Flow sensor and program

Abstract

This flow sensor has: a detection unit that outputs each of a first detection signal that is for calculating the thermal conductivity of a fluid, a second detection signal that is for calculating the heat capacity of the fluid, and a third detection signal that is for calculating flow rate information for the fluid; and a processing unit that executes processing that corrects the flow rate information using a correction coefficient that is based on the thermal conductivity as calculated from the first detection signal and the heat capacity as calculated from the second detection signal.

Description

Flow sensor and program

[0001] The present invention relates to a flow sensor and a program.

[0002] Conventionally, flow sensors for detecting the flow rate of a fluid such as air or gas have been known. Patent Document 1 discloses a thermal flow sensor including a heater and a side temperature sensor disposed in a direction substantially perpendicular to the flow direction of the fluid relative to the heater so that heat generated from the heater is transferred only by the thermal diffusion effect of the fluid without being affected by the flow velocity of the fluid, the side temperature sensor detecting the temperature of the fluid and outputting a temperature detection signal for calculating the physical property values ​​of the fluid.

[0003] JP 2008-46143 A

[0004] The detected flow rate output from a flow sensor may vary due to the influence of thermophysical properties resulting from the type and composition of the fluid (hereinafter referred to as "type of fluid"). In other words, there may be a discrepancy between the detected flow rate output from the flow sensor and the actual flow rate that flows through the flow sensor (hereinafter referred to as "actual flow rate"). Therefore, it is required for the flow sensor to reduce the influence of the thermophysical properties of the fluid and detect the actual flow rate with high accuracy.

[0005] An object of the present invention is to provide a flow sensor that reduces the influence of the thermophysical properties of a fluid.

[0006] This flow sensor has a detection unit that outputs a first detection signal for calculating the thermal conductivity of a fluid, a second detection signal for calculating the heat capacity of the fluid, and a third detection signal for calculating flow rate information of the fluid, and a processing unit that executes a process to correct the flow rate information using a correction coefficient based on the thermal conductivity calculated from the first detection signal and the heat capacity calculated from the second detection signal.

[0007] According to the present invention, it is possible to provide a flow sensor that reduces the influence of the thermophysical properties of a fluid.

[0008] 3A. FIG. 3B is a block diagram schematically showing an example of the overall configuration of a flow sensor according to an embodiment. FIG. 3C is a graph showing an example of the relationship between [ρCp / λ] of multiple types of fluids and the detection sensitivity ratio in the third sensor unit according to an embodiment. FIG. 3D is a top view schematically showing an example of a detection unit of a flow sensor according to an embodiment. FIG. 3E is a schematic partial enlarged view of a framed region IIIB indicated by a dashed line in FIG. 3A. FIG. 3F is a cross-sectional view schematically showing an example of a cross section taken along line IV-IV in FIG. 3A. FIG. 3G is a block diagram schematically showing an example of the hardware configuration of a flow sensor according to an embodiment. FIG. 3H is a flowchart showing an example of a detection method using a flow sensor according to an embodiment. FIG. 3I is an example of a diagram explaining an outline of the principle of detecting the heat capacity ρCp of a fluid. FIG. 3I is an example of a diagram explaining an outline of the principle of detecting the heat capacity ρCp of a fluid. FIG. 3I is a diagram schematically showing an example of the overall configuration of a flow sensor according to a modified embodiment. FIG. 3I is a graph showing an example of a temperature profile of a fourth heater that switches between a temperature rise operation and a constant temperature operation. FIG. 3I is a graph showing an example of a temperature profile of a fourth heater that repeats a temperature rise operation and a constant temperature operation.

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations will be omitted where appropriate.

[0010] In each drawing, directions are expressed using a Cartesian coordinate system having an X-axis, a Y-axis, and a Z-axis. The X-axis, the Y-axis, and the Z-axis are perpendicular to one another. The Z direction along the Z-axis indicates the direction along which the fluid to be detected (hereinafter referred to as "fluid") of the flow sensor according to the embodiment flows (hereinafter sometimes referred to as "flow direction").

[0011] The direction in which the X-axis arrow points is referred to as the +X direction or +X side, and the direction opposite to the +X direction is referred to as the -X direction or -X side. The direction in which the Y-axis arrow points is referred to as the +Y direction or +Y side, and the direction opposite to the +Y direction is referred to as the -Y direction or -Y side. The direction in which the Z-axis arrow points is referred to as the +Z direction or +Z side, and the direction opposite to the +Z direction is referred to as the -Z direction or -Z side. In this specification, the fluid to be detected flows in the +Z direction. With respect to the object, the -Z side is referred to as "upstream" and the +Z side is referred to as "downstream." Furthermore, the +Y side is referred to as "upper" and the -Y side is referred to as "lower."

[0012] In this specification and claims, "along a direction" includes an error of ±5 degrees or less between two axes or directions. Also, "orthogonal" includes an angle of 90 degrees ±5 degrees relative to any direction. However, these directional expressions do not limit the directions of the embodiments. The flow sensor may be oriented in any direction when in use.

[0013] [Embodiment] <Example of Overall Configuration> An example of the overall configuration of a flow sensor 1 according to an embodiment will be described with reference to Fig. 1 . Fig. 1 is a block diagram that schematically shows an example of the overall configuration of the flow sensor 1. As shown in Fig. 1 , the flow sensor 1 has a detection unit 10 and a processing unit 80. The flow sensor 1 may have other components. The detection unit 10 and the processing unit 80 are electrically connected to each other via wiring or the like. Various detection signals detected by the detection unit 10 are output to the processing unit 80. The detection unit 10 has a first sensor unit 20, a second sensor unit 30, and a third sensor unit 40.

[0014] The first sensor unit 20 outputs a voltage signal for calculating the thermal conductivity λ of the fluid. The voltage signal output from the first sensor unit 20 is an example of a "first detection signal." The second sensor unit 30 outputs a voltage signal for calculating the heat capacity ρCp of the fluid. The voltage signal output from the second sensor unit 30 is an example of a "second detection signal." The third sensor unit 40 outputs a voltage signal for calculating the flow rate information F1 of the fluid. The voltage signal output from the third sensor unit 40 is an example of a "third detection signal." Note that the type of heat capacity calculated by the voltage signal from the second sensor unit 30 is not limited to the constant pressure heat capacity ρCp, but may be other types of heat capacity such as a constant volume heat capacity. Hereinafter, unless otherwise specified, the constant pressure heat capacity ρCp will be referred to as "heat capacity." Note that "heat capacity" as used in this specification includes "specific heat."

[0015] The processing unit 80 calculates the thermal conductivity λ of the fluid based on the voltage signal output from the first sensor unit 20. The processing unit 80 calculates the heat capacity ρCp of the fluid based on the voltage signal output from the second sensor unit 30. The processing unit 80 calculates flow rate information F1 of the fluid based on the voltage signal output from the third sensor unit 40. Here, the "flow rate information F1" corresponds to information that is the basis for calculating the flow rate FL that is ultimately output from the flow sensor 1. Examples of the flow rate information F1 include a flow rate detection value based on the voltage signal output from the third sensor unit 40.

[0016] The detection sensitivity of the third sensor unit 40 (e.g., the third temperature sensor 42, which will be described separately) may vary depending on the thermal properties of the fluid. In other words, the detection sensitivity of the third sensor unit 40 may vary depending on the type of fluid. For example, for fluids A and B flowing at the same actual flow rate, the voltage value corresponding to the detected flow rate of fluid A output from the third sensor unit 40 may differ from the voltage value corresponding to the detected flow rate of fluid B output from the third sensor unit 40. The inventors discovered that by using the parameter [ρCp / λ], obtained by dividing the heat capacity ρCp by the thermal conductivity λ, the value of "ρCp / λ" for each fluid is approximately proportional to the detection sensitivity ratio of the third sensor unit 40. To reduce the influence of the detection sensitivity of the third sensor unit 40, the processing unit 80 corrects the flow rate information F1 using a correction coefficient Ak based on the thermal conductivity λ and heat capacity ρCp of the fluid. The processing unit 80 also calculates the flow rate FL of the fluid based on the flow rate information F1 corrected using the correction coefficient Ak.

