JPS6326731Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the flow rate or flow velocity of a fluid to be measured using ultrasonic waves.

As is well known, when a columnar vortex generator is inserted into a fluid, the flow separates on both sides of the vortex generator, and regular vortices, that is, Karman vortices, are generated alternately on the downstream side of the vortex generator.

Since the number of Karman vortices generated is proportional to the flow rate or flow rate of the fluid, the flow rate or flow rate can be accurately measured by detecting the Karman vortices.

Conventional vortex detection means that have been put into practical use include installing a thermal detection element such as a thermistor in the vortex generator, or installing a thermal detection element such as a thermistor in the vortex generator or a detection element installed within the vortex generator or on the downstream side of the vortex generator. A pressure detection element may be installed, or a movable element such as a ball or disk may be placed inside the vortex generator, and the movement of the ball or disk may be detected electromagnetically, optically, or otherwise using the pressure difference caused by the vortex generation. Detection methods are used.

However, with the above-mentioned conventional detection means, it is impossible to measure a wide flow rate measurement range of 100:1 or more, which is the most important feature of the Karman vortex flowmeter, with sufficient and high accuracy, and the response is also poor. Because it's bad,
It was impossible to apply it to a wider temperature range.

In order to cover the above points, ultrasonic flow rate devices that take advantage of the characteristics of ultrasonic waves have been proposed, but they are prone to measurement errors because stable detection is difficult, and the devices themselves are complicated. However, it has not been put into practical use due to the disadvantageous problem of being overly complex and lacking in versatility.

The present invention was developed in view of the above-mentioned disadvantages, and uses a continuous ultrasonic signal to detect the number of Karman vortices occurring in a fluid, thereby accurately measuring the number of Karman vortices. The purpose of this device is to provide a flow rate or flow rate measuring device that uses ultrasonic waves that can measure the flow rate or velocity of a fluid. Specifically, ultrasonic signal waves that are transmitted and received through a flow path are generated in a fluid. Utilizing the fact that the frequency is modulated by the Karman vortex, the output of the ultrasonic receiving transducer is sent back to the transmitting transducer via a high gain amplifier to amplify the modulation of the ultrasonic signal and increase the frequency. An object of the present invention is to provide a flow rate or flow velocity measuring device that measures the flow rate or flow velocity of a fluid by detecting the number of Karman vortices per unit time using a demodulator.

Another objective of the present invention is to satisfy the condition of a positive feedback loop that starts self-excited oscillation in the vicinity of the frequency that resonates with the natural frequency of the wave receiving oscillator, and once activated, it continues to oscillate continuously. An object of the present invention is to provide a flow rate or flow rate measuring device that excites ultrasonic waves and continuously obtains detection signals corresponding to the Karman vortex street.

Embodiments of the present invention will be described below based on the drawings.

Reference numeral 1 in the figure is a flow path for the fluid to be measured, and a well-known vortex generator 2 is inserted and arranged perpendicular to the flow. The pipe wall of the flow path 1 includes a wave transmitting transducer 3 that emits an ultrasonic signal to a desired distance downstream from the vortex generator 2, and a wave receiving transducer that faces the wave transmitting transducer 3. The ultrasonic signal wave of the desired frequency emitted from the transmitting transducer 3 reaches the receiving transducer 4 via the fluid flowing through the flow path 1. It is made to spread.

Further, a high gain amplifier 5 is connected to the output part of the wave receiving vibrator 4, and the output end of the high gain amplifier 5 is connected to the input part of the wave transmitting vibrator 3, and also connected to the frequency demodulator 6. is also connected to the output terminal of the frequency demodulator via an amplifier 7.
is connected.

In the above configuration, when the transmitting transducer 3 is excited and an ultrasonic wave having a natural vibration frequency of the transmitting transducer 3 is emitted, the ultrasonic signal propagates through the fluid and becomes a receiving vibration. However, at this time, between the input and output of the high gain amplifier 5, that is, the transmitting oscillator 3
, an ultrasonic signal emitted thereby, which propagates through the channel 1 and reaches the receiving transducer 4, and a receiving transducer 4 that receives the ultrasonic signal. The oscillation frequency is changed so that the phase of the return path satisfies the condition of a positive return path, and oscillation is automatically maintained.

That is, as shown in the drawing, in a self-excited oscillation loop consisting of the transmitting transducer 3 → fluid medium in the flow path ↑ ↓ high gain amplifier 5 ← receiving transducer 4, if the loop gain is G _L , the oscillation The condition for maintaining is that G _L <1.

The loop gain G _L of the self-excited oscillation loop is the gain G _A of the high gain amplifier 5, the gain G _T of the transmitting transducer 3, the gain G _R of the receiving transducer 4, and the transmitting transducer 3. and fluid propagation gain (loss) G _F between the wave receiving transducers 4. The wider the frequency range of this loop gain G _L , the more the oscillation will continue even if there is a large change in frequency. Therefore,
In the present invention, it is advantageous for the frequency characteristics of the transmitting transducer 3 and the receiving transducer 4, which are oscillating elements that determine the frequency range, to have a lower Q.

