JPS60151516A - Ultrasonic flow meter - Google Patents

Abstract

PURPOSE:To measure the velocity and quantity of flow without reference to temperature variation by providing a columnar ultrasonic-wave transmission body in an enclosure body made of a material which differs in acoustic impedance from the material of said transmission body or absorbs an ultrasonic wave so that the axial core is at 50-65 deg. to the flow axis of fluid during measurement. CONSTITUTION:A transmitter 1 and a receiver 2 for an ultrasonic wave are adhered to the upper end surface of the columnar ultrasonic-wave transmission body 11, which is installed in the enclosure body 12 and provided in the through- hole 13 of the enclosure body 12 so that the axial core of the ultrasonic transmission body 11 is at 50-65 deg. to the flow axis of fluid during measurement. Then, the velocity of the fluid is measured by utilizing Doppler effect based upon the difference between the ultrasonic wave frequency transmitted from the transmitter 1 to the fluid and the ultrasonic wave frequency received by the receiver 2; the range of the transmission and reception of ultrasonic wave energy is within an invariably effective direction range even if the temperature of the columnar ultrasonic-wave transmission body 11 varies to cause variation in the effective direction range of the fluid, and there is no influence of the variation.

Description

[Detailed Description of the Invention] [Technical field to which the invention pertains] The present invention comprises a transmitter that transmits ultrasonic waves to a fluid and a receiver that receives the ultrasonic waves reflected from the fluid, and has a Doppler effect. This invention relates to an ultrasonic flowmeter that utilizes 1) 1) to measure the flow rate and flow rate of a fluid.

[Prior art and its problems]

This type of conventional ultrasonic flow meter is generally shown in Figures 1 and 2.
It is configured as shown in the figure.

That is, it consists of a transmitter 1 that transmits ultrasonic waves into the flow of fluid, and a receiver 2 that receives ultrasound reflected from solid objects or bubbles in the fluid, and these transmitters 1 and receivers 2 are arranged side by side. and is integrally embedded in an ultrasonic transmitting material 3 such as an organic synthetic resin material. 4 is a cap, and 5 is an electric wire cable.

The ultrasonic flowmeter configured in this way uses the so-called Doppler effect, which changes the difference between the ultrasonic frequency transmitted to the fluid by the transmitter 1 and the ultrasonic frequency received by the receiver 2, depending on the flow velocity of the fluid. Measure the flow rate and flow rate of fluid using In this case, the frequency of the ultrasound that reaches the receiver 2 is
It is matched with the ultrasonic frequency from the transmitter 1 and amplitude-modulated by the beat frequency, that is, the Doppler frequency, which is the difference between this image frequency.

This Doppler frequency is given by the following well-known formula, where f
d is the Doppler frequency, fo is the ultrasonic frequency from the transmitter l, ■ is the flow velocity of the fluid, C is the sound velocity in the ultrasonic transmitting material 3, θ
is the angle between the axis of fluid flow and the propagation path of ultrasound energy in the ultrasound-transmitting material.

In this equation, fo is a constant, and cos θ is also considered a constant since θ is set at a predetermined angle, and C changes depending on the temperature of the ultrasonic transmitting material 3, but its width is small and there is no significant temperature change. Temperature correction is performed only when 2. cos θ
・F o /c is made constant. Therefore, the Doppler frequency fd is proportional to the velocity V of the fluid, and the flow rate or flow rate of the fluid can be measured.

However, in the case of the conventional ultrasonic flowmeter shown in FIG. 1 and FIG. 2
The directivity angle of transmitter 1 and receiver 2 changes depending on the temperature.
The effective directivity range for the fluid, that is, the range in which ultrasonic energy can reach the fluid, or the range in which ultrasonic waves reflected by solid objects, bubbles, etc. in the fluid can reach the receiver, is the ultrasonic range. This has the drawback of poor measurement accuracy because it changes depending on the sound velocity of the sound-transmitting material 3 and the sound velocity of the fluid in contact with the flow rate pipe or the pipe through which the fluid is transferred.

The directivity angle and directivity range of the transmitter 1 and the receiver 2 will be explained in detail with reference to FIGS. 3A and 3B. FIG. 3A and FIG. 3 13 show the directivity angles a, b, directivity characteristics c, d, and effective directivity range e for the fluid when the temperature of the ultrasonic transmitting material 3 is low and high, respectively.
It shows f.

