JP2010236983A - Sensor assembly, and instrument for measuring physical property value of fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the measuring precision of the physical property value of a fluid such as natural gas. <P>SOLUTION: This sensor assembly includes a sensor unit 6 having a substrate 60, the insulator 65 arranged on the surface of the substrate 60 and the first resistor 61 provided on the insulator 65 and used for measuring the physical property value of the fluid coming into contact with the surface of the insulator 65 on the basis of the first drive power applied to the first resistor 61 and the temperature of the first resistor 61, the cover 7 provided to the sensor unit 6 so as to cover the insulator 65 while ensuring a space 72 permitting the fluid to flow along the surface of the insulator 65, and a second resistor 64 for controlling the temperature of at least one of the sensor unit 6 and the cover 7 corresponding to second drive power to be applied. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for measuring a physical property value of a gas such as natural gas, which is an example of a fluid, for example, a thermal conductivity, a calorific value, a composition component, and the like.

  As a technique for measuring a physical property value of a gas such as a gas, for example, a thermal conductivity, a heat amount, a component, or the like, a technique described in Patent Document 1 below is known. According to the description in Patent Document 1, a heat dissipation coefficient is obtained from the power applied to the microheater provided through the diaphragm having heat insulation on the sensor chip and the heater temperature at that time, and the heat dissipation coefficient is calculated based on the heat dissipation coefficient. In addition, when obtaining the thermal conductivity of the atmospheric gas, the temperature in the vicinity of the sensor chip can be made constant by an auxiliary heater provided in the sensor chip. Therefore, it is possible to easily measure the thermal conductivity of pure gas or mixed gas regardless of the temperature without using a constant temperature layer or the like.

JP 2007-248220 A

  In the prior art described above, there are cases where it is desired to further improve the measurement accuracy. The above-described prior art tries to control the temperature in the vicinity of the sensor chip constant by the auxiliary heater. However, since the surface of the sensor chip (diaphragm provided with the micro heater) is exposed, the gas in the vicinity of the sensor chip is exposed. If there is a large variation in temperature, the temperature of the diaphragm, that is, the heater temperature also varies according to the variation.

  For example, when the ambient temperature varies by 10 ° C., the temperature of the diaphragm may vary by about 0.5 ° C. Such a temperature fluctuation causes a measurement error of thermal conductivity, and a measurement error that cannot be ignored depending on the application may occur, and the required measurement accuracy may not be satisfied.

  Accordingly, one of the objects of the present invention is to improve the measurement accuracy of physical property values of fluids such as gas.

  In addition, the present invention is not limited to the above-described object, and other effects of the present invention can be achieved by the functions and effects derived from the respective configurations shown in the embodiments for carrying out the invention which will be described later. It can be positioned as one of

  Aspects of the present invention that can achieve the above-described object can be grasped as a sensor assembly and a fluid property value measuring device described below.

  In other words, one aspect of the sensor assembly includes a base, an insulator disposed on the surface of the base, and a first resistor provided on the insulator, and is provided to the first resistor. A sensor unit used to measure a physical property value of the fluid in contact with the surface based on the first driving power and the temperature of the first resistor, and the fluid flows through the surface of the insulator. A cover provided on the sensor unit so as to cover the insulator while ensuring a permissible space, and a second for controlling the temperature of at least one of the sensor unit and the cover in accordance with the applied second driving power. A resistor.

  In the sensor assembly having such a configuration, the cover and the cover are heated by the heat generated by the second resistor in a state where the insulator is covered while the space allowing the fluid to flow is secured by the cover. At least one of the temperatures is controlled. Thereby, the other temperature can also be controlled by the heat conduction of the heat generation, and the temperature of the fluid touching the sensor unit (first resistor) can be stabilized constant.

  Here, the measurement of the physical property value can be further performed based on the temperature of the fluid in contact with the surface of the insulator.

  The second resistor may also serve as a temperature sensor that detects the temperature of the fluid. The second resistor may be provided on at least one of the sensor unit and the cover. For example, only one second resistor may be provided on the sensor unit.

  Furthermore, the cover may have a thermal conductivity equal to or higher than the thermal conductivity of the substrate. The cover includes a cover base and a plurality of convex portions provided on the cover base, and the space is a space formed by the cover base, the convex portions, and the surface of the insulator. It's good.

  Further, the measured physical property value may be the thermal conductivity of the fluid. Further, the measured physical property value may be the amount of heat of the fluid obtained based on the thermal conductivity. Further, the fluid may be a mixed gas containing a plurality of types of gases in the composition component, and the measured physical property value may be a value related to the composition component obtained based on the thermal conductivity.

  Further, one aspect of the fluid property value measuring apparatus includes the sensor assembly described above and a measurement unit that measures the property value of the fluid in a state where the temperature is controlled to be constant by the second resistor. Prepare.

  By using such a configuration, the physical property value of the fluid can be measured in a state where the temperature of the fluid in contact with the insulator is constantly stabilized in the space allowing the fluid to flow to the surface of the insulator as described above. Can be implemented.

