JPS6348005B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic flowmeter that uses ultrasonic waves to measure the flow rate of a liquid flowing through a pipe.

[Prior art]

Ultrasonic flowmeters are generally well known, and many devices have been proposed to measure the flow rate of liquid flowing through a pipe and monitor the flow conditions using a transducer attached to the outside of the pipe. . For example, there are two
Transducers are installed at intervals along the length of the pipe, and ultrasonic pulses are sent from one transducer to the other.
A device has also been devised that sends an ultrasonic pulse in the opposite direction, measures the difference in propagation time when the ultrasonic pulse travels in the direction of the flow and in the direction against the flow, and calculates the flow rate from this time difference.

However, in conventional devices of this type, the beam width of the ultrasonic pulse traveling through the liquid is the same as the beam width when sent out from the transducer, so if the transducer mounting distance is incorrect, a reliable received signal cannot be obtained. Furthermore, even if the initial mounting interval is correct, reception may not be received as the temperature or composition of the liquid changes, making it difficult to adjust the transducer mounting interval.

[Purpose of the invention]

An object of the present invention is to make the beam width of the ultrasonic pulse sent into the liquid from the pipe wall wider than the beam width when sent out from the transducer, thereby eliminating reception failures and ensuring that the beam width remains constant even when the state of the liquid changes. The object of the present invention is to provide a flow meter that can provide a reliable flow rate.

[Structure of the invention]

The ultrasonic flowmeter of the present invention has coupling fluids interposed on opposite sides of the outside of the pipe at intervals in the longitudinal direction of the pipe to improve acoustic coupling with the outside surface of the pipe. two transducers of the same structure each having an ultrasonic transmitting/receiving element and a casing attached to the transducer; When the element transmits an ultrasonic pulse and the ultrasonic transmitting/receiving element of the second transducer receives it, and when the ultrasonic transmitting/receiving element of the second transducer transmits an ultrasonic pulse and the ultrasonic pulse is transmitted to the first transducer. and a control device that measures the difference in propagation time from when the ultrasonic wave is received by the ultrasonic transmitting/receiving element, and calculates and displays the flow rate of the liquid flowing in the pipe from this difference in propagation time.

The first important feature of the present invention is that the beam width of the ultrasonic pulse sent into the liquid from the wall of the pipe is smaller than the beam width of the ultrasonic pulse sent out from the vibration surface of the ultrasonic transmitting/receiving element of the transducer. A transverse ultrasonic wave whose vibration direction is within a plane that includes the normal to the vibration surface of the ultrasonic transceiver element and the central axis of the pipe is transmitted from the vibration plane of the ultrasonic transducer element of the transducer in order to spread it in the longitudinal direction. The phase velocity of the pulse, which travels longitudinally through the transducer enclosure along the outer surface of the pipe, causes the propagation of a transverse ultrasound pulse that enters the pipe from the enclosure and travels longitudinally through the pipe wall. The structure is configured so that the velocity is equal to the velocity of the pipe, so that the molecules on the wall of the pipe are driven from the outer surface in the same phase as the transverse ultrasonic pulse traveling in the longitudinal direction within the pipe wall. This is because the vibration plane of the ultrasonic transceiver element is tilted at an angle α with respect to the central axis of the pipe, and the vibration is transmitted from this vibration plane perpendicularly to the plane and travels through the enclosure at a speed V _c , with the vibration direction having the above bias. The phase velocity V _c /sin α of the transverse ultrasound pulse traveling along the outer surface of the pipe is equal to the propagation velocity V _ps of the shear ultrasound pulse entering the pipe from the enclosure and traveling longitudinally through the pipe wall. This is achieved by doing.

The transverse ultrasonic pulse propagates through the wall of the pipe in the longitudinal direction of the pipe, and since the direction of vibration is perpendicular to the inner surface of the pipe, the ultrasonic waves are sent into the liquid from the inner surface. This is because waves that have traveled parallel to the inner surface of the pipe through the wall of the pipe are incident on the inner surface, are refracted, and enter the liquid, so the refraction angle θ From Snell's law, sinθ=V _L /V _ps where V _L is the propagation velocity of the ultrasonic pulse in the liquid. The ultrasonic pulse that has traveled through the liquid reaches the inner surface on the opposite side of the pipe, and the ultrasonic pulse that enters the tube wall passes through the tube wall and the other transducer housing before transmitting and receiving the ultrasonic wave. Enter Motoko.

