JP7456404B2 - Thermal sensors and measurement methods using thermal sensors - Google Patents

Description

The present invention relates to a thermal sensor and a measurement method using the thermal sensor.

Conventionally, a thermal gas sensor has been proposed that changes little over time, is highly resistant to contamination, and alleviates thermal stress caused by temperature cycles. A known thermal gas sensor has a heating element (5) and a heating control means (12) that controls the heating of the heating element, and the heating control means controls the heating of the heating element by setting a period during which the heating element is heated to a first temperature and a period during which the heating element is heated to a second temperature lower than the first temperature, and sets the period during which the heating element is heated to the second temperature longer than the period during which the heating element is heated to the first temperature (see, for example, Patent Document 1).

The above-mentioned thermal gas sensor detects slight differences in physical property values, such as by measuring oxygen concentration in nitrogen atmosphere gas, for example. Further, in the above invention, the heat generated from the heater is conducted not only through the fluid around the heater but also through the heater and the wiring connected to the heater. Therefore, for example, a minute change in physical quantity such as a change over time in the thermal conductivity of the heater and the wiring connected to the heater may affect the measurement results regarding the thermal conductivity of the fluid. Due to such causes, the accuracy of the measuring device may be reduced.

JP2014-089048A

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to eliminate the influence of noise caused by changes over time in the thermal conductivity of the heater and the wiring connected to the heater when measuring the components of a fluid. The final objective of the present invention is to provide a thermal sensor capable of suppressing a decrease in measurement accuracy as a measuring device.

The present invention for solving the above problems is as follows:
a substrate having a cavity area opening on its surface;
a thin film portion formed to cover the opening of the cavity area;
a heater disposed in the thin film portion and generating heat when supplied with power from a power source;
a temperature detector disposed in the thin film portion and detecting the temperature of the heater or the surroundings of the heater;
a control unit that controls power supplied to the heater;
a calculation unit that calculates a value corresponding to the thermal conductivity of the atmospheric gas based on the value of the supplied power and the value of the temperature rise acquired by the temperature detector when power is supplied to the heater;
A thermal sensor comprising:
The control unit changes power supplied to the heater,
The thermal sensor is characterized in that the calculation unit further calculates an amount of change or a rate of change in a value corresponding to the thermal conductivity calculated before and after the change in the supplied power.

Here, through intensive research by the inventors, the amount of change or rate of change in the value corresponding to the thermal conductivity calculated before and after the change in the power supplied to the heater is the thermal conductivity of the heater and the wiring connected to the heater. It has become clear that this is not easily affected by changes over time. Therefore, in the present invention, the calculation unit calculates the amount of change or the rate of change in the value corresponding to the thermal conductivity calculated before and after the change in the power supplied to the heater, and uses this value to evaluate the composition of the atmospheric gas. I decided to do so. According to the present invention, it is possible to remove the influence of noise caused by temporal changes in the thermal conductivity of the heater and the wiring connected to the heater, which is included in the measured value of the thermal conductivity of the atmospheric gas. It is possible to suppress a decrease in the measurement accuracy of the gas composition. In addition, even after the measured value of the thermal conductivity of the atmospheric gas changes due to changes in the thermal conductivity of the heater and the wiring connected to the heater over time, the measurement accuracy of the atmospheric gas composition hardly decreases, making it possible to extend the life of the measuring device. can be achieved.

Further, in the present invention, the control unit changes the power supplied to the heater in two stages, and the calculation unit calculates a value corresponding to the thermal conductivity calculated before and after the two-stage change in the power supply. It may also be a thermal sensor, which is characterized by calculating the amount or rate of change in . The heater is connected to a power source through wiring, and heat generated by supplying power to the heater is conducted through the heater and the wiring connected to the heater. The thermal conductivity of the wiring at this time changes over time, and this change over time can be a factor in reducing measurement accuracy. The rate of change hardly changes over time. Therefore, it is possible to suppress a decrease in the measurement accuracy of the gas composition of the atmospheric gas.

Further, in the present invention, the control section may be a thermal sensor that changes the power supplied to the heater in a pulsed or sinusoidal manner. According to this, when increasing the temperature of the heat generated from the heater in order to obtain the thermal conductivity before and after the two-step change in the supplied power, the mode of temperature increase can be adjusted. When the power supplied to the heater is changed in a pulsed manner, the temperature rises rapidly and the target temperature is reached relatively quickly. When the power supplied to the heater is changed in a sinusoidal manner, the temperature rises slowly, so that the target temperature can be reached with relatively high accuracy.

