JPH1062222A - Flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a flow rate of a fluid in a wide range by setting a heat- generating body in the middle of a first and a second-heat-generating parts and bringing about a large temperature difference between the first and second heart-generating parts. SOLUTION: A driving power source is connected to an electrode 8 of a central thermistor thin film heater 6, so that the heater 6 is driven to generate heat at a constant temperature. A drive detection circuit is connected to electrodes 8 of thermistor thin film heaters 5 and 7 at both sides. The drive detection circuit constitutes a bridge circuit by the heaters 5, 7 and a fixed resistor. The heaters 5-7 are driven to generate heat by an impressed power from the driving power source and drive detection circuit. A ratio of resistance values is detected by the drive detection circuit. At this time, a first and a second heat-generating parts 9, 10 show no temperature difference unless a fluid moved and the ratio of resistance values is not changed. Therefore, a flow rate of the fluid is detected to be zero. When the fluid flows, the heaters 5-7 are sequentially cooled by the fluid coming from the upstream. However, the presence of the heater 6 in the middle of the heat-generating parts 9, 10 causes a large temperature difference between the heat-generating parts 9 and 10, so that the flow rate of the fluid can be detected with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a flow sensor for detecting a flow rate of a fluid.

[0002]

2. Description of the Related Art Conventionally, there is a flow sensor as a sensor for detecting a flow rate of a fluid such as city gas or tap water. In a general flow sensor, a support having a cross-linked structure perpendicular to the flow direction of a fluid is formed on the surface of a silicon substrate by anisotropic etching, and a first temperature sensor, a heating element, and a second And temperature sensors are sequentially arranged in the flow direction of the fluid. In such a flow sensor, when the fluid flows, the thermal balance centering on the heating element shifts from the first temperature sensor to the second temperature sensor,
A flow rate of the fluid is measured from a temperature difference between the first temperature sensor and the second temperature sensor.

[0003] Similarly, there is a flow sensor in which a first heat generating portion and a second heat generating portion having a heat generating function and a temperature measuring function are sequentially arranged in the direction of fluid flow. In such a flow sensor, when the fluid flows, the heat of the first heat generating portion is transmitted to the second heat generating portion, and based on the temperature difference between the first heat generating portion and the second heat generating portion. Measure the fluid flow.

[0004] For example, Japanese Patent Application Laid-Open No. H2-259527 and
In the flow sensor described in Japanese Patent Publication No. 52028, the first thin film heater and the second thin film heater are arranged in order from upstream to downstream of the fluid. In the flow sensor described in Japanese Patent Publication No. 6-43906, a first thin-film temperature sensor, a first thin-film heater, a second thin-film heater, and a second thin-film temperature sensor are arranged from upstream to downstream of a fluid. It is arranged in order toward.

The flow sensor described in Japanese Patent Publication No. 6-43906 has a structure in which first and second heat generating portions having a heat generating / temperature measuring function are sequentially arranged in the flow direction of a fluid. At the same time, the structure is such that the first temperature sensor, the heating element, and the second temperature sensor are sequentially arranged in the flow direction of the fluid. In other words, the structure in which the first temperature sensor, the heating element, and the second temperature sensor are arranged in order has a heating function and a temperature measurement function, considering that the central heating element is shared by the temperature sensors on both sides. It is also a structure in which the first and second heating parts are arranged in order.

[0006]

The above-mentioned various flow sensors measure the flow rate of the fluid based on the temperature difference between the first and second heat generating portions arranged in order in the flow direction of the fluid.

However, even with such a flow sensor, the rate at which the downstream heat generating portion is deprived increases as the flow rate increases, rather than the rate at which heat is added. Therefore, when the flow rate of the fluid is actually measured by such a flow sensor, as shown in FIG. 13, the linearity of the measurement result is lost at a certain flow rate, and the measurement result is saturated in an extreme case. In such a state, the flow rate of the fluid cannot be measured accurately, so that the conventional flow sensor has a narrow range in which the flow rate can be measured.

