JPH0312692B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex detection method and an ultrasonic vortex flowmeter.

Vortex detection methods and vortex flowmeters that utilize the fact that the frequency of Karman vortices is proportional to flow velocity are widely used.

A vortex generator is installed in a pipe that forms a flow path in a vortex flowmeter, and the fluid that flows in from the upstream side of the vortex generator flows out to the downstream side of the vortex generator. Karman vortices will be generated on the left and right sides of the vortex generator.

By detecting vibrations, pressure fluctuations, etc. of the vortex generating body due to the generation of the Karman vortices, the flow rate or flow velocity of the fluid can be measured.

However, the vortex detection signal of the vortex flowmeter using this method includes not only a flow rate signal whose frequency changes significantly depending on flow velocity fluctuations, but also low-frequency and high-frequency noise components such as turbulence contained in the flow. Because it is
A high-performance automatic tracking filter circuit had to be used to remove these noise components.

However, no matter how high-performance an automatic follow-up filter circuit is used, it is difficult to completely eliminate the above-mentioned noise component. Therefore, the noise component is included in the vortex signal as an error signal, making it difficult to accurately measure the flow rate. There was a problem that I couldn't do it.

In order to solve this problem, ultrasonic waves are emitted across the Karman vortices generated on the left and right sides of the vortex generator, the ultrasonic waves that cross the Karman vortex street are received, and the output of the receiver is A vortex flowmeter was developed that performs phase detection and then measures the detected output.

This ultrasonic vortex flowmeter was able to accurately measure flow rates with fewer errors than vortex flowmeters that detect vibrations, etc., but it continuously oscillates ultrasonic signals and uses the Karman vortex described above. The ultrasonic waves that traversed the row were received by a receiver, and then the received signal was detected by a phase detector. In this case, it is difficult to accurately measure the flow rate because the receiver receives not only the ultrasonic waves that go straight from the oscillator to the receiver, but also all signals that cause errors such as reflected waves and scattered waves. There was a problem.

The present invention has been made based on the above-mentioned viewpoints, and its purpose is to improve the shortcomings of conventional ultrasonic vortex flowmeters, to have a simple configuration, to reduce errors, and to achieve constant The present invention aims to provide an ultrasonic vortex flow meter that can accurately measure both quantities.

The gist of this is that the ultrasonic waves used are oscillated as burst waves that are intermittent at least several times during one cycle of vortex generation, and the ultrasonic waves emitted continuously at one time are received. After the reflected waves, etc. have disappeared, subsequent ultrasonic waves are oscillated, and the receiver is configured to receive only the sound waves that reach the receiver directly from the oscillator, thereby eliminating the effects of reflected waves, etc. be. In order to obtain vortex signals from such intermittent ultrasonic waves, the oscillation time of the ultrasonic waves is configured to be short so that the phase difference or amplitude within each continuous ultrasonic wave is approximately constant, and the oscillation time of each continuous ultrasonic wave is shortened. The device is configured to detect and record the modulation of wave amplitude or phase difference, calculate the period of fluctuation of these data, count the cycles, and find out the number of Karman vortices generated.

Hereinafter, the details of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is an explanatory diagram showing one embodiment of an ultrasonic vortex flowmeter according to the present invention, and FIG. 2 is an explanatory diagram showing output waveforms of each part thereof.

In FIG. 1, 1 is a pipe having a flow passage whose cross section perpendicular to the axis is circular, and 2 is the pipe 1.
3 is a Karman vortex generated by the vortex generator 2; 4 is an excitation power supply circuit;
6 is an ultrasonic oscillator capable of emitting ultrasonic waves across the Karman vortex 3 based on the input from the excitation power supply circuit 4; 6 is an ultrasonic receiver that receives the ultrasonic waves that have crossed the Karman vortex 3; 8 is an amplifier circuit that amplifies the output signal of the ultrasonic receiver 6; 8 is a phase detection circuit that detects the phase of the output signal of the amplifier circuit 7; and 9 has a desired phase difference with respect to the input of the excitation power supply circuit 4. a voltage-controlled phase shifter that generates an output;
10 is an arithmetic circuit that detects and calculates a predetermined point of the output signal of the phase detection circuit 8; 11 is a counter that counts the output of the arithmetic circuit 10; 12 is a low-pass filter; and 13 is a stage subsequent to the low-pass filter 12. The servo controller is connected to the servo controller and controls the control amount of the voltage-controlled phase shifter 9 so that the output of the phase detection circuit 8 is always zero or at the center of the operating point. 4 output waveform,
is the output waveform of the ultrasonic oscillator 5, and is the output waveform of the ultrasonic receiver 6.

Due to the flow of fluid, Karman vortices are generated on the left and right sides of the vortex generator 2 installed in the pipe 1, and as a result, the fluid flowing in from the upstream side of the vortex generator 2 generates a vortex. It flows out to the downstream side of body 2,
Due to the generation and separation of the Karman vortex 3, the velocity components in the direction perpendicular to the tube axis and the vortex generator on the downstream side of the vortex generator 2 alternate in direction.

