JP2007248220A - Heat conductivity measuring method, its measuring instrument, and gas component ratio measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat conductivity measuring method which enables the simple measurement of the heat conductivity of a pure gas or a mixed gas regardless of the temperature of the gas, and a heat conductivity measuring instrument. <P>SOLUTION: The microheater provided on the thin-walled region (e.g., microbridge) formed to a sensor chip and positioned in an atmosphere gas is used and the heat conductivity of the atmosphere gas is calculated according to the radiation coefficient of the microheater calculated from the power applied to the microheater and the heater temperature at the time of application of power. The sensor chip is supported in the atmosphere gas through a heat insulating body and the resistance value of the auxiliary heater provided to the sensor chip is controlled constant while the temperature of the atmosphere gas in the vicinity of the periphery of the sensor chip is made constant. The heat conductivity of the atmosphere gas is calculated from the drive power of the microheater at this time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal conductivity measuring method and apparatus capable of easily measuring the thermal conductivity of a gas whose component ratio is unknown but whose component ratio is unknown, such as natural gas, and a gas using the thermal conductivity measuring apparatus. The present invention relates to a component ratio measuring apparatus.

As a method for measuring the thermal conductivity of a gas, it is known to drive a heater placed in a gas (atmospheric gas) kept at a constant temperature at a constant temperature and measure the amount of heat generated (for example, Patent Documents). 1). This method utilizes the fact that the heat value of the heater is proportional to the thermal conductivity of the ambient gas. It has also been proposed to remove the thermal influence from the pedestal by supporting the flow sensor through a thermal insulator in a thermal flow meter (see, for example, Patent Document 2).
Japanese Patent No. 3114137 JP 2002-296086 A

  However, when the thermal conductivity of the gas is measured by adopting the above-described method, it cannot be denied that the configuration becomes large, for example, a thermostatic bath for keeping the gas at a constant temperature is required. In general, the thermal conductivity of a gas has an inherent temperature change characteristic according to its type. Therefore, if the calorific value of a heater is simply measured, the thermal conductivity cannot be accurately measured. There is an essential problem to say. In particular, in the case of a mixed gas in which plural kinds of gases are mixed like natural gas, it is very difficult to measure the thermal conductivity.

  By the way, it is also possible to pass the mixed gas through a member called a column, analyze the composition ratio of the gas species using the difference in flow rate due to the difference in molecular weight, and then measure the thermal conductivity of the mixed gas. (See, for example, JP-A-11-14572). However, in such a method, it takes a lot of time to analyze the composition ratio of the mixed gas using the column, and there are also problems that the entire configuration of the analyzer is complicated and expensive.

The present invention has been made in consideration of such circumstances, and its purpose is to provide a thermal conductivity measurement method and a thermal conductivity measurement method that can easily measure the thermal conductivity of pure gas or mixed gas regardless of its temperature. It is to provide a conductivity measuring device.
Furthermore, it is intended to provide a gas component ratio measuring device capable of obtaining the composition ratio of a known mixed gas, for example, natural gas, using the above-described thermal conductivity measuring method and its apparatus, and evaluating the calorific value thereof. It is aimed.

  In order to achieve the above-described object, the thermal conductivity measurement method and apparatus according to the present invention, and the gas component ratio measurement apparatus using the thermal conductivity measurement apparatus, the average heat transfer coefficient from the microheater to the atmospheric gas is It is determined by the thermal conductivity of the gas and the thickness of the temperature boundary layer near the microheater, and the thickness of the temperature boundary layer and the effective heat dissipation area of the microheater depend on the thermal conductivity of the ambient gas, respectively. I pay attention to it. In particular, it is noted that the thickness of the temperature boundary layer and the effective heat dissipation area of the microheater depend exclusively on the thermal conductivity of the ambient gas in a local region around the sensor chip on which the microheater is formed. ing.

Therefore, the thermal conductivity measurement method according to the present invention uses a microheater provided on a thin area formed on a sensor chip, for example, a thin diaphragm or a microbridge, and positioned in an atmospheric gas, and the electric power applied to the microheater. And determining the thermal conductivity of the ambient gas according to the heat dissipation coefficient of the micro heater determined from the heater temperature at that time,
The sensor chip is supported in the atmospheric gas via a thermal insulator, and the resistance value of an auxiliary heater formed on the sensor chip, for example, a heating resistance element for detecting ambient temperature, is controlled to be constant. The temperature of the entire chip is controlled to be constant, and the thermal conductivity of the atmospheric gas is obtained from the driving power of the microheater that is driven at a constant condition.