If the liquid is stationary, the refraction angle θ does not change even if the transmission and reception of the ultrasonic pulse are reversed, so the propagation time also remains the same. When the liquid is flowing at a velocity V _n , the ultrasonic pulses sent from either transducer will be received by the other transducer as a beam directed upstream compared to when the liquid is stationary. , the propagation time is shorter when a transducer mounted upstream transmits than when a transducer mounted downstream transmits. This difference in propagation time △T and flow velocity V _n
Since the relationship is expressed by a mathematical formula, the flow rate per unit time is calculated by a computer that stores the inner diameter d of the pipe, and the total flow rate integrated by this value and time is shown on the display. In the present invention,
The propagation time is measured by a clock pulse. The propagation time when the upstream transducer transmits is counted as negative, and the propagation time when the downstream transducer transmits is counted as positive, so the algebraic sum of these counts is the difference in propagation time △T The measured value is

A second feature of the invention is the method of attaching two transducers to a pipe using spacer bars and a tightening belt. There are two spacer bars running diagonally between the two transducers to determine their spacing. There is one tightening belt for each transducer, which secures the transducer to the outer surface of the pipe with a coupling fluid interposed therebetween to improve acoustic coupling between the outer surface and the transducer. The transducer is fixed to the pipe by simply screwing in the single tightening screw in the center of the tightening belt, and it does not rotate on the pipe, making it easy to attach and detach the transducer and adjust its mounting position. It is.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows how two transducers 10, 11 of an ultrasonic flowmeter according to the invention are attached to a pipe 12 through which a liquid whose flow rate is to be measured flows. A control device 13 is connected to the transducers 10 and 11 for generating transmission signals and processing received signals. The surfaces of the transducers 10 and 11 that come into contact with the pipe 12 are made into a cylindrical shape with the same curvature as the outer diameter of the pipe so as to be in close contact with the pipe. The inner diameter of the pipe 12 to which the ultrasonic flowmeter of the present invention can be used is in the range of 15 mm to 3 mm, and the material may be iron, plastic, concrete, or any other material, and the wall thickness may be arbitrary. Further, the liquid may be water, oil, or any other liquid.

The two transducers 10 and 11 are attached to opposite sides of the outside of the pipe 12 by tightening belts 15 and 16, respectively, at intervals as will be described later in the longitudinal direction of the pipe. , 3). In order to maintain the correct spacing between the transducers 10 and 11, spacer bars 17,
18 are provided and the two spacer bars are fixed to the transducers 10, 11 by screws 19, 20 and 21, 22, respectively. The fixing method is as shown in FIG.
It is screwed into the screw hole drilled in the 0, 11 case. Since the distance between the transducers 10 and 11 must be changed depending on the liquid flowing through the pipe 12, a plurality of holes are drilled in the bars 17 and 18 as shown at 30 to 33 in FIG. There is.

To attach the transducers 10, 11 to the pipe 12, screws 40-43, shown in FIGS. Then, screw the transducers 10 and 11 into the screw holes drilled in the casings of the transducers 10 and 11, and then attach the belt 1
Tightening screws 52, .
Screw in 53 and tighten. However, the final tightening is performed after the transducers 10, 11 have been spaced by the spacer bars 17, 18. In addition, in order to improve the acoustic coupling at the contact surfaces between the transducers 10 and 11 and the pipe 12, a viscous coupling fluid 14 (Fig. 4) such as grease is interposed between the transducer and the pipe. .

