JPH08313316A - Ultrasonic wave type flow meter - Google Patents

Abstract

PURPOSE: To take flow rate measurement with high precision without increasing a pressure loss by using a flow rate measuring portion having a rectangular cross section. CONSTITUTION: A ultrasonic wave flow meter is equipped with a flow rate measuring portion 4 having a rectangular cross section, first ultrasonic wave vibrator 9 arranged sandwiching the flow rate measuring portion 4, second ultrasonic wave vibrator, and a flow rate computing portion computing a flow rate on the basis of the signal of the vibrator, and the short side length of the rectangular cross section of the flow rate measuring portion 4 is set so that the Reynolds number becomes within a laminar flow range when the Reynolds number is computed taking the length as a representative length, Thereby, the flow in the flow rate measuring portion 4 becomes a laminar flow without increasing a pressure loss so that flow rate measurement with high precision can be taken.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In a conventional measuring device of this type, as shown in FIG. 8, ultrasonic transducers 2 and 3 are installed so as to face each other at both ends of a measuring section 1 having a circular cross section. The radius is set so that the flow in Fig. 2 maintains a laminar flow state, the time until the ultrasonic wave emitted from the vibrator 2 is detected by the vibrator 3 is measured, and the velocity of the fluid is calculated from this time. The flow rate was calculated.

[0003]

However, when using a flow path having a circular cross section, it is necessary to make the radius small in order to achieve laminar flow, which results in a small cross-sectional area and a large pressure loss. It was a thing.

The present invention is to solve the above-mentioned problems. The measurement channel is formed in a rectangular cross section, and the length on the short side of the cross section is calculated by using this length. By setting so that the flow rate can be measured accurately without increasing the pressure loss of the flow in the measurement flow path, and without generating the transition state to the turbulent region while maintaining the laminar flow state of the flow. Is intended to do.

[0005]

In order to achieve the above object, the present invention provides a flow rate measuring section having a rectangular cross section, and first and second ultrasonic transducers arranged so as to sandwich the flow rate measuring section. And a flow rate calculation unit that calculates a flow rate based on the signal of the ultrasonic transducer, and the Reynolds number calculated by using the length as a representative length for the length of the short side in the rectangular cross section of the flow rate measurement unit. Is set so that it becomes a laminar basin.

Further, the inflow port and the outflow port of the flow rate measuring section are formed by smooth curved surfaces.

Further, the flow rate measuring section having a rectangular cross section, the first and second ultrasonic transducers arranged on one side of the flow rate measuring section, and the first and second ultrasonic transducers arranged on the other side of the flow rate measuring section. The ultrasonic wave emitted from the ultrasonic oscillator of the second ultrasonic oscillator is reflected by a reflector, and a flow rate calculation unit that calculates a flow rate based on the signal of the oscillator is provided, The length of the short side in the rectangular cross section is set so that the Reynolds number calculated by using the length as a representative length is a laminar flow region.

Further, a flow rate measuring section having a rectangular cross section, upstream and downstream chambers disposed upstream and downstream of the flow rate measuring section, and first and second ultrasonic vibrations disposed in the respective chambers. A flow rate calculation unit that calculates a flow rate based on the signal of the vibrator, and the Reynolds number calculated by using the length as a representative length for the length of the short side in the rectangular cross section of the flow rate measurement unit. It is set so that it becomes a laminar basin.

[0009]

According to the present invention, with the above configuration, the flow rate measurement in the flow rate measuring section is performed in the laminar flow state without increasing the pressure loss, and the transition state to the turbulent flow state in which the flow velocity distribution fluctuates irregularly. The measurement can be performed without passing through, and accurate measurement can be performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS.

1 to 3, 4 is a flow rate measuring unit, 5 is an upstream chamber provided upstream of the flow rate measuring unit 4, and 6 is a downstream chamber provided downstream of the flow rate measuring unit 4. Reference numeral 7 is an inlet portion connected to the upstream chamber 5, and 8 is an outlet portion connected to the downstream chamber 6.

Reference numeral 9 is a first ultrasonic vibrator, and 10 is a second ultrasonic vibrator. 11 is the first ultrasonic transducer 9
Is a dent caused by the arrangement, and 12 is a dent caused by the arrangement of the second ultrasonic transducer 10.

Reference numeral 13 is an inflow port of the flow rate measuring unit 4, and 14 is an outflow port. In FIG. 4, reference numeral 15 is a flow rate calculation unit that receives signals from the first and second ultrasonic transducers 9 and 10 and performs flow rate calculation. Among them, 16 is a start signal generating section, 17 is a transmitting section, 18 is a receiving section, and 19 is a switching section.