  Incidentally, the control for stabilizing the resistance value of the auxiliary heater is performed, for example, by feedback control of the driving voltage applied to the resistance bridge circuit according to the voltage between the bridges of the resistance bridge circuit having the auxiliary heater as one bridge side. . The driving power of the microheater is, for example, a voltage applied to the microheater when the resistance value (temperature) of the microheater is controlled to be constant using a resistance bridge circuit, and a circuit constant of the resistance bridge circuit. It is calculated by calculating from

  In addition, for the detection of the thermal conductivity of the atmospheric gas from the driving power of the microheater described above, for example, the heat dissipation coefficient of the microheater is obtained from the driving power of the microheater and is supported via the thermal insulator. When the resistance value of the auxiliary heater in the sensor chip is controlled to be constant, this keeps the temperature of the auxiliary heater constant, and also keeps the temperature of the sensor chip forming the micro heater constant. This is performed by utilizing a unified correspondence between the thermal conductivity of the atmospheric gas and the heat dissipation coefficient of the microheater obtained as described above, regardless of the temperature of the atmospheric gas.

The thermal conductivity measuring device according to the present invention is
<a> a sensor chip with an auxiliary heater;
<b> In this sensor chip, for example, a micro heater provided on a thin region formed as a thin diaphragm, a micro bridge, or the like;
<c> a thermal insulator that thermally insulates the sensor chip from a base and supports the sensor chip in an atmospheric gas;
<d> a heater drive circuit for controlling the resistance value of the auxiliary heater to be constant;
<e> Power detection means for obtaining a driving power Ph of the microheater when the microheater is heated under a certain condition;
<f> A heat dissipation coefficient calculating means for obtaining a heat dissipation coefficient C from the microheater according to the detected drive power;
<g> Based on a unified correspondence between the thermal conductivity λ of the ambient gas in the vicinity of the sensor chip and the heat dissipation coefficient C of the microheater when the resistance value of the auxiliary heater is controlled to be constant, Thermal conductivity calculation means for determining the thermal conductivity of the ambient gas from the heat dissipation coefficient determined by the heat dissipation coefficient calculation means.

  Specifically, the heater drive circuit feedback-controls a resistance bridge circuit configured with, for example, the auxiliary heater as one bridge side, and a drive voltage applied to the resistance bridge circuit according to a bridge voltage of the resistance bridge circuit. And a voltage control circuit. Further, the thermal conductivity calculation means refers to a table describing a correspondence relationship between the heat dissipation coefficient C of the microheater determined in advance according to the composition of the atmospheric gas and the thermal conductivity λ of the atmospheric gas at a specific temperature T. Thus, it is realized as a method for obtaining the thermal conductivity of the atmospheric gas.

The gas component ratio measuring device according to the present invention is realized by using the above-described thermal conductivity measuring device,
<h> Using the thermal conductivity measurement device, changing the resistance value of the microheater to be controlled to be constant, respectively, control means for respectively obtaining the thermal conductivity of the atmospheric gas at different heater temperatures;
<i> An analysis means for analyzing the composition ratio of the atmospheric gas from simultaneous equations of thermal conductivity at each heater temperature.

  Furthermore, it is desirable to provide a function for obtaining the calorific value of the atmospheric gas from the composition ratio of the atmospheric gas obtained by the analyzing means.

  According to the thermal conductivity measuring method and the thermal conductivity measuring apparatus having the above configuration, the sensor chip is supported in the atmospheric gas via the thermal insulator, and the resistance value of the auxiliary heater provided in the sensor chip is controlled to be constant. Therefore, it is possible to keep the temperature of the entire sensor chip and thus the temperature of the ambient gas in the vicinity of the sensor chip constant. That is, it is a local region in the vicinity of the sensor chip, and the temperature of the ambient gas around the microheater becomes the temperature of the sensor chip.

  As a result, regardless of the temperature of the atmospheric gas, the temperature of the atmospheric gas around the microheater is made constant at a specific temperature, specifically the temperature of the sensor chip, and in this state, the temperature obtained from the driving power of the microheater is obtained. From the heat dissipation coefficient C of the microheater, the heat transfer coefficient of the atmospheric gas can be obtained easily and accurately. That is, the thermal conductivity λ can be easily measured regardless of the temperature of the atmospheric gas.

  Further, according to the gas component ratio measuring apparatus realized by using the above-described thermal conductivity measuring apparatus, the calorific value of each gas is changed from the relationship between the gas density and the calorific value, for example, to the total amount of the mixed gas and its composition ratio. Accordingly, it is possible to calculate the calorific value of the mixed gas. Specifically, 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. Furthermore, the calorific value of the atmospheric gas can be easily calculated from the composition ratio and the type of each gas.

