JP3528436B2 - Ultrasonic flow meter and current meter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter for measuring a flow rate by ultrasonic waves.

[0002]

2. Description of the Related Art FIG. 10 shows a conventional measuring device of this type.
As shown in FIG. 2, a pair of ultrasonic transducers 2 and 3 are arranged in the vertical direction across a measurement flow path 1 having a rectangular cross section and long sides thereof arranged in the vertical direction. Some have found the flow rate from the difference in propagation time between two and three.

[0003]

However, in this case, when convection such as Vf shown in FIG. 10 occurs when the fluid to be measured is not flowing, the flow velocity is Vf.cos.
Since it is detected as θ, incorrect measurement is performed.

An object of the present invention is to eliminate the influence of erroneous measurement due to such convection.

[0005]

In an ultrasonic flowmeter of the present invention, a flow rate measuring section having a flow path, a pair of ultrasonic transducers for measuring the flow velocity of a fluid flowing through the flow rate measuring section, and A flow rate calculation unit that calculates a flow rate based on the flow velocity measured by the ultrasonic transducer, wherein the flow rate measurement unit is a flat
It has a rectangular cross section and is positioned so that the long side is horizontal.
The ultrasonic transducer on the short side of the flow rate measurement unit.
However, a pair in a direction substantially perpendicular to the flow passing through the flow path
It suppresses the influence of the flow on the measurement .

According to the present invention, the velocity component can be measured with high accuracy.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION To achieve the above object, the present invention provides a flow rate measuring section, a pair of ultrasonic transducers for measuring the flow velocity of a fluid flowing through the flow rate measuring section, and measurement with the ultrasonic transducers. And a flow rate calculation unit that calculates a flow rate based on the calculated flow velocity, the flow rate measurement unit is configured to suppress convection, and the convection suppression unit is a flat flow rate measurement unit. Along with the cross section, it is conceivable to set the position so that the long side is horizontal so that the ultrasonic wave propagation of the ultrasonic transducer is parallel to the long side, or to make the flow rate measurement unit adiabatic. Ah

Further, assuming that convection occurs, it is set such that the flow velocity of the fluid caused by the convection is equal to or less than the minimum measurement velocity, or the flow velocity of the fluid caused by the convection is If the cross-sectional area of the flow rate measurement unit is set so as to be equal to or less than the minimum measurement flow velocity, the measurement will not be substantially affected.

Then, convection may be determined by the temperatures above and below the flow rate measuring unit.

Further, the ultrasonic flowmeter is provided with a flow passage and a pair of ultrasonic transducers for measuring the flow velocity of the fluid flowing through the flow passage. The development of can be considered enough.

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, 4 is a flow rate measuring unit, and 5
Is the flow path. The flow path 5 has a rectangular cross section. The flow rate measurement unit 4 is arranged such that the long side 4a of the rectangular cross section is horizontal. Reference numerals 6 and 7 denote ultrasonic transducers, which are horizontally opposed to each other so that the ultrasonic wave propagation path p is horizontal. Reference numeral 8 is a flow rate calculation unit.

FIG. 2 shows an apparatus 9 incorporating this flow rate measuring unit 4.
Is shown. In FIG. 2, 10 is an upstream chamber provided upstream of the flow rate measuring unit 4, and 11 is a downstream chamber provided downstream of the flow rate measuring unit 4. 12 is an inlet connected to the upstream chamber 10, and 13 is an outlet connected to the downstream chamber 11.

FIG. 3 shows a flow rate calculator 8 which receives signals from the first and second ultrasonic transducers 6 and 7 and calculates the flow rate. In FIG. 3, 14 is a start signal generator, 15 is a transmitter, and 16 is a receiver. Reference numeral 17 is a switching unit.

The transmitting section 15 comprises a trigger signal generating section 18 and an oscillating section 19. The reception unit 16 is composed of a reception signal amplification unit 20 and a reference value comparison unit 21. 22 is a repeating unit, 23 is a timekeeping unit, and 24 is an arithmetic unit.

