JPS633245B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a flow meter.

Conventionally available mechanical flowmeters such as area flowmeters, positive displacement flowmeters, and impeller flowmeters have low accuracy due to friction, inertia, and fluid resistance of moving parts, making it difficult to accurately measure small flow rates. In addition, positive displacement flowmeters had the drawback of being complex and expensive.
On the other hand, electromagnetic flowmeters cannot be used to measure the flow rate of non-conducting materials such as gas and oil, and ultrasonic flowmeters, thermal flowmeters, etc. still have problems in terms of measurement accuracy, responsiveness, etc. There is.

The present invention has been made based on the above-mentioned viewpoints, and its purpose is to have a simple configuration, excellent responsiveness, and high precision, and in particular to measure small gas flow rates, which have been difficult in the past. The object of the present invention is to provide a completely new flowmeter suitable for use in various applications.

The flowmeter of the present invention belongs to a type of positive displacement flowmeter, and its gist is as follows:
Let's measure the flow rate by placing a thin band-shaped band piece made of synthetic resin or other material in a bent state in advance in the flow path, and measuring the frequency of the band piece as it vibrates in a wave-like manner due to the flow of fluid. That is. As the band piece, in addition to the above-mentioned synthetic resin, flexible and somewhat elastic film-like coatings such as thin metal films, cloth, and paper are widely used, depending on the purpose of use. Since such a band piece sensitively generates undulating vibration even with a slight flow of fluid, a highly sensitive flow meter can be obtained. As a detector for measuring the frequency of the band piece, various conventionally known sensors such as an optical type, a magnetic type, a pressure type, a thermal type, a capacitance type, etc. can be used.

Hereinafter, details of the configuration of the present invention will be explained with reference to the drawings.

FIG. 1 is a partially cutaway perspective view showing an embodiment of the flowmeter according to the present invention, FIGS. 2 and 3 are explanatory diagrams showing the operating principle of the flowmeter according to the present invention, and FIGS. 4 to 7
The figures are explanatory diagrams showing different embodiments of the flowmeter of the present invention, Figure 8 is a plan view showing other embodiments of the flowmeter of the present invention, and Figure 9 is a sectional view taken along the line - in Figure 8. , FIG. 10 and FIG. 11 are explanatory diagrams showing further different embodiments of the flowmeter of the present invention, respectively.
FIG. 12 is an explanatory diagram showing different embodiments of the band piece, and FIG. 13 is a graph showing the relationship between the flow rate and the vibration frequency of the band piece and the relationship between the flow rate and pressure loss in one embodiment of the flowmeter of the present invention. . In each figure, the same reference numerals indicate components having the same or equivalent functions.

In FIG. 1, 1 is a hollow casing having a flow passage whose cross section perpendicular to the axis is rectangular, 2 is a band piece stored in the casing in a bent state, and 3 is the band piece. This is a detector mounted on the side wall of the housing to detect vibrations of the housing.

The fluid to be measured is introduced from the inlet port 1a on the left side of the housing 1 in the figure, and is discharged from the outlet port 1b on the right side. A fixing rod 2a is attached to the upstream end of the band piece 2, and both ends of the fixing rod 2a are fixed to the inner walls 1c and 1d of the housing 1. In addition, a fixed rod 2 is attached to the downstream end of the band piece 2.
b is attached, and both ends of the fixing rod 2b are also fixed to the inner walls 1c and 1d of the housing 1. In addition,
Here, fixing the ends of the fixing rods 2a and 2b does not necessarily mean fixing them to the inner wall of the housing. For example, the ends of the fixing rods 2a and 2b may be rotatably supported on the inner wall of the housing. In short, any fixing method may be used as long as the positions of the upstream and downstream ends of the band piece 2 do not change relative to the housing 1. However, depending on the case, both ends may be supported elastically or supported so as to be movable over a minute distance, and these are also included in the present invention. The length of the band piece 2 in the axial direction is longer than the distance between the fixed rods 2a and 2b, so the band piece 2 is stored in the flow path of the housing 1 in a bent state. Both sides of the wavy bent band piece 2 are
At the top of the wave, the inner walls 1e and 1 of the housing 1
The length of the band piece 2 is set in advance to such an extent that it can come into contact with f. Both end sides 2 in the longitudinal direction of band piece 2
c and 2d are in contact with the inner walls 1c and 1d of the housing 1. Therefore, when fluid is introduced from the inlet 1a, the band piece 2 vibrates vertically in a wave-like manner.

