JPH037783Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring the flow rate or flow velocity of a fluid to be measured using ultrasonic waves, and particularly to a device suitable for measuring the flow rate or flow velocity in a large-diameter flow path.

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 velocity or flow rate of the fluid, the flow rate or flow velocity can be accurately measured by detecting the Karman vortices.

As a device for measuring the number of Karman vortices generated as described above and measuring the flow rate or flow velocity of the fluid to be measured,
The present applicant previously proposed a device as shown in FIG. 1 (see Japanese Utility Model Publication No. 57-25141). That is, FIG. 1 is a diagram for explaining the flow rate or flow velocity measurement device previously proposed by the present applicant. In the figure, 1 is a flow path, 2 is a vortex generator, and 3 is a vibration for transmitting waves. 4 is a receiving oscillator, 5 is an oscillator, 6 is a phase shifter, 7 is a phase comparator, 8 is a bandpass filter, 9 is a low-pass filter, 10 is an amplifier, 11 is an output terminal, 12 indicates an amplifier and operates as follows.

First, the oscillator 5 oscillates a signal with a frequency matching the natural frequency of the wave transmitting vibrator 3, and the output signal excites the wave transmitting vibrator 3 to transmit a predetermined ultrasonic signal. The signal is also input to the shifter 6. On the other hand, the ultrasonic signal propagated through the flow path is received by the wave receiving transducer 4, but this ultrasonic signal is phase-modulated by the Karman vortex generated in the fluid. Now, the amplifier 12
Assuming that the phase of the output signal wave of the receiving transducer 4 after passing through is φ ₂ , the average phase of the output signal is φ' ₂ , and the phase fluctuation caused by the Karman vortex is ±△φ,
The phase of the output signal is φ ₂ =φ' ₂ ±Δφ, which is applied to the first input terminal 7a of the phase comparator 7. Since the second input terminal 7b of the phase comparator 7 receives a signal having a phase of φ ₁ via the phase shifter 6, the output terminal of the phase comparator 7 receives the phase difference φ ₁ −φ. ₂ is output, and of the output, only the DC signal component based on φ ₁ −φ′ ₂ is input to the phase shifter 6 via the low-pass filter 9, and is also input to the band-pass filter 8.
A Karman vortex signal based on the fluctuation phase component ±△φ due to the Karman vortex is obtained from the output terminal 11.
The output from can measure the flow rate or velocity of the fluid.

According to the above-mentioned flowmeter, the output from the low-pass filter 9, that is, the DC signal component based on the phase difference φ ₁ −φ' ₂ is returned to the phase shifter 6, and the signal is transmitted to the phase shifter 6. As a result of controlling _the phase amount _of Since changes due to physical conditions, etc. are automatically corrected, Karman vortex signal detection is not affected by the above-mentioned disturbances, and accurate measurement is always possible.

As mentioned above, the flowmeter previously proposed by the present applicant is accurate because it detects only the phase modulation component caused by the Karman vortex in the fluid and automatically corrects the operating state of the phase comparator to always be optimal. Not only that, but compared to measurement methods that use frequency modulation, it provides much higher output, has a higher signal-to-noise ratio, and can perform highly accurate measurements with a simplified configuration. Although it has advantages, in order to drive the ultrasonic oscillator most efficiently, the oscillation frequency of the ultrasonic wave is driven at the natural frequency of the vibrator as described above. Therefore, the detectable phase range due to vortex fluctuations is limited, and the vortex velocity component on the ultrasonic surface is within one wavelength of the ultrasonic wave. Therefore,
In vortex flowmeters with similar shapes, as the diameter increases, the wavelength must become longer and the oscillation frequency of the ultrasonic waves must be lowered. However, driving the vibrator at such a low frequency results in extremely low efficiency, requiring a high-power oscillator, which is not effective.