[0017] Next, an example of correcting the flow rate information F1 using the correction coefficient Ak will be described with reference to FIG. 2. FIG. 2 is a graph showing the relationship between [ρCp / λ] of each fluid and the detection sensitivity ratio of the third sensor unit 40. The horizontal axis of FIG. 2 shows the value of [ρCp / λ] of each fluid. The vertical axis of FIG. 2 shows the detection sensitivity ratio of the third sensor unit 40 for each fluid. Here, the "detection sensitivity ratio" is a relative voltage value corresponding to the flow rate detection value of each fluid output by the third sensor unit 40, when the voltage value corresponding to the flow rate detection value of the reference gas output by the third sensor unit 40 is set to "1". For example, when air, methane gas (CH ４), nitrogen gas (N ２ 2, natural gases each containing different mixture ratios of gas components can be used.

[0018] As shown in FIG. 2 , the value of "ρCp / λ" for each fluid and the detection sensitivity ratio of the third sensor unit 40 are roughly proportional to each other. Therefore, by using the detection sensitivity ratio corresponding to "ρCp / λ" as a correction coefficient Ak and correcting the flow rate information F1 based on the voltage signal output from the third sensor unit 40, it is possible to obtain flow rate information that is independent of the type of fluid. This allows the processing unit 80 to calculate the flow rate FL of the fluid with reduced influence from the detection sensitivity of the third sensor unit 40. Furthermore, this correction process can reduce the calculation load on the processing unit 80 when correcting the flow rate information F1.

[0019] <Configuration Example of Detection Unit 10> The components of the flow sensor 1 will be described in detail below. First, a configuration example of the detection unit 10 of the flow sensor 1 will be described with reference to Figures 3A, 3B, and 4. Figure 3A is a top view schematically showing an example of the detection unit 10 of the flow sensor 1. Figure 3B is a schematic partial enlarged view of the frame-shaped region IIIB indicated by the dashed line in Figure 3A. Figure 4 is a cross-sectional view schematically showing a cross section taken along line IV-IV in Figure 3A.

[0020] 3A and 4, the detection unit 10 has a first membrane 51, a second membrane 52, a third membrane 53, and a support member 60. The first sensor unit 20 is disposed on the first membrane 51, the second sensor unit 30 is disposed on the second membrane 52, and the third sensor unit 40 is disposed on the third membrane 53. In FIG. 3A, the second sensor unit 30, the third sensor unit 40, and the first sensor unit 20 are disposed in this order along the Z direction. However, the relative positions of the first sensor unit 20, the second sensor unit 30, and the third sensor unit 40 are not limited to this.

[0021] (First Sensor Unit 20) The first sensor unit 20 is disposed, for example, downstream of the third sensor unit 40. The first sensor unit 20 has a first heater 21 and a plurality of first temperature sensors 22. The first heater 21 heats the fluid. The plurality of first temperature sensors 22 output voltage signals corresponding to the temperature of the fluid heated by the first heater 21.

[0022] The first heater 21 has a longitudinal direction in the Z direction. The first heater 21 includes, for example, a heating resistor that generates heat when energized. However, the first heater 21 may be another type of heating element.

[0023] 3A , two of the first temperature sensors 22 (221, 222) are disposed on the +X side of the first heater 21. The other two first temperature sensors 22 (223, 224) are disposed on the −X side of the first heater 21. However, the number of first temperature sensors 22 is not limited to four. The multiple first temperature sensors 22 may include two first temperature sensors 22 each disposed on either the +X side or the −X side of the first heater 21.

[0024] The multiple first temperature sensors 22 include one of thermistors, linear resistors, platinum resistance temperature detectors, thermocouples, thermopiles, etc. It is preferable to select the same type of first temperature sensors 22 from the viewpoint of characteristics. However, the multiple first temperature sensors 22 do not necessarily have to be the same type, as they can detect temperature even if they are not the same type. Each of the multiple first temperature sensors 22 shown in FIG. 3A is a thermopile including a resistance temperature detector.

[0025] The multiple first temperature sensors 22 are aligned in a direction perpendicular to the Z direction. That is, the direction in which the multiple first temperature sensors 22 are aligned is perpendicular to the direction of fluid flow. By arranging the multiple first temperature sensors 22 perpendicular to the direction of fluid flow, it is possible to reduce the inclusion of information about temperature changes due to the fluid flow in the voltage signals output by the multiple first temperature sensors 22. As a result, the voltage signals output by the multiple first temperature sensors 22 mainly reflect information about the amount of heat transferred from the periphery of the first heater 21 to the fluid side, thereby improving the detection accuracy of the thermal conductivity λ of the fluid.

[0026] For example, the multiple first temperature sensors 22 are arranged in the X direction. As shown in Fig. 3A , the first temperature sensor 221 is disposed closer to the first heater 21 than the first temperature sensor 222. The first temperature sensor 221 is disposed a distance L1 away from the first heater 21. The first temperature sensor 222 is disposed a distance L2 away from the first heater 21 that is longer than the distance L1.

[0027] The first temperature sensor 223 is disposed closer to the first heater 21 than the first temperature sensor 224. For example, the first temperature sensor 223 is disposed a distance L1 away from the first heater 21. That is, the distance between the first temperature sensor 223 and the first heater 21 may be substantially the same as the distance between the first temperature sensor 221 and the first heater 21. However, the distance between the first temperature sensor 223 and the first heater 21 may be different from the distance between the first temperature sensor 221 and the first heater 21. Furthermore, the first temperature sensor 224 is disposed a distance L2 away from the first heater 21. That is, the distance between the first temperature sensor 224 and the first heater 21 may be substantially the same as the distance between the first temperature sensor 222 and the first heater 21. However, the distance between the first temperature sensor 224 and the first heater 21 may be different from the distance between the first temperature sensor 222 and the first heater 21. The distance between the first heater 21 and the first temperature sensor 22 is the center-to-center distance between the first heater 21 and the first temperature sensor 22 .

[0028] (Second Sensor Unit 30) The second sensor unit 30 is disposed upstream of the third sensor unit 40. The second sensor unit 30 has a second heater 31 and a plurality of second temperature sensors 32. The second heater 31 heats the fluid. The plurality of second temperature sensors 32 output voltage signals corresponding to the temperature of the fluid heated by the second heater 31.

[0029] The second heater 31 has a longitudinal direction in the Z direction. The second heater 31 includes, for example, a heating resistor that generates heat when energized. However, the second heater 31 may be another type of heating element.

[0030] The plurality of second temperature sensors 32 include, for example, two second temperature sensors 321 and 322. The second temperature sensor 321 is disposed on the +X side of the second heater 31. The second temperature sensor 322 is disposed on the −X side of the second heater 31. However, the number of second temperature sensors 32 is not limited to two. The number of second temperature sensors 32 may be three or more.

[0031] The second heater 31 is disposed between the second temperature sensors 321 and 322. That is, the second temperature sensors 321 and 322 are disposed in positions close to the second heater 31. This allows the second temperature sensors 321 and 322 to be disposed in high-temperature regions near the second heater 31. This allows the second temperature sensors 321 and 322 to output voltage signals with relatively large values. This increases the signal-to-noise ratio of the signals and improves the detection accuracy of the heat capacity ρCp.