  According to the present invention described above, the temperature of the fluid to be measured that touches the insulator, and hence the first resistor, can be stabilized at a constant level. Accordingly, it is possible to suppress fluctuations to a minimum. Therefore, it is possible to improve the accuracy of the measurement by minimizing the measurement error of the physical property value of the fluid.

It is a perspective view which illustrates the schematic structure of the sensor assembly of one Embodiment. FIG. 2 is an exploded perspective view of the sensor assembly illustrated in FIG. 1. FIG. 3 is a cross-sectional view illustrating a schematic cross-sectional structure of a sensor chip illustrated in FIGS. 1 and 2. It is a figure which shows typically an example of the temperature distribution of the gas in the micro heater vicinity illustrated in FIG.2 and FIG.3. It is a figure which shows the relationship between the thermal radiation coefficient C which changes with the temperature of the mixed gas from which a composition ratio differs, and thermal conductivity (lambda) (T) of gas. It is a block diagram which shows the structural example of the heat conductivity measuring apparatus which concerns on one Embodiment. It is a figure which shows the structural example of the heater drive circuit which makes constant the resistance value of the auxiliary heater of this embodiment, and a micro heater. (A) is a figure which shows an example of the relationship between the thermal conductivity C in temperature To and the thermal conductivity (lambda) (T) of gas measured by the thermal conductivity measuring apparatus of this embodiment, (b) is this embodiment. It is a figure which shows an example of the relationship between the thermal radiation coefficient C measured by the thermal conductivity measuring apparatus of this, and a propane gas density | concentration. It is a block diagram which shows the structural example of the gas component ratio measuring apparatus of one Embodiment.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. In addition, there may be a portion where the dimensional relationships and ratios are different between the drawings.

  1 is a perspective view schematically showing a sensor assembly 1 according to an embodiment, FIG. 2 is an exploded perspective view of the sensor assembly 1 illustrated in FIG. 1, and FIG. 3 is II-II of a sensor chip 6 illustrated in FIG. It is arrow sectional drawing.

  The sensor assembly 1 of this embodiment is, for example, a flat sensor chip (sensor unit) 6, a pedestal 5 that supports the sensor chip 6 from one surface (back surface), and a hollow support on the sensor chip 6. And a cover 7 that covers the other surface (front surface) of the sensor chip 6.

  The sensor chip 6 includes a micro heater (heating resistor) 61 as an example of a first resistor, and measures the thermal conductivity of a gas (eg, gas) that is an example of a fluid based on the amount of generated heat. Used for. The gas may be, for example, a pure gas such as methane, ethane, propane, or butane, or may be a mixed gas such as natural gas containing any of these as a component.

  As illustrated in FIGS. 2 and 3, the sensor chip 6 includes a substrate 60 that is an example of a base provided with a cavity (concave portion) 66, and an insulator provided on the substrate 60 so as to cover at least the cavity 66. 65. The insulator 65 can be formed as a film-like insulating layer, for example.

The thickness of the substrate 60 is, for example, 0.5 mm, and the vertical and horizontal dimensions of the substrate 60 are, for example, about 1.5 mm. However, the size and shape of the substrate 60 are not limited to these. As a material of the substrate 60, for example, silicon (Si) or the like can be used. For example, silicon oxide (SiO ₂ ) or the like can be used as the material of the insulator 65.

  The cavity 66 can be formed in a substantially central portion of one surface of the substrate 60 by using anisotropic etching, MEMS (Micro Electro Mechanical Systems) technology, or the like. FIG. 2 and FIG. 3 illustrate a state in which a boat-shaped concave cavity 66 is formed as an example.

  The insulator 65 has a small heat capacity and is also used as a member (heat insulation part) having heat insulation properties with respect to the substrate 60, and the insulator 65 in a portion covering the cavity 66 has heat insulation properties with respect to the substrate 60. Make a diaphragm. The diaphragm is illustratively provided with a plurality of through holes 67, and both surfaces of the diaphragm are opened to the outside air through these through holes 67.

  The entire sensor chip 6 is supported by a pedestal 5 as illustrated in FIGS. 1 and 2. The pedestal 5 exemplarily has four leg portions (convex portions) 51 (one in a blind spot in FIGS. 1 and 2) at four corners of a flat substrate 50.

  The pedestal 5 is supported (hollow support) and fixed in a state where the sensor chip 6 is floated substantially in the air (in the gas to be measured) by joining these leg portions 51 and the four corners of the sensor chip 6. can do. Thereby, a cross-shaped space 52 formed by the base body 50 of the base 5, each leg portion 51 of the base 5 and the sensor chip 6 is secured between the base body 50 of the base 5 and the sensor chip 6. Gas circulation is allowed to the space 52. That is, the space 52 is positioned as a gas flow path.

  Such a pedestal 5 can have a size and shape corresponding to the size and shape of the sensor chip 6 to be supported. For example, the length of one side is about 1.5 mm, the thickness is about 0.3 mm, the height of the leg 51 (depth of the flow path 52) is about 0.7 mm, and the length of one side of the leg 51 is It can be about 0.3 mm.