[0008]

According to the first aspect of the present invention,
A first heat generating portion and a second heat generating portion each having a heat generating function and a temperature measuring function are sequentially arranged in the flow direction of the fluid, and the first heat generating portion and the second heat generating portion are caused by the flow of the fluid. In the flow sensor for detecting the flow rate of the fluid based on the temperature difference generated between the first and second heating units, a heating element is provided between the first and second heating units. Accordingly, the heating element generates heat at the center between the first heating section and the second heating section, and the first heating section and the second heating section generate heat and measure the temperature. If the fluid does not flow, there is no temperature difference between the first heating section and the second heating section, and if the fluid flows, the temperature difference corresponding to the flow rate between the first heating section and the second heating section. Occurs. At this time, the first heat generating portion located upstream is cooled in the same manner as when there is no heating element, but the second heat generating portion located downstream is difficult to be cooled due to the presence of the heating element. For this reason, a temperature difference between the first heat generating portion and the second heat generating portion is remarkably generated as compared with a case where there is no heat generating element, and this temperature difference occurs in a wide range of the flow rate of the fluid. Here, the flow rate means a volume of a fluid passing through a unit area per unit time, and is synonymous with a flow rate.

According to a second aspect of the present invention, in the first aspect of the invention, each of the first heating section and the second heating section has a temperature measuring element thin film heater. Therefore, the temperature measuring element thin film heater generates a heat generating function and a temperature measuring function in one of them,
The first heating section and the second heating section are formed with a simple structure. Note that the temperature measuring element thin film heater here generates a heat generation function and a temperature measurement function as described above.
It is a thermistor or a platinum thin film.

According to a third aspect of the present invention, in the first aspect of the present invention, the first heating section and the second heating section each include a thin-film heater and a thin-film temperature sensor. Therefore, since the thin-film heater for generating the heat generation function and the thin-film temperature sensor for generating the temperature measurement function are separately formed, it is possible to use an optimum material for each.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, a slit is formed between the first heating section and the heating element, and the second heating section and the heating element are formed. And a slit was formed in between. Therefore, the conduction of heat from the heating element to the first heating section and the second heating section via the support is prevented by the slit.

[0012] According to the fifth aspect of the present invention, the first, second, and third aspects are provided.
In the invention described in 3 or 4, a support having a cross-linked structure substantially perpendicular to the flow direction of the fluid is bridged on the surface of the substrate, and the first heat generating portion, the heat generating member, and the second heat generating portion are formed on the surface of the support. Was located. Therefore, since the fluid flows well on the front side and the back side of the support, the amount of heat of the first heating section, the heating element, and the second heating section is transmitted well by the fluid, and the heat capacity of the support is small. , The flow rate of the fluid is measured with high sensitivity.

According to the sixth aspect of the present invention, the first, second and third aspects of the present invention are provided.
In the invention described in 3 or 4, a support having a cross-linking structure substantially parallel to the flow direction of the fluid is bridged on the surface of the substrate, and the first heat generating portion, the heat generating member, and the second heat generating portion are formed on the surface of the support. Was located. Therefore, since the support does not hinder the flow of the fluid, the measurement error of the flow rate due to the generation of the turbulent flow is prevented, and since the heat capacity of the support is small, the flow rate of the fluid is measured with high sensitivity, and the dust floating in the fluid is reduced. Accumulation on the back side of the support and dust colliding with the support are also reduced.

According to the seventh aspect of the present invention, the first, second, and third aspects of the present invention are provided.
In the invention described in 3 or 4, a support having a diaphragm structure is formed on the surface of the substrate, and the first heating section, the heating element, and the second heating section are located on the surface of the support. Therefore, since the support does not hinder the flow of the fluid, the measurement error of the flow rate due to the generation of the turbulent flow is prevented, and the dust floating in the fluid accumulates on the back side of the support and the dust collides with the support. Nor.

[0015]

FIG. 1 shows a first embodiment of the present invention.
This will be described below with reference to FIG. First, the structure of the flow sensor 1 of the present embodiment is shown in FIGS. The flow sensor 1 has a square substrate 2. Since a cavity 3 is formed in the substrate 2 in a tunnel shape penetrating from the surface to the inside and opening to the surface, a support 4 having a bridge structure is formed on the cavity 3 by a thin film. Since the communication direction of the cavity 3 is parallel to the flow direction of the fluid (not shown), the support 4 is bridged at right angles to the flow direction of the fluid.

