JP6587129B2 - Flowmeter - Google Patents

Description

  The present invention relates to a flow meter, and in particular, a field that requires pressure and flow measurement with a small and light pressure flow meter, for example, a medical pressure flow meter such as an artificial heart, a plant such as petroleum, petrochemical, and chemical. Related to fluids and gases flowing through pipes, cleaning water for bottles, wafer and substrate cleaning fluids, flowmeters for chemicals, etc., or those used for measuring resistance in pipelines to detect clogging of filters in pipelines .

Conventionally, various types of industrial flowmeters, such as vortex flowmeters, resistance flowmeters, and float flowmeters, are known. Therefore, measurement of blood pressure and blood flow volume is important, and the practical application of a small blood flow meter that can be embedded is desired, and a flow meter with an ultralight and simple measurement method is required.
Therefore, the present inventors have focused on flowmeters using centrifugal force and centripetal force generated in fluid by bent pipes (see Patent Documents 1 and 2), and developed flowmeters that are miniaturized using bent pipes. Patent applications have already been filed (see Patent Documents 3 to 5).
In addition, the present inventors have developed and filed a flow meter that uses at least two thin portions of different thicknesses in a straight pipe that is further downsized without using a bent pipe (Patent Document 6). reference).

The flow meter of Patent Document 6, which is a previous patent application by the present inventors, will be described below.
The flow meter of Patent Document 6 includes a conduit through which a fluid flows, at least two thin portions having different thicknesses provided on a pipe wall of a straight pipe portion of the conduit, and a strain gauge attached to the thin portion. And a flow meter for measuring the flow rate in the pipe line provided with an arithmetic processing unit for processing the output of the strain gauge, wherein the thickness of the thin wall portion is influenced by the flow rate in addition to the static pressure. The calculation processing means has a relationship between the output difference between the strain gauge affixed to the thin part on the thin side and the strain gauge affixed to the thin part on the thick side and the flow rate obtained in advance by a calibration test. A calibration formula is stored, and the flow rate is obtained using the calibration formula from the output difference between the strain gauge attached to the thin portion on the thin side and the strain gauge attached to the thin portion on the thick side. .
For example, as shown in FIG. 6, in a pipeline through which fluid flows, when a thin wall is provided on the pipe wall and a strain gauge is attached to the thin wall and the output is measured, the thickness of the thin wall is reduced. Since the effect of the flow rate is measured by the strain gauge in addition to the internal pressure, a strain gauge is attached to the thin wall parts with different thicknesses provided on the tube wall, and the flow meter measures the flow rate in the pipeline from the output difference The calibration formula representing the relationship between the output difference and the flow rate is obtained in advance by calibration.

To make the explanation easy to understand, the measurement principle will be described in accordance with an actual measurement example. As shown in FIG. 7, the straight pipe has an inner diameter of 12 mmφ, a wall thickness of 1 mm, and a length of 40 mm. The straight pipe is made of titanium alloy with excellent biocompatibility. As a strain measurement part, thin processing of 6 mm in diameter was performed so that local strain was easily generated at positions 20 mm from both ends, and two thin parts were provided. The thickness on the thin side of the two thin portions as the strain measurement portion is 0.11 mm, and the thickness on the thick side is 0.18 mm. Two strain gauges with a gauge length of 0.2 mm are affixed to the strain measurement unit by the two-active gauge method, and the strain in the circumferential direction of the tube caused by the fluid in the conduit is measured.
As shown in FIG. 8, the fluid circuit actually measured by incorporating a flow meter using a straight pipe is a closed circuit simulating an extracorporeal circulation system including a blood pump, a reservoir, a flow path resistance, and a straight pipe. The pressure in the closed circuit was measured using a pressure gauge at the inlet and outlet of the straight pipe. The flow rate in the closed circuit was measured using an ultrasonic flow meter at the blood pump outlet.
A static pressure measurement test was carried out using the straight pipe made of the titanium alloy. In the static pressure measurement test, first, the circuit is closed and the number of rotations of the pump is increased, so that the static pressure in the circuit is reduced from 0 to 150 [mmHg] to 25 [ mmHg] in increments. The results of the static pressure measurement test are shown in FIG. In the graph of FIG. 9, the horizontal axis is the pressure [mmHg] measured by the pressure gauge, the vertical axis is the strain gauge output [μST], and the ● plot is the thinner part (thin side: thickness 0) .11 mm) of the strain gauge output, and the plot of ▲ is the output of the strain gauge of the thinner part (thick side: 0.18 mm thickness) of the thicker one.
Two calibration formulas are obtained for the relationship between the strain measured from the strain gauge and the static pressure measured by the pressure gauge.
P _S = α _A × ε _0.11S + β _A (1A)
P _S = α _B × ε _0.18S + β _B (1B)
Here, P _S represents the strain of the thin portion of the strain and the thick side of the thin portion of the thin wall side by it and, ε _0.11S and epsilon _0.18S each static pressure indicates static pressure. α _A , β _A , α _B and β _B are constants determined by the static pressure measurement test.