The transmission section 17 comprises a trigger signal generation section 20 and an oscillation section 21. The receiving unit 18 includes an amplifying unit 22 for a received signal and a comparing unit 23 with a reference value.

Reference numeral 24 is a repeating unit, 25 is a time counting unit, and 26 is an arithmetic unit. Next, the operation will be described.

The fluid flows in through the inlet portion 7, passes through the upstream chamber 5, enters the flow rate measuring portion 4, and then passes through the downstream chamber 6 and flows out through the outlet portion 8.

The flow rate measuring unit 4 has a rectangular cross section, and the length (h) of its short side is set so that the Reynolds number calculated by using the length as a representative length will be a laminar flow region. I am doing it.

That is, the maximum flow velocity measured is v (m
ax), the Reynolds number (Re) is determined by the following equation, where kinematic viscosity coefficient is ν.

Re = v (max) h / ν (1) On the other hand, in order for the flow to reach the laminar flow region, it is necessary to satisfy the following equation.

Re ≦ 2300 (2) Therefore, the short side length (h) satisfying (1) and (2) is determined within the range of the following equation.

H ≦ 2300 · ν / v (max) When a signal is input from the start signal generator 16 in such a state, the trigger signal generator 20 operates and the oscillator 21 sends the signal to the switching unit 19. The switching unit 19 is initially set so that the transmitting unit 17 is connected to the first ultrasonic transducer 9 and the receiving unit 18 is connected to the second ultrasonic transducer 10.
Therefore, an ultrasonic signal is emitted from the first ultrasonic transducer 9 into the flow rate measuring unit 4 by the trigger signal. This signal is received by the second ultrasonic transducer 10, and the amplification unit 22
Is amplified by and compared with the reference signal in the comparison unit 23,
When the signal exceeding the reference value is obtained, the trigger 20 is driven again. This process is performed the number of times set by the repeater 24.

When the predetermined number of repetitions has been completed, a signal is sent to the timer unit 25, and the elapsed time (T1) from the generation of the trigger signal to the signal sent at this time is counted. On the other hand, when the predetermined number of repetitions are completed, a signal is sent from the repeating unit 24 to the switching unit 19, and the transmitting unit 17 is used as the second ultrasonic transducer 10 and the receiving unit 18 is used as the first ultrasonic vibration. Connect to child 9.

At the same time, the drive signal to the trigger signal generator 20 is also sent again, the same operation as above is performed in the opposite direction to the flow, and the elapsed time (T2) is measured.

Based on the elapsed times T1 and T2 measured in this way, the flow rate is calculated by the calculation unit 26 by the following calculation formula.

Now, assuming that the angle between the flow and the ultrasonic wave propagation path is θ and the length of the flow rate measuring portion is L, the flow velocity v is calculated by the following equation.

V = L / 2cos θ (1 / T1-1 / T2) The flow rate (Q) is calculated by multiplying this flow rate by the cross-sectional area (s) of the flow rate measuring unit 4.

Q = k · v · s Here, k is a flow rate correction coefficient for obtaining the average flow rate from the measured flow rate.

By setting the short side length of the flow rate measuring unit 4 in this manner, the flow rate can be measured in a laminar flow state,
Since it is possible to avoid measurement in the transition state where the flow velocity distribution shape is unstable, it is possible to use a constant value in the laminar flow region as the flow rate correction coefficient over the entire measurement region, and it is highly accurate without increasing pressure loss. Flow rate measurement is realized.

Next, a second embodiment will be described. Figure 5
In, the inflow port 27 of the flow rate measuring unit 4 and the outflow port 2
It is the same as the first embodiment except that 8 is arcuate.

Next, the operation will be described. The fluid is measured by the flow rate measuring unit 4, and at that time, the inflow port 2 of the flow rate measuring unit 4
Since 7 is formed in an arc shape, introduction into the flow rate measuring unit 4 is performed without causing turbulence when flowing into the flow rate measuring unit 4 from the upstream chamber 5. This further ensures that the measurement is carried out in laminar flow.

Next, a third embodiment will be described. Figure 6
In the first embodiment, except that the first ultrasonic transducer 29 and the second ultrasonic transducer 30 are provided on the same side of the flow rate measuring unit 4 and the reflecting plate 31 is provided on the opposite side thereof. Is the same as.