  For fixing (joining) the leg 51 and the sensor chip 6, various known joining methods can be used. For example, an adhesive may be used, or mechanical connection such as fitting and locking may be used. A structure may be used. As a material of the pedestal 5, for example, glass or ceramic can be used. The base 5 can be a member having a high thermal conductivity, for example, a member of 10 W / (m · K) or more. If a member having a high thermal conductivity is used, the amount of current used for constant control of the entire sensor chip 6 to a predetermined temperature can be suppressed, and efficient temperature control is possible even with a power supply with a small capacity. An example of a member having a thermal conductivity of 10 W / (m · K) or more includes a porous member.

  The pedestal 5 is described in, for example, Japanese Patent No. 3740026, Japanese Patent No. 3740027, Japanese Patent Application Laid-Open No. 2002-29688, Japanese Patent Application Laid-Open No. 2002-318148, Japanese Patent Application Laid-Open No. 2002-318149, and the like. A thing can be employ | adopted suitably.

  The cover 7 exemplarily includes a flat substrate (cover substrate) 70 and four leg portions (convex portions) 71 protruding from the four corners of the substrate 70 (one is a blind spot in FIGS. 1 and 2). And). By joining these leg portions 71 and the four corners of the sensor chip 6, the cover 7 maintains the predetermined space 72 and the surface of the sensor chip 6 (insulator 65) where the micro heater 61 is provided. The sensor chip 6 is covered.

  Accordingly, the sensor chip 6 is covered with the cover 7 while ensuring a space 72 that allows the gas to be measured to flow to the microheater 61. As a result, a cross-shaped space 72 is formed by the base body 70 of the cover 7, each leg portion 71 of the cover 7, and the surface of the sensor chip 6 (insulator 65), and gas flow is allowed in this space 72. Thus, the gas can be brought into contact with the surface of the sensor chip 6. Therefore, the space 72 is positioned as a gas flow path, like the space 52.

  In other words, it is sufficient that the cover 7 has a shape that can be covered with the surface of the sensor chip 6 (insulator 65) where the microheater 61 is provided exposed to the gas. For example, the cover 7 may have a dome shape. Further, the joints between the cover 7 and the sensor chip 6 are not limited to the four corners of the sensor chip 6. Depending on the strength required for the sensor assembly 1, the number of joints and the number thereof may be changed as appropriate.

  For fixing (joining) the leg 71 and the sensor chip 6, various known joining methods can be used. For example, an adhesive may be used, or a mechanical fitting or engagement structure may be used. May be used. Further, the size, shape, and material of the cover 7 may be the same as or different from the size and shape of the base 5. If they are the same, the cover 7 and the pedestal 5 can be shared, and the number of parts of the sensor assembly 1 can be reduced.

  The cover 7 can be made of a member having a thermal conductivity equal to or higher than that of the sensor chip 6 (substrate 60). By using a member having a high thermal conductivity, as will be described later, the ambient temperature sensor (auxiliary heater) 64 is driven by being supplied with a voltage, so that the heat generated is efficiently transmitted to the cover 7, and the sensor chip 6. And the cover 7 can be easily controlled to a desired temperature.

  In the case where an adhesive is used for joining the sensor chip 6 and the cover 7, if an adhesive having a high thermal conductivity is used, the heat conduction between the sensor chip 6 and the cover 7 can be efficiently prevented. Can be done. Further, the cover 7 may not be dedicated to the sensor chip 6. For example, a part of a side wall of a pipe forming a flow path through which a gas to be measured flows is used as the cover 7 (that is, also used as a cover). Also good.

  The sensor chip 6 includes the above-described microheater 61 provided on the insulator 65 and an ambient temperature sensor 64 provided on the insulator 65 so as to be isolated from the microheater 61.

  In other words, the sensor chip 6 supports the microheater 61 in a substantially floating state by providing the microheater 61 on the diaphragm having heat insulation properties, as illustrated in FIG. As a result, the sensor chip 6 is converted into gas flowing along the spaces (flow paths) 52 and 72 formed by both sides of the diaphragm, in other words, the pedestal 5, the cover 7, and the sensor chip 6 as described above. You can touch. The direction when the sensor chip 6 (sensor assembly 1) is arranged in the gas to be measured is, for example, the direction in which the long sides of the microheater 61 intersect the gas flow direction F.

  For example, the microheater 61 is disposed at the center of the insulator 65 covering the cavity 66 and heats the gas in contact with the microheater 61. The ambient temperature sensor 64 can be disposed at a position isolated from the micro heater 61. Thereby, the ambient temperature sensor 64 can detect the temperature of the gas in contact with the surface of the sensor chip 6 (ambient temperature) without being affected by the temperature of the microheater 61.