Next, a measurement test is performed by flowing a fluid through the fluid circuit and changing the flow rate.
FIG. 10 shows the result of pressure-converting the output of the strain gauge at the thin-walled portion on the thin-walled side when the fluid is flowed based on the above formula (1A). In FIG. 10, the horizontal axis is the pressure [mmHg] measured with a pressure gauge, the vertical axis is the pressure conversion value [mmHg], and the plots are as follows: ■: 1 [L / min], ◆: 2 [L / min] , ▲: 3 [L / min], x: 4 [L / min], *: 5 [L / min], ● ● when the flow rate is 0 [L / min] The measured pressure and the pressure conversion value on the vertical axis are the same).
From FIG. 10, it was found that when the fluid flows, the pressure conversion value calculated from the strain gauge output of the thin portion on the thin side increases as the flow rate increases. Therefore, the pressure P _A in the pressure of the thin portion that is increased by the flow rate and P _D at flow generator is represented by the following formula (2).
P _A = P _S + P _D = α _A × (ε _0.11S + ε _0.11D ) + β _A (2)
Here, ε _0.11D indicates the distortion of the thin portion on the thin side increased by the flow rate.
FIG. 11 shows the result of pressure-converting the output of the strain gauge on the thin-walled portion on the thick-wall side when a fluid is flowed based on the above equation (1B). In FIG. 11, the horizontal axis represents the pressure [mmHg] measured with a pressure gauge, the vertical axis represents the pressure conversion value [mmHg], and each plot mark represents the difference in flow rate as in FIG. , ■: 1 [L / min], ◆: 2 [L / min], ▲: 3 [L / min], x: 4 [L / min], *: 5 [L / min] ● indicates a reference when the flow rate is 0 [L / min] (the pressure measured by the pressure gauge on the horizontal axis is the same as the pressure converted value on the vertical axis).
From FIG. 11, it was found that when the fluid flows, the pressure conversion value calculated from the strain gauge output of the thin portion on the thick side decreases as the flow rate increases. Therefore, if the pressure of the thin wall portion reduced by the flow rate is P _DB , the pressure P _B when the flow rate is generated is expressed by the following equation (3).
P _B = P _S −P _DB = α _B × (ε _0.18S −ε _0.18D ) + β _B (3)
Here, ε _0.18D indicates the distortion of the thin portion on the thick side reduced by the flow rate.
In order to exert the influence of the flow rate as shown in FIG. 10 and FIG. 11, it is desirable to make the thin part thinner than the thickness (about 0.5 mm) used for the diaphragm of a normal pressure gauge. It is preferable to reduce the thickness of the thin portion as much as possible.

Therefore, the differential pressure ΔP, which is the difference between the subtraction of the pressure conversion value of the output of the strain gauge on the thin wall side from the pressure conversion value of the output of the strain gauge on the thin wall side when the fluid is flowed, is From the above equations (2) and (3), the following equation (4) is obtained.
P _A -P _B = P _DA + P _DB
= Α _A × (ε _0.11S + ε _0.11D ) −α _B × (ε _0.18S −ε _0.18D ) + C (4)
Here, C is a constant. Further, when the outputs of the thin-walled strain gauge and the thick-walled strain gauge are arranged as ε _0.11 and ε _0.18 , respectively, the above equation (4) becomes the following equation (5).
ΔP = P _A −P _B = α _A × ε _0.11 −α _B × ε _0.18 + C (5)
By taking the difference between the two strain gauges from this equation, pressure compensation is performed and only the flow rate term remains. Therefore, if the relationship between the difference between the two strain gauges and the flow rate is previously calibrated and obtained as a calibration formula (for example, see the graph shown in FIG. 12 described later), the difference between the two strain gauges is measured and the calibration formula is obtained. The flow rate can be obtained by fitting.

