JP2005010153A - Flow rate measuring method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flowmeter which precisely measures the flow rate of a fluid by use of a heating source and a temperature detecting element and further precisely measuring even a minute flow rate. <P>SOLUTION: The flow rate measuring method is applied to a passage of the fluid comprising the heating source 3, a first temperature detecting element 2 arranged on the upstream side to the heating element, and a second temperature detecting element 4 arranged on the downstream side to the heating source. This method comprises: a procedure for heating the heating source in a pulse manner by a heating drive pulse; a procedure for detecting the temperature rise of the fluid by the heating drive pulse by the first temperature detecting element; a procedure for detecting the temperature rise of the fluid by the heating drive pulse by the second temperature detecting element; and a first flow rate computing procedure for determining the flow rate of the fluid by a first peak value that is the maximum value of temperature rise detected by the first temperature detecting element and a second peak value that is the maximum value of temperature rise detected by the second temperature detecting element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a flow rate measuring method and apparatus for measuring the flow rate of a fluid flowing in a passage, and more specifically, the flow rate of a fluid can be accurately measured using a heat generation source and a temperature detection element. The present invention relates to a flow rate measuring method and apparatus capable of accurately measuring the flow rate of the flow rate.

  Conventional flow meters exist based on various measurement principles such as mechanical, pressure type, ultrasonic type, and mass type, but none of them can accurately measure a small amount of flow rate. There was a problem. That is, accurate measurement is difficult at a minute flow rate due to an increase in measurement error. Further, in the measurement of an extremely small flow rate of about 0.1 to several tens [μL / min], it has been difficult to obtain an effective measurement value with the flow meter as described above.

  For example, a minute flow rate of 1 mL per day is 0.69 [μL / min], and a flow rate when a cross-sectional shape having an inner diameter of 0.2 mm flows through a circular tube is 0.37 [mm / s]. In the case of measuring the flow velocity by driving the mechanical movable portion with the flow velocity of the fluid, it is extremely difficult to create a mechanical movable portion capable of measuring such a slow flow velocity. Further, if the flow rate is measured by the differential pressure due to passage resistance or orifice, the differential pressure is too small to measure. In the case where the flow velocity of the fluid is measured using ultrasonic waves or the like, the flow velocity is extremely small as described above, and thus cannot be measured. Similarly, Coriolis flowmeters cannot measure because the flow velocity is extremely small.

  In addition to the flow meter as described above, a flow meter as in Patent Document 1 below and a flow measurement method and apparatus as in Patent Document 2 are known as being capable of accurately measuring a very small flow rate. is there. In Patent Document 1, a heat generation source and a temperature detection element are arranged in a fluid passage to cause the heat generation source to generate heat in pulses, and the temperature of the fluid passing therethrough is detected by the temperature detection element. A flow meter is described in which the flow rate of a fluid is obtained from the time difference from the time until the time at which the temperature detected by the temperature detecting element reaches the maximum value.

Further, Patent Document 2 discloses that a heat generation source disposed in a fluid passage, first and second temperature detection elements disposed downstream of the heat generation source, and the heat generation source are driven to generate heat. A flow rate measuring method and apparatus having a pulse power source that generates heat in a pulsed manner by a pulse and a flow rate calculation unit that determines the flow rate of a fluid are described. In this flow measurement method and apparatus, the heat generation drive time and the time when the difference between the fluid temperature detected by the first temperature detection element and the fluid temperature detected by the second temperature detection element changes from positive to negative (zero crossing). The flow rate of the fluid is obtained from the time difference from the time.
JP 2002-211401 A JP 2003-28692 A

  According to the flow meter of Patent Document 1 and the flow rate measuring method and apparatus of Patent Document 2, it is possible to accurately measure a very small amount of flow in a normal case. However, as described above, when the flow velocity of the fluid is extremely slow, in addition to the heat transfer due to the fluid flow, the influence of the heat transferred by the heat conduction of the tube itself and the fluid appears. There was a problem that the heat transfer component caused by the increased measurement error.

  In addition, when the flow rate of the fluid is extremely slow, the time until the heated fluid reaches the position of the temperature detection element increases, the amount of heat released from the fluid increases, and the change in detection temperature becomes flat. End up. For this reason, it has become difficult to detect the time when the temperature reaches the peak value, and there has been a problem that the error in the detection time becomes large. Also, in the case of the zero crossing time of the difference between the detected temperatures of the two temperature detecting elements, the error tends to increase when the fluid flow velocity is extremely small.

  Therefore, the present invention can accurately measure the flow rate of a fluid using a heat generation source and a temperature detection element, and can accurately measure the flow rate of a fluid even when the flow rate of the fluid is extremely slow. An object is to provide a measurement method and apparatus.

  In order to achieve the above object, a flow rate measuring method according to the present invention includes a heat source, a first temperature detection element disposed upstream of the heat source, and a downstream side of the heat source. A flow rate measuring method in a fluid passage provided with the second temperature detection element, wherein the heat generation source generates a pulse with a heat generation drive pulse, and the heat generation by the first temperature detection element. A procedure for detecting a temperature rise of the fluid due to the drive pulse; a procedure for detecting a temperature rise of the fluid due to the heat-generating drive pulse by the second temperature detection element; and a temperature rise detected by the first temperature detection element. A first flow rate calculation procedure for determining a fluid flow rate by using a first peak value that is a maximum value and a second peak value that is a maximum value of the temperature rise detected by the second temperature detection element; It is.

  In the above flow rate measurement method, it is preferable that the first flow rate calculation procedure obtains a fluid flow rate based on a ratio between the first peak value and the second peak value.

  In the above flow rate measurement method, it is preferable that the first temperature detection element and the second temperature detection element are arranged at a position equidistant from the heat generation source in the flow direction of the passage. .

  Further, in the above flow rate measurement method, a second flow rate calculation procedure for obtaining a fluid flow rate based on a time difference between an application time of the heat generation drive pulse and a time when the second peak value is detected, and the first flow rate calculation And a procedure for obtaining a flow rate as a measurement result using the procedure and the second flow rate calculation procedure.

  Further, in the above flow rate measuring method, a third temperature detection element is disposed on the downstream side of the heat generation source of the passage, and the third temperature detection element causes the fluid generated by the heat generation driving pulse to flow. A time difference between a procedure for detecting a temperature rise, a time when the second peak value is detected, and a time when the third peak value, which is a maximum value of the temperature rise detected by the third temperature detecting element, is detected. And a second flow rate calculation procedure for obtaining a flow rate of the fluid, and a procedure for obtaining a flow rate as a measurement result using the first flow rate calculation procedure and the second flow rate calculation procedure. .

  In the above flow rate measurement method, the first flow rate calculation procedure and the second flow rate calculation procedure can be switched and applied according to the flow rate range as a procedure for obtaining the flow rate as the measurement result. . In this case, each of the application ranges of the first flow rate calculation procedure and the second flow rate calculation procedure is such that the application range of the first flow rate calculation procedure is the application range of the second flow rate calculation procedure. It is preferable that the flow rate is in a small range.