Next, the vibration state and the operating principle of the flow meter of the present invention will be explained with reference to FIG. It is assumed that the band piece 2 is constantly vibrating, and at a certain moment the band piece is in the state 2', that is, the state O ₁ DEFO ₂ (O ₁ and O ₂ correspond to the positions of the fixed rods 2a and 2b). ). When comparing the S ₁ area and the S ₂ area on both sides of the O ₁ D part, the pressure on the S ₂ side is lower due to fluid entrainment, so the band piece
The O ₁ D portion is deformed so as to be convex toward the S ₂ region side. At this time, since the band support point O ₁ is fixed, the contact point D gradually shifts from D to H to B while maintaining contact with the inner wall 1f, and the band piece is in the state indicated by 2'', that is, O ₁ After going through the state of GHIFO ₂ , 2
It reaches the state shown in , that is, the state O ₁ ABCO ₂ . During this period, the upper surface of the band piece remains in contact with the upper inner wall 1e of the housing 1, and the E→I→C
If we assume that the band piece moves to point B while keeping its lower side surface in contact with the inner wall 1f until it comes into contact with the inner wall 1e at point A, this deformation causes the band piece to move in the downstream direction ( The amount of fluid sent to the right direction in the figure is the area surrounded by DECB (the shaded area in the figure). Next, state 2, i.e.
When the O ₁ ABCO ₂ state is deformed in the opposite manner to the above case and returns to the 2' state, that is, the O ₁ DEFO ₂ state, the fluid in the portion surrounded by ABFE is further pushed out. Therefore, the flow rate can be determined by measuring the number of vertical vibrations of the band piece 2. Further, it will be understood from this that the flowmeter of the present invention belongs to a type of positive displacement flowmeter. In addition, band piece 2
The lengths are D, E, and F when the band piece is at 2' at the position where the band piece contacts the inner wall of the housing.
In state 2, the length is set so that at least three points, such as A, B, and C, can always be in contact, so that, for example, the contact at point D in the figure does not separate midway. It is desirable to transition continuously from D to H to B to F to ensure that the fluid sealed by the contact at point D is sent downstream without the seal being compromised along the way. . To this end, it is preferable to set the length of the band piece 2 to a length such that when the band piece is at rest, its side surface forms three or more lines of contact with the inner wall of the channel.

The frequency of the band piece 2 is detected by a detector 3 attached to the side wall of the housing 1. As the detector 3, various types of conventionally known detectors can be used. When the detector 3 is an optical type, for example, a light beam is irradiated into the flow path through a glass fiber or the like through a window in which a hole made in the side wall of the housing 1 is closed with a transparent material, and the band piece is detected. The reflected light generated when the end side 2d of 2 crosses in front of the detector may be used for detection by a photoelectric element within the detector. In the case of a magnetic type, a small permanent magnet piece is attached to the end side 2d of the band piece 2, and detection is performed using a reed switch or a magnetic head installed in the detector, or the band piece 2 itself is made magnetic. The body is made of metal thin film,
What is necessary is to detect changes in the magnetic field generated by a magnetic field generating device provided in the detector as the band piece metal passes. In the case of a pressure type, the pressure is different between the _S1 region and the _S2 region as shown in FIG. 2, and pressure fluctuations occur each time the band piece passes, so this can be detected. In the case of thermal type,
If a heat-generating resistance wire or a combination of it and a temperature sensing element such as a thermistor is exposed in the flow path of the detector section, the generation of fluid vortices and the flow velocity can be checked in the _S1 and _S2 regions. Therefore, the amount of heat taken away from the heating resistance wire is different, so if the periodic change is detected by the change in the resistance value of the resistance wire or thermistor, the number of vibrations of the band piece 2 can be known. In the case of a capacitance type, for example, the detector 3
An electrode provided on the inner wall 1d of the housing on the side where the
Since the capacitance between the capacitance and the electrode provided on c changes as the band piece moves, this can be detected.

In the embodiment shown in FIG. 1, the detector 3 is
Side wall 1 where the housing 1 contacts the side 2d of the band piece 2
Although it is provided on the side wall 1e or 1f where the housing 1 contacts the side surface of the band piece 2, this may be more advantageous depending on the type of detector. many.