  In other words, it is sufficient that the ambient temperature sensor 64 is provided at a position that is not affected by the heat radiation of the microheater 61, and the number thereof is not limited to one. As the ambient temperature sensor 64, a heating resistor (second resistor) similar to the micro heater 61 can be used. In this case, the ambient temperature sensor 64 also functions as an auxiliary heater (hereinafter also referred to as “auxiliary heater”) that controls the temperature of the insulator 65 to heat the entire sensor chip 6 (or the cover 7) to a constant temperature. Can do. That is, the second resistor has a function as an auxiliary heater and a function as the ambient temperature sensor 64.

  2 and 3, only one auxiliary heater 64 is provided on the sensor chip 6 (substrate 60) side by way of example. However, the auxiliary heater 64 may be provided on the cover 7 side, or the cover 7 One or a plurality of sensors can be provided on both the sensor chip 6 side and the sensor chip 6 side.

  Due to the constant temperature control by the auxiliary heater 64, the influence of the temperature fluctuation (heater temperature) on the gas in contact with the surface of the sensor chip 6 (microheater 61) caused by the gas temperature fluctuation in the vicinity of the sensor chip 6 (sensor assembly 1). Can be suppressed. Moreover, in this embodiment, the cover 7 is made of a member having a thermal conductivity equal to or higher than that of the sensor chip 6 (base 60), so that the heat generated by the auxiliary heater 64 can be efficiently transmitted to the cover 7. Thus, both the sensor chip 6 and the cover 7 can be efficiently controlled to a desired temperature. Therefore, it is possible to more effectively suppress the influence of the ambient temperature change.

  Note that one or both of the microheater 61 and the ambient temperature sensor 64 can be formed using platinum (Pt) or the like, and a lithography method or the like can be applied as a forming method.

By the way, a heating resistor (thermal resistor) such as platinum used for the micro heater 61 and the auxiliary heater 64 has a property that its resistance value changes with temperature. For example, when the resistance value of the microheater 61 at a standard temperature Tstd of 20 ° C. is expressed as Rstd, the primary resistance temperature coefficient is α, and the secondary resistance temperature coefficient is β, the resistance value of the microheater 61 at the temperature Th Rh can be obtained by the following equation (1).

Rh = Rstd · [1 + α (Th−Tstd) + β (Th−Tstd) ² ] (1)

  Therefore, if the resistance value Rh of the microheater 61 is specified, the heating temperature (heater temperature) Th of the microheater 61 can be obtained from the resistance value Rh by the above formula (1). This also applies to the ambient temperature sensor (auxiliary heater) 64.

The temperature Th of the microheater 61 is stabilized when the heat generated by the microheater 61 and the heat released from the microheater 61 to the gas are balanced (thermal equilibrium state). In the thermal equilibrium state, when the heater temperature is Th, the ambient temperature is To, and the heat dissipation coefficient from the microheater 61 to the gas is C, the driving power Ph of the microheater 61 can be expressed by the following equation (2).

C · (Th−To) = Ph (2)

In other words, when the condition satisfying the above equation (2) is satisfied, the microheater 61 and the gas are in a thermal equilibrium state and stabilized. Therefore, the heat dissipation coefficient C from the micro heater 61 to the gas can be obtained from the condition of this thermal equilibrium state by the following equation (3).

C = Ph / (Th−To) (3)

On the other hand, the driving power Ph of the microheater 61 can be obtained by the following equation (4), where Vh is a voltage applied across the microheater 61 and Ih is a current flowing through the microheater 61 at that time.

Ph = Vh · Ih (4)

Further, the resistance value Rh of the microheater 61 at that time can be obtained by the following equation (5).

Rh = Vh / Ih = Ph / Ih ² (5)

  Therefore, if the driving power Ph of the microheater 61 is obtained, the resistance value Rh of the microheater 61 can be obtained based on the driving power Ph and the current Ih flowing through the microheater 61, and further based on the resistance value Rh. The temperature Th of the micro heater 61 can be obtained.

  As described above, the ambient temperature To can be obtained from the control conditions when the heat generation temperature (ambient temperature) To itself of the auxiliary heater 64 is controlled to be constant. If the driving power Ph of the microheater 61, the heater temperature Th of the microheater 61, and the ambient temperature To can be obtained, the heat dissipation coefficient C from the microheater 61 to the gas can be calculated by the above equation (3). It is.

On the other hand, the heat dissipation coefficient C can be expressed by, for example, the following equation (6), where h is the average heat transfer coefficient from the microheater 61 to the gas and S is the heat dissipation area of the microheater 61.

C = 2 · h · S (6)

Note that the average heat transfer coefficient h may vary depending on the natural convection state of the gas and the surface state of the microheater 61. In addition, the coefficient [2] takes into consideration that heat transfer from the microheater 61 to the gas is performed on the two front and back surfaces of the microheater 61, as schematically shown in FIG.

  The element area (heat generation area) of the microheater 61 is minute, the range of temperature change caused by the heat generation of the microheater 61 is minute, and only spot-like temperature displacement occurs, and the natural convection of gas also occurs. When it is assumed that there is no microheater 61, the temperature distribution around the microheater 61 gradually decreases as the distance from the microheater 61 increases as illustrated in FIG. For example, the temperature at the portion in contact with the microheater 61 is increased to the heater temperature Th, and the temperature gradually decreases to the ambient temperature To as the distance from the microheater 61 increases.