On the surface of the support 4, three thermistor thin-film heaters 5 to 7 are sequentially formed in the direction of fluid flow as three temperature-measuring thin-film heaters, and electrodes of these thermistor thin-film heaters 5 to 7 are formed. 8 are formed on the surface of the substrate 2 on both sides of the support 4. For this reason, the first heating section 9 is formed by the thermistor thin film heater 5 on the upstream side and the upstream portion of the support 4, and the first heat generating section 9 is formed on the downstream side of the thermistor thin film heater 7 and the support 4. A second heating portion 10 is formed by the side portions, and the thermistor thin film heater 6 at the center is formed as a heating element. The electrode 8 is provided to connect the thermistor thin film heaters 5 to 7 to a drive circuit (not shown).
The connection is performed by, for example, wire bonding.

Here, a specific example of a method of manufacturing the flow sensor 1 of the present embodiment will be briefly described below. First, as the substrate 2, a 3.0 (mm) × 3.0 (mm) × 525 (μm) single crystal silicon substrate having a thermal oxide film SiO ₂ having a thickness of 1.0 (μm) formed on the surface is prepared. A 3000 (3000) thick Si
A C thin film is formed by a high frequency sputtering method, and is patterned by a photolithography method to form the thermistor thin film heaters 5 to 7. On this surface, a SiO ₂ thin film having a thickness of 1.0 (μm) is formed as a passivation film by a high frequency sputtering method to form an upper layer of the support 4.

Next, the passivation film and the thermal oxide film are etched in the shape of the pair of openings 11 and 12 of the cavity 3, and the substrate 2 is anisotropically etched from these openings 11 and 12 with a KOH solution. Depth 300 (μm)
Is formed. Then, the support 4 composed of a thermal oxide film and a passivation film is formed in a crosslinked structure on the cavity 3, and the three thermistor thin film heaters 5 to 7 are located on the support 4. become.

In one specific example of the above-described manufacturing method,
Although SiO ₂ is exemplified as the material of the support 4, it is sufficient that the material satisfies insulation, mechanical strength, and thermal conductivity.
_{a 2 O 5, Si 3 N} 4, SiON and the like can also be used. Similarly,
The material of the thermistor thin film heaters 5 to 7 is exemplified by SiC, which also has a sufficient heat generation temperature with power saving, has a resistance temperature coefficient capable of detecting a temperature change satisfactorily, has little change over time, and has stable characteristics. Various materials are available, for example,
Permalloy, Pt, polycrystalline Si, amorphous Si (H)
Etc. can also be used.

Further, the method of forming various thin films is not limited to the above-described sputtering method, but may be a vacuum evaporation method or a CVD (Chemical Vapor Deposition) method in consideration of the characteristics of the material.
Law etc. can be used. In addition, the dimensions and shapes of the respective parts are not limited to the above-described numerical values, and are optimally set in consideration of various conditions such as the flow rate and characteristics of the fluid.

In such a configuration, in the flow sensor 1 of the present embodiment, for example, a driving power source (not shown) is connected to the electrode 8 of the thermistor thin film heater 6 at the center, and the thermistor thin film heaters 5 and 7 on both sides are connected. A drive detection circuit (not shown) is connected to the electrode 8. The drive power supply has a constant current source, and drives the thermistor thin film heater 6 to generate heat at a constant temperature. The drive detection circuit includes a thermistor thin film heater 5,
A bridge circuit is formed by 7 and two fixed resistors, and a change in the ratio of the resistance values of the thermistor thin film heaters 5 and 7 is detected with high sensitivity.

In such a state, the thermistor thin film heaters 5 to 7 are driven to generate heat by the applied power between the drive power supply and the drive detection circuit, and the ratio of the resistance values of the thermistor thin film heaters 5 and 7 is detected by the drive detection circuit. . At this time, if the fluid does not flow, no temperature difference occurs between the first and second heat generating portions 9 and 10, so that the ratio of the resistance values of the thermistor thin film heaters 5 and 7 does not change, and the fluid is detected by the drive detection circuit. Is detected as "0".

On the other hand, when the fluid flows, the three thermistor thin film heaters 5 to 7 are sequentially cooled by the fluid flowing in from the upstream, so that the heat quantity is propagated in order from the upstream to the downstream by the flowing fluid. Thus, the upstream thermistor thin film heater 5 is cooled well, but the downstream thermistor thin film heater 7 is hardly cooled.

