JPH11287680A - Vortex flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vortex flowmeter which can make accurate flow measurements by surely extracting the frequency components of a Karman vortex from a vortex signal even if the frequency of the vortex signal is unstable, and thus computing flow rates. SOLUTION: A vortex flowmeter 1 is provided with an amplitude modulation circuit 14 which detects the frequency of variation in amplitude of a vortex signal for output as an amplitude variation frequency, a frequency/voltage conversion circuit 15 and a voltage/frequency conversion circuit 16 which convert the amplitude variation frequency into a frequency proportional to the amplitude variation frequency at a predetermined proportional constant of 1 or more and output the frequency, and a switched capacitor filter 11 whereby the frequency inputted from the voltage/frequency conversion circuit 16 is set as a cutoff frequency, the switched capacitor filter 11 eliminating from the vortex signal those components which vary the amplitude of the vortex signal. Therefore, the amplitude of the vortex signal can be stabilized by eliminating the noises of the vortex signal caused by fluctuation and pulsation, and since the lack of pulses can be prevented when the vortex signal is converted into a pulse, the accuracy of flow measurements is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter for measuring a flow rate of a fluid to be measured by using Karman vortices generated by a vortex generator provided in a pipe.

[0002]

2. Description of the Related Art There are various types of Karman vortex detection systems in vortex flow meters. Here, an ultrasonic vortex flowmeter that detects Karman vortices using ultrasonic waves will be described as an example.

In a conventional vortex flowmeter, a vortex generator is provided in a pipe through which a fluid flows, and a Karman vortex is generated downstream of the vortex generator. On the downstream side of the vortex generator in the pipeline, an ultrasonic transmitter connected to the oscillation circuit and an ultrasonic receiver connected to the conversion circuit are provided facing each other so as to sandwich the fluid flowing in the pipeline. ing. Further, an oscillation circuit and an ultrasonic receiver are connected to the two input terminals, respectively, and a phase comparison circuit is provided which obtains a modulation amount of the ultrasonic wave received by the ultrasonic receiver, generates a vortex signal, and outputs the vortex signal. ing. The output terminal of the phase comparison circuit is connected to a flow rate calculation circuit via a bandpass filter and a waveform shaping circuit that can change the transmission frequency range.

In this vortex flowmeter, a Karman vortex having a frequency proportional to the flow velocity of the fluid is generated by the vortex generator, and the ultrasonic wave from the ultrasonic transmitter is modulated by the Karman vortex and received by the ultrasonic receiver. The transmitted and received ultrasonic waves are compared by a phase comparison circuit to determine the amount of modulation of the ultrasonic waves, and the flow rate is calculated based on the frequency of the signal (vortex signal) representing the amount of modulation (the generation frequency of the Karman vortex). The circuit calculates the flow rate of the fluid to be measured.

At this time, the bandpass filter to which the signal from the phase comparison circuit, that is, the vortex signal is input, performs noise (mainly Karman vortex) superimposed on the vortex signal in order to accurately perform waveform shaping in the waveform shaping circuit described later. The vortex signal from which fluctuations and fluid pulsations having a lower frequency than the generation frequency of the vortex are removed) is output to the waveform shaping circuit, and the waveform shaping circuit pulsates the signal to generate a signal having a frequency equal to the Karman vortex generation frequency. The pulse signal is output to the flow rate calculation circuit.

However, since the frequency of the vortex signal changes according to the flow rate of the fluid, if the transmission frequency range of the band-pass filter is fixed, the frequency of the vortex signal depends on the flow rate depending on the flow rate. Not included in
It is removed by the band pass filter, and the flow rate calculation cannot be performed accurately. Therefore, in order to avoid this problem, an arithmetic circuit is interposed between the output side of the phase comparison circuit and the bandpass filter, and the transmission frequency region of the bandpass filter is changed based on the frequency of the eddy signal ( Tracking control). That is,
The generation frequency of the Karman vortex is obtained from the vortex signal containing noise, and this frequency is used as a reference signal so that the transmission frequency region of the bandpass filter matches the generation region of the Karman vortex.

