JPH05281005A - Vortex flowmeter - Google Patents

Abstract

(57) [Abstract] [Purpose] The signal conversion unit of the vortex flowmeter has been improved to improve S /
An object of the present invention is to provide a vortex flowmeter for improving N. A first signal including a vortex signal converted by a first charge amplifier and a second signal including a vortex signal converted by a second charge amplifier are added by an adder via a variable resistance element to obtain a third signal. In the output vortex flowmeter, band stop filter means for outputting the noise signal by blocking the vortex signal by applying the third signal, and the resistance of the variable resistance element by minimizing the noise signal. A control means for calculating a value and controlling the value is provided.

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 a measurement fluid flows in a pipe, and more particularly to a vortex flowmeter. The present invention relates to a vortex flowmeter having an improved S / N by improving the configuration of the signal conversion unit.

[0002]

2. Description of the Related Art The structure of a first conventional vortex flowmeter will be described below with reference to FIGS. FIG. 3 is a vertical cross-sectional view showing a cross section of a conventional vortex sensor. Reference numeral 10 is a pipe through which a fluid flows, and 11 is a cylindrical nozzle provided at a right angle to the pipe 10. Reference numeral 12 denotes a columnar vortex generator having a trapezoidal cross section which is inserted at a right angle into the pipe line 10 with a distance from the nozzle 11, one end of which is fixed to the pipe line 10 by a screw 13 and the other end of which is a flange portion 14. It is fixed to the nozzle 11 by screws or welding.

Reference numeral 15 is a concave portion provided on the side of the flange portion 14 of the vortex generator 12, and a pair of piezoelectric elements 16 and 17 are vertically arranged in the concave portion 15 at a predetermined interval. The elements 16 and 17 are insulated and sealed by a sealing body 18 such as glass.

Piezoelectric elements 16 and 17 are provided with semi-circular electrodes divided in two, which are arranged one above the other. In each of the piezoelectric elements 16 and 17, the piezoelectric body sandwiched by the upper and lower electrodes on the left side and the piezoelectric body sandwiched by the upper and lower electrodes on the right side are polarized in opposite directions, and are subjected to stress in the same direction. Charges of opposite polarity are generated in the upper and lower electrodes.

The vortex signal from the vortex sensor constructed as described above is input to the conversion circuit shown in FIG. The 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 the charge converters 19 and 20 as shown in FIG. Converted to a signal.

Then, the voltage signal of the charge converter 19 and the voltage signal of the charge converter 20 are adjusted to the volume 21.
The added voltage is added by the adder 22. The added output is low-pass filtered by the low-pass filter 23 and then amplified by the amplifier 24 to a predetermined size. The low-pass filter 23 is used to remove noise generated due to variations in the piezoelectric elements 16 and 17 themselves 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 this hysteresis width is added to the vortex frequency at a ratio of 1: 1.
Is converted into a pulse signal corresponding to. This pulse signal is galvanically isolated by the transformer 26 and input to the frequency / voltage converter 27, where it is converted by the volume 28 into an analog voltage signal corresponding to the span.

This voltage signal is applied to the transistor 31 by the DC amplifier 30 whose zero point is set by the volume 29.
Is converted into a current output I _L by controlling the base current of the above and is transmitted from the collector end and the emitter end thereof to the receiving resistance R _L of the receiving instrument having the external power supply E _s through the output terminals T ₁ and T _2. It 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 end voltage signal
It is controlled in a unified current output I _L of A.

In addition, approximately 4 mA of the base portion of the current output I _L is used to make the internal power supply of the conversion circuit. That is, a part of this current is supplied to the constant voltage circuit 33 through the constant current circuit 32, and the reference voltage generated here is used to generate a zero voltage across the volume 29.
Further, another part of the current of 4 mA is supplied to the transistor 34 and input to the AC / DC conversion circuit 35, where it is converted into an AC voltage, and the converted AC voltage is passed through the transformer 36 to the internal power supply circuit. 37. The internal power supply circuit 37 is an internal voltage + V, -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. 7 and 8. When the fluid flows, vibrations due to Karman vortices are generated in the vortex generator 12 shown in FIG. 5 in the direction indicated by arrow F. This vibration causes the vortex generator 12 to repeat the stress distribution as shown in FIG. 7A and the reverse stress distribution, so that a signal stress having the same frequency as the vortex frequency is generated in each piezoelectric element 16, 17. Corresponding charge +
Repetition of Q and -Q occurs.