Hereinafter, a thermal conductivity measurement method, a thermal conductivity measurement device, and a gas component ratio measurement device according to the present invention will be described with reference to the drawings.
The present invention uses a microheater 3 formed on a sensor chip 1 such as silicon as shown schematically in FIG. 1, for example. Basically, an atmospheric gas (pure gas) is generated from the calorific value of the microheater 3. Alternatively, the thermal conductivity of the mixed gas) is measured. The sensor chip 1 is made of, for example, silicon having a thickness of 0.5 mm and vertical and horizontal dimensions of about 1.5 mm, respectively, and a MEMS (micro electro mechanical system) technology is provided at a substantially central portion of the upper surface of the substrate 1a. Is used to form a boat-shaped concave cavity (recess) 1b, and the cavity 1b is bridged to form a thin film diaphragm (thin film portion) 1c. The thin film diaphragm 1c is provided with a large number of through holes 1d except for the central region thereof, and both surfaces of the thin film diaphragm 1c are open to the outside air through the through holes 1d.

  A micro heater (Rh) 3 which is a minute heating resistor made of platinum or the like is formed on such a thin film diaphragm 1c, and a pair of temperatures in a fluid flow direction F with the micro heater (Rh) 3 interposed therebetween. Sensors Ru and Rd are formed. An ambient temperature sensor 2 that is a heating resistor similar to the micro heater 3 is provided on the base portion 1 a around the cavity 1 b in the sensor chip 1.

  The sensor chip 1 having such a structure is substantially formed by forming a microheater (Rh) 3 and a pair of temperature sensors Ru and Rd on a thin film diaphragm 1c as shown in a schematic sectional structure in FIG. In particular, it is supported in a state of floating in the air and comes into contact with the atmospheric gas flowing along both surfaces (front and back surfaces) of the diaphragm 1c. And in this apparatus, the said ambient temperature sensor 2 which consists of a thermal resistor mentioned above is used as an auxiliary heater which heats the whole sensor chip 1 to a fixed temperature.

Incidentally, the microheater 3 and the temperature sensor (auxiliary heater) 2 made of a heating resistor (thermal resistor) such as platinum have a property that their resistance values change depending on the temperature. For example, when the resistance value of the microheater 3 at the standard temperature Tstd of 20 ° C. is Rstd, the microheater 3 at the temperature Th when the primary resistance temperature coefficient is α and the secondary resistance temperature coefficient is β. Resistance value Rh is Rh = Rstd · [1 + α (Th−Tstd) + β (Th−Tstd) ² ]
As given. Therefore, if the resistance value Rh of the microheater 3 is known, the heat generation temperature (heater temperature) Th of the microheater 3 can be obtained from the resistance value Rh. The same applies to the temperature sensor (auxiliary heater) 2.

The temperature Th of the microheater 3 is stable when the heat generated by the microheater 3 and the heat radiation from the microheater 3 to the atmosphere gas are balanced, that is, when the temperature is in a thermal equilibrium state with the atmosphere gas. To do. The driving power Ph of the microheater 3 in this equilibrium state is C · (Th−To) between the heater temperature Th and the ambient temperature To, where C is the heat dissipation coefficient from the microheater 3 to the atmospheric gas. = Ph
Have the relationship In other words, when the condition satisfying the above equation is satisfied, the microheater 3 and the atmospheric gas are thermally balanced and stabilized. Therefore, from this thermal equilibrium condition, the heat dissipation coefficient C from the micro heater 3 to the atmospheric gas is C = Ph ÷ (Th−To)
Can be obtained as

On the other hand, the driving power Ph of the microheater 3 is obtained from the voltage Vh applied across the microheater 3 and the current Ih flowing through the microheater 3 at that time, Ph = Vh · Ih
Can be obtained as The resistance value Rh of the microheater 3 at that time is
Rh = Vh ÷ Ih = Ph ÷ Ih ²
Can be obtained as

Therefore, when the driving power Ph of the microheater 3 is obtained, the resistance value Rh of the microheater 3 is obtained according to the driving power Ph and the current Ih flowing through the microheater 3, and further, as described above, the resistance value Rh is reduced according to the resistance value Rh. The temperature Th of the heater 3 can be obtained. The ambient temperature To can be measured by the temperature sensor 2 provided in the peripheral portion of the sensor chip 1 described above. However, as will be described later in the present apparatus, the heat generation temperature (ambient temperature) of the temperature sensor (auxiliary heater) 2. To itself is controlled to be constant. The driving power Ph of the microheater 3, the heater temperature Th of the microheater 3, and the ambient temperature To are obtained, respectively, so that C = Ph ÷ (Th−To) as described above.
It is possible to calculate the heat dissipation coefficient C from the microheater 3 to the atmospheric gas.