In FIG. 12, in order to obtain the flow rate Flow using this relationship, the circuit resistance is changed to change the pipe internal pressure from 25 [mmHg] to 150 [mmHg], and the measurement result when the flow rate is changed by the pump. Indicates. In FIG. 9, the vertical axis represents the difference (ΔP) obtained by subtracting the pressure converted value of the output of the strain gauge on the thin wall side from the pressure converted value of the output of the strain gauge on the thin wall side, and the horizontal axis represents It is the flow rate [L / min] measured with a commercially available flow meter, and the plot marks are the pipe internal pressure ●: 25 [mmHg], ■: 50 [mmHg], ◆: 75 [mmHg], ▲: 100 [mmHg], X: 125 [mmHg], *: 150 [mmHg]. From the graph of FIG. 9, the difference (ΔP) obtained by subtracting the pressure converted value of the output of the strain gauge on the thin wall side from the pressure converted value of the output of the strain gauge on the thin wall side and the flow rate is the circuit resistance. Regardless of the size, one-to-one correspondence can be confirmed, and if the graph of FIG. 12 is obtained as a calibration formula by performing a calibration test in advance, the pressure conversion value of the strain gauge output of the thin part on the thin side The flow rate can be obtained by applying the difference value obtained by subtracting the pressure converted value of the output of the strain gauge at the thin wall portion on the thick wall side to the calibration equation.
If the graph of FIG. 12 is stored in the storage means or the like, it can be used as a calibration formula as it is, but the graph of FIG. 12 can be expressed by an approximate formula and the flow rate Flow can be calculated using the approximate formula as a calibration formula. .

Japanese Patent Laid-Open No. 04-276519 Japanese Unexamined Patent Publication No. 09-79881 JP 2007-218775 A JP 2009-150671 A Japanese Patent Application No. 2014-543220 (International Application PCT / JP2013 / 077423) Japanese Patent Application No. 2014-259224

An implantable artificial heart is used as a support for cardiac function in patients with severe heart failure and as a bridge to heart transplantation. Measuring the blood flow volume of the artificial heart to obtain the driving status of the implantable artificial heart and the physiological information of the patient to whom the artificial heart is applied is a measure of the patient's survival rate and QOL (Quality of Life). It is important for improvement. Currently, methods for measuring the blood flow of an artificial heart include a flow rate estimation method and a method using a commercially available flow meter such as an ultrasonic flow meter. The flow rate estimation method is a method for estimating the flow rate from the power consumption and the rotation speed of the artificial heart. Since the power consumption of the centrifugal artificial heart has a correlation with the flow rate, the flow rate estimation method can be applied. However, when a thrombus occurs in the artificial heart, the flow rate estimation becomes difficult. In an axial flow type artificial heart, power consumption has no correlation with the flow rate, and therefore it is difficult to estimate the flow rate. Commercially available flow meters include ultrasonic flow meters and electromagnetic flow meters. However, these commercially available flow meters are difficult to miniaturize because of the complicated measurement principle, and it is not easy to implant them together with an artificial heart. Therefore, there is a need for a blood flow meter that can be used regardless of the type of artificial heart and can be miniaturized. So far, mass flowmeters using bent tubes have been proposed as small and simple flowmeters, but it has been necessary to use bent tubes. The present inventors have previously proposed a flow meter using a straight pipe of Patent Document 6, but the measurement part that is a thin part on the thin side needs to be extremely thin so that the influence of static pressure and flow rate appears. However, there is a problem that the thinner the wall, the higher the sensitivity but the processing becomes difficult.
Therefore, the problem to be solved by the present invention is to improve the thin portion where the influence of static pressure and flow rate appears.

