the third temperature measuring resistor becomes a set temperature difference;
The temperature of the fluid measured by the first resistance temperature detector and the temperature of the fluid measured by the second resistance temperature detector while the heating resistor is controlled by the control unit. and a flow rate calculation section configured to calculate the flow rate of the fluid from the difference.

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