On the other hand, in the pipeline 10, pipeline vibration that causes noise is also generated. This pipeline vibration is divided into three directions components: (a) a drag force direction in the same direction as the fluid flow, (b) a lift force direction F perpendicular to the fluid flow, and (c) a longitudinal direction of the vortex generator. . Of these, the stress distribution with respect to vibration in the drag direction is as shown in FIG. 7B, and positive and negative charges are canceled out within one electrode, and noise charges are not generated. Further, with respect to the vibration in the longitudinal direction, as shown in FIG. 7 (c), it is canceled in the electrode and no noise charge is generated as in the drag direction. However, the vibration in the lift direction F has the same stress distribution as the signal stress, and noise charge is generated. Therefore, the following calculation is executed in order to erase this noise charge. Piezoelectric elements 16, 1
The respective electric charges of 7 are Q _v1 , Q _v2 , the signal components are S ₁ , S ₂ , the noise components in the lift direction are N ₁ , N ₂ , and the piezoelectric elements 16, 1
If the polarization is reversed at 7, Q _v1 and Q _v2 are expressed by the following equations.

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, and the relationship between the noise in the lift direction and the bending moment of the vortex generator with respect to the signal are as shown in FIG. When the output of the charge converter 20 on the piezoelectric element 17 side is added by the adder 22, it is multiplied by N ₁ / N ₂ together with the volume 21 and added to the output of the charge converter 19 on the piezoelectric element 16 side. , Q _v1 −Q _v2 (N ₁ / N ₂ ) = S ₁ −S ₂ (N ₁ / N ₂ ), and the pipeline noise is removed.

Among the noises superposed on the vortex generator as described above, the noise in the drag force direction and the longitudinal direction of the vortex generator takes into consideration the polarities of the piezoelectric elements 16 and 17, and the noise in the lift direction is determined by the piezoelectric element. It is removed as a two-element system in consideration of the balance of 16 and 17. However, this conventional vortex flowmeter is troublesome because the volume 21 is adjusted and the noise is minimized so that the noise is minimized.

Therefore, in order to automate this noise adjustment, there is a configuration as shown in FIG. The output signal V _{1 of the charge} converter 19 and the charge converter 20
And the output signal V ₂ obtained via the variable resistance element 38 is added by the adder 22 and output as the output signal V ₃ .

The output signal V ₃ is amplified by the amplifier 39 and output to the band filter 40, where noise outside the range of the measurement frequency is removed and output as the output signal V ₄ . The output signal V ₄ is rectified by the rectifying circuit 41 and output to the smoothing circuit 42.

The smoothing circuit 42 smoothes the output of the rectifying circuit 41 and outputs it as a smoothed output V ₅ to the variable resistance element 38. This variable resistance element 38 has its resistance so that the magnitude of the smoothed output V ₅ is minimized. The value is adjusted.

[0018]

However, in the conventional vortex flowmeter as described above, when the variable resistance element is automatically adjusted while the fluid is flowing, the vortex signal is also canceled. Therefore, there is an inconvenience that the automatic noise balance adjustment can be performed only when the flow rate is zero.

[0019]

The present invention has, as a structure for solving the above problems, a first signal converted by a first charge amplifier and containing a vortex signal and a vortex signal converted by a second charge amplifier. In a vortex flowmeter that adds the second signal with an adder via a variable resistance element and outputs the third signal, a band in which the third signal is applied and the vortex signal is blocked to output a noise signal. A blocking filter means and a control means for calculating the resistance value of the variable resistance element and controlling it so as to minimize this noise signal are provided.

[0020]

[Operation] The band stop filter means to which the third signal, which is the sum of the first signal and the second signal obtained via the variable resistance element, is applied, outputs the noise signal by blocking the vortex signal contained therein. To do.

The control means calculates the resistance value of the variable resistance element and controls it so that the noise signal becomes minimum. As a result, the resistance value of the variable resistor is automatically selected so that the noise signal outside the range of the measurement band is minimized even when the measurement fluid is flowing.

[0022]

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. The parts having the same functions as those of the conventional vortex flowmeter shown in FIGS. 5 to 9 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

A piezoelectric element 16 fixed in the vortex generator,
The charges Q _v1 and Q _v2 having a frequency corresponding to the vortex frequency of the vortex signal generated in 17 are input to the charge converters 19 and 20 and converted into alternating voltage signals V ₁ ′ and V ₂ ′.

The output signal of the output end of the charge converter 19
Issue V₁'Is resistance R₁Output signal via₁As a char
Output signal V at the output end of the converter 20₂'Is resistance R₂When
Output signal V via variable resistance element 43₂Taken out as
And these output signals V₁And V ₂Is added by the adder 22
Output signal V₆Is output as.