In order to solve the above-mentioned problems, the flowmeter of the present invention is affixed to a pipe line through which a fluid flows, at least two thin parts provided on a pipe wall of a straight pipe part of the pipe, and the thin part A flow meter for measuring the flow rate in the pipe line provided with a strain gauge and an arithmetic processing unit for processing the output of the strain gauge, wherein a minute protrusion is formed in the flow path inside the pipe line of the thin part on one side. The arithmetic processing means includes an output difference and a flow rate between a strain gauge attached to a thin portion having a fine protrusion obtained in advance by a calibration test and a strain gauge attached to a thin portion having no fine protrusion. A calibration equation representing the relationship is stored, and the flow rate is obtained from the output difference using the calibration equation.
Further, the present invention is characterized in that, in the flowmeter, the thin portion having the fine protrusion and the thin portion not having the fine protrusion are provided in the same cross section of the straight pipe portion.
Further, the present invention provides the above-described flowmeter, wherein the compensation strain gauge is provided with a thick thin portion in addition to the thin portion having the fine protrusion and the thin portion not having the fine protrusion, and is attached to the thin portion. The effect of disturbance is compensated by the output of.
In the above flow meter, the present invention is characterized in that a static pressure is measured from a flow rate obtained by using the calibration formula and an output of a strain gauge attached to the thin portion.
In the above flow meter, the present invention is characterized in that the pipe resistance is measured by dividing the measured static pressure by the flow rate.
Further, the present invention is characterized in that, in the above flow meter, the calibration formula is expressed using different approximate formulas in a low flow rate region and a high flow rate region.
Further, the present invention provides at least two thin wall portions having different thicknesses on a pipe wall of a straight pipe portion of a pipe through which a fluid flows, and a strain gauge is attached to the thin wall portion. A microprojection is provided in the flow path on the inside, and the output difference and flow rate between the strain gauge attached in advance to the thin part with microprotrusions and the strain gauge attached to the thin part without microprotrusions by a calibration test. A calibration equation that expresses the relationship between the strain gauge and the strain gage applied to the thin portion with no microprotrusions and the output difference between the strain gauge attached to the thin portion without microprotrusions is used. This is a flow rate measurement method for obtaining the flow rate in the pipeline.

In the present invention, it is possible to measure the flow rate with only a straight pipe without using a bent pipe, and therefore, an extremely compact flow meter can be realized, and a minute protrusion is formed in the flow path inside the pipe line of the thin part on one side. Since the influence of the static pressure and the flow rate appears greatly by providing the portion, it is not necessary to increase the sensitivity by ultra-thin processing as in the conventional patent document 6.
Moreover, it is possible to measure the static pressure inside the pipe line from the result of the flow rate measurement and the output of the strain gauge attached to the thin wall portion.
Further, the resistance in the pipe line (= static pressure / flow rate) can be obtained from the measurement result of the static pressure and the flow meter. For this reason, it is possible to detect abnormalities in the pipeline such as clogging or narrowing of the pipeline.
In the present invention, it is possible to realize a simple flow rate measuring method capable of measuring the flow rate in the pipe line with only a straight pipe without using a bent pipe.

FIG. 1 shows a cross-sectional view of a straight pipe type flow meter according to an embodiment of the present invention. A thin portion for flow rate measurement having a minute projection in a flow path and a thin wall for static pressure compensation having no minute projection. Have a part. Strain gauges are affixed to the two measurement units, and the circumferential strain generated in each measurement unit is measured. The flow rate can be obtained from the output difference between the strain gauges at the two thin portions. FIG. 2 is a diagram for explaining a main part of a manufacturing example of the flowmeter of the present invention. FIG. 3 shows a thin portion for flow rate measurement having a fine projection in the flow path in the manufacturing example of FIG. FIG. 4 shows a simulated circulation circuit that simulates a systemic circulation system by incorporating a production example of the flow meter of the present invention shown in FIG. The simulated circulation circuit includes a blood pump, a vinyl chloride tube, a blood reservoir, an acrylic pipe, and a straight pipe type flow meter. In the evaluation test, the flow rate was adjusted by the number of rotations of the pump, and the measurement accuracy was compared with a commercially available ultrasonic flow meter. FIG. 5 is a graph showing the results of the evaluation test. The horizontal axis of the graph shows the output difference between two strain gauges of the straight pipe flow meter, and the vertical axis shows a commercially available ultrasonic flow meter. Indicates the flow rate measured by. The graph of FIG. 5 is a calibration formula representing the relationship between the output difference and the flow rate obtained in advance. FIG. 6 shows an example of a conventional flowmeter using a straight pipe in Patent Document 6, in which thin portions having different thicknesses are provided at two locations on the same cross section of the straight pipe, and how to distort due to the flow rate. The flow rate is calculated using the difference. FIG. 7 is a diagram for explaining a main part of a flowmeter of Patent Document 6 using a conventional straight pipe manufactured for actual measurement. FIG. 8 is an overall external view of a flow meter of Patent Document 6 using a conventional straight pipe that has been actually measured, and a fluid circuit. FIG. 9 shows the static pressure measurement test results at a flow rate of 0 [L / min] measured with a flowmeter of Patent Document 6 using a conventional straight pipe, with the horizontal axis: pressure [mmHg] and the vertical axis: strain gauge output [ In the [μST] graph, the output of the strain gauge of the thin part on the thin side (thickness 0.11) is plotted with ●, and the thin part on the thick side (thickness of 0.1) is plotted with ▲. 18 is a plot of the strain gauge output of 18). FIG. 10 shows the result of pressure-converting the output of the strain gauge on the thin-walled portion on the thin-walled side when the fluid is flowed by the flow meter of Patent Document 6 using a conventional straight pipe, based on the equation (2). FIG. 11 shows the result of pressure-converting the output of the strain gauge on the thin-walled portion on the thick-wall side when the fluid is flowed with the flowmeter of Patent Document 6 using a conventional straight pipe, based on Equation (3). . FIG. 12 is a graph showing the relationship between the differential pressure and the flow rate (calibration equation) in the flow meter of Patent Document 6 using a conventional straight pipe.