On the other hand, the heat dissipation coefficient C described above is generally C = 2 · h · S, where h is the average heat transfer coefficient from the microheater 3 to the atmospheric gas and S is the heat dissipation area of the microheater 3.
Can be expressed as The average heat transfer coefficient h generally changes depending on the natural convection state of the atmospheric gas and the surface state of the microheater 3. The coefficient [2] takes into consideration that heat transfer from the microheater 3 to the atmospheric gas is performed on the two front and back surfaces of the microheater 3 as schematically shown in FIG. is there.

  Further, the element area (heat generation area) of the microheater 3 is minute, the range of temperature change caused by the heat generation of the microheater 3 is minute, and only spot-like temperature displacement occurs, and natural convection of atmospheric gas If not, the temperature distribution around the microheater 3 gradually decreases as the distance from the microheater 3 increases as shown in FIG. In particular, the temperature at the portion in contact with the microheater 3 is increased to the heater temperature Th, and the temperature gradually decreases to the ambient temperature To as the distance from the microheater 3 increases.

A region where the temperature of the atmospheric gas having such a temperature distribution is reduced from the heater temperature Th to the ambient temperature To is defined as a temperature boundary layer, and the thickness is d, the above-mentioned average heat transfer coefficient h is It is considered that it is proportional to the thermal conductivity λ of the atmospheric gas and inversely proportional to the thickness d of the temperature boundary layer. That is, the average heat transfer coefficient h is h = λ ÷ d
As determined.

Incidentally, the thermal conductivity λ of the atmospheric gas generally tends to increase as the temperature increases, and the thermal conductivity λ _(T) of the atmospheric gas at the temperature T is λ _(T) = λo (1 + γ · T)
As given. Where λo is the thermal conductivity of the atmospheric gas at a reference temperature (for example, 0 ° C.), and γ is a first-order temperature coefficient.

Further, the thickness d of the temperature boundary layer varies depending on the thermal conductivity λ of the atmospheric gas, and the heat transfer is faster as the thermal conductivity λ increases, so that the thickness d becomes thinner. On the contrary, when the thermal conductivity λ of the atmospheric gas is small, the temperature change gradient becomes gentle and the thickness d of the temperature boundary layer becomes thick because heat transfer is slow. That is, the thickness d of the boundary layer varies depending on the thermal conductivity λ of the atmospheric gas, and the thermal conductivity λ of the atmospheric gas varies depending on the temperature. Therefore, the thickness d _(T) of the temperature boundary layer at the temperature _T is d _(T) = f [λ _(T) ].
Can be expressed using a function f [α] with the parameter α as the thermal conductivity λ _(T) of the atmospheric gas that varies with the temperature T.

The heat radiation area S of the microheater 3 generally refers to the entire area of the diaphragm 1c on which the heating resistor (heater) 1d described above is formed, and the temperature distribution of the atmospheric gas in the vicinity of the microheater 3 is It varies depending on the temperature distribution on the diaphragm 1c. However, when the thermal conductivity λ of the atmospheric gas is large, the temperature distribution becomes a sharp shape. Therefore, the effective heat radiation area S of the microheater 3 is reduced according to the thermal conductivity λ of the atmospheric gas. , And can be regarded as an area smaller than the area So of the diaphragm 1c. In particular, in combination with the micro heater 3 itself being minute, it can be considered that the heat radiation area S of the micro heater 3 is spot-like and substantially forms a point heat source. Therefore, the effective heat radiation area S is defined as S _(T) = g [λ _(T) ]
As a function g [α] having the parameter α as the thermal conductivity λ _(T) of the atmospheric gas that changes according to the temperature T.

From the above considerations, the relationship between the heat dissipation coefficient C of the microheater 3 and the thermal conductivity λ _(T) of the atmospheric gas is summarized as follows:
= 2 ・ (λ _(T) ÷ d _(T) ) ・ S _(T)
= 2 · (λ _(T) ÷ f [λ _(T) ]) · g [λ _(T) ]
Can lead to a relationship. However, from the relationship shown in the above equation, it can be seen that the heat dissipation coefficient C of the microheater 3 is considerably affected by the thermal conductivity λ _{(T) of} the ambient gas that varies with the temperature T, that is, the temperature characteristics of the ambient gas.

  Incidentally, FIG. 4 shows the heat radiation of the microheater 3 when the temperature is changed to 0 ° C., 20 ° C., and 40 ° C. with respect to a plurality of types of atmospheric gases having different mixing ratios of propane gas and air whose components are known. The relationship between the coefficient C and the thermal conductivity λ of the atmospheric gas is examined. As shown in FIG. 4, although there is a certain degree of correlation between the heat dissipation coefficient C of the microheater 3 and the thermal conductivity λ of each ambient gas, the corresponding relationship depends on the mixing ratio and temperature. Can be seen to be quite disturbed. In particular, it cannot be denied that the correspondence between the heat dissipation coefficient C and the thermal conductivity λ changes under the influence of temperature. Accordingly, when obtaining the thermal conductivity λ of the atmospheric gas from the heat dissipation coefficient C of the microheater 3, for example, some temperature correction is required.

