JP2008046143A - Thermal fluid sensor and flow sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the flow rate of fluid to be measured with high accuracy, even by a flow sensor that causes changes in the output characteristics, when the type and composition of the fluid to be measured are changed. <P>SOLUTION: When a micro heater 4 heats the fluid with an external drive current, an upstream thermopile 8 detects the temperature of the fluid before being heated by the micro heater 4, in parallel with the heating of the micro heater 4, and outputs a first temperature detection signal. A downstream thermopile 5 detects the temperature of the fluid before being heated by the micro heater 4, outputs a second temperature detection signal, and calculates the flow rate, based on the differential signal of both the signals. In this case, the temperature of the fluid is detected by a right thermopile 11 and a left thermopile 13, arranged substantially orthogonal to the flow direction of the fluid to the micro heater 4, and right and left temperature detection signals are outputted, thus correcting the calculated flow rate, based on the calculated values of properties of the fluid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal fluid sensor that can be used to discriminate the type of fluid, and a flow rate sensor (hereinafter referred to as a flow sensor) that can be used as a flow rate measurement, and in particular, the type and composition of the fluid to be measured. The present invention relates to a thermal fluid sensor and a flow sensor that can accurately measure the flow rate of a fluid even when the flow rate changes or the flow rate measurement range is wide.

  FIG. 9 shows a configuration diagram of a conventional thermal type microflow sensor. The microflow sensor 101 supplies a driving current to the Si substrate 102, the diaphragm 103, the microheater 104 formed on the diaphragm 103, the downstream thermopile 105 formed on the diaphragm 103 at the lower end of the microheater 104, and the microheater 104. Power supply terminals 106A and 106B to be supplied, an upstream thermopile 108 formed on the diaphragm 103 at the upper end of the microheater 104, and first output terminals 109A and 109B for outputting a first temperature detection signal output from the upstream thermopile 108, Second output terminals 107A and 107B for outputting a second temperature detection signal output from the downstream thermopile 105 are provided.

  According to the microflow sensor 101 configured as described above, the microheater 104 heats the measurement target fluid such as gas existing around the microheater 104 by an external driving current, and the downstream side from the microheater 104. A uniform temperature distribution is generated over the thermopile 105 and between the microheater 104 and the upstream thermopile 108.

  In this state, when a flow from P to Q occurs in the measurement target fluid such as gas, the temperature distribution around the microheater 104 is biased to the downstream side of the flow of the measurement target fluid, that is, the downstream side thermopile 105. The side thermopile 108 detects a temperature lower than the flow rate = 0 when no flow is generated in the measurement target fluid, and outputs a first temperature detection signal having a value corresponding to the detected temperature.

  On the other hand, the downstream thermopile 105 detects a temperature higher than the flow rate = 0 when no flow is generated in the measurement target fluid by the amount that the temperature distribution around the micro heater 104 is biased to the downstream side, and the detection. A second temperature detection signal having a value corresponding to the temperature is output. For this reason, the flow rate measuring device (not shown) can calculate the flow rate of the measurement target fluid based on the difference signal between the first temperature detection signal from the upstream thermopile 108 and the second temperature detection signal from the downstream thermopile 105. it can.

  However, in the conventional microflow sensor as shown in FIG. 9, when the type of fluid to be measured (hereinafter abbreviated as fluid) and the composition of the fluid change, the output characteristics also change. There was a point.

  That is, if the type and composition of the fluid changes, the physical properties of the fluid, such as thermal conductivity, specific heat, viscosity, and density, change, so the temperature distribution of the fluid heated by the microheater changes and the output changes. End up.

  Therefore, in order to solve such problems, a gas analysis sensor is arranged separately from the microflow sensor, or the characteristic value of the fluid is recognized in advance by the microflow sensor or a device equipped with the microflow sensor. The method of letting it leave is adopted.

  However, for example, in a gas meter, even if the gas has the same standard, the composition of the raw material gas differs slightly depending on the lot, and there is a limit to the accuracy of the composition adjustment for controlling the amount of heat performed in the gas production factory. Therefore, even if the gas has the same standard, its composition may change. For this reason, there is a limit to let the microflow sensor or its mounting device recognize the characteristic value of the fluid in advance.

  In addition, when the gas analysis sensor is arranged separately, not only the gas meter will be enlarged, but there are many points that have to be devised, such as a method for correcting the flow rate, the location of the gas analysis sensor, A gas meter could not be manufactured at low cost.

  The present invention has been made in view of the above circumstances, and an object thereof is to make it possible to accurately measure the flow rate of a measurement target fluid in a small size and at low cost even if the type or composition of the measurement target fluid changes. It is an object of the present invention to provide a thermal fluid sensor and a flow sensor.

  The present invention described in claim 1 and claim 2 that achieves the above object relates to a thermal fluid sensor, and the present invention described in claim 3 relates to a flow sensor.

  The thermal fluid sensor according to the first aspect of the present invention includes a heater that heats a measurement target fluid that flows through a flow path by an external drive current, and heat generated from the heater is a flow rate of the measurement target fluid. The temperature of the measurement target fluid is arranged in a direction substantially orthogonal to the flow direction of the measurement target fluid with respect to the heater so as to be transmitted only by the thermal diffusion effect of the measurement target fluid with almost no influence. The heater has a lateral temperature sensor that detects a temperature and outputs a temperature detection signal for calculating a physical property value of the measurement target fluid, and a diaphragm portion to which a peripheral portion is fixed, and is formed in the diaphragm portion And a support substrate for supporting the lateral temperature sensor.