Next, the operation will be described. The fluid flows in through the inlet portion 12, passes through the upstream chamber 10, enters the flow rate measuring unit 4, then passes through the downstream chamber 11, and flows out through the outlet portion 13. When a signal is input from the start signal generation unit 14 in such a state, the trigger signal generation unit 18 operates and the oscillation unit 19 sends the signal to the switching unit 17.

The switching unit 17 is initially set so that the transmitting unit 15 is connected to the first ultrasonic transducer 6 and the receiving unit 16 is connected to the second ultrasonic transducer 7. Therefore, an ultrasonic signal is emitted from the first ultrasonic transducer 6 into the flow rate measuring unit 4 by the trigger signal.

This signal is received by the second ultrasonic transducer 7, amplified by the amplification section 20, and compared with the reference signal by the comparison section 21. This process is repeated a set number of times by the repeater 22, and then a signal is sent to the timer 23.

The timer section 23 measures the elapsed time (T1) from the generation of the trigger signal to the signal sent at this time.
On the other hand, when the predetermined number of repetitions are completed, a signal is sent from the repeating unit 22 to the switching unit 17, the transmitting unit 15 is the second ultrasonic transducer 7, and the receiving unit 16 is the first ultrasonic transducer. Connect to 6.

At the same time, the drive signal to the trigger signal generator 18 is sent again. As a result, the same operation as above is performed in the direction opposite to the flow, and the elapsed time (T
2) is measured. Based on the elapsed times T1 and T2 measured in this way, the calculation unit 2 is calculated by the following calculation formula.
The flow rate is calculated at 4.

Assuming that the angle between the flow to be measured and the ultrasonic wave propagation path is θ and the length of the flow rate measuring section is L, the flow velocity v is calculated by the following equation.

V = (L / 2cos θ) ((1 / T1) − (1 / T2)) From the flow velocity v thus obtained and the cross-sectional area s of the flow rate measuring unit 4, the flow rate Q is calculated by the following equation. .

Q = kvs where k is the flow velocity v and the cross-sectional area s
It is a conversion factor for converting to the average flow velocity in. Although the measurement of T1 and T2 is repeated in the above description, it may be performed once if accurate measurement is performed.

Here, as shown in FIG. 1, it is assumed that the flow a due to convection is generated in the vertical direction when the flow to be measured is not generated. In this case, the flow rate measuring unit 4 is arranged such that its long side 4a is horizontal, and the ultrasonic wave propagation paths p of the first and second ultrasonic transducers 6 and 7 are horizontal. Therefore, even if the flow a due to convection occurs, the velocity vector Va due to the ascending air flow is orthogonal to the ultrasonic wave propagation path p, so that the velocity component is not erroneously measured.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In FIG. 4, (a) is a vertical sectional view of the flow rate measuring unit 4, and (b) is a horizontal sectional view. Reference numeral 25 is an upper wall of the flow path 5, and 26 is a lower wall. The height (h) of the flow path 5 is determined by the upper wall 25 and the lower wall 26.
It is set assuming that the maximum temperature difference occurs in the.

That is, the flow velocity when the convection V generated at this time crosses the ultrasonic wave propagation path p is Vb, and the relationship between this value and the measured minimum flow velocity Vmin is set so as to satisfy the following equation.

Vb <Vmin Next, the operation will be described. Due to the above settings, even if a flow due to convection occurs when there is no flow to be measured, the measured flow velocity value is less than the minimum measurement flow velocity, so it is excluded as a convection error. It

(Embodiment 3) Next, a third embodiment will be described. In FIG. 5, 2
Reference numeral 7 is a flow rate measuring unit, and 28 is its flow path. Channel 2
8 has a rectangular cross section. 29 and 30 are ultrasonic transducers. 31 is an inflow path, 32 is a throttle part, 33 is an outflow path,
Reference numeral 34 is an enlarged portion. The other parts are the same as those in the first embodiment and will not be described. In this case, the cross-sectional area (s) of the channel 28 is set so as to satisfy the following formula.

