JP2005003678A - Flow measuring instrument, flow rate measuring instrument, and flow rate instrumentation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To find a proper method of correction factor setting in flow rate instrumentation that uses a two-pressure tube or wake flow differential pressure measuring tube, and to conduct accurate flow measurement by means of a simple system, and to provide a method using the correction factor setting. <P>SOLUTION: In this method, the bi-pressure tube 1 is used to measure both total pressure P1, produced by fluid flow at a total pressure pore 11 and wake flow pressure P2, produced by fluid flow at a wake flow pressure pore 12, in obtaining flow measurement values of a measuring object fluid. Additionally, a flow measurement value arithmetic circuit 3 computes the flow measurement value of the measuring object fluid by compensating, such that it multiplies the value computed as a square root of the value twice P, the differential pressure between the wake flow pressure P2 and the total pressure P1 divided by mass density of the fluid, by the reciprocal of the substantial fill factor for a channel 4, the value of substantial opening area obtained by deducing the two-pressure tube 1 interrupted cross section from the total cross section as a stream tube of the channel 4 and then divided by the total cross section as the correction factor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a flow rate measurement device, a flow rate measurement device, and a flow rate measurement method that accurately measure the flow rate or flow rate of a fluid using a simple method.

  Known techniques for accurately measuring the flow velocity of fluids such as liquids and gases using a simple measurement device include flow velocity measurement methods using pitot tubes and flow rate measurement methods using orifices and venturi tubes. ing.

  The Pitot tube calculates the dynamic pressure, which is the difference between the total pressure (total pressure) of the fluid to be measured and the static pressure, and calculates the pitot to the square root of the value obtained by dividing twice the dynamic pressure by the fluid density. This is used to calculate the flow velocity value (measurement value of the flow velocity) of the fluid by performing calibration (calibration or correction) by multiplying the so-called Pitot tube coefficient k inherent to the tube, and is used in various wide fields. . The Pitot tube coefficient k is used when measuring the flow velocity and flow rate of fluid passing through the Pitot tube used in a so-called shroud such as a conduction path or a wind tunnel (in a shroud). It is known that it is influenced by the distance from the wall surface to the position where the Pitot tube is arranged.

  More specifically, the pitot coefficient k becomes smaller as it approaches the wall surface, for example, by various experiments conducted from the necessity of measuring an accurate flow velocity during the wind tunnel experiment, for example, at the center of the wind tunnel It is known that as the distance from the wall surface becomes sufficiently long like the position, the distance approaches 1. In addition, a so-called total pressure hole (also referred to as a total pressure hole) is provided at the longitudinal end of the Pitot tube. In many cases, the static pressure hole is provided on the cylindrical side surface of the Pitot tube. The static pressure hole is affected by the acceleration and deceleration of the flow at the tip of the pitot tube as the position where the static pressure hole is provided is only a short distance from the tip of the pitot tube. For this reason, it is known that it is desirable to provide the static pressure hole at a position separated by a sufficiently long distance from the tip of the Pitot tube, such as a position separated by a distance of 10 times or more the diameter of the Pitot tube. ing.

  In addition, in the flow rate measurement method using an orifice or a venturi pipe, the flow rate is obtained from the pressure difference before and after the orifice or the venturi pipe is used to intentionally increase / decrease the pressure in the flow to be measured. I have to. Also in this case, the flow rate coefficient α is obtained in advance by experiments or the like, and the theoretical flow rate value is corrected using the α to obtain a flow rate measurement value. For example, in the case of a JIS standard orifice, the flow coefficient α is set to a value of α = 0.60 when provided near the pipe inlet, and α = 0.60 to 0.80 when provided at the middle or outlet. It is experimentally known to be good. More specific numerical values can be appropriately set for each orifice based on experiments or the like. The Venturi tube is almost the same as the orifice.

  By the way, with the conventional Pitot tube as described above, it is possible to measure the flow velocity or flow rate for a predetermined flow in one direction, but it is not possible to measure the flow in the opposite direction. Further, with respect to the orifice or the venturi tube, it was practically possible to measure the flow in one predetermined direction.

  In particular, in the case of the conventional pitot tube, the total pressure hole is provided so as to face the flow. For example, mist (water droplets or oil droplets such as condensation) and dust are mixed in the fluid to be measured. If this is done, it may block the total pressure hole and prevent accurate measurement from continuing.

  Therefore, the present inventor opens a hole facing the flow of the fluid to be measured flowing through the conduction path, and measures the so-called total pressure generated by the flow of the fluid at that position, and the flow of the fluid. In the opposite direction to the opposite direction, using a double pressure pipe that opens to face the downstream side of the flow and has a wake pressure hole that measures the pressure of the fluid at the opening position as the wake pressure, A flow measuring device and a flow measuring method for measuring the flow value of the fluid to be measured based on the differential pressure between the total pressure and the wake pressure measured by the double pressure pipe were proposed. According to the flow measuring device and the flow measuring method, there is a possibility that even if mist (water droplets or oil droplets such as condensation) or dust is mixed in the fluid to be measured, it may block the total pressure hole. This eliminates the need for continuous accurate flow measurement.

  According to the flow rate measuring device and the flow rate measuring method, since the double pressure tube is symmetric in the front-rear direction, the flow rate can be accurately and symmetrically measured in either the forward or reverse flow in the conduction path.

  However, since the flow measuring device and the flow measuring method are new, in practical use, what kind of correction coefficient and correction method can be used to make more accurate flow measurement possible. It was not confirmed. Also, considering the correction coefficient in the double pressure tube based on the analogy from the conventional Pitot tube, the double pressure tube is different from the conventional Pitot tube in which the longitudinal direction is arranged almost parallel to the flow to be measured. The usage is completely different as described above. For this reason, it is extremely difficult to analogize the correction method based on the analogy from the conventional Pitot tube. In addition, the conventional Pitot tube is generally used to measure the flow velocity value in wind tunnel experiments as described above, so the method of setting the correction coefficient corresponding to the distance from the wall surface of the wind tunnel is applied. The possibility that it may be possible can be immediately conceived. However, even in consideration of such a possibility, in the case of a double pressure tube, it may be considered that it is desirable to provide a total pressure hole or a wake pressure hole in the center of the cross section of the conduit of the conduction path. However, it is completely unknown what method is used, in other words, what factor should be used to determine the correction coefficient.

