JPH1194609A - Vortex flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent main causes of unstableness of a flow-rate signal or lowering of output, by converting a vortex signal into digital signals, then computing the ratio of the vortex signals, and forecasting the status within a piping from the ratio. SOLUTION: Alternating current electric charges QV1 , QV2 generated by Karman vortex in sensors 1, 2 constituted of piezoelectric elements are converted into voltage signals by charge-voltage converting circuits 23, 24, respectively, and put to conversion by anti-aliasing filters 25, 26 and analog-digital converters 27, 28, respectively. Digitized digital signals X1 (KT), X2 (KT) are taken into a computing block 29, a ratio of the digital signal X1 (KT) to X2 (KT) is computed, and then they are added together and outputted to a band-pass filter 30. An output of the band-pass filter 30 is taken into a microprocessor 31, a flow- rate signal computed therein is converted into an analog signal by a digital- analog converter 32, then converted into a current signal of 4 to 20 mA and the like by an output circuit 33, and transmitted to a receiving instrument 37 via a transmission wire 36.

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, via a pair of sensors, the number of Karman vortices that change in accordance with the measured flow rate flowing through a pipe. In particular, the present invention relates to an improved vortex flowmeter which can detect in advance that a foreign substance adheres to the inside of a pipe to cause a malfunction.

[0002]

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

[0003] Reference numerals 3 and 4 denote a charge-voltage conversion circuit for converting a weak AC charge signal output from the sensors 1 and 2 into a voltage signal, 5 a noise balance circuit, and 6 a charge obtained through the noise balance circuit 5. This is an addition circuit that adds and amplifies the output of the voltage conversion circuit 3 and the output of the charge-voltage conversion circuit 4.

[0004] Reference numeral 7 denotes an active filter for removing noise contained in the output of the adder circuit 6, and reference numeral 8 denotes 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, a memory, etc., converts the pulse output of the Schmitt trigger circuit 8 into a digital signal by the frequency / digital converter, and stores the digital signal in the memory. The flow rate is calculated using constants and a calculation program necessary for the flow rate calculation, and the calculated result is output as a pulse signal.

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

Reference numeral 13 denotes a high-frequency attenuation circuit for changing a corner frequency of the active filter 7 based on a control signal of the microprocessor 9, reference numeral 14 denotes a noise determination circuit for determining a noise component included in the output of the addition circuit 6, and reference numeral 15 denotes a noise determination. This is a voltage / frequency conversion circuit that converts a voltage signal, which is a result of determination by the circuit 14, into a frequency signal and outputs the frequency signal to the microprocessor 9.

FIG. 4 is a longitudinal sectional view showing a specific configuration of the detecting section composed of the sensors 1 and 2 shown in FIG. Reference numeral 16 denotes a pipe through which a fluid flows, and reference numeral 17 denotes a cylindrical nozzle provided at right angles to the pipe 16.

Reference numeral 18 denotes the nozzle 17 and the periphery thereof is an interval ΔL.
Is a column-shaped vortex generator having a trapezoidal cross-section inserted at right angles to the conduit 16 while holding one end thereof, one end of which is fixed to the conduit 16 by a screw 19, and the other end of which is screwed to the nozzle 17 by a flange 20. It is fixed by welding.

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

Each of the piezoelectric elements of the sensors 1 and 2 has two divided semi-annular electrodes arranged vertically. In each piezoelectric element, 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. To generate charges of opposite polarity.

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

Next, the operation of the vortex flowmeter configured as described above will be described with reference to FIGS. When the measurement fluid flows, vibrations due to Karman vortices are generated in the vortex generator 18 shown in FIG.

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

On the other hand, the pipe line 16 also generates a pipe line vibration which causes 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. 5B, and the positive and negative charges are canceled in one electrode and no noise charge is generated. Further, as shown in FIG. 5C, the vibration in the longitudinal direction 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 generates noise charges. Therefore, the following calculation is performed to eliminate this noise charge. The 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 polarization in the sensors 1 and 2 is reversed, 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. FIG. 6 shows the relationship between the signal components and the noise components of the sensors 1 and 2 and the relationship between the noise and the signal in the lift direction and the bending moment of the vortex generator.

Therefore, when the output of the charge-to-voltage conversion circuit 3 on the sensor 1 side shown in FIG. 5 is added by the addition circuit 6, it is multiplied by N ₂ / N ₁ by the noise balance circuit 5 and the charge-to-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.

Among the noises superimposed on the vortex generator as described above, noise in the drag direction and longitudinal direction of the vortex generator consider the polarity of the sensors 1 and 2, and noise in the lift direction is sensors 1 and 2. Is removed as a two-element system considering the balance of

[0021]

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

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

[0023] In the normal state, and the moment M ₂ generated at the moment M ₁ and sensor 2 generated by the force f by Karman vortex sensor, the difference as shown in FIG. 7 (a) ΔM (= M 1 -M ₂ ) is large and a good S / N is obtained.

However, rust or the like is generated, and
When it is formed in L, the difference ΔM ′ (= M ₁ ′ −M ₂ ′) is reduced due to the shift of the fulcrum as shown in FIG. 7B, and the S / N is reduced. As a result, there arises a problem that the flow signal becomes unstable or the output drops.

