JP3360458B2 - Flow 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 rate measuring device for measuring a flow rate of a gas or the like using an ultrasonic wave.

[0002]

2. Description of the Related Art In a conventional fluid flow meter of this type, as shown in FIG. 5, ultrasonic vibrators 2 and 3 are provided on a part of a wall of a flow path 1 so as to be oblique to the direction of flow. An ultrasonic wave is generated in the flow direction from the vibrator 2, and when this ultrasonic wave is detected by the vibrator 3, a trigger is activated by the detection signal, and the ultrasonic wave is generated again from the vibrator 2. This repetition is performed a plurality of times and the time is measured. On the contrary, ultrasonic waves are generated from the vibrator 3 against the flow, the same repetition time is measured, and the flow velocity of the fluid is calculated from the difference between these times to calculate the flow rate of the fluid.

[0003]

However, in the above-mentioned conventional fluid flow meter, noise is generated in the detection signal due to the reflection of the ultrasonic wave on the surface of the vibrator. That is, first, the ultrasonic signal transmitted from the transducer 2 reaches the transducer 3, and when this signal is received, amplified, compared, and detected, the next trigger signal is immediately excited and the second transmission is performed. Will be
On the other hand, the ultrasonic signal reflected by the surface of the vibrator 3 is
When the second signal reaches the vibrator 3 and the trigger of the third signal starts, the first reflected signal arrives.
This is because the time for receiving, amplifying, comparing, and retriggering the signal is extremely short, less than 0.1 microsecond, while the propagation time of the ultrasonic wave is about 500 microseconds. Therefore, since the reflected wave is received when transmitting, the transmitted signal has a distorted waveform. Further, the first reflected signal is reflected again on the surface of the vibrator 2 and travels to the vibrator 3.
The signal is superimposed on the third transmission signal and reaches the vibrator, and the detection signal is affected by these reflected signals. In addition, since the arrival time of the reflected wave varies slightly depending on the flow velocity in the measurement flow path 1, the measurement accuracy is affected due to complicated noise, and high-precision measurement is difficult.

[0004] An object of the present invention is to solve the above problems.

[0005]

In order to achieve the above object, a fluid flow meter according to the present invention has the following configuration.

That is, a transducer for transmitting and receiving ultrasonic waves,
The ultrasonic wave counter provided on the outer peripheral portion of the transducer on the receiving side
A first reflecting plate for transmitting light, wherein the first reflecting plate transmits
Forward or backward from the surface of the vibrator in the direction
The configuration is such that the ultrasonic wave is shifted by 波長 wavelength.

Also, the ultrasonic wave reflected from the surface of the transducer
The structure is such that the area of the first reflector is variable according to the intensity.
Was.

Further, a second reflector for emitting ultrasonic waves is provided.
Digit configuration.

Also, a non-reflection plate for absorbing ultrasonic waves is provided.
The configuration was adopted.

Also, the first reflector is installed inclining inward.
Configuration.

[0011]

According to the present invention, with the above-described structure, repeated ultrasonic transmission / reception is performed with little influence of the reflected wave.

[0012]

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

In FIG. 1, a first vibrator 5 for transmitting ultrasonic waves in the middle of a fluid conduit 4 as a flow path, and a second vibrator 6 for receiving ultrasonic waves from the first vibrator 5 Are arranged obliquely to the flow direction. 7 is the first vibrator 5
Is a circuit for amplifying a signal received by the second vibrator 6, and the amplified signal is used as a reference signal and a comparator 9
And when a signal equal to or greater than the reference signal is detected, the repetition means 11 repeatedly transmits an ultrasonic signal by the number of times set by the number-of-times setting circuit 10. The time when the number of times set by the number-of-repetitions setting circuit 10 is repeated is obtained by a timer means 14 such as a timer counter. Next, the transmission / reception of the first vibrator 5 and the second vibrator 6 is switched by the switching means 15, and the second vibrator 6 switches to the first vibrator 5,
That is, an ultrasonic signal is transmitted from downstream to upstream,
This transmission is repeated as described above, and the time is measured. The flow velocity of the fluid is determined from the time difference, and the flow rate calculating means 16 determines the flow rate value of the fluid in consideration of the size of the pipeline and the state of the flow.

Next, the vibrator used in the flow meter will be described. FIG. 2 shows a cross-sectional shape of the vibrators constituting the first and second vibrators 5 and 6. Reference numeral 21 denotes an ultrasonic transducer made of piezoelectric ceramic, and reference numeral 22 denotes an annular quarter-wave reflector provided on the outer peripheral portion of the ultrasonic transducer 21.

The transmitted ultrasonic wave partially reflects on the surface 23 of the ultrasonic transducer 21. In addition, annular 1
The light is also reflected on the surface 24 of the 波長 wavelength reflector 22. The surface 23 of the ultrasonic transducer 21 and the surface 24 of the annular quarter-wave reflecting plate 22 have a distance of one-half of the wavelength of the propagating ultrasonic wave.
It is set to be shifted back and forth by four. Arrow 25 indicates the propagation direction of the ultrasonic wave. As indicated by 26, the position of the surface 23 of the ultrasonic transducer 21 is located closer to the front than the position 27 of the surface 24 of the annular quarter-wave reflector 22. Therefore, the surface 23 of the ultrasonic transducer 21
The ultrasonic wave reflected on the surface of the annular quarter-wave reflecting plate 22 and the ultrasonic wave reflected on the annular quarter-wave reflecting plate 22 are reflected just in a state shifted by ず れ wavelength. Therefore, when the reflected ultrasonic wave reaches the surface of the transmitted transducer, the phase is shifted by 180 degrees.