That is, since a temperature difference corresponding to the flow rate of the fluid is generated in the first and second heat generating portions 9 and 10, the ratio of the first and second resistance values changing according to the temperature difference causes the fluid to flow. The flow rate is detected. FIG. 3 is a graph showing the relationship between the flow rate of the fluid and the outputs of the first and second heat generating units 9 and 10. In FIG. 3, is a flow rate-output characteristic of the first heat generating portion 9 located on the upstream side, and is a second heat generating portion 10 located on the downstream side.
The flow rate-output characteristics of the above are shown. For reference, FIG. 3 shows a flow rate-output characteristic of a temperature sensor arranged on the downstream side in a conventional flow sensor. As shown in FIG. 3, when the flow rate increases, the output of the first heating section 9 decreases linearly, whereas the output of the second heating section 10 hardly fluctuates until it reaches a predetermined flow rate value. The flow rate of the fluid is detected according to the difference between the output of the first heat generating unit 9 and the output of the second heat generating unit 10.
In this case, the flow sensor 1 of the present embodiment
A thermistor thin film heater 6 is provided between the second heat generating portions 9 and 10.
Is located, a remarkable temperature difference occurs between the first heating section 9 and the second heating section 10, and the flow rate of the fluid is measured with high sensitivity.

Here, as shown in FIG. 3, in the conventional flow sensor, the flow rate value at which the output of the downstream temperature sensor starts to fluctuate with an increase in the flow rate of the fluid is low. In the sensor 1, the flow value at which the output of the second heat generating portion 10 starts to fluctuate is high. Therefore, it can be seen from the graph of FIG. 3 that the flow sensor 1 of the present embodiment has a high limit until the linearity of the measurement result is lost.
That is, even if the flow rate of the fluid increases, the second heat generating unit 10 is hardly cooled, and as shown in FIG. 4, the measurement result of the flow rate is hardly saturated, and the flow rate can be measured in a wide range.

Moreover, in the flow sensor 1 of the present embodiment, the first and second heat generating portions 9 and 10 generate a heat generating function and a temperature measuring function by the thermistor thin film heaters 5 and 7, respectively.
Its structure is simple and its productivity is good.

The present invention is not limited to the above-described embodiment, but allows various modifications. For example, in the above embodiment, the thermistor thin-film heaters 5 to 7 are formed to be elongated in the middle of the flow direction of the fluid. However, if the thermistor thin film heaters 5 to 7 can be sequentially positioned in the flow direction of the fluid, they can be formed in various shapes.

In the flow sensor 1 of the above-described embodiment, one support 4 is heated by three thermistor thin-film heaters 5 to 7, thereby saving power. However, the flow rate measurement sensitivity due to the heat conduction of the support 4 is low. It may decrease. If this poses a problem, a slit 22 is formed between the thermistor thin film heaters 5 and 6 and between the thermistor thin film heaters 6 and 7 as shown in a flow sensor 21 shown in FIG. It is preferable to improve the measurement sensitivity of the flow rate by preventing the above.

Although such a flow sensor 21 can improve the sensitivity of the flow measurement, the strength of the support 4 is reduced, and it is complicated to form a fine mask of the slit 22. is there. That is, since these flow sensors 1 and 21 have advantages and disadvantages, it is preferable to select them in consideration of necessary performance and use environment.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described below based on Note that, with respect to the flow sensor 31 of the present embodiment, the same portions as those of the flow sensor 1 described above have the same names and reference numerals, and detailed description thereof will be omitted.

First, in the flow sensor 31 of the present embodiment, three thin film heaters 32 to 34 are provided continuously on the surface of the support 4 and the thin film temperature sensors are provided on the surfaces of the thin film heaters 32 and 34 on both sides. 35 and 36 are formed. Therefore, the first heating section 3 is formed by the upstream thin film heater 32, the thin film temperature sensor 35, and the upstream portion of the support 4.
7, a second heat generating portion 38 is formed by the thin film heater 34 on the downstream side, the thin film temperature sensor 36, and the portion on the downstream side of the support 4, and the central thin film heater 33 is It is formed as a heating element.