  By the way, when the sensor chip 1 on which the microheater 3 is formed is supported by being thermally insulated from the surroundings, the heat radiation from the sensor chip 1 can be generated only to the atmospheric gas. If the heat generation temperature of the temperature sensor (auxiliary sensor) 2 is controlled to be constant under this condition, the heat generated from the temperature sensor (auxiliary heater) 2 is exclusively the sensor chip 1 except for heat transfer to the atmospheric gas. Will be transmitted to only. Since the sensor chip 1 made of silicon has a high thermal conductivity, the sensor chip 1 is heated uniformly by the heat generated by the temperature sensor (auxiliary heater) 2 and is stabilized in a thermal equilibrium state with the atmospheric gas. Accordingly, the temperature of the sensor chip 1 is made constant as the temperature sensor 2 generates heat, and is stabilized at the temperature T (temperature of the sensor chip 1) T of the temperature sensor (auxiliary heater) 2.

  On the other hand, the ambient gas in the vicinity of the periphery of the sensor chip 1 is heated by receiving heat from the entire sensor chip 1 and is stabilized in a state of being in thermal equilibrium with the sensor chip 1. Therefore, the atmospheric gas in the vicinity of the periphery of the sensor chip 1 is partially stabilized depending on the temperature of the sensor chip 1 regardless of the temperature of the atmospheric gas. In other words, in the vicinity of the periphery of the sensor chip 1, the atmospheric gas is stabilized at the temperature T of the sensor chip 1 (the heat generation temperature of the temperature sensor 2) T regardless of the temperature. Then, the ambient gas in the vicinity of the sensor chip 1 where the temperature is stabilized receives heat from the microheater 3 as described above to form a temperature boundary layer.

Therefore, the thickness d of the temperature boundary layer at that time is expressed as follows when the thermal conductivity of the atmospheric gas at the constant temperature Tcnst is λ:
d = f [λ]
Is uniquely determined. The effective heat dissipation area S of the micro heater 3 is also S = g [λ].
Is uniquely determined depending on the thermal conductivity λ of the atmospheric gas at the constant temperature Tcnst. Therefore, the relationship between the heat dissipation coefficient C of the microheater 3 and the thermal conductivity λ of the ambient gas at the constant temperature Tcnst is C = 2 · (λ ÷ f [λ]) · g [λ]
Thus, these are associated one-to-one without depending on the temperature characteristics of the atmospheric gas.

  In the present invention, based on such consideration, the sensor chip 1 on which the micro heater 3 is formed is thermally insulated and supported in the atmospheric gas, and in this state, the resistance value Rr of the temperature sensor (auxiliary heater) 2 is made constant to The heat generation temperature is made constant to keep the entire sensor chip 1 at a constant temperature, thereby forming a measurement environment in which the temperature of the ambient gas in the vicinity of the sensor chip 1 is made constant. In the measurement environment, the heat dissipation coefficient C and the thermal conductivity λo described above are obtained in accordance with the heat dissipation coefficient C obtained from the driving power Ph of the microheater 3 when the microheater 3 is driven under constant conditions by, for example, constant resistance value control. As described below, the thermal conductivity λ of the atmospheric gas at the constant temperature Tcnst is obtained as shown below.

  FIG. 5 is a conceptual diagram showing an embodiment of the present invention. In FIG. 5, reference numeral 2 denotes a microheater formed on the sensor chip 1 as shown in FIG. In particular, as shown in FIG. 1, the sensor chip 1 is structurally supported in an atmospheric gas via a thermally insulating base (thermal insulator) 4 made of, for example, glass or ceramic. The pedestal 4 is, for example, a so-called reverse table type that has four leg portions that respectively support the four corners of the sensor chip 1 and floats the sensor chip 1 in the air.

  Incidentally, as the thermally insulating pedestal (thermal insulator) 4, for example, Japanese Patent No. 3740026, Japanese Patent No. 3740027, Japanese Patent Laid-Open No. 2002-29688, and Japanese Patent Laid-Open No. 2002-318148 previously proposed by the present applicant. As long as the techniques described in Japanese Patent Laid-Open No. 2002-318149 and the like are appropriately employed, the desired heat insulation effect can be obtained in the present invention. The base 4 for holding the sensor chip 1 is preferably a member having a thermal conductivity of 10 W / (m · K) or less. Examples of such a member include a porous member. When the thermal conductivity is 10 W / (m · K) or more, the current required for constant control of the entire sensor chip 1 to the first temperature increases, so it is necessary to prepare a power supply with a large capacity. It is not practical. Therefore, as the pedestal 4 for holding the sensor chip 1, a member having a thermal conductivity of 10 W / (m · K) or less is desirable as described above.