Here, in the variable resistance element 43, for example, resistors R ₃ , R ₄ , R ₅ , and R ₆ are connected in series,
Switch SW ₁ at both ends of the resistor R ₃ is, the resistance R ₃ and R ₄
The switch S is connected between the connection point of and the connection point of the resistors R ₄ and R _5.
A switch SW ₃ is connected in parallel between W ₂ and a connection point between the resistors R ₄ and R _{5 and} a connection point between resistors R ₅ and R ₆ , and a switch SW ₄ is connected in parallel between both ends of the resistor R ₆ . It is composed.

The output signal V ₆ is output to the bandpass filter 44. The bandpass filter 44 is composed of, for example, a switched capacitor, and its center frequency f ₀ is controlled by the control signal CS1.

Further, the bandpass filter 44 removes noise contained in the output signal V ₆ and outputs it to the Schmitt trigger circuit 45 as a voltage signal V ₇ . The Schmitt trigger circuit 45 pulsates this voltage signal V ₇ and outputs it as a frequency signal V _f to the counter 46. Counter 4
6 digitizes this frequency signal V _f and outputs it to a microprocessor (CPU) 47.

The microprocessor 47 includes a ROM (Read Only Memory), a RAM (Random Access Memory), a clock generator and the like. The ROM stores programs for executing various calculations, and the RAM has a detector. The data necessary for calculating the flow rate, such as the diameter, the type of fluid (gas, liquid, etc.), the span, or the noise adjustment calculation described later is stored.

Further, the output signal V ₆ of the adder 22 is output to a band stop filter (notch filter) 48, and the band stop filter 48 has a band stop range set by a control signal CS2 in association with the band pass filter 44. Then, the output signal V ₆ in the measurement range is removed and the noise outside the band stop range is output as the noise signal V _N1 . The band stop filter 48 is composed of, for example, a switched capacitor.

FIG. 2 is a characteristic diagram showing the characteristics of the band stop filter 48. The horizontal axis is frequency and the vertical axis is filter gain. It has a characteristic that the gain in the band rejection range sandwiched by the corner frequencies f _L and f _H is significantly reduced.

The noise that has passed through this band stop filter 48
Signal V_N1Is rectified by the diode D1 and smoothed by the smoothing circuit 49.
Is output to. This smoothing circuit 49 includes an operational amplifier OA and a resistor.
Anti-R ₇, R₈, Capacitor C₁It is composed of.

The non-inverting input terminal (+) is connected to the common potential point COM, and the inverting input terminal (-) of the operational amplifier OA is connected.
Is connected to the cathode of the diode D1 via the resistor R ₇ and is also connected to the output terminal of the operational amplifier OA via the parallel circuit of the resistor R ₈ and the capacitor C ₁ .

The DC noise signal V _N2 generated at the output terminal of the operational amplifier OA is converted into an analog / digital converter (A / D).
It is output to the converter 50, converted into a digital signal here, and output to the microprocessor (CPU) 47.

On the other hand, a microprocessor (CPU) 47
From a control signal CS3 that controls the opening and closing of the switches SW ₁ to SW ₄ for switching the resistance value of the variable resistor element 43,
A control signal CS2 that changes the corner frequencies f _L and f _H of the band stop filter 48 and a control signal CS1 that changes the center frequency f ₀ of the band pass filter 44 are output.

Further, the RAM of the microprocessor 47
Is the diameter of the detector, the type of fluid (gas, liquid, etc.),
Setting data is input from the setter 51 for setting specifications such as span as required. The setting device 51 is also provided with a calculation start key for starting a calculation for determining an optimum resistance value of the variable resistance element 43, which will be described later.

The microprocessor 47 uses the data output from the detector to execute the flow rate calculation by the calculation program stored in the ROM and outputs it as a pulse signal to the insulating circuit 52.

The insulating circuit 52 converts this pulse signal into a voltage signal in a DC manner and outputs it to the voltage / current conversion circuit 53 at the final stage. The voltage / current conversion circuit 53 converts this voltage signal into a current signal, for example, 4 to 20 mA, and transmits the load via the output terminal 54.

Next, the operation of the vortex flowmeter constructed as described above will be described with reference to FIGS. FIG. 3 is a flow showing a calculation procedure for automatically setting the minimum noise balance point, and FIG. 4 is a timing chart showing calculation timing.