In the present invention, the temperature detector may be a thermal sensor having two or more thermopiles arranged in the thin film portion so that a pair of thermopiles face each other across the heater. This allows the temperature around the heater to be detected more accurately.

Further, the present invention further includes a thermal sensor having the above characteristics, and a second calculation unit that calculates the composition of the atmospheric gas based on the amount of change or rate of change of the value corresponding to the thermal conductivity. It may also be used as a gas sensor. Here, the amount or rate of change in the value corresponding to the thermal conductivity measured by the above-mentioned thermal sensor changes depending on the composition of the atmospheric gas. Therefore, if the type of gas that makes up the atmospheric gas is specified in advance, the composition of the atmospheric gas can be calculated by measuring the amount or rate of change in the value corresponding to the thermal conductivity of the atmospheric gas using the thermal sensor described above. It is possible to do so. When calculating the atmospheric gas, the above gas sensor calculates the composition of the atmospheric gas by calculating the amount or rate of change of the value corresponding to the thermal conductivity measured by the thermal sensor according to a predetermined formula. You may. Alternatively, it may be calculated by reading out from a pre-stored table the composition of the atmospheric gas that corresponds to the amount or rate of change in the value corresponding to the thermal conductivity measured by the thermal sensor. For example, when measuring the oxygen concentration in a nitrogen atmosphere gas, if argon is mixed in, there will be a large error in the thermal conductivity of the nitrogen atmosphere gas, but the amount of change or change in the value corresponding to the thermal conductivity of the nitrogen atmosphere gas There is almost no error in the ratio even if argon is mixed in. Therefore, the gas sensor of the present invention can improve the measurement accuracy of oxygen concentration.

The present invention also provides a measurement method for measuring the characteristics of the atmospheric gas by supplying power to the heater to heat it and measuring the temperature rise of the atmospheric gas during heating, the method comprising: a supply power changing step of changing the power; a measurement step of measuring the value of temperature rise before and after the change in the power supply to the heater; and a value of the supply power before and after the change in the power supply to the heater. and a calculation step of calculating a value corresponding to the thermal conductivity of the atmospheric gas before and after the change in the power supplied to the heater, based on the value of the temperature rise, and the thermal conductivity due to the change in the power supply. The measuring method may include a second calculation step of calculating an amount of change or a rate of change in a value corresponding to the rate.

According to the present invention, even when the thermal conductivity of an atmospheric gas is repeatedly measured, it is possible to suppress a decrease in measurement accuracy. Since this method is capable of measuring the components of the atmospheric gas while maintaining a constant level of measurement accuracy, it is possible to extend the life of the measuring device.

Further, in the present invention, the measurement method may be characterized in that in the supply power changing step, the power supply to the heater is changed in two stages. According to this, even if the thermal conductivity of the heater and the wiring connected to the heater changes over time, the amount or rate of change in the value corresponding to the thermal conductivity calculated before and after the two-step change in supplied power is Since there is almost no change over time, it is possible to suppress a decrease in the measurement accuracy of the gas composition of the atmospheric gas.

Further, in the present invention, the measurement method may be characterized in that in the supply power changing step, the power supplied to the heater is changed in a pulse shape or a sine wave shape. According to this, when increasing the temperature of the heat generated from the heater by the supplied power, the mode of temperature increase can be adjusted.

The present invention may also be a measurement method characterized by further comprising a gas composition calculation step of calculating the composition of the atmospheric gas based on the amount or rate of change in the value corresponding to the thermal conductivity due to the change in the supplied power. With this, for example, when measuring the oxygen concentration in a nitrogen atmospheric gas, even if argon is mixed in, it is hardly affected. Therefore, the measurement accuracy of the oxygen concentration can be improved. As a result, it becomes easier to distinguish between nitrogen and oxygen, which have almost the same thermal conductivity values.

The means for solving the above problems can be used in combination with each other whenever possible.

According to the present invention, when measuring the components of a fluid using a thermal sensor, it is possible to eliminate the influence of noise caused by changes over time in the thermal conductivity of the heater and the wiring connected to the heater. As a result, a more accurate parameter regarding the thermal conductivity of the fluid to be measured can be obtained, and the gas composition (concentration ratio) of the fluid can be measured from the parameter of the thermal conductivity of the fluid. That is, it is possible to suppress a decrease in measurement accuracy of the thermal sensor according to the present invention as a measuring device.