A region where the temperature of the gas having such a temperature distribution is lowered from the heater temperature Th to the ambient temperature To is defined as a temperature boundary layer, and the thickness is d, the average heat transfer coefficient h is the heat conduction of the gas. It is considered that it is proportional to the rate λ and inversely proportional to the thickness d of the temperature boundary layer. That is, the average heat transfer coefficient h can be determined by the following equation (7).

h = λ / d (7)

Here, the thermal conductivity λ of the gas tends to increase as the temperature increases, and the thermal conductivity λ (T) of the gas at the temperature T can be expressed by the following equation (8), for example.

λ (T) = λo (1 + γ · T) (8)

Here, λo represents the thermal conductivity of the gas at a reference temperature (for example, 0 ° C.), and γ represents a first-order temperature coefficient.

  The thickness d of the temperature boundary layer varies depending on the thermal conductivity λ of the gas, and the greater the thermal conductivity λ, the faster the thermal conduction, so the thickness d becomes thinner. On the other hand, when the thermal conductivity λ of the gas is small, the gradient of the temperature change becomes gentle and the thickness d of the temperature boundary layer becomes thick because the thermal conduction is slow.

That is, the thickness d of the boundary layer varies with the thermal conductivity λ of the gas, and the thermal conductivity λ of the gas varies with the temperature. Therefore, the thickness d (T) of the temperature boundary layer at the temperature T is a function f [α with the parameter α as the thermal conductivity λ (T) of the gas that changes with the temperature T, as shown in the following equation (9). ] Can be used.

d (T) = f [λ (T)] (9)

  The heat radiation area S of the microheater 61 indicates, for example, the entire area of the diaphragm provided with the microheater 61, and the temperature distribution of the gas in the vicinity of the microheater 61 changes depending on the temperature distribution on the diaphragm. . However, when the thermal conductivity λ of the gas is large, the temperature distribution becomes a sharp shape, so that the effective heat radiation area S of the microheater 61 is reduced according to the thermal conductivity λ of the gas. Therefore, the heat radiation area S can be considered as an area smaller than the area So of the diaphragm.

In this case, coupled with the microheater 61 being minute, the heat radiation area S of the microheater 61 is spot-like, and can be regarded as a substantial point heat source. Therefore, the effective heat radiation area S can be expressed as a function g [α] having the parameter α as the thermal conductivity λ (T) of the gas that changes with the temperature T, for example, as shown in the following equation (10). .

S (T) = g [λ (T)] (10)

  From the above, when the relationship between the heat dissipation coefficient C of the microheater 61 and the thermal conductivity λ (T) of the gas is summarized, the relationship represented by the following equation (11) can be derived from the above-described equations.

C = 2 · h · S
= 2 ・ (λ (T) ÷ d (T)) ・ S (T)
= 2 · (λ (T) ÷ f [λ (T)]) · g [λ (T)] (11)

  From the relationship shown in this equation (11), it can be understood that the heat dissipation coefficient C of the microheater 61 is affected by the thermal conductivity λ (T) of the gas that changes with the temperature T, that is, the temperature characteristics of the gas.

  FIG. 4 shows the heat dissipation coefficient C of the microheater 61 when the temperature is changed to 0 ° C., 20 ° C., and 40 ° C. with respect to a plurality of kinds of gases having different mixing ratios of propane gas and air whose components are known. And an example of a relationship (characteristic) between the thermal conductivity λ of the gas.

  As shown in FIG. 4, although there is a certain correlation between the heat dissipation coefficient C of the microheater 61 and the thermal conductivity λ of each gas, the heat dissipation coefficient C and the heat are affected by the temperature. The correspondence with the conductivity λ changes. Therefore, when obtaining the thermal conductivity λ of the gas from the heat dissipation coefficient C of the microheater 61, it is preferable to perform some temperature correction.

  Therefore, as described above, when the sensor chip 6 having the microheater 61 is insulated from the surroundings and supported, the heat transmitted to the gas is predominantly due to the heat radiation of the sensor chip 6. Therefore, if the heat generation temperature of the auxiliary heater 64 is controlled to be constant, the heat generated from the auxiliary heater 64 is transmitted to the sensor chip 6 except for the heat released to the gas.

  Thereby, the sensor chip 6 is heated uniformly as a whole, and the temperature is stabilized by being in thermal equilibrium with the gas. That is, it may be considered that the temperature of the sensor chip 6 is stabilized by the heat generation temperature T of the auxiliary heater 64 (temperature of the sensor chip 6).

  On the other hand, the gas in the vicinity of the sensor chip 6 receives heat from the entire sensor chip 6 and is heated, and is stabilized when a thermal equilibrium state is established with the sensor chip 6. Therefore, the gas in the vicinity of the periphery of the sensor chip 6 is partially stabilized depending on the temperature of the sensor chip 6. That is, it may be considered that the gas is stabilized at the temperature of the sensor chip 6 (the heat generation temperature of the auxiliary heater 64) T in the vicinity of the periphery of the sensor chip 6.