[0032] The second temperature sensors 32 each include one of thermistors, linear resistors, platinum resistance temperature detectors, thermocouples, thermopiles, etc. It is preferable to select the same type of second temperature sensors 32 in terms of characteristics. However, the second temperature sensors 32 do not necessarily have to be of the same type, as they can detect temperature even if they are not the same type. Each of the second temperature sensors 32 shown in FIG. 3A is a thermopile including a resistance temperature detector.

[0033] As shown in FIG. 3B , the thermopile is configured by connecting multiple thermocouples, each consisting of a first conductor 91 and a second conductor 92, in series. The configuration of this thermopile will be described using the second temperature sensor 321 as an example. The thermocouples, each consisting of the first conductor 91 and the second conductor 92, are arranged in the Y direction. The first conductor 91 and the second conductor 92 also extend in the X direction, which is perpendicular to the direction in which the second heater 31 extends. The junction between the first conductor 91 and the second conductor 92 that is closest to the second heater 31 is the hot junction 93, and the junction between the first conductor 91 and the second conductor 92 that is farthest from the second heater 31 is the cold junction 94. Temperature information can be obtained by measuring the voltage across the second temperature sensor 321, which is a voltage obtained by amplifying the electromotive force due to the temperature difference between the hot junction 93 and the cold junction 94 of each thermocouple. Although the number of thermocouples shown in the figure is three, the number of thermocouples constituting the thermopile is not limited to this. Similarly, the second temperature sensor 322 and the first temperature sensor 22 each have a plurality of thermocouples connected in series with each other.

[0034] The multiple second temperature sensors 32 are aligned in a direction perpendicular to the Z direction. That is, the direction in which the multiple second temperature sensors 32 are aligned is perpendicular to the direction of fluid flow. By arranging the multiple second temperature sensors 32 perpendicular to the direction of fluid flow, it is possible to reduce the inclusion of information about temperature changes due to the fluid flow in the voltage signals output by the multiple second temperature sensors 32. As a result, the voltage signals output by the multiple second temperature sensors 32 mainly reflect information about the amount of heat transferred from the periphery of the second heater 31 to the fluid side, thereby improving the detection accuracy of the heat capacity ρCp of the fluid.

[0035] For example, the multiple second temperature sensors 32 are aligned in the X direction. The second temperature sensor 321 is disposed, for example, at a distance L3 from the second heater 31. The distance L3 is preferably shorter than the distance L1 between the first heater 21 and the first temperature sensor 221.

[0036] The second temperature sensor 322 is disposed, for example, a distance L3 away from the second heater 31. That is, the distance between the second temperature sensor 322 and the second heater 31 may be substantially the same as the distance between the second temperature sensor 321 and the second heater 31. However, the distance between the second temperature sensor 322 and the second heater 31 may be different from the distance between the second temperature sensor 321 and the second heater 31. Note that the distance between the second heater 31 and the second temperature sensor 32 is the center-to-center distance between the second heater 31 and the second temperature sensor 32.

[0037] Thus, the distance L3 between the second heater 31 and the second temperature sensor 32 (e.g., the second temperature sensor 321) that is closest to the second heater 31 among the multiple second temperature sensors 32 is smaller than the distance L1 between the first heater 21 and the first temperature sensor 22 (e.g., the first temperature sensor 221) that is closest to the first heater 21 among the multiple first temperature sensors 22. That is, the distance between the second heater 31 and the second temperature sensor 32 is relatively small. As will be described separately, the second temperature sensor 32 sequentially detects the temperature of the fluid to detect a temperature change in the fluid associated with an increase in temperature of the second heater 31. The processing unit 80 also calculates the heat capacity ρCp by referring to information regarding the temperature change in the fluid output from the second temperature sensor 32. However, since the temperature change in the fluid associated with an increase in temperature of the second heater 31 is relatively small, it may be difficult to detect the temperature change in the fluid. Therefore, by arranging the second temperature sensor 32 in a high-temperature region near the second heater 31, it is possible to increase the value of the voltage signal corresponding to the temperature detected by the second temperature sensor 32. This increases the accuracy of detecting the temperature change of the fluid that accompanies the temperature rise of the second heater 31. As a result, it is possible to increase the accuracy of detecting the heat capacity ρCp.

[0038] (Third Sensor Unit 40) The third sensor unit 40 is disposed between the first sensor unit 20 and the second sensor unit 30 in the Z direction. The third sensor unit 40 has a third heater 41 and a plurality of third temperature sensors 42. The third heater 41 heats the fluid. The plurality of third temperature sensors 42 output voltage signals corresponding to the temperature of the fluid heated by the third heater 41.

[0039] The third heater 41 has a longitudinal direction that is orthogonal to the Z direction, for example, in the X direction. The third heater 41 includes, for example, a heating resistor that generates heat when energized. However, the third heater 41 may be another type of heating element.

[0040] The multiple third temperature sensors 42 include, for example, two third temperature sensors 421, 422. The third temperature sensor 421 is disposed on the −Z side of the third heater 41. The third temperature sensor 422 is disposed on the +Z side of the third heater 41. However, the number of third temperature sensors 42 is not limited to two. The number of third temperature sensors 42 may be three or more.

[0041] The multiple third temperature sensors 42 include one of thermistors, linear resistors, platinum resistance temperature detectors, thermocouples, thermopiles, etc. It is preferable to select the same type of sensor for the multiple third temperature sensors 42 in terms of characteristics. However, the multiple third temperature sensors 42 do not necessarily have to be the same type, as they can detect temperature even if they are not the same type. Each of the multiple third temperature sensors 42 shown in FIG. 3A is a thermopile including a resistance temperature detector. Like the second temperature sensor 322, the third temperature sensor 42 also has multiple thermocouples connected in series with each other.

[0042] The multiple third temperature sensors 42 are arranged in the Z direction with the third heater 41 between them. The distance between the third temperature sensor 421 and the third heater 41 may be the same as or different from the distance between the third temperature sensor 422 and the third heater 41.

[0043] (First membrane 51, second membrane 52, third membrane 53) The first membrane 51 carries the first heater 21 and first temperature sensor 22 of the first sensor unit 20. The first membrane 51 corresponds to a region above an opening 61 of a support member 60, of a thin film structure 66 fixed on the support member 60 (described separately). Note that it is sufficient that at least a portion of the first heater 21 and the plurality of first temperature sensors 22 are placed on the first membrane 51.

[0044] The second membrane 52 carries the second heater 31 and the second temperature sensors 32 of the second sensor unit 30. The second membrane 52 corresponds to the region of the thin film structure 66 above the opening 62 of the support member 60. It is sufficient that the second heater 31 and at least some of the multiple second temperature sensors 32 are placed on the second membrane 52.

[0045] The third membrane 53 carries the third heater 41 and the third temperature sensors 42 of the third sensor unit 40. The third membrane 53 corresponds to a region of the thin film structure 66 above the opening 63 of the support member 60. It is sufficient that the third heater 41 and at least some of the multiple third temperature sensors 42 are placed on the third membrane 53.

[0046] (Supporting Member 60) The supporting member 60 supports each of the first membrane 51, the second membrane 52, and the third membrane 53. The supporting member 60 is a frame that includes substantially rectangular openings 61, 62, and 63 in a top view. The supporting member 60 includes, for example, silicon.

[0047] <Example of Hardware Configuration of Flow Sensor 1> Next, an example of the electrical hardware configuration of the flow sensor 1 will be described with reference to Fig. 5. Fig. 5 is a block diagram that schematically shows an example of the hardware configuration of the flow sensor 1. In this example, the first temperature sensor 22, the second temperature sensor 32, and the third temperature sensor 42 are each a thermopile including a resistance temperature sensor.

[0048] The flow sensor 1 includes terminals 210a to 210j, multiplexers 304 and 305, an analog-to-digital converter 306, a power supply 307, and a microcontroller 309. The power supply 307 generates a voltage and outputs the voltage to the multiplexer 305. The multiplexer 305 outputs a voltage to terminals 210f, 210h, and 210g in accordance with instructions from the microcontroller 309.