1 is a schematic diagram showing an example of a sensor element constituting a thermal gas sensor in Example 1. FIG. 2 is a schematic diagram showing how heat generated from a heater is conducted in a sensor element that constitutes a thermal gas sensor in Example 1. FIG. FIG. 2 is a block diagram showing a functional configuration of the thermal gas sensor when measuring the gas composition of an atmospheric gas. It is a flowchart which shows the process when measuring the gas composition of atmospheric gas by a thermal type gas sensor. 2 is a schematic diagram showing a method for measuring thermal conductivity in Example 1. FIG. FIG. 4 is a schematic diagram showing the influence of argon contamination when measuring an oxygen concentration using the thermal gas sensor in Example 1.

[Application example]
In this application example, a case where the thermal sensor is a thermal gas sensor will be described. The thermal gas sensor according to this application example changes the temperature of the heater when heating the fluid to be measured (hereinafter also referred to as "atmospheric gas") with the heater that generates heat when energized from the power supply. A value corresponding to the thermal conductivity of the atmospheric gas at each temperature is calculated. Then, the difference in thermal conductivity of the atmospheric gas at each temperature is used as a parameter.

FIG. 2 is a schematic diagram showing how heat generated from the heater 3 is conducted in the sensor element 2 constituting the thermal gas sensor 1 to which the present invention is applicable. The sensor element 2 includes a heater 3 and a thermopile (temperature detection section) 4 provided symmetrically with the heater 3 in between. Although two thermopiles 4 are shown in FIG. 2, the number of thermopiles 4 is not limited as long as there are two or more. Heater 3 is a resistor made of polysilicon, for example. The shape of each thermopile 4 is approximately rectangular in plan view. The heater 3 and the thermopile 4 are provided within an insulating thin film 5, and the insulating thin film 5 is formed on a silicon substrate 6.

Although shown in a simplified manner in FIG. 2, each thermopile 4 is composed of a plurality of thermocouples 7 (see FIG. 1(b)) arranged in a line at predetermined intervals within an insulating thin film 5. . Among these, the part connected on the side near the heater 3 is the hot junction 8 (see Fig. 1(b)), and the part connected on the opposite side to the heater 3 is the cold junction 9 (see Fig. 1(b)). ).

A cavity area 10 that is a recess is provided in the silicon substrate 6 below the heater 3 and thermopile 4 in the insulating thin film 5 . Note that a cross-sectional view of the cavity area 10 is shown in FIG. 1(b). The heater 3 is arranged across the opening of the cavity area 10. Further, the power source 11 is arranged outside the sensor element 2, and a conductive wire is connected to an electrode 12 that conducts electricity to the heater 3. When power is applied from the power source 11 to the electrode 12, the heater 3 generates heat.

Here, the heat generated from the heater 3 is conducted not only through the atmospheric gas but also through the heater 3 and the wiring connected to the heater 3 (hereinafter also simply referred to as "wiring"). λg in FIG. 2 represents the thermal conductivity of the atmospheric gas, and λm represents the thermal conductivity of the wiring. Therefore, the thermal conductivity actually measured can be expressed as the sum of λg and λm. However, since λm changes over time, errors in the actually measured thermal conductivity (hereinafter also simply referred to as "overall thermal conductivity") may occur over time.

FIG. 5 is a schematic diagram showing a method for measuring thermal conductivity to which the present invention is applicable. FIG. 5(a) shows a graph before the overall thermal conductivity changes over time, and FIG. 5(b) shows a graph after the overall thermal conductivity changes over time. In this application example, when heating the atmospheric gas with the heater 3, the temperature of the heater 3 is changed to two temperatures T1 and T2 (T1<T2).

In FIG. 5A, the thermal conductivity of the wiring before aging is λm, the thermal conductivity of the atmospheric gas at T1 is λg1, and the thermal conductivity of the atmospheric gas at T2 is λg2. As the temperature is higher, the thermal momentum of the particles constituting the atmospheric gas increases and the thermal conductivity becomes higher, so λg1<λg2 holds true. Here, compared to the thermal conductivity of the atmospheric gas, the thermal conductivity of the wiring hardly changes in value due to temperature change, so it may be considered that λm at T1 and λm at T2 are the same value. The thermal conductivity λ(T1) at T1 before aging can be expressed as the sum of λg1 and λm. Similarly, the thermal conductivity λ(T2) at T2 before aging can be expressed as the sum of λg2 and λm. Let the difference between λ(T2) and λ(T1) be Δλ.

