JP5454129B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic transducer for transmitting and receiving ultrasonic pulses and an apparatus for measuring the flow rate and flow velocity of gas and liquid using the ultrasonic transducer.

  Conventionally, as shown in FIG. 6, this type of ultrasonic flow rate measuring apparatus has transceivers 101a and 101b attached with the sound wave transmission / reception surface facing downward. The reflectors 102a and 102b reflect sound waves and change their directions. In the figure, the directions are changed by 90 degrees. When the sound wave is transmitted from the transmitter / receiver 101a, it travels downward, is reflected by the reflector 102a, propagates horizontally in the flow path 103, is reflected by the reflector 102b, and is received by the transmitter / receiver 101b. When transmitting from the transceiver 101b, it has propagated to the transceiver 101a through the reverse path.

JP 2004-69529 A

  However, in the conventional ultrasonic flow measurement device, as shown in FIG. 6, the sound wave transmitted from the transceiver 101a propagates in the flow path 3 and spreads radially in the space provided in front of the transceiver 101b. In particular, unnecessary sound waves may be generated in the portion A, and unnecessary sound waves may reach the transceiver 101b before the main sound waves are received by the transceiver 101b. FIG. 7 shows a signal obtained by receiving the sound wave including such an unnecessary sound wave by the receiver 101b, and the unnecessary sound wave exists before the main sound wave. For this reason, an unnecessary received signal becomes a noise source and affects the received signal used for measurement, so that the measurement accuracy may be deteriorated.

In order to solve the above-described conventional problems, an ultrasonic flow measuring device according to the present invention includes a channel through which a fluid to be measured flows and a pair of transmission / reception units that transmit or receive sound waves disposed upstream and downstream of the channel. A counter, a measuring means for measuring a propagation time of an ultrasonic signal between the transceiver, a flow rate calculating means for calculating a fluid flow rate according to the propagation time, and a transmission / reception surface of each of the pair of transceivers And the pair of transmitters / receivers are both disposed on the side of the flow path, and the ultrasonic waves transmitted from one transmitter / receiver can be turned 90 degrees by the reflectors. Then, after propagating through the fluid to be measured, it is arranged so that the direction is again changed by 90 degrees by the reflector and received by the other transceiver, and is unnecessary for the path from the flow path to the transceiver. Attenuator to eliminate ultrasonic signal And location, the damping unit, by characterized in that it is constituted by a stepped space, it is possible to receive the signals required for measurement without being affected by unwanted signals.

  According to the ultrasonic flow measuring device of the present invention, when the ultrasonic wave propagates from the flow path toward the transmitter / receiver, the transmitter / receiver does not receive a signal unnecessary for measurement of the sound waves that spread radially. Since the attenuation unit is provided, it is possible to measure the sound wave propagation time without being affected by noise caused by unnecessary signals, so that highly accurate measurement is possible.

1 is a block diagram of an ultrasonic flow rate measuring apparatus according to Embodiment 1 of the present invention. (A) Ultrasonic flow measuring device sectional view concerning the embodiment, (b) AA sectional view of (a), (c) BB sectional view of (a) CC sectional view of FIG. Sectional drawing of the ultrasonic type flow measuring device concerning a 2nd embodiment. Sectional drawing of the ultrasonic type flow measuring device concerning a 3rd embodiment Cross-sectional view of a conventional ultrasonic flow measurement device The figure which shows the received waveform of the conventional ultrasonic flow measuring device

The first invention provides a flow path through which a fluid to be measured flows, a pair of transceivers that transmit or receive sound waves disposed upstream and downstream of the flow path, and a propagation time of an ultrasonic signal between the transceivers. A measuring means for measuring, a flow rate calculating means for calculating a flow rate of the fluid according to the propagation time, and a reflector provided to oppose each transmitting / receiving surface of the pair of transceivers, Both are placed on the side of the flow path, and after the ultrasonic wave transmitted from one transmitter / receiver is changed in direction by 90 degrees by the reflector and propagates through the fluid to be measured, the reflector again The attenuator is arranged so that the direction is changed by 90 degrees and is received by the other transmitter / receiver, and an attenuator that eliminates unnecessary ultrasonic signals is arranged on the path from the flow path to the transmitter / receiver. It is constructed with a step-like space With symptom, it is possible to receive the signals required for measurement without being affected by unwanted signals.

  Hereinafter, an ultrasonic flow measuring device according to an embodiment of the present invention will be described with reference to the drawings. In addition, what attaches | subjects the same code | symbol in drawing is the same thing, and abbreviate | omits detailed description.