Then, the output signal from the detector 3 related to the vibration of the band piece 2 obtained as described above is amplified and waveform-shaped, and then counted by a counter to obtain the frequency of vibration, which is sent to a calculation device to determine the flow rate. Calculate. At this time, if compensation is required between the vibration frequency and the flow rate, the compensation calculation is performed using a program installed in the calculation device in advance.

Any material can be used for the band piece 2 as long as it is thin and flexible, such as synthetic resin film, metal thin film, cloth, paper, etc. It is desirable to have a certain degree of elasticity. If the material is as described above, it is possible to make the band piece extremely thin and lightweight, thereby providing a highly sensitive flowmeter with excellent responsiveness capable of sensing even a small flow rate.

In addition, the longitudinal end sides 2c and 2d of the band piece 2
In order to minimize the coefficient of friction when the body vibrates in contact with the inner surfaces 1c and 1d of the side walls of the casing 1, the inner surfaces 1c and 1d of the side walls of the casing are coated with a low-friction material such as polytetrafluoroethylene resin. It is also highly recommended that you do so.

Thus, the waveforms formed when the band piece 2 vibrates are not necessarily the same on the upstream and downstream sides. That is, as shown in FIG. 3, the wavelength λ 1 ' on the upstream side and the wavelength λ ₂ ' on the downstream side of waveform 2' when the flow rate is 0 are approximately equal, but when the flow rate is 0, the wavelength λ ₁ ' on the upstream side and the wavelength λ 2 ' on the downstream side are approximately equal, but The upstream wavelength λ ₁ ″ and the downstream wavelength λ ₂ ″ of
Since the band pieces are swept downstream by the flow, there is generally a tendency for λ ₁ ″>λ ₂ ″. In this case, since the length of the band piece is fixed, if you try to maintain contact with the inner walls 1e and 1f of the housing 1 on the upstream side, the length of the band piece will be insufficient, and the waveform on the downstream side will be The apex no longer reaches the inner wall 1f, and a gap P is created between the two. Therefore, the seal between the band piece and the inner wall of the casing is damaged, resulting in a so-called "tube leakage" condition, making it difficult to accurately measure the flow rate. Therefore, in order to prevent such a situation,
The width of the channel in the amplitude direction of the band piece (i.e. the width between the inner walls 1e and 1f in the embodiment shown)
As shown by dotted lines 1e' and 1f' in Fig. 3,
It is recommended that the width be made gradually narrower from the upstream side to the downstream side.

Furthermore, the meter constant (band frequency per unit flow rate) and optimal band length are determined by the density of the fluid,
It varies somewhat depending on viscosity, flow rate, etc.

FIG. 4 shows an embodiment of the flowmeter of the present invention in which the width of the flow path in the amplitude direction of the band piece can be adjusted in order to solve this problem. In the figure, 1
1E and 11F are wall members that form the upper and lower walls of the housing, respectively; 1E and 1F are flexible inner wall members that are attached inside the housing and form inner wall surfaces 1e and 1f, respectively; 12E and 12F are flexible inner wall members that form inner wall surfaces 1e and 1f, respectively; bolts attached via connectors 13E, 13F to intermediate positions of the inner wall members 1E, 1F, respectively;
14E and 14F are adjustment screws screwed into the bolts 12E and 12F, respectively, on the outside of the wall members 11E and 11F, and 15E and 15F are adjustment screws screwed into the bolts 12E and 12F, respectively, between the wall member 11E and the inner wall member 1E and the wall member 11.
Push-out springs 16E and 16F are provided between F and the inner wall member 1F, respectively.
Connectors 17E and 17F near the downstream end of E and 1F
Bolts installed through, 18E, 18F
are adjustment screws screwed into the bolts 16E and 16F on the outside of the wall members 11E and 11F, respectively;
19E and 19F are between the wall member 11E and the inner wall member 1E and between the wall member 11F and the inner wall member 1, respectively.
An extrusion spring provided between F and 20
E and 20F are elastic seal members made of rubber or the like that close the spaces between the downstream ends of the inner wall members 1E and 1F and the outlet member 1B, respectively.