  For this reason, the present inventor performs various experiments on the flow rate measurement using the double pressure tube, and is calculated by theoretical calculation based on the pressure difference actually measured using the double pressure tube (that is, correction coefficient = 1). It was confirmed what kind of error occurred in the measured flow rate value (calculated as follows) with respect to the true value of the flow rate. As a result, it was confirmed that the appearance was completely different from the error generated in the case of the conventional general Pitot tube. In addition, as a method for setting the correction coefficient of the double pressure tube, it was considered that the correction coefficient method in the case of flow rate measurement using an orifice or a venturi tube could not be applied. In other words, the correction coefficient setting method in the flow rate measurement using the double pressure tube cannot be analogized or diverted from the conventional flow rate measurement using the Pitot tube, the orifice, or the Venturi tube. It has been confirmed. Therefore, it is necessary to find an appropriate setting method of the correction coefficient in the flow rate measurement using the double pressure tube, but this is still an unsolved problem.

  In addition, including the conventional Pitot tube, if the angle of attack of the total pressure hole with respect to the fluid to be measured changes over a large angle of a certain degree or more (that is, when the flow becomes oblique with respect to the total pressure hole), the flow rate or Various experiments have confirmed that the measurement accuracy of the flow velocity may be significantly impaired.

That is, when performing flow rate measurement, a pitot tube or a double pressure tube having a total pressure hole is generally fixedly disposed in the conduction path so as to face the fluid flow. It is unlikely that the angle of attack will change. However, in reality, when a significant turbulent flow or vortex is generated in the flow in the conduction path, the angle of attack of the total pressure hole with respect to the substantial flow changes over a large angle of a certain degree or more. There is a risk of it.
Moreover, when a Pitot tube or a double pressure tube is applied to flow velocity measurement, the angle of attack of the total pressure hole with respect to the flow may change significantly. For example, assume that a Pitot tube or a double pressure tube is used to measure the airspeed of an aircraft. Since aircraft generally adjust lift by changing the angle of attack, the angle of attack of the total pressure hole in a Pitot tube or a double pressure tube installed in an aircraft flying in the atmosphere is, for example, ± 30 degrees or It may vary over such a significant angle. Thus, if the angle of attack of the total pressure hole with respect to the flow changes more than a certain level, there is a risk that accurate measurement of the flow velocity and airspeed with a Pitot tube or a twin pressure tube may be difficult. It was.

  The present invention has been made to solve such a problem, and its object is to find an appropriate setting method of a correction coefficient in flow rate measurement using a twin-pressure tube and to use a simple method using the setting of the correction coefficient. A flow rate measuring device, a flow velocity measuring device, and a flow velocity measuring method capable of performing accurate flow rate measurement by a simple method using a device, and capable of performing accurate flow rate measurement even when the angle of attack to the flow changes. It is to provide.

  In the first flow rate measuring device according to the present invention, a total pressure hole is provided in a direction opposite to the flow of the fluid to be measured flowing through the conduction path, and the total pressure generated by the flow of the fluid is measured at the total pressure hole. In addition, a wake pressure hole is provided at a position opposite to the direction directly facing the fluid flow, and a double pressure tube that measures the wake pressure generated by the fluid flow at the wake pressure hole, A pressure sensor that performs output corresponding to the total pressure and the wake pressure, and twice the value of the differential pressure between the total pressure and the wake pressure that is obtained based on the output from the pressure sensor. The value obtained by calculating the square root of the value divided by the density is subtracted from the total cross-sectional area as the flow pipe of the conduction path from the cross-sectional area blocked by the double pressure pipe, and the value of the substantial opening area is the total cross-sectional area. Multiply by the reciprocal of the substantial aperture ratio of the conduction path divided by Performing a correction comprising the calculation, and a flow rate value calculation circuit for calculating a flow rate value of the fluid.

  In the first flow rate measuring device according to the present invention, the total pressure hole is provided in a direction facing the flow of the fluid to be measured flowing through the conduction path, and at a position opposite to the direction facing the fluid flow. In obtaining the measurement value of the flow rate of the fluid to be measured using the double pressure pipe provided with the wake pressure hole, the total pressure generated by the total pressure hole directly facing the fluid flow and the fluid by the wake pressure hole Measures the wake pressure generated downstream from the flow of the fluid, and calculates the square root of the value obtained by dividing twice the value of the differential pressure by the fluid density to the flow tube of the conduction path. Correction by multiplying as a correction coefficient the reciprocal of the substantial opening ratio of the conductive path obtained by dividing the value of the substantial opening area obtained by subtracting the sectional area blocked by the twin pressure tube from the total sectional area as the total sectional area. By doing so, a more accurate flow rate measurement value can be obtained.

  The second flow rate measuring device according to the present invention is arranged in the conduction path, and the static pressure hole for measuring the static pressure of the flow of the fluid to be measured flowing through the conduction path and the direction facing the fluid flow are as follows. A wake differential pressure measuring pipe provided to open toward the opposite downstream side and provided with a wake pressure hole for measuring the wake pressure of the fluid at the opening position, and the wake differential pressure A pressure sensor that outputs an output corresponding to a differential pressure between the static pressure and the wake pressure measured by the measurement pipe, and is blocked by the wake differential pressure measurement pipe from a total cross-sectional area as a flow pipe of the conduction path The reciprocal number of the substantial opening ratio of the conduction path obtained by dividing the value of the substantial opening area obtained by subtracting the sectional area by the total sectional area is the value of the differential pressure value obtained based on the output from the pressure sensor. An operation of multiplying a value obtained by calculating a square root of a value obtained by dividing twice by the density of the fluid. Performing no correction, and a flow rate value calculation circuit for calculating a flow rate value of the fluid.

  In the second flow rate measuring device according to the present invention, the theoretical calculation regarding the downstream differential pressure measuring tube is performed using the differential pressure between the static pressure measured at the static pressure hole and the pressure measured at the downstream pressure hole. Calculate the theoretical flow rate of the fluid. Then, with respect to the theoretical flow rate value, a value obtained by dividing the value of the substantial opening area obtained by subtracting the cross-sectional area blocked by the wake differential pressure measuring pipe from the total cross-sectional area as the flow pipe of the conduction path by the total cross-sectional area. A more accurate flow rate measurement value can be obtained by performing a correction including an operation of multiplying the reciprocal of the substantial opening ratio of the passage as a correction coefficient.

  In the first flow measurement device or the second flow measurement device, the pressure sensor measures the total pressure measured at the total pressure hole or the static pressure measured at the static pressure hole and the wake pressure hole. The flow value calculation circuit has a function of performing an output individually corresponding to each of the wake pressures, and the flow rate value calculation circuit, as the above correction, has a ratio between the static pressure and the wake pressure or the total pressure and the wake flow. A function of correcting the density by multiplying the ratio of the pressure and the theoretical density of the fluid (or the value of the density of the fluid at rest) may be further included. In this way, in addition to reducing the measurement error by performing the correction using the basic correction coefficient as described above, the measurement error due to the density error is reduced, and finally It becomes possible to make the measurement accuracy of the obtained flow rate value higher.