(Embodiment 1)
In FIG. 1, reference numeral 4 denotes a flow path through which the fluid to be measured flows, reference numerals 5 and 6 denote transmitters / receivers arranged upstream and downstream of the flow of the flow path 4, and the measuring unit 1 oscillates to transmit a use frequency of the transmitter / receivers 5 and 6 A circuit 7; a drive circuit 8 connected to the oscillation circuit 7 for driving the transceivers 5 and 6; a switching circuit 9 for switching between transmission and reception of the transceivers 5 and 6; a reception detection circuit 10 for detecting an ultrasonic pulse; And a control unit 13 that outputs a control signal to the timer 11, and the flow rate calculation means 12 calculates the flow rate from the output of the timer 11.

  The operation of the ultrasonic flowmeter configured as described above will be described. In the present embodiment, the gas to be measured is assumed to be a city gas and the household gas meter is an ultrasonic flow meter, and the material constituting the flow path 4 is an aluminum alloy die casting.

In addition, about 500 kHz is selected as the operating frequency of the transceivers 5 and 6. The oscillation circuit 7 is composed of, for example, a capacitor and a resistor, and transmits a square wave of about 500 kHz. The drive circuit 8 drives the transmitters and receivers 5 and 6 from the signal of the oscillation circuit 7, so that the square wave is composed of several burst signals. The signal can be output.

  The control unit 13 outputs a transmission start signal to the drive circuit 8 and starts time measurement of the timer 11 at the same time. When receiving the transmission start signal, the drive circuit 8 drives the transmitter / receiver 5 and transmits ultrasonic pulses. The transmitted ultrasonic pulse propagates through the flow path 4 and is received by the transceiver 6. The received ultrasonic pulse is converted into an electrical signal by the transceiver 5 and output to the reception detection circuit 10. The reception detection circuit 10 determines the reception timing of the reception signal and outputs the reception detection signal to the control unit 13. When receiving the reception detection signal, the control unit 13 outputs a transmission start signal to the drive circuit 8 again after the elapse of a preset delay time td, and performs the second measurement. After repeating this operation N times, the timer 11 is stopped. The flow rate calculation means 12 calculates the propagation time t1 by dividing the time measured by the timer 11 by the number of times N and subtracting the delay time td.

  Subsequently, the transmitter / receiver 5 and 6 connected to the drive circuit 8 and the reception detection circuit 10 are switched by the switching circuit 9, and the control unit 13 again outputs a transmission start signal to the drive circuit 8 and simultaneously starts the time measurement of the timer 11. Contrary to the measurement of the propagation time t1, the transmitter / receiver 5 transmits an ultrasonic pulse, the measurement received by the transceiver 5 is repeated N times, and the flow rate calculation means 12 calculates the propagation time t2.

Here, the distance connecting the centers of the transceivers 5 and 6 is L, the speed of sound in the absence of air is C, the flow velocity in the flow path 4 is V, the flow direction of the non-measurement fluid and the transceivers 5 and 6 If the angle with the line connecting the centers is θ, the propagation times t1, t2 are
t1 = L / (C + V cos θ) (Formula 1)
t2 = L / (C−Vcos θ) (Expression 2)
Indicated by (Equation 1) Erasing the sound velocity C from (Equation 2) and obtaining the flow velocity V, V = L / 2 cos θ (1 / t1-1 / t2) (Equation 3)
Is obtained. Since L and θ are known, the flow velocity V can be obtained by measuring t1 and t2. If the flow velocity V and the area of the flow rate measuring unit 1 are S and the correction coefficient is K, the flow rate Q is Q = KSV (Equation 4)
It can be calculated with.

  FIG. 2A is a plan view of the ultrasonic flow rate measuring apparatus according to the present embodiment, and shows the arrangement of the transceivers 5 and 6. The flow path 4 has a rectangular cross section as shown in FIG. 2 (b), and the transceivers 5 and 6 are both arranged on the side surface 4 a on the short side of the flow path 4, and are transmitted from the transceiver 5. The reflected ultrasonic wave is changed by 90 degrees by the reflector 14 and enters the flow path, and then propagates through the fluid to be measured. Then, the reflected wave is again changed by 90 degrees by the reflector 14 and received by the transmitter / receiver 6. It is arranged so that. Note that the ultrasonic signal travels obliquely across the flow path 4 in the flow path, is reflected on the other side surface 4b of the flow path 4, and is bent in a V shape.