[0049] Terminals 210a to 210j are included in, for example, the detection unit 10. One end of each of the first heater 21, the second heater 31, and the third heater 41 is connected to ground GND via terminal 210i. Of the multiple first temperature sensors 22, one end of first temperature sensors 223 and 224 is connected to ground GND via terminal 210j. Of the multiple second temperature sensors 32, one end of second temperature sensor 322 is connected to ground GND via terminal 210j. Of the multiple third temperature sensors 42, one end of third temperature sensors 421 and 422 is connected to ground GND via terminal 210j.

[0050] The multiplexers 304 and 305, the analog-to-digital converter 306, the power supply 307, and the microcontroller 309 are included in, for example, the processing unit 80. Note that the power supply that operates these circuits is not shown in the figure.

[0051] The other end of first temperature sensor 224 is connected to one end of first temperature sensor 222, and the other end of first temperature sensor 222 is connected to terminal 210b. The other end of first temperature sensor 223 is connected to one end of first temperature sensor 221, and the other end of first temperature sensor 221 is connected to terminal 210a.

[0052] The first temperature sensors 221 and 223 are connected in series. The voltage signal V11 is a signal relating to the temperature T11 output by the first temperature sensors 221 and 223. The voltage signal V11 is, for example, the electromotive force of the first temperature sensors 221 and 223. The first temperature sensors 221 and 223 output information about the detected temperature T11 through the voltage signal V11. The first temperature sensors 222 and 224 are connected in series. The voltage signal V12 is a signal relating to the temperature T12 output by the first temperature sensors 222 and 224. The voltage signal V12 is, for example, the electromotive force of the first temperature sensors 222 and 224. The first temperature sensors 222 and 224 output information about the detected temperature T12 through the voltage signal V12.

[0053] Here, the voltage signal V11 is output to the multiplexer 304 via the terminal 210a, and the voltage signal V12 is output to the multiplexer 304 via the terminal 210b.

[0054] The other end of the second temperature sensor 322 is connected to one end of the second temperature sensor 321, and one end of the second temperature sensor 321 is connected to the terminal 210c.

[0055] The second temperature sensor 321 and the second temperature sensor 322 are connected in series. The voltage signal V21 is a signal related to the temperature T21 output by the second temperature sensor 321. The voltage signal V21 is, for example, the electromotive force of the second temperature sensors 321 and 322. The second temperature sensor 321 outputs information about the detected temperature T21 through the voltage signal V21.

[0056] Here, the voltage signal V21 is output to the multiplexer 304 via the terminal 210c.

[0057] The other end of the third temperature sensor 421 is connected to the terminal 210d, and the other end of the third temperature sensor 422 is connected to the terminal 210e.

[0058] The voltage signal V31 is a signal related to the temperature T31 output by the third temperature sensor 421. The voltage signal V31 is, for example, the electromotive force of the third temperature sensor 421. The third temperature sensor 421 outputs information about the detected temperature T31 through the voltage signal V31. The voltage signal V32 is a signal related to the temperature T32 output by the third temperature sensor 422. The voltage signal V32 is, for example, the electromotive force of the third temperature sensor 422. The third temperature sensor 422 outputs information about the detected temperature T32 through the voltage signal V32.

[0059] The voltage signal V31 is output to the multiplexer 304 via a terminal 210d. The voltage signal V32 is output to the multiplexer 304 via a terminal 210e.

[0060] The multiplexer 304 selects and outputs analog voltage signals such as voltage signals V 11 , V 12 , V 21 , V 31 , and V 32 to the analog-to-digital converter 306 in response to a selection signal from the microcontroller 309 .

[0061] The analog-to-digital converter 306 converts each of the analog voltage signals input from the multiplexer 304 into a digital signal. The analog-to-digital converter 306 also outputs the converted digital signal to the microcontroller 309.

[0062] The microcontroller 309 includes, for example, a central processing unit (CPU) 3091 and a read-only memory (ROM) 3092. The CPU 3091 of the microcontroller 309 executes arithmetic processing based on the digital signal input from the analog-to-digital converter 306 in accordance with a program. The program is stored in a storage medium such as the ROM 3092. The ROM 3092 of the microcontroller 309 may also store various coefficients for calculating information such as the thermal conductivity λ, heat capacity ρCp, flow rate information F1, correction coefficient Ak, and flow rate FL of the fluid. The microcontroller 309 may also include an electronic circuit (arithmetic processing circuit) other than the CPU 3091. Examples of the electronic circuit (arithmetic processing circuit) include a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), and a field programmable gate array (FPGA). The microcontroller 309 may also include a storage medium other than the ROM 3092. Examples of other storage media include an EEPROM (Electrically Erasable Programmable Read-Only Memory) and an HDD (Hard Disk Drive). Note that storage media such as the ROM 3092 are examples of storage media that can non-temporarily store programs. Hereinafter, the operation of the arithmetic processing in the CPU 3091 will be described as the operation of the microcontroller 309.

[0063] The program may be stored in an external storage medium such as a flexible disk, a hard disk, a CD-ROM, an MO (magnetic disk), a DVD-ROM, or a memory card. The program may also be transmitted to the microcontroller 309 via a communication line. The transmitted program is installed in the ROM 3092 of the microcontroller 309.

[0064] The microcontroller 309 calculates the thermal conductivity λ of the fluid based on, for example, a digital signal corresponding to the voltage signals V11 and V12 output by the first temperature sensor 22. The microcontroller 309 also calculates the heat capacity ρCp of the fluid based on, for example, a digital signal corresponding to the voltage signal V21 output by the second temperature sensor 32. The microcontroller 309 also calculates the flow rate information F1 of the fluid based on, for example, a digital signal corresponding to the voltage signals V31 and V32 output by the third temperature sensor 42.

[0065] Furthermore, the microcontroller 309 calculates a correction coefficient Ak based on the thermal conductivity λ and the heat capacity ρCp, and executes a process of correcting the flow rate information F1 using the correction coefficient Ak. Furthermore, the microcontroller 309 calculates the flow rate FL of the fluid based on the corrected flow rate information F1. The microcontroller 309 outputs a voltage signal DT corresponding to the flow rate FL to an external device such as a measurement terminal.

[0066] The power supply 307 generates voltages V41, V42, and V43 to be input to the first heater 21, the second heater 31, and the third heater 41, respectively. The power supply 307 outputs the voltages V41, V42, and V43 to the multiplexer 305.

[0067] The multiplexer 305 outputs a voltage V41 to the first heater 21 in response to a selection signal from the microcontroller 309. The multiplexer 305 outputs a voltage V42 to the second heater 31 in response to a selection signal from the microcontroller 309. The multiplexer 305 outputs a voltage V43 to the third heater 41 in response to a selection signal from the microcontroller 309.

[0068] Voltage V41 is output to the first heater 21 via terminal 210f. The first heater 21 is heated to a temperature corresponding to the voltage value of voltage V41. Voltage V42 is output to the second heater 31 via terminal 210g. The second heater 31 is heated to a temperature corresponding to the voltage value of voltage V42. Voltage V43 is output to the third heater 41 via terminal 210h. The third heater 41 is heated in accordance with the voltage value of voltage V43.

[0069] <Detection Method> Next, a detection method using the flow sensor 1 will be described with reference to Fig. 6 to Fig. 8. Fig. 6 is a flowchart showing an example of the detection method using the flow sensor 1. Fig. 7 and Fig. 8 are diagrams outlining the principle of detecting the heat capacity ρCp of a fluid.