  In addition, the flow value calculation circuit described above may further include a function of calculating the Reynolds number of the fluid based on the output from the pressure sensor and performing a correction corresponding to the calculated Reynolds number as the correction. Good. In addition to reducing the measurement error by performing the correction using the basic correction coefficient as described above by further performing the correction corresponding to the Reynolds number in this way, the Reynolds number of the fluid to be measured is set. By performing corresponding correction, it becomes possible to further increase the measurement accuracy of the finally obtained flow rate value.

  Here, the Reynolds number of the fluid to be measured is calculated from the measured differential pressure, and when the Reynolds number is less than the critical Reynolds number (generally, Re (th) = 2000), the calculated Reynolds number It is also possible to perform correction using.

  Also, calculate the Reynolds number of the fluid to be measured from the measured differential pressure, etc., and if the Reynolds number is greater than or equal to the critical Reynolds number, it corresponds to the conduction path and the double pressure pipe or the wake differential pressure measurement pipe. It is also possible to perform correction using a predetermined correction constant.

  Alternatively, the Reynolds number of the fluid to be measured is calculated from the measured differential pressure, and if the Reynolds number is less than the critical Reynolds number, correction is performed using the calculated Reynolds number. In the case of more than a few, it is also possible to perform correction using a predetermined correction constant corresponding to the conduction path and the double pressure pipe or the wake differential pressure measuring pipe.

  That is, when the Reynolds number of the fluid to be measured is less than the critical Reynolds number, the flow rate measurement value is strongly influenced by the Reynolds number at that time, and there is a tendency for a large error to occur to the true value. It is necessary to significantly change the correction coefficient corresponding to the Reynolds number. If the Reynolds number of the fluid to be measured is greater than or equal to the critical Reynolds number, the flow rate measurement tends to be hardly affected by the Reynolds number even if the Reynolds number changes. As a coefficient, it is possible to use a constant that is almost uniquely determined by the twin pressure tube or the wake differential pressure measuring tube and the dimension of the conduction path (representative dimension related to the flow).

  Here, the wake differential pressure measuring tube has a cylindrical outer shape, and a cylindrical cavity is formed inside, and the wake pressure hole is provided on the cylindrical side surface so as to communicate with the cavity. Crossing the fluid flow from the outside of the side wall of the conduction path to the inside of the conduction path so that the wake pressure hole faces the downstream side opposite to the direction facing the fluid flow. Is inserted and measures the downstream pressure of the fluid at the opening position on the downstream side of the cylindrical shape when viewed from the flow direction, and on the other hand, between the side wall of the conduction path and the cylindrical side surface. A gap having a predetermined size is provided as the static pressure hole, the static pressure of the fluid is measured by the static pressure hole, and the wake pressure is transmitted from the wake pressure hole to the pressure sensor through the cavity. The static pressure is set to be transmitted from the static pressure hole to the pressure sensor. Unisuru it is desirable aspect. By adopting such an aspect, the structure of the wake differential pressure measuring tube can be simplified.

  The flow velocity measuring device of the present invention is provided so as to open toward the downstream side opposite to the direction facing the fluid flow, and the static pressure hole for measuring the static pressure of the fluid flow to be measured. A wake differential pressure measuring pipe provided with a wake pressure hole for measuring the wake pressure of the fluid at the opening position, the static pressure and the wake pressure measured by the wake differential pressure measuring pipe, And a flow rate value measuring means for measuring the flow rate value of the fluid based on the differential pressure.

  Further, the flow velocity measuring method of the present invention is provided so as to open toward the downstream side opposite to the static pressure hole for measuring the static pressure of the fluid flow to be measured and the direction facing the fluid flow. And a wake pressure hole for measuring the wake pressure of the fluid at the opening position. The flow velocity value of the fluid is measured based on the differential pressure with respect to the wake pressure measured by.

  In the flow velocity measuring device or flow velocity measuring method of the present invention, the wake pressure of the fluid at the opening position is measured by the wake pressure hole provided so as to open toward the downstream side. Then, the flow velocity value of the fluid is measured based on the differential pressure between the flow pressure and the static pressure. According to the downstream pressure hole that opens toward the downstream side as described above, even if the angle of attack with respect to the fluid changes over a large angle such as 30 degrees or more, measurement disturbance due to the angle changes. It does not occur. This is a new finding confirmed by various experiments by the present inventors.

  According to the flow rate measuring device, the flow velocity measuring device, and the flow velocity measuring method of the present invention, an appropriate setting method of the correction coefficient in the flow rate measurement using the double pressure tube is found, and a simple apparatus using the setting of the correction coefficient is used. Thus, it is possible to perform accurate flow measurement by a simple method and to perform accurate flow measurement even if the angle of attack with respect to the flow changes.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram illustrating a schematic configuration of a flow rate measuring device according to a first embodiment of the present invention. This flow measuring device is composed mainly of a double pressure tube 1, a pressure sensor 2, and a flow value calculation circuit 3.

  The double pressure tube 1 has a cylindrical outer shape and is provided in a conduction path (conduction tube) 4 so as to cross the flow of fluid. On the cylindrical side surface, the flow of the fluid to be measured (gas or liquid) flowing through the conduction path 4 in the positive direction (here, as an example for convenience, the direction in which the fluid flows from left to right in FIG. A total pressure hole 11 is provided in a direction opposite to the direction). The total pressure generated by the fluid flow is measured at the total pressure hole 11. Further, there is provided a wake pressure hole 12 that is open toward the downstream side of the flow in the direction opposite to the direction facing the fluid flow in the forward direction. In the wake pressure hole 12, the pressure generated by the fluid flow at the position where the wake pressure hole 12 itself is provided is measured as the wake pressure.

  The total pressure P 1 picked up by the total pressure hole 11 in the double pressure tube 1 is transmitted to the pressure sensor 2 through the first path 111 provided in the double pressure tube 1. On the other hand, the wake pressure P2 picked up by the wake pressure hole 12 is transmitted to the pressure sensor 2 through the second path 121 provided in the double pressure tube 1. The total pressure hole 11 and the wake pressure hole 12 have reverse functions when the flow is reversed.

  The pressure sensor 2 outputs a voltage or an electric signal corresponding to the total pressure P1 and the wake pressure P2 transmitted from the twin pressure tube 1. FIG. 4 shows an actual example of the correlation between the differential pressure output from the pressure sensor 2 and the flow rate value (true value Qo). In this example, the differential pressure output changes in a quadratic function corresponding to the flow rate value Qo. As described above, the differential pressure output and the flow rate have a clear one-to-one correspondence relationship.