  As described above with reference to FIG. 4, the gas in the vicinity of the sensor chip 6 in which the temperature is stabilized in this way receives heat from the microheater 61 to form a temperature boundary layer. Therefore, the thickness d of the temperature boundary layer at that time can be uniquely determined as d = f [λ] where λ is the thermal conductivity of the gas at the stabilized temperature Tcnst.

  Further, the effective heat radiation area S of the microheater 61 can also be uniquely determined as S = g [λ] depending on the thermal conductivity λ of the gas at the temperature Tcnst. Therefore, the relationship between the heat dissipation coefficient C of the microheater 61 and the thermal conductivity λ of the gas at a constant temperature Tcnst is C = 2 · (λ ÷ f [λ]) · g [λ], which is the gas temperature. There is a one-to-one correspondence without depending on the characteristics.

  Based on the above consideration, the sensor chip 6 having the microheater 61 is thermally insulated from the surroundings and supported in the gas. In this state, for example, the resistance value Rr of the auxiliary heater 64 is made constant to make the heat generation temperature constant. Thus, the entire sensor chip 6 can be kept at a constant temperature. Further, the heat generated by the auxiliary heater 64 is also transmitted to the cover 7, and the entire cover 7 can be kept at a constant temperature.

  As a result, the temperature of the gas to be measured in the space (flow path) 72 formed by the surface of the sensor chip 6 (insulator 65), the inner surface of the cover 7 (base 70), and the legs 71 is provided. It is possible to provide a measurement environment that is more stable than the case where there is not.

  Thus, in the measurement environment in which the gas temperature is stabilized, the heat dissipation coefficient C is obtained from the driving power Ph when the microheater 61 is driven, and based on the correlation between the obtained heat dissipation coefficient C and the thermal conductivity λo. Thus, if the thermal conductivity λ is obtained as an example of the physical property value of the gas at the temperature Tcnst, the thermal conductivity of the gas can be obtained with high accuracy while minimizing measurement errors due to temperature fluctuations.

  Hereinafter, an example of a device (thermal conductivity measuring device) for obtaining the thermal conductivity λ as described above will be described with reference to FIG. FIG. 6 is a block diagram illustrating a configuration example of a thermal conductivity measuring device as an example of a gas property value measuring device according to the present embodiment.

  The thermal conductivity measuring device (hereinafter also simply referred to as “measuring device”) illustrated in FIG. 6 exemplarily includes an ambient temperature sensor (auxiliary heater) 64 and a micro as a measuring unit for measuring the thermal conductivity of gas. Heater drive power supplies 20 and 30 that supply heat to each of the heaters 61 to drive heat, a drive power detection unit 401, a heater current detection unit 402, a heater temperature detection unit 403, an ambient temperature detection unit 404, and heat dissipation A coefficient calculation unit 405, a thermal conductivity calculation unit 406, and a memory 407 are provided.

For example, as shown in FIG. 7, the heater drive power supplies 30 and 20 include a resistance bridge circuit 30a having a micro heater 61 or an ambient temperature sensor (auxiliary heater) 64, which is a temperature control target, as one bridge side, and the resistance bridge circuit. 30a in response to the bridge voltage V ₂ of and a voltage control circuit 30b for feedback control of the driving voltages V ₁ applied to the resistance bridge circuit 30a.

In other words, the heater drive power supplies 30 and 20 include a resistance bridge circuit 30a using fixed resistors R1, R2 and R3 having known resistance values and a micro heater 61 having a resistance value Rh or an auxiliary heater 64 having a resistance value Rr. The bridge voltages V _2a and V _2b are input voltages of a differential amplifier as an example of the voltage control circuit 30b, and the bridge voltage V _2a on the micro heater 61 side is always the bridge voltage V _2b on the fixed resistors R2 and R3 side. The bridge drive voltage V ₁ is feedback-controlled. Thereby, the resistance value Rh of the micro heater 61 or the resistance value Rr of the auxiliary heater 64 is controlled with high accuracy. As a result, the measurement accuracy of the thermal conductivity λ can be improved.

At this time, the current Ih flowing through the microheater 61 is Ih = (V ₁ −V _2a ) / R1. Further, the bridge voltage V _2a on the micro heater 61 side can be obtained as V _2a = V _2b = V1 · R3 / (R2 + R3).

  Therefore, by obtaining the current Ih by the heater current detection unit 402, the drive power detection unit 401 can obtain the drive power Ph of the microheater 61 as Ph = Ih · V2a. Further, the heater resistance Rh can be obtained as Rh = Vh / Ih as described above.

  The heater temperature detection unit 403 obtains the temperature Th of the microheater 61 based on the drive power Ph and the energization current Ih detected by the detection units 401 and 402. The ambient temperature detection unit 404 obtains the gas temperature (ambient temperature) To in the vicinity of the sensor chip 6 based on the driving power supplied from the heater driving power source 20 to the ambient temperature sensor (auxiliary heater) 64.