FIG. 4 is a cross-sectional view of the transducers 10, 11 and the pipe 12 to which they are attached.
The transducers 10 and 11 have the same structure; the structure is a rectangular parallelepiped casing with a concave surface that contacts the pipe 12, and a cylindrical hole 60 diagonally facing the surface that contacts the pipe 12. , 61, and ultrasonic transmitting/receiving elements 62, 63 are arranged on the flat bottom surfaces 64, 65 of each hole such that their respective flat vibration surfaces are in contact with the bottom surfaces 64, 65,
The rear surfaces of the transmitting and receiving elements 62 and 63 are covered with layers of sound absorbing materials 64a and 65a such as cork and sandpaper.
The voids in the cylindrical holes 60, 61 are filled with a suitable plastic filler 66, 67, and the transmitting/receiving element 62
Terminals 70, 71 and 72, 73 of and 63 are drawn out of the case. The material of the casing is nylon or the like having good acoustic transmission properties, and the material used is one in which the speed of the transverse ultrasonic wave propagating through the casing is smaller than the speed of the transverse ultrasonic wave propagating inside the wall of the pipe 12.
The transmitting and receiving elements 62 and 63 are preferably flat barium titanate ceramic elements. Transmitting/receiving elements 62, 63
Terminals 70 to 73 are connected to a control device 13 that oscillates a transmission signal and processes a reception signal.

One of the features of the present invention is that the rear surfaces of the transmitting/receiving elements 62, 63 are covered with a layer of sound absorbing material 64a, 65a such as cork or sandpaper, and this sound absorbing layer attenuates the tail of the received signal and substantially eliminates it. This simplifies signal processing.

FIG. 5 shows the path of an ultrasonic pulse (hereinafter referred to as "ultrasonic wave") transmitted from the transmitting/receiving element 62 until it is received by the transmitting/receiving element 63 on the same cross-sectional view as FIG. 4. . Liquid is flowing in the pipe 12 in the direction indicated by the arrow 90, but initially,
We will explain how ultrasound waves travel when the liquid is stationary.

In FIG. 5, the transverse ultrasonic beam f _t sent out perpendicularly from the vibrating surface of the transmitting/receiving element 62 (in contact with the bottom surface 64) is such that the bottom surface 64 is at an angle α with respect to the central axis of the pipe 12. Since it is slanted, it enters the pipe 12 at an angle. The ultrasonic wave that has entered the wall of the pipe 12 can be divided into a component f _t that vibrates in the longitudinal direction of the pipe and a component f _v that vibrates in a direction perpendicular to the longitudinal direction of the pipe. The component f _t is an ultrasonic wave that vibrates parallel to the surface at the interface with the liquid, so it does not enter the liquid where transverse sound waves do not exist.
Only component f _v induces ultrasound in the liquid.

Ultrasonic transmitting/receiving element 62 of transducer 10
The angle α between the vibration surface of the pipe 12 and the central axis of the pipe 12 is
The velocity V _c of the transverse ultrasonic wave propagating through the casing of the transducer 10 and the velocity V _ps of the transverse ultrasonic wave in the wall of the pipe 12 are configured to have the following relationship.

sinα=V _c /V _ps ...(1) When the transverse ultrasonic wave sent out perpendicularly to the vibration surface of the transmitting/receiving element 62 with the inclination of this angle α reaches the pipe 12, the wave front of the same phase is
It moves to the right in the figure along the outer surface of the figure at a speed of V _c /sinα. Also, among the ultrasonic components f _v that have entered the pipe wall of the pipe 12, the transverse ultrasonic waves that propagate through the pipe wall in the direction of arrow 91 travel at a speed V _ps , but according to equation (1), this speed is The wavefront of the ultrasonic wave incident on the outer surface of the pipe is equal to the velocity V _c /sinα of propagation along the outer surface, and therefore the molecules of the pipe wall have the same phase as the ultrasonic wave propagating in the longitudinal direction inside the pipe wall. Since the drive is received from the outer surface, the ultrasonic waves vibrating in the direction perpendicular to the central axis of the pipe are transmitted to the center of the pipe within the wall of the pipe 12, rather than the width of the beam sent out from the transmitting/receiving element 62. It will exist widely in the axial direction. This is one important feature of the present invention; the width of the ultrasonic beam sent into the liquid flowing inside the pipe 12 is wider in the longitudinal direction of the pipe 12 than the width of the beam sent out by the transmitting/receiving element 62. , there is no reception failure due to temperature changes or composition differences in the liquid, which can occur when the beam width sent into the liquid is narrow, and the transducer 10,
It also becomes easier to adjust the mounting position of item 11. Angle α
ranges from 20 to 90°.