For this reason, if the intensity of the ultrasonic wave reflected on the surface 23 of the ultrasonic transducer 21 and the intensity of the ultrasonic wave reflected on the surface 24 of the annular quarter-wave reflector 22 are substantially the same, As a result of mutual interference and weakening, the reflection intensity of the ultrasonic wave becomes very weak. Each transducer can perform high-accuracy measurement without receiving complicated noise due to reflected waves. The reflection intensity from the annular quarter-wave reflector 22 can be adjusted by the area of the annular quarter-wave reflector 22. The reflection intensity of the ultrasonic waves reflected on the surface of the vibrator and the annular intensity can be adjusted. The reflection intensity of the ultrasonic wave reflected on the surface of the quarter-wave reflector can be made substantially equal.
For this reason, the reflection intensity of the ultrasonic wave can be greatly reduced.

FIG. 3 shows a cross section of the vibrator used in the second embodiment. Reference numeral 21 denotes an ultrasonic transducer made of a piezoelectric ceramic, and reference numeral 22 denotes an annular first reflecting plate provided on the outer peripheral portion of the ultrasonic transducer 21, which is constituted by a quarter-wave plate. Reference numeral 28 denotes an annular second reflector provided on the outer peripheral portion of the first reflector 22, which is provided so as to radiate the transmitted ultrasonic waves. The first reflection plate 22 operates in the same manner as in the first embodiment, and minimizes the interference intensity on the surface of the transducer that has transmitted the reflection intensity of the ultrasonic wave. By providing the second reflecting plate 28, the reflected wave from other portions is reflected so as to diverge, so that it can be suppressed on the surface of the transmitted vibrator.

FIG. 4 shows a cross-sectional shape of the vibrator used in the third embodiment. Reference numeral 21 denotes an ultrasonic transducer made of a piezoelectric ceramic, and reference numeral 22 denotes an annular first reflecting plate provided on the outer peripheral portion of the ultrasonic transducer 21, which is constituted by a quarter-wave plate. Reference numeral 29 denotes an annular non-reflection plate provided on the outer peripheral portion of the first reflection plate 22, and is made of a material such as felt so as to absorb transmitted ultrasonic waves. The annular first reflecting plate 22 operates in the same manner as in the first embodiment, and minimizes the reflection intensity of the ultrasonic wave by interference. By providing the annular non-reflective plate 29, reflected waves from other portions can be absorbed and suppressed.

In FIG. 1, the ultrasonic wave propagation direction is oblique to the fluid flow direction. However, the ultrasonic wave propagation direction is parallel to the fluid flow direction. However, the effect as shown in the embodiment of the present invention can be obtained.

Further, in the above embodiment, the annular quarter-wave plate for reflecting the ultrasonic wave is configured to be orthogonal to the propagation direction of the ultrasonic wave. The reflection efficiency is improved, and the reflection intensity can be reduced with a smaller area.

Further, in FIG. 2 of the above embodiment, the annular quarter reflector is installed behind the surface of the vibrator, but it may be installed ahead.

As is clear from the above description, the above embodiment
According to the above, the following effects can be obtained.

(1) A quarter-wavelength reflector is provided on the outer periphery
A pair of transducers that transmit and receive ultrasonic signals are
And it is installed so that it faces the downstream.
Noise due to the reflected wave of the moving element can be reduced and measurement accuracy can be reduced.
The degree improves.

(2) First and second reflections on the outer periphery of the vibrator
A plate is provided, and the first reflector is a quarter-wave reflector and the reflected wave is
Converged and reflected wave diverges on the second reflector
And a pair of vibrators for transmitting and receiving this ultrasonic signal.
The rotor was installed so as to face the upstream and downstream of the flow path
Because of the configuration, noise due to reflected waves from near the vibrator
Can be reduced, and the measurement accuracy is improved.

(3) The reflected wave converges on the outer periphery of the vibrator
A quarter-wave reflector is provided, and the outer periphery of the reflector is further provided.
A non-reflective plate is provided in the part, and a pair of
Is installed so that it faces upstream and downstream of the flow path
Configuration, the extra reflected waves from the vibrator
Absorb and reduce noise due to reflected waves
The accuracy is improved.

[0026]

As described above, according to the present invention, the repeated
Transmit and receive ultrasonic waves in a state where the effects of reflected waves are small.
Can be.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a flow rate measuring device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a vibrator of the device.

FIG. 3 is a sectional view of a vibrator according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a vibrator according to a third embodiment of the present invention.

FIG. 5 is a control block diagram of a conventional flow measurement device.

[Explanation of symbols]

 Reference Signs List 4 fluid pipeline 5 first vibrator 6 second vibrator 11 repetition means 14 timekeeping means 15 switching means 16 flow rate calculation means 17 time setting means 21 ultrasonic transducer 22 annular quarter-wavelength reflector

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Jiyo Sho 62-86511 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1/66

Claims (5)

(57) [Claims] An oscillator for transmitting and receiving an ultrasonic wave and a receiving side
A fourth ultrasonic reflection device provided on an outer peripheral portion of the vibrator.
And a first reflector, wherein the first reflector is arranged in the transmission direction.
Of the ultrasonic wave before or after the surface of the vibrator.
Flow meter that is shifted by 1/4 wavelength . 2. The intensity of an ultrasonic wave reflected from a surface of a vibrator.
Characterized in that the area of the first reflector is made variable according to
The flow meter according to claim 1, wherein 3. An apparatus for providing a second reflector for radiating ultrasonic waves.
The flowmeter according to claim 1 . 4. A non-reflective plate for absorbing an ultrasonic wave.
Item 7. A flow meter according to Item 1 . 5. A first reflecting plate which is installed to be inclined inward.
The flowmeter according to any one of claims 1 to 4 .