JP3031389B2 - Vortex 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 vortex flowmeter for measuring the flow rate of a measurement fluid by counting the number of vortices generated by a vortex generator when the measurement fluid flows through a pipe, and more particularly to a vortex flowmeter. The present invention relates to a vortex flowmeter which improves the S / N by improving the configuration of a signal conversion unit.

[0002]

2. Description of the Related Art The structure of a conventional vortex flowmeter will be described below with reference to FIGS. FIG. 5 is a longitudinal sectional view showing a section of a conventional vortex sensor. 10 is a conduit through which fluid flows,
Reference numeral 11 denotes a cylindrical nozzle provided at a right angle to the pipeline 10. Numeral 12 denotes a column-shaped vortex generator having a trapezoidal cross-section inserted into the conduit 10 at right angles to the nozzle 11 at an interval from the nozzle 11, one end of which is fixed to the conduit 10 by a screw 13, and the other end of which is a flange 14. And is fixed to the nozzle 11 by screws or welding.

[0005] Reference numeral 15 denotes a concave portion provided on the flange portion 14 side of the vortex generator 12, and a pair of piezoelectric elements 16 and 17 are arranged in the concave portion 15 at predetermined intervals above and below. The elements 16 and 17 are insulated and sealed by a sealing body 18 such as glass. Piezoelectric elements 16, 1
In 7, two semi-annular electrodes are vertically arranged. In each of the piezoelectric elements 16 and 17, the piezoelectric body sandwiched between the upper and lower electrodes on the left side and the piezoelectric body sandwiched between the upper and lower electrodes on the right side are polarized in opposite directions. Reverse polarity charges are generated in the upper and lower electrodes.

A vortex signal from the vortex sensor configured as described above is input to a conversion circuit shown in FIG. Charges Q _v1 and Q _v2 having a frequency corresponding to the vortex frequency of the vortex signal generated in the piezoelectric elements 16 and 17 of the vortex sensor are input to charge converters 19 and 20 as shown in FIG. Converted to a signal. The voltage signal of the charge converter 19 and the voltage signal of the charge converter 20 are added by the adder 22 to the voltage signal via the volume 21, and the added output is low-pass filtered by the low pass filter 23. After that,
The signal is amplified to a predetermined size by the amplifier 24. The low-pass filter 23 is used to remove noise generated due to variations in the piezoelectric elements 16 and 17 or improper adjustment of the noise balance of the volume 21.

The output of the amplifier 24 is input to a Schmitt trigger 25 having a predetermined hysteresis width, and a vortex signal having an amplitude larger than the hysteresis width is converted into a vortex frequency of 1: 1.
Is converted into a pulse signal corresponding to. This pulse signal is DC-insulated by a transformer 26 and input to a frequency / voltage converter 27, where it is converted by a volume 28 into an analog voltage signal corresponding to the span.

This voltage signal is supplied to a transistor 31 by a DC amplifier 30 whose zero point is set by a volume 29.
Of base - controls the scan current is converted to a current output I _L and is transmitted to the receiving resistance R _L of the receiving instrument having an external power source E _s via its collector terminal and the output terminal T ₁ from the emitter end, T ₂ You. In this case, the feedback voltage E _f generated across the feedback resistor R _f feedback resistor R _f is inserted between the transistor 31 and the output terminal T ₂ are fed back to the input end of the DC amplifier 30, the input 4-20m corresponding to the voltage signal at the end
It is controlled in a unified current output I _L of A.

[0007] Among base current output I _L - approximately 4mA of the scan portion is used to make the internal power supply of the converter circuit. That is, a part of this current is supplied to the constant voltage circuit 33 via the constant current circuit 32, and a zero voltage is generated at both ends of the volume 29 by using the generated reference voltage.
Further, another part of the 4 mA current is supplied to a transistor 34 and input to an AC / DC conversion circuit 35, where it is converted to an AC voltage, and the converted AC voltage is supplied via a transformer 36 to an internal power supply circuit. 37. The internal power supply circuit 37 includes internal voltages + V and -V necessary for the operation of the conversion circuit.
make.

Next, the operation of the vortex flowmeter configured as described above will be described with reference to FIGS. When the fluid flows, vibrations due to Karman vortices are generated in the vortex generator 12 shown in FIG. This vibration causes the vortex generator 12 to repeat a stress distribution as shown in FIG. 7A and a reverse stress distribution, and the piezoelectric elements 16 and 17 have the same vortex frequency as shown in FIG. 7A. Of the charges + Q and -Q corresponding to the signal stress having the frequency of

On the other hand, the pipe line 10 also generates pipe line vibrations that cause noise. This pipeline vibration is divided into three components: (a) a drag direction in the same direction as the fluid flow, (b) a lift direction F perpendicular to the fluid flow, and (c) a longitudinal direction of the vortex generator. . Among them, the stress distribution with respect to the vibration in the drag direction is as shown in FIG. 7B, and the positive and negative charges are canceled in one electrode, and no noise charge is generated. Also, as shown in FIG. 7C, the vibration in the longitudinal direction is canceled in the electrode, and no noise charge is generated as in the case of the drag direction. However, the vibration in the lift direction F has the same stress distribution as the signal stress, and generates noise charges. Therefore, the following calculation is performed to eliminate this noise charge. Piezoelectric elements 16, 1
7 are Q _v1 and Q _v2 , the signal components are S ₁ and S ₂ , and the noise components in the lift direction are N ₁ and N _2.
If the polarization is reversed at 7, Q _v1 and Q _v2 are expressed by the following equations.