  According to the thermal fluid sensor of the first aspect of the present invention, the heater heats the measurement target fluid by a driving current from the outside while being supported by the support substrate. In parallel with the heating of the heater, the lateral temperature sensor arranged in a direction substantially orthogonal to the flow direction of the measurement target fluid detects the thermal conductivity of the measurement target fluid and outputs a temperature detection signal. Therefore, the physical property value (temperature distribution parameter) of the fluid can be calculated based on the temperature detection signal. Further, by forming the heater and the lateral temperature sensor on the diaphragm part, the heat capacity of the heater and the temperature sensor can be reduced, and the power consumption can be reduced.

  The thermal fluid sensor of the present invention described in claim 2 is the thermal fluid sensor of the present invention described in claim 1, wherein the lateral temperature sensor is substantially orthogonal to the flow direction of the fluid to be measured. It arrange | positions on the substantially straight line which passes along a heater, It is characterized by the above-mentioned.

  In the thermal fluid sensor, the lateral temperature sensors can be arranged on both sides of the heater in a direction substantially orthogonal to the flow direction of the measurement target fluid. In this way, the thermal conductivity of the measurement target fluid is detected by the two lateral temperature sensors respectively disposed on both sides of the heater in a direction substantially orthogonal to the flow direction of the measurement target fluid, so that the flow direction is substantially the same. Even if there is variation in the flow of the measurement target fluid in the flow path in the orthogonal direction, the physical property value of the fluid can be accurately calculated based on the temperature detection signals from the lateral temperature sensors.

  Further, in the thermal fluid sensor, when the lateral temperature sensor is a thermopile, the characteristic change depending on the temperature of the temperature detection signal is reduced, and accurate flow rate measurement is facilitated. Further, since no self-heating occurs, there is no need for correction. Moreover, since it is an output signal by self-electromotive force, no current is consumed.

  Furthermore, in the thermal fluid sensor, the lateral temperature sensor is a pyroelectric body, so that the response speed and sensitivity to the output of the temperature detection signal are increased, and the flow rate is quickly measured. Moreover, since it is an output signal by self-electromotive force, no current is consumed.

  A flow sensor according to a third aspect of the present invention includes a heater that heats a fluid to be measured that flows through a flow path by an external drive current, and is disposed upstream of the fluid to be measured with respect to the heater. An upstream temperature sensor that detects the temperature of the target fluid and outputs a first temperature detection signal; and is disposed downstream of the measurement target fluid with respect to the heater, detects the temperature of the measurement target fluid, and second A downstream temperature sensor for outputting a temperature detection signal, and the heater so that heat generated from the heater is transmitted only by a thermal diffusion effect of the measurement target fluid without being affected by the flow velocity of the measurement target fluid. A third temperature detection signal which is arranged in a direction substantially orthogonal to the flow direction of the measurement target fluid and which detects the temperature of the measurement target fluid and calculates a physical property value of the measurement target fluid A lateral temperature sensor for output and a diaphragm portion having a fixed peripheral portion and supporting the heater, the upstream temperature sensor, the downstream temperature sensor, and the lateral temperature sensor formed in the diaphragm portion And a supporting substrate.

  According to the flow sensor of the present invention described in claim 3, the heater is heated by the driving current from the outside while being supported by the support substrate, and is heated from the heater to the downstream temperature sensor. A uniform temperature distribution is generated from to the upstream temperature sensor. In this state, when a flow from the upstream temperature sensor to the downstream temperature sensor occurs in the measurement target fluid, the temperature distribution around the heater is biased toward the downstream side of the flow of the measurement target fluid, that is, the downstream temperature sensor. The upstream temperature sensor detects a temperature lower than the flow rate = 0 when no flow is generated in the measurement target fluid, and outputs a first temperature detection signal having a value corresponding to the detected temperature.

  In addition, the downstream temperature sensor detects a temperature higher than the flow rate = 0 when no flow is generated in the measurement target fluid by the amount that the temperature distribution around the heater is biased toward the downstream side, and according to the detected temperature Since the value of the second temperature detection signal is output, the flow rate can be calculated based on the difference signal between the first temperature detection signal and the second temperature detection signal. Further, the lateral temperature sensor arranged in a direction substantially orthogonal to the flow direction of the measurement target fluid with respect to the heater detects the thermal conductivity of the measurement target fluid and outputs a third temperature detection signal. The physical property value of the fluid can be calculated based on the temperature detection signal.

  Furthermore, by forming the heater, the upstream temperature sensor, the downstream temperature sensor, and the lateral temperature sensor on the diaphragm portion, the heat capacity of the heater and the temperature sensor can be reduced, and the power consumption can be reduced.

  In the flow sensor, the lateral temperature sensors can be arranged on both sides of the heater in a direction substantially orthogonal to the flow direction of the measurement target fluid. In this way, the thermal conductivity of the measurement target fluid is detected by the two lateral temperature sensors respectively disposed on both sides of the heater in a direction substantially orthogonal to the flow direction of the measurement target fluid, so that the flow direction is substantially the same. Even if there is a variation in the flow of the measurement target fluid in the flow path in the orthogonal direction, the physical property value of the fluid can be accurately calculated based on the third temperature detection signals from both lateral temperature sensors.

