JP2013024620A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter having constant flow sensitivity irrelevant to a type or temperature of fluid.SOLUTION: In a so-called propagation time difference type ultrasonic flowmeter, annular ultrasonic vibrators 2 and 3 are provided separated at a constant interval L from each other, on an upstream side and a downstream side of a straight measurement tube 1; each of the annular ultrasonic vibrators alternately operates one as an ultrasonic transmitter and the other as an ultrasonic receiver, and measures a time difference ΔT between a downstream-directional ultrasonic propagation time Tand an upstream-directional ultrasonic propagation time Tto calculate a flow rate v. An acoustic velocity cof fluid is represented as a predetermined function f(c) of the propagation speed c of an ultrasonic wave, and the flow rate v of the fluid is calculated by an expression: v=f(c)*c*ΔT/2L incorporating derivatives of the function, using the actually measured propagation speed c and propagation time difference ΔT.

Description

  In the present invention, two annular ultrasonic transducers are provided on a measurement tube having the same diameter over the entire length with a certain distance so that the inner peripheral surface thereof is in contact with the measurement tube. The ultrasonic transducer is operated alternately as one ultrasonic transmitter and the other as an ultrasonic receiver, and the flow rate is calculated by measuring the time difference between the downstream ultrasonic propagation time and the upstream ultrasonic propagation time, so-called The present invention relates to a propagation time difference type ultrasonic flowmeter.

In general, the ultrasonic flowmeter has excellent characteristics such as that the flow rate can be measured from the outside of the pipe, there is no pressure loss accompanying the measurement, and both forward and reverse can be measured from zero flow velocity.
Ultrasonic flowmeters include a propagation time difference method and a Doppler method, but a propagation time difference method with stable performance is generally used.

  As a general form of the propagation time difference type ultrasonic flowmeter, two wedge-type ultrasonic transducers are obliquely arranged on the outer surface of the tubular body as in the structure of the oblique incident angle type detection unit shown in FIG. The two ultrasonic transducers are alternately operated as one ultrasonic transmitter and the other as an ultrasonic receiver. The generated ultrasonic waves flow through the fluid in the pipe. (See, for example, Patent Document 1).

  In contrast to the above-described method in which ultrasonic waves are applied obliquely to the tube with a wedge-shaped ultrasonic transducer, the measurement interval is shortened and sufficient measurement accuracy is achieved as the outer diameter of the tube is reduced. It was not obtained.

Therefore, for the purpose of ensuring sufficient spacing between the upstream and downstream ultrasonic transducers, the pipe is bent at a right angle at the upstream and downstream portions as shown in FIG. A method of propagating ultrasonic waves in parallel with the flow velocity direction is widely used.
However, if the diameter of the measuring tube is further reduced, the cross-sectional area of the tube body becomes much smaller than the vibrational cross-sectional area of the ultrasonic transducer, and the proportion of ultrasonic waves propagating through the fluid in the pipe decreases, making measurement more difficult. become.

Therefore, in order to make it possible to measure the flow rate in a small-diameter pipe, an annular ultrasonic transducer is used (for example, see Patent Document 2).
As shown in FIG. 1, this ultrasonic transducer is one in which two annular ultrasonic transducers are penetrated by a straight measuring tube and loaded at a distance so as to contact the outer surface of the tube. It is.
By adopting this shape, flow measurement by ultrasonic waves can be applied even to a small diameter tube.

  Moreover, in this method, since the ultrasonic wave propagates through the entire cross section of the straight pipe, it is not affected by the flow velocity distribution such as turbulent flow and laminar flow. There are advantages to be gained.

  Furthermore, since the distance between the pair of ultrasonic flowmeter transducers arranged upstream and downstream can be made sufficiently long, the difference in propagation time between the upstream direction and the downstream direction can be increased, and the measurement sensitivity can be increased. is there.

By the way, in a general measurement method of the propagation time difference type ultrasonic flowmeter, first, an ultrasonic wave is transmitted from the upstream vibrator and received by the downstream vibrator. The propagation time of this time is T _1. Next, the transmitter / receiver is switched, and ultrasonic waves are transmitted from the downstream side and received at the upstream side. The propagation time of this time is T _2.

  At this time, when the distance between the upstream and downstream ultrasonic transducers is L, the propagation velocity of the ultrasonic wave is c, and the flow velocity of the fluid is v, the following equation is established.