  In the above flow rate measurement method, it is preferable that the heat generation driving pulse has a waveform in which the slope of the rising portion is gentler than the slope of the falling portion.

  The flow rate measuring device according to the present invention includes a passage through which a fluid can flow, a heat generation source disposed in the vicinity of the passage, and a first temperature disposed in the vicinity of the passage on the upstream side of the heat generation source. A detection element, a second temperature detection element disposed in the vicinity of the passage downstream of the heat generation source, the heat generation source generates heat in pulses, and the first temperature detection element and the second temperature detection element A control calculation unit that detects the temperature of the fluid by the temperature detection element and obtains the flow rate of the fluid flowing through the passage based on the information on the temperature change of the fluid. The control calculation unit includes a procedure for causing the heat source to generate heat in a pulsed manner with a heat generation drive pulse, a procedure for detecting an increase in fluid temperature due to the heat generation drive pulse with the first temperature detection element, A temperature detecting element for detecting a temperature rise of the fluid due to the heat generation driving pulse, a first peak value which is a maximum value of the temperature rise detected by the first temperature detecting element, and the second A first flow rate calculation procedure for determining the flow rate of the fluid based on the second peak value that is the maximum value of the temperature rise detected by the temperature detection element is executed.

  In the above flow rate measuring apparatus, it is preferable that the first flow rate calculation procedure is to obtain a flow rate of the fluid based on a ratio between the first peak value and the second peak value.

  In the above flow rate measuring device, it is preferable that the first temperature detection element and the second temperature detection element are arranged at a position equidistant from the heat generation source in the flow direction of the passage. .

  Further, in the above flow rate measuring device, the control calculation unit includes a second flow rate calculation procedure for obtaining a fluid flow rate by a time difference between an application time of the heat generation drive pulse and a time at which the second peak value is detected; A procedure for obtaining a flow rate as a measurement result using the first flow rate calculation procedure and the second flow rate calculation procedure may be executed.

  Further, in the above flow rate measuring device, it has a third temperature detection element disposed in the vicinity of the passage on the downstream side of the heat generation source, and the control calculation unit is configured by the third temperature detection element, A procedure for detecting a temperature rise of the fluid due to the heat generation drive pulse, a time when the second peak value is detected, and a third peak value which is a maximum value of the temperature rise detected by the third temperature detecting element A second flow rate calculation procedure for obtaining a fluid flow rate based on a time difference from the detected time, and a first flow rate calculation procedure and a procedure for obtaining a flow rate as a measurement result using the second flow rate calculation procedure are executed. Can be.

  Further, in the above flow rate measuring apparatus, as a procedure for obtaining the flow rate as the measurement result, the first flow rate calculation procedure and the second flow rate calculation procedure are switched and applied according to the range of the flow rate. be able to. In that case, the application range of each of the first flow rate calculation procedure and the second flow rate calculation procedure is such that the application range of the first flow rate calculation procedure is the application range of the second flow rate calculation procedure. It is preferable that the flow rate is in a small range.

  In the above flow rate measuring device, two temperature detection elements are disposed upstream of the heat generation source in the vicinity of the passage, and two temperature detection elements are downstream of the heat generation source. Is preferably arranged.

  In the above flow rate measuring device, it is preferable that the four temperature detection elements are arranged at positions symmetrical to the heat generation source in the fluid flow direction of the passage.

  In the above flow rate measuring device, it is preferable that the heating drive pulse has a waveform in which the slope of the rising portion is gentler than the slope of the falling portion.

  Since this invention is comprised as mentioned above, there exist the following effects.

  Since the fluid is heated in pulses and the flow rate is calculated from the peak value of the fluid temperature rise at two points on the passage, the flow rate can be measured with high accuracy even in the extremely small flow rate region. For example, a very small flow rate of 1 mL per day can be accurately measured. The heating of the fluid is a pulse-like heat generation, so the heat influence on the fluid is small and the fluid is not altered by heat. In addition, power consumption for flow rate measurement can be reduced, and even in battery-powered devices, it is possible to perform long-time flow rate measurement using a battery as a power source. Further, since the flow rate can be measured without waiting until the fluid reaches a steady state after the fluid is heated, the fluid flow rate can be measured in real time with high accuracy. For this reason, it is also possible to use it as a flow rate monitor for infused drugs or the like in an implantable artificial organ.

  Since the flow rate is calculated from the ratio of the peak values of the temperature rise of the fluid, the flow rate in the extremely small flow rate region can be measured with high accuracy by a simple calculation. For this reason, the calculation time required for calculating the flow rate is small, and real-time measurement is possible.

  Since the first temperature detection element and the second temperature detection element are arranged at the same distance from the heat source in the flow direction of the passage, the side wall of the passage can be obtained by taking the ratio or difference of the peak values of the temperature rise. The influence of the heat transmitted by the above can be eliminated, and the flow rate can be measured with high accuracy.

  Since the fluid is heated in pulses and the time difference between the times when the temperature reaches the maximum value is measured on the downstream side of the fluid, it can be measured accurately even when the fluid velocity is very small. It can be measured accurately. The calculation of the flow rate due to the time difference can obtain a stable result in a relatively large flow rate range even in a minute flow rate, and can obtain a stable measurement result that is hardly affected by the temperature of the fluid, the temperature of the external environment, or the like.

  Since the first flow rate calculation procedure and the second flow rate calculation procedure are switched and applied according to the range of the flow rate, high accuracy is achieved by using an optimal calculation method with little error in a wide range of flow rates. And stable measurement results can be obtained.

  Since two temperature detection elements are arranged upstream and two temperature detection elements are arranged downstream of the heat source, the temperature detection result by the temperature detection element is used regardless of the flow direction. The fluid flow rate can be calculated. Also, the direction of fluid flow can be detected.

  Since the four temperature detection elements are arranged at positions symmetrical to the heat source in the flow direction of the fluid in the passage, the flow rate can be measured under the same conditions regardless of the flow direction of the passage. . Moreover, the thermistor which takes a peak ratio can be suitably changed according to the flow velocity and the heat conduction conditions of the fluid. For this reason, various setting changes can be performed according to the measurement conditions, and it becomes possible to perform flow rate measurement with a high degree of freedom of setting and a wide measurable range.

  The heating drive pulse applied to the heating source has a gentler waveform at the rising edge than the falling edge, so the electrical shock at the start of driving applied to the heating source element is reduced, and the lifetime of the heating source element Can be extended.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an overall configuration of a flow rate measuring apparatus according to the present invention. The flow sensor unit 10 is a sensor that detects a flow rate, and a linear passage 11 through which a fluid to be measured flows is provided inside the flow sensor unit 10. In FIG. 1, the flow sensor unit 10 is represented by a cross section parallel to the fluid flow direction of the passage 11. The flow sensor unit 10 detects the flow rate (flow velocity) of the fluid flowing through the passage 11.