[0010] Q _v1 = S ₁ + N ₁ -Q _v2 = -S ₂ -N ₂

However, the vector directions of S ₁ and S ₂ and N ₁ and N ₂ are the same. Here, the relationship between the signal component and the noise component of the piezoelectric elements 16 and 17 is as shown in FIG. 8 showing the relationship between the noise and the signal in the lift direction and the bending moment of the vortex generator, and FIG. the piezoelectric element 17 side of the tea, as shown in - Jikonba - with volume 21 when adding the output of the motor 20 in the adder 22 of the N ₁ / N ₂ times to the piezoelectric element 16 side Cha - Jikonba - motor 19 output and By adding, Q _v1 −Q _v2 (N ₁ / N ₂ ) = S ₁ −S ₂ (N ₁ / N ₂ ), and the line noise is removed.

Of the noise superimposed on the vortex generator as described above, the noise in the drag direction and the longitudinal direction of the vortex generator consider the polarity of the piezoelectric elements 16 and 17, and the noise in the lift direction is generated by the piezoelectric element. It is removed as a two-element system considering the balance between 16 and 17.

[0013]

However, in the conventional vortex flowmeter as described above, the filter constant of the low-pass filter 23, the trigger level of the Schmitt trigger 25 are determined by the diameter of the vortex flowmeter, and the type of fluid (gas, liquid). ), Specific weight, etc., must be changed each time. Then, when changing the filter constant, μ
It is necessary to add an F-order capacitance, which requires a large area for the circuit portion mounted on the principal board, which is a constraint on miniaturizing the amplifier case, and consequently, a constraint on improving the vibration resistance.

[0014]

According to the present invention, a vortex frequency generated corresponding to a flow rate of a measurement fluid is detected and converted into a flow rate signal corresponding to the vortex frequency. In a vortex flowmeter, an analog / digital converter which samples a vortex frequency which changes at a low frequency over time at a high frequency sampling period and converts it into a digital signal is stored in a predetermined storage area. Data memory means, high-speed Fourier transform of the digital signal to a frequency signal to generate a spectrum distribution of the amplitude with respect to the frequency, and predetermined parameters which are set from the outside. -When a peak of a plurality of frequencies falls within a predetermined range of the spectrum distribution corresponding to the above-mentioned spectrum, or when it does not fall at all, it is determined to be abnormal and only one frequency has a peak. - When the click entered will and a determination calculation means for determining a normal vortex signals, which operations such as is obtained by to run a microprocessor.

[0015]

[Operation] The analog / digital converter samples the eddy frequency generated at a low frequency over time corresponding to the flow rate of the measurement fluid at a high frequency sampling period and converts it into a digital signal. This digital signal is stored in a predetermined storage area. Fourier transform operation means F
The above digital signal is subjected to a high-speed Fourier transform into a frequency signal to create a spectrum distribution of amplitude with respect to frequency.

The judgment operation means is abnormal when a predetermined parameter is set from the outside and a peak of a plurality of frequencies falls within a predetermined range of the spectrum distribution corresponding to this parameter or does not enter at all. When a peak of only one frequency enters, it is determined that the signal is a normal vortex signal. And
These calculations are executed by a microprocessor, and a normal vortex signal is output as a flow signal.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of one embodiment of the present invention. Parts having the same functions as those of the conventional vortex flowmeter shown in FIGS. 5 to 8 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

A piezoelectric element 16 fixed in the vortex generator,
Charges Q _v1 and Q _v2 having a frequency corresponding to the vortex frequency of the vortex signal generated at 17 are input to the charge converters 19 and 20 and converted into AC voltage signals. Charge converter
The voltage signal of the converter 19 and the voltage signal obtained by charging the voltage signal of the charge converter 20 via the volume 21 are added by an adder 22, amplified to a predetermined size by an automatic gain amplifier 40, and converted into an analog / digital signal. Output to the unit 41.

The analog / digital converter 41 samples a low-frequency AC voltage obtained at the output of the automatic gain amplifier 40 at a high-frequency sampling period under the control of the microprocessor CPU to produce a digital signal. It is stored in a predetermined area TM of the random access memory RAM. Therefore, the amplitude of the vortex signal is stored as a discrete signal in a time series in the predetermined area TM of the random access memory RAM.

On the other hand, in a read-only memory ROM, a high-speed Fourier transform (FFT) calculation program for converting discrete time-series data into a frequency spectrum is stored in advance. The microprocessor CPU uses a high-speed Fourier transform (FFT) calculation program stored in the read-only memory ROM for the eddy signal data in the time domain stored in the predetermined area TM of the random access memory RAM. To convert to frequency space frequency data,
This calculation result is stored in a predetermined area FM of the random access memory RAM.