T ₁ = L / (c + v), T ₂ = L / (c−v) (1)
Therefore, from the measured upstream and downstream propagation times T ₁ and T ₂ , T ₀ = (T ₁ + T ₂ ) / 2 (2)
c = L / T ₀ (3)

And the flow velocity v of the fluid from the equation (4) is

It can be expressed.

That is, the upstream / downstream propagation times T ₁ and T ₂ are measured, the propagation time difference ΔT and the propagation velocity c are calculated therefrom, and the fluid flow velocity v is calculated.

JP-A-8-313317 JP-A-8-86675

  In the case of a structure in which an ultrasonic wave is propagated through a measurement tube using an annular ultrasonic transducer as described above, the ultrasonic wave propagates not only through the fluid in the measurement tube but also through the measurement tube itself. It is.

Therefore, in actuality, the value of the propagation velocity c is far from the sound velocity of the fluid.
For example, when the measurement tube is a PFA tube having an outer diameter of 6 mm and an inner diameter of 4 mm and the fluid is water, the propagation velocity c is about 1.15 km / s at room temperature when the sound speed of water is 1.5 km / s. It was.

Therefore, the assumption that the propagation velocity c changes to c ± v depending on the flow velocity v as in the above equation (1) does not hold. The above equation (1) can be applied only when it is assumed that the propagation of the ultrasonic wave is performed through the fluid.
Actually, the ratio of ultrasonic waves propagating through water was 30% or less when measured using the above-mentioned PFA tube having an outer diameter of 6 mm and an inner diameter of 4 mm.

  If equation (1), which is the basic premise of an ultrasonic flowmeter, breaks down, a large error will occur in the indicated value of the flowmeter calibrated with water at a constant temperature when the temperature change of the measurement fluid or the type of the measurement fluid changes. It will be.

  The present invention has been made in view of the above circumstances, and by correcting the relationship between the propagation velocity c and the flow velocity v in the above equation (1), an accurate and appropriate flow rate can be obtained regardless of the fluid temperature or the type of fluid. An object of the present invention is to provide an ultrasonic flowmeter capable of measuring.

In order to achieve the above object, the ultrasonic flowmeter of the present invention has two annular ultrasonic transducers separated by a distance so as to be penetrated by a measurement tube through which a fluid to be measured flows and to contact the measurement tube. The two annular ultrasonic transducers are alternately operated as one ultrasonic transmitter and the other as an ultrasonic receiver, and the ultrasonic transducer upstream of the fluid to be measured is used as the ultrasonic transmitter. In the ultrasonic flowmeter that calculates the flow velocity by the time difference between the downstream ultrasonic propagation time and the upstream ultrasonic propagation time when the ultrasonic transducer downstream of the fluid to be measured is an ultrasonic transmitter, The ultrasonic propagation time measuring means for measuring the downstream ultrasonic propagation time T ₁ and the upstream ultrasonic propagation time T ₂ , and the respective measurement results are input, and the following (6), (7) and (8) are used. A first calculation unit for calculating a propagation time difference ΔT and a propagation speed c; The distance L between the number of ultrasound transducers, outer diameter b and an inner diameter a of the measuring tube, the measuring tube material Young's modulus E and Poisson's ratio σ and the density [rho ₁ of the fluid flowing through the measuring tube from the ultrasonic wave propagation velocity c Groenwall A second calculation unit that calculates the calculation coefficient y based on the equation (9), and a third calculation unit that calculates a derivative of the equation (11) in which the fluid sound velocity c ₀ is expressed as a function of the ultrasonic propagation velocity c. From a calculation unit and a fourth calculation unit that calculates the flow velocity v of the fluid from the propagation time difference ΔT, the distance L between the ultrasonic transducers, and the ultrasonic propagation velocity c by the following equation (12) It is configured.

Here, the value of A is obtained by extracting a portion specific to the material and dimensions of the measuring tube.

Here, Equation (9) is rewritten with respect to the fluid sound velocity c ₀ and is expressed by a function f (c).
Here, f ′ (c) is a derivative of the function f (c).

In the ultrasonic flowmeter of the present invention,
Omitting the third and higher terms of y in the Groenwall equation (9);
And approximate
In the fourth calculation unit, a part that is an eigenvalue of the material and dimensions of the measurement tube is extracted.

Set the value of A, the inter-vibrator distance L and the fluid density ρ ₁ ,
From the measured propagation velocity c and ΔT, equation (24)
May be calculated to obtain the flow velocity v.