  In the flow rate sensor unit 10, thermistors 1 to 5 are sequentially arranged at positions near the passage 11 along the flow direction of the passage 11. The central thermistor 3 is used as a heat source for heating the fluid. The thermistors 1, 2, 4, and 5 disposed on the upstream side and the downstream side of the flow with respect to the thermistor 3 are used as temperature detection elements for detecting the temperature of the fluid. Glass, plastic, or the like can be used as the main body material of the flow sensor unit 10. As the main body material, a substance having as low a thermal diffusivity as possible and a low thermal conductivity is preferable.

  The passage 11 has a rectangular cross-sectional shape and is surrounded by four planar side walls. Thermistors 1 to 5, which are planar thin film thermistors, are disposed on one of the four side walls. Here, the thermistors 1 to 5 are arranged at regular intervals (for example, 0.5 mm pitch) at a constant distance. The thermistors 1 to 5 are not necessarily arranged at equal intervals, but it is desirable that other thermistors be arranged symmetrically with respect to the central thermistor 3 in the flow direction. With such an arrangement, it is possible to measure under the same conditions whether the flow is in the direction of the arrow in FIG. 1 or the flow in the opposite direction.

  If the thermistors 1 to 5 are arranged so as to be flush with the surface of the side wall as illustrated, the thermistors 1 to 5 do not hinder the flow. However, the thermistors 1 to 5 may be arranged so that the surface of the thermistors 1 to 5 protrudes into the passage 11. Conversely, the surfaces of the thermistors 1 to 5 may be arranged to retract into the side wall of the passage 11 by a predetermined amount. Furthermore, the thermistors 1 to 5 may be supported by a support in the passage, and the thermistors 1 to 5 may be located in the fluid. In the present invention, the vicinity of the passage 11 includes all of the above arrangements.

  Note that four thermistors as temperature detection elements are not necessarily arranged, and one (thermistor 1 or thermistor 2) on the upstream side and two (thermistors 4 and 5) on the downstream side may be arranged. . Alternatively, one may be arranged on the upstream side and one on the downstream side. In the case of one on the upstream side and one on the downstream side, it is desirable that the thermistors 2 and 4 or the thermistors 1 and 5 be arranged symmetrically with respect to the heat source. .

  In FIG. 1, the thermistors 1 to 5 are arranged on the same side wall. However, the thermistors may be arranged on different side walls. For example, the heat source and the temperature detection element may be disposed on opposite side walls facing each other. Further, the thermistors 1 to 5 may be alternately arranged on the opposite side wall. Furthermore, either one or both of the heat source and the temperature detection element may be disposed on opposite side walls, or may be disposed so as to surround the entire circumference of the flow path.

  When the thermistors 1 to 5 are arranged on the same side wall as shown in FIG. 1, the manufacturing process is relatively simple and the manufacturing is easy, so that the manufacturing cost can be reduced. Moreover, the homogeneity of the manufacturing quality of the flow sensor unit can be improved. In addition, when a fluid has electroconductivity, it is necessary to cover the fluid side surface of the thermistors 1 to 5 with an electrical insulating film. It is desirable that this electrical insulating film has a good thermal conductivity.

  Further, in order to efficiently conduct heat from the heat source to the fluid, it is effective to reduce the size of the passage 11 in the direction (vertical direction in FIG. 1) perpendicular to the surface of the side wall where the heat source is disposed. It is. Moreover, although the flow of the fluid to be measured can be measured even by turbulent flow, if the flow is laminar, more stable flow rate measurement can be performed. Therefore, the fluid flow is desirably laminar. In order to make the fluid flow laminar, it is effective to reduce the vertical dimension (depth) of the passage 11.

  As an example of the dimension of the passage, the depth of the passage 11 (vertical direction dimension in FIG. 1) is 36 μm, and the width of the passage 11 (dimension in the vertical direction in FIG. 1) is 500 μm. Thus, the flow of fluid can be made into a laminar flow by making the flow path depth smaller than the flow path width. Further, the efficiency of heat conduction from the heat source to the fluid when the heat source is arranged on a wide wall surface can be improved.

  The central thermistor 3 is connected to a heat generating drive unit 61 in the drive detection unit 6. Then, a heat generation drive pulse, which is a pulsed drive current, is supplied from the heat generation drive unit 61 to the thermistor 3 to cause the thermistor 3 to generate pulsed heat generation. The flow rate can be sufficiently measured even when the pulse width of the heat generation drive pulse is 100 msec or less. The generated heat is transmitted to the fluid flowing in the passage 11, and the temperature rises in a predetermined pattern. The temperature rise of the fluid is detected by the thermistors 1, 2, 4, and 5, and the flow rate of the fluid is obtained from the temperature rise pattern.

  Here, the thermistor 3 is used as the heat source, but a normal heating resistor can be used as the heat source, and a heat generating element other than the resistor can be used as the heat source. However, it is preferable to use a thermistor element as the heat source. In the case of the thermistor element, the temperature of the heat source can be easily monitored.

  The thermistors 1, 2, 4, and 5 are connected to a temperature detection unit 62 in the drive detection unit 6. The temperature detector 62 can detect the temperature of the fluid at each position from the resistance values of the thermistors 1, 2, 4, and 5. The heat generation drive unit 61 and the temperature detection unit 62 of the drive detection unit 6 are connected to the control calculation unit 9. The control calculation unit 9 sends a control signal for heat generation driving to the heat generation driving unit 61 and also receives a detection signal from the temperature detection unit 62 and obtains the flow rate of the fluid flowing in the passage 11 by the detection signal.

  A display unit 7 and an input unit 8 are connected to the control calculation unit 9. The input unit 8 is used for the operator to input data necessary for the measurement start instruction and the flow rate calculation such as the cross-sectional area of the passage 11. Characters and images can be displayed on the display unit 7, and flow rate measurement data is displayed on the display unit 7 as numerical values, graphs, or the like.

  Next, the measurement principle of the flow rate measurement according to the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing a drive current waveform and a detected temperature waveform of the flow rate sensor unit 10. As shown in FIG. 2A, the thermistor 3 is supplied with a pulsed drive current (heat generation drive pulse) from the heat generation drive unit 61 to cause pulsed heat generation. As shown in the figure, the end time of the drive current is T0.

  It is assumed that the fluid to be measured flows in the passage 11 in the direction of the arrow in FIG. At this time, the temperature of the thermistor 3 changes as shown in FIG. Further, the temperature d1 of the fluid detected by the thermistor 4 on the downstream side of the thermistor 3 changes as shown in FIG. That is, the temperature d1 indicates the peak value p1 that is the maximum value of the temperature rise at time T1. Further, the temperature d2 of the fluid detected by the thermistor 5 further downstream changes as shown in FIG. That is, the temperature d2 indicates the peak value p2 that is the maximum value of the temperature rise at time T2.