  The flow rate calculation circuit 3 calculates twice the value (2ΔP) of the differential pressure ΔP (= P1−P2) between the total pressure P1 and the wake pressure P2 obtained based on the output from the pressure sensor 2 as a measurement target. The cross-sectional area blocked by the double pressure tube 1 from the total cross-sectional area D as the flow tube of the conduction path 4 to a value obtained by calculating the square root √ (2ΔP / ρ) of the value (2ΔP / ρ) divided by the density ρ of the fluid The reciprocal (1 / of the substantial aperture ratio Kd (Kd = D / (D−d)) of the conduction path 4 obtained by dividing the value of the substantial aperture area (D−d) by subtracting d by the total cross-sectional area D. Multiply by Kd = (D−d) / D).

  Further, by calculating the ratio (P1 / P0) of the static pressure (P0) of the fluid to be measured and the total pressure (P1) to the value ρ0 of the density of the fluid at rest ((P1 / P0)). ) · Ρ0 = ρ1), the fluid density value ρ is corrected. The density value ρ1 subjected to the correction is used for the calculation for calculating the flow rate measurement value (Q).

  Further, the Reynolds number (Re) of the fluid is calculated based on the output from the pressure sensor 2, and correction corresponding to the calculated Reynolds number is performed. More specifically, when the Reynolds number of the fluid to be measured estimated by the pressure difference or the total pressure calculated based on the output from the pressure sensor 2 is less than the critical Reynolds number (generally Re-th = 2000) (Re <Re-th), correction is performed using the calculated Reynolds number. If the Reynolds number is greater than the critical Reynolds number (Re ≧ Re-th), it corresponds to the conduction path 4 and the double pressure tube 1. Then, correction using a predetermined correction constant is performed.

  That is, assuming that the correction coefficient for correction corresponding to this Reynolds number is F (Re) (where F is a function of Re), it is shown in FIG. 2 when the Reynolds number is less than the critical Reynolds number. A monotonically decreasing function as shown in FIG. In addition, FIG. 2 has shown the experimental result about the case where the diameter of the conduction path 4 is 16 [mm] and the diameter of the double pressure tube 1 is 3 [mm], 4 [mm], 6 [mm] FIG. 3 shows experimental results when the diameter of the conduction path 4 is 20 [mm] and the diameter of the double pressure tube 1 is 3 [mm], 4 [mm], and 8 [mm].

  Further, it can be clearly seen from FIGS. 2 and 3 that when the Reynolds number is greater than or equal to the critical Reynolds number, F (Re) is almost constant. More specifically, according to the examples shown in FIGS. 2 and 3, when the diameter of the conduction path 4 is 16 [mm], F (Re) = about 0.65, and the diameter of the conduction path 4 is 20. In the case of [mm], F (Re) = about 1.01.

  The calculation performed by the flow value calculation circuit 3 to calculate the flow rate measurement value Q including the correction as described above is expressed by a mathematical formula as shown in the block of the flow value calculation circuit 3 in FIG. Will be. That is, if the arithmetic expression is also written here, Q = F (Re) · (1 / Kd) · √ {(P0 / P1) · ΔP / ρ0}). By the calculation including such correction, the flow rate measurement value (Q) with less error can be calculated.

  The flow value calculation circuit 3 includes an input device 5 for inputting information on the total cross-sectional area as a flow tube of the conduction path 4 and the cross-sectional area blocked by the double pressure pipe 1. Further, when such information is input, a function of automatically calculating and updating a correction constant (F (Re)) used when the number of critical Reynolds numbers is exceeded is further provided.

  With such a function, the flow value calculation circuit 3 also uses the conduction path 4 and the double pressure tube 1 used at that time when performing flow measurement using the conduction path 4 and the double pressure pipe 1 having different dimensions and specifications. The correction coefficient corresponding to the fixed Reynolds number can be automatically changed to an appropriate value to always calculate an accurate flow rate measurement value (Q).

  Further, when information on the total cross-sectional area as the flow tube of the conduction path 4 and the cross-sectional area blocked by the twin pressure pipe 1 are input, the flow value calculation circuit 3 receives the reciprocal of the substantial aperture ratio ( A function of automatically calculating and updating 1 / Kd) is further provided.

  With such a function, the flow value calculation circuit 3 can also be used for the conduction path 4 and the double pressure tube 1 used at that time, even when performing flow measurement using the conduction path 4 and the double pressure pipe 1 having different dimensions and specifications. Correspondingly, it is automatically changed to an appropriate correction coefficient (Kd), and an accurate flow rate measurement value (Q) can always be obtained.

  Next, the background and results of various experiments conducted by the inventor in order to set the correction coefficient as described above will be described.

(1) If only the diameter d of the double pressure tube 1 is increased without changing the diameter D (also referred to as the diameter of the flow path) D of the conduction path 4, the differential pressure ΔP increases even when the same flow rate (true value Qo) flows. Turned out to be.
(2) When the diameter d of the conduction path 4 is increased without changing the diameter d of the double pressure tube 1, the measurable range with stable accuracy is expanded.
(3) When the fluid pressure (static pressure or total pressure) was increased without changing the diameter D of the conduction path 4 and the diameter d of the double pressure tube 1, the differential pressure ΔP decreased.

  Various considerations were made based on the results of these experiments. The above (2) “When the diameter of the conduction path 4 is increased without changing the diameter d of the double-pressure tube 1, the measurable range with a stable accuracy is expanded” is an increase in the cross-sectional area of the flow path. Along with this, it was speculated that the allowable flow rate of the conduction path 4 increased and the Reynolds number of the fluid increased.

  Here, when the correction coefficient is set to q and the diameter D of the double pressure tube 1 is increased without changing the diameter D of the conduction path 4 as in (1) above, the same flow rate (Qo) is applied. However, the differential pressure ΔP increases. At this time, if the correction coefficient is set to q, an inversely proportional correlation (Kd · q = const.) May be established between the substantial aperture ratio (opening area ratio) Kd of the conduction path 4 and the correction coefficient q. found. For example, assuming that the diameter of the conduction path 4 is constant at 16 [mm] and the diameter of the double pressure tube 1 is φ = 6 [mm], 4 [mm], and 3 [mm], the flow rate at that time is The average value of the correction coefficient q that can correct the error from the true value Qo was calculated based on the experimental results. As a result, the average value of the correction coefficient q was 0.257, 0.204, and 0.190 in descending order of the diameter of the double pressure tube 1.

  On the other hand, the substantial aperture ratio Kd = D / (D−d) for each diameter of each double pressure tube 1 is 0.534, 0.685, 0.763 in descending order of the diameter of the double pressure tube 1. there were. Therefore, when the substantial aperture ratio Kd and the correction coefficient q are multiplied for each diameter φ of each twin pressure tube 1 and confirmed, the value of the multiplication result is substantially constant.