A so-called burst signal-like voltage wave is supplied from the excitation power supply circuit 4 to the ultrasonic oscillator 5 at a predetermined frequency and intermittently with a fixed pause time.

The ultrasonic oscillator 5 receiving this voltage wave generates an ultrasonic signal having a substantially constant frequency and amplitude and intermittent with a constant pause time so as to cross the Karman vortex street 3 generated in the pipe 1. is emitted, and the phase of the ultrasonic signal is changed by the velocity component of the Karman vortex 3 in the propagation direction of the ultrasonic wave.

That is, when Karman vortex 3 is not generated,
Since the ultrasonic waves emitted from the ultrasonic oscillator 5 propagate at a constant speed, no change in phase occurs, but when the Karman vortex street 3 is generated, the influence of the velocity component of the fluid in the Karman vortex 3 in the ultrasonic propagation direction is As a result, the propagation speed changes, and as a result, the phase of the ultrasonic wave changes periodically.

Therefore, during one period of this phase fluctuation, the above-mentioned ultrasonic waves are interrupted at least ten times, preferably several tens to hundreds of times, and the phase difference is approximately constant during a series of continuous ultrasonic waves. The duration of each continuous wave is shortened so that .

The ultrasonic signal whose phase has been changed in this manner is received by the ultrasonic receiver 6, amplified to a predetermined value by the amplifier circuit 7, and then input to the phase detection circuit 8.

This input signal has the phase of the output signal of the ultrasonic receiver 6 as φ ₂ , the average phase of the output signal of the ultrasonic receiver 6 as φ ₂ ', and the fluctuating phase distribution caused by the Karman vortex as ±. If △φ, then φ ₂ =φ ₂ ′±△φ
becomes.

The voltage-controlled phase shifter 9 receives a signal from the servo controller 13 that controls the average output of the phase detection circuit 8 to be always at the center (or the center of the operating point), and inputs a signal from the amplifier circuit 7. With the input of the signal φ ₂ , the phase of the signal Δφ is subjected to phase detection.

Since the signal phase-detected by the phase detection circuit 8 has a waveform approximately similar to a sine wave with one cycle per two Karman vortices, this output data is recorded by the arithmetic circuit 10 and, for example, the waveform The Karman vortex number can be counted by oscillating an output pulse at each zero crossing point and inputting it to the counter 11.

The counter 11 counts the output of the arithmetic circuit 10 and calculates the flow rate of the fluid passing through the pipe 1.

Since the present invention is configured as described above, when using the ultrasonic vortex flowmeter according to the present invention, ultrasonic signals are not emitted continuously but are emitted in burst signals, which causes errors such as reflected waves. Since signals such as

Note that the present invention is not limited to the embodiments described above. That is, for example, in this embodiment, phase fluctuations of the received waves are used, but amplitude fluctuations may also be used. Furthermore, the configurations of the ultrasonic oscillator and ultrasonic receiver, their mounting positions, the configurations of the phase detection circuit and voltage-controlled phase shifter, and their control methods can be freely changed within the scope of the purpose of the present invention. Therefore, the present invention encompasses all of them.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of an ultrasonic vortex flowmeter according to the present invention, and FIG. 2 is an explanatory diagram showing output waveforms of each part thereof. DESCRIPTION OF SYMBOLS 1... Pipe, 2... Vortex generator, 3... Karman vortex, 4... Excitation power supply circuit, 5... Ultrasonic transmitter, 6... Ultrasonic receiver, 7... Amplifier, 8...
Phase detection circuit, 9... Voltage control phase shifter, 10...
Arithmetic circuit, 11... Counter, 12... Low pass filter, 13... Servo controller,... Output waveform of excitation power supply circuit,... Output waveform of ultrasonic oscillator,... Output waveform of ultrasonic receiver.

Claims (1)

[Claims] 1. Vortex detection that detects Karman vortices generated in the wake of a vortex generator arranged perpendicular to the flow in a fluid transport pipe from changes in the propagation speed of ultrasonic waves emitted in a direction perpendicular to the flow. In the method, the ultrasonic wave is intermittent at a frequency higher than the vortex frequency, and the modulation based on the fluid vibration of the received ultrasonic signal is intermittent, and the ultrasonic reception signal is determined for a predetermined time width after each of the received ultrasonic signals reaches a steady value. , a vortex detection method characterized in that a vortex signal is obtained by detecting a change in the modulation over time. 2 Ultrasonic waves can be emitted intermittently at predetermined intervals across a vortex generator installed perpendicular to the flow in a fluid transport pipe and a vortex train generated on the downstream side of the vortex generator. an ultrasonic oscillator, an ultrasonic receiver that receives the ultrasonic waves that have traversed the vortex row, and a detection circuit that is connected after the ultrasonic receiver and detects amplitude fluctuations or phase differences of the received waves; The ultrasonic wave detector is characterized by comprising an arithmetic circuit which is connected to the latter stage of the phase detection circuit and which emits an output pulse every one period or half period of the fluctuation of the output data, and a counter which counts the output of the arithmetic circuit. Sonic vortex flow meter.