  Here, the time difference t1 from the end time T0 of the drive current to the time T1 at which the fluid temperature d1 detected by the thermistor 4 exhibits the peak value p1 changes corresponding to the fluid flow velocity V. Similarly, the time difference t2 from the end time T0 of the drive current to the time T2 at which the fluid temperature d2 detected by the thermistor 5 exhibits the peak value p2 also changes corresponding to the fluid flow velocity V. The time difference Δt (= T2−T1 = t2−t1) from the time T1 to the time T2 similarly changes corresponding to the fluid flow velocity V.

  As described above, since the time difference Δt changes corresponding to the fluid velocity V, the fluid velocity can be obtained by detecting the time difference Δt. The relationship between the fluid velocity V and the time difference Δt may be measured in advance by experiment, or these relationships may be derived by a calculation formula. For example, assuming that the sum of the fluid velocity V and the heat propagation velocity is detected as the propagation velocity of the peak value between the thermistor 4 and the thermistor 5, the velocity V may be obtained therefrom. And since the cross-sectional area of the channel | path 11 of the flow sensor part 10 is known, a flow volume can be calculated from the flow velocity of a fluid.

  In this way, since the time difference at which the downstream temperature of the fluid reaches the maximum value is measured, if a time at which the temperature rise at the two points reaches the maximum value can be accurately measured, a minute amount of flow rate can also be accurately measured. In the case of a minute flow rate, the time of the maximum temperature point can be determined by obtaining a temperature gradient from a change in temperature measurement value with respect to a minute time difference and obtaining a time at which this temperature gradient changes from positive to negative.

  Although the flow rate of the fluid can be obtained from the time difference t1 or the time difference t2, it is preferable to obtain the flow rate of the fluid from the time difference Δt. When the flow rate is obtained by the time difference Δt, the time difference between the time T1 and the time T2 can be taken to cancel the influence of the time delay of heat transfer from the thermistor 3 to the fluid and the effect of heat diffusion from the heated fluid. Therefore, the measurement accuracy can be improved.

  When the flow rate is obtained from the time difference t1, the time difference between the application end time T0 of the heat generation drive pulse and the time T1 at which the detection value by the thermistor 4 indicates the peak value p1 is obtained, but the application start time is used instead of the application end time. Other application times such as pulse application center time can also be used. Further, as another method for obtaining the time difference t1, immediately after the application of the heat generation driving pulse, the thermistor 3 is switched to temperature detection immediately to obtain the peak value of the temperature rise, and the time indicating the peak value and the downstream peak value time You may obtain | require the time difference with T1. The same applies to the time difference t2.

  FIG. 3 shows the result of measuring the time difference Δt by actually flowing a fluid through the flow sensor unit 10. Ultrapure water is used as the fluid, and the passage 11 of the flow sensor unit 10 has a rectangular shape with a cross section of 500 μm × 36 μm, and the thermistors 1 to 5 are arranged at equal intervals of 0.5 mm pitch. A pulse driving current having a pulse width of 40 msec was supplied to the thermistor 3 to generate heat in pulses. At this time, the time difference Δt between the time T1 when the temperature d1 of the fluid detected by the thermistor 4 exhibits the peak value p1 and the time T2 when the temperature d2 of the fluid detected by the thermistor 5 exhibits the peak value p2 is measured. . In the graph of FIG. 3, the horizontal axis represents the flow rate of the fluid, and the vertical axis represents the time difference Δt.

  Black dots in the graph of FIG. 3 indicate actual measured values. The solid line is an approximate curve chosen to approximate the measured value. This approximate curve is obtained by determining each coefficient of a straight line that minimizes an error from an actual measurement value by the least square method or the like. As shown in the figure, when the flow rate is approximately 5 [μL / min] or more, the measured value substantially matches the approximate curve. However, in the region where the flow rate is smaller than 5 [μL / min], the difference between the measured value and the approximate curve is large. Moreover, the measured value itself also shows a large variation.

  The reason for this will be described below. When the flow rate becomes extremely small, the flow velocity becomes very small. Therefore, the time differences t1 and t2 shown in FIGS. 2C and 2D become large, and the peak values p1 and p2 become small. That is, the measurement curve of the temperature d1 detected by the thermistor 4 and the measurement curve of the temperature d2 detected by the thermistor 5 become a flat curve having a large spread. Therefore, it becomes difficult to obtain the time T1 indicating the peak value p1 and the time T2 indicating the peak value p2, and the error in measuring these times increases. Therefore, there is a problem that variations in measured values as shown in FIG. 3 occur.

  Therefore, in the present invention, in order to solve such problems and to enable highly accurate flow measurement even in a region where the flow rate is extremely small, the time T1 indicating the peak value p1 and the time T2 indicating the peak value p2 are measured. Instead, the flow rate is obtained from the peak value p1 and the peak value p2 itself. Further, by obtaining the flow rate from the peak value p1 and the peak value p2 itself as in the present invention, it is possible to measure the flow rate with high accuracy even when heat conduction through the side wall of the passage cannot be ignored. For this reason, even when the thermal insulation such as the side wall of the passage is relatively small, the present invention can perform the flow rate measurement with high accuracy.

  As shown in FIGS. 2C and 2D, the temperature rise of the fluid detected by the thermistors 4 and 5 shows peak values p1 and p2, respectively. The peak values p1 and p2 change corresponding to the flow rate of the fluid. Further, when the ratio between the peak value p1 and the peak value p2 is taken, this ratio also changes corresponding to the flow rate of the fluid. In FIG. 2, the peak values p1 and p2 are detected by the thermistors 4 and 5, but the temperature detection elements may be arranged separately on the upstream side and the downstream side of the heat generation source. Even if the ratio of the peak value of the temperature rise detected by the temperature detection elements on the upstream side and the downstream side of the heat generation source is taken, this ratio similarly changes corresponding to the flow rate of the fluid.

  FIG. 4 shows the result of measuring the ratio of the peak value of the temperature rise by actually flowing the fluid through the flow rate sensor unit 10. Various measurement conditions are the same as those described in FIG. However, the peak value q1 detected by the thermistor 2 and the peak value q2 detected by the thermistor 4 are measured as the peak value of the temperature rise. And the ratio (q2 / q1) of these peak values is made into the vertical axis | shaft of the graph of FIG. 4 as temperature peak ratio. The horizontal axis of the graph is the flow rate of the fluid.