In the state where the minimum noise balance point described later is automatically set, the vortex signal detected by the piezoelectric elements 16 and 17 is based on the vortex generated in the piezoelectric elements 16 and 17 fixed in the vortex generator. Charges Q _v1 and Q _v2 are charge converters
It is converted into AC voltage signals V ₁ ′ and V ₂ ′ by the switches 19 and 20.

Output signal V₁'Is resistance R₁Output signal through
V₁As the output signal V₂'Is resistance R ₂And variable resistance element 4
Output signal V via 3₂Each taken out as
These output signals V₁And V₂Is added by the adder 22
Output signal V at the output end₆Is output as.

This output signal V ₆ is applied to the bandpass filter 4
4, via the Schmitt trigger circuit 45 and the counter 46, it is read as digital data into the RAM of the microprocessor 47.

The microprocessor 47 is, for example, a ROM
RA from the flow rate calculation program and setter 51 stored in
A flow rate calculation is executed using the specification data set in a predetermined area of M, and the calculation result is output to the insulating circuit 52,
After that, it is transmitted as a current signal to a load (not shown) via the voltage / current conversion circuit 53.

Next, the procedure for calculating the automatic noise balance setting will be described. First, the setting device 51 is keyed in to start the automatic setting calculation for minimizing the noise balance point (FIG. 3, step 1).

By this key-in, the microprocessor 4
7 is data such as specifications stored in the internal RAM
Read out (step 2 in FIG. 3). And the control signal CS
The center frequency f of the bandpass filter 44 set by 1
₀In connection with, the corner frequency f of the band stop filter 48_L
And f_HAccording to the calculation program stored in ROM
Is calculated (step 3 in FIG. 3).

After that, the control signal CS2 is output to the band stop filter 48 to set the corner frequencies f _L and f _H (step 4 in FIG. 3). Next, the process proceeds to step 5 in FIG. 3 and the switching signals S _{1 to} S constituting the control signal CS 3 are made.
₄ (FIGS. 4B to 4E), the switches SW _{1 to} SW ₄ are opened and closed in a fixed sequence to change the combined resistance of the resistors R _{3 to} R ₆ of the variable resistance element 43.

In step 6, the combined resistance is changed and generated.
Output signal V₆A band stop filter 48, diode
D1, smoothing circuit 49, analog / digital converter 50
To the RAM of the microprocessor 47 via the
Calculation cycle T shown in_cCorresponding to each cycle T₀, T₁, ~ T₁₅
The timing signal output from the microprocessor 47 by
Issue T_iA / D at each time point in synchronization with (Fig. 4 (f))₀,, A /
D_1,With switch SW ₁~ SW_FourData for opening and closing
Is read.

The microprocessor 47 calculates the combination of the switches SW _{1 to} SW ₄ that minimizes noise by the selection program stored in the ROM and selects the resistance value (FIG. 3, step 7).

Based on this selection result, the minimum noise combination of the switches SW ₁ to SW ₄ is set to this via the control signal CS3 (FIG. 3, step 8), and the process is ended (FIG. 3, FIG. 3).
Step 9).

[0049]

As described above in detail with reference to the embodiments, according to the present invention, the value used for the determination of the noise balance adjustment can be adjusted through only the noise component by removing the vortex signal through the notch filter. ， Automatic balance adjustment is possible even when fluid is flowing.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing characteristics of the notch filter shown in FIG.

FIG. 3 is a flowchart showing a noise balance calculation procedure of the embodiment in FIG.

FIG. 4 is a timing chart showing the timing of the calculation shown in FIG.

FIG. 5 is a vertical cross-sectional view showing a cross section of a conventional vortex sensor.

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

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

FIG. 8 is an explanatory diagram for explaining a noise removing operation by the vortex sensor shown in FIG.

FIG. 9 is a block diagram showing a configuration of a conventional vortex flowmeter.

[Explanation of symbols]

 10 Pipe Line 12 Vortex Generator 16, 17 Piezoelectric Element 19, 20 Charge Converter 22 Adder 23 Low Pass Filter 25, 45 Schmidt Trigger 44 Band Pass Filter 46 Counter 47 Microcomputer 48 Notch Filter 49 Smoothing Circuit 50 Analog / Digital converter 51 Setting device

Claims (1)

[Claims] 1. A third signal obtained by adding a first signal converted by a first charge amplifier and containing a vortex signal and a second signal converted by a second charge amplifier and containing a vortex signal by an adder via a variable resistance element. In a vortex flowmeter for outputting as a signal, band stop filter means for applying the third signal to block the vortex signal and outputting a noise signal, and a resistance value of the variable resistance element for minimizing the noise signal. And a control means for calculating and controlling the vortex flowmeter.