  In addition, the flow sensor uses a thermopile for the upstream temperature sensor and the downstream temperature sensor, so that the temperature characteristic of the difference value between the first temperature detection signal and the second temperature detection signal is reduced, and accurate flow rate measurement is possible. It becomes easy to do. Further, since no self-heating occurs, there is no need for correction. Moreover, since it is an output signal by self-electromotive force, no current is consumed.

  Furthermore, the flow sensor uses a pyroelectric body as the upstream temperature sensor and the downstream temperature sensor, so that the response speed and sensitivity to the output of the first temperature detection signal and the second temperature detection signal are increased, and the flow rate can be measured. Become quick. Moreover, since it is an output signal by self-electromotive force, no current is consumed.

  Further, in the flow sensor, when the lateral temperature sensor is a thermopile, the temperature characteristic of the third temperature detection signal is reduced, and it is easy to calculate the physical property value of the fluid accurately. Further, since no self-heating occurs, there is no need for correction. Moreover, since it is an output signal by self-electromotive force, no current is consumed.

  Further, the flow sensor uses a pyroelectric body as the lateral temperature sensor, so that the response speed and sensitivity to the output of the third temperature detection signal are increased, and the flow rate is quickly measured. Moreover, since it is an output signal by self-electromotive force, no current is consumed.

  According to the thermal fluid sensor of the first aspect of the present invention, the heater heats the measurement target fluid by a driving current from the outside while being supported by the support substrate. In parallel with the heating of the heater, the lateral temperature sensor arranged in a direction substantially orthogonal to the flow direction of the measurement target fluid detects the thermal conductivity of the measurement target fluid and outputs a temperature detection signal. Therefore, the physical property value of the fluid can be calculated based on this temperature detection signal. Further, by forming the heater and the lateral temperature sensor on the diaphragm part, the heat capacity of the heater and the temperature sensor can be reduced, and the power consumption can be reduced.

  According to the flow sensor of the present invention described in claim 3, the heater heats the fluid to be measured by a driving current from the outside while being supported by the support substrate. In parallel with the heating of the heater, the upstream temperature sensor detects the temperature of the measurement target fluid before being heated by the heater, and outputs a first temperature detection signal. Since the downstream temperature sensor detects the temperature of the fluid to be measured after being heated by the heater and outputs a second temperature detection signal, the downstream temperature sensor is based on the difference signal between the first temperature detection signal and the second temperature detection signal. The flow rate can be calculated. Further, the lateral temperature sensor arranged in a direction substantially orthogonal to the flow direction of the measurement target fluid with respect to the heater detects the temperature of the measurement target fluid and outputs a third temperature detection signal. The physical property value of the fluid can be calculated based on the signal. Further, by forming the heater, the upstream temperature sensor, the downstream temperature sensor, and the lateral temperature sensor on the diaphragm portion, the heat capacity of the heater and the temperature sensor can be reduced, and the power consumption can be reduced.

  Hereinafter, a flow measuring device using the flow sensor of the present invention and an embodiment of the method thereof will be described in detail with reference to the drawings together with an embodiment of the fluid discrimination device using the thermal fluid sensor of the present invention and the method thereof. Explained.

<First Embodiment>
FIG. 1 is a configuration diagram of the microflow sensor according to the first embodiment. FIG. 2 is a cross-sectional view of the microflow sensor according to the first embodiment.

  The microflow sensor 1 includes an Si substrate 2, a diaphragm 3, a microheater 4 made of platinum or the like formed on the diaphragm 3, a downstream thermopile 5 formed on the diaphragm 3 on the downstream side of the microheater 4, and the microheater 4. The power supply terminals 6A and 6B for supplying drive current from a power source (not shown), the upstream thermopile 8 formed on the diaphragm 3 on the upstream side of the microheater 4, and the first temperature detection signal output from the upstream thermopile 8 are output. First output terminals 9A and 9B, and second output terminals 7A and 7B for outputting a second temperature detection signal output from the downstream thermopile 5.

  The microflow sensor 1 is arranged in a direction substantially orthogonal to the flow direction of the fluid (direction from P to Q) with respect to the microheater 4, detects the physical property value of the fluid, and detects the right side temperature detection signal (third temperature). The right thermopile 11 that outputs the detection signal), the third output terminals 12A and 12B that output the right temperature detection signal output from the right thermopile 11, and the micro heater 4 in a direction substantially perpendicular to the fluid flow direction. A left thermopile 13 that detects the physical property value of the fluid and outputs a left temperature detection signal (corresponding to the third temperature detection signal), and a fourth output terminal that outputs a left temperature detection signal output from the left thermopile 13 14A and 14B, resistors 15 and 16 for obtaining a fluid temperature, and output terminals 17A and 17B for outputting a fluid temperature signal from the resistors 15 and 16 are provided.The right thermopile 11 and the left thermopile 13 constitute a temperature sensor.

  The upstream thermopile 8, the downstream thermopile 5, the right thermopile 11, and the left thermopile 13 are composed of thermocouples. This thermocouple is composed of p ++-Si and Al, has a cold junction and a hot junction, detects heat, and generates a thermoelectromotive force from a temperature difference between the cold junction and the hot junction, A temperature detection signal is output.