  Black dots in the graph of FIG. 4 indicate actual measured values. The solid line is an approximate curve (hereinafter referred to as a calibration curve) selected so as to approximate the measured value. This calibration curve is obtained by determining each coefficient of a quadratic curve (parabola) that minimizes an error from an actual measurement value by the least square method or the like. By appropriately selecting each coefficient of the quadratic curve, one that substantially matches the measured value can be obtained. In the range of the flow rate shown in the figure, the measured value almost coincides with the calibration curve. From this measurement result, it can be seen that if the ratio of the peak values of temperature rise measured by the two temperature detecting elements is obtained, the flow rate of the fluid can be obtained from the ratio.

  The calibration curve in FIG. 4 can be obtained by using, for example, the least square method, but is not limited to the least square method, and can be obtained by any other function approximation method.

  Based on the results shown in FIG. 4, in the present invention, the thermistor 3 that is a heat generation source performs pulsed heat generation, detects the ratio of the peak values of the temperature rise detected by the thermistor 2 and the thermistor 4, and The flow rate of the fluid is obtained from the ratio value. The fluid flow rate can also be obtained from the ratio of peak values of temperature rise detected by the thermistor 1 and the thermistor 5.

  These peak values of temperature rise can be obtained with high accuracy even if the temperature measurement curve is flat. Therefore, even in a very small flow rate region where the flow rate is smaller than 5 [μL / min], it is possible to obtain a highly accurate measurement result with a small measurement error and to obtain the fluid flow rate with high accuracy. It becomes.

  FIG. 5 is a diagram showing a state in which the flow rate is measured by the flow rate measuring device of the present invention. The flow sensor unit 10 is disposed and attached between the flow passages 12, 12 such as pipes through which the fluid to be measured flows. The passage 11 and the flow passage 12 of the flow sensor unit 10 are connected so as not to leak. The flow rate sensor unit 10 is connected to the drive detection unit 6, and the drive detection unit 6 is connected to the control calculation unit 9. The control calculation unit 9 is configured by a computer, and the control calculation unit 9 detects the ratio of the peak value of the temperature increase and the time difference Δt as described above, and obtains the flow rate of the fluid. A display unit 7 and an input unit 8 are connected to the control calculation unit 9.

  FIG. 6 is a block diagram illustrating a configuration of the control calculation unit 9. The control arithmetic unit 9 is provided with a CPU 90 for performing various data processing, and a memory 92 such as a ROM or a RAM is connected to the CPU 90 via a bus 91. The CPU 90 operates according to programs and data stored in the memory 92. The memory 92 includes an OS (operating system) that is a basic program, a flow rate calculation program 921 that calculates the flow rate of the fluid according to the temperature rise of the fluid detected by the thermistors 1, 2, 4, and 5, A measurement control program 922 for performing heating control of the thermistor 3 and reading control of temperature detection values by the thermistors 1, 2, 4, 5, a display control program for displaying characters and images on the display unit 7, and the like are stored. ing.

  The memory 92 also includes data indicating the relationship between the fluid velocity V and the time difference Δt, data indicating the relationship between the fluid velocity V and the peak value ratio of the temperature rise, cross-sectional area data of the passage 11, and the like. It is remembered. Further, the control arithmetic unit 9 is provided with a fixed disk device 93. The fixed disk device 93 stores various programs and data to be loaded into the memory 92, flow rate measurement data in time series, and the like.

  A display unit 7 for displaying characters and images is connected to the control arithmetic unit 9 via an interface circuit 94, and an input unit 8 for an operator to input data and the like is connected via the interface circuit 95. Connected. A CRT, a liquid crystal display panel or the like can be used as the display unit 7, and a keyboard or a pointing device can be used as the input unit 8. The display unit 7 displays flow rate measurement data as numerical values, graphs, or the like. The input unit 8 is used for inputting data necessary for calculating a flow rate such as a cross-sectional area of the passage 11.

  Further, a clock circuit 96 such as a clock circuit that constantly updates and holds current time data or a timer circuit capable of measuring a time difference is connected to the control arithmetic unit 9. The clock circuit 96 can measure the time difference Δt and the like. In addition, a drive detection unit 6 (see FIG. 1) and a flow rate sensor unit 10 are connected to the control calculation unit 9 via an interface circuit 97. The drive detection unit 6 includes a heat generation drive unit 61 that supplies a heating current to the thermistor 3 of the flow rate sensor unit 10 and a temperature detection unit 62 that detects the temperature by the thermistors 1, 2, 4, and 5.

  A pulse current is supplied from the heat generating drive unit 61 to the thermistor 3 at regular intervals to cause pulsed heat generation. Further, the temperature of the fluid is detected by supplying a resistance value detection current to the thermistors 1, 2, 4, and 5. The control calculation unit 9 measures, for each thermistor, the peak value (maximum value) of the temperature rise of the fluid and the time when the temperature rise shows the peak value. Then, the ratio of the temperature rise peak value as described above and the time difference Δt are obtained, and the fluid velocity V and the flow rate are calculated from the measured values by the flow rate calculation program 921. In this way, the flow rate of the fluid passing through the passage 11 can be continuously measured at regular intervals.

  In the flow rate sensor unit 10, thermistors 1, 2, 4, and 5 as temperature detection elements are arranged symmetrically with respect to the thermistor 3 that is a heat generation source. That is, the thermistors 1 to 5 are arranged along the passage 11 at equal intervals in the flow direction. For this reason, even if the flow direction is opposite to the arrow direction in FIG. 1, the fluid flow rate can be calculated using the temperature detection results of the thermistors 1, 2, 4, and 5. Also, the direction of fluid flow can be detected. Therefore, even if the flow direction is temporarily reversed (for example, pulsating flow), the total discharge flow rate is measured by integrating the forward flow rate and the reverse flow rate in consideration of the direction. Can do.

  In order to accurately measure the flow rate in a pulsating flow, it is necessary that the intervals in the flow direction of the thermistors 1 to 5 as the heat generation source and the temperature detection element be equal to or less than a certain pitch. For example, when the cross section of the passage 11 is a rectangular shape having a size of 500 μm × 36 μm, in order to accurately measure a pulsating flow with a volume discharged in one cycle of 0.1 μL, the pitch of the thermistors 1 to 5 is set to 1. It is necessary to be 85 mm or less. However, this is a numerical example of the pitch when the sampling frequency of flow measurement is 10 times the pulsation frequency. In the case of measuring a pulsating flow having a smaller one-cycle discharge volume, it is necessary to arrange it at a smaller pitch or less proportional to the volume.

  Furthermore, since the thermistors 1 to 5 of the flow sensor unit 10 are all equivalent elements, any thermistor can be used as a heat generation source, and any thermistor can be used as a temperature detection element. Therefore, in some cases, it is also possible to measure a thermistor that is not at the center position as a heat source. For this reason, various setting changes can be performed according to the measurement conditions, and flow rate measurement with a high degree of freedom can be performed.

  In addition, as a flow sensor part, things other than said structure may be sufficient. That is, the temperature detection elements do not have to be arranged symmetrically with respect to the heat generation source, and may not be arranged at equal intervals. Further, the heat source and the temperature detection element may not all be equivalent elements.