[0025]

SUMMARY OF THE INVENTION The present invention has a main structure for predicting in advance that such a problem will occur before the above-mentioned problems occur, and is adapted to respond to a measured flow rate flowing through a pipe. In a vortex flowmeter that calculates and outputs the previously measured flow rate by detecting the number of changing Karman vortices through a pair of sensors, a vortex flow rate signal output from each of the above sensors is converted to a pair of analog / digital conversions. Analog / digital conversion means for converting the signals into a pair of digital signals, ratio calculating means for calculating the ratio of the pair of digital signals, and normal operation of the inside of the pipe when the ratio is not within a predetermined range. Abnormality detecting means for detecting that it is not in a state.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. The portions having the same functions as those of the conventional vortex flowmeter shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

A cell composed of piezoelectric elements by Karman vortex
Charge Q generated in sensors 1 and 2 _V1, Q_V2Each
Are converted into voltage signals by the charge-voltage conversion circuits 23 and 24,
Anti-aliasing filter that functions as a low-pass filter
Filters 25 and 26 and analog / digital converters 27 and 2
8 via the digital signal X₁(k
T), X_Two(kT).

The digital signals X ₁ (kT) and X ₂ (k
T) is taken into an operation block 29 formed by hardware, and the operation block 29
Calculate the ratio between ₁ (kT) and X ₂ (kT), then add,
The signal is output to a band-pass filter 30 composed of a digital low-pass filter and a high-pass filter.

The output of the band-pass filter 30 is taken into a microprocessor 31 and the flow rate is calculated by the same operation as in the prior art. The calculated flow signal is converted into an analog signal by a digital / analog converter 32, and furthermore, an output circuit. The signal 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 are stored in the read-only memory (R) 34.
The OM) 35 stores, for example, a program necessary for the flow rate calculation, parameters necessary for the calculation, and the like, and the operation thereof is controlled by the microprocessor 31 via the bus 36.

Further, a hand-held terminal 38 is connected to the transmission line 36 as required, and a distance of 4 to 20 m from the hand-held terminal 38.
A digital communication signal is superimposed on the current signal of A, and the communication signal is transmitted to and received from the microprocessor 31 via the output circuit 33. The communication signal transmits and receives various information such as, for example, setting of a span, transmission and reception of a failure diagnosis command, transmission of an alarm, and setting of various parameters.

Next, the operation of the embodiment shown in FIG. 1 configured as described above will be described with reference to the flowchart 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, proceeding to step 2, the arithmetic 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 =} 0ΣN ^-1 | X ₂ (kT) | ² The ratio λ, which is the result of this operation, is
Is stored in a predetermined area of the random access memory 34 under the control of.

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

Then, the microprocessor 31 sets the ratio λ obtained in step 2 to a predetermined range, for example, 1 <λ <
5 is compared with reference data for each aperture transferred from the read-only memory 35 to the random access memory 34 by an arithmetic program stored in the read-only memory 35 to determine.

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

However, if it is determined in step 3 that the value of the ratio λ is within the range of 1 <λ <5, there is clogging due to rust or the like, and the state shown in FIG. 7B, that is, X ₁ (kT ) And X ₂ (kT) are close to each other.
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 to the receiving instrument 37 if the receiving instrument 37 has a function of receiving a communication signal.

Next, the routine 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 smaller. Therefore, even in this case, the microprocessor 31 performs the flow rate calculation using the digital signal X ₁ (kT). Then, the flow rate signal is output to the receiving instrument 37.

After executing the above steps 4 and 6, the process returns to step 1 and repeats the above steps. 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 a criterion for the determination.

Further, 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, but the present invention is not limited to this. Alarms can also be issued externally via wires.

In particular, in the field bus, the self-diagnosis function of the device can be provided by attaching alarm information as data reliability information to data such as the PV value.
This alarm function is important.

[0044]

As described above in detail with the embodiments of the present invention, according to the present invention, after converting a vortex signal into a digital signal, the ratio of the vortex signal is calculated, and the state of the pipe is predicted from the ratio. Therefore, it is possible to prevent an unstable factor of the flow signal or a decrease in output beforehand. In addition, since the action can be taken based on the prediction, the maintainability is improved.

[Brief description of the drawings]

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

FIG. 2 is a flowchart for explaining the operation of the embodiment shown in FIG. 1;

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

FIG. 4 is a longitudinal sectional view showing a specific configuration of the sensor shown in FIG.

FIG. 5 is a first explanatory diagram illustrating an operation of the vortex flowmeter shown in FIG. 3;

FIG. 6 is a second explanatory view for explaining the operation of the vortex flowmeter shown in FIG. 3;

FIG. 7 is a moment diagram for explaining a problem of the vortex flow meter shown in FIG. 3;

[Description of Signs] 1, 2 sensor 3, 4 charge-voltage conversion circuit 5 noise balance circuit 6 addition circuit 7 active filter 8 Schmitt trigger circuit 9 microprocessor 16 pipeline 18 vortex generator 25, 26 anti-aliasing filter 27, 28 Analog / Digital Converter 29 Arithmetic Block 30 Bandpass Filter 31 Microprocessor 34 Random Access Memory 35 Read Only Memory 36 Transmission Line 37 Receiving Instrument 38 Handheld Terminal

Claims (4)

[Claims] 1. A vortex flowmeter for calculating and outputting the measured flow rate by detecting, via a pair of sensors, the number of Karman vortices that change in accordance with the measured flow rate flowing through a pipe, Analog / digital conversion means for converting the vortex flow signal to be converted into a pair of digital signals by analog / digital conversion, ratio calculating means for calculating the ratio of the pair of digital signals, and the ratio being within a predetermined range. A vortex flowmeter, comprising: abnormality detection means for detecting that the inside of the pipe is not in a normal state when the pipe is not present. 2. The vortex flowmeter according to claim 1, wherein said analog / digital conversion means comprises a digital filter. 3. The vortex flowmeter according to claim 1, wherein a digital bandpass filter is arranged between said ratio calculating means and said abnormality detecting means. 4. The vortex flowmeter according to claim 3, wherein said digital bandpass filter comprises a digital lowpass filter and a digital highpass filter.