The heat dissipation coefficient calculator 405 obtains the heat dissipation coefficient C of the microheater 61 as C = Ph / (Th−To) based on the heater temperature Th, the ambient temperature To, and the drive power Ph. The memory 407 stores, for example, the correspondence (C-λ ₀ characteristic) between the thermal conductivity λo at the temperature To of the gas having a known component and the heat dissipation coefficient C of the microheater 61 as data in a table format or the like. .

  The thermal conductivity calculation unit 406 corresponds to the heat dissipation coefficient C by referring to the data (table) stored in the memory 407 based on the heat dissipation coefficient C obtained by the heat dissipation coefficient calculation unit 405. The thermal conductivity λo of the gas at the temperature To can be obtained.

  As described above, according to the present embodiment, the sensor chip 6 and the cover 7 are supported by supporting the sensor chip 6 in the gas in a state of being insulated from the substrate 60 and controlling the heat generation temperature of the auxiliary heater 64 to be constant. Both of them can be kept at a constant temperature. Therefore, the temperature of the gas in the space (measurement space) 72 formed by the surface of the sensor chip 6 and the inner surface of the cover 7 can be stabilized to a higher degree than when the cover 7 is not provided.

  For example, when the cover 7 is not provided, if the ambient temperature fluctuates by 10 ° C., the temperature in the vicinity of the diaphragm of the sensor chip 6 fluctuates by 0.5 degrees. The temperature fluctuation can be suppressed to about 0.25 degrees). Therefore, the measurement error can be reduced as compared with the case without the cover 7 and the thermal conductivity λ of the gas in the vicinity of the sensor chip 6 can be obtained with high accuracy. As a result, for example, it is possible to sufficiently cope with an application where the measurement accuracy of thermal conductivity is severe.

  FIG. 8A shows a heat release coefficient C and a thermal conductivity measured as described above while changing the temperature using a plurality of types of mixed gas of propane gas and air having different mixing ratios as gas. The relationship with λ is illustrated.

  As shown in FIG. 8A, according to the measuring apparatus of the present embodiment, regardless of the difference in gas temperature, depending on the difference in mixing ratio between propane gas and air, that is, the component ratio of gas. In addition, the relationship between the heat dissipation coefficient C and the thermal conductivity λ can be associated with one to one. Therefore, if the correspondence is checked in advance and stored in the memory 407, the heat conductivity λ of the mixed gas can be obtained by obtaining the heat dissipation coefficient C of the microheater 61.

  FIG. 8B illustrates the relationship between the concentration of propane gas obtained from the mixing ratio of propane gas and air in the mixed gas described above and the heat dissipation coefficient C of the microheater 61. The thermal conductivity λmix of the mixed gas is λmix = x · λpg + y · λair (where the mixing ratio is [x: y] where λpg is the thermal conductivity of propane gas and λair is the thermal conductivity of air. x + y = 1).

  Therefore, by obtaining the heat dissipation coefficient C of the micro heater 61 as described above, as another example of the physical property value of the gas, the component ratio of the mixed gas whose component is known, for example, the propane gas concentration in the case of the mixed gas, is obtained. It can be easily obtained from the correspondence with the heat dissipation coefficient C shown in FIG.

  Further, if the ratio of the composition components of a plurality of gases constituting the mixed gas is obtained as described above, for example, the calorific value of each gas can be determined from the relationship between the gas density and the calorific value, still another example of the physical property value of the gas. As follows, depending on the total amount of the mixed gas and its composition ratio. Therefore, the calorific value of the mixed gas can be calculated. For example, the calorific value (energy amount) of the mixed gas per unit volume can be calculated easily and accurately from the component ratio obtained as described above.

  FIG. 9 shows an example of a measuring apparatus for obtaining the component ratio of the mixed gas in this way and further obtaining the calorific value thereof.

  The measurement apparatus illustrated in FIG. 9 exemplarily includes a memory 408, a component ratio calculation unit 409, a memory 410, and a heat generation amount calculation unit 411 in addition to the configuration illustrated in FIG. Note that some or all of the memories 407, 408, and 410 may be integrated as a shared memory.

  The memory 408 associates the thermal conductivity λ (T) of the mixed gas at the temperature T with the thermal conductivity λ (T) at the temperature T for a plurality of gases that are considered to be included in the mixed gas. Stored data is stored. The data includes, for example, controlling the heat generation temperature of the heater power supply 30 according to measurement conditions corresponding to a plurality of different temperatures T, and heat conduction at each temperature T obtained by the thermal conductivity calculation unit 406 under each measurement condition. The rate λ (T) can be set by writing to the memory 408.

  The component ratio calculation unit 409 can determine the component ratio of each gas by solving the above-described simultaneous equations based on the mixed gas stored in the memory 408 and the thermal conductivity λ (T) of each gas.

  The memory 410 stores data (a calorific value table) representing the relationship between the gas density and the calorific value corresponding to the type of gas.

  The calorific value calculation unit 411 refers to the calorific value table of the memory 410 based on the component ratio calculated by the component ratio calculation unit 409, thereby calculating the calorific value and / or the total calorific value for each composition component of the mixed gas. Can be sought.