  As shown in FIG. 2, a diaphragm 3 is formed on the Si substrate 2. The diaphragm 3 includes a microheater 4, an upstream thermopile 8, a downstream thermopile 5, a right thermopile 11, and a left thermopile 13. The respective hot junctions are formed.

  According to the microflow sensor 1 configured as described above, when the microheater 4 starts to be heated by an external driving current, the heat generated from the microheater 4 is transferred from the downstream thermopile 5 and the upstream using the fluid as a medium. It is transmitted to each hot junction of the side thermopile 8. Since the cold junction of each thermopile is on the Si substrate (Si substrate), it is at the substrate temperature, and since each hot junction is on the diaphragm, it is heated by the transferred heat, and from the Si substrate temperature The temperature rises. Each thermopile generates a thermoelectric power from the temperature difference between the hot junction and the cold junction, and outputs a temperature detection signal.

  The heat transferred by using the fluid as a medium is transferred to each thermopile by a synergistic effect of the heat diffusion effect of the fluid and the flow velocity of the fluid flowing from P to Q. That is, when there is no flow velocity, the heat is diffused evenly to the upstream thermopile 8 and the downstream thermopile 5, and the first temperature detection signal from the upstream thermopile 8 and the second temperature detection signal from the downstream thermopile 5 are transmitted. The difference signal becomes zero.

  On the other hand, when a flow velocity is generated in the fluid, the amount of heat transferred to the hot junction of the downstream thermopile 5 increases due to the flow velocity, and the difference signal between the second temperature detection signal and the first temperature detection signal is a positive signal corresponding to the flow velocity. Value.

  On the other hand, when the microheater 4 starts to be heated by an external drive current, the heat generated from the microheater 4 is hardly affected by the flow velocity of the fluid and is only affected by the thermal diffusion effect of the fluid. It is transmitted to the right thermopile 11 arranged in a direction substantially orthogonal to the fluid flow direction. In addition, similar heat is transmitted to the left thermopile 13 disposed in a direction substantially orthogonal to the fluid flow direction with respect to the microheater 4. Therefore, the right temperature detection signal output from the third output terminals 12A and 12B by the electromotive force of the right thermopile 11 and / or the left temperature detection output from the fourth output terminals 14A and 14B by the electromotive force of the left thermopile 13 Based on the signal, it becomes possible to calculate a physical property value of the fluid such as a thermal diffusion constant determined by heat conduction, thermal diffusion, specific heat, and the like.

  Furthermore, according to the microflow sensor 1, since the micro heater 4, the upstream thermopile 8, the downstream thermopile 5, the right thermopile 11 and the left thermopile 13 are formed on the diaphragm 3, the heat capacity is reduced and consumed. Electric power can be reduced. Further, since the configuration of the microflow sensor 1 is simple, there is an effect that it can be manufactured at low cost.

  Next, a description will be given of a flow rate measuring apparatus that uses the above-described microflow sensor 1 and can always accurately measure the flow rate of the fluid regardless of the change in the type and composition of the fluid.

  FIG. 3 is a block diagram showing the configuration of the flow rate measuring apparatus using the microflow sensor according to the first embodiment. This flow rate measuring device measures, for example, the flow rate of a fluid such as gas, the second temperature detection signal from the downstream thermopile 5 in the microflow sensor 1, and the upstream thermopile 8 in the microflow sensor 1. A differential amplifier 33 for amplifying a difference signal from the first temperature detection signal from the first temperature detection signal, an amplifier 35a for amplifying a right temperature detection signal from the right thermopile 11 in the microflow sensor 1, and a left thermopile in the microflow sensor 1. 13 includes an amplifier 35b for amplifying the left side temperature detection signal from 13 and a microcomputer 40.

  The microcomputer 40 adds the right side temperature detection signal from the amplifier 35a and the left side temperature detection signal from the amplifier 35b, and the second temperature detection signal and the first temperature detection signal obtained by the differential amplifier 33. The division unit 47 that divides the difference signal by the addition signal output from the addition unit 45, the flow rate calculation unit 41 that calculates the flow rate of the fluid based on the division signal output from the division unit 47, and the output from the addition unit 45 And a fluid property value calculation unit 43 that calculates a property value such as thermal conductivity, specific heat, viscosity, density, etc. of the fluid based on the addition signal.

  Next, a flow rate measuring method realized by the flow rate measuring apparatus according to the first embodiment will be described with reference to the flowchart shown in FIG.

  First, when the microheater 4 is heated by a driving current generated by an external pulse signal (step S11), a second temperature detection signal is output from the downstream thermopile 5 and a first temperature detection signal is output from the upstream thermopile 8. (Step S13). The second temperature detection signal is output to the differential amplifier 33, and the first temperature detection signal is output to the differential amplifier 33. FIG. 5 shows responses of the first temperature detection signal and the second temperature detection signal to the pulse signal.

  Next, the differential amplifier 33 amplifies the difference signal between the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8 (step S15).

  Then, the adding unit 45 adds the right side temperature detection signal from the amplifier 35a and the left side temperature detection signal from the amplifier 35b to obtain an addition signal (step S17). FIG. 6 shows a timing chart of the right side temperature detection signal, the left side temperature detection signal, and the addition signal. Next, the division unit 47 divides the amplified difference signal obtained in step S15 by the addition signal obtained in step S17 to obtain a division signal (step S19).