  From this, Kd · q = const. Therefore, the correction coefficient q is found to be q = c / Kd (where c in the left equation is a constant). This is because the flow rate of the fluid is increased corresponding to the reduced substantial opening area of the conduction path 4 because the substantial opening ratio of the conduction path 4 is reduced by the installation of the twin pressure tube 1, and as a result, This is thought to be due to an increase in the differential pressure. Based on such experiments and considerations, the present inventors have invented the correction method as described above.

  As described above, according to the flow rate measuring apparatus according to the first embodiment, the square root of a value obtained by dividing twice the value of the differential pressure measured using the double pressure tube 1 by the density of the fluid is calculated. The value of the substantial opening area obtained by dividing the value of the substantial opening area obtained by subtracting the sectional area blocked by the double pressure tube 1 from the total sectional area as the flow tube of the conducting path 4 by the total sectional area. By performing the correction of multiplying the reciprocal as a correction coefficient, the flow rate measurement value of the fluid to be measured was obtained, so that an accurate correction using the correction coefficient could be performed, thereby providing an accurate flow rate. Can be obtained.

[Second Embodiment]
Instead of the twin pressure tube 1, a wake differential pressure measuring tube 20 as shown in FIGS. 5 and 6 can be used. The wake differential pressure measuring tube 20 includes a main body 21 having a cylindrical outer shape and a flange portion 22, and the main part thereof is configured.

  The main body 21 has a substantially cylindrical outer shape and a cylindrical cavity 23 inside. A wake pressure hole 24 is provided substantially at the center in the longitudinal direction of the side surface of the main body 21.

  The wake pressure hole 24 is provided so as to communicate with the cavity 23 inside the main body 21. And it arrange | positions so that it may face in the direction opposite to the direction which opposes the flow of the fluid of measurement object, ie, the downstream of a flow, and picks up the wake pressure P2 of the fluid in the position.

  The flange portion 22 is provided at the base (one end) of the main body 21. On the first main surface 26, support pins 27a and 27b are disposed at point-symmetric positions on both sides of the main body 21 as a center. On the surface of the side wall of the conduction path 4, fitting holes 29a and 29b are formed on both sides of the static pressure hole 28 as a center. The support pins 27a and 27b are fitted into the fitting holes 29a and 29b at portions extending from their tips to a predetermined length. Here, since the support pins 27a and 27b are arranged symmetrically with respect to the main body 21, when the fluid flow in the conduction path 4 is in the opposite direction, the wake differential pressure measuring tube is accordingly adjusted. By rearranging the front-rear direction of 20 with 180 degrees reversed, the rear pressure hole 24 can be directed downstream of the flow at any time.

  This wake differential pressure measuring tube 20 is inserted into the main body 2 from the outside of the side wall of the conduction path 4 to the inside thereof through the center of the static pressure hole 28 in a loose state, so that the main body 2 flows in the fluid flow. It is assembled | attached to the conduction path 4 so that it may be hold | maintained in the state which crossed. At this time, the wake pressure hole 24 faces the downstream side of the fluid flow. As the wake differential pressure measuring tube 20 is assembled to the conduction path 4 in this way, the flange portion 22 is separated on the outward surface (surface) of the side wall of the conduction path 4 by a support pin 27a, 27b. It will be in a state of being placed floating.

  The lid body portion 30 is fixed on the surface of the side wall on the conduction path 4 so as to cover the flange portion 22 and to maintain airtightness with the side wall of the conduction path 4. A concave portion 31 is provided inside the lid body portion 30, and the flange portion 22 is accommodated in the concave portion 31. An O-ring 36 is inserted in the gap between the second main surface 34 of the flange portion 22 and the top surface 35 of the recess 31 so that the inner side and the outer side of the ring are isolated from each other in an airtight state. In addition, the lid 30 is provided with a first pressure guiding path 32 and a second pressure guiding path 33.

  The static pressure P0 of the fluid to be measured is defined as a substantial static pressure hole in the gap between the main body 21 and the static pressure hole 28, and further from there the surface of the side wall of the conduction path 4 and the first main surface of the flange portion 22. 26 through the gap between the flange portion 22 and the concave portion 31 of the lid body portion 30 through the first pressure guiding path 32, and the pressure sensor 2 (not shown in FIG. 5 because it is similar to FIG. 1). Is transmitted to. Further, the wake pressure P2 picked up by the wake pressure hole 24 is transmitted to the pressure sensor 2 through the cavity 23 to the inner side of the ring of the O-ring 36 to the second pressure guide path 33. Here, it goes without saying that as a structural means for ensuring a gap between the flange portion 22 and the conduction path 4, for example, an O-ring may be inserted in addition to the support pin. Alternatively, the static pressure hole 28 may be formed in the side surface of the base portion near the flange portion 22 of the main body 21 itself.

  The pressure sensor 2 corresponds to the differential pressure ΔP (= P 2 −P 0) between the static pressure P 0 and the wake pressure P 2 measured by the wake pressure differential measuring tube 20, as in the case of the first embodiment. Output.

  The flow rate value calculation circuit 3 calculates a flow rate measurement value (Q) based on the differential pressure ΔP. Specifically, the value of the pressure difference ΔP (= P2−P0) between P0 and P2 obtained based on the output from the pressure sensor 2 (however, the absolute value of P2−P0 is taken as this value). 2) (2ΔP) divided by the density ρ of the fluid to be measured (2ΔP / ρ) is calculated as a square root √ (2ΔP / ρ). And the substantial opening area (Dd) which subtracted the cross-sectional area d interrupted | blocked by the wake differential pressure | voltage measurement pipe | tube 20 (more specifically the main body 21) from the total cross-sectional area D as a flow pipe of the conduction path 4. Is multiplied by the reciprocal (1 / Kd = (D−d) / D) of the substantial aperture ratio Kd (Kd = D / (D−d)) of the conduction path 4 To do. Further, by calculating the ratio (P2 / P0) of the static pressure (P0) and the wake pressure (P2) of the fluid to be measured to the value ρ0 of the density of the fluid at rest ((P2 / P0) · ρ0 = ρ1), the fluid density value ρ is corrected. The density value ρ1 subjected to the correction is used for the calculation for calculating the flow rate measurement value (Q).

  Further, the Reynolds number (Re) of the fluid is calculated based on the output from the pressure sensor 2, and correction corresponding to the calculated Reynolds number is performed.

  Here, the flow value calculation circuit 3 includes an input device 5 for inputting information on a total cross-sectional area as a flow pipe of the conduction path 4 and a cross-sectional area blocked by the wake differential pressure measuring pipe 20. Further, when such information is input, a function of automatically calculating and updating a correction constant (F (Re)) used when the number of critical Reynolds numbers is exceeded is further provided.