In this flowmeter, adjustment screws 14E, 14
By adjusting F, the distance between the inner wall members 1E and 1F at the intermediate portion can be adjusted, and by adjusting the adjusting screws 18E and 18F, the distance between the inner wall members 1E and 1F at the downstream end can be adjusted. It is adjustable. Therefore, the width of the flow path in the amplitude direction of the band piece may be changed to a desired ratio between the upstream side and the downstream side, or in some cases, the inner wall members 1E and 1F may be changed to the dotted line 1E' in FIG. It is possible to change the shape of the flow path in various ways by curving it as shown by 1F'. Therefore, even if the vibration waveform of the band piece 2 changes due to changes in the flow rate, etc., if the width of the flow path is adjusted according to the flow rate within the range in which accuracy is desired, it is possible to at least stay within that range. The seal between the band piece and the inner wall surfaces 1e and 1f is not damaged at the flow rate of It is particularly useful for use in automatic control of maintaining a constant flow rate in a fluid transport line, as it provides a highly accurate measurement of a range of flow rates.

Further, in the embodiment shown in FIG. 4, the length of the band piece 2 can be adjusted as appropriate depending on the flow rate to be measured. That is, the fixing rod 2a for fixing the upstream end of the band piece 2 is connected to a knob 2a' provided on the outer surface of the side wall of the casing in this embodiment, and the knob 2a' is connected to the clock in the figure. When turned in the direction, the band piece 2 wrapped around the rod 2a
is untied and the length of the band piece in the flow path is extended, and when turned counterclockwise, the band piece 2 becomes the rod 2a.
The length of the band piece in the flow path is contracted as it is wound up. 2a'' is a cover that surrounds the fixed rod 2a, and is fixed by being stretched between the inner surfaces of both side walls of the casing, and a band piece wound around the fixed rod 2a is inserted through a slit opened on the downstream side of the cover. In this way, in the embodiment shown in Fig. 4, the width of the flow path and the length of the band piece can be adjusted, so it can accommodate a wide range of flow rates. It serves as a flow meter.

FIG. 5 is an explanatory diagram showing still another embodiment of the flowmeter according to the present invention. This embodiment shows a configuration for preventing cutting accidents due to fatigue of the band piece due to long-term use. That is, when the upstream and downstream ends of the band piece are fixed with the fixing rods 2a and 2b as shown in FIG. 1, the band piece suffers fatigue at the part where it is attached to the fixing rod due to the vibration of the band piece many times. It occurs and is finally severed. In particular, the band piece is aluminum,
If it is made of a thin metal film such as stainless steel, it is not uncommon for it to break after a few hours of use. It is possible to alleviate this problem to some extent by not fixing the fixed rod to the inner walls 1c and 1d of the housing, but by rotatably supporting the fixed rod, but it is possible to alleviate this problem to some extent by not fixing the fixed rod to the inner walls 1c and 1d of the housing. However, there is no way that such a cutting accident will occur sooner or later. In order to deal with such problems, the fifth
In the embodiment shown in the figure, a long band piece prepared in advance is sent continuously or intermittently as appropriate to the measuring section in the flow path, so that the band piece in the measuring section is automatically updated. That is, in FIG. 5, 21 is a band piece supply drum that is rotatably installed in the housing 1 with several meters to several tens of meters of band pieces 2 wound around it, and 22 and 23 are band pieces 2 between them. Feed roller 24 that pinches and pulls out from the drum 21
and 25, a take-up roller 26 which is provided on the downstream side of the flow path and pinches and takes off the band piece 2 between the two;
is a collection drum that winds up used band pieces. The band piece 2 pulled out from the drum 21 by the feed rollers 22 and 23 is bent in a wave shape and passed through the measurement section, and then passed through the measurement section by the take-up rollers 24 and 25.
and is taken up by the collecting drum 26. Feed rollers 22, 23 and take-up roller 2
4 and 25 are rotated in a completely synchronized state by a roller drive device installed outside the housing, so that the actual length of the band piece bent at the measurement part is always kept constant. ing. Each roller
The band piece may be slowly rotated at all times during the measurement period to continuously feed the band piece slowly, or it may be rotated intermittently at predetermined time intervals to intermittently feed a fixed amount. When the band pieces collected in the collection drum 26 are still usable, each roller and drum are rotated in the opposite direction.
The measurement may be performed while feeding the band piece from the drum 26 to the drum 21. In order to replace used band pieces, a sealable window may be provided on the side wall of the housing 1 to take the drums 21 and 26 in and out, or in some cases, the drums 21 and 26 may be provided outside the housing 1. It is also possible to send the band piece into the flow path through a slit in the wall of the casing provided with a means to prevent fluid leakage.