[0070] First, the flow sensor 1 detects the flow rate information F1 of the fluid. First, in step S11, the processing unit 80 outputs a voltage V43 to the third heater 41 to heat the third heater 41 to a predetermined temperature. Specifically, the microcontroller 309 outputs a selection signal to the multiplexer 305 to output the voltage V43 to the third heater 41. The multiplexer 305 outputs the voltage V43 to the third heater 41 in accordance with the input selection signal. After the temperature of the third heater 41 reaches the predetermined temperature, it is maintained at an approximately constant temperature. The operation of maintaining a constant temperature is called a "constant temperature operation." Furthermore, the period during which the third heater 41 operates in constant temperature operation is called a "constant temperature period." The "constant temperature operation" and "constant temperature period" also apply to the first heater 21 and the second heater 31.

[0071] When a fluid flows through the flow sensor 1, the high-temperature region of the temperature distribution formed around the third heater 41 is biased toward the third temperature sensor 422, which is located on the +Z side (upstream) of the third heater 41. In contrast, the low-temperature region of the temperature distribution formed around the third heater 41 is biased toward the third temperature sensor 421, which is located on the −Z side (downstream) of the third heater 41. In other words, when a fluid flows through the flow sensor 1, the temperature T32 detected by the third temperature sensor 422 becomes higher than the temperature T31 detected by the third temperature sensor 421.

[0072] Subsequently, in step S12, the third temperature sensor 422 of the third sensor unit 40 outputs a voltage signal V32 corresponding to the detected temperature T32 to the processing unit 80. Specifically, the voltage signal V32 output from the third temperature sensor 422 is output to the microcontroller 309 via the multiplexer 304 and the analog-to-digital converter 306. Furthermore, the third temperature sensor 421 outputs a voltage signal V31 corresponding to the detected temperature T31 to the processing unit 80. Specifically, the voltage signal V31 output from the third temperature sensor 421 is output to the microcontroller 309 via the multiplexer 304 and the analog-to-digital converter 306.

[0073] Next, in step S13, the processing unit 80 calculates the difference in voltage value between the voltage signal V32 and the voltage signal V31. Specifically, the microcontroller 309 calculates the difference in voltage value between the input voltage signal V32 and the voltage signal V31. The difference in voltage value between the voltage signal V32 and the voltage signal V31 corresponds to the flow rate detection value detected by the third temperature sensor 42. In other words, the difference in voltage value between the voltage signal V32 and the voltage signal V31 is an example of flow rate information F1. The difference in voltage value between the voltage signal V32 and the voltage signal V31 may be referred to as "pre-correction flow rate information F1."

[0074] Next, the flow sensor 1 detects the thermal conductivity λ of the fluid. First, in step S14, the processing unit 80 outputs a voltage V41 to the first heater 21 to heat the first heater 21 to a predetermined temperature. Specifically, the microcontroller 309 outputs a selection signal to the multiplexer 305 to output the voltage V41 to the first heater 21. The multiplexer 305 outputs the voltage V41 to the first heater 21 in accordance with the input selection signal. After the temperature of the first heater 21 reaches the predetermined temperature, it is maintained at a roughly constant temperature. In other words, the first heater 21 operates at a constant temperature.

[0075] Subsequently, in step S15, the multiple first temperature sensors 22 output voltage signals corresponding to the respective detected temperatures to the processing unit 80. The first temperature sensors 221, 223 output voltage signals V11 corresponding to the detected temperature T11 to the processing unit 80. Specifically, the voltage signals V11 output from the first temperature sensors 221, 223 are output to the microcontroller 309 via the multiplexer 304 and the analog-to-digital converter 306. The first temperature sensors 222, 224 output voltage signals V12 corresponding to the detected temperature T12 to the processing unit 80. Specifically, the voltage signals V12 output from the first temperature sensors 222, 224 are output to the microcontroller 309 via the multiplexer 304 and the analog-to-digital converter 306.

[0076] Subsequently, in step S16, the processing unit 80 calculates the thermal conductivity λ of the fluid. Here, the temperature T11 detected by the first temperature sensors 221 and 223 disposed near the first heater 21 is higher than the temperature T12 detected by the first temperature sensors 222 and 224 disposed farther from the first heater 21 than the first temperature sensor 221.

[0077] A specific process flow for calculating the thermal conductivity λ is as follows, for example. First, the microcontroller 309 calculates a differential voltage DT2 between a voltage corresponding to the higher-temperature temperature T11 from the voltage signal V11 and a voltage corresponding to the lower-temperature temperature T12 from the voltage signal V12. The differential voltage DT2 is approximately proportional to the temperature difference [T11 - T12]. Next, the microcontroller 309 multiplies the differential voltage DT2 by a conversion coefficient Bk stored in a storage medium provided in the microcontroller 309, for example. The conversion coefficient Bk is a coefficient for converting the differential voltage DT2 into the thermal conductivity λ. The conversion coefficient Bk may be calculated in advance from measurement data. Alternatively, the conversion coefficient Bk may be stored in the storage medium in advance. In this way, the microcontroller 309 calculates the thermal conductivity λ of the fluid.

[0078] The microcontroller 309 can also calculate the thermal conductivity λ of the fluid based on, for example, the differential voltage DT3 between the first temperature sensors 221 and 222, or the differential voltage DT4 between the first temperature sensors 223 and 224. That is, the thermal conductivity λ of the fluid can be calculated by multiplying the differential voltage DT3 or the differential voltage DT4 by the conversion coefficient Bk.

[0079] However, each of the differential voltages DT3 and DT4 is a differential voltage based on the voltage signals of one pair of temperature sensors (the pair of first temperature sensors 221 and 222, or the pair of first temperature sensors 223 and 224). On the other hand, the differential voltage DT2 is a differential voltage based on the voltage signals of two pairs of temperature sensors (the pair of first temperature sensors 221 and 222, and the pair of first temperature sensors 223 and 224). Therefore, the voltage value of the differential voltage DT2 is approximately twice as high as the voltage values ​​of the differential voltages DT3 and DT4. This improves the signal-to-noise ratio of the signal. As a result, using the differential voltage DT2 can improve the detection accuracy of the thermal conductivity λ.

[0080] Next, the flow sensor 1 detects the heat capacity ρCp of the fluid. First, the principle of detecting the heat capacity ρCp of the fluid will be described with reference to FIGS.

[0081] First, let us refer to Fig. 7. The horizontal axis of Fig. 7 represents the elapsed time t from the start of heating by the second heater 31. The vertical axis of Fig. 7 represents the detected temperature value of the fluid, which is heated according to the elapsed time t from the start of heating, detected by the second temperature sensor 32. The detected temperature value corresponds to the value of the voltage signal output from the second temperature sensor 32. The temperature of the fluid can be obtained by dividing the value of the voltage signal output from the second temperature sensor 32 by the temperature conversion coefficient S.

[0082] Line L71 in Fig. 7 shows the temperature profile of an ideal fluid F71 that has no heat capacity. The ideal fluid F71 corresponds to a hypothetical reference fluid. The ideal fluid F71 can be rephrased as, for example, a measurement environment in a vacuum state. The vertical axis of Fig. 7 for the ideal fluid F71 represents the hypothetical temperature value (voltage value). The temperature of the ideal fluid F71 can be calculated by dividing the hypothetical temperature value by the temperature conversion coefficient S.

[0083] 7 shows a temperature profile of an arbitrary fluid F72 having a heat capacity β1. A line L73 shows a temperature profile of an arbitrary fluid F73 having a heat capacity β2. Note that the heat capacity β2 is set to be greater than the heat capacity β1.

[0084] The virtual temperature value Vi1 of the ideal fluid F71 increases in proportion to the elapsed time t. The relationship between the virtual temperature value Vi1 of the ideal fluid F71 and the elapsed time t is expressed by the following equation (1).