Furthermore, in the ultrasonic flowmeter of the present invention,
In the second calculation unit, equation (20)

Instead of directly setting and inputting the value of A at the site of use, the material and dimensions of the measuring tube are fixed as the product model, and the water temperature was changed in advance before shipment from the factory to support the fluid temperature t ° C. A characteristic curve of the A value in the above equation (20) is created, incorporated in the arithmetic unit, and the fluid temperature t ° C is set and input locally, so that the A value corresponding to the temperature at that time can be captured. You may provide the calculated operation part.

  According to the present invention, by defining the relationship between the flow velocity v and the change in the propagation velocity c due to the flow velocity change, the calibration accuracy with water at the time of shipment from the factory can be widened with respect to the type of fluid and the change in fluid temperature. By being applicable, accurate and appropriate flow rate measurement can be performed regardless of the type of fluid and the fluid temperature, and the practical value as an ultrasonic flow meter can be increased.

It is an external appearance perspective view which shows the structure of the detection part of the ultrasonic flowmeter which concerns on one Embodiment. It is a circuit block diagram which shows the circuit structure of the embodiment ultrasonic flowmeter. It is a flowchart for demonstrating the measurement operation | movement of the embodiment ultrasonic flowmeter. It is the schematic for demonstrating the conventional ultrasonic flowmeter of an oblique incident angle system. It is the schematic for demonstrating the 90 degree bending shape detection part used conventionally.

  Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is an external perspective view showing an installation state of an ultrasonic transducer of an ultrasonic flowmeter according to an embodiment of the present invention. In this embodiment of the ultrasonic flowmeter, two annular ultrasonic transducers 2 and 3 are used as ultrasonic transducers in the measurement tube 1 for flowing a fluid whose flow rate is to be measured. It is inserted so as to be in contact with the outer wall, and is installed at a predetermined distance L.

  When the fluid to be measured flows through the measurement tube 1 from left to right, in FIG. 1, the ultrasonic transducer 2 is an ultrasonic transducer installed on the upstream side, and the right ultrasonic transducer 3 is This is an ultrasonic transducer installed on the downstream side.

  FIG. 2 is a circuit block diagram showing a basic circuit configuration of the ultrasonic flowmeter according to this embodiment. In this embodiment, the ultrasonic flowmeter is configured such that the upstream ultrasonic transducer 2, the downstream ultrasonic transducer 3, and one of the upstream ultrasonic transducer 2 and the downstream ultrasonic transducer 3 are connected to the transmitter. The switching circuit 4 for switching the function with the other as a receiver and a signal for driving one of the ultrasonic vibrators 2 and 3 as a transmitter are added to the ultrasonic vibrator via the switching circuit 4 A transducer driving circuit 5, a receiving circuit 6 that receives an ultrasonic signal from an ultrasonic transducer for a receiver through a switching circuit 4, and a transmission ultrasonic transducer from the transducer driving circuit 5 through a switching circuit 4. A control / arithmetic unit 7 for performing a control calculation for calculating the flow rate signal by transmitting the ultrasonic signal from the reception ultrasonic transducer / switching circuit 4 via the reception circuit 6, It has.

  However, the basic configurations of the annular ultrasonic transducers 2 and 3 and the switching circuit 4, the transducer driving circuit 5, the receiving circuit 6 and the control / calculation unit 7 shown here are the conventional transmission time difference type ultrasonic transducers. The configuration of the flow meter is not particularly different, and the most characteristic feature of the ultrasonic flow meter of this embodiment is the processing function of the control / calculation unit 7.

In the ultrasonic flowmeter of this embodiment, the control / calculation unit 7 switches the switching circuit 4 to the a contact side at the start of flow measurement, and moves the ultrasonic transducer 2 from the transducer driving circuit 5 via the switching circuit 4. is driven as a transmitter, the ultrasonic waves propagating in the measurement pipe 1 is received by the ultrasonic oscillator 3, via the receiver circuit 6 uptake, it has a function of measuring and storing the downstream ultrasonic wave propagation time T ₁ .

Similarly, the control / arithmetic unit 7 switches the switching circuit 4 to the b-contact side so that the ultrasonic transducer 3 on the downstream side functions as a transmitter, and is transmitted toward the upstream side from the ultrasonic transducer 2. and the ultrasonic wave is received by the ultrasonic oscillator 2, through the reception circuit 6 Shi measures the uptake upstream ultrasonic wave propagation time T ₂ has a function of storing.