FIG. 6 shows an embodiment in which partition plates 27, 27 are installed in the flow path along the direction of fluid flow, and the band piece 2 is vibrated within the area separated by the partition plates. There is. With this configuration, even in a flowmeter that has a large-diameter flow path in preparation for large flow rates, there is no need to make the band piece particularly long in order to bring the band piece into contact with the side wall of the flow path, and accurate measurement can be achieved. It can be done. In order to obtain the flow rate of the entire flow path, a compensation calculation such as multiplying the flow rate within the area partitioned by the partition plate by a predetermined multiple may be performed.

FIG. 7 shows an embodiment in which band pieces 2, 2 are individually provided in each area divided by partition plates 27, 27, and the overall flow rate is the sum of the values measured by each band piece. or from the average value of the frequency of each band piece. With this configuration, the amplitude of the band piece can be reduced, thereby extending its life.

FIG. 8 shows an embodiment in which the flow path is annularly curved along the flow direction in order to make the flowmeter of the present invention compact in shape. FIG. 9 is a sectional view taken along the - line in FIG. 8. In both figures, reference numeral 28 indicates a base plate having a groove 28' carved in one side thereof to serve as an annularly curved flow path, and reference numeral 29 indicates a base plate having the groove 28' formed in the base plate 28 with screws 29', 29'. 30 is a fluid inlet installed in a hole formed in the lid 29 so as to communicate with one end of the groove 28'; 31 is a fluid inlet hole formed in the lid 29 so as to communicate with the other end of the groove 28'; 2 is a band piece bent and housed in the flow path formed by the groove 28', and 3 is a detector attached to the base plate 28. The fluid introduced from the inlet 30 passes through the channel 28' while vibrating the band piece 2, and is discharged from the outlet 31. The frequency of the band piece 2 is detected by a detector 3. In this way, a compact configuration can be achieved even when a relatively long flow path is provided for accurate measurement. Discharge port 31
may be provided on a side other than the inlet 30, that is, on the back side of the base 28.

FIG. 10 shows an embodiment in which a curved tube 32 curved in an arc shape is used and the band piece 2 is housed inside the curved tube 32 in order to form the curved flow path as described above.

In addition, in the explanation regarding FIG. 2, in order for the flowmeter of the present invention to function as a positive displacement flowmeter, the length of the band piece should be set so that the band piece contacts the inner wall of the flow path at at least three places. However, even if the length of the band piece is shorter than this length, the flow meter of the present invention can function satisfactorily. This is because if the density, viscosity, length of the band piece, etc. of the fluid are specified, even if the length of the band piece is short, its frequency has a certain correlation with the flow velocity, so from that frequency, It is possible to determine the flow rate. Therefore, for example, if the length of the band piece is such that when the band piece is at rest, its side surface is at two points with the inner wall of the channel.
It may be long enough to have a contact line of a strip,
In some cases, it may be even shorter than that. 1st
FIG. 1 shows an embodiment of the flowmeter of the present invention using such a short band piece 2. As shown in FIG. In this embodiment, the band piece 2 is designed to freely vibrate up and down within the flow path without contacting the inner wall of the flow path at all. The flow rate can be determined by determining the flow velocity from this frequency and multiplying it by the cross-sectional area of the flow path. Therefore, the present invention also includes such a structure in which the band piece is short. In this case, since there is no need for the band piece to contact the inner wall of the channel,
The axis-perpendicular cross section of the flow path is not limited to a rectangle, and may have any shape.

FIG. 12 shows an embodiment of a band piece 2 consisting of a film having a number of fine folds or wrinkles in the direction perpendicular to the flow. In the figure, A is a band piece having a fine sawtooth cross-sectional shape, B is a band piece having a fine wavy cross-sectional shape, and C is a band piece having a fine rectangular wave-like cross-sectional shape. If a band piece with such fine undulations is used, the ability to follow the fluid flow will be improved, and accidents such as cutting of the band piece at the fixed parts at the upstream and downstream ends will be much less likely than when using a smooth band piece. becomes less.

In addition, FIG. 13 shows the relationship between the flow rate and the vibration frequency of the band piece [graph A] and the flow rate and pressure when air flow rate is measured by the flowmeter of the present invention having the configuration shown in FIG. It shows the loss relationship [Graph B]. From graph A, it can be seen that the frequency of the band piece has an almost linear correlation with the flow rate, and therefore, the flow meter of the present invention can measure the flow rate with extremely high accuracy.