Here, the flow sensor 31 of the present embodiment
A specific example of the manufacturing method will be briefly described below. On the thermal oxide film having a thickness of 1.0 of the single-crystal silicon substrate second surface ([mu] m), the Ta ₂ N thin film having a thickness of 3000 (Å) was deposited by a DC sputtering method, the thin film was patterned to The heaters 32 to 34 are formed. A film thickness of 50 on this surface as an insulating film
After forming an SiO ₂ thin film of 00 (Å) by a high frequency sputtering method, an SiC thin film of 2000 (Å) thickness is formed by a high frequency sputtering method, and the SiC thin film is patterned and the thin film temperature sensor 35, 36 is formed. In the following, as in the case of the flow sensor 1 described above, a SiO ₂ thin film having a thickness of 1.0 (μm) is formed as a passivation film by a high frequency sputtering method, and a depth of 300 (300 μm) is formed on the substrate 2 by anisotropic etching with a KOH solution. μm) to form a support 4.

In one specific example of the above-described manufacturing method,
Although Ta ₂ N has been exemplified as a material for the thin film heaters 32 to 34, various materials satisfying the heat generation temperature, power consumption, durability, and the like can be used. For example, TaSiO ₂ , NiC
r can also be used. As a material of the thin film temperature sensors 35 and 36, SiC which is one material of the semiconductor thermistor is exemplified. However, since various materials satisfying the temperature coefficient of resistance and the durability can be used, for example, Pt, Ge, MnO, Fe
Metal oxides such as ₂ O ₃ can be used.

In such a configuration, in the flow sensor 31 of the present embodiment, for example, the thin film heaters 32 to 34
Is connected to a drive power supply, and the thin film temperature sensors 35 and 36 are connected to a detection circuit. The drive power supply has a constant current source and drives the thin-film heaters 32-34 to generate heat at a constant temperature.
The detection circuit forms a bridge circuit with the thin film temperature sensors 35 and 36 and two fixed resistors, and detects a change in the ratio of the resistance values of the thin film temperature sensors 35 and 36 with high sensitivity.

In such a state, the thin film heaters 32 to 34 are driven to generate heat by the applied power of the driving power supply, and the ratio of the resistance values of the thin film temperature sensors 35 and 36 is detected by the detection circuit. At this time, if the fluid does not flow, no temperature difference occurs between the first and second heat generating portions 37 and 38, so that the ratio of the resistance values of the thin film temperature sensors 35 and 36 does not change and the detection circuit detects the fluid. The flow rate is detected as "0".

On the other hand, when the fluid flows, the three thin film heaters 32 to 34 are sequentially cooled by the fluid flowing from the upstream, so that the temperature difference corresponding to the flow rate of the fluid causes the first and second heat generating portions 37 to be cooled. , 38, and the flow rate of the fluid is detected from the ratio of the first and second resistance values that change according to the temperature difference.

In particular, in the flow sensor 31 of the present embodiment, since the thin film heater 33 is located between the first and second heat generating portions 37 and 38, the first heat generating portion 37 and the second heat generating portion 38 are provided. Then, a significant temperature difference occurs, and the flow rate of the fluid is measured with high sensitivity. Further, even if the flow rate of the fluid increases, the second heat generating portion 38 is hardly cooled, so that the measurement result of the flow rate is hardly saturated, and the flow rate can be measured in a wide range.

In addition, the flow sensor 31 of the present embodiment
Then, the first and second heat generating parts 37 and 38 are used as the thin film heater 3.
2 and 34 and the thin film temperature sensors 35 and 36,
The heat-generating function and the temperature-measuring function can be best realized by dedicated elements. On the other hand, as compared with the flow sensor 1 described above, the structure of the first and second heat generating portions 37 and 38 is complicated and the productivity is reduced.
31 is preferably selected in consideration of necessary performance and productivity.

In the flow sensor 31 described above, similarly to the flow sensor 21 described above, a slit corresponding to the slit 22 of the flow sensor 21 can be formed in the support 4 to improve the sensitivity of flow measurement. is there.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
This will be described below based on In the flow sensor 41 of the present embodiment, the same portions as those of the flow sensor 1 described above are denoted by the same names and reference numerals, and detailed description is omitted.