  Subsequently, the flow rate calculation unit 41 calculates an accurate flow rate of the fluid based on the division signal obtained in step S19 (step S21). Further, the fluid property value calculation unit 43 calculates the fluid property values such as the thermal conductivity, specific heat, viscosity, density, etc. of the fluid based on the addition signal obtained in step S17 and the accurate flow rate of the fluid calculated in step S21. Calculate (step S23).

  As described above, the right thermopile 11 and the left thermopile 13 arranged in the direction orthogonal to the fluid flow direction measure the thermal conductivity of the fluid by detecting the physical property value of the fluid. When the flow velocity of the fluid is zero, the speed at which heat is transferred by the fluid depends on the thermal diffusion constant (one of the physical properties of the fluid) determined by thermal conductivity, thermal diffusion, specific heat, and the like. When the flow velocity is zero, the thermal diffusion constant is obtained from the temperature difference between the right thermopile 11, the left thermopile 13, and the micro heater 4. The larger this temperature difference, the smaller the thermal diffusion constant.

  The magnitude of this thermal diffusion constant also affects the first temperature detection signal output from the upstream thermopile 8 and the second temperature detection signal output from the downstream thermopile 5, and these values depend on the magnitude of the thermal diffusion constant. Change. Therefore, in principle, the first temperature detection signal and the second temperature detection signal, or the difference between them can be divided by the heat diffusion constant, so that fluids having different heat diffusion constants can be used. Even if it is a kind of fluid, an accurate flow rate can be calculated.

  On the other hand, when the flow rate is not zero, heat is carried downstream by the fluid flow, and the amount of heat reaching the right thermopile 11 and the left thermopile 13 decreases accordingly. That is, the thermal diffusion around the right thermopile 11 and the left thermopile 13 is increased by the flow of the fluid. Here, it is generally known that the rate of increase of the thermal diffusion is proportional to the square root of the flow velocity of the fluid, so in principle, the thermal diffusion constant of the fluid can even be solved in some way. For example, it can be estimated at any flow rate.

  On the other hand, the increase in thermal diffusion (decrease in the amount of heat transferred from the microheater 4) occurs around the upstream side thermopile 8 and the downstream side thermopile 5 as well as around the right side thermopile 11 and the left side thermopile 13 due to the fluid flow. Therefore, as the flow rate of the fluid increases, the difference between the temperature of the fluid around the downstream thermopile 5 and the temperature of the fluid around the upstream thermopile 8 decreases due to the accompanying increase in thermal diffusion.

  For this reason, the difference signal between the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8 that should be increased in proportion to the increase in the flow velocity of the fluid, If the fluid flow rate becomes too large due to an increase in the thermal diffusion, the increase due to the increase in the flow rate exceeds the decrease due to the increase in the thermal diffusion, and the second temperature detection is performed despite the increase in the flow rate. The difference signal between the signal and the first temperature detection signal may decrease.

  Therefore, when the flow rate is zero, the addition value of the right temperature detection signal output by the right thermopile 11 and the left temperature detection signal output by the left thermopile 13 is considered as “1”, and there is a flow rate for this. The ratio of the added value of the right side temperature detection signal and the left side temperature detection signal is regarded as a coefficient representing the rate of change of the amount of heat to be moved, and this coefficient is used as the second temperature detection signal from the downstream thermopile 5 and the upstream side. An operation of multiplying the difference signal from the first temperature detection signal from the thermopile 8 is performed.

  In other words, by dividing the difference signal between the second temperature detection signal and the first temperature detection signal by the added value of the right temperature detection signal and the left temperature detection signal, it is possible to calculate the flow rate without the influence of changes in thermal diffusion. Thus, it is possible to obtain an accurate and high-resolution flow rate.

  In the above-described embodiment, the difference signal obtained by amplifying the second temperature detection signal from the downstream thermopile 5 obtained from the differential amplifier 33 and the first temperature detection signal from the upstream thermopile 8 is used as the division unit 47. , The flow rate calculation is performed by eliminating the influence of the change in thermal diffusion by dividing the right side temperature detection signal from the amplifier 35a and the left side temperature detection signal from the amplifier 35b by the addition signal obtained by adding by the addition unit 45. It is possible.

  In the above-described embodiment, the division signal is obtained by the division unit 47 prior to the flow rate calculation by the flow rate calculation unit 41. This is because the second temperature detection signal and the first temperature detection signal are different from each other. This is because it is not necessary to grasp the physical property value of the fluid as strictly accurate values such as thermal conductivity, specific heat, viscosity, and density in order to eliminate the influence of the thermal diffusion change that appears in the difference signal after amplification.

  That is, in the above-described embodiment, in order to calculate the thermal conductivity, specific heat, viscosity, and density of a fluid that cannot be specified unless the state of thermal diffusion is grasped with high accuracy, An accurate flow rate of the fluid excluding the influence of the change in diffusion is calculated in advance by the flow rate calculation unit 41, and this is reflected in the calculation of the physical property value by the fluid physical property value calculation unit 43.