  FIG. 7 is a flowchart showing the processing contents of the flow rate calculation program 921 and the measurement control program 922. In FIG. 7, the processing contents of these programs are combined and displayed in one flowchart in order to improve the overall perspective of the measurement operation.

  When the measurement operation is started, first, in step 100, the temperature of the fluid before heating is detected by the thermistors 1, 2, 4, and 5. That is, a current for resistance value detection is supplied to the thermistors 1, 2, 4, and 5, and the temperature of the fluid at each position is detected by each resistance value. Next, in step 101, a pulsed heating current is supplied from the heat generating drive unit 61 to the thermistor 3 to cause the thermistor 3 to generate a pulsed heat. Next, in step 102, a resistance value detection current is passed through the thermistors 1, 2, 4, and 5 to detect a temperature rise of the fluid at each position. Next, in step 103, the peak value of the temperature rise in the thermistors 2 and 4 on the upstream side and the downstream side of the heat source (thermistor 3) is detected, and the ratio of these peak values is obtained.

  Next, in step 104, the time when the temperature rise reaches the peak value in the thermistors 4 and 5 is obtained, and the above-described time difference Δt is obtained. Next, in step 105, it is determined whether or not the time difference Δt is smaller than a preset value. When the time difference Δt is smaller than the set value, the process proceeds to step 107, and the fluid flow rate is calculated from the time difference Δt. For the calculation of the flow rate, the relationship between the time difference and the flow rate as shown in FIG. 3 is stored, and the flow rate corresponding to the measured value of the time difference may be obtained from this relationship.

  In step 105, when the time difference Δt is equal to or larger than the set value, the process proceeds to step 106, and the flow rate of the fluid is calculated from the ratio of the peak value of the temperature rise. For the calculation of the flow rate, the relationship between the ratio of the peak value of the temperature rise and the flow rate as shown in FIG. 4 is stored, and the flow rate corresponding to the measured value of the ratio of the peak value of the temperature rise may be obtained from this relationship. .

  The set value in step 105 is set in advance in order to switch which of the two calculation methods is applied as the flow rate calculation method. That is, in an extremely small flow rate region where the flow rate is, for example, 5 [μL / min] or less, the method of calculating the flow rate from the time difference Δt is not used because the error becomes large. In such an extremely small flow rate region, a method of calculating the fluid flow rate from the ratio of peak values of temperature rise is used.

  This set value can be set to 0.3 sec, for example, under the conditions shown in FIG. In FIG. 3, the time difference of 0.3 sec corresponds to about 10 [μL / min] in flow rate. In this case, when the flow rate is 10 [μL / min] or less, the flow rate is calculated from the ratio of peak values of temperature rise, and when the flow rate is larger than 10 [μL / min], the flow rate is calculated from the time difference Δt. In this way, it is possible to use an optimal calculation method with little error in accordance with the flow rate range.

  After the flow rate is calculated in step 106 or step 107, the calculation result is output in step 108. That is, the calculation result of the flow rate is displayed on the display unit 7 by a numerical value, a graph, or the like. As described above, one measurement operation is completed. Such a measurement operation is repeated at regular intervals.

  In the flowchart of FIG. 7, when the flow rate is 10 [μL / min] or less, the flow rate is calculated from the ratio of peak values of temperature rise, and in the region where the flow rate is greater than 10 [μL / min], the flow rate is calculated from the time difference Δt. However, the present invention is not necessarily limited to this. Each calculation method may be used in an appropriate area.

  In addition, when the flow rate is calculated from the time difference Δt, if the flow rate becomes larger than a certain level, the value of the time difference Δt itself becomes small, thereby reducing the measurement accuracy. For example, in FIG. 3, when the flow rate is increased to about 25 [μL / min], the value of the peak time difference becomes too small and it becomes difficult to measure with high accuracy. The upper limit value of the measurable flow rate depends on the interval between the thermistors. The measurement example in FIG. 3 is when the thermistor interval is 0.5 mm.

  On the other hand, when the flow rate is calculated from the ratio of peak values, it has been confirmed that measurement is possible even at 100 [μL / min]. Therefore, when the flow rate is about 20 [μL / min] or more, it is preferable to calculate the flow rate from the ratio of peak values. As described above, by using the respective calculation methods in combination in an appropriate region, the measurable flow rate range is increased, and the measurement accuracy can be improved.

  FIG. 8 is a diagram showing a modification of the waveform of the heat generation drive pulse applied to the thermistor 3. In addition to the rectangular wave pulse shown in FIG. 8A, the thermistor 3 that is a heat generation source may be applied with heat generation drive pulses having various waveforms as shown in FIGS. 8B to 8E. A heat generation driving pulse having an arbitrary waveform other than this may be applied. FIG. 8B shows a triangular wave heat generation drive pulse, and the slopes of the rising and falling portions of the drive current are substantially equal.

  FIG. 8C shows a trapezoidal heat generation drive pulse, and the slopes of the rising and falling portions of the drive current are substantially equal. FIG. 8D shows a heat generation drive pulse of a modified trapezoidal wave, and the slope of the rising portion of the drive current is gentler than the slope of the falling portion. FIG. 8E shows a heat generation drive pulse having a curved chevron waveform, and the drive current changes into a smooth curve.

  In the waveforms shown in FIGS. 8B to 8E, the rising slope of the drive current is gentler than that of the rectangular wave pulse in FIG. 8A, and the electric shock at the start of driving applied to the element of the heat source is small. Become. For this reason, the lifetime of the heat source element can be extended. Moreover, the shorter the pulse width, the shorter the measurement cycle. Therefore, as shown in FIG. 8D, a deformed trapezoidal wave in which the slope of the rising portion is gentler than the slope of the falling portion, a modified triangular wave having the same slope, or the like is preferable.

  It should be noted that the slope of the rising portion of the heat generation drive pulse is desirably set to an optimum value in consideration of the load applied to the heat source element and the measurement cycle. In FIG. 8, the heat generation drive pulse is shown by the waveform of the drive current, but the same applies to the waveform of the drive voltage.

  As described above, according to the flow rate measuring method and apparatus of the present invention, the fluid is heated in pulses, and the flow rate is calculated from the ratio of the peak values of the fluid temperature rise at two points on the passage. The flow rate can be measured with high accuracy even in the extremely small flow rate region. For example, a very small flow rate of 1 mL per day can be accurately measured. In addition, the fluid is pulsed and the time difference between the time when the temperature reaches the maximum value is measured on the downstream side of the fluid, so it can be measured accurately even when the fluid velocity is very small. The flow rate can also be accurately measured.

  The heating of the fluid is a pulse-like heat generation, so the heat influence on the fluid is small and the fluid is not altered by heat. In addition, power consumption for flow rate measurement can be reduced, and even in battery-powered devices, it is possible to perform long-time flow rate measurement using a battery as a power source. In addition, since the flow rate can be measured without waiting until the fluid reaches a steady state after the fluid is heated, the flow rate of the fluid can be measured in real time with high accuracy. For this reason, it is also possible to use it as a flow rate monitor for infused drugs or the like in an implantable artificial organ.

