JP3381766B2 - 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 calculating and outputting a measured flow rate by detecting the number of Karman vortices that change corresponding to the measured flow rate flowing in a pipe through a pair of sensors. In particular, the present invention relates to an improved vortex flowmeter capable of detecting in advance that foreign matter has adhered to the inside of piping to cause malfunction.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the overall structure of a conventional vortex flowmeter. Reference numerals 1 and 2 denote sensors composed of piezoelectric elements for detecting the Karman vortices generated by the vortex generator when the measurement fluid flows, and detect the strain generated by the Karman vortices as a change in charge.

3 and 4 are charge-voltage conversion circuits for converting the weak AC charge signals output from the sensors 1 and 2 into voltage signals, 5 is a noise balance circuit, and 6 is charges obtained through the noise balance circuit 5. It is an adding circuit that adds and amplifies the output of the voltage converting circuit 3 and the output of the charge-voltage converting circuit 4.

Reference numeral 7 is an active filter for removing noise contained in the output of the adder circuit 6, and 8 is a Schmitt trigger circuit for converting the output of the active filter 7 into a pulse signal corresponding to the vortex frequency.

The microprocessor 9 has a built-in frequency / digital converter, memory, etc., converts the pulse output of the Schmitt trigger circuit 8 into a digital signal by the frequency / digital converter, and stores this digital signal in the memory. The flow rate is calculated using the constants necessary for the flow rate calculation and the calculation program, and the calculated result is output as a pulse signal.

Reference numeral 10 is a transformer for insulating and transmitting the pulse signal output from the microprocessor 9, 11 is a frequency / voltage converter for converting the insulated and transmitted pulse signal into a voltage signal, and 12 is a converted voltage signal, for example. 4 to 20 mA
Is a voltage / current converter that converts the current signal of
The current converter 12 transmits this current signal to the load via the two transmission lines.

Reference numeral 13 is a high frequency attenuator circuit for changing the corner frequency of the active filter 7 based on the control signal of the microprocessor 9, 14 is a noise judgment circuit for judging the noise component contained in the output of the adder circuit 6, and 15 is noise judgment. The voltage / frequency conversion circuit converts the voltage signal, which is the determination result of the circuit 14, into a frequency signal and outputs the frequency signal to the microprocessor 9.

FIG. 4 is a vertical cross-sectional view showing a specific structure of the detecting section composed of the sensors 1 and 2 shown in FIG. Reference numeral 16 is a pipeline through which the fluid flows, and 17 is a cylindrical nozzle provided at a right angle to the pipeline 16.

Reference numeral 18 is a nozzle 17 and its periphery is spaced by a distance ΔL.
Is a columnar vortex generator having a trapezoidal cross section inserted at a right angle into the pipe line 16 and holding one end to the pipe line 16 by a screw 19 and the other end to the nozzle 17 with a flange 20. It is fixed by welding.

Reference numeral 21 denotes a concave portion provided on the side of the flange portion 20 of the vortex generator 18, and in this concave portion 21, sensors 1 and 2 composed of a pair of piezoelectric elements are arranged vertically with a predetermined interval. The sensors 1 and 2 are insulated and sealed by a sealing body 22 such as glass.

The piezoelectric elements of the sensors 1 and 2 have semicircular electrodes divided in two, which are arranged one above the other. In each piezoelectric element, 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. To generate an electric charge of opposite polarity.

Sensors 1 and 2 composed of the above piezoelectric elements
The charges Q _v1 and Q _v2 having the same frequency as the vortex frequency of the vortex signal from are input to the charge-voltage conversion circuits 3 and 4 shown in FIG. 3 and converted into an alternating voltage signal.

Next, the operation of the vortex flowmeter constructed as above will be described with reference to FIGS. 5 and 6. When the measurement fluid flows, vibrations due to Karman vortices occur in the vortex generator 18 shown in FIG. 4 in the direction indicated by arrow F.

As a result of this vibration, the vortex generator 18 will be shown in FIG.
The stress distribution as shown in (a) and the reverse stress distribution are repeated, and charges + Q and -Q corresponding to signal stress having the same frequency as the vortex frequency are repeated in each sensor 1 and 2.

On the other hand, in the pipeline 16, pipeline vibration that causes noise is also generated. This pipeline vibration is divided into three directions: (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 the vibration in the drag direction is as shown in FIG. 5 (b), and the positive and negative charges are canceled out within one electrode, and noise charges are not generated. Further, as to the vibration in the longitudinal direction, as shown in FIG. 5C, it is canceled in the electrode, and noise charge is not 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. The electric charges of the sensors 1 and 2 are Q _v1 and Q _v2 , and the signal components are S ₁ and S
₂ , assuming that the noise components in the lift direction are N ₁ and N ₂ , and the polarizations of the sensors 1 and 2 are reversed, Q _v1 and Q _v2 are represented 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 sensors 1 and 2 is as shown in FIG. 6, and the relationship between the noise in the lift direction and the bending moment of the vortex generator with respect to the signal is as shown in FIG.