  As another example of the physical property value of the gas to be measured, the humidity of the gas corresponding to the temperature T may be obtained alternatively or additionally.

  As described above, according to the present embodiment, the sensor chip 6 (sensor assembly 1) with the cover 7 is thermally cut off from the external environment and the sensor chip 6 is controlled to a constant temperature by the auxiliary heater 64. By obtaining the heat dissipation coefficient C of the microheater 61, the thermal conductivity λ (T) of the gas (pure gas or mixed gas), the component ratio, the amount of heat generation, etc. can be accurately and easily obtained. . In addition, the thermal conductivity λ (T) of the gas to be measured can be easily obtained without using a large facility such as providing a thermostatic bath, which contributes to cost reduction.

  In addition, in this embodiment, by providing the sensor chip 6 with the cover 7, as described above, the measurement error of the thermal conductivity λ (T) obtained by the thermal conductivity calculation unit 406 is reduced, and the measurement accuracy is improved. Therefore, the measurement accuracy of the gas component ratio and the calorific value required based on the thermal conductivity λ (T) can be improved as compared with the case where the cover 7 is not provided. Therefore, it is possible to sufficiently cope with an application in which an allowable measurement error is very small and severe measurement accuracy is required.

  Note that the above-described embodiment of the present invention is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described above. That is, the present invention can be implemented with various modifications without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the case where the fluid to be measured for the physical property value such as the thermal conductivity is a gas (gas), but the liquid may be the measurement target.

  In addition, each calculation function in the measuring apparatus can be realized by software in a microcomputer. Further, the structure of the micro heater 61 is not particularly limited, and a heater element provided in an existing thermal flow sensor can be used.

  Further, the means for driving the auxiliary heater 64 and the micro heater 61 is not limited to the example using the above-described resistance bridge circuit 30a and the differential amplifier 30b that feedback-controls the bridge voltage.

DESCRIPTION OF SYMBOLS 1 Sensor assembly 5 Base 20, 30 Heater drive power supply 50 Base | substrate 51 Leg part (convex part)
52 space (flow path)
6 Sensor chip (sensor unit)
60 Substrate (base)
61 Micro heater (first resistor)
64 Ambient temperature sensor (auxiliary heater; second resistor)
65 Insulator (heat insulation part)
66 Cavity (recess)
7 Cover 70 Base 71 Leg (convex)
72 space (flow path)
401 Driving power detection unit 402 Heater current detection unit 403 Heater temperature detection unit 404 Ambient temperature detection unit 405 Heat dissipation coefficient calculation unit 406 Thermal conductivity calculation unit 407, 408, 410 Memory 409 Component ratio calculation unit 411 Heat generation amount calculation unit

Claims (11)

A first resistor that is provided on the insulator; a first driving power that is applied to the first resistor; and a first resistor that is provided on the insulator. A sensor unit used to measure a physical property value of a fluid in contact with the surface based on the temperature of one resistor;
A cover provided on the sensor unit so as to cover the insulator while ensuring a space allowing the fluid to flow on the surface of the insulator;
A second resistor for controlling the temperature of at least one of the sensor unit and the cover in accordance with a second driving power applied;
A sensor assembly.   The sensor assembly according to claim 1, wherein the measurement of the physical property value is further performed based on a temperature of the fluid in contact with a surface of the insulator.   The sensor assembly according to claim 2, wherein the second resistor also serves as a temperature sensor that detects a temperature of the fluid.   The sensor assembly according to claim 1, wherein the second resistor is provided on at least one of the sensor unit and the cover.   The sensor assembly according to claim 4, wherein only one second resistor is provided in the sensor unit.   The sensor assembly according to claim 5, wherein the cover has a thermal conductivity equal to or higher than a thermal conductivity of the substrate. The cover includes a cover base and a plurality of convex portions provided on the cover base,
The sensor assembly according to any one of claims 1 to 6, wherein the space is a space formed by the cover base, the convex portion, and a surface of the insulator.   The sensor assembly according to claim 1, wherein the measured physical property value is thermal conductivity of the fluid.   The sensor assembly according to claim 8, wherein the measured physical property value is an amount of heat of the fluid obtained based on the thermal conductivity. The fluid is a mixed gas containing a plurality of types of gas in the composition component,
The sensor assembly according to claim 8, wherein the measured physical property value is a value related to the composition component determined based on the thermal conductivity. A first resistor that is provided on the insulator; a first driving power that is applied to the first resistor; and a first resistor that is provided on the insulator. A sensor unit used to measure the physical property value of the fluid based on the temperature of one resistor, and covers the insulator while ensuring a space allowing the fluid to flow on the surface of the insulator; A sensor assembly including a cover provided on the sensor unit, and a second resistor for controlling a temperature of at least one of the sensor unit and the cover according to a second driving power applied thereto,
A fluid property value measuring apparatus comprising: a measurement unit that measures the property value of the fluid in a state where the temperature is controlled to be constant by the second resistor.

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