The directivity angles a and b will be explained. This directivity angle is determined as the spread angle of the sound pressure point of 07, where the sound pressure on the central axis of the ultrasound transducer is 1, and the ultrasound energy transmitted from the ultrasound transducer to the ultrasound transmission side is set as 1. . The directivity angle is proportional to the sound speed of the ultrasound transmitting material and inversely proportional to the diameter and frequency of the ultrasound transducer. The explanation will proceed assuming that sound waves within the range defined by the directivity angle are effective. The ultrasonic transmitting material 3 made of organic synthetic resin has a characteristic that the sound speed decreases as the temperature rises, so the directivity angle proportional to the sound speed is as shown in FIGS. 3A and 3.
As shown in Figure B, it decreases as the temperature increases (a)
b).

Next, the above-mentioned pointing ranges e and f will be explained.

The well-known side of Snell's law, ie, cos θ/c = cos θ//C/, holds between the ultrasonic transmitting material 3 and the fluid in contact with the flow meter or the pipe 6 for transferring the fluid.

Here, C' is the speed of sound in the fluid, and θ' is the angle between the flow axis of the fluid and the propagation direction of the ultrasonic wave in the fluid. As mentioned above, since the directivity angles a and b have a certain size and range,
The emitted ultrasonic energy is incident on the interface between the fluid or tube 6 and the flowmeter at various angles. In this case co
sθI-(c'/c), for a larger θ such that cosθ≧1 (d, total reflection occurs at the boundary and the ultrasonic wave does not enter the fluid.

For this reason, only the ultrasonic waves in the shaded ranges e and f in FIGS. 3A and 3B reach the fluid, and are reflected by solid objects, bubbles, etc. in the fluid and reach the receiver 2. I will be going back. Therefore, if the directivity angle changes due to the influence of temperature as described above, the effective directivity range of the ultrasonic waves that can reach the fluid also changes from e to f (elf).

To explain the relationship between the directivity angles a, b and directivity ranges e, f and the above equations, ultrasonic energy emitted into a fluid is also reflected by solid objects, bubbles, etc. in the fluid and reaches the receiver. The ultrasonic energy to be transmitted also has all angular components within the range determined by the above-mentioned directivity angle and directivity range, and furthermore, the above-mentioned directivity changes as the temperature of the ultrasound-transmitting material, fluid, or tube changes. Since the angle and pointing range change, θ in the above equation will take the average value of these. Therefore, in the case of the conventional ultrasonic flowmeter described above, in order to prevent a decrease in measurement accuracy due to changes in the directivity angle and effective directivity range for the fluid, temperature correction must be made to cos θ in the above equation. . Note that the conventional ultrasonic flowmeter in which the transmitter 1 and the receiver 2 are placed on the same ultrasonic transmitting material 3 has been described.
41: A similar problem exists in ultrasonic flowmeters in which the Nobuko and the receiver are independent.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to create an ultrasonic flowmeter that can always measure the flow rate and flow rate of a fluid with high accuracy without being affected by temperature changes.

[Key points of the invention]

According to the present invention, this object is achieved by installing an ultrasonic transmitter and a receiver on the upper end surface of a columnar ultrasonic transmissive body made of a material with good ultrasonic transmission characteristics on the ultrasonic flow rate side of the type mentioned at the beginning. The columnar ultrasound transmitting body is placed in an enclosure made of a material that has an acoustic impedance different from that of the material or absorbs ultrasonic waves, and the axis of the columnar ultrasound transmitting body and the flow axis of the fluid angle ry of 50 to 65°
This is achieved by being installed in such a way that the

[Embodiments of the invention]

Next, the present invention will be explained in detail based on two embodiments shown in FIGS. 4 and 5 and 7 and 8. In these drawings, the same or corresponding parts as those of the conventional ultrasonic flowmeter shown in FIGS. 1 and 2 are given the same reference numerals, and detailed explanation thereof will be omitted.

4 and 5, the ultrasonic transmitter 1 and receiver 2 are made of a columnar ultrasonic transmitter I made of a material having good ultrasonic transmission characteristics, such as an organic synthetic resin, based on the present invention.
The columnar ultrasonic transmissive body 11 is attached to the north end face of the column L and is installed in an envelope 12 made of a material that has a different acoustic impedance from that of the columnar ultrasonic transmissive body 11 or absorbs ultrasonic waves. In this case, the columnar ultrasound transmitting body 11 is arranged so that the enclosing body 12 is such that the axis b of the columnar ultrasound transmitting body 11 and the flow axis of the fluid form an angle of 50 to 65 degrees when measuring the flow rate or flow rate of the fluid. It is fitted and installed in the through hole I3 of.