[0007]

By the way, the frequency of the vortex signal can be irregular or dropped due to the turbulence of the flow, which tends to make the frequency of the vortex signal unstable. In the conventional vortex flowmeter that performs tracking control using the frequency of the vortex signal, the setting of the transmission frequency region of the bandpass filter becomes unstable, and noise cannot be sufficiently removed, and the flow measurement accuracy decreases. There is a possibility that it will be.

Further, since the band-pass filter is used, if the vortex signal is stable and the frequency component of the occurrence of the Karman vortex can be obtained as the reference signal, the transmission frequency region of the band-pass filter should Since it matches the frequency domain, highly accurate flow rate calculation can be performed based on the frequency of occurrence of Karman vortices.On the other hand, if the noise component is larger than the Karman vortex component included in the vortex signal, the noise frequency component It is used as a signal, and incorrectly sets the frequency domain of the noise component as the transmission frequency domain of the band-pass filter, and removes the frequency of the Karman vortex that is higher in frequency than the noise component. Calculation of flow rate based on frequency reduces reliability of flow rate measurement A.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a vortex flowmeter for measuring a flow rate by accurately extracting a frequency component of a Karman vortex generated from a vortex signal.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a vortex generator provided in a pipe through which a fluid to be measured flows and a Karman vortex generated by the vortex generator are detected at a predetermined position. Vortex detection means for outputting the generated frequency as a vortex signal, and calculation means for calculating the flow rate of the fluid to be measured in the pipe from the frequency of the vortex signal detected by the vortex detection means,
A vortex flowmeter comprising: an amplitude change detecting means for detecting an amplitude change of the vortex signal from the vortex signal detected by the vortex detection means; and a frequency of the amplitude change detected by the amplitude change detecting means. A predetermined frequency removing means for removing from the vortex signal detected in the above, the arithmetic means,
The flow rate of the fluid to be measured in the pipe is calculated from the frequency of the vortex signal from which the frequency of the amplitude change has been removed by the predetermined frequency removing means.

Thus, the predetermined frequency removing means removes, from the vortex signal, a frequency component including a frequency caused by noise that changes the amplitude of the vortex signal.

Further, the invention according to a second aspect is characterized in that the predetermined frequency removing means removes a frequency lower than the frequency detected by the amplitude change detecting means.

Thus, the predetermined frequency removing means removes, from the vortex signal, frequency components equal to or lower than the frequency caused by the noise that changes the amplitude of the vortex signal.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vortex flowmeter 1 according to an embodiment of the present invention will be described below with reference to the schematic diagram of FIG.

A vortex generator 3 for generating Karman vortices is provided in a pipe 2 in which the vortex flowmeter 1 is installed. 4, 4 are formed so as to face each other. A pair of ultrasonic sensors 5 including an ultrasonic oscillator 5a and an ultrasonic receiver 5b are fitted into the holes 4 and 4 and are closed. The ultrasonic oscillator 5a is connected to the oscillating circuit 6, and oscillates ultrasonic waves by applying a drive voltage from the oscillating circuit 6, and the ultrasonic receiver 5b filters the received ultrasonic waves into the filter 7, the amplifier 8, and the like. , A phase comparison circuit 10 via a conversion circuit 9
Output to

The filter 7 cuts a noise portion out of the ultrasonic waves received by the ultrasonic receiver 5b and outputs only a signal in a frequency region required as a signal (a signal corresponding to a frequency band in which a Karman vortex is generated). Is used. The amplifier 8 amplifies the ultrasonic wave transmitted through the filter 7, and the conversion circuit 9 outputs the ultrasonic wave output as an analog signal as a digital signal.

In the phase comparison circuit 10, the oscillation circuit 6
The frequency of the ultrasonic wave oscillated by the ultrasonic oscillator 5a is captured, the ultrasonic wave received by the ultrasonic receiver 5b is captured via the filter 7, the amplifier 8, and the conversion circuit 9, and the phases of the respective ultrasonic waves are compared. Thus, when the ultrasonic wave is transmitted through the pipe 2, the modulation of the ultrasonic wave received by the Karman vortex generated in the pipe 2 is detected, and the modulated component is converted into a signal and output.