First, the flow sensor 41 of the present embodiment
Since the cavities 42 are formed in the substrate 2 at right angles to the flow direction of the fluid, the support 43 that bridges the cavities 42
The thin film is formed as a crosslinked structure parallel to the flow direction of the fluid.

Since three thermistor thin film heaters 5 to 7 are sequentially formed on the surface of the support 43 in the flowing direction of the fluid, the thermistor thin film heater 5 on the upstream side and the upstream of the support 43 are formed. The first heating part 4 by the side part
4, and a second heat generating portion 45 is formed by the thermistor thin film heater 7 on the downstream side and a portion on the downstream side of the support 43.

With such a configuration, the flow sensor 41 of the present embodiment can measure the flow rate of the fluid over a wide range similarly to the flow sensor 1 described above. And
In the flow sensor 41 of the present embodiment, since the support body 43 having the cross-linking structure is formed in parallel with the flow direction of the fluid,
As compared with the flow sensor 1 in which the support 4 is perpendicular to the flow direction of the fluid, dust floating in the fluid is less likely to be deposited inside the cavity 42, and the characteristic change due to this deposition is less likely to occur. Similarly, since dust hardly collides with the support 43, the support 4
3 also has good durability and can be used stably for a long period of time. In addition, since the support 43 does not hinder the flow of the fluid, a measurement error due to the turbulent flow of the fluid hardly occurs.

On the other hand, the flow sensor 4 of this embodiment
1 has a cavity 42 compared with the flow sensor 1 described above.
Since the fluid does not easily flow through the inside, the sensitivity and responsiveness of the first and second heat generating portions 44 and 45 may be reduced. That is, since these flow sensors 1 and 41 also have advantages and disadvantages, it is preferable to select them in consideration of various conditions.

As in the case of the flow sensor 21 for the flow sensor 1 described above, a slit 22 is formed in a support 43 as shown in FIG. It is also possible to improve the measurement sensitivity of the flow rate. As a flow sensor 61 of the second modification, as shown in FIG. 9, first and second heat generating portions 62 and 63 are formed on a support 43 with the same structure as the flow sensor 31 described above. It is also possible to optimize the heat generation function and the temperature measurement function.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
0 will be described below. Regarding the flow sensor 71 of the present embodiment, the same portions as those of the flow sensor 1 described above are denoted by the same names and reference numerals, and detailed description is omitted.

First, the flow sensor 71 of the present embodiment
Since a concave cavity 72 is formed on the back side of the substrate 2, a support 73 having a diaphragm structure is formed on the front side of the substrate 2 which is the bottom of the cavity 72.

Since three thermistor thin film heaters 5 to 7 are sequentially formed on the surface of the support 73 in the flow direction of the fluid, the upstream of the thermistor thin film heater 5 and the upstream of the support 73 are formed. The first heating part 7 by the side part
4, and a second heat generating portion 75 is formed by the thermistor thin film heater 7 on the downstream side and a portion on the downstream side of the support body 73.

Here, the flow sensor 71 of the present embodiment
A specific example of the manufacturing method will be briefly described below. First,
3.0 (mm) × 3.0 (mm) × 525 (μm) made of single crystal silicon with a thermal oxide film SiO ₂ having a thickness of 1.0 (μm) formed on the front and back surfaces
The substrate 2 is prepared, and a 3000 (Å) -thick SiC thin film is formed on the surface by high-frequency sputtering, and then patterned by photolithography to form thermistor thin-film heaters 5-7. On this surface, a SiO ₂ thin film having a thickness of 1.0 (μm) is formed as a passivation film by a high frequency sputtering method to form an upper layer of the support 73.

Next, the thermal oxide film on the back surface of the
Etching only the area of 2.0 (mm), the substrate 2
By anisotropically etching with a KOH solution,
The cavity 72 is formed up to the thermal oxide film on the surface. Then, the support 73 composed of a thermal oxide film and a passivation film is formed in a crosslinked structure on the cavity 72, and three thermistor thin film heaters 5 to 7 are located on the support 73. become.