In the case of the ultrasonic flowmeter according to the present invention having such f2 configuration, as shown in FIG. and enclosure 1
It is attenuated by repeating reflection and transmission at the interface with the inner peripheral surface of the through hole 13 of No. 2. Therefore, the beam and beam intensity of the ultrasonic waves along the path 1 running substantially parallel to the axis of the columnar ultrasonic transmissive body 11 becomes large, and the apparent directivity angle becomes small. Further, by setting the angle between the axis of the columnar ultrasound transmitting body 11 and the flow axis of the fluid to 50 to 65 degrees, the directivity angle of the ultrasound transmitter 1 and receiver 2 is made small.

Since the directivity angles and apparent directivity angles of the transmitter 1 and the receiver 2 are reduced in this way, the temperature of the columnar ultrasound transmitting body 11 changes, and accordingly, as shown in FIG. Even if the effective pointing range for the fluid changes, the range at which ultrasonic energy is emitted and received will always remain within and be influenced by the effective pointing range (l
'I don't. Therefore, the temperature correction of the directivity angle due to the temperature change of the columnar ultrasonic transmitter 1.1, that is, c in the above equation.
Temperature correction of osθ is not required, and there is no need for temperature correction of the ultrasonic flowmeter.

This increases stability against changes and improves measurement accuracy.

7 and 8 show different embodiments of the ultrasonic flowmeter according to the present invention, which basically have the same structure as the ultrasonic flowmeter in FIGS. 4 and 5, but with a columnar ultrasonic flowmeter. The sound-transmitting body 11 has a male thread 14, and the through-hole 1 of the enclosure 12
The difference is that 3 is a screw hole, and the columnar ultrasound transmitting body 1 is screwed into a screw hole 13 of the enclosure 12. In the case of this embodiment, the ultrasonic energy that reaches the threaded connection between the columnar ultrasound transmitting body 11 and the enclosure 12 is attenuated by being repeatedly reflected and transmitted to the enclosure 12 at this threaded connection. The path of this ultrasonic energy is longer than in the embodiments shown in FIGS. 4 and 5 due to the action of the threaded connection, resulting in a greater damping effect.

The apparent directivity angles of emitter 1 and receiver 2 are therefore correspondingly reduced.

For this reason, the stability of the ultrasonic flowmeter against temperature changes is further improved than in the embodiments shown in FIGS. 4 and 5, and the measurement accuracy is improved.

〔Effect of the invention〕

According to the present invention, changes in the directivity angles of the transmitter and receiver due to temperature changes in the ultrasonic transmitting material in an ultrasonic flowmeter are suppressed to a small level, and changes in the effective directivity range for the fluid are suppressed.
There is no need for temperature correction of the directivity angle of the transmitter and receiver due to temperature changes of the ultrasonic flowmeter, and the stability of the ultrasonic flowmeter with respect to temperature changes is increased. Flow velocity and flow rate can be measured with high accuracy.

[Brief explanation of drawings]

Figures 1 and 2 are partially cutaway perspective views and vertical cross-sectional views of conventional ultrasonic flowmeters, and Figures 3A and 3 are
Figure B is an explanatory diagram of the directivity angle, directivity characteristics, and effective directivity range for the fluid when the temperature of the ultrasonic transmitting material in a conventional ultrasonic flowmeter is low and high, respectively. FIG. 6 is a partially cutaway perspective view and longitudinal cross-sectional view of an embodiment of an ultrasonic flowmeter according to the present invention, and FIG. 7 and 8 are partially cutaway perspective views and longitudinal cross-sectional views of different embodiments of the ultrasonic flowmeter according to the present invention. 1: Transmitter, 2: Receiver, 4: Cap, 5: Electric wire cable, 11: Columnar ultrasound transmitting body, 12: Encircling body,
13: Through hole, 14: Male thread. Figure 2: Garden 5

Claims (1)

[Claims] 1) Consists of a transmitter that transmits ultrasonic waves to a fluid and a receiver that receives ultrasonic waves reflected from the fluid, and measures the flow velocity and flow rate of the fluid using the Doppler effect. Ultrasonic flow h1. In this system, a transmitter and a receiver are installed on the upper end surface of a columnar ultrasound transmitting body made of a material with good ultrasound transmission characteristics, and the ultrasound transmitter is placed on the upper end surface of a columnar ultrasound transmitting body made of a material with good ultrasound transmission characteristics. An ultrasonic device characterized in that it is installed in an envelope made of an absorbing material so that the axis of the columnar ultrasonic transmissive body and the axis of the fluid flow form an angle of 50 to 65 degrees during measurement. Sonic flow meter. 2. The ultrasonic flowmeter according to claim 1, wherein the columnar ultrasonic transmitting body has a male thread and is screwed into a screw hole in the surrounding body. Total.