Based on the downstream ultrasonic wave propagation time T ₁ , the upstream ultrasonic wave propagation time T _2, and the distance L between the two ultrasonic transducers ₂ and 3, the control / calculation unit 7 determines the propagation time difference ΔT and the average propagation time T. ₀ , equation for calculating the propagation velocity c ΔT = T ₂ −T ₁ (6)
T ₀ = (T ₁ + T ₂ ) / 2 (7)
c = L / T ₀ (8)
And has a function to calculate each. In other words, the control / calculation unit 7 has a function as a first calculation unit that calculates the propagation time difference ΔT and the propagation speed c by the above equations (6), (7), and (8).

The control / calculation unit 7 also determines the Groenwall from the outer diameter b and inner diameter a of the measuring tube 1, the Young's modulus E and Poisson's ratio σ of the measuring tube, the density ρ _{1 of the} fluid flowing through the measuring tube 1, and the ultrasonic propagation velocity c. Equation (9)

And an expression (10) for obtaining the calculation coefficient y based on this,

And has a function of calculating the calculation coefficient y. In this regard, the control / calculation unit 7 has a function as a second calculation unit that calculates the calculation coefficient y.

Further, the control / calculation unit 7 rewrites the equation (9) for the fluid sound velocity c ₀ as the following equation (11)
Stores the, has a function of calculating the fluid sound speed c _0. In this regard, the control / calculation unit 7 has a function as a third calculation unit that calculates a derivative of Expression (11) in which the fluid sound velocity c ₀ is expressed as a function of the ultrasonic propagation velocity c.

Further, the control / calculation unit 7 differentiates the function f (c) of the equation (11) by the following equation (12)

That is, as a fourth calculation unit that calculates the fluid flow velocity v from the propagation time difference ΔT, the distance L between the ultrasonic transducers, the propagation velocity c, and the derivative f ′ (c) of the fluid sound velocity c _0. It has the function of. Since the control / calculation unit 7 has such a function, the ultrasonic flowmeter of this embodiment can accurately calculate the fluid flow velocity regardless of the fluid temperature and the fluid.
Here, the derivation of the relational expression (12) between the flow velocity v and the propagation time difference ΔT will be described along the following expressions (13) to (18).

First, assuming that a small change Δc in the propagation velocity occurs corresponding to the flow velocity v,
T ₁ = L / (c + Δc), T ₂ = L / (c−Δc) (13)
Is established.
From these two equations, when Δc is obtained,

Substituting the following equation into the above equation

The relationship between the sound velocity c _{0 of} fluid and the propagation velocity c is as defined above.
c ₀ = f (c) (17)
The differential value is
Δc ₀ = f ｀ (c) Δc (18)
Here, f ｀ (c) is a derivative of the function f (c).

Since the flow velocity v corresponds to the amount of change in the sound velocity c ₀ of the fluid,
v = f ｀ (c) Δc (19)
Therefore, substituting equation (16) for Δc in equation (18)
Can be derived.

  Next, the flow velocity (flow rate) detection processing operation of the embodiment ultrasonic flowmeter will be described with reference to the flowchart shown in FIG. When the process is started, first, in step ST1, the control / calculation unit 7 sends a switching signal to the switching circuit 4, and the contact pieces of the respective switches of the switching circuit 4 are put into the a contacts. By turning on the contact a, the ultrasonic transducer 2 is set as a transmitter, and the ultrasonic transducer 3 is set as a receiver. Next, the process proceeds to step ST2.

In step ST <b> 2, a transmission command is applied from the control / calculation unit 7 to the transducer driving circuit 5, and the transducer driving circuit 5 drives the ultrasonic transducer 2 in response to the transmission command. As a result, an ultrasonic signal is transmitted from the ultrasonic transducer 2 in the downstream direction of the measuring tube 1 and received by the ultrasonic transducer 3, and is received by the control / arithmetic unit 7 from the contact a of the switching circuit 4 via the receiving circuit 6. Is included. As a result, the downstream ultrasonic transmission time T ₁ from when the ultrasonic wave is transmitted from the ultrasonic transducer 2 to when it is received by the ultrasonic transducer 3 is obtained and stored by the control / calculation unit 7. Next, the process proceeds to step ST3.

  In step ST3, the control / arithmetic unit 7 sends a switching signal to the switching circuit 4, and the contact piece of each switching switch of the switching circuit 4 is inserted into the b contact. With this b contact ON, the ultrasonic transducer 3 is set as a transmitter and the ultrasonic transducer 2 is set as a receiver. Next, the process proceeds to step ST4.