With such a configuration, the flow sensor 71 of the present embodiment can measure the flow rate of the fluid over a wide range, similarly to the flow sensor 1 described above. And
In the flow sensor 71 of the present embodiment, since the support 73 is formed in a diaphragm structure, dust floating in the fluid hardly accumulates inside the cavity 72, and a change in characteristics due to the accumulation hardly occurs. Similarly, since the mechanical strength of the support 73 is good and dust hardly collides, the durability of the support 73 is good and stable use for a long time is possible. Also,
Since the support body 73 does not hinder the flow of the fluid, a measurement error due to the turbulent flow of the fluid hardly occurs. Further, since the support 73 has a diaphragm structure, the thermistor thin film heaters 5 to 7 and the electrodes 8 can be formed in a free layout.

On the other hand, the flow sensor 7 of the present embodiment
Reference numeral 1 denotes a support 7 as compared with the flow sensor 1 described above.
3 tends to have a large heat capacity, so that the sensitivity and responsiveness of the first and second heat generating portions 74 and 75 may be reduced. That is, since these flow sensors 1 and 71 also have advantages and disadvantages, it is preferable to select them in consideration of various conditions.

As in the case of the flow sensor 21 for the flow sensor 1 and the like described above, a slit 22 is formed in a support 73 as shown in FIG. It can be formed to improve the sensitivity of flow measurement. As a flow sensor 91 of the second modification, as shown in FIG. 12, first and second heat generating portions 92 and 93 are formed on a support 73 with the same structure as the flow sensor 31 described above. It is also possible to optimize the heat generation function and the temperature measurement function.

[0054]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments (flow sensors 1, 21, 3)
1, 41, 51, 61, 71, 81, 91), the flow sensor of the present invention is used for measuring the flow velocity of gas and liquid, and can be used as a flow sensor if the flow path is constant. . More specifically, there are applications such as a sensor for a gas meter, a sensor for adjusting an air intake amount of an automobile, and a sensor for measuring a flow rate of a duct.

In each of the embodiments supporting the present invention, the flow sensors 1, 21, 31 in which the direction of the support of the bridge structure is perpendicular to the flow of the fluid, and the flow sensors 41, 51, 61, the flow sensors 71, 81, and 91 each having a support having a diaphragm structure have been introduced. However, preferable characteristics are different depending on the arrangement direction and the structure of the support having such a cross-linked structure. Table 1
2 shows the relationship between the arrangement direction and structure of the support and various characteristics.

[0056]

[Table 1]

In Table 1, "energy amount for obtaining the same output", "mechanical strength", and "strength against dust" are listed as characteristics.

[0058]

According to the first aspect of the present invention, by providing a heating element between the first heating section and the second heating section, the temperature of the first heating section and the second heating section can be increased. Since a significant difference occurs, the flow rate of the fluid can be measured over a wide range.

According to the second aspect of the present invention, the first heating section and the second heating section each have a thermometer thin-film heater, thereby simplifying the first heating section and the second heating section. Thus, the flow sensor can be improved in productivity and can be reduced in size and weight.

According to the third aspect of the present invention, the first heating section and the second heating section each include a thin-film heater and a thin-film temperature sensor, so that the first heating section and the second heating section are separated from each other. The heat generation function and the temperature measurement function can be realized by the respective optimum materials, and the flow sensor can be formed with high performance.

According to the fourth aspect of the present invention, a slit is formed in the middle between the first heating part and the heating element, and a slit is formed in the middle between the second heating part and the heating element. Since the heat can be prevented from being conducted from the body to the first heating section and the second heating section via the support by the slit, the flow rate of the fluid can be measured with high sensitivity.

According to the fifth aspect of the present invention, a support having a crosslinked structure substantially perpendicular to the flow direction of the fluid is bridged on the surface of the substrate,
By locating the first heating section, the heating element, and the second heating section on the surface of the support, the calorific value of the first heating section, the heating element, and the second heating section can be improved by the fluid. Since the heat can be transmitted and the heat capacity of the support is small, the flow rate of the fluid can be measured with high sensitivity.

According to the sixth aspect of the present invention, a support having a cross-linked structure substantially parallel to the flow direction of the fluid is bridged on the surface of the substrate,
By positioning the first heating element, the heating element, and the second heating element on the surface of the support, the support does not hinder the flow of the fluid, thereby preventing flow rate measurement errors due to turbulence. Since the heat capacity of the support is small, the flow rate of the fluid can be measured with high sensitivity, and the dust floating in the fluid accumulates on the back side of the support to deteriorate the measurement performance. Destruction by collision with the support can also be prevented.