  In the figure, reference numerals 30 and 20 denote heater driving power sources for driving the micro heater 3 and the temperature sensor (auxiliary heater) 2 to generate heat. For example, as shown in FIG. 6, the heater driving power sources 30 and 20 include a resistance bridge circuit 3a configured with the micro heater 3 or the temperature sensor (auxiliary heater) 2 that is a temperature control target as one bridge side. And a voltage control circuit 3b that feedback-controls the drive voltage V1 applied to the resistance bridge circuit 3a in accordance with the bridge voltage V2 of the resistance bridge circuit 3a.

  That is, the heater drive power supplies 30 and 20 are configured of a resistance bridge circuit 3a using fixed resistors R1, R2, and R3 having known resistance values and a micro heater 3 having a resistance value Rh or an auxiliary heater 2 having a resistance value Rr. The bridge voltages V2a and V2b are input to the differential amplifier (voltage control circuit) 3b, and the bridge drive voltage V1 is set so that the bridge voltage V2a on the microheater 3 side always becomes the bridge voltage V2b on the fixed resistors R2 and R3 side. By performing feedback control, the resistance value Rh of the micro heater 3 or the resistance value Rr of the auxiliary heater 2 is made constant.

At this time, the current Ih flowing through the microheater 3 is
Ih = (V1-V2a) / R1
It becomes. The bridge voltage V2a on the micro heater 3 side is V2a = V2b = V1 / R3 / (R2 + R3)
As given. At this time, the electric power Ph applied to the micro heater 3 is Ph = Ih · V2a.
The heater resistance Rh can be calculated as follows: Rh = Vh ÷ Ih
It becomes.

  As shown in FIG. 5, the method and apparatus for measuring thermal conductivity according to the present invention basically uses the heater driving power source 30 under the condition that the sensor chip 1 is heated to a constant temperature To by the heater driving power source 20. Electric power detection means 5a for determining the driving power Ph of the microheater 3 driven to generate heat, current detection means 5b for the energization current Ih of the microheater 3, and heater temperature detection for determining the heater temperature Th according to the heater driving power Ph and the heater current Ih Means 5c are provided. Further, the thermal conductivity measuring device includes an ambient temperature detecting means 5d for obtaining the heater temperature Th and the sensor chip temperature To obtained by the temperature sensor 2 as the ambient gas temperature (ambient temperature) in the vicinity of the sensor chip 1. Prepare.

In the heat conductivity measuring method and apparatus, the heat dissipation coefficient calculation means 6 sets the heat dissipation coefficient C of the microheater 3 according to the heater temperature Th and the ambient temperature To and the driving power Ph of the microheater 3 as follows: C = Ph ÷ ( Th-To)
Further, in the thermal conductivity calculation means 7, the atmosphere at the temperature To corresponding to the heat dissipation coefficient C is referred to by referring to the table 8 according to the heat dissipation coefficient C determined by the heat dissipation coefficient calculation means 6. The thermal conductivity λo of the gas is obtained.

  Thus, according to the thermal conductivity measuring method and apparatus configured in this way, the temperature of the ambient gas in the vicinity of the sensor chip 1 is partially made constant at the temperature of the sensor chip 1 regardless of the temperature of the ambient gas. be able to. The temperature can be detected as a sensor chip temperature (ambient temperature) To obtained from the driving conditions of the ambient temperature sensor (auxiliary heater) 2. Further, the heat generation temperature (heater temperature) Th of the microheater 3 can be detected from the driving power Ph of the microheater 3 and its energization current Ih as described above. Therefore, if the correspondence relationship between the thermal conductivity λo at the temperature To of the atmospheric gas whose component is known and the heat radiation coefficient C of the microheater 3 is registered in the table 8 in advance, the microheater 3 is heated as described above. By obtaining the heat dissipation coefficient C from the drive power Ph and referring to the table 8, the thermal conductivity of the atmospheric gas can be easily obtained.

  In particular, according to the thermal conductivity measuring method and apparatus according to the present invention, the sensor chip 1 is supported in the atmospheric gas via the thermal insulator 3 and the auxiliary heater (ambient temperature sensor) 2 provided on the sensor chip 1 is supported. Since the temperature is controlled to be constant and the resistance value (heater temperature) of the micro heater 3 is controlled to be constant and the driving power P is obtained only under this condition, the temperature characteristics of the atmospheric gas can be simply and effectively obtained. Without being concerned, it becomes possible to measure the thermal conductivity λo of the atmospheric gas at a constant temperature To with high accuracy.