The cut-off frequency of the switched capacitor filter 11 is set according to the frequency of a frequency control signal input from a voltage / frequency conversion circuit 16 described later.
This is a high-pass filter that removes signal components below the cutoff frequency from the modulation signal (vortex signal) output from the phase comparison circuit 10.

The waveform shaping circuit 12 raises a pulse when a signal input from the switched capacitor filter 11 exceeds a predetermined value, and lowers a pulse when the signal is lower than a predetermined value, thereby converting an analog signal. The digital signal is output to the flow rate calculation circuit 13 and the amplitude demodulation circuit 14.

The flow rate calculation circuit 13 counts the number of generated Karman vortices by counting the pulses of the input digital signal, and calculates the flow rate based on the count. The pulse count is a meter constant (unit =
[Pulse / unit flow rate]) to calculate the integrated flow rate, and by dividing the pulse count number by the unit time, the number of pulses per unit time, that is, the frequency of occurrence of Karman vortex, is obtained. The flow rate per unit time (instantaneous flow rate) is calculated by dividing the number of pulses per unit time by the meter constant.

The amplitude demodulation circuit 14 extracts only the amplitude change input from the waveform shaping circuit 12, converts the amplitude change into a signal, and outputs the signal to the frequency / voltage conversion circuit 15. The frequency / voltage conversion circuit 15 outputs a voltage value proportional to the frequency of the input signal to the voltage / frequency conversion circuit 16, and the voltage / frequency conversion circuit 16 outputs a voltage having a frequency proportional to the input voltage value. The signal is output to the switched capacitor filter 11. Therefore, the amplitude change signal output from the amplitude demodulation circuit 14 is output to the frequency / voltage conversion circuit 15
And through the voltage / frequency conversion circuit 16, the signal is converted into a signal having a frequency proportional to the frequency of the amplitude change, and a signal having a frequency proportional to the frequency of the amplitude change is a frequency indicating the cutoff frequency of the switched capacitor filter 11. It is output as a control signal. In the present embodiment, the switched capacitor filter 11 is used as a predetermined frequency removing unit, and the amplitude demodulation circuit 14 is used as an amplitude change detecting unit.

Here, the switched capacitor filter 1
The operation of removing a component that changes the amplitude of the vortex signal, which is a noise component, from the vortex signal in step 1 will be described.

The vortex signal output from the phase comparison circuit 18 has a waveform in which a low-frequency component, which is noise, is superimposed on the frequency component of the Karman vortex as shown in FIG.
A component that changes the amplitude of the eddy signal indicated by a broken line in FIG. 2 by removing signal components below a specific frequency based on a cutoff frequency set as described later in the switched capacitor filter 11 ( Noise) is removed, and only the frequency component of the occurrence of the Karman vortex shown in FIG. From the signal converted by the waveform shaping circuit 12, only an amplitude change (a component indicated by a broken line in FIG. 2) of the vortex signal is extracted by the amplitude demodulation circuit 14, and output as an amplitude change signal.

The frequency / voltage conversion circuit 15 and the voltage / frequency conversion circuit 16 convert the amplitude change signal into a frequency control signal having a frequency proportional to the frequency of the amplitude change signal. By output, the cut-off frequency is set in the switched capacitor filter 11 in accordance with the frequency of the frequency control signal input from the voltage / frequency conversion circuit 16.

The signal output from the switched capacitor filter 11 is also output to a flow rate calculation circuit 13 via a waveform shaping circuit 12, and the flow rate calculation circuit 13 calculates the integrated flow rate and the flow rate per unit time (instantaneous flow rate). Desired.

As described above, in this embodiment,
Switched capacitor filter 11, waveform shaping circuit 1
2. Phase-Locked-Loop is formed by the amplitude demodulation circuit 14, the frequency / voltage conversion circuit 15, and the voltage / frequency conversion circuit 16. The amplitude demodulation circuit 14 extracts a component that changes the amplitude of the vortex signal, and The voltage conversion circuit 15 and the voltage / frequency conversion circuit 16 convert the cutoff frequency of the switched capacitor filter 11 to a cut-off frequency, and the switched capacitor filter 11 removes a frequency component that changes the amplitude of the eddy signal. Is stabilized, and pulse dropout is prevented, so that the accuracy of flow rate measurement can be improved.