According to the present invention, a support having a diaphragm structure is formed on the surface of the substrate, and the first heat generating portion, the heat generating member, and the second heat generating portion are located on the surface of the support. By doing so, since the support does not hinder the flow of the fluid, it is possible to prevent a measurement error of the flow rate due to the occurrence of turbulence, and that the dust floating in the fluid accumulates on the back side of the support and the measurement performance is deteriorated. In addition, it is possible to prevent the dust from colliding with the support and causing destruction.

[Brief description of the drawings]

FIG. 1 is a plan view showing a flow sensor according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional front view thereof.

FIG. 3 is a graph showing a relationship between a flow rate of a fluid and outputs of first and second heat generating units 9 and 10;

FIG. 4 is a characteristic diagram showing measurement results.

FIG. 5 is a plan view showing a modified example thereof.

FIG. 6 is a plan view showing a flow sensor according to a second embodiment of the present invention.

FIG. 7 is a plan view showing a flow sensor according to a third embodiment of the present invention.

FIG. 8 is a plan view showing a first modified example thereof.

FIG. 9 is a plan view showing a second modified example thereof.

FIG. 10 is a plan view showing a flow sensor according to a fourth embodiment of the present invention.

FIG. 11 is a plan view showing a first modified example.

FIG. 12 is a plan view showing a second modified example thereof.

FIG. 13 is a characteristic diagram showing measurement results obtained by a conventional flow sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flow sensor 2 Substrate 3 Cavity 4 Support body 5-7 Temperature measuring element thin film heater 6 Heating element 9 First heating section 10 Second heating section 21 Flow sensor 22 Slit 31 Flow sensor 32 to 34 Thin film heater 33 Heating element 35 , 36 Thin film temperature sensor 37 First heat generating part 38 Second heat generating part 41 Flow sensor 43 Support body 44 First heat generating part 45 Second heat generating part 51 Flow sensor 61 Flow sensor 62 First heat generating part 63 Second Heat generating part 71 Flow sensor 72 Cavity 73 Support body 74 First heat generating part 75 Second heat generating part 81 Flow sensor 91 Flow sensor 92 First heat generating part 93 Second heat generating part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Yamaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Hiroyoshi Shoko 1-3-6 Nakamagome, Ota-ku, Tokyo Share Inside Ricoh Company (72) Inventor Junichi Azumi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Seishin Kaminishi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company Inside

Claims (7)

[Claims] 1. A first heat generating section and a second heat generating section each having a heat generating function and a temperature measuring function are sequentially arranged in the direction of fluid flow, and the first heat generating section and the second heat generating section are arranged by fluid flow. In a flow sensor for detecting a flow rate of a fluid based on a temperature difference generated between a second heat generating portion and a second heat generating portion, a heat generating element is provided between the first heat generating portion and the second heat generating portion. Flow sensor. 2. The flow sensor according to claim 1, wherein the first heating section and the second heating section each include a temperature measuring element thin film heater. 3. The flow sensor according to claim 1, wherein the first heating section and the second heating section each include a thin film heater and a thin film temperature sensor. 4. The method according to claim 1, wherein a slit is formed between the first heat generating portion and the heat generating element, and a slit is formed between the second heat generating portion and the heat generating element.
4. The flow sensor according to 2 or 3. 5. A support having a cross-linked structure substantially perpendicular to the flow direction of the fluid is bridged on the surface of the substrate, and the first heat generating portion, the heat generating member, and the second heat generating portion are positioned on the surface of the support. The flow sensor according to claim 1, 2, 3, or 4, wherein 6. A support having a cross-linking structure substantially parallel to the flow direction of the fluid is bridged on the surface of the substrate, and the first heat generating portion, the heat generating member, and the second heat generating portion are positioned on the surface of the support. The flow sensor according to claim 1, 2, 3, or 4, wherein 7. A support having a diaphragm structure is formed on a surface of a substrate, and a first heat generating portion, a heat generating member, and a second heat generating portion are located on the surface of the support. The flow sensor according to 1, 2, 3, or 4.