  With such a function, the flow value calculation circuit 3 can also be used when the flow path 4 having different dimensions and specifications or the flow rate measurement using the wake differential pressure measuring tube 20 is performed. An accurate flow rate measurement value (Q) can always be calculated by automatically changing the correction coefficient corresponding to the Reynolds number determined by the wake differential pressure measuring tube 20 to an appropriate value.

  In addition, when the information of the total cross-sectional area as the flow pipe of the conduction path 4 and the cross-sectional area blocked by the wake differential pressure measuring pipe 20 is input, the flow value calculation circuit 3 is substantially based on the information. A function of automatically calculating and updating the reciprocal of the aperture ratio (1 / Kd) is further provided.

  With such a function, the flow value calculation circuit 3 can also be used when the flow path 4 having different dimensions and specifications or the flow rate measurement using the wake differential pressure measuring tube 20 is performed. It is possible to always obtain an accurate flow rate measurement value (Q) by automatically changing to an appropriate correction coefficient (Kd) corresponding to the wake differential pressure measuring tube 20.

  Note that the basic arithmetic logic and the like related to the correction and the automatic update function are the same as those described in the first embodiment. However, specific values of constants and coefficients used for the calculation are selected and used in the case of the second embodiment and the case of the first embodiment. Needless to say.

  Thus, in the flow rate measuring apparatus according to the second embodiment, the differential pressure ΔP between the static pressure P0 measured at the static pressure hole 28 and the wake pressure P2 measured at the wake pressure hole 24 is used. Then, the theoretical flow calculation of the flow differential pressure measuring tube 20 is performed to calculate the theoretical flow rate value of the fluid. An accurate flow rate measurement value Q can be obtained by correcting the theoretical flow rate value corresponding to the substantial opening ratio Kd of the conduction path 4.

  Moreover, the wake differential pressure measuring tube 20 used for the flow rate measurement has a very simple structure as described above, and as a result, the manufacturing cost and parts cost of the entire flow rate measuring device are reduced, and It is possible to achieve a reduction in the probability of occurrence of mechanical failure or defect.

  Further, as will be described later, according to the wake differential pressure measuring tube 20 described above, accurate flow measurement is always performed even if the angle of attack of the wake pressure hole 24 with respect to the flow changes significantly, such as 30 degrees or more. Can be done.

  The inventor conducted various experiments on the relationship between the angle of attack θ of the pressure hole for such a flow and the differential pressure ΔP measured by the pressure hole.

  Then, next, the experimental result and the new knowledge considered based on it are demonstrated.

  FIG. 7 schematically shows the main part of the configuration of the experimental apparatus used in the experiment in which the angle of attack θ of the pressure hole with respect to the flow to be measured is changed. In this experiment, it is assumed that the flow 71 always flows parallel to the conduit formed by the conduction path 4. In addition, the direction that is completely opposite to the flow 71 is an angle of attack θ = 0 degrees, and the declination angle of the pressure hole 70 from that θ = 0 (angle formed with the directly facing direction) is the angle of the pressure hole 70. The angle of attack θ with respect to the flow 71 is defined. Further, the pressure hole 70 is provided in the main body 21 similar to the wake pressure differential measuring tube 20 with the same size and shape as the wake pressure hole 24.

  Specifically, the tube diameter of the main body 21 used in this experiment was 4 [mm], the diameter of the pressure hole 70 was 3 [mm], and the inner diameter (tube diameter) of the conduction path 4 was 10 [mm]. The flow rate of the stream 71 was 50 to 95 NL (liter) / min (minutes)] in a standard state, and the Reynolds number was 2500 to 5000. As the differential pressure ΔP, the pressure difference between the static pressure P 0 of the flow 71 and the wake pressure P 2 measured at the pressure hole 70 was taken. This differential pressure ΔP was made dimensionless by taking the voltage output from the pressure sensor when θ = 90 degrees as a reference value of 1, and taking the ratio to that. Using such an experimental apparatus, the angle of attack θ of the pressure hole 70 was changed from 0 degrees to 180 degrees by rotating the main body 21 around the axis of the cylinder.

  When such an experiment was conducted, results as shown in FIG. 8 were obtained. First, when the angle of attack θ is in the range of 0 to 30 degrees, the differential pressure ΔP can be stably measured.

  However, when the angle of attack θ is in the range of 30 to 90 degrees, the output from the pressure sensor 2 (that is, the measurement of the differential pressure ΔP) becomes extremely unstable over time or measurement times, and the measured value is large. In addition, it was significantly reduced compared to the case of θ = 0 to 30 degrees. In particular, when θ is in the range of 60 ° to 90 °, the measured value of the differential pressure ΔP rises and falls randomly in the vicinity of approximately 0 and becomes extremely unstable, making it substantially impossible to measure. This is because when the angle of attack θ is 60 to 90 degrees, a significant separation or turbulence phenomenon such as vortex or turbulence occurs in the flow in the vicinity of the wake pressure hole 24, which becomes a significant disturbance and becomes the wake pressure P 2. It is presumed that the situation would be extremely unstable. In any case, when the angle of attack θ is in the range of 30 to 90 degrees, it has been confirmed that accurate measurement of the differential pressure ΔP is substantially impossible.

  When the angle of attack θ becomes 90 degrees, the differential pressure ΔP is changed from the previous positive pressure (the pressure value when the static pressure P0 is the gauge pressure = 0) to the negative pressure (similarly, The pressure was reversed to a negative pressure value with respect to the static pressure P0. At this time, the magnitude (absolute value) of the measured value of the differential pressure ΔP was maximized.

  When the angle of attack θ is further increased from 90 degrees, the magnitude (absolute value) of the measured value of the differential pressure ΔP gradually decreases, but within the range of θ = 90 to 180 degrees. The differential pressure ΔP could always be measured extremely stably. That is, as apparent from FIG. 8, the change in the differential pressure ΔP with respect to the change in the angle of attack θ has no discontinuities or singular points, and is extremely good and gentle in continuity. In addition, in the range of θ = 90 to 180 degrees, a value always larger (compared with absolute values) than that in the case of θ = 0 to 30 degrees was measured.

  In an experiment in which the angle of attack θ is changed, the flow rate Q of the flow 71 is 53 [L / min], 62 [L / min], 70 [L / min], 78 [L / min], 85 [L]. L / min] and 93 [L / min] were tried, and as shown in FIG. 8, the dimensionless pressure difference ΔP was reduced in all the above six flow rates as shown in FIG. The measurement results (all of the six curves) overlapped almost on one function curve.