[0085] Vi1=(α·t)·S (1) where α is the temperature rise coefficient [K / sec] of the ideal fluid F71, and S is the aforementioned temperature conversion coefficient [mV / K].

[0086] In contrast, the detected temperature value of the fluid F72 rises later than the virtual temperature value of the ideal fluid F71. The reason the detected temperature value of the fluid F72 rises later than the virtual temperature value of the ideal fluid F71 is because the fluid F72 has a heat capacity β1. The relationship between the detected temperature value Vg1 of the fluid F72 and the elapsed time t is expressed by equation (2).

[0087] Vg1=(α・t)・S+β1・(exp －γｔ −1)·S (2) where γ is an arbitrary constant determined by the fluid.

[0088] From the formulas (1) and (2), the heat capacity β1 of the fluid F72 is calculated as follows: First, the formula (2) is subtracted from the formula (1) to obtain the formula (3).

[0089] Vi1-Vg1=-β1・(exp －γｔ -1)・S...(3)

[0090] [Vi1-Vg1] calculated by equation (3) corresponds to the difference between the detected temperature value of the fluid output from the second temperature sensor 32 and the virtual temperature value of the ideal fluid. Changes in the difference value according to the elapsed time t will be described with reference to FIG. 8. The horizontal axis of FIG. 8 represents the elapsed time t from the start of heating by the second heater 31. The vertical axis of FIG. 8 represents the difference between the detected temperature value of the fluid and the virtual temperature value of the ideal fluid.

[0091] As shown in FIG. 8, when the elapsed time t is sufficiently large, "exp－γｔ " can be approximated to "0". In other words, the difference between the detected temperature value of the fluid and the virtual temperature value of the ideal fluid is saturated. As a result, equation (3) is transformed into equation (4). Furthermore, equation (4) is transformed into equation (5). From equation (5), the heat capacity β1 can be calculated.

[0092] Vi1-Vg1=β1・S...(4) β1=(Vi1-Vg1) / S...(5)

[0093] Examples of the time point at which the difference between the detected temperature value of the fluid and the hypothetical temperature value of the ideal fluid becomes saturated (hereinafter referred to as the "saturation time point") include t=50 milliseconds and t=100 milliseconds.

[0094] The processing unit 80 can calculate the virtual temperature value of the ideal fluid after the saturation point by referring to the temperature rise coefficient α, the temperature conversion coefficient S, and the elapsed time t counted by the counter circuit, all stored in the microcontroller 309. The processing unit 80 can also calculate the heat capacity of the fluid by referring to the difference between the detected temperature value of the fluid after the saturation point and the virtual temperature value of the ideal fluid.

[0095] Because the heat capacity β2 of the fluid F73 is greater than the heat capacity β1 of the fluid F72, the detected temperature value of the fluid F73 rises later than that of the fluid F72. However, other characteristics of the fluid F73 are similar to those of the fluid F72. Therefore, the heat capacity β2 of the fluid F73 can be calculated using equation (6).

[0096] β2=(Vi1-Vg2) / S...(6)

[0097] By replacing the voltage signal V21 corresponding to the temperature T21 detected by the second temperature sensor 32 with "Vg1" in equation (5) or "Vg2" in equation (6), the processing unit 80 can calculate the heat capacity ρCp of any fluid.

[0098] ρCp=(Vi1-V21) / S...(7)

[0099] Next, an example of the flow of detecting the heat capacity ρCp of the fluid will be described. First, in step S17, the processing unit 80 outputs the voltage V42 to the second heater 31. Specifically, the microcontroller 309 outputs a selection signal to the multiplexer 305 to output the voltage V42 to the second heater 31. The multiplexer 305 outputs the voltage V42 to the second heater 31 in accordance with the input selection signal. At this time, the microcontroller 309 increases the voltage value of the voltage V42 in accordance with, for example, the elapsed time t, thereby raising the temperature of the second heater 31 at a constant rate. This heater operation of raising the temperature in accordance with the elapsed time t is referred to as a "heating operation." Furthermore, the period during which the second heater 31 performs the heating operation is referred to as a "heating period." The "heating operation" and "heating period" are similarly defined for the first heater 21 and the third heater 41.

[0100] Next, in step S18, the second temperature sensor 32 sequentially outputs a plurality of voltage signals corresponding to the temperature of the fluid at a plurality of time points during the temperature rise period. As a result, the second temperature sensor 32 outputs information on the temperature change of the fluid during the temperature rise period. Specifically, the second temperature sensors 321, 322 output a plurality of voltage signals V21 at a plurality of time points during the temperature rise period.

[0101] The plurality of voltage signals V21 sequentially output from the second temperature sensors 321 and 322 are output to the microcontroller 309 via the multiplexer 304 and the analog-to-digital converter 306.

[0102] Subsequently, in step S19, the processing unit 80 calculates the heat capacity ρCp of the fluid using, for example, equation (7). Specifically, the microcontroller 309 refers to, for example, the temperature rise coefficient α, the temperature conversion coefficient S, and the elapsed time t counted by the counter circuit stored in the microcontroller 309, and calculates the heat capacity ρCp of the fluid based on the multiple voltage signals V21 input sequentially.

[0103] Next, the flow sensor 1 calculates the flow rate FL of the fluid. First, in step S20, the processing unit 80 calculates a correction coefficient Ak, which is the detection sensitivity ratio with respect to the reference gas, using [ρCp / λ]. For example, the processing unit 80 calculates the correction coefficient Ak by multiplying [ρCp / λ] by the conversion coefficient Ck. Here, the conversion coefficient Ck can use the proportional relationship between the detection sensitivity ratio and ρCp / λ shown in FIG. 2. The conversion coefficient Ck may be stored in advance in a storage medium included in the microcontroller 309, for example.

[0104] Next, in step S21, the microcontroller 309 of the processing unit 80 calculates a voltage value corresponding to the corrected flow rate information F1 by dividing the voltage value corresponding to the uncorrected flow rate information F1 by the correction coefficient Ak. At this time, the microcontroller 309 may subtract a predetermined offset value from the voltage value corresponding to the uncorrected flow rate information F1, and divide the resulting value by the correction coefficient Ak to calculate the voltage value corresponding to the corrected flow rate information F1. The corrected flow rate information F1 roughly matches the flow rate information F1 of the reference gas, for example. In other words, flow rate information F1 that is independent of the type of fluid, etc., is calculated.

[0105] Next, in step S22, the processing unit 80 converts the voltage value corresponding to the corrected flow rate information F1 into the flow rate FL of the fluid using a predetermined conversion formula. Specifically, the microcontroller 309 calculates the flow rate FL corresponding to the corrected flow rate information F1 by referring to a formula (predetermined conversion formula) for converting the flow rate information F1 (voltage information) of the reference gas into the flow rate FL, which is stored in a storage medium provided in the microcontroller 309, for example. In this way, the microcontroller 309 calculates the flow rate FL of the fluid.

[0106] 6, the flow sensor 1 detects information about the fluid in the order of uncorrected flow rate information F1, thermal conductivity λ, and heat capacity ρCp. However, the order in which these pieces of information about the fluid are detected is not limited.

[0107] [Modification] <Overall Configuration> Next, an example of the overall configuration of a flow sensor 1A according to a modification of the embodiment will be described with reference to Fig. 9. Fig. 9 is a diagram schematically showing an example of the overall configuration of the flow sensor 1A according to the modification. Note that in the flow sensor 1A according to the modification, components that are the same as those in the flow sensor 1 according to the embodiment are given the same reference numerals, and descriptions thereof will be omitted where appropriate.

[0108] As shown in Fig. 9, the detection unit 10A of the flow sensor 1A includes a fourth sensor unit 70. In the example shown in Fig. 9, the fourth sensor unit 70 is disposed on the +Z side (downstream) of the third sensor unit 40. However, the position of the fourth sensor unit 70 is not limited to this.

