JP2006220670A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase flexibility in the installation position of an ultrasonic transducer by reducing the total length for miniaturization, reducing power consumption, and sharing the ultrasonic transducer even if an aperture or the maximum flow rate differs. <P>SOLUTION: Fluid flowing in from an inlet 2A flows downstream along a channel 4 having a rectangular section, and flows out of an outlet 2B. The channel 4 is formed by wall surfaces 2, 3 that oppose each other with a small interval H, and creates a stable steady flow. Ultrasonic transducers Tu and Td installed at the boss section measure the flow rate in a single-path system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in an ultrasonic flow meter.

  The basic method of the measurement principle of the ultrasonic flowmeter is divided into two methods, a Doppler method and a propagation time measurement method.

  There are three propagation time measurement methods: a time difference method, a time reciprocal difference method, and a phase difference method. In addition, as a method of passing an ultrasonic path in the propagation time measurement method, a single pass method in which a transducer (vibrator) is passed diagonally opposite to a pipe and a single reflection method in which the light is reflected once in the pipe ( The reflection method is well known.

  4 shows a single path system, FIG. 5 shows a single reflection system, Tu is a transducer disposed upstream, and Td is a transducer disposed downstream.

  The time difference method is a basic idea of the propagation time measurement method and is based on the principle that the propagation speed of sound waves in a fluid is different when going from upstream to downstream and when going from downstream to upstream. Switch and measure the flow velocity from the difference in propagation time.

In FIG. 6, the propagation time td of the sound wave from the upstream transducer Tu to the downstream transducer Td is
td = L / (C + V cos θ) (1)
The propagation time tu of the sound wave from the downstream transducer Td to the upstream transducer Tu is
tu = L / (C−V cos θ) (2)
It is.

  L is the distance between the transducers, C is the speed of sound in the static fluid, V is the flow velocity, and θ is the angle between the ultrasonic wave propagation axis and the central axis of the pipe 1.

The propagation time difference Δt is tu−td. Under normal conditions,
(Vcos θ) ² << C ² (3)
Therefore, from these, Δt is
Δt = 2VL cos θ / {C ² + (V cos θ) ² } (4)
Therefore,
Δt = 2VL cos θ / C ² (5)
And the flow velocity V is
V = C ² Δt / 2L cos θ (6)
Asking.

In FIG. 6, D is the inner diameter of the cylindrical pipe line 1, that is, the flow path diameter.
Measurement can be performed in a flow velocity range of 0 to 30 m / s where the flow velocity V is considerably smaller than the sound velocity C so that the condition of the expression (3) is satisfied. This is because, when the flow velocity exceeds 30 m / s, the calculation error of the equation (6) due to ignoring the term (Vcos θ) ² of the equation (4) and the error due to the influence of the compressibility of the gas increase.

  Further, since the flow rate is (flow velocity) × (channel cross-sectional area), a channel cross-sectional area corresponding to the flow rate is required.

  Therefore, in order to stabilize the flow velocity in the pipe and perform accurate measurement, if the length of the flow rate measurement unit (the length in the axial direction of the pipe line) is set to 10D, the total length naturally becomes longer as it is, and ultrasonic transmission / reception is performed. The distance L between the corrugators also increases.

  Therefore, if the maximum flow rate to be measured increases, the entire flow meter increases accordingly, and the length of the straight pipe section required on the upstream and downstream sides accordingly increases, requiring a large space for flow measurement. There was a problem that there were many restrictions on installation.

  Further, as described above, there is a problem that the transmitter / receiver driving power is increased by increasing the distance L between the ultrasonic transducers and the power consumption of the flowmeter is increased.

  Accordingly, an object of the present invention is to provide an ultrasonic flowmeter that can solve these problems.

  The present invention has an inlet (2A) of the flange (7) and an outlet (2B) of the flange (8), and the fluid flowing from the inlet (2A) flows into the channel (4) having a rectangular channel cross section. Thus, the main feature is that it flows linearly in the flow path (4) and flows out from the outlet (2B).