Qmin / s = Vmin> Vc where Qmin is the minimum flow rate measured and Vc is the flow velocity value that can be generated by convection. The flow channel cross-sectional area (s) is defined by the following equation.

S = wh Here, w is the flow channel width and h is the flow channel height.

Next, the operation will be described. Since the settings are as described above, when there is no flow to be measured,
Even if a flow due to convection occurs, the measured flow velocity value is less than or equal to the measured minimum flow velocity, and thus is excluded as a convection error.

Fourth Embodiment Next, a fourth embodiment will be described. In FIG. 6, 3
5 is a flow rate measuring unit, 36 is its flow path, and 37 and 38 are ultrasonic transducers. Reference numeral 39 is a flow path wall forming the flow path 36, and 40 is a heat insulating material, which covers the outer periphery of the flow path wall 39. The other parts are the same as those in the first embodiment and will not be described.

Next, the operation will be described. In this case, the flow path 36
Since the entire outer circumference of is covered with the heat insulating material 40, convection is unlikely to occur in the flow rate measuring unit 35.
Therefore, when there is no flow to be measured, the generation of convection is suppressed, and there is no risk of convection error.

(Fifth Embodiment) Next, a fifth embodiment will be described. In FIG. 7, 4
1 is a temperature sensor mounted near the upper wall 25,
Reference numeral 42 is a temperature sensor attached near the lower wall 26. Others are the same as in FIG. 4 in FIG.
Reference numeral 3 denotes a convection determination calculation unit, which stores a table of convection flow velocities estimated to occur corresponding to the temperature difference between the temperature sensors 41 and 42. Others are the same as those in FIG.

Next, the operation will be described. In this case, the temperature sensors 41 and 42 detect the temperature difference in the flow path 5, and the convection determination calculation unit 43 refers to the previously stored convection-based flow velocity estimation table. This value is compared with the value from the calculation unit 24, and when it is considered that the influence of convection is large, this value is excluded.

(Sixth Embodiment) Next, a sixth embodiment will be described. In FIG. 9, 4
Reference numeral 4 is a flow rate measuring unit, and 45 is its flow path. 46 is an upper wall and 47 is a lower wall. 48 is the upper wall 46
The ultrasonic transducer 49 is attached to the lower wall 47. The ultrasonic oscillator 48 is attached upstream of the ultrasonic oscillator 49. In addition,
The other parts are the same as those in the first embodiment, and therefore omitted.

Next, the operation will be described. In this case, the ultrasonic wave propagation path q goes from the upstream side to the downward side. Therefore, when the convection Vd occurs in the flow path 45, it is measured as a negative flow velocity. As a result, when a negative value is generated in the measurement value during measurement when there is no flow, convection can be eliminated and it can be eliminated.

The signal processing in the present invention can be realized by software using a microcomputer such as a one-chip microcomputer. Further, since the flow rate calculation in the present invention is performed based on the flow velocity measurement, the method described in the present invention can be applied to the ultrasonic velocity meter.

The effects of the above-described embodiment can be summarized as follows.

(1) The flow rate measuring section having a rectangular cross section is arranged so that the long side direction is horizontal, and the ultrasonic transducer is
By arranging the ultrasonic wave propagation paths so as to face each other in the horizontal direction, even if a flow due to convection occurs, the velocity vector due to the ascending air current is orthogonal to the ultrasonic wave propagation path, so that the velocity component is not erroneously measured.

(2) The flow measuring unit is arranged so that the long side direction is horizontal, and the height of the cross section of the flow measuring unit is set to a value such that convection in the flow channel does not affect the measurement. As a result, even if a flow due to convection occurs when the flow to be measured does not occur, the measured flow velocity value becomes equal to or less than the minimum measurement flow velocity, and thus is eliminated as a convection error.