  In Patent Document 6 previously proposed by the present inventors, the sensitivity can be increased by making the thin part on the thin side thinner, but the thinner it becomes, the more difficult it is to process the thin part. We had to consider the possibility of damage at the club. Therefore, as a result of diligent research by the present inventors, the influence of static pressure and flow rate appears greatly by providing a minute projection in the flow path inside the duct of the thin part on one side instead of ultra-thinning. And at least two thin wall portions provided on the pipe wall of the straight pipe portion, a strain gauge affixed to the thin wall portion, and an arithmetic processing device for processing the output of the strain gauge In the flowmeter for measuring the flow rate in the pipe line provided with a micro projection provided in the flow channel inside the pipe line of the thin part on one side, the arithmetic processing means has a micro projection obtained in advance by a calibration test A calibration equation representing the relationship between the output difference between the strain gauge affixed to the thin-walled portion and the strain gauge affixed to the thin-walled portion not having the microprojections and the flow rate is stored, and from the output difference using the calibration equation A flow meter was developed to determine the flow rate in the pipeline.

A cross-sectional view of a straight pipe type flow meter which is an embodiment of the present invention is shown in FIG. In the figure, there are a thin portion for flow rate measurement having fine protrusions in the flow path and a thin portion for static pressure compensation having no fine protrusions. Strain gauges are affixed to the two measurement units, and the circumferential strain generated in each measurement unit is measured. The flow rate can be obtained from the output difference between the strain gauges at the two thin portions.
With reference to the description of the measurement principle of Patent Document 6 by the present inventors described in the above paragraphs 0003 to 0006, the equations (1) to (5) in the description can be expressed by subscripts of ε. By simply replacing “0.11” and “0.18” with “thin-walled portion having fine protrusions” and “thin-walled portion not having fine protrusions” of the present invention, equations (1) to (5) should hold as they are. I understand. Therefore, if the relationship between the flow rate and the difference between the two strain gauges of the “thin wall with micro-projections” and “thin wall without the micro-projections” is calibrated in advance and the calibration equation is obtained, the difference between the two strain gauges The flow rate can be obtained by measuring and applying to the calibration equation.

FIG. 2 is a diagram for explaining a main part of a production example of a straight pipe type flow meter according to the present invention, and FIG. In the production example, a straight tube made of a titanium alloy that can be used regardless of the type of the artificial heart and can be reduced in size is used as the flowmeter probe. The length of the straight pipe is 40 mm, and the inner diameter and the outer diameter are 12 mm and 14 mm, respectively. This flow meter was provided with two thin portions having a diameter of 6 mm and different thicknesses on both sides of a pipe outer wall 20 mm from both ends as a flow measurement unit and a static pressure compensation unit. The two thin portions were a thin portion with a thickness of 0.01 mm for flow rate measurement having fine protrusions in the flow path and a thin portion with a thickness of 0.75 mm for static pressure compensation without fine protrusions. A strain gauge is attached to each measurement unit, and the circumferential strain generated in the measurement unit is measured.
The flow rate measuring unit measures strain generated in the strain measuring unit by the static pressure and the flow rate, and the static pressure compensating unit measures strain generated in the strain measuring unit by the static pressure. The flow rate is measured from the output difference between the strain gauges of the flow rate measurement unit and the static pressure compensation unit.