[0109] The fourth sensor unit 70 includes a fourth heater 71 and a plurality of fourth temperature sensors 72. The fourth heater 71 has a longitudinal direction in the Z direction. The fourth heater 71 includes, for example, a heating resistor that generates heat when energized. However, the fourth heater 71 may be another type of heating element.

[0110] 10A, two fourth temperature sensors 72 (721, 722) are disposed on the +X side of the fourth heater 71. The other two fourth temperature sensors 72 (723, 724) are disposed on the −X side of the fourth heater 71. However, the number of fourth temperature sensors 72 is not limited to four.

[0111] The multiple fourth temperature sensors 72 include one of thermistors, linear resistors, platinum resistance temperature detectors, thermocouples, thermopiles, etc. It is preferable to select the same type of sensor for the multiple fourth temperature sensors 72 in terms of characteristics. However, the multiple fourth temperature sensors 72 do not necessarily have to be the same type, as they can detect temperature even if they are not the same type. Each of the multiple fourth temperature sensors 72 shown in FIG. 9 is a thermopile including a resistance temperature detector.

[0112] The multiple fourth temperature sensors 72 are arranged in a direction perpendicular to the Z direction. For example, the multiple fourth temperature sensors 72 are arranged in the X direction. As shown in Fig. 9 , the fourth temperature sensor 721 is arranged closer to the fourth heater 71 than the fourth temperature sensor 722. The fourth temperature sensor 723 is arranged closer to the fourth heater 71 than the fourth temperature sensor 724.

[0113] The fourth heater 71 is configured to be switchable between constant temperature operation and temperature increase operation. For example, the fourth heater 71 performs a temperature increase operation after starting heating, and then performs a constant temperature operation. The multiple fourth temperature sensors 72 output voltage signals for calculating the heat capacity ρCp of the fluid during a temperature increase period when the fourth heater 71 performs a temperature increase operation. The multiple fourth temperature sensors 72 also output voltage signals for calculating the thermal conductivity λ of the fluid during a constant temperature period when the fourth heater 71 performs a constant temperature operation. That is, the fourth sensor unit 70 corresponds to a sensor unit that also serves as the first sensor unit 20 and the second sensor unit 30 according to the embodiment. The processing unit 80 calculates the thermal conductivity λ and heat capacity ρCp of the fluid based on the voltage signal output from the fourth sensor unit 70. Similar to the flow sensor 1 according to the embodiment, the processing unit 80 calculates a correction coefficient Ak based on the thermal conductivity λ and heat capacity ρCp of the fluid, corrects the flow rate information F1 of the fluid, and calculates the flow rate FL.

[0114] <Detection Operation of Thermal Conductivity λ and Heat Capacity ρCp> Next, an example of the detection operation of the thermal conductivity λ and heat capacity ρCp in the flow sensor 1A will be described with reference to FIGS. 10 and 11 . FIG. 10 is a graph showing an example of a temperature profile of the fourth heater 71 that switches between a temperature increase operation and a constant temperature operation. The horizontal axis of FIG. 10 indicates the elapsed time t after the fourth heater 71 starts heating. The vertical axis of FIG. 10 indicates the temperature T71 of the fourth heater 71. FIG. 11 is a graph showing an example of a temperature profile of the fourth heater 71 that alternates between a temperature increase operation and a constant temperature operation. The horizontal axis of FIG. 11 indicates the elapsed time t after the fourth heater 71 starts heating. The vertical axis of FIG. 11 indicates the temperature T71 of the fourth heater 71.

[0115] 10 , the fourth heater 71 performs a temperature increase operation in response to a voltage signal from the processing unit 80. That is, the temperature T71 of the fourth heater 71 increases, for example, at a uniform rate. Accordingly, the temperature of the fluid also increases. Furthermore, during the temperature increase period, the fourth temperature sensor 72 sequentially outputs voltage signals V71 related to the temperature of the fluid to the processing unit 80 at predetermined time intervals. The processing unit 80 calculates the heat capacity ρCp of the fluid based on the multiple voltage signals V71 sequentially output from the fourth temperature sensor 72. When calculating the heat capacity ρCp of the fluid, the processing unit 80 executes processing based on, for example, equation (8).

[0116] ρCp=(Vi1-V71) / S...(8)

[0117] Next, the fourth heater 71 performs a constant temperature operation in response to a voltage signal from the processing unit 80. That is, the temperature T71 of the fourth heater 71 is maintained constant. During this constant temperature period, the fourth temperature sensor 72 outputs a voltage signal V61 related to the detected temperature of the fluid to the processing unit 80. The processing unit 80 calculates the thermal conductivity λ of the fluid based on the voltage signal V61 output from the fourth temperature sensor 72. As in the embodiment, the processing unit 80 calculates the thermal conductivity λ of the fluid based on the voltage signals corresponding to the temperatures output from each of the multiple fourth temperature sensors 721, 722, 723, and 724.

[0118] 11 , the fourth heater 71 may perform a second temperature increase operation in response to a voltage signal from the processing unit 80. After the second temperature increase operation, the fourth heater 71 may perform a second constant temperature operation in response to a voltage signal from the processing unit 80. The fourth heater 71 may repeat a set of a temperature increase operation and a constant temperature operation N times, where N is a natural number of 2 or greater.

[0119] During the second temperature rise period, the fourth temperature sensor 72 sequentially outputs voltage signals corresponding to the temperature of the fluid, as in the first temperature rise period. During the second temperature rise period, the processing unit 80 calculates the heat capacity ρCp of the fluid based on the voltage signals sequentially output from the fourth temperature sensor 72. Furthermore, during the second constant temperature period, the fourth temperature sensor 72 outputs voltage signals corresponding to the temperature of the fluid, as in the first constant temperature period. During the second constant temperature period, the processing unit 80 calculates the thermal conductivity λ of the fluid based on the voltage signals output from the fourth temperature sensor 72.

[0120] When the fourth heater 71 repeats a set of a temperature increase operation and a constant temperature operation N times, the processing unit 80 calculates a set of values ​​related to the N heat capacities ρCp (ρCp1, ρCp2, ..., ρCpn). The processing unit 80 may calculate an average value of the heat capacities ρCp from the values ​​related to the N heat capacities ρCp (ρCp1, ρCp2, ..., ρCpn). The processing unit 80 may also calculate a set of values ​​related to the N thermal conductivities λ (λ1, λ2, ..., λn). The processing unit 80 may also calculate an average value of the thermal conductivity λ from the values ​​related to the N thermal conductivities λ (λ1, λ2, ..., λn). By using the respective average values ​​of the heat capacity ρCp and the thermal conductivity λ, the heat capacity ρCp and the thermal conductivity λ can be detected with high accuracy.

[0121] The processing unit 80 may also calculate the correction coefficient Ak based on the average value of the heat capacity ρCp and the average value of the thermal conductivity λ. Because the correction coefficient Ak is calculated using the heat capacity ρCp and the thermal conductivity λ that are detected with high accuracy, the correction accuracy of the flow rate information F1 can be improved. This allows the flow rate FL of the fluid to be detected with high accuracy.

[0122] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention.