In step ST4, a transmission command is applied from the control / arithmetic unit 7 to the transducer driving circuit 5, and the transducer driving circuit 5 drives the ultrasonic transducer 3 in response to the transmission command. As a result, an ultrasonic signal is transmitted from the ultrasonic transducer 3 in the upstream direction of the measuring tube 1 and received by the ultrasonic transducer 2, and is received by the control / calculation unit 7 from the contact b of the switching circuit 4 via the receiving circuit 6. Is included. Thus, the upstream ultrasonic transmission time T ₂ from when the ultrasonic wave is transmitted from the ultrasonic transducer 3 to when it is received by the ultrasonic transducer ₂ is obtained and stored by the control / calculation unit 7. Next, the process proceeds to step ST5.

In step ST5, the difference using equation (6), that is, the propagation time difference ΔT is calculated and stored. Subsequently, the process proceeds to step ST6. In step ST6, using Equation (7), upstream ultrasonic transmission time T ₂ and the downstream ultrasonic transmission average time T _1, that is, calculated and stored an average propagation time T _0. Next, the process proceeds to step ST7.

  In step ST7, it is determined whether or not the distance L between the two ultrasonic transducers 2 and 3 is set. If the inter-vibrator distance L has not yet been set with the new measurement tube 1 set, the process proceeds to step ST8. In step ST 8, the current inter-vibrator distance L is set and stored in the control / calculation unit 7. After the setting is stored, the process proceeds to step ST9. On the other hand, if the inter-vibrator distance L has already been set in step ST7, the determination is YES, step ST8 is skipped, and the process proceeds to step ST9.

In step ST9, using equation (8), that calculates the propagation speed c of the division to ultrasonic ultrasonic transducer distance L, which is previously set and stored in the mean propagation time T _0, is stored. Next, the process proceeds to step ST10.

In step ST10, it is determined whether or not the constant A and the fluid density ρ1 corresponding to the parts unique to the material and dimensions of the measuring tube ₁ are set. A Before begins to conduct new fluid to the new measuring tube 1, if it is not set yet constants A, fluid density [rho ₁ is transitioning determined NO to step ST11.

In step ST11, sets stored constant A, the fluid density [rho ₁ to the control and operation unit 7. After the setting is stored, the process proceeds to step ST12. On the other hand, in step ST10, if it is already constant A, fluid density [rho ₁ is stored, by skipping step ST11 the determination YES the process proceeds to step ST12.

In step 12, the distance L between the ultrasonic transducers, the outer diameter b and inner diameter a of the measurement tube, the Young's modulus E and Poisson's ratio σ of the measurement tube, the density ρ1 of the fluid flowing in the measurement tube, and the propagation velocity c of the ultrasonic wave From the equation (9), the calculation coefficient y is calculated and stored from the equation (10) using the set constant A, fluid density ρ ₁ , and propagation velocity c. Next, the process proceeds to step ST13.

In step ST13, computes the derivative of formula (11) where the fluid sound speed c ₀ as a function of the propagation speed c of the ultrasonic wave. Subsequently, the process proceeds to step ST14.
In step ST14, the derivative f '(c) is calculated by differentiating the fluid sound velocity c ₀ = f (c) obtained by the equation (11). Next, the process proceeds to step ST15. In step ST15, using equation (12), the fluid velocity v is calculated from the propagation time difference ΔT, the ultrasonic wave propagation velocity c, the distance L between the ultrasonic transducers, and the derivative f ′ (c). To do.

Next, other embodiment ultrasonic flowmeters that can be implemented with simple modifications to the above-described ultrasonic flowmeters will be described.
First, in the relational expression between the sonic velocity c ₀ and the propagation velocity c of the fluid described above, Groenwall's equation (9), the third and higher terms of y may be omitted.

The actual value of y defined in the Groenwall equation (9) was y = 0.16 at room temperature when a PFA tube having an outer diameter of 6 mm and an inner diameter of 4 mm was used as the measuring tube 1. Then the third-order term of y is
y = 0.004
It can be ignored compared to 1.
Therefore, in Groenwall's formula (9), if the third-order term of y is omitted,


In addition, the portion of the value of y that becomes a constant value at the time of measurement depending on the material and dimensions of the measuring tube used is A,

Y is

Can be expressed.
Substituting equation (21) for y in equation (19) above

Differentiating equation (22)

Substituting Δc in equation (23) as f ′ (c) in equation (12)
It becomes.