Since the present invention is constructed as described above, the present invention provides an excellent flowmeter that has a simple construction, has excellent responsiveness, and is particularly capable of measuring the flow rate of small gas flow rates, which has been difficult in the past. provided.

Note that the configuration of the present invention is not limited to the above-mentioned embodiments, and may vary depending on the shape of the casing 1, the shape of the flow path inside it, or means for changing the shape, the shape and material of the band piece, and the flow path of the band piece. The fixing method and means within the belt, means for detecting the vibration frequency of the band piece, means for updating the band piece, etc. can be freely changed in design as necessary using known means within the scope of the object of the present invention. It is something. That is, the gist of the flow meter of the present invention is that it has a band piece provided in a flow path and a detector that detects the frequency of the band piece. This includes all flowmeters equipped with.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view showing an embodiment of the flowmeter according to the present invention, FIGS. 2 and 3 are explanatory diagrams showing the operating principle of the flowmeter according to the present invention, and FIGS. 4 to 7
The figures are explanatory diagrams showing different embodiments of the flowmeter of the present invention, Figure 8 is a plan view showing other embodiments of the flowmeter of the present invention, and Figure 9 is a sectional view taken along the line - in Figure 8. , FIG. 10 and FIG. 11 are explanatory diagrams showing further different embodiments of the flowmeter of the present invention, respectively.
FIG. 12 is an explanatory diagram showing different embodiments of the band piece, and FIG. 13 is a graph showing the relationship between the flow rate and the vibration frequency of the band piece and the relationship between the flow rate and pressure loss in one embodiment of the flowmeter of the present invention. . 1... Housing, 2... Band piece, 2a, 2b...
Fixed rod, 3...Detector, 1E, 1F...Flexible inner wall member, 14E, 14F, 18E, 18F...
... Adjustment screw, 21 ... Band piece supply drum, 26
... Band piece collection drum, 27, 27 ... Partition plate, 28 ... Base, 28' ... Annular groove, 29
... Lid body, 30 ... Fluid inlet, 31 ... Fluid discharge port.

Claims (1)

[Scope of Claims] 1. A casing having a flow path therein, and both fixed positions in which both the upstream and downstream end sides of the flow path are fixed and the length thereof is measured along the center line of the flow path. detecting a band-shaped thin and flexible band piece that is bent in the flow path and vibrates in a wave-like manner by the fluid passing through the flow path, and the frequency of the band piece; A flowmeter consisting of a detector and a detector. 2 The cross section perpendicular to the axis of the channel is rectangular, and the length of the band piece in the axial direction is such that when the band piece is at rest, its side surface has two lines of contact with the inner wall of the channel. Flowmeter according to scope 1. 3. A patent claim in which the cross section perpendicular to the axis of the channel is rectangular, and the length of the band piece in the axial direction is such that when the band piece is at rest, its side surface has three or more lines of contact with the inner wall of the channel. The flowmeter according to item 1. 4. The flowmeter according to any one of claims 1 to 3, wherein the flow path is a straight pipe. 5. Any one of claims 1 to 3, wherein the flow path is a curved pipe curved in an arc shape.
Flowmeter described in . 6. The flowmeter according to any one of claims 1 to 3, wherein the flow path is annularly curved. 7. The flowmeter according to any one of claims 1 to 6, wherein the width of the band piece of the flow path in the amplitude direction is uniform. 8. Claim 1, wherein the width of the band piece of the flow path in the amplitude direction is narrower on the downstream side than on the upstream side.
The flowmeter according to any one of items 6 to 6. 9. The flowmeter according to any one of claims 1 to 6, wherein the width of the band piece of the flow path in the amplitude direction is adjustable. 10. The flowmeter according to any one of claims 1 to 9, wherein the length of the band piece in the axial direction is adjustable. 11 A patent in which the casing forming the flow path has a partial flow path with a rectangular cross section defined by a partition plate parallel to the central axis within the flow path, and a band piece is provided within the partial flow path. A flowmeter according to any one of claims 1 to 10. 12 Claims 1 to 10, wherein the casing forming the flow path has a partition plate that divides the flow path into a plurality of regions each having a rectangular cross section, and a band piece is provided in each region. any one of the terms
Flowmeter described in . 13. The flowmeter according to any one of claims 1 to 12, comprising a mechanism for updating the band piece between the fixed positions. 14. The flowmeter according to any one of claims 1 to 13, wherein the band piece is a wavy band piece having folds or wrinkles perpendicular to the longitudinal direction.