  FIG. 3 shows the details of the AA cross section of FIG. 2 and the ultrasonic wave propagation path. The transceiver 5 has a sound wave receiving surface 5a attached downward. Although the transceiver 6 is not shown, it is the same as the transceiver 5. The reflector 14 reflects the sound wave and changes the direction. In the figure, the direction is changed by 90 degrees. The transmitter / receiver 6 side has the same configuration as that of FIG. When the sound wave is transmitted from the transmitter / receiver 5, it travels downward in the figure and is reflected by the reflector 14, propagates horizontally in the channel 4, is reflected by the inner wall surface 4 b of the channel 4, and is reflected on the other reflector (see FIG. (Not shown) and then received by the receiver 6. When transmitting from the transmitter / receiver 6, the signal passes through the reverse path and propagates to the transmitter / receiver 5.

An arrow C in FIG. 3 represents a state in which the center of the sound wave propagates when the transmitter / receiver 5 is set to the receiving side, and arrows D1, D2, and D3 indicate that the sound wave exits the flow path toward the transmitter / receiver 5. Shows how it propagates while spreading radially. And the reflection surface 15 as an attenuation part which attenuates an unnecessary sound wave is provided in the near side of the channel side of the transceiver 5. By providing the reflecting surface 15, it is possible to prevent the sound waves unnecessary for measurement such as arrows D1, D2, and D3 from reaching the receiver 5, so that the sound wave propagation time can be measured without being affected by noise. Therefore, highly accurate measurement is possible. A similar reflecting surface is provided on the other transmitter / receiver 6 side, and the same effect is obtained.

  In this embodiment, the sound wave transmitted from the transmitter / receiver has been described as being reflected on the inner wall surface of the flow path. However, as shown in FIG. 6 used in the description of the conventional example, the transmitter / receiver is opposed to the transmitter / receiver. Needless to say, the present invention can also be applied to a configuration in which the light is not reflected in the flow path.

(Embodiment 2)
FIG. 4 is a cross-sectional view showing a second embodiment of the present invention, in which a sound absorbing material 16 as an attenuating portion for attenuating unnecessary sound waves is provided in front of the channel side of the transceiver 5. As the material of the sound absorbing material 16, a material that can withstand the fluid to be measured was selected, and a porous body having a pore diameter larger than ¼ of the wavelength λ of the sound wave was used. The sound absorbing material 16 absorbs the sound wave that causes noise until the sound wave emitted from the flow path 4 reaches the transmitter / receiver 5, so that it is possible to reduce the sound wave that resonates in the space in front of the transmitting / receiving surface 5a. , More accurate measurement is possible. A similar sound absorbing material is also provided on the other transmitter / receiver 6 side, and has the same effect.

(Embodiment 3)
FIG. 5 is a cross-sectional view showing a third embodiment of the present invention, in which a hollow portion 17 as an attenuation portion for attenuating unnecessary sound waves is provided in front of the channel side of the transceiver 5. The height h of the hollow portion 17 is larger than ¼ of the wavelength λ of the sound wave, so that the sound wave unnecessary for the measurement from the flow path 4 is reflected and does not propagate to the transceiver 5. . Therefore, by reflecting the sound wave on the wall surface so as not to directly receive the unnecessary sound wave, it is possible to perform highly accurate measurement with an easy shape. A similar recess is provided on the other transmitter / receiver 6 side, which has the same effect.

  The present invention is suitable for application to an ultrasonic flow measurement device that measures the flow velocity of a fluid flowing in a measurement channel.

DESCRIPTION OF SYMBOLS 1 Measuring means 4 Flow path 6, 6 Transmitter / receiver 12 Flow volume calculating means 14 Reflector 15 Reflecting surface (attenuation part)
16 Sound absorbing material (attenuation part)
17 Indentation (Attenuation)

Claims (1)

A flow path through which a fluid to be measured flows, a pair of transmitters / receivers that transmit or receive sound waves disposed upstream and downstream of the flow path, and a measuring unit that measures a propagation time of an ultrasonic signal between the transmitter / receiver, A flow rate calculating means for calculating a flow rate of the fluid according to the propagation time; and a reflector provided to oppose each transmission / reception surface of the pair of transceivers. An ultrasonic wave placed on the side of the road and transmitted from one transmitter / receiver is changed in direction by 90 degrees by the reflector, propagates through the fluid to be measured, and then changed in direction by 90 degrees by the reflector again. And an attenuation unit that eliminates unnecessary ultrasonic signals is arranged in a path from the flow path to the transmitter / receiver, and the attenuation unit is a stepped space. in ultrasonic characterized by being configured Formula flow rate measuring device.