The ultrasonic beam transmitted into the liquid from the inner surface of the pipe 12 travels in the direction shown by arrow 92 in FIG. This is thought to be because ultrasonic waves traveling at a velocity V _ps in the direction of arrow 91 within the pipe wall enter the inner surface of the pipe, are refracted into the liquid, and proceed. If the velocity of the ultrasonic wave in the liquid is V _L , and the direction of arrow 92 is expressed by the refraction angle θ, then θ is sinθ/V _L = sin90°/V _ps from Snell's law. Therefore, sinθ = V _L /V _ps ...(2) The ultrasonic waves traveling in the liquid in the direction of the refraction angle θ shown by the arrow 92 reach the inner surface on the opposite side of the pipe 12, and the ultrasonic waves travel through the pipe wall and the casing of the transducer 11 attached to the outside thereof. After passing through the body, it enters the transmitting/receiving element 63. Even if the transducer 11 is used for transmitting ultrasonic waves and the transducer 10 is used for receiving ultrasonic waves, when the liquid is stationary, the ultrasonic waves proceed along a path with the same refraction angle θ. The value of the refraction angle θ is in the range 15-50°.

In the device of the present invention, the ultrasonic component _fv that enters the wall of the pipe 12 is used to measure the flow rate, but this component is reflected from the inner surface of the pipe and returns to the outer surface. In order to avoid interference and cancellation with the incident ultrasonic waves, the frequency of the ultrasonic waves used for measurement is determined by considering the velocity of longitudinal ultrasonic waves in the pipe wall, V _pL , and the thickness of the pipe wall, w. choose.

Furthermore, if solid particles are dispersed in a liquid, the ultrasonic waves at a frequency determined by the diameter of the solid particles will be attenuated, so a frequency with less attenuation must be selected. The ultrasound frequencies used in the present invention range from 100 kilohertz to 10 megahertz.

Next, when the liquid is flowing in the direction of arrow 90 at a velocity V _n , the ultrasonic waves sent in the upstream direction are received more than when the liquid is stationary.
When the flowmeter according to the invention is used, the velocity V _n ranges from 0 to 12〓/s, and the velocity of ultrasonic waves in the liquid V _L
, the difference in the direction in which the ultrasonic waves are sent out is slight, and it is thought that sufficient energy is sent out in this direction as well. The distance that the ultrasonic waves travel in the liquid is shorter when the transducer 10 on the upstream side transmits than when the transducer 11 on the downstream side transmits, so the propagation time is also shorter. When transducer 10 transmits and when transducer 11 transmits,
The respective propagation times T ₁ and T ₂ in the liquid are V _n and V _L
Considering that d is much smaller than , the following two equations hold true, where d is the inner diameter of the pipe 12.

T ₁ (V _L + V _n sin θ) = d/cos θ T ₂ (V _L − V _n sin θ) = d/cos θ Therefore, the difference in propagation time in the liquid △T = T ₂ − _{T 1} is
An approximation in which V _n ² is omitted from V _L ² results in the following equation.

△T = 2dV _n tanθ / V _L ² = 2dV _n /V _ps V _L cosθ ...(3) If the cross-sectional area of the pipe is fixed, the flow rate F of the liquid per unit time is equal to the flow velocity V _n Since it is proportional, it can be seen from equation (3) that it is also proportional to ΔT. When time is measured using clock pulses of frequency f _c , the number of clock pulses from upstream transducer 10 transmitting to downstream transducer 11 receiving is negative, and transmission and reception are reversed. If the number of clock pulses is counted as positive and the counted value of subtraction is N, then
The flow rate F per unit time is proportional to N. If the constant of proportionality is m, then F=mN=mf _c △T...(4) Substituting equation (3), F=2mf _c . dV _n /V _ps V _L cosθ ...(5) In this equation, d/V _L cosθ is considered to be the time it takes for the ultrasonic wave to propagate in the liquid, so if we set this as T _L , F=2mf _c V _n T _L /V _ps (6) The flow rate F per unit time is calculated by the computer in the control device 13 and displayed in units such as 〓/min, 〓/hour, etc.