The random access memory RAM
In the predetermined area SM, the diameter of the vortex flowmeter, the type of fluid, the specific weight, and the like are input from the setting device 43 via the input / output interface I / O. These data may be set by using a digital signal connected to the output terminal 45 by a microprocessor via a modem and using the digital signal. The microprocessor CPU sets a determination area DA for determining whether or not the frequency data is a vortex signal using the set value set in the predetermined area SM of the random access memory RAM in a predetermined area of the random access memory RAM. Is set.

The microprocessor CPU calculates whether or not the frequency data stored in the predetermined area FM of the random access memory RAM is included in the determination area DA in the predetermined area DM of the random access memory RAM.
Is executed by using the judgment calculation program stored in the.

One frequency data is stored in the determination area DA.
When only frequency data is included, the frequency data is determined to be a correct vortex signal, and the read only memory R is used by using this vortex signal.
The flow rate calculation is executed by using a flow rate calculation program stored in the OM, and is output to the output terminal 45 via the bus 42 and the digital / analog converter 44 as a flow rate signal.

On the other hand, when a plurality of frequency data are included in the determination area DA or when the frequency data is not included at all, the normal measurement is disabled and the microprocessor CPU outputs an abnormal signal. FIG. 2 shows a waveform of a vortex signal which is time-lapse data obtained at the output terminal of the automatic gain amplifier 40. The vortex signal is transferred to a predetermined area TM of the random access memory RAM via an analog / digital converter 41. After being stored, it is converted into frequency data in the frequency space domain using a fast Fourier transform (FFT) calculation program and stored in a predetermined area FM of the random access memory RAM when the frequency data shown in FIG. It has become.

The horizontal axis is frequency and the vertical axis is amplitude. Normally, the amplitude of the vortex frequency fv has the largest value, but peaks due to the resonance frequency fN of the vortex generator and other noises also occur. A determination area DA is set in this frequency space. If only one peak exists in this determination area, this peak is a vortex signal and a normal flow signal is output. On the other hand, when a plurality of peaks are included in the determination area DA or no peaks exist,
Displays an error indicating that normal measurement is impossible.

FIG. 4 is a configuration diagram showing the configuration of the second embodiment of the present invention. In this case, the eddy signals output from the piezoelectric elements 16 and 17 are amplified by a predetermined number in automatic gain amplifiers 40 and 46, respectively, and then the analog / digital converter 4
The digital signals are converted into digital signals at 1 and 48 and stored in a predetermined area of the random access memory RAM under the control of the microprocessor CPU.

These stored digital signals are subjected to a noise balance operation having the same function as that of the volume 21 by the microprocessor CPU, and then to an addition operation to perform signal processing similar to that of the embodiment shown in FIG. That's what I did.

As described above in detail with the embodiment, according to the present invention, the eddy signal is digitized, and it is converted into a frequency domain by performing a high-speed Fourier transform on the digitized eddy signal. Since the presence / absence of noise is determined by the determining means, the S / N can be determined with high accuracy, and it is necessary to add a large-sized μF-order capacitor for noise removal as in the prior art. This makes it easier to reduce the size of the amplifier case, thereby contributing to improved vibration resistance.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a waveform of an eddy signal obtained at an output terminal of the automatic gain amplifier in the embodiment shown in FIG.

FIG. 3 is a spectrum diagram showing a spectrum in a frequency domain after fast Fourier transform.

FIG. 4 is a configuration diagram showing a configuration of a second example of the present invention.

FIG. 5 is a longitudinal sectional view showing a section of a conventional vortex sensor.

FIG. 6 is a block diagram showing a conversion circuit connected to an output terminal of the vortex sensor shown in FIG.

FIG. 7 is an explanatory diagram illustrating the operation of the vortex sensor shown in FIG.

FIG. 8 is an explanatory diagram illustrating a noise removing operation of the vortex sensor shown in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Pipeline 12 Vortex generator 16, 17 Piezoelectric element 19, 20 Charge converter 22 Adder 23 Low pass filter 25 Schmitt trigger 41, 48 Analog / digital converter RAM Random access memory ROM Read only memory CPU Micro Processor I / O I / O interface

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/32

Claims (1)

(57) [Claims] 1. A vortex flowmeter for detecting a vortex frequency generated in accordance with a flow rate of a measurement fluid and converting the vortex frequency into a flow signal corresponding to the vortex frequency. An analog / digital converter that samples at a sampling period of and converts it into a digital signal;
Data memory means for storing the digital signal in a predetermined storage area; fast Fourier transform of the digital signal into a frequency signal to generate a spectrum distribution of amplitude with respect to frequency; When a predetermined parameter is set and a peak of a plurality of frequencies falls within a predetermined range of the spectrum distribution corresponding to this parameter or when it does not enter at all, it is regarded as abnormal, and a peak of only one frequency enters. A vortex flowmeter, comprising: a determination operation means for determining a normal vortex signal when the vortex signal is detected.