(3) By setting the cross-sectional area of the flow rate measuring portion so that the flow velocity at the minimum measurement flow rate is larger than the flow velocity generated by convection, when the flow to be measured does not occur, Even if a flow occurs, the measured flow velocity value is less than the minimum measurement flow velocity, so it is eliminated as a convection error.

(4) By covering the entire outer circumference of the flow rate measuring section with a heat insulating material, it becomes difficult for convection to occur in the flow rate measuring section, the generation of convection is suppressed, and there is no risk of convection error.

(5) It is determined that the influence of convection is large by installing at least two temperature sensors arranged in the flow rate measuring unit and a determination unit for determining convection generation based on the signal from the temperature sensor. Data can be rejected.

[0045]

As described above, according to the present invention, an erroneous measurement due to convection can be eliminated, and a highly reliable ultrasonic measuring instrument can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view of an ultrasonic flowmeter according to a first embodiment of the present invention.

FIG. 2 is a vertical sectional view of a device incorporating the same flow meter.

FIG. 3 is a control block diagram of a flow rate calculation unit in the flow meter.

FIG. 4A is a vertical sectional view of an ultrasonic flowmeter according to a second embodiment of the present invention, and FIG. 4B is a horizontal sectional view of the same flowmeter.

FIG. 5 is a horizontal sectional view of an ultrasonic flowmeter according to a third embodiment of the present invention.

FIG. 6 is a sectional view of an ultrasonic flowmeter according to a fourth embodiment of the present invention.

FIG. 7 is a perspective view of an ultrasonic flowmeter according to a fifth embodiment of the present invention.

FIG. 8 is a control block diagram of a flow rate calculation unit in the flow meter.

FIG. 9 is a partially cutaway perspective view of an ultrasonic flowmeter according to a sixth embodiment of the present invention.

FIG. 10 is a partially cutaway perspective view of a conventional ultrasonic flowmeter.

[Explanation of symbols]

4 Flow rate measurement unit 4a long side 6 First ultrasonic transducer 7 Second ultrasonic transducer 8 Flow rate calculator

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-249690 (JP, A) JP-A-8-105776 (JP, A) Fukuihei 6-80130 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (5)

(57) [Claims] 1. A flow rate measuring unit having a flow path, a pair of ultrasonic transducers for measuring a flow velocity of a fluid flowing through the flow rate measuring unit, and a flow rate calculated based on the flow velocity measured by the ultrasonic transducer. ; and a flow rate calculation unit that, the flow rate measurement unit, flat
It has a rectangular cross section and is positioned so that the long side is horizontal.
The ultrasonic transducer on the short side of the flow rate measurement unit.
However, a pair in a direction substantially perpendicular to the flow passing through the flow path
An ultrasonic flow meter that suppresses the influence of flow on measurement . 2. A method according to claim 1 Symbol placement of the ultrasonic flowmeter flow velocity of the fluid is set to be below the minimum measurement flow rate when the convection is generated. 3. Ultrasonic flowmeter according to claim 1, wherein the flow velocity of the fluid has set the cross-sectional area of the flow measuring unit to be less than the minimum measurement flow rate when the convection is generated. 4. The ultrasonic flowmeter according to claim 1, wherein convection is determined based on the temperatures above and below the flow rate measuring unit. 5. A flow rate measuring unit having a flow path, and the flow rate measuring unit.
A pair of ultrasonic transducers for measuring the flow velocity of fluid flowing in a fixed part
And calculate the flow rate based on the flow velocity measured by the ultrasonic transducer.
And a flow rate calculating section for outputting the flow rate measuring section,
It has a rectangular cross section and is positioned so that the long side is horizontal.
The ultrasonic transducer on the short side of the flow rate measurement unit.
However, a pair in a direction substantially perpendicular to the flow passing through the flow path
An ultrasonic velocity meter that suppresses the influence of flow on measurement.