FIG. 6 is a block diagram of the ultrasonic signal oscillation circuit and the received signal processing circuit, in which the ultrasonic transmitting/receiving element 62,
The components other than 63 are housed in the control device 13 shown in FIGS. 1 and 4. The input module 150 supplies a transmission pulse to one of the transmission and reception elements 62 and 63, and receives and amplifies the reception pulse from the other one of the transmission and reception elements 62 and 63. Note that the transmitting/receiving element 6
The transmission/reception of 2.63 changes its role every n pulses. The scale computer 151 receives the amplified received signal from the input module 150,
One fixed point in the signal is recognized and the ultrasonic propagation time is calculated.

The pulse oscillation circuit 152 receives a fixed point recognition signal from the scale computer 151, and at that point oscillates a pulse signal and sends it to the input module 150. This pulse signal is immediately sent out as an ultrasonic pulse from the transducer selected by the input module 150, so that the computer 151
One fixed point of the received signal recognized by the user is also the point at which the next ultrasonic pulse is transmitted. The N counting circuit 153 receives a signal from the pulse oscillation circuit 152 at the time of pulse oscillation, and measures the time between pulse oscillations using a clock pulse having a frequency f _c . Note that a timing logic circuit is provided in this circuit, and the pulse count value is negative when the upstream transducer 10 transmits,
The time when the transducer 11 on the downstream side transmits is counted as positive. The flow rate counter 154 receives the count value from the N counting circuit 153 and calculates the flow rate per unit time from time to time.

The display 155 digitally displays the latest value of the flow rate per unit time calculated by the flow rate counter 154. The display 155a digitally displays the total flow rate during a predetermined period of time. The display 155b is
The flow rate per unit time calculated by the flow rate counter 154 is displayed in analog form, converted into voltage, and supplied to, for example, an alarm device or a flow rate control device, and is used to maintain the flow rate at an appropriate value.

Another embodiment of the ultrasonic flowmeter according to the present invention is shown in the seventh embodiment.
- Shown in Figure 9. FIG. 7 shows a pipe 12 and transmitting/receiving transducers 10, 11 attached to it.
FIG. 8 is a cross-sectional view taken along one plane including the central axis of the pipe 12, and FIG. 8 is a view of the pipe 12 and transducer 10 shown in FIG. 7 viewed from above.
In addition, FIG. 9 shows that the pipe 12 shown in FIG.
It is a view cut at position 9 and looking to the right. The vibration planes of the transmitting and receiving elements 62 and 63 vibrate at right angles to the central axis of the pipe 12, as shown by arrows in FIGS. 7 to 9, and the angle α between the vibration plane and the central axis of the pipe is
is configured so that the angle is 90°. As already mentioned, one major feature of the ultrasonic flowmeter of the present invention is that the width of the ultrasonic beam sent into the liquid from the wall of the pipe 12 is widened, and for this purpose, the width of the ultrasonic beam sent into the liquid from the wall of the pipe 12 is increased. The transducer 10, This condition is automatically satisfied if the enclosure 11 is made of the same material as the pipe 12. The transducer housing of this embodiment is typically made of steel and is used with steel pipes. Holes 300, 301, and 302 in FIGS. 7 and 8 are holes made in the casing of the transducer 10, and these holes are similarly made in the casing of the transducer 11. Without such holes, the ultrasonic waves transmitted by the transmitting/receiving element 62 may interfere with the ultrasonic waves reflected from the end face of the casing, resulting in weakened energy. If there are holes, the ultrasonic waves sent out from the transmitting/receiving element 62 will travel in the direction of the arrow shown by the chain line in FIG. 8, and will not be affected by interference due to reflected waves.