Therefore, in order to achieve the above object, the invention of claim 1 is characterized in that the wall surface constituting the flow path (4) of the flow velocity measuring unit has at least two wall surfaces (2) (2) facing each other at an interval (H). 3), fluid flows in a straight line through the flow path (4) of the flow velocity measuring unit sandwiched between at least these two wall surfaces (2) and (3), and the both wall surfaces (2) and (3) are The flow direction (Z) perpendicular to the interval (H) direction and the third direction (Y) perpendicular to the interval (H) direction and the flow direction (Z) are larger than the size of the interval (H). Extended,
The two wall surfaces (2) and (3) are formed in parallel planes, the flow channel cross section perpendicular to the flow direction (Z) is rectangular, and the long side of the rectangle is on the two wall surfaces (2) and (3). And the length of the short side of the rectangle is the same as the distance (H),
It has an inlet (2A) of the flange (7) and an outlet (2B) of the flange (8), and the fluid flowing in from the inlet (2A) flows into the rectangular cross-section channel (4) and flows out from the outlet (2B). This is an ultrasonic flowmeter.

  According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect of the present invention, the ultrasonic flowmeter has a boss portion, and an ultrasonic transducer is installed on the boss portion.

  According to a third aspect of the present invention, in the ultrasonic flowmeter according to the second aspect, the flow velocity of the fluid flowing through the flow path (4) is measured by a single-pass method.

  The ultrasonic flowmeter of the present invention is configured as described above, has a compact structure with stable streamlines and flow velocity distribution, and has a uniform flow velocity distribution as a whole rectangular channel. Further, a stable flow velocity is obtained by an interval (H) between two parallel wall surfaces (2) and (3) forming the wall surface of the channel (4), that is, the short sides (2 'and 3') of the rectangular channel. Thus, since a steady flow can be obtained at a short distance, the overall length can be shortened to be compact. Moreover, it is hard to receive the influence of upstream and downstream from the flow-path cross-sectional shape of a flow velocity measurement part.

  In addition, the channel cross-sectional area of the inlet and outlet portions can be made substantially the same as the channel cross-sectional area of the rectangular channel, and the pressure loss can be reduced. Moreover, connection with piping becomes easy by making an entrance part and an exit part into a flange.

  And since the distance (H) has a short width | variety also in the flowmeter for large flow rates, since the distance between transducers can be made small, the drive electric power as a transmitter can be reduced. Further, if the interval (short width) (H) is constant regardless of the difference in the diameter of the flow meter, there is an advantage that the same ultrasonic transducer can be shared regardless of the maximum flow rate.

  In the invention of claim 2, since the ultrasonic transducer can be installed not only on the outer wall of the flow path but also on the boss portion, the flexibility of the installation location of the transducer is large.

  Further, the distance between the two ultrasonic transducers can be increased. Therefore, since the propagation time of the ultrasonic wave can be increased, the measurement accuracy is improved.

  In the invention of claim 3, since there is no attenuation of the ultrasonic wave due to reflection on the wall surface of the flow path, the signal level of the received wave is increased, so that the S / N can be increased, and the accuracy of the flow rate measurement can be improved. It becomes.

Next, the best mode for carrying out the present invention will be described based on the embodiments shown in the drawings.
[Example 1]
1 (a), (b), and (c), the flow path 4 of the flow velocity measuring section has a rectangular cross section, and the two short sides of the rectangle are formed by parallel wall surfaces 2 'and 3'. The sides are formed by wall surfaces 2 and 3 parallel to each other. The distance between the wall surfaces 2 and 3 is determined to be short by H.

The fluid that has flowed in from the inlet 2A of the flange 7 flows into the flow path 4 having a rectangular cross section of the flow velocity measuring section as indicated by an arrow, and flows out from the outlet 2B of the flange 8. The flow velocity of the fluid flowing through the flow path 4 is measured by a single-pass method using ultrasonic transducers Tu and Td that are installed opposite to the boss portion.
[Control example]
Next, the total length of the ultrasonic flowmeter will be described with reference to FIGS. 2A and 2B is not included in the claims of the present invention.