  In addition, the present invention is applied to fluid flow measurement in various wide ranges such as portable artificial organs, portable chemical solution injection devices, portable fuel cells, general water supply devices, and fuel monitors for combustion devices. be able to. In addition, the present invention is particularly suitable for a minute flow rate, but can naturally be applied to a flow rate measurement that is not a minute flow rate. When the flow rate of the measurement channel is large, a bypass channel having a small flow rate can be provided, the flow rate in the bypass channel can be measured, and the overall flow rate can be monitored.

  In the above embodiment, a thermistor is used as a heat source. However, a normal heat generating resistor can be used as the heat source, and a heat generating element other than the resistor (for example, the Peltier effect). It is also possible to use a heating element utilizing the above. In this embodiment, the fluid is heated by heat conduction from the heating element, but the fluid may be heated by radiant heat by radiation such as infrared rays.

  As the temperature detection element, a resistance temperature detector other than the thermistor, a thermocouple element, a thermopile, or the like can be used. In the case of a thermistor, a high temperature sensitivity is advantageous, and in the case of a resistance temperature detector, manufacture is easy. As the thermistor, in addition to a thermistor mixture, a thermistor can be used. As the temperature detection element, any element having temperature sensitivity such as a silicon single crystal can be used.

  Further, the relationship between the ratio of the peak value of the temperature rise of the fluid at two points on the passage and the flow rate of the fluid is expressed as a calibration curve as shown in FIG. This calibration curve is not easily influenced by the temperature of the fluid before heating and the ambient temperature around the passage (the temperature of the passage member, the ambient temperature, etc.) and can measure the flow rate with high accuracy. Strictly speaking, however, the calibration curve in the present invention slightly changes under the influence of the fluid temperature and the environmental temperature as described above. This change in the calibration curve appears as a change in each coefficient of the mathematical expression representing the curve of the calibration curve.

  Immediately before each cycle of flow measurement, measure the fluid temperature and environmental temperature, and use a calibration curve that matches those temperatures to eliminate the influence of fluid temperature and environmental temperature and further improve the accuracy of flow measurement. be able to. Specifically, calibration curves (coefficients of mathematical expressions) for various fluid temperatures and environmental temperatures are measured and stored in advance, and appropriate coefficients are used according to the temperature immediately before the measurement. Alternatively, the correction amount of the flow rate for each temperature may be stored, and the correction amount corresponding to the temperature immediately before the measurement may be added.

  In addition, the temperature detection element of the present invention can be used as it is for the measurement of the fluid temperature immediately before the measurement. For the measurement of the environmental temperature immediately before the measurement, an additional temperature sensor or the like can be provided and the sensor can be used.

  Further, the calibration curve in the present invention is slightly affected by radiant heat from the surroundings in addition to the fluid temperature and the environmental temperature. For this reason, it is possible to improve measurement accuracy by blocking radiation from the surroundings. Alternatively, the influence of the radiant heat may be measured in advance, and the influence of the radiant heat may be corrected at the time of measurement in the same manner as the correction based on the temperature.

  Further, the flow rate is calculated from the ratio of the peak value of the temperature rise of the fluid at two points on the passage. Even if the difference between the peak values of the temperature rise at the two points is taken, the difference between the peak values is calculated. The flow rate can be calculated. Furthermore, another calculation may be performed on the peak value of the temperature rise at the two points to obtain an amount corresponding to the flow rate.

  Further, in order to switch the flow rate calculation method, the time difference Δt is switched in comparison with the set value, but it may be switched by the ratio of the peak value of the temperature rise or the like. If the measured value indicates the magnitude of the flow rate, the flow rate calculation method can be switched depending on the measured value.

  Further, although the flow rate calculation method is switched according to the flow rate, the flow rate may be basically calculated from the ratio of peak values of temperature rise without switching the calculation method. In that case, since there is a possibility of being affected by the temperature of the fluid, the temperature of the external environment, etc., calibration can be performed using the result of calculating the flow rate from the time difference Δt in order to eliminate such influence. This is because the time difference Δt is hardly affected by the temperature of the fluid, the temperature of the external environment, or the like. For example, the flow rate is calculated from the time difference Δt at a constant time period, and the calibration is performed by changing various constants of the function indicating the relationship between the ratio of the peak value and the flow rate so as to coincide with the calculation result. It can be carried out.

  In addition, it is preferable to perform such calibration in a flow rate range in which a flow rate calculation result based on the time difference Δt can be obtained with high accuracy. For example, in the measurement example of FIG. 3 (the thermistor interval is 0.5 mm), the flow rate can be calculated with high accuracy from the time difference Δt in the range of 10 to 20 [μL / min]. Therefore, the flow rate is calculated from the time difference Δt while the fluid in the flow rate range is flowing, and the constants of the function indicating the relationship between the peak value ratio and the flow rate are changed so as to match the calculation result. That's fine.

  Such calibration can eliminate the influence of the temperature of the fluid, the temperature of the external environment, and the like. In addition, the influence of the specific heat, viscosity, etc. of the fluid can be eliminated. Further, when an electrical insulating film is formed on the fluid side surface of each thermistor, the influence of the electrical insulating film can be eliminated. When such calibration is performed, the flow rate measured by the present invention is a volume flow rate.

  It should be noted that the embodiment disclosed above and the modifications thereof are merely examples, and do not limit the scope of the present invention.

  According to the present invention, it is possible to accurately measure the flow rate of a fluid using a heat generation source and a temperature detection element, and to measure a minute amount of flow rate at a high accuracy in real time even when the flow rate of the fluid is extremely slow. it can. For this reason, the present invention includes, for example, a flow monitor of an infusion medicine in an implantable artificial organ, a portable artificial organ, a portable chemical injection device, a portable fuel cell, a general water supply device, a combustion device. It can be applied to fluid flow measurement in a wide range such as a fuel monitor.