  A simulated circulation circuit simulating the systemic circulation system of FIG. 4 was constructed to perform an evaluation test on the above-described production example of the flowmeter of the present invention. The simulated circulation circuit is composed of a blood pump, a tube made of vinyl chloride, a blood reservoir, an acrylic pipe, and the straight pipe type flow meter of the present invention. The pressure and flow rate in the simulated circulation circuit are adjusted by the channel resistance installed in the circuit. Tap water was used as the working fluid and the temperature was room temperature. The flow at the outlet of the blood pump was expected to be very turbulent, so there was a run-up section between the blood pump and the straight pipe flow meter, and a 1 m acrylic with a distance of about 80 times the inner diameter of the straight pipe flow meter. Connected with a pipe. The strain measured with the strain gauge attached to the straight pipe flowmeter was amplified about 20,000 times with a DC strain amplifier. Data measured by each measuring instrument is digitized by an AD card and is taken into a measuring personal computer at a sampling frequency of 100 Hz. In the evaluation test, the flow rate was adjusted by the number of rotations of the pump, and the measurement accuracy was compared with a commercially available ultrasonic flow meter.

The result of the evaluation test is shown in FIG. The horizontal axis of the graph indicates the output difference between two strain gauges of the straight pipe flow meter, and the vertical axis indicates the flow rate measured by a commercially available ultrasonic flow meter. The relationship between the strain gauge output difference and the flow rate changed at a flow rate of 2 L / min. Therefore, in order to calculate the flow rate, two calibration formulas were created at a flow rate of about 2 L / min. As a result of comparing the flow rate obtained from the calibration formula of the straight pipe type flow meter with the flow rate measured with a commercially available ultrasonic flow meter, it was found that the average measurement error was within 0.5 L / min.
A possible change in the flow velocity around the microprojection can be considered as a cause of the flow rate measurement by providing the microprojection. The dynamic pressure generated when the flow rate is generated varies depending on the fluctuation of the flow velocity. For this reason, it was considered that the strain amount of the strain measurement unit increased due to the dynamic pressure generated by the fluctuation of the flow velocity in the strain measurement unit provided with the minute projections. According to the present invention, it is possible to measure the flow rate using only a straight pipe without using a bent pipe. Therefore, it is considered that a blood flow meter that can be used regardless of the type of artificial heart and can be miniaturized can be realized.

  The flowmeter of the present invention is a field that requires pressure and flow measurement with a compact and lightweight pressure flowmeter. For example, it is used as a flow meter for medical pressure flowmeters such as artificial hearts, fluids and gases flowing through the piping of plants such as petroleum, petrochemicals, and chemicals, cleaning water for bottles, cleaning liquids for wafers and substrates, and chemicals. be able to.

Claims (6)

Processes the pipe through which fluid flows, at least two thin parts provided on the same cross-section pipe wall of the straight pipe part of the pipe, the strain gauge affixed to the thin part, and the output of the strain gauge A flow meter for measuring a flow rate in a pipe line equipped with an arithmetic processing unit,
Said one first thin portion of the thin portion is provided small collision outs in the conduit inside the flow path, the first thin portion obtained by the calibration test in advance to the arithmetic processing unit calibration equation representing the pasted the strain gauge and the other second output difference of the strain gauge was attached to the thin portion and the flow rate of the relationships among the thin portion are stored, said using said calibration equation A flow meter characterized by obtaining a flow rate from an output difference. 2. A thick third thin portion is provided in addition to the first and second thin portions, and the influence of disturbance is compensated by the output of a compensation strain gauge attached to the third thin portion. The flow meter described. The strain gauge sticking to the thin portion of the inner portion provided with at least two thin-walled portion in the tube wall of the same section of the straight pipe portion of the pipe in which the fluid flows, the pre Me calibration test of the thin portion one of pasted to the first thin portion having a small protrusion of the strain gauge and calibration equation representing the other of the second output difference of the strain gauge was attached to the thin portion and the flow rate of the relationships among the thin portion Asking
Flow rate and obtains the flow rate of the the output difference between the strain gauge and the second said strain gauge affixed to the thin portion adhered to the first thin portion, the conduit using the calibration equation Measurement method. 4. A thick third thin portion is provided in addition to the first and second thin portions, and the influence of a disturbance is compensated for by an output of a compensation strain gauge attached to the third thin portion. The flow rate measuring method described. The pipe resistance is measured by dividing a static pressure measured in advance from an output of the strain gauge attached to the first and second thin portions by the flow rate. 4. The flow rate measuring method according to 4. The flow rate measuring method according to claim 3, wherein the calibration formula uses different approximate formulas for a low flow rate region and a high flow rate region.

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