JP3857373B2 - Ultrasonic flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in an ultrasonic flow meter.
[0002]
[Prior art]
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.
[0003]
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.
[0004]
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.
[0005]
In FIG. 6 , the propagation time td of the sound wave from the upstream transducer Tu to the downstream transducer 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.
[0006]
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.
[0007]
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.
[0008]
Further, since the flow rate is (flow rate) × (flow path cross-sectional area), the flow path cross-sectional area in response to the flow rate is required.
[0009]
[Problems to be solved by the invention]
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, and ultrasonic transmission / reception is performed. The distance L between the corrugators also increases.
[0010]
Therefore, if the maximum flow rate to be measured increases, the entire flow meter will increase accordingly, and the length of the straight pipe section required upstream and downstream will correspondingly increase, requiring a large space for flow measurement. There was a problem that there were many restrictions regarding.
[0011]
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.
[0012]
Accordingly, an object of the present invention is to provide an ultrasonic flowmeter that can solve these problems.
[0013]
[Means for Solving the Problems]
In order to achieve the object, the invention of claim 1
The two wall surfaces (2) and (3) constituting the flow path (4) of the flow velocity measuring unit are formed of a coaxial cylindrical surface, and the one wall surface (2) is configured by a cylindrical surface formed on the casing (5). The other wall surface (3) is formed on the outer periphery of the large diameter portion of the substantially bullet-shaped member (6) disposed in the central portion of the flow path (4),
The two wall surfaces (2) and (3) are opposed to each other with an interval (H) in the radial direction between the two cylindrical surfaces, and the velocimeter side portion sandwiched between these two wall surfaces (2) and (3) ( 4), the fluid flows linearly in the generatrix direction of the cylindrical surface, and both the wall surfaces (2) and (3) extend in the circumferential direction (Y) of both the cylindrical surfaces larger than the size of the interval (H). Exist,
And the upstream part and downstream part of one wall surface (2) comprised by the cylindrical surface formed in the casing (5) have a small diameter, and form the inlet and outlet of the fluid to the current meter side part, An upstream-side transducer (Tu) is installed on the entrance side and a downstream-side transducer (Td) is installed on the exit side in the middle of the diameter-changing portion that becomes smaller in diameter toward the entrance and exit. It is an ultrasonic flowmeter.
[0014]
In this invention, it becomes a thing of the compact structure used as a stable streamline and flow velocity distribution, and becomes uniform flow velocity distribution as the whole flow path .
[0015]
Then, ing a stable flow rate by radially short distance between the two cylindrical surfaces forming the flow path wall surface (H).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Next, an outline of the flow velocity measuring unit of the present invention will be described with reference to FIGS.
[0018]
A fluid to be measured passes through the flow path 4 of the cylindrical flow velocity measuring unit sandwiched between two cylindrical wall surfaces (cylindrical surfaces) 2 and 3 disposed coaxially with each other at an interval H (see FIG. It flows from left to right as shown by the thick arrow in b). 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.
[0019]
Therefore, the direction of both the cylindrical surface (wall) 2,3 interval H in the radial direction between the cylindrical surface, the third direction with respect to the perpendicular flow Direction immediate Chi generatrix direction Z with respect to the radial direction H That is, they are formed by curved surfaces facing each other extending in the circumferential direction Y with a dimension larger than the size of the interval H. L ₁ is the length of the straight pipe portion.
[0020]
However, both wall surfaces 2 and 3 cylindrical surface der as they may disposed coaxially with each other, we claim 1, both walls 2 and 3 are to each other in pairs towards Then expressed at intervals H.
[0021]
By the way, as shown in FIGS. 2A and 2B, in the conventional technique using the circular pipe 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.
[0022]
In the case of the present invention shown in FIGS. 1 (a) and 1 (b), in order to make the channel cross-sectional area the same as that of the prior art of FIG.
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. Further, if the introduction / exit flow path is appropriately constructed, the measurement section is less susceptible to upstream and downstream influences.
[0023]
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. .
[0024]
[Example 1]
The embodiment of FIG. 3 (a) (b) are those having the FIGS. 1 (a) passage 4 which is sandwiched between two walls 2 and 3 consisting of a cylindrical surface as described in (b).
[0025]
The wall surface 2 is composed of a cylindrical surface formed in the casing 5. The wall surface 3 is formed of a cylindrical surface formed on the outer periphery of the large-diameter portion of a substantially bullet-shaped member 6 disposed in the central portion of the flow path 4.
[0026]
The ultrasonic transducers Tu and Td are disposed opposite to each other in the casing 5 upstream and downstream of the flow path 4 as shown in the figure to constitute a single-pass system.
[0027]
The upstream portion and the downstream portion of the cylindrical surface 2 have a small diameter as indicated by reference numerals 2A and 2B, and form an inlet and an outlet for fluid to the flow velocity measuring portion.
As is clear from the above description, in the embodiment of FIG. 3, the flow path 4 has a double circular tube shape (doughnut shape) as in FIG. 1 , and a stable flow velocity is achieved by a short width H in the radial direction. Can do.
[0028]
【The invention's effect】
Since the ultrasonic flowmeter of the present invention is configured as described above and a steady flow can be obtained at a short distance, the total 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.
[0029]
Their to, the interval in the flow meter for large flow rate (H) can reduce the distance between the transducer in that Tanhaba can reduce the driving power of the transmitters. 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.
[Brief description of the drawings]
1A and 1B are diagrams showing a flow channel shape of a flow velocity measuring unit according to the present invention, in which FIG. 1A is a front sectional view and FIG. 1B is a side sectional view;
FIGS. 2A and 2B are diagrams showing the shape of a flow channel according to the prior art, in which FIG. 2A is a front sectional view and FIG. 2B is a side sectional view;
3A is a longitudinal sectional view of the first embodiment of the present invention, and FIG. 3B is a transverse sectional view taken along line AA of FIG. 3A.
FIG. 4 is a diagram illustrating a conventional single-pass method.
FIG. 5 is a diagram illustrating a conventional single reflection method.
FIG. 6 is a diagram for explaining the principle of a conventional single-pass method.
[Explanation of symbols]
1 Pipe line 2 Wall surface 3 Wall surface 4 Flow path H Interval Y, Z direction

Claims (1)

The two wall surfaces (2) and (3) constituting the flow path (4) of the flow velocity measuring unit are formed of a coaxial cylindrical surface, and the one wall surface (2) is configured by a cylindrical surface formed on the casing (5). The other wall surface (3) is formed on the outer periphery of the large diameter portion of the substantially bullet-shaped member (6) disposed in the central portion of the flow path (4),
The two wall surfaces (2) and (3) are opposed to each other with an interval (H) in the radial direction between the two cylindrical surfaces, and the velocimeter side portion sandwiched between these two wall surfaces (2) and (3) ( 4), the fluid flows linearly in the generatrix direction of the cylindrical surface, and both the wall surfaces (2) and (3) extend in the circumferential direction (Y) of both the cylindrical surfaces larger than the size of the interval (H). Exist,
And the upstream part and downstream part of one wall surface (2) comprised by the cylindrical surface formed in the casing (5) have a small diameter, and form the inlet and outlet of the fluid to the current meter side part, An upstream-side transducer (Tu) is installed on the entrance side and a downstream-side transducer (Td) is installed on the exit side in the middle of the diameter-changing portion that becomes smaller in diameter toward the entrance and exit. Ultrasonic flow meter.

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