  From such an experimental result, the angle of attack θ with respect to the flow 71 of the pressure hole 70 is set within the range of 90 ° to 180 °, that is, the flow 71 flows through the wake pressure hole 24 like the wake differential pressure measuring tube 20. (In other words, θ is set in the range of 90 to 180 degrees), the measurement of the flow rate Q of the flow 71 is always prevented without being hindered by the change in the angle of attack θ. It was confirmed that it was possible to perform stably.

  Further, by taking advantage of the characteristic of the measurement function by the wake pressure hole 24 as described above for the flow rate measurement, from laminar flow to turbulent flow, there is an adverse effect due to flow disturbance in the conduction path (in the pipe line). It has been confirmed that accurate and accurate flow measurement can always be realized without any problems.

  Further, as shown in FIG. 9, by changing the static pressure P0, the gas density of the fluid is equivalently changed, and an experiment for confirming the relationship between the differential pressure ΔP and the flow rate Q in each case. went. Specifically, for each case where the static pressure P0 is 0.1 [MPa], 0.2 [MPa], and 0.4 [MPa], the theoretical value and the experimental value (measured value) are respectively Examined. As a result, in all cases, it was confirmed that the theoretical value and the experimental value agreed very clearly. Further, it was confirmed that the higher the static pressure P0, that is, the higher the gas density, the smaller the differential pressure ΔP for the same flow rate Q. Therefore, also in the flow rate measuring device according to the second embodiment, the flow rate measurement value can be corrected by the correction coefficient Kd using the same arithmetic logic as that of the flow rate measuring device according to the first embodiment. It was confirmed that it was possible.

  Here, taking advantage of the characteristic in the measurement function that the wake differential pressure measuring tube 20 as described above can stably measure regardless of the angle of attack θ, the wake differential pressure measuring tube 20 is used to measure the flow velocity. It is also possible to apply to. That is, for example, as shown in FIG. 10, for example, the wake differential pressure measuring tube 20 is provided so as to protrude outward from the fuselage side surface 9 of the aircraft, and the wake pressure P2 is measured by the wake pressure hole 24. In addition, the static pressure P0 can be measured by the static pressure hole 28, and the airspeed of the aircraft can be measured based on the differential pressure ΔP between the wake pressure P2 and the static pressure P0. Here, it goes without saying that the outer shape of the tube portion of the wake differential pressure measuring tube 20 is not limited to a cylindrical shape. For example, in the case of applying to the airspeed measurement or the flow velocity measurement of the moving body as described above, in order to reduce the air resistance, the shock wave, etc. received by the wake differential pressure measuring tube 20, it is shown in FIG. You may form in such a flat cylinder shape.

  In this way, when the wake differential pressure measuring tube 20 is applied to, for example, an aircraft, when the aircraft changes its attitude or performs dynamic maneuver, the angle of attack θ changes significantly, for example, ± 30 degrees or more. Even if it makes it, it will become possible to always measure the airspeed of the aircraft accurately without falling into an unstable measurement state or being unable to measure. Measurement of a stable flow velocity against such a large change in the angle of attack θ is not possible with a conventional general Pitot tube in which the total pressure hole is provided in a direction facing the flow. It was possible or extremely difficult.

  By the way, when this wake differential pressure measuring tube 20 is used for flow velocity measurement, the flow velocity value for actually measuring the fluid flow velocity value V based on the voltage output corresponding to the differential pressure ΔP from the pressure sensor 2. An arithmetic circuit (not shown) is required.

  In the flow velocity value calculation and measurement circuit, the absolute value of the differential pressure P2 -P0 between P0 and P2 obtained based on the output from the pressure sensor 2 (that is, ΔP = − (P2−) is used as the basic flow velocity value calculation logic. P0)) is divided by twice the density ρ of the fluid to be measured, and the value of the square root √ (2ΔP / ρ) of the value (2ΔP / ρ) is calculated to obtain the flow velocity measurement value (V ) Is calculated. In some cases, the accuracy of the flow velocity measurement value may be further improved by multiplying V calculated by the basic arithmetic logic by a predetermined correction value k. .

  In addition, in the state which forcedly produced the unsteady flow with respect to the fluid of measurement using an unsteady flow generator, the flow measurement by the conventional general Pitot tube, and this 2nd Embodiment An experiment for comparing the flow rate measurement with the wake differential pressure measuring tube 20 according to the above was performed. As a result, results as shown in FIGS. 11 and 12 were obtained.

  Specifically, as a measurement environment, an experiment was performed in which the static pressure of the fluid to be measured was P0 = 0.3 [MPa] and a flow rate measurement was performed in a state where an unsteady flow of 5 [Hz] was generated. . As a result, as shown in FIG. 11A, the waveform measured using a conventional general Pitot tube with θ = 0 has an unsteady flow generated by an unsteady flow generator (not shown). There was a maximum amplitude shift of 10% or more relative to the flow waveform. In comparison, as shown in FIG. 11B, the waveform measured by the wake differential pressure measuring tube 20 is 3 to 4 with respect to the waveform of the unsteady flow generated by the unsteady flow generator. % Or less amplitude deviation occurred. Thereby, the waveform of the measured differential pressure ΔP is a dull waveform in the case of the conventional general Pitot tube, and in the case of the wake differential pressure measuring tube 20, the unsteady flow generator It was confirmed that the waveform has a clear (large) amplitude almost in phase with the waveform of the unsteady flow generated by the above.

In addition, as a measurement environment, an experiment was performed in which the static pressure of the fluid to be measured was set to P0 = 0.4 [MPa] and a flow rate measurement was performed in a state where an unsteady flow of 20 [Hz] was generated. As a result, as shown in FIGS. 12A and 12B, the difference between the measurement result of the conventional general Pitot tube and the measurement result of the wake differential pressure measurement tube 20 is as shown in FIG. Even more prominent. That is, as shown in FIG. 12 (a), the waveform measured using a conventional general Pitot tube with θ = 0 has a waveform of the unsteady flow generated by the unsteady flow generator. As a result, a maximum amplitude deviation of 50% or more occurred. In comparison, as shown in FIG. 12B, the waveform measured by the wake differential pressure measuring tube 20 is 10% or less than the waveform of the unsteady flow generated by the unsteady flow generator. Only smaller amplitude deviations occurred. Thereby, the waveform of the measured differential pressure ΔP is clearly dull and disturbed in the case of the conventional general Pitot tube, but in the case of the wake differential pressure measuring tube 20, It was confirmed that the waveform was almost in phase with the waveform of the unsteady flow generated by the unsteady flow generator and had a firm and clear amplitude. As described above, according to the flow rate measuring apparatus according to the second embodiment, even in a state where an unsteady flow such as pulsation is generated in the fluid to be measured, the conventional general Pitot tube It is possible to realize more accurate flow rate measurement more reliably than measurement using the.
In the first and second embodiments described above, gas is assumed as the fluid to be measured, but it is needless to say that liquid can also be used as the measurement target.