  However, depending on the type of factor calculated by the fluid property value calculation unit 43 as the physical property value, the physical property value is calculated in advance by the fluid property value calculation unit 43, and the downstream from the differential amplifier 33. Based on the amplified difference signal between the second temperature detection signal from the side thermopile 5 and the first temperature detection signal from the upstream side thermopile 8, the accurate flow rate of the fluid excluding the influence of the change in thermal diffusion is reduced. You may make it calculate from.

  As described above, according to the flow rate measuring apparatus of the first embodiment, the right thermopile 11 and the left thermopile 13 are arranged in the direction substantially perpendicular to the fluid flow direction with respect to the microheater 4, and the right temperature detection signal and the left temperature are detected. Since the detection signal is output, the physical property value of the fluid such as the thermal diffusion constant can be accurately calculated based on the right temperature detection signal and the left temperature detection signal without being affected by the flow direction of the fluid. .

  Since the fluid flow rate calculated by the flow rate calculation unit 41 is corrected based on the calculated physical property value of the fluid, the type and composition of the fluid change without any special contrivance. However, the flow rate can be accurately measured.

  In addition, by dividing the output of the microflow sensor 1 by the output of the right thermopile 11 and / or the left thermopile 13 as a new output, for example, it is easier to cope with subtle changes in fuel gas. The flow rate-output characteristic can be made sufficiently independent of the fluid component, and the flow rate can be accurately measured.

<Second Embodiment>
Next, a flow rate measuring device using the flow sensor of the present invention and a method of the second embodiment of the method will be described. A fluid discrimination device using the thermal fluid sensor of the present invention and a method of the second embodiment of the method will be described. Along with the form, it will be described in detail with reference to the drawings. FIG. 7 is a configuration diagram of the microflow sensor according to the second embodiment. FIG. 8 is a block diagram showing the configuration of a flow rate measuring apparatus using the microflow sensor according to the second embodiment.

  The microflow sensor 1a includes a Si substrate 2, a diaphragm 3, a micro heater 4, a downstream thermopile 5, power supply terminals 6A and 6B, first output terminals 7A and 7B, an upstream thermopile 8, and second output terminals 9A and 9B. .

  The microflow sensor 1a is arranged in a direction substantially perpendicular to the fluid flow direction (direction from P to Q) with respect to the microheater 4, detects the temperature of the fluid, and outputs a right side temperature detection signal. The temperature resistor 21, the third output terminals 12 A and 12 B that output the right temperature detection signal output from the right temperature measuring resistor 21, and the micro heater 4 are arranged in a direction substantially orthogonal to the fluid flow direction, and the temperature of the fluid The left temperature measuring resistor 23 that outputs the left temperature detection signal, the fourth output terminals 14A and 14B that output the left temperature detection signal output from the left temperature measuring resistor 23, the resistors 15 and 16, and the output terminal 17A and 17B are provided. The right temperature measuring resistor 21 and the left temperature measuring resistor 23 constitute a temperature sensor, and are made of platinum or the like, like the micro heater 4.

  Thus, according to the microflow sensor 1a of the second embodiment, instead of the right thermopile 11 and the left thermopile 13 of the first embodiment shown in FIG. The resistor 23 is disposed, the right temperature measuring resistor 21 detects the temperature of the fluid, and outputs a right temperature detection signal to the third output terminals 12A and 12B. Further, the left temperature measuring resistor 23 arranged in a direction substantially orthogonal to the fluid flow direction with respect to the microheater 4 detects the temperature of the fluid and outputs a left temperature detection signal to the fourth output terminals 14A and 14B.

  For this reason, based on the right side temperature detection signal and the left side temperature detection signal, it becomes possible to calculate the physical property value of the fluid such as the thermal diffusion constant determined by the thermal conductivity, thermal diffusion, specific heat and the like.

  Further, as shown in FIG. 8, the flow measuring device for measuring the flow rate using the microflow sensor 1a includes the second temperature detection signal from the downstream thermopile 5 in the microflow sensor 1a, and the microflow sensor 1a. The differential amplifier 33 that amplifies the difference signal from the first temperature detection signal from the upstream thermopile 8 and the right temperature measuring resistor 21 and the left temperature measuring resistor 23 in the microflow sensor 1a are fixed to two equal in resistance value. And a bridge circuit 39 that is bridge-connected by resistors 38a and 38b.

  Further, the flow rate measuring device applies a constant voltage between the connection point between the right temperature measuring resistor 21 and the fixed resistor 38b of the bridge circuit 39 and the connection point between the left temperature measuring resistor 23 and the fixed resistor 38a. A differential amplifier that differentially amplifies the potential between the connection point A of the source 37 and the right temperature measuring resistor 21 and the fixed resistor 38a of the bridge circuit 39 and the connection point B of the left temperature measuring resistor 23 and the fixed resistor 38b. 36 and a microcomputer 40. The microcomputer 40 includes a division unit (or parameter selection unit) 49, a flow rate calculation unit 41, and a fluid property value calculation unit 43.

  According to the flow rate measuring apparatus of the second embodiment having such a configuration, when the temperature of the right temperature measuring resistor 21 rises, the potential at the connection point A between the right temperature measuring resistor 21 and the fixed resistor 38a rises, and the left side measuring resistor 21 When the temperature of the temperature resistor 23 increases, the potential at the connection point B between the left temperature measuring resistor 23 and the fixed resistor 38b increases. Therefore, when differential amplification is performed by the differential amplifier 36 so that the potential at the connection point A is subtracted from the potential at the connection point B, the right temperature detection signal from the right temperature measurement resistor 21 and the left temperature from the left temperature measurement resistor 23 are obtained. An amplified addition signal obtained by amplifying the addition value with the detection signal is obtained by the differential amplifier 36.