  In the fourth calculation unit corresponding to the processing of step ST15, from the known values, such as fluid density ρ1, measurement tube constant A, distance L between ultrasonic transducers, measured propagation velocity c, and propagation time difference ΔT. The flow velocity v is calculated using the equation (24).

Another embodiment ultrasonic flowmeter that can be implemented with further simple modifications to the above-described embodiment ultrasonic flowmeter will be described.
Regarding ultrasonic flowmeters, a calibration test using water is generally performed at the time of shipment from a factory. When the type of the measurement solution is different from the water used in the factory calibration test at the actual use site, the value of the calculation coefficient y in the above equation (10) is different, resulting in a difference between the scale at the time of shipment.

As another embodiment of the present invention, by making it possible to set and input the density ρ _{1 of the} measurement fluid appearing in the above equation (10) even in the field, it is possible to measure with a constant accuracy regardless of the type of the measurement fluid. It becomes.
Further, when the temperature of the measurement solution at the actual use site is different from that at the time of the factory calibration test, the value of the calculation coefficient y in the above equation (10) changes mainly depending on the temperature characteristics of the Young's modulus E and the Poisson's ratio σ. The measured flow rate deviates from the calibration value.

  As still another embodiment of the present invention, since the material and dimensions of the measuring tube are fixed as the product type, the temperature of the water flowing before the factory shipment is changed in advance to correspond to the fluid temperature t ° C. (20) By creating a characteristic curve of the A value of the equation and storing it in the calculation / control unit (calculation device), the fluid temperature t ° C can be input at the site, and the temperature at that time can be obtained. A corresponding A value is obtained, and this A value is set and input, and an actual measurement using this A value enables accurate flow rate measurement.

1 Measurement tube 2 Upstream ultrasonic transducer
3 downstream ultrasonic transducer 4 switching circuit 5 transducer drive circuit 6 receiving circuit 7 control / arithmetic unit circuit

Claims (3)

Two annular ultrasonic transducers are provided at a distance so as to be penetrated by a measurement tube through which a fluid to be measured flows and to contact the measurement tube, and one of the two annular ultrasonic transducers is ultrasonic When the transmitter and the other are alternately operated as an ultrasonic receiver, and the ultrasonic transducer upstream of the fluid to be measured is an ultrasonic transmitter, the ultrasonic propagation time in the downstream direction and the downstream of the fluid to be measured In the ultrasonic flowmeter that calculates the flow velocity based on the time difference from the upstream ultrasonic propagation time when the ultrasonic transducer is an ultrasonic transmitter, the downstream ultrasonic propagation time T ₁ and the upstream ultrasonic propagation time T ₂ are calculated. An ultrasonic propagation time measuring means for measuring the above, a first calculation unit that inputs the measurement results and calculates the propagation time difference ΔT and the propagation velocity c by the following formulas (6), (7), and (8); Distance L between two ultrasonic transducers, outer diameter b and inner diameter of measuring tube A second arithmetic unit for calculating the operation coefficient y based the density [rho ₁ of the fluid flowing through the Young's modulus E and Poisson's ratio σ and measuring tube of the measuring tube material from the ultrasonic wave propagation velocity c in equation (9) Groenwall A third calculation unit that calculates a derivative of the equation (11) in which the fluid acoustic velocity co is expressed as a function of the ultrasonic propagation velocity c, and the propagation time difference ΔT, the ultrasonic transducer distance L, and An ultrasonic flowmeter comprising: a fourth calculation unit that performs a calculation for calculating a fluid flow velocity v from the ultrasonic propagation velocity c according to the following equation (12).
Here, f ^′ (c) is a derivative of the function f (c). In the Groenwall equation (9), the third-order term of y is omitted.

And approximate
In the fourth calculation unit, a part that is an eigenvalue of the material and dimensions of the measurement tube is extracted.
Set the value of A, the inter-vibrator distance L and the fluid density ρ ₁ ,
From the measured propagation velocity c and ΔT, equation (24)

The ultrasonic flowmeter according to claim 1, wherein a flow velocity v is obtained by calculating In the second calculation unit, equation (20)
Instead of directly setting and inputting the value of A at the site of use, the material and dimensions of the measuring tube are fixed as the product model, and the water temperature was changed in advance before shipment from the factory to support the fluid temperature t ° C. A characteristic curve of the A value of the above equation (20) is created, and an arithmetic unit is incorporated therein, and the A temperature corresponding to the temperature at that time can be captured by setting and inputting the fluid temperature t ° C on site. An ultrasonic flowmeter according to claim 1 or 2, further comprising an arithmetic unit as described above.