  FIG. 7 (a) uses a plurality of mixed gases of propane gas and air having different mixing ratios as the atmospheric gas, and the heat dissipation coefficient C and the thermal conductivity measured as described above while changing the temperature. The relationship with λ was investigated. As shown in FIG. 7 (a), according to the thermal conductivity measurement method and apparatus according to the present invention, regardless of the difference in the temperature of the atmospheric gas, depending on the difference in the mixing ratio of propane gas and air, That is, the relationship between the heat radiation coefficient C and the thermal conductivity λ is associated with the component ratio of the atmospheric gas on a one-to-one basis. Therefore, if the correspondence relationship is examined in advance and registered in the table 8, the heat conductivity λ of the mixed gas (atmosphere gas) can be obtained by obtaining the heat dissipation coefficient C of the microheater 3.

FIG. 7B shows the relationship between the concentration of propane gas determined from the mixing ratio of propane gas and air in the above-described mixed gas and the heat dissipation coefficient C of the microheater 3. Incidentally, the thermal conductivity λmix of the mixed gas is λmix = x · λpg + y · λair, assuming that the mixing ratio is [x: y], where propane is the thermal conductivity and λair is the thermal conductivity of propane gas.
x + y = 1
Can be expressed as Accordingly, by obtaining the heat dissipation coefficient C of the microheater 3 as described above, the component ratio of the mixed gas whose component is known, specifically, the propane gas concentration in the case of the above mixed gas is shown in FIG. It can be easily obtained from the correspondence with the heat dissipation coefficient C shown.

  Further, if the composition ratio of a plurality of gases forming the mixed gas is obtained as described above, for example, the calorific value of each gas is determined according to the total amount of the mixed gas and the composition ratio from the relationship between the gas density and the calorific value. Since each can be obtained, the calorific value of the mixed gas can be calculated. Specifically, 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.

In this way, the gas component ratio measuring device that determines the component ratio of the mixed gas and further calculates the heat generation amount forms the mixed gas with the thermal conductivity λ _(T) of the mixed gas at the temperature T. What is necessary is just to prepare the table 8 which matched and registered thermal conductivity ₍ lambda _{) (T) in} the said temperature T about several gas considered. Then, the thermal conductivity λ _(T) at each temperature T obtained by referring to the table 8 is written in the memory 9.

In the component ratio calculation means 10, the above-described simultaneous equations are established from the mixed gas stored in the memory 9 and the thermal conductivity λ _{(T) of} each gas, and the simultaneous equations are analyzed to obtain the component ratio of each gas. Like that. Further, the calorific value calculation means 11 may calculate the total calorific value of the mixed gas in accordance with the calculated component ratio. The calculation of the total calorific value may be performed by referring to the relationship between the gas density and the calorific value corresponding to the type of gas registered in advance in the calorific value table 12.

As described above, according to the present invention, as described above, the heat dissipation coefficient C of the microheater is set under the condition that the sensor chip 1 is thermally cut off from its external environment and the sensor chip 1 itself is controlled at a constant temperature. Only by obtaining, the thermal conductivity λ _(T) of pure gas or mixed gas can be obtained with high accuracy and in a simple manner. In addition, the thermal conductivity λ _(T) of the atmospheric gas to be measured can be easily obtained without using a large-scale facility such as providing a constant temperature bath as in the prior art.

  The present invention is not limited to the embodiment described above. For example, each calculation function described above in the heat transfer amount measuring device can be realized by software in a microcomputer. Further, the structure of the microheater is not particularly limited, and the heater element provided in the existing thermal flow sensor can be used as it is. Needless to say, the heat generating driving means of the auxiliary heater 2 and the micro heater 3 is not limited to the example using the above-described resistance bridge circuit 3a and the operational amplifier 3b that feedback-controls the bridge voltage. Further, as the sensor chip 1, a bridge-like microbridge (thin film portion) is provided across the cavity (concave portion) 1b provided at the center of the upper surface of the base portion 1a, and the second heater 3 and the like are provided on the microbridge. May be formed. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

The figure which shows the rough element structure of the sensor chip provided with the micro heater used by this invention. The figure which shows schematic sectional structure of a sensor chip. The figure which shows typically the temperature distribution of the atmospheric gas in the micro heater vicinity when the micro heater is driven to generate heat. The 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} atmospheric gas. The principal part schematic block diagram of the heat conductivity measuring method and apparatus which concern on one Embodiment of this invention. The figure which shows the structural example of the heater drive circuit which makes the resistance value of an auxiliary heater and a micro heater constant. The figure which shows the relationship between the heat dissipation coefficient C in the temperature To measured by the thermal conductivity measuring method and apparatus which concerns on this invention, and thermal conductivity ₍ lambda _{) (T) of} atmospheric gas, and the relationship between the heat dissipation coefficient C and a propane gas density | concentration. . The figure which shows schematic structure of the gas component ratio measuring apparatus which concerns on this invention.