It is a figure showing the whole flow measuring device composition of the present invention. It is a figure which shows the drive current waveform and detected temperature waveform of a flow sensor part. It is a figure which shows the result of having measured the time difference of the temperature rise peak value with the flow sensor part. It is a figure which shows the result of having measured the ratio of the temperature rise peak value by the flow sensor part. It is a figure which shows the state at the time of the flow measurement of the flow measuring device of this invention. It is a block diagram which shows the structure of a flow volume calculating part. It is a flowchart which shows the processing content of a flow volume calculation program and a measurement control program. It is a figure which shows the modification of the waveform of the heat generation drive pulse applied to a heat source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1-5 ... Thermistor 6 ... Drive detection part 7 ... Display part 8 ... Input part 9 ... Control calculating part 10 ... Flow rate sensor part 11 ... Passage 12 ... Flow path 61 ... Heat generation drive part 62 ... Temperature detection part 90 ... CPU
91: Bus 92 ... Memory 93 ... Fixed disk device 96 ... Clock circuit 97 ... Interface circuit

Claims (17)

A heat generation source (3), a first temperature detection element (2) disposed upstream of the heat generation source (3), and a second disposed downstream of the heat generation source (3) A flow rate measuring method in a fluid passage (11) comprising a temperature detecting element (4) of
A procedure for causing the heat source (3) to generate heat in a pulse form by a heat generation drive pulse;
Detecting a temperature rise of the fluid due to the heat generation drive pulse by the first temperature detection element (2);
A procedure for detecting a temperature rise of the fluid due to the heat generation drive pulse by the second temperature detection element (4);
A first peak value that is a maximum value of the temperature rise detected by the first temperature detection element (2) and a second peak value that is a maximum value of the temperature rise detected by the second temperature detection element (4). A flow rate measurement method comprising: a first flow rate calculation procedure for obtaining a fluid flow rate based on a peak value. The flow rate measuring method according to claim 1,
The first flow rate calculation procedure is a flow rate measurement method in which a flow rate of a fluid is obtained by a ratio between the first peak value and the second peak value. The flow rate measuring method according to any one of claims 1 and 2,
The first temperature detection element (2) and the second temperature detection element (4) are arranged at equidistant positions from the heat generation source (3) in the flow direction of the passage (11). Flow rate measurement method. It is a flow measurement method given in any 1 paragraph of Claims 1-3,
A second flow rate calculation procedure for obtaining a fluid flow rate by a time difference between an application time of the heat generation drive pulse and a time at which the second peak value is detected;
A flow rate measuring method comprising: obtaining a flow rate as a measurement result using the first flow rate computation procedure and the second flow rate computation procedure. It is a flow measurement method given in any 1 paragraph of Claims 1-3,
A third temperature detection element (5) is disposed downstream of the heat generation source (3) in the passage (11),
Detecting a temperature rise of the fluid due to the heat generation drive pulse by the third temperature detection element (5);
The fluid flow rate is determined by the time difference between the time when the second peak value is detected and the time when the third peak value, which is the maximum value of the temperature rise detected by the third temperature detection element (5), is detected. A second flow rate calculation procedure to be obtained;
A flow rate measuring method comprising: obtaining a flow rate as a measurement result using the first flow rate computation procedure and the second flow rate computation procedure. A flow rate measuring method according to any one of claims 4 and 5,
The procedure for obtaining the flow rate as the measurement result is a flow rate measurement method in which the first flow rate calculation procedure and the second flow rate calculation procedure are switched and applied in accordance with a flow rate range. The flow rate measuring method according to claim 6,
The application range of each of the first flow rate calculation procedure and the second flow rate calculation procedure is greater in the application range of the first flow rate calculation procedure than in the application range of the second flow rate calculation procedure. A flow rate measurement method that is a small range of flow rate. It is a flow measurement method given in any 1 paragraph of Claims 1-7,
The heat generation drive pulse is a flow rate measuring method in which the slope of the rising portion has a gentler waveform than the slope of the falling portion. A passage (11) through which fluid can flow;
A heat source (3) disposed in the vicinity of the passage (11);
A first temperature detection element (2) disposed in the vicinity of the passage (11) upstream of the heat source (3);
A second temperature detection element (4) disposed in the vicinity of the passage (11) downstream of the heat source (3);
The heat source (3) generates heat in pulses, and the temperature of the fluid is detected by the first temperature detection element (2) and the second temperature detection element (4). A control calculation unit (9) for obtaining a flow rate of the fluid flowing through the passage (11),
The control calculation unit (9)
A procedure for causing the heat source (3) to generate heat in a pulse form by a heat generation drive pulse;
Detecting a temperature rise of the fluid due to the heat generation drive pulse by the first temperature detection element (2);
A procedure for detecting a temperature rise of the fluid due to the heat generation drive pulse by the second temperature detection element (4);
A first peak value that is a maximum value of the temperature rise detected by the first temperature detection element (2) and a second peak value that is a maximum value of the temperature rise detected by the second temperature detection element (4). A flow rate measuring device for executing a first flow rate calculation procedure for obtaining a flow rate of a fluid from a peak value. The flow rate measuring device according to claim 9, wherein
The first flow rate calculation procedure is a flow rate measurement device for obtaining a flow rate of a fluid based on a ratio between the first peak value and the second peak value. It is a flow measuring device given in any 1 paragraph of Claims 9 and 10,
The first temperature detection element (2) and the second temperature detection element (4) are arranged at equidistant positions from the heat generation source (3) in the flow direction of the passage (11). Flow measurement device. It is a flow measuring device given in any 1 paragraph of Claims 9-11,
The control calculation unit (9)
A second flow rate calculation procedure for obtaining a fluid flow rate by a time difference between an application time of the heat generation drive pulse and a time at which the second peak value is detected;
A flow rate measurement device that executes a procedure for obtaining a flow rate as a measurement result using the first flow rate calculation procedure and the second flow rate calculation procedure. It is a flow measuring device given in any 1 paragraph of Claims 9-11,
A third temperature detection element (5) disposed in the vicinity of the passage (11) downstream of the heat source (3);
The control calculation unit (9)
Detecting a temperature rise of the fluid due to the heat generation drive pulse by the third temperature detection element (5);
The fluid flow rate is obtained from the time difference between the time when the second peak value is detected and the time when the third peak value, which is the maximum value of the temperature rise detected by the third temperature detecting element (5), is detected. A second flow rate calculation procedure;
A flow rate measurement device that executes a procedure for obtaining a flow rate as a measurement result using the first flow rate calculation procedure and the second flow rate calculation procedure. It is a flow measuring device given in any 1 paragraph of Claims 12 and 13,
The procedure for obtaining the flow rate as the measurement result is to switch and apply the first flow rate calculation procedure and the second flow rate calculation procedure according to the flow rate range,
The application range of each of the first flow rate calculation procedure and the second flow rate calculation procedure is greater in the application range of the first flow rate calculation procedure than in the application range of the second flow rate calculation procedure. A flow rate measuring device that has a small flow rate range. It is a flow measuring device given in any 1 paragraph of Claims 9-14,
In the vicinity of the passage (11), two temperature detection elements are disposed upstream of the heat generation source (3), and two temperature detection elements are disposed downstream of the heat generation source (3). Is a flow measuring device. The flow rate measuring device according to claim 15,
The four temperature detecting elements are flow rate measuring devices arranged at positions symmetrical to the heat source (3) in the fluid flow direction of the passage (11). It is a flow measuring device given in any 1 paragraph of Claims 9-16,
The heat generation drive pulse is a flow rate measuring device in which the rising portion has a gentler waveform than the falling portion.

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