Here, when the temperature of the fluid changes, the frequency of the ultrasonic signal wave changes, and the relationship between the oscillation frequency and temperature in this self-oscillation system will be explained.

The frequency changes depending on the temperature t of the fluid to be measured, and n: the number of waves existing between the ultrasonic wave transmitting and receiving transducers.
(in fluid) C: Speed of sound (=C ₀ + αt) α: Temperature coefficient of sound speed: Ultrasonic frequency (self-excited oscillation frequency) λ: Wavelength of ultrasound (in fluid) L: Between transducers for ultrasonic wave transmission and reception If the distance t is the temperature difference (with respect to the reference temperature), then there is a relationship of n=L/λ...λ=C/....

, from the formula, n=L/C, so = (C ₀ + αt)/L... can be obtained.

Here, when the amplifier is a non-inverting type, the self-excited oscillation system automatically selects the oscillation frequency so that an integral number of ultrasonic waves exist between the ultrasonic wave transmitting and receiving transducers, and The frequency is a value close to the resonant frequency of the ultrasonic wave transmitting/receiving transducer.

Therefore, n in the above equation is a constant value, the frequency changes with the temperature t, and self-sustained oscillation is performed while being automatically corrected as the temperature changes.

In a system that performs positive feedback oscillation, the phenomenon in which the oscillation frequency automatically changes so that the oscillation conditions as described above are satisfied is an example of the phenomenon in which an audio signal detected by a microphone is electrically amplified by an amplifier, and the signal is In a system that makes sound louder by applying it to a speaker, when a closed loop called speaker → air ↑ ↓ amplifier ← microphone is formed, this system causes positive feedback oscillation, a phenomenon similar to the so-called "howling" phenomenon. With this "howling" phenomenon, even if the distance between the speaker and microphone changes slightly,
As long as the loop gain of the system exceeds 1, oscillation is maintained even if the oscillation frequency is automatically changed so that the phase relationship is such that the oscillation conditions are satisfied. The phenomenon of the present invention is similar to this "howling" phenomenon, and moreover, this operation occurs naturally without the intervention of any special device for automatically controlling the phase.

As mentioned above, the self-excited oscillation frequency in the configuration of the present invention, in which the ultrasonic wave transmitting/receiving transducer is disposed oppositely through the flow path on the downstream side of the vortex generator, propagates through the fluid in the flow path as shown in the above equation. It is proportional to the sound speed C of the ultrasonic wave.
Therefore, when a Karman vortex passes close to the ultrasonic propagation path, the flow component of the vortex in the direction of the ultrasonic propagation path is added to or subtracted from the ultrasonic propagation velocity C, and as a result, the self-oscillation frequency is increased by the Karman vortex street. Subject to frequency modulation. Since the modulation frequency is proportional to the number of vortices per unit time, a vortex signal is detected by demodulating the modulation frequency, and a flow velocity proportional to the number of vortices per unit time can be calculated. The device of this invention is affected by the temperature of the fluid as shown in the equation, but in general, the change in fluid temperature is slow relative to the vortex frequency and can be ignored, so as a result, it is not affected by the temperature. Easily detects vortices.

According to the present invention, noisy minute flow components, which are extremely small in proportion to Karman vortices such as turbulent vortices passing within the ultrasonic propagation path, are averaged within the propagation path and can be modulated by this. Therefore, it is possible to detect vortices with an excellent S/N ratio without being affected by turbulent eddies. In addition, when the detection element is in contact with the fluid to be measured, as in the thermistor detection method,
Compared to conventional devices that have movable elements such as balls and desks inside the vortex generator, it is simpler and has a structure that does not have any moving parts, allowing stable vortex detection, good responsiveness, and A robust, inexpensive vortex flowmeter with a wide range is obtained. Furthermore, an ultrasonic detection type vortex flowmeter that is not affected by temperature can be obtained despite its simple configuration.

[Brief explanation of the drawing]

The figure is a block diagram of a flow rate or flow rate measuring device according to the present invention. DESCRIPTION OF SYMBOLS 1... Flow path, 2... Vortex generator, 3... Vibrator for transmitting waves, 4... Vibrator for receiving waves, 5... High gain amplifier, 6... Frequency demodulator, 7... Amplifier, 8...
Output terminal.

Claims (1)

[Scope of utility model registration request] A pair of ultrasonic wave transmitting/receiving transducers are provided oppositely through a flow path on the downstream side of the vortex generator inserted into the fluid to be measured, and a high gain amplifier is connected between the ultrasonic wave receiving transducers. to form a closed loop, self-oscillate the closed loop as a positive feedback loop with a loop gain greater than 1, and generate an ultrasonic wave propagating in the fluid at the self-oscillation frequency to generate a Karman vortex on the downstream side of the vortex generator. 1. A flow rate or flow rate measuring device characterized in that the frequency is modulated by the frequency modulated signal and the number of Karman vortices per unit time is detected from the frequency modulated signal.