1 is a partially omitted cross-sectional view showing a schematic configuration of a flow rate measuring device according to a first embodiment of the present invention. It is a table | surface figure which shows an example of the relationship between the Reynolds number and a correction coefficient. FIG. 3 is a table showing an example of a relationship between a Reynolds number and a correction coefficient at a flow path diameter different from that in FIG. 2. It is a table | surface figure which shows the actual example of the correlation with the differential pressure | voltage output from a pressure sensor, and a flow value true value. It is sectional drawing which shows the state which installed the wake differential pressure measuring tube in the conduction path. It is a perspective view which shows the external appearance of a wake differential pressure measuring tube. It is a schematic diagram which shows the main structures of the experimental apparatus which changes the attack angle (theta) of the pressure hole with respect to the flow of a measuring object. It is a table | surface figure which shows the experimental result about the relationship between the angle of attack (theta) and differential pressure (DELTA) P. It is a table | surface figure which shows the relationship between the flow volume Q when changing the static pressure P0, and differential pressure | voltage (DELTA) P. It is a perspective view which shows the external appearance of the wake differential pressure measuring tube used as a part of aircraft flow velocity measuring device. It is a table | surface figure which shows an example of the experimental result at the time of performing flow volume measurement by producing unsteady flow with respect to the fluid compulsorily. It is a table | surface figure which shows another example of the experimental result at the time of performing flow rate measurement by producing unsteady flow with respect to the fluid compulsorily.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Double pressure pipe, 2 ... Pressure sensor, 3 ... Flow rate value calculation circuit, 4 ... Conduction path, 5 ... Input device, 11 ... Total pressure hole, 12 ... Back pressure hole, 20 ... Back differential pressure measuring pipe, 21 DESCRIPTION OF SYMBOLS ... Main body, 22 ... Flange part, 23 ... Cavity, 24 ... Back pressure hole, 28 ... Static pressure hole, 30 ... Lid part, 32 ... 1st pressure guide path, 33 ... 2nd pressure guide path

Claims (9)

A total pressure hole is provided in a direction facing the flow of the fluid to be measured flowing through the conduction path, and the total pressure generated by the flow of the fluid is measured at the total pressure hole, and the direction facing the flow of the fluid A double pressure pipe that is provided with a wake pressure hole at a position opposite to the directional pressure, and that measures the wake pressure generated by the fluid flow at the wake pressure hole;
A pressure sensor for performing output corresponding to the total pressure and the wake pressure measured by the double pressure pipe;
A value obtained by calculating a square root of a value obtained by dividing twice the value of the differential pressure between the total pressure and the wake pressure obtained based on the output from the pressure sensor by the density of the fluid, Multiplying the reciprocal of the substantial aperture ratio of the conducting path by dividing the value of the substantial opening area obtained by subtracting the sectional area blocked by the double pressure tube from the total sectional area as a flow tube of the current by the total sectional area. A flow rate measurement device comprising: a flow rate value calculation circuit that performs correction including calculation to calculate a flow rate value of the fluid. A static pressure hole that is disposed in the conduction path and measures the static pressure of the flow of the fluid to be measured flowing through the conduction path, and opens toward the downstream side opposite to the direction facing the fluid flow. A wake differential pressure measuring pipe provided with a wake pressure hole provided to measure the wake pressure of the fluid at the opening position;
A pressure sensor that performs an output corresponding to a differential pressure between the static pressure and the wake pressure measured by the wake pressure differential measurement tube;
Substantial opening of the conduction path obtained by dividing the value of the substantial opening area obtained by subtracting the cross-sectional area blocked by the wake differential pressure measuring pipe from the total cross-sectional area as the flow pipe of the conduction path by the total cross-sectional area. A correction including an operation of multiplying a reciprocal of a rate by a value obtained by calculating a square root of a value obtained by dividing twice the value of the differential pressure obtained by the output from the pressure sensor by the density of the fluid. And a flow rate value calculation circuit for calculating the flow rate value of the fluid. The flow value calculation circuit further includes a function of correcting the density by multiplying the density of the fluid by a ratio of the total pressure and the wake pressure or the static pressure and the wake pressure. The flow rate measuring device according to claim 1, wherein the flow rate measuring device is provided. The flow rate calculation circuit further includes a function of calculating a Reynolds number of the fluid based on an output from the pressure sensor and performing a correction corresponding to the Reynolds number. The flow rate measuring device according to any one of 3. When the Reynolds number calculated based on the output from the pressure sensor is less than the critical Reynolds number, the flow rate value calculation circuit performs correction using the calculated Reynolds number as the correction. The flow rate measuring device according to claim 4. When the Reynolds number calculated based on the output from the pressure sensor is greater than or equal to the critical Reynolds number, the flow rate calculation circuit performs correction using a predetermined correction constant as the correction. The flow rate measuring device according to claim 4 or 5. The wake differential pressure measuring tube has a cylindrical outer shape and forms a cylindrical cavity inside, and the wake pressure hole is provided on the cylindrical side surface so as to communicate with the cavity. The wake pressure hole is inserted across the fluid flow from the outside of the side wall of the conduction path to the inside of the conduction path so that the downstream pressure hole faces the downstream side opposite to the direction facing the fluid flow. The downstream pressure of the fluid is measured at the opening position on the downstream side of the cylindrical shape when viewed from the flow direction, and the static pressure is measured between the side wall of the conduction path and the cylindrical side surface. A gap having a predetermined dimension is provided as a pressure hole, the static pressure of the fluid is measured by the static pressure hole, the wake pressure is transmitted from the wake pressure hole to the pressure sensor through the cavity, and It is set to transmit static pressure from the static pressure hole to the pressure sensor. The flow rate measuring device according to claim 2. A static pressure hole for measuring the static pressure of the flow of the fluid to be measured, and a rear side of the fluid at the opening position provided to open toward the downstream side opposite to the direction facing the fluid flow. A wake differential pressure measuring tube provided with a wake pressure hole for measuring the fluid pressure;
A flow velocity measurement comprising: a flow velocity value measuring means for measuring a flow velocity value of the fluid based on a differential pressure between the static pressure and the wake pressure measured by the wake differential pressure measuring tube. apparatus. A static pressure hole for measuring the static pressure of the flow of the fluid to be measured, and a rear side of the fluid at the opening position provided to open toward the downstream side opposite to the direction facing the fluid flow. The difference between the static pressure measured by the static pressure hole and the wake pressure measured by the wake pressure hole using the wake differential pressure measuring pipe provided with the wake pressure hole for measuring the flow pressure. A flow velocity measurement method, comprising: measuring a flow velocity value of the fluid based on pressure.

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