The present invention was developed in view of the above-mentioned circumstances. The transmitter/receiver oscillators 3 and 4 are driven at the natural frequency of the oscillator that drives them most efficiently, and this is used as a carrier wave. Phase detection of the vortex signal is separately provided. The low frequency oscillation output is used as an amplitude modulation (hereinafter referred to as AM modulation) signal as a modulating wave, and the vortex is detected by phase detection using the low frequency signal included in the AM modulation signal, and the low frequency oscillation frequency is selected. The purpose of this method is to enable flow rate detection over a substantially wider range than conventional methods which are limited to natural frequencies.

FIG. 2 shows a block diagram of the present invention. Components that are the same as those in FIG. 1 are given the same reference numerals as in FIG. 1, and their explanations will be omitted. In FIG. 2, reference numeral 13 denotes a low frequency oscillator which can be arbitrarily varied within a range of 10 to 50 times the number of Karman vortices per unit time, and is sufficiently lower than the frequency of the oscillator 5. 3A and 3B conceptually illustrate the output waveforms of the oscillator 5 and the low frequency oscillator 13. c performs AM modulation using the output a of the oscillator 5 as a carrier wave and the output b of the low frequency oscillator 13 as a modulation wave.
The output waveform of the AM modulator 14 is applied to the wave transmitting vibrator 3. The AM modulated wave c is propagated from the wave transmitting vibrator 3 to the wave receiving vibrator 4, and is phase-modulated by the vortex flowing out from the vortex generator 2 into the flow path 1. The phase-modulated AM modulated wave of the wave receiving transducer 4 is amplified by the amplifier 12, then detected and shaped by the demodulator 15, and input to one side of the phase comparator 7. The waveforms of d, e and e' are the detection signal 1 in the demodulator 15.
5 ₁ , demodulated signal 15 ₂ and shaped output signal 7
It is a. The other input signal 7b of the phase comparator 7 is a rectangular signal b' obtained by shifting the modulated wave of the output signal b of the low frequency oscillator 13 to an optimum phase by the phase shifter 6. The circuit operations of the phase comparator 7, low-pass filter 9, band-pass filter 8, and amplifier 10 are the same as in the case of FIG.
A vortex signal is output. As mentioned above,
According to the present invention, the output wave a of the oscillator 5 becomes a carrier wave for driving the wave transmitting/receiving oscillators 3 and 4 at a natural frequency that does not reduce their sensitivity, and the carrier wave itself is not modulated by eddies. Demodulator 1 even if received
5 is eliminated by a low-pass filter (not shown), and it has no relation to vortex detection, and vortex detection is performed by phase modulating it with a low frequency modulation signal, and the detection phase margin increases due to the lower frequency. Since it detects phases over a substantially wide range, it can also be applied to large-diameter vortex flowmeters. Furthermore,
By arbitrarily changing the low frequency oscillation frequency, it is possible to select the applicable range.

Therefore, according to the present invention, phase changes caused by Karman vortices can be accurately measured even in high-diameter flow pipes, and large flow rates of fluid can be measured with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a conventional vortex flowmeter, Fig. 2 is a configuration diagram for explaining an embodiment of the vortex flowmeter according to the present invention, and Fig. 3 is a diagram illustrating the operation of the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Channel, 2... Vortex generator, 3... Transmitting transducer, 4... Receiving transducer, 5... Oscillator, 6...
...Phase shifter, 7... Phase comparator, 8...
Band pass filter, 9...Low pass filter, 10...Amplifier, 11...Output terminal,
12...Amplifier, 13...Low frequency oscillator, 14...
...AM modulator, 15...demodulator.

Claims (1)

[Scope of utility model registration request] A pair of ultrasonic wave transmitting/receiving elements are provided on the downstream side of the vortex generator inserted into the fluid to be measured, which are arranged opposite each other via a flow path, and the ultrasonic wave transmitted from the wave transmitting element generates a vortex. In a flow rate or flow velocity measuring device that measures the flow rate or flow velocity of a fluid to be measured by detecting a phase change caused by a Karman vortex generated by a body, the wave transmitting element is configured to adjust the natural frequency of the wave transmitting and receiving element. The received signal is demodulated, and the received signal is demodulated, and the demodulated signal and the modulated signal are A flow rate or flow rate measuring device characterized by detecting a Karman vortex by a phase difference signal with a wave.