In FIG. 5(b), the thermal conductivity of the wiring after aging is assumed to be λm'. If the atmospheric gas is the same before and after the change over time at each of the same temperatures T1 and T2 as before the change over time, λg1 and λg2 are the same values before and after the change over time. On the other hand, the thermal conductivity λm' of the wiring at T1 and T2 after aging is smaller than λm. Note that similarly to λm, λm' at T1 and λm' at T2 may be considered to have the same value. The thermal conductivity λ' (T1) at T1 after aging can be expressed as the sum of λg1 and λm'. Similarly, the thermal conductivity λ'(T2) at T2 after aging can be expressed as the sum of λg2 and λm'. Let the difference between λ'(T2) and λ'(T1) be Δλ'.

Here, as shown in FIG. 5, the relationship Δλ≒Δλ' holds true. That is, the difference Δλ between λ(T2) and λ(T1) does not change before and after the thermal conductivity of the wiring changes over time. Therefore, when outputting the thermal conductivity of the atmospheric gas, by using Δλ (≈Δλ') as the measured value, it is possible to eliminate the influence of the temporal change in the thermal conductivity of the wiring on the measured value.

[Example 1]
EMBODIMENT OF THE INVENTION Hereinafter, the thermopile type sensor based on Example 1 of this invention is demonstrated in detail using drawings. In the following embodiments, an example in which the present invention is applied to a thermal gas sensor will be described, but the present invention may also be applied to an oxygen concentrator or the like. Note that the thermopile type sensor according to the present invention is not limited to the following configuration.

<Device configuration>
FIG. 1 is a schematic diagram showing an example of a sensor element 2 that constitutes a thermal gas sensor 1 in Example 1. FIG. 1(a) is a plan view of a sensor element 2 constituting a conventional thermal gas sensor 1, and FIG. 1(b) is a sectional view taken along the section XX in FIG. 1(a). The sensor element 2 is a type of MEMS (Micro Electro Mechanical Systems), and is used, for example, to measure the gas composition (concentration ratio) of atmospheric gas. Here, the thermal gas sensor 1 corresponds to a thermopile type sensor in the present invention.

As shown in FIG. 1(b), when the hot junction 8 of the thermocouple 7 constituting the thermopile 4 detects the heat generation in the heater 3, an electromotive force is generated due to the temperature difference with the cold junction 9 due to the Seebeck effect. When the sensor element 2 is exposed to the ambient gas, the heat generated from the heater 3 diffuses into the insulating thin film 5 with the heater 3 at the center. The hot junctions 8 are located side by side at the top of the cavity area 10, and the cold junctions 9 are located in the area of the silicon substrate 6 other than the cavity area 10. Since the heat generated in the heater 3 is released into the ambient gas, the diffusion of heat to the silicon substrate 6 is suppressed. Therefore, a temperature difference is more likely to occur between the cold junction 9 located in the area of the silicon substrate 6 other than the cavity area 10 and the hot junction 8 located around the heater 3. Here, the insulating thin film 5 and the silicon substrate 6 correspond to the thin film portion and the substrate in the present invention, respectively.

The heater 3 generates heat by supplying power from the power source 11 to the sensor element 2 via the electrode 12. By measuring the temperature of the heat generated in the heater 3 with the thermopile 4, a value corresponding to the thermal conductivity of the atmospheric gas around the sensor element 2 can be measured. Since thermal conductivity is a unique value depending on the type of gas, by measuring a value corresponding to the thermal conductivity of the atmospheric gas around the sensor element 2, the gas composition of the atmospheric gas can be measured. For example, when the atmospheric gas is air, it is also possible to measure the oxygen concentration in the air. Here, the power supplied from the power source 11 may be a constant voltage or a constant current.

In the sensor element 2, when the electric power in the heater 3 is W and the amount of temperature increase measured by the thermopile 4 is ΔT, the relationship λ=W/ΔT holds true for the thermal conductivity λ of the atmospheric gas. Based on the value of λ, the gas composition of the atmospheric gas can be measured.