The switched capacitor filter 11
Is a high-pass filter, so even if the noise component is larger than the component due to the Karman vortex, the low-frequency noise component is transmitted and the component due to the high-frequency Karman vortex is transmitted as in the case of using a conventional bandpass filter. Removal can be prevented, and the reliability of the flow measurement can be improved.

In this embodiment, an ultrasonic type vortex flowmeter has been described as an example. However, the present invention is not limited to this, and a piezoelectric element type or a capacitance type type which detects a pressure change due to Karman vortex may be used. In addition, even a type such as an ultrasonic type or a thermistor type, which detects a change in flow velocity due to Karman vortex, can be applied to a vortex flowmeter which detects a generation frequency of Karman vortex and measures a flow rate.

[0029]

According to the vortex flowmeter of the present invention, an amplitude change detecting means for detecting an amplitude change of the vortex signal from the vortex signal detected by the vortex detecting means, and a frequency of the amplitude change detected by the amplitude change detecting means. A predetermined frequency removing means for removing a frequency including the vortex signal detected by the vortex detecting means,
The arithmetic means is configured to calculate the flow rate of the fluid to be measured in the pipe from the frequency of the vortex signal from which the frequency including the frequency of the amplitude change has been removed by the predetermined frequency removing means. Unlike a vortex flowmeter that performs tracking control based on the frequency of the vortex signal, even when the vortex signal is unstable, the noise component that changes the amplitude of the vortex signal can be sufficiently removed to stabilize the amplitude of the vortex signal. The accuracy is improved.

Also, the predetermined frequency removing means removes frequencies below the frequency detected by the amplitude change detecting means, which is different from a conventional vortex flowmeter which performs tracking control using a band-pass filter. Even if the noise component is large, the occurrence frequency of the high-frequency Karman vortex is not removed, and the flow rate calculation based on an erroneous frequency other than the frequency of the Karman vortex can be prevented. Reliability is improved.

[0031]

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a vortex flowmeter 1 according to an embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of a vortex signal output from a phase comparison circuit 10 of the vortex flowmeter 1;

FIG. 3 is a diagram showing a waveform when a noise component that changes the amplitude is removed from a vortex signal output from a phase comparison circuit 10 of the vortex flowmeter 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Vortex flowmeter 2 Piping 3 Vortex generator 4 Hole 5 Ultrasonic sensor 5a Ultrasonic oscillator 5b Ultrasonic receiver 6 Oscillation circuit 7 Filter 8 Amplifier 9 Conversion circuit 10 Phase comparison circuit 11 Switched capacitor filter (predetermined frequency removing means) 12 Waveform shaping circuit 13 Flow rate operation circuit 14 Amplitude demodulation circuit (amplitude change detection means) 15 Frequency / voltage conversion circuit 16 Voltage / frequency conversion circuit

Claims (2)

[Claims] 1. A vortex generator provided in a pipe through which a fluid to be measured flows, a Karman vortex generated by the vortex generator is detected at a predetermined position, and a generation frequency of the Karman vortex is output as a vortex signal. A vortex flowmeter comprising: a vortex detecting means; and a calculating means for calculating a flow rate of the fluid to be measured in the pipe from a frequency of the vortex signal detected by the vortex detecting means. Amplitude change detecting means for detecting an amplitude change of the eddy signal from the signal; and a predetermined frequency removing means for removing a frequency including the frequency of the amplitude change detected by the amplitude change detecting means from the vortex signal detected by the vortex detecting means. The calculating means calculates the flow rate of the fluid to be measured in the pipe from the frequency of the vortex signal from which the frequency including the frequency of the amplitude change has been removed by the predetermined frequency removing means. Vortex flowmeter, characterized in that. 2. The vortex flowmeter according to claim 1, wherein the predetermined frequency removing unit removes a frequency lower than a frequency detected by the amplitude change detecting unit.