Therefore, when the output of the charge-voltage conversion circuit 3 on the sensor 1 side shown in FIG. 5 is added by the addition circuit 6, the noise balance circuit 5 multiplies by N ₂ / N ₁ and the charge-voltage conversion circuit on the sensor 2 side. 4 and output the _{adding, Q v2 -Q v1 (N 2} / N 1) = S 2 -S 1 (N 2 / N 1) becomes line noise is removed.

Of the noises superposed on the vortex generator as described above, the noises in the drag force direction and the longitudinal direction of the vortex generator take into consideration the polarities of the sensors 1 and 2, and the noises in the lift force direction are measured in the sensors 1 and 2. It is removed as a two-element method in consideration of the balance.

[0021]

However, even in the vortex flowmeter as described above, the vortex generator 18 is inserted with a distance ΔL between the vortex generator 18 and the nozzle 17, so that foreign matter may enter the pipe 16. When rust is generated, solid substances due to these are also formed in the interval ΔL, and as a result, these act as a fulcrum of vibration of the vortex generator 18 or an elastic body.

The above points will be further described with reference to the bending moment diagram shown in FIG. FIG. 7A shows a state of bending moment when the vortex generator is formed as a cantilever beam in a normal state, and FIG. 7B shows when the vortex generator is formed as a cantilever beam in an abnormal state. Shows the state of the bending moment of.

In a normal state, the difference between the moment M ₁ generated by the force f of the Karman vortex in the sensor and the moment M ₂ generated in the sensor 2 is ΔM (= M ₁ −M) as shown in FIG. 7A. ₂ ) is large and good S / N is obtained.

However, rust or the like is generated and the solid matter is separated by an interval Δ.
When it is formed in L, the fulcrum is displaced as shown in FIG. 7B, and the difference ΔM ′ (= M ₁ ′ −M ₂ ′) becomes small, and the S / N decreases. As a result, there arises a problem that the flow rate signal becomes unstable and the output goes down.

[0025]

According to the present invention, as a main configuration for predicting the occurrence of such a problem before the above-mentioned problems occur, it is possible to correspond to a measured flow rate flowing through a pipe. In a vortex flowmeter that calculates and outputs the preceding measured flow rate by detecting the number of changing Karman vortices via a pair of sensors, the vortex flow rate signal output from each of the preceding sensors is converted into a pair of analog / digital signals. Analog / digital converting means for converting into a pair of digital signals, a ratio calculating means for calculating a ratio of the pair of preceding digital signals, and the inside of the preceding pipe being normal when the ratio is not within a predetermined range. And an abnormality detecting means for detecting that it is not in a state.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The parts having the same functions as those of the conventional vortex flowmeter shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

[0027] A Karman vortex-based piezoelectric element
AC charge Q generated in sensors 1 and 2 _V1, Q_V2Is that
Are converted into voltage signals by the charge-voltage conversion circuits 23 and 24,
Anti-aliasing function as a low-pass filter
Filters 25 and 26 and analog / digital converters 27 and 2
Digital signals X which are respectively discretized via 8₁(k
T), X₂converted to (kT).

Discretized digital signals X ₁ (kT), X ₂ (k
T) is taken into an arithmetic block 29 formed by hardware, and the arithmetic block 29 receives these digital signals X.
Calculate the ratio of ₁ (kT) and X ₂ (kT), then add,
It outputs to the band pass filter 30 composed of a digital low pass filter and a high pass filter.

The output of the bandpass filter 30 is fetched by the microprocessor 31, the flow rate is calculated by the same calculation as in the prior art, the calculated flow rate signal is converted into an analog signal by the digital / analog converter 32, and further the output circuit. It is converted into a current signal of 4 to 20 mA at 33 and transmitted to the receiving instrument 37 via the transmission line 36.

The microprocessor 31 controls the operation timing of the anti-aliasing filters 25 and 26, the analog / digital converters 27 and 28, the operation block 29, and the like.

A random access memory (RAM)
The vortex flow rate signal data and the flow rate calculation result data that have been taken in are stored in a read-only memory (R 34).
The OM) 35 stores, for example, a program required for the flow rate calculation, parameters required for the calculation, etc., and their operations are controlled by the microprocessor 31 via the bus 36.

Further, a handheld terminal 38 is connected to the transmission line 36 as required, and 4 to 20 m from the handheld terminal 38.
The digital communication signal is superimposed on the current signal of A, and the communication signal is exchanged with the microprocessor 31 via the output circuit 33. This communication signal transmits / receives various information such as span setting, failure diagnosis command transmission / reception, alarm transmission, and various parameter setting.

Next, the operation of the embodiment shown in FIG. 1 configured as described above will be described with reference to the flow chart shown in FIG. Starting from the start, in step 1, digital signals X ₁ (kT) and X ₂ (kT) which are discretized vortex signals under the control of the microprocessor 31 are read into the arithmetic block 29.