Here, we return to the explanation of FIG. 2. As described above, regarding the thermal conductivity λ around the heater 3, the relationship λ=λg+λm (=W/ΔT) holds true. That is, in reality, the heat generated from the heater 3 is conducted not only through the atmospheric gas around the heater 3 but also through the wiring, so λ calculated from the amount of temperature increase also includes the factor of λm. As λm changes over time, λ also changes over time.

FIG. 3 is a block diagram showing the functional configuration of the thermal gas sensor 1 when measuring the gas composition of atmospheric gas. The thermal gas sensor 1 includes a control section 13, and an input section 14, a measurement section 15, a first storage section 16, a second storage section 17, and an output section 18, which are connected to the control section 13 wirelessly or by wire. We are prepared.

The control unit 13 includes a calculation unit (not shown) and a second calculation unit (not shown) that perform calculation processing using a CPU, ROM, RAM, etc. Conductivity information is stored. The calculation unit has a function of calculating the difference in thermal conductivity at each of two temperatures of the heater 3, for example. The second calculation unit has a function of calculating the gas composition of the atmospheric gas, for example, based on the difference in thermal conductivity calculated by the calculation unit.

The input unit 14 is equipped with a function of inputting in advance the type of gas contained in the atmospheric gas to be measured, for example. Thereby, by measuring the value corresponding to the thermal conductivity of the atmospheric gas that has flowed into the sensor element 2, it is possible to measure the gas composition of each input gas in the atmospheric gas.

The measurement unit 15 includes a gas flow path (not shown), a heater 3, a thermopile 4, and the like, and measures parameters such as the electric power of the heater 3 and the temperature of heat generated from the heater 3, for example. The measured parameters are stored in the first storage section 16 and the second storage section 17.

The control unit 13 calculates a value corresponding to the thermal conductivity of the atmospheric gas based on the output of the thermopile 4 in the measurement unit 15 and the parameters stored in the first storage unit 16. At this time, the power supplied from the power source 11 is changed in two ways, and in each case, two types of thermal conductivity of the atmospheric gas are determined based on the output of the thermopile 4 and the parameters stored in the first storage section 16. The value corresponding to can be calculated. Then, based on the parameters stored in the first storage section 16, the calculation section calculates the difference in thermal conductivity between the two atmospheric gases, and the second calculation section calculates the difference in thermal conductivity and the second storage section 16. Based on the parameters accumulated in step 17, the gas composition of the atmospheric gas is calculated. The calculated gas composition is displayed on the output section 18. The output unit 18 is, for example, a liquid crystal monitor. Note that the value corresponding to the thermal conductivity of the atmospheric gas calculated by the control unit 13 may be a value that corresponds one-to-one to the gas composition, and may not be an exact value of thermal conductivity.

FIG. 4 is a flowchart showing a process when the thermal gas sensor 1 measures the gas composition of the atmospheric gas. The flow of processing will be described below using FIG. 4. In this flowchart, first, an atmospheric gas whose type is specified in the input section 14 is introduced into the thermal gas sensor 1 (S101). The atmospheric gas that has flowed in is heated by the heater 3, which generates heat using the electric power W1 supplied from the power source 11 (S102). Next, the control unit 13 calculates a value corresponding to the thermal conductivity of the atmospheric gas at W1 based on the amount of temperature rise of the atmospheric gas detected by the thermopile 4 and the parameters stored in the first storage unit 16. (S103). Here, S103 corresponds to a measurement step and a calculation step in the present invention. Similarly, the atmospheric gas is heated by the heater 3 that generates heat by the electric power W2 supplied from the power source 11 (S104), and the control unit 13 calculates the amount of temperature rise of the atmospheric gas and the parameters stored in the first storage unit 16. Based on this, a value corresponding to the thermal conductivity of the atmospheric gas at W2 is calculated (S105). Here, S104 corresponds to the supply power changing step in the present invention. Further, S105 also corresponds to a measurement step and a calculation step in the present invention. Then, the control unit 13 calculates the difference between the two types of thermal conductivity based on the values corresponding to the two types of thermal conductivity and the parameters stored in the first storage unit 16, and calculates the difference between the two types of thermal conductivity. The gas composition of the atmospheric gas is calculated based on the difference in conductivity and the parameters stored in the second storage unit 17 (S106). Here, S106 corresponds to a second calculation step and a gas composition calculation step in the present invention. The measured parameters of the gas composition of the atmospheric gas are newly stored in the second storage section 17. Finally, the gas composition of the atmospheric gas is displayed on the output section 18 (S107). According to this, for example, the concentration of a specific gas in the atmospheric gas can be grasped. Note that W1 is the power value at T1, W2 is the power value at T2, and the following is similarly considered.