[0123] The present invention provides, for example, the following aspects: <1> A flow sensor comprising: a detection unit that outputs a first detection signal for calculating the thermal conductivity of a fluid, a second detection signal for calculating the heat capacity of the fluid, and a third detection signal for calculating flow rate information of the fluid, and a processing unit that executes a process of correcting the flow rate information using a correction coefficient based on the thermal conductivity calculated from the first detection signal and the heat capacity calculated from the second detection signal. <2> The flow sensor according to <1>, wherein the processing unit calculates the correction coefficient based on a value obtained by dividing the heat capacity of the fluid by the thermal conductivity. <3> The flow sensor according to <1> or <2>, wherein the detection unit includes a first sensor unit that outputs the first detection signal and a second sensor unit that outputs the second detection signal, the first sensor unit includes a first heater that heats the fluid to acquire the first detection signal and a first temperature sensor that outputs the first detection signal corresponding to the temperature of the fluid heated by the first heater, and the second sensor unit includes a second heater that heats the fluid to acquire the second detection signal and a second temperature sensor that outputs the second detection signal corresponding to the temperature of the fluid heated by the second heater. <4> The flow sensor according to <3>, wherein the second heater increases the temperature of the fluid in accordance with the elapsed time after heating is started, the second temperature sensor sequentially outputs a plurality of second detection signals corresponding to the temperatures of the fluid to the processing unit at a plurality of time points during a temperature rise period in which the temperature of the fluid increases, and the processing unit calculates the heat capacity based on the plurality of second detection signals sequentially output from the second temperature sensor. <5> The flow sensor according to <4>, wherein the processing unit calculates the heat capacity based on a difference value between the temperature detection value of the fluid indicated by the second detection signal and a virtual temperature value of an ideal fluid having no heat capacity after a point in time when a change in the difference value has saturated. <6> The flow sensor according to any one of <3> to <5>, wherein the first sensor unit has a plurality of the first temperature sensors, and a direction in which the plurality of first temperature sensors are arranged is perpendicular to a flow direction of the fluid.<7> The flow sensor according to any one of <3> to <6>, wherein the second sensor unit has a plurality of the second temperature sensors, the second heater is disposed between the plurality of second temperature sensors, and the arrangement direction of the plurality of second temperature sensors is perpendicular to the flow direction of the fluid. <8> The flow sensor according to <7>, wherein the distance between the second heater and the second temperature sensor of the plurality of second temperature sensors that is disposed closest to the second heater is shorter than the distance between the first heater and the first temperature sensor of the plurality of first temperature sensors that is disposed closest to the first heater. <9> The flow sensor according to <1> or <2>, wherein the detection unit has a heater and a temperature sensor for outputting the first detection signal and the second detection signal, the heater is configured to be switchable between a constant temperature operation and a temperature rise operation, and the temperature sensor outputs the first detection signal during a constant temperature period when the heater is operating at a constant temperature, and outputs the second detection signal during a temperature rise period when the heater is operating at a temperature rise. <10> The flow sensor according to <9>, wherein the heater repeats N times an operation consisting of a set of the constant temperature operation and the temperature rise operation, the temperature sensor sequentially outputs the first detection signal in each of the N constant temperature periods corresponding to the N constant temperature operations, and sequentially outputs the second detection signal in each of the N temperature rise periods corresponding to the N temperature rise operations, and the processing unit calculates the correction coefficient based on an average value of the thermal conductivity based on a plurality of the first detection signals input for each constant temperature period and an average value of the heat capacity based on a plurality of the second detection signals input for each temperature rise period. <11> A program that causes a processing unit electrically connected to a detection unit to execute the following processes: calculating a thermal conductivity of a fluid from a first detection signal output from the detection unit; calculating a heat capacity of the fluid from a second detection signal output from the detection unit; calculating flow rate information of the fluid from a third detection signal output from the detection unit; calculating a correction coefficient based on the thermal conductivity and the heat capacity; and correcting the flow rate information using the correction coefficient.

[0124] This international application claims priority based on Japanese Patent Application No. 2024-008144, filed on January 23, 2024, the entire contents of which are incorporated herein by reference.

[0125] DESCRIPTION OF SYMBOLS 1, 1A...flow sensor, 10, 10A...detection unit, 20...first sensor unit, 21...first heater, 22...first temperature sensor, 30...second sensor unit, 31...second heater, 32...second temperature sensor, 40...third sensor unit, 41...third heater, 42...third temperature sensor, 51...first membrane, 52...second membrane, 53...third membrane, 60...support member, 70...fourth sensor unit, 71...fourth heater, 72...fourth temperature sensor, 80...processing unit, 309...microcontroller

Claims

1. A detection unit that outputs a first detection signal for calculating the thermal conductivity of a fluid, a second detection signal for calculating the heat capacity of the fluid, and a third detection signal for calculating the flow rate information of the fluid, respectively; and a processing unit that executes a process of correcting the flow rate information using a correction coefficient based on the thermal conductivity calculated from the first detection signal and the heat capacity calculated from the second detection signal. A flow sensor having the above components.

2. The processing unit calculates the correction coefficient based on a value obtained by dividing the heat capacity of the fluid by the thermal conductivity. The flow sensor according to claim 1.

3. The detection unit includes a first sensor unit that outputs the first detection signal and a second sensor unit that outputs the second detection signal. The first sensor unit includes a first heater that heats the fluid to obtain the first detection signal, and a first temperature sensor that outputs the first detection signal corresponding to the temperature of the fluid heated by the first heater. The second sensor unit includes a second heater that heats the fluid to obtain the second detection signal, and a second temperature sensor that outputs the second detection signal corresponding to the temperature of the fluid heated by the second heater. The flow sensor according to claim 1 or claim 2.

4. The second heater increases the temperature of the fluid according to the elapsed time after the start of heating. The second temperature sensor sequentially outputs a plurality of the second detection signals corresponding to the temperature of the fluid to the processing unit at a plurality of time points during the temperature increase period when the temperature of the fluid increases. The processing unit calculates the heat capacity based on the plurality of second detection signals sequentially output from the second temperature sensor. The flow sensor according to claim 3.

5. The processing unit calculates the heat capacity based on the difference value after the change in the difference value between the temperature detection value of the fluid indicated by the second detection signal and the virtual temperature value of an ideal fluid having no heat capacity has saturated. The flow sensor according to claim 4.

6. The first sensor unit includes a plurality of the first temperature sensors. The direction in which the plurality of the first temperature sensors are arranged is orthogonal to the flow direction of the fluid. The flow sensor according to claim 3.

7. The second sensor unit has a plurality of the second temperature sensors, the second heater is disposed between the plurality of the second temperature sensors, and a direction in which the plurality of the second temperature sensors are arranged is orthogonal to a flow direction of the fluid. The flow sensor according to claim 6.

8. A distance between the second heater and the second temperature sensor disposed closest to the second heater among the plurality of the second temperature sensors is smaller than a distance between the first heater and the first temperature sensor disposed closest to the first heater among the plurality of the first temperature sensors. The flow sensor according to claim 7.

9. The detection unit has a heater and a temperature sensor for outputting the first detection signal and the second detection signal. The heater is configured to be able to switch between a constant temperature operation and a temperature increase operation. The temperature sensor outputs the first detection signal during a constant temperature period when the heater performs the constant temperature operation, and outputs the second detection signal during a temperature increase period when the heater performs the temperature increase operation. The flow sensor according to claim 1 or claim 2.

10. The heater repeats an operation including the constant temperature operation and the temperature increase operation N times. The temperature sensor sequentially outputs the first detection signal during each of N constant temperature periods corresponding to the N constant temperature operations, and sequentially outputs the second detection signal during each of N temperature increase periods corresponding to the N temperature increase operations. The processing unit calculates the correction coefficient based on an average value of the thermal conductivity based on the plurality of the first detection signals input for each constant temperature period and an average value of the heat capacity based on the plurality of the second detection signals input for each temperature increase period. The flow sensor according to claim 9.

11. A program that causes a processing unit electrically connected to a detection unit to execute a process of calculating a thermal conductivity of a fluid from a first detection signal output from the detection unit, a process of calculating a heat capacity of the fluid from a second detection signal output from the detection unit, a process of calculating flow rate information of the fluid from a third detection signal output from the detection unit, a process of calculating a correction coefficient based on the thermal conductivity and the heat capacity, and a process of correcting the flow rate information using the correction coefficient.

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