Next, the operation will be described. The measurement of the fluid is performed by the flow rate measurement unit 4, and at that time, the ultrasonic wave propagation path in the flow rate measurement unit 4 is emitted from the first ultrasonic transducer 29, reflected by the reflection plate 31, and then the second ultrasonic wave. Ultrasonic transducer 3
Reach 0. As a result, the flow velocity v passes through the cross section of the flow rate measurement unit 4 twice, so that a more averaged flow velocity can be obtained.

Next, a fourth embodiment will be described. Figure 7
2 is the same as that of the first embodiment except that the first ultrasonic transducer 32 and the second ultrasonic transducer 33 are arranged in the upstream chamber 5 and the downstream chamber 6, respectively.

Next, the operation will be described. Flow velocity is measured in the upstream chamber 5
Between the first ultrasonic transducer 32 arranged in the lower chamber 6 and the second ultrasonic transducer 33 arranged in the downstream chamber 6. At this time, since the respective transducers are installed away from the flow rate measuring unit 4, there is no dent formed when the ultrasonic transducer is arranged in the flow rate measuring unit 4, and the flow is measured in the flow rate measuring unit 4. It does not cause a transition to a turbulent state. Therefore, more accurate measurement can be performed.

[0035]

As described above, according to the present invention, the following effects can be obtained.

(1) The flow rate can be measured in a laminar flow state without increasing the pressure loss, and the flow rate distribution can be accurately measured without passing through an unstable transition state.

(2) Since the inflow port of the flow rate measuring section is formed in an arc shape, the state of laminar flow measurement in the flow rate measuring section can be more guaranteed.

(3) By making the ultrasonic wave propagation path in the flow rate measuring section into a V-shape, the ultrasonic wave propagation path will pass through the cross section of the flow rate measuring section twice, so that a more averaged flow velocity can be obtained. You can

(4) By measuring the flow velocity between the first ultrasonic transducer arranged in the upstream chamber and the second ultrasonic transducer arranged in the downstream chamber, each transducer is separated from the flow rate measuring section. Since there is no dent formed when the ultrasonic transducer is placed in the flow rate measurement unit, the flow rate measurement unit does not transition the flow to a turbulent state. Therefore, more accurate measurement can be performed.

[Brief description of drawings]

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

FIG. 2 is a horizontal sectional view of the same flow meter.

FIG. 3 is a perspective view of the flow meter.

FIG. 4 is a control block diagram of the flow meter.

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

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

FIG. 7 is a horizontal sectional view of an ultrasonic flowmeter according to a fourth embodiment of the present invention.

FIG. 8 is a vertical sectional view of a conventional ultrasonic flowmeter.

[Explanation of symbols]

 4 Flow Rate Measuring Section 5 Upstream Chamber 6 Downstream Chamber 9, 29, 32 First Ultrasonic Transducer 10, 30, 33 Second Ultrasonic Transducer 15 Flow Rate Calculator 27 Inlet 28 Outlet 31 Reflector

Claims (4)

[Claims] 1. A flow rate measuring section having a rectangular cross section, first and second ultrasonic transducers arranged with the flow rate measuring section sandwiched therebetween, and a flow rate calculated based on signals from the ultrasonic transducers. An ultrasonic flowmeter, comprising: a flow rate calculating section for controlling the flow rate measuring section so that the Reynolds number calculated with the length as a representative length is a laminar flow region. 2. The ultrasonic flowmeter according to claim 1, wherein the inflow port and the outflow port of the flow rate measuring section are formed by smooth curved surfaces. 3. A flow rate measuring section having a rectangular cross section, first and second ultrasonic transducers arranged on one side of the flow rate measuring section, and a first flow rate measuring section arranged on the other side of the flow rate measuring section. The ultrasonic wave emitted from the ultrasonic oscillator of the second ultrasonic oscillator is reflected by a reflector, and a flow rate calculation unit that calculates a flow rate based on the signal of the oscillator is provided, An ultrasonic flowmeter in which the length of the short side in a rectangular cross section is set such that the Reynolds number calculated by using the length as a representative length is a laminar flow region. 4. A flow measuring unit having a rectangular cross section, upstream and downstream chambers arranged upstream and downstream of the flow measuring unit, and first and second ultrasonic vibrations arranged in the respective chambers. A flow rate calculation unit that calculates a flow rate based on the signal of the vibrator, and the Reynolds number calculated by using the length as a representative length for the length of the short side in the rectangular cross section of the flow rate measurement unit. An ultrasonic flow meter set to be in the laminar flow region.