〔Effect of the invention〕

The two main effects of the present invention are as follows: (a) Since the width of the ultrasonic beam sent into the liquid is wide, there is no reception failure due to the mounting position of the transducer; (b) There is no failure in reception due to the mounting position of the transducer It is easy to attach and detach from the pipe and adjust the mounting position.

[Brief explanation of the drawing]

FIG. 1 shows a transducer and a control device of an ultrasonic flowmeter according to the invention attached to a pipe through which a liquid whose flow rate is to be measured; FIG. 2 shows an ultrasonic flowmeter according to the invention; Diagram showing how to attach the transducer to the pipe; 3rd
The figure is an end view of Figure 2; Figure 4 is a cross-sectional view of the transducer and pipe shown in Figure 2; Figure 5 shows the path of the ultrasonic wave on the same cross-sectional view as Figure 4. Explanatory diagram: FIG. 6 is a block diagram of an electronic circuit used for oscillating ultrasonic signals and processing received signals of the ultrasonic flowmeter according to the present invention; FIG. 7 is a block diagram of another ultrasonic flowmeter according to the present invention. A side sectional view of the transducer of the embodiment attached to a pipe;
Plan view of the figure; Figure 9 shows the pipe shown in Figure 7.
It is an end view cut at the -9 position and looking to the right. Explanation of symbols 10, 11...transducer, 12...pipe, 13...control device, 14...
...Coupling fluid, 15,16...Tightening belt, 17,18...Spacer bar, 19,2
0, 21, 22...screw, 23, 24, 25, 2
6... Cylindrical spacer, 30, 31, 32, 33
... Hole, 40, 41, 42, 43 ... Screw, 5
0,51...Thread receiving clip, 52,53...
...Tightening screw, 60, 61...Cylindrical hole, 6
2,63...Ultrasonic transmitting/receiving element, 64,65...
Bottom of hole, 64a, 65a... Sound absorbing material, 66, 6
7...Plastic filler, 70, 71, 72,
73...Terminal, 90...Liquid flow direction, 9
1, 92... Direction in which the ultrasonic wave advances, 150... Input module, 151... Scale computer, 152... Pulse oscillation circuit, 153... N counting circuit, 154... Flow rate counter, 155, 15
5a, 155b...Indicator, 300, 301, 3
02...Vacancy.

Claims (1)

[Claims] 1. An ultrasonic flowmeter for measuring the flow rate of a liquid flowing in a pipe, having the following components: On opposite sides of the outside of the pipe, at intervals in the longitudinal direction of the pipe. , first and second transducers having an ultrasonic transmitting/receiving element and a casing, which are attached with a coupling fluid interposed between them and the outer surface of the pipe to improve acoustic coupling; and the second transducer, such that when the ultrasonic transmitting/receiving element of the first transducer transmits an ultrasonic pulse and the ultrasonic transmitting/receiving element of the second transducer receives the ultrasonic pulse, The difference in propagation time between when the ultrasonic transmitting/receiving element of the second transducer transmits an ultrasonic pulse and when the ultrasonic transmitting/receiving element of the first transducer receives the ultrasonic pulse is measured, and from this difference in propagation time, the A control device that calculates and displays the flow rate of liquid flowing through a pipe. 2 The vibration plane of the ultrasonic transmitting/receiving element is tilted at an angle α with respect to the central axis of the pipe, and the vibration direction of the ultrasonic wave is transmitted from this vibration plane at right angles to the plane and travels through the enclosure at a speed V _c . The phase velocity V _c /sinα at which the wavefront of a transverse ultrasonic pulse in a plane including the normal to the vibration plane of the transmitting/receiving element and the central axis of the pipe advances along the outer surface of the pipe is incident on the pipe from the casing. 2. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is made equal to the propagation velocity V _ps of the transverse ultrasonic pulse traveling in the longitudinal direction in the wall of the pipe. 3. Claim 1, wherein the difference in propagation time is measured by a difference in the number of clocked pulses.
Ultrasonic flowmeter as described in section.