  Therefore, in the division unit (or parameter selection unit) 49, an amplified difference signal between the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8 from the differential amplifier 33. Is divided by the added signal after amplification from the differential amplifier 36 to obtain a division signal. Based on the division signal, the flow rate calculation unit 41 calculates an accurate flow rate of the fluid, and the flow rate calculation unit 41 calculates Based on the correct flow rate of the fluid and the amplified signal from the differential amplifier 36, the fluid property value calculation unit 43 calculates the fluid property values such as the thermal conductivity, specific heat, viscosity, and density of the fluid. To do.

  Therefore, it is possible to accurately measure the flow rate without depending on the type and composition of the fluid without special measures, and the same effect as the effect of the first embodiment can be obtained.

  Note that the present invention is not limited to the microflow sensor, the flow rate measuring device, and the method thereof according to the first and second embodiments. In the first embodiment, a thermopile is exemplified as the temperature sensor, and in the second embodiment, a temperature measuring resistor made of platinum resistance or the like is exemplified as the temperature sensor. However, the temperature sensor is not limited to this. Any sensor may be used as long as it is a commonly used temperature sensor such as a pyroelectric material or a thermistor.

  In the first embodiment and the second embodiment, the thermal fluid sensor for detecting the physical property value of the fluid composed of the right thermopile 11, the left thermopile 13, and the microheater 4 is used as the downstream thermopile 5. In the above description, the microflow sensor 1, 1a that measures the flow velocity (flow rate) of the fluid composed of the upstream thermopile 8 and the micro heater 4 is described as an example. May be separated to constitute a thermal fluid sensor including the right thermopile 11, the left thermopile 13, and the micro heater 4.

  In such a configuration, the right temperature detection signal output from the third output terminals 12A and 12B by the electromotive force of the right thermopile 11 and / or the fourth output terminals 14A and 14B by the electromotive force of the left thermopile 13 are used. The microcomputer 40 may further determine the type of the fluid from the physical property value of the fluid calculated by the fluid property value calculation unit 43 of the microcomputer 40 based on the output left temperature detection signal.

  In addition, as described at the end of the first embodiment, the physical property value is calculated in advance by the fluid physical property value calculation unit 43, and from the downstream thermopile 5 from the differential amplifier 33. Based on the amplified difference signal between the second temperature detection signal and the first temperature detection signal from the upstream thermopile 8, the accurate flow rate of the fluid excluding the influence of the change in thermal diffusion is calculated later. In this case, a correction coefficient corresponding to the type of fluid determined by the microcomputer 40 is determined in advance, and the amplified difference signal from the differential amplifier 33 is corrected by this correction coefficient to calculate the flow rate. You may comprise as follows.

  If so, a table in which the type of fluid and the correction coefficient are linked is stored in an internal memory (ROM) of the microcomputer 40 or an external memory (preferably non-volatile) connected to the microcomputer 40. If the correction coefficient corresponding to the type of fluid is read from the internal memory (ROM) or external memory and multiplied by the amplified difference signal from the differential amplifier 33, the flow rate calculation is completed. , Processing burden can be reduced.

  In addition, when the physical property value is calculated in advance by the fluid physical property value calculation unit 43 and the accurate flow rate of the fluid excluding the influence of the change in thermal diffusion is calculated later, instead of the correction coefficient, The physical property value and the type calculated from the physical property value are linked to the flow rate conversion formula used to obtain the flow rate of the fluid from the amplified difference signal from the differential amplifier 33 corresponding to the physical property value or type. The table may be stored in an internal memory (ROM) of the microcomputer 40 or an external memory (preferably non-volatile) connected to the microcomputer 40.

  Furthermore, the fluid flow calculated by the flow rate calculation unit 41 based on the output of the differential amplifier 33 that amplifies the difference signal between the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8. A table in which the flow rate and the reference value of the third temperature detection signal from the right thermopile 11 and the left thermopile 13 corresponding to the flow rate are linked to an internal memory (ROM) of the microcomputer 40 or an external memory connected to the microcomputer 40 You may make it store in (nonvolatility is preferable).

  In that case, the fluid property value calculation unit 43 of the microcomputer 40 takes out the flow rate of the fluid calculated by the flow rate calculation unit 41 from the external memory as an address pointer, and the reference of the third temperature detection signal corresponding to the flow rate The physical property value of the fluid is calculated from the ratio between the value and the third temperature detection signal actually acquired from the right thermopile 11 or the left thermopile 13.

  The physical property value of the fluid in this case is calculated by calculating the ratio between the third temperature detection signal actually acquired from the right thermopile 11 or the left thermopile 13 and the reference value of the third temperature detection signal extracted from the external memory. The difference signal between the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8 is multiplied by the output of the amplified differential amplifier 33.

  Further, in the first embodiment and the second embodiment, the temperature sensors for detecting the physical property value of the fluid are provided on the right side and the left side with respect to the micro heater 4. It may be provided on one of the right side and the left side with respect to the heater 4 to detect the temperature of the fluid and calculate the physical property value of the fluid.