Explanation of symbols

1 Sensor chip 2 Auxiliary heater (ambient temperature sensor)
3 Microheater 4 Thermal insulator 5a Drive power detection means 5b Heater current detection means 5c Heater temperature detection means 5e Ambient temperature detection means 6 Heat dissipation coefficient calculation means 7 Thermal conductivity calculation means 8 Table (C-λo characteristics)
DESCRIPTION OF SYMBOLS 9 Memory 10 Component ratio calculation means 11 Heat generation amount calculation means 12 Heat generation amount table 20,30 Heater drive power supply

Claims (9)

Using the microheater provided on the thin area formed in the sensor chip and positioned in the atmosphere gas, the atmosphere gas is determined according to the heat dissipation coefficient of the microheater determined from the electric power applied to the microheater and the temperature at that time. A thermal conductivity measurement method for obtaining the thermal conductivity of
The sensor chip is supported in the atmospheric gas via a thermal insulator, and the resistance value of the auxiliary heater provided in the sensor chip is controlled to be constant to keep the temperature of the sensor chip constant. A thermal conductivity measurement method, wherein the thermal conductivity of the atmospheric gas is obtained from the driving power of the microheater.   The control for stabilizing the resistance value of the auxiliary heater is performed by feedback control of the drive voltage applied to the resistance bridge circuit in accordance with the voltage between the bridges of the resistance bridge circuit having the auxiliary heater as one bridge side. The thermal conductivity measuring method according to claim 1.   The driving power of the microheater includes the voltage applied to the microheater when the resistance value of the microheater is controlled to be constant using a resistance bridge circuit having the microheater as one bridge side, and the resistance bridge circuit The thermal conductivity measuring method according to claim 1, wherein the thermal conductivity is calculated from a circuit constant. Detection of the thermal conductivity of the atmospheric gas from the driving power of the microheater
When the heat dissipation coefficient of the microheater is obtained from the driving power of the microheater and the resistance value of the auxiliary heater supported via the thermal insulator is controlled to be constant, the microheater is controlled regardless of the temperature of the ambient gas. The thermal conductivity measurement method according to claim 1, wherein the thermal conductivity measurement method is performed by utilizing a unified relationship between a heat dissipation coefficient of a heater and a thermal conductivity of the ambient gas in the vicinity of the sensor chip. A sensor chip with an auxiliary heater;
A micro heater provided on a thin region formed in the sensor chip;
A thermal insulator that thermally insulates the sensor chip from a base that supports the sensor chip and positions the sensor chip in an atmospheric gas;
A heater driving circuit for heating the entire sensor chip by controlling the resistance value of the auxiliary heater to be constant;
Power detection means for determining the driving power of the microheater when the microheater is heated under a certain condition;
A heat dissipation coefficient calculating means for obtaining a heat dissipation coefficient from the microheater according to the detected drive power;
Based on a unified correspondence between the thermal conductivity of the ambient gas in the vicinity of the sensor chip and the heat dissipation coefficient of the microheater when the resistance value of the auxiliary heater is controlled to be constant, the heat dissipation coefficient calculating means A thermal conductivity measuring device comprising thermal conductivity calculating means for obtaining the thermal conductivity of the atmospheric gas from the heat dissipation coefficient obtained in (1).   The heater drive circuit includes a resistance bridge circuit configured with the auxiliary heater as one bridge side, and a voltage control circuit that feedback-controls a drive voltage applied to the resistance bridge circuit according to a bridge voltage of the resistance bridge circuit. The thermal conductivity measuring device according to claim 5, which is provided.   The thermal conductivity calculation means refers to a table describing a correspondence relationship between the heat dissipation coefficient of the microheater and the thermal conductivity of the atmospheric gas at a specific temperature, which is obtained in advance according to the composition of the atmospheric gas. The thermal conductivity measuring device according to claim 5, wherein the thermal conductivity of the atmospheric gas is obtained. Control means for obtaining the thermal conductivity of the atmospheric gas at different heater temperatures by changing the resistance value of the microheater controlled to be constant using the thermal conductivity measuring device according to any one of claims 5 to 7. When,
An apparatus for measuring a gas component ratio, comprising: analysis means for analyzing the composition ratio of the atmospheric gas from the simultaneous equations of thermal conductivity at each heater temperature. In the gas component ratio measuring apparatus according to claim 8,
Furthermore, the gas component ratio measuring apparatus is provided with a function of obtaining a calorific value of the atmospheric gas from the composition ratio of the atmospheric gas obtained by the analyzing means.

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