Here, we return to the explanation of FIG. 5. As mentioned above, by calculating the difference Δλ (≒Δλ') between the thermal conductivities of the two atmospheric gases obtained by the temperature change of the heater 3, the influence of noise due to the change in the thermal conductivity of the wiring over time is removed. be able to. Δλ is a parameter based on two types of temperatures T1 and T2 of the heater 3 and two types of electric power W1 and W2. In addition, by calculating Δλ, the effects of disturbance factors that are not temperature-dependent on the heater 3, such as changes in the thermal conductivity of the insulating thin film 5 over time, and changes in the environmental temperature and atmospheric pressure around the heater 3, can also be calculated. can be removed or reduced. In addition, the same applies to the effects of noise due to changes in circuit constants over time, such as changes in the voltage in the power supply 11 over time, changes in the temperature coefficient of resistance of the heater 3 over time, and changes in the bridge fixed resistance over time when a bridge circuit is constructed. can be removed or reduced.

The control unit 13 changes the power supplied from the power supply 11 to the heater 3 in a pulse shape or a sine wave shape. When increasing the temperature of the heater 3 from T1 to T2, the degree of temperature increase can be adjusted by changing the electric power in a pulsed or sinusoidal manner. Specifically, when the power is changed in a pulsed manner, the temperature rises steeply, so that the temperature reaches T2 from T1 relatively quickly. When the power is changed in a sinusoidal manner, the temperature rises slowly, so that the temperature reaches T2 from T1 with relatively high accuracy.

FIG. 6 is a schematic diagram showing the influence of argon mixing when measuring oxygen concentration using the thermal gas sensor 1 in Example 1. The graphs in FIG. 6 each show the thermal conductivity, the change in thermal conductivity, and the rate of change in thermal conductivity (described later) for each of the three-component systems of oxygen, nitrogen, and argon. The effect of argon inclusion changes depending on whether the oxygen concentration is measured using thermal conductivity, thermal conductivity change, or thermal conductivity change rate.

FIG. 6(a) shows the thermal conductivity λ normalized by oxygen for each of the three component systems. λ of oxygen and λ of nitrogen are close in value, but λ of nitrogen and λ of argon have a large difference in value. Therefore, when measuring the oxygen concentration in a nitrogen atmosphere, if argon is mixed in, even if the amount is very small, an error will occur in the measured value of λ of the mixed gas, resulting in an error in the measured value of the oxygen concentration. An error will occur. FIG. 6(b) shows the thermal conductivity change Δλ depending on the temperature normalized by oxygen for each of the three component systems. Compared to the respective values of λ shown in FIG. 6(a), the difference between the values of Δλ of oxygen and Δλ of nitrogen increases, and the difference between the values of Δλ of nitrogen and Δλ of argon decreases. Therefore, when measuring the oxygen concentration in the nitrogen atmosphere gas using the value of Δλ, the influence of argon mixing can be relatively suppressed, and a more accurate measured value of the oxygen concentration can be obtained. FIG. 6(c) shows the rate of change in thermal conductivity depending on temperature normalized by oxygen for each of the three component systems. Here, the rate of change in thermal conductivity is a value obtained by dividing Δλ by λ before temperature change (hereinafter expressed as Δλ/λ). Compared to the respective values of Δλ shown in FIG. 6(b), Δλ/λ of nitrogen and Δλ/λ of argon are close values. Therefore, when measuring the oxygen concentration in the nitrogen atmosphere gas using the value of Δλ/λ, the influence of argon inclusion can be almost ignored. By using the value of Δλ/λ instead of Δλ, the influence of argon contamination can be further reduced and the selectivity to oxygen can be improved.

Further, in the control unit 13, the second calculation unit calculates the value of Δλ/λ and the gas composition of the atmospheric gas based on the value of Δλ and the parameters stored in the second storage unit 17. Based on the parameters stored in the second storage unit 17, the gas composition of the atmospheric gas can be calculated.