  When the temperature sensors are provided on the right side and the left side of the microheater 4 as in the first embodiment and the second embodiment, the average value of the output signals from both temperature sensors is When only one temperature sensor is provided, the value of the output signal from the temperature sensor may be used as a basis for detecting the physical property value of the fluid.

  Further, the division by the division unit 47 is performed according to the output value of the differential amplifier 33 that amplifies the difference signal between the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8. Alternatively, this may be done selectively.

  In particular, according to an experiment conducted by the inventors of the present invention, the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8 have a flow rate in a relatively low flow rate region. Although the output signal value increases in proportion, the output signal value does not increase in proportion to the flow rate in a region where the comparatively low flow rate is high, and the output tends to be saturated.

  Therefore, in a relatively low flow rate region where the output signal value rises in proportion to the flow rate, a differential amplifier between the second temperature detection signal from the downstream thermopile 5 and the first temperature detection signal from the upstream thermopile 8. In the region of relatively high flow rate in which the difference signal amplified by 33 is treated as a flow rate signal as it is and the output signal value does not increase in proportion to the flow rate but slows down, in the transpiration unit 49, the output from the downstream thermopile 5 is increased. The difference signal amplified by the differential amplifier 33 between the two temperature detection signals and the first temperature detection signal from the upstream thermopile 8 is the average value of the third temperature detection signals from the right thermopile 11 and the left thermopile 13, or By dividing by the value of the third temperature detection signal of one of these, the influence of saturation of the temperature detection signal may be removed, and this may be handled as a flow signal.

  If configured as such, the second temperature detection signal from the downstream thermopile 5 and the upstream thermopile that could not be used for flow rate measurement in a relatively high flow rate region due to low reliability due to output saturation. 8, the difference signal amplified by the differential amplifier 33 with the first temperature detection signal from the average temperature of the third temperature detection signal from the right thermopile 11 or the left thermopile 13, or one of these. Along with the value of the third temperature detection signal, it can be used for flow rate measurement in a relatively high flow rate region, and the flow rate measurement range (range) where the flow rate can be measured accurately has been increased from the conventional 100 times unit to 10,000 times unit. For example, various leak states in the gas meter can be detected by one sensor.

  In addition, it is needless to say that various modifications can be made without departing from the technical idea of the present invention.

It is a block diagram of the microflow sensor of 1st Embodiment. It is sectional drawing of the microflow sensor of 1st Embodiment. It is a block diagram of the flow rate measuring device using the microflow sensor of the first embodiment. It is a flowchart which shows the flow measuring method implement | achieved by the flow measuring device of 1st Embodiment. It is a figure which shows a 1st temperature detection signal and a 2nd temperature detection signal. It is a figure which shows a right side temperature detection signal and a left side temperature detection signal. It is a block diagram of the microflow sensor of 2nd Embodiment. It is a block diagram of the configuration of a flow rate measuring device using the microflow sensor of the second embodiment. It is a block diagram of the conventional thermal type micro flow sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1a Micro flow sensor 2 Si substrate 3 Diaphragm 4 Micro heater 5 Downstream thermopile 8 Upstream thermopile 11 Right side thermopile 13 Left side thermopile 21 Right side resistance thermometer 23 Left side resistance thermometer resistor 33 Differential amplifier 35a, 35b Amplifier 40 Microcomputer 41 Flow rate calculation unit 43 Fluid property value calculation unit 45 Addition unit 47 Division unit

Claims (3)

A heater for heating the fluid to be measured that flows through the flow path by an external drive current;
The direction of flow of the measurement target fluid is substantially the same as the flow direction of the measurement target fluid so that the heat generated from the heater is transmitted only by the thermal diffusion effect of the measurement target fluid without being affected by the flow velocity of the measurement target fluid. A lateral temperature sensor that is arranged in an orthogonal direction, detects a temperature of the measurement target fluid, and outputs a temperature detection signal for calculating a physical property value of the measurement target fluid;
A support substrate that has a diaphragm portion with a fixed peripheral portion and supports the heater and the lateral temperature sensor formed in the diaphragm portion;
A thermal fluid sensor comprising:   2. The thermal fluid sensor according to claim 1, wherein the lateral temperature sensor is disposed on a substantially straight line passing through the heater substantially orthogonal to a flow direction of the fluid to be measured. A heater for heating the fluid to be measured that flows through the flow path by an external drive current;
An upstream temperature sensor that is disposed upstream of the measurement target fluid with respect to the heater, detects the temperature of the measurement target fluid, and outputs a first temperature detection signal;
A downstream temperature sensor that is disposed downstream of the measurement target fluid with respect to the heater, detects a temperature of the measurement target fluid, and outputs a second temperature detection signal;
The flow direction of the measurement target fluid is substantially the same as the flow direction of the measurement target fluid to the heater so that the heat generated from the heater is transmitted only by the thermal diffusion effect of the measurement target fluid without being affected by the flow velocity of the measurement target fluid. A lateral temperature sensor that is arranged in an orthogonal direction, detects a temperature of the measurement target fluid, and outputs a third temperature detection signal for calculating a physical property value of the measurement target fluid;
A support substrate for supporting the heater, the upstream temperature sensor, the downstream temperature sensor, and the lateral temperature sensor having a diaphragm portion with a fixed peripheral portion and formed in the diaphragm portion;
A flow sensor comprising:

Images