Next, in step 2, the calculation block 29 calculates the ratio λ between these digital signals X ₁ (kT) and X ₂ (kT) in the following form. λ = [ _{k = 0} Σ ^N-1 ｜ X ₁ (kT) ｜ ² / N] / [ _{k = 0} Σ ^N-1 ｜ X ₂ (kT) ｜ ² / N] = _{k = 0} Σ ^N-1 ｜ X ₁ (kT) | ² / _{k = 0} Σ ^N-1 | X ₂ (kT) | ² The ratio λ that is the result of this calculation is the microprocessor 31
It is stored in a predetermined area of the random access memory 34 under the control of.

Go to step 3. The value of the ratio λ varies depending on the diameter of the vortex flowmeter in a state where there is no clogging due to rust or the like, but normally 5 or more is secured, and the data for each diameter is stored in the read-only memory 35. .

Therefore, the microprocessor 31 causes the ratio λ obtained in step 2 to fall within a predetermined range, for example, 1 <λ <.
5 is compared with the reference data for each aperture transferred from the read-only memory 35 to the random access memory 34 by the arithmetic program stored in the read-only memory 35 to determine whether or not it is present.

As a result, when the value of the ratio λ is not within the range of 1 <λ <5, it is determined that the pipe is in the normal state, the process proceeds to step 4, and the digital signal X ₁ ( kT) and X ₂ (kT) are added and calculated to calculate the flow rate, and digital /
Receiving instrument 3 via analog converter 32 and output circuit 33
The flow rate signal is transmitted to 7.

However, when it is determined in step 3 that the value of the ratio λ is within 1 <λ <5, there is clogging due to rust or the like, and the state of FIG. 7B, that is, X ₁ (kT ) And X ₂ (kT) are close to each other, the microprocessor 31
Is determined and the process proceeds to step 5.

In step 5, an alarm is transmitted to the outside, for example, the handheld terminal 38, or the receiving instrument 37 if the receiving instrument 37 has a function of receiving a communication signal.

Then, the process proceeds to step 6. Even if the value of the ratio λ is in the range of 1 <λ <5, the vortex signal itself does not become small. Therefore, even in this case, the microprocessor 31 calculates the flow rate by using the digital signal X ₁ (kT). It executes and outputs a flow rate signal to the receiving instrument 37.

After the above steps 4 and 6 are executed, the process returns to step 1 and is repeated again. Although 1 <λ <5 is used as the criterion in step 3 here, a predetermined threshold value within this range is usually provided and used as the criterion.

Further, although the transmission line 36 shown in FIG. 1 has been described as a type in which a digital communication signal is superimposed on a two-wire type current transmission line, the present invention is not limited to this, and for example, transmission corresponding to a field bus. The alarm can be sent to the outside with a line.

In particular, in the field bus, since it is possible to attach alarm information as data reliability information to data such as PV value, it is possible to have a self-diagnosis function of the equipment.
This alarm function is important.

[0044]

As described above in detail with the embodiments of the invention, the present invention converts the vortex signal into a digital signal, calculates the ratio of the vortex signal, and predicts the state of the pipe from the ratio. Therefore, it is possible to prevent instability factors of the flow rate signal or output reduction. In addition, since action can be taken based on the prediction, maintainability is improved.

[Brief description of drawings]

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

FIG. 2 is a flow chart for explaining the operation of the embodiment shown in FIG.

FIG. 3 is an overall block diagram showing a configuration of a conventional vortex flowmeter.

FIG. 4 is a vertical cross-sectional view showing a specific configuration of the sensor shown in FIG.

FIG. 5 is a first explanatory diagram explaining the operation of the vortex flowmeter shown in FIG.

FIG. 6 is a second explanatory diagram illustrating the operation of the vortex flowmeter shown in FIG.

FIG. 7 is a moment diagram illustrating a problem of the vortex flowmeter shown in FIG.

[Explanation of symbols]

1, 2 sensor 3, 4 charge-voltage conversion circuit 5 noise balance circuit 6 adder circuit 7 Active filter 8 Schmitt trigger circuit 9 microprocessors 16 pipelines 18 Vortex generator 25,26 Anti-aliasing filter 27, 28 Analog / digital converter 29 operation blocks 30 Band Pass Filter 31 microprocessors 34 Random access memory 35 read-only memory 36 transmission lines 37 Receiving instrument 38 Handheld Terminal

Claims (4)

(57) [Claims] 1. A vortex flowmeter which calculates and outputs the measured flow rate by detecting the number of Karman vortices that change corresponding to the measured flow rate flowing in a pipe through a pair of sensors, and outputs from each sensor. A pair of analog / digital conversion of the vortex flow rate signal to be converted into a pair of digital signals; a ratio calculation means for calculating a ratio of the pair of digital signals; and a ratio within a predetermined range. A vortex flowmeter, comprising: an abnormality detecting unit that detects that the inside of the pipe is not in a normal state when there is no abnormality. 2. The vortex flowmeter according to claim 1, wherein the analog / digital conversion means is composed of a digital filter. 3. A vortex flowmeter according to claim 1, wherein a digital bandpass filter is arranged between the ratio calculation means and the abnormality detection means. 4. The vortex flowmeter according to claim 3, wherein the digital bandpass filter comprises a digital lowpass filter and a digital highpass filter.