In the above embodiment, a thermopile type sensor using a thermopile 4 as a temperature detector has been described as an example, but the sensor to which the present invention is applied is not limited to a thermopile type sensor. For example, it can be applied to sensors that have a temperature sensor other than a thermopile, or to gas sensors that do not have a thermopile, but instead supply power to the heater to raise the temperature of the heater and detect the temperature based on changes in the resistance of the heater itself. It is.

Note that in order to make it possible to compare the constituent features of the present invention and the configurations of the embodiments, the constituent features of the present invention will be described below with reference numerals in the drawings.
<Invention 1>
a substrate (6) having a cavity area (10) opening on its surface;
a thin film portion (5) formed to cover the opening of the cavity area;
a heater (3) disposed in the thin film portion and generating heat when supplied with power from a power source (11);
a temperature detector (4) disposed in the thin film portion and configured to detect the temperature of the heater or the vicinity of the heater;
a control unit (13) that controls power supplied to the heater;
a calculation unit that calculates a value corresponding to the thermal conductivity of the atmospheric gas based on the value of the supplied power and the value of the temperature rise acquired by the temperature detector when power is supplied to the heater;
A thermal sensor (1) comprising:
The control unit changes power supplied to the heater,
The thermal sensor, wherein the calculation unit further calculates an amount of change or a rate of change in a value corresponding to the thermal conductivity calculated before and after the change in the supplied power.

1: Thermal gas sensor 2: Sensor element 3: Heater 4: Thermopile 5: Insulating thin film 6: Silicon substrate 7: Thermocouple 8: Hot junction 9: Cold junction 10: Cavity area 11: Power supply 12: Electrode 13: Control unit 14 : Input section 15 : Measurement section 16 : First storage section 17 : Second storage section 18 : Output section

Claims (9)

a substrate having a cavity area opening on its surface;
a thin film portion formed to cover the opening of the cavity area;
a heater disposed in the thin film portion and generating heat when supplied with power from a power source;
a temperature detector disposed in the thin film portion and detecting the temperature of the heater or the surroundings of the heater;
a control unit that controls power supplied to the heater;
a calculation unit that calculates a value corresponding to the thermal conductivity of the atmospheric gas based on the value of the supplied power and the value of the temperature rise acquired by the temperature detector when power is supplied to the heater;
A thermal sensor comprising:
The control unit changes power supplied to the heater,
The thermal sensor, wherein the calculation unit further calculates an amount of change or a rate of change in the value corresponding to the thermal conductivity calculated before and after the change in the supplied power. The control unit changes power supplied to the heater in two stages,
The thermal sensor according to claim 1, wherein the calculation unit calculates an amount of change or a rate of change of the value corresponding to the thermal conductivity calculated before and after the two-step change in the supplied power. . The thermal sensor according to claim 1, wherein the control unit changes the power supplied to the heater in a pulse shape or a sine wave shape. 4 . The temperature sensor according to claim 1 , wherein the temperature sensor includes two or more thermopiles arranged in the thin film portion such that a pair of thermopiles face each other with the heater in between. thermal sensor. The thermal sensor according to any one of claims 1 to 4,
A gas sensor further comprising a second calculation unit that calculates the composition of the atmospheric gas based on the amount or rate of change in the value corresponding to the thermal conductivity. A measurement method for measuring the characteristics of the atmospheric gas by supplying power to a heater to heat it and measuring the temperature rise of the atmospheric gas during heating, the method comprising:
a power supply changing step of changing the power supplied to the heater;
a measuring step of measuring a temperature increase before and after the change in power supplied to the heater;
The thermal conductivity of the atmospheric gas before and after the change in the power supplied to the heater is based on the value of the power supply and the value of the temperature increase before and after the change in the power supplied to the heater. an arithmetic process for calculating a value;
A measuring method comprising: a second calculation step of calculating an amount or rate of change in the value corresponding to the thermal conductivity due to a change in the supplied power. 7. The measuring method according to claim 6, wherein in the power supply changing step, the power supplied to the heater is changed in two stages. 8. The measuring method according to claim 6, wherein in the power supply changing step, the power supplied to the heater is changed in a pulse shape or a sine wave shape. From claim 6, further comprising a gas composition calculation step of calculating the composition of the atmospheric gas based on the amount or rate of change in the value corresponding to the thermal conductivity due to the change in the supplied power. 8. The measurement method according to any one of 8.

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