  In FIG. 2, a fluid to be measured is flown in a flow path 4 of a cylindrical flow velocity measuring unit sandwiched between two cylindrical wall surfaces (cylindrical surfaces) 2 and 3 that are coaxially arranged with a distance H. Flows from the left to the right as shown by the thick arrows in FIG. This flow direction is the left-right direction shown by the symbol Z in FIG. 4B and corresponds to the generatrix direction of both cylindrical surfaces 2 and 3, and in FIG.

Accordingly, the cylindrical surfaces (wall surfaces) 2 and 3 are third in the flow direction Z perpendicular to the direction of the radial interval H between the cylindrical surfaces, and in the interval or radial direction H and the flow direction or bus direction Z. In other words, it is formed of a curved surface extending in a direction larger than the distance H in the circumferential direction Y. L ₁ is the length of the straight pipe portion.

Incidentally, as shown in FIGS. 3 (a) and 3 (b), in the conventional technique using the circular pipe line 1, when the length L ₀ of the straight pipe portion is 10 times (provisional) or more of the diameter φD ₀ , If φD ₀ is large, the total length of the flow meter becomes considerably long. For example, if φD ₀ = φ60, L ₀ = 600.

In the case of the control example shown in FIGS.
D ₀ ² = D ₁ ² -d ₁ ²
And Since the flow velocity distribution is formed by the distance H between the wall surface (cylindrical surface) 2 and the wall surface (cylindrical surface) 3, a steady flow is obtained when L ₁ = 10H. If H = 15, L ₁ becomes a steady flow at 150 mm, and even if it is a fraction of the length of FIG. 3, it becomes a steady flow. Further, if the introduction / exit flow path is appropriately constructed, the measurement section is less susceptible to upstream and downstream influences. The same applies to the case of the present invention shown in the first embodiment.

Further, if the values of the interval H and the length L ₁ are limited to a certain range, the total length is single regardless of the maximum flow rate of the flow meter, and the electronic circuit related to the ultrasonic transducer can be shared. .

In the first embodiment of the present invention, (a) is a plan sectional view, (b) is a longitudinal side view, and (c) is a cross-sectional view taken along the line BB of (b). It is a figure which shows the flow-path shape of a control example, (a) is a front sectional view, (b) is a sectional side view. It is a figure which shows the flow-path shape of a prior art, (a) is a front sectional view, (b) is a sectional side view. It is a figure which shows the single path | pass system of a prior art. It is a figure which shows the single reflection system of a prior art. It is a figure explaining the principle of the single pass system of a prior art.

Explanation of symbols

1 Pipe line 2 Wall surface 3 Wall surface 2 'Wall surface 3' Wall surface 4 Channel H interval Y, Z direction

Claims (3)

The wall surface constituting the flow path (4) of the flow velocity measuring unit has at least two wall surfaces (2) and (3) facing each other with an interval (H), and at least these two wall surfaces (2) and (3) The fluid flows in a straight line through the flow path (4) of the flow velocity measurement unit sandwiched between the two wall surfaces (2) and (3), and the flow direction (Z) perpendicular to the interval (H) direction, Extending in a third direction (Y) perpendicular to the interval (H) direction and the flow direction (Z) to be greater than the size of the interval (H),
The two wall surfaces (2) and (3) are formed in parallel planes, the flow channel cross section perpendicular to the flow direction (Z) is rectangular, and the long side of the rectangle is on the two wall surfaces (2) and (3). And the length of the short side of the rectangle is the same as the distance (H),
It has an inlet (2A) of the flange (7) and an outlet (2B) of the flange (8), and the fluid flowing in from the inlet (2A) flows into the rectangular cross-section channel (4) and flows out from the outlet (2B). An ultrasonic flowmeter characterized by that. The ultrasonic flowmeter according to claim 1, further comprising a boss portion, and an ultrasonic transducer installed in the boss portion. The ultrasonic flowmeter according to claim 2, wherein the flow velocity of the fluid flowing through the flow path (4) is measured by a single-pass method.

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