JPS5862516A - Vortex flow meter - Google Patents

Abstract

PURPOSE:To improve an S/N ratio of a vortex flow meter, by a method wherein two inverted polarization type piezo-electric sensors are located at a given distance in a sensor part, and the influence of a noise due to a disturbance vibration is eliminated through computation of a sensor output. CONSTITUTION:A cylindrical nozzle 12 is positioned at a right angle to a line 11 through which measuring fluid in a vortex discharge detector 10 flows, and a vortex generating body 13 is inserted through a nozzle 12 at a right angle to the line 11. Two inverted polarization type piezo-electric sensors 14a and 14b are fastened by press at a given distance in a concavity 13d in the vortex generating body 13. The sensors 14a and 14b are formed such that electrodes, separated to the right and left facing a flow direction of measuring fluid, are symmetrically mounted to the surface and the back of a piezo-electric element on a disc positioned so that its center coincides with the neutral axis of the vortex generating body 13, a charge in a reverse direction is generated between the two electrodes against a stress in a bending direction, and a charge due to a stress in a flow direction of fluid is cancelled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex flow needle that utilizes Karman vortices to measure fluid velocity or flow rate.

It has been known for a long time that when an object is placed in a fluid, vortices are generated alternately and regularly from the side of the object and flow downstream in a straight line. This true train is called a Karman vortex street, and the number of vortices generated per unit time (vortex frequency) is proportional to the flow velocity of the fluid.

Therefore, a vortex generator is placed in the pipe that guides the measurement fluid, and a piezoelectric sensor installed in the G recess of the vortex generator (also a social square) detects stress changes based on changes in lift caused by the vortex generation. A vortex flow needle that converts signals to measure fluid flow velocity and flow rate has been put into practical use. However, this type of vortex flow meter is affected by noise caused by external vibrations such as piping vibrations excited by a pump or the like. That is, when a disturbance vibration is applied, the vortex generator (t or force receiving body) vibrates, and the mounted object such as a transducer attached to the conduit also vibrates.

When the vortex generating body (9 is the force receiving body) vibrates, a bending moment based on its mass distribution etc. acts on the vortex generating body (t or force receiving body), and when the loaded object vibrates, pipe distortion occurs. This distortion also causes a bending moment to act on the vortex generating body (or force receiving body). As a result, the piezoelectric sensor has a signal component due to the bending moment F based on the lift of the vortex, a noise component due to the bending moment based on the vibration of the vortex generator (or force receiving body), and a noise component due to the bending moment due to pipe distortion. are detected in a superimposed manner. As described above, the conventional vortex flowmeter has a problem in that it is affected by noise caused by disturbance vibration, and the 8/N ratio deteriorates particularly at low flow speeds.

The present invention provides a stress distribution of a signal component due to the lift of a vortex generated in a sensor section provided in a recess of a vortex generating body (t or force receiving body);
Focusing on the fact that the stress distribution of noise components due to disturbance vibrations is different, a first inverted polarization type piezoelectric sensor and a second inverted polarization type piezoelectric sensor are arranged at a predetermined interval in the sensor part. By converting the output of each piezoelectric sensor into a signal and then calculating it, the effects of noise caused by disturbance vibration can be effectively removed, and a good 8/'N ratio has been achieved with a simple configuration of the vortex flow needle. be.

FIG. 1 is an explanatory diagram of the t-turn configuration showing one embodiment of the present invention, FIG. 2 is a configuration explanatory diagram showing the detector section in section and plane, and FIG. FIG. 3 is an electrical connection diagram showing an example. In the figure, 10 is a vortex flowmeter detector, and 20 is a vortex flowmeter converter.

In the vortex flow meter detector 10, 11 is a pipe through which the fluid to be measured flows, 12 is a cylindrical nozzle provided perpendicularly to the pipe 11, and 13 is a columnar vortex inserted perpendicularly into the pipe 11 through the nozzle 12. The generating body is made of stainless steel, etc., and its upper end 13 m is fixed to the nozzle 12 by screws or welding.
The lower end 13b is supported by the paper conduit 11 with a screw. The portion 13c ij of the vortex generator 13 in contact with the fluid to be measured has a cross-sectional shape, such as a trapezoid, so as to generate a Karman vortex street in the fluid to be measured and to stabilize and strengthen changes in lift, and the upper end 1
It has a recess 13d on the side 3a. 14 is a sensor section, and a piezoelectric sensor 14 is installed in the recess 13d of the vortex generator 13.
m and the second piezoelectric sensor 14b are fixed and suppressed at a constant interval.

Senna IM! 14, underlay 14c of stainless steel etc.
serves as a buffer between the second piezoelectric sensor 14b and the bottom surface of the recess 13d, and compensates for the difficulty in controlling roughness during processing of the bottom surface of the recess 13d.The first spacer is made of stainless steel or the like. 14d table Ceramic insulation board 1
4e and a second spacer 14f made of stainless steel etc.
This is to determine the distance between the second piezoelectric sensor 14a and the second piezoelectric sensor 14b, and to insulate them. The push rod 14g made of stainless steel etc. is the sensor 14a, 14
It is welded to the upper end 13a of the vortex generator 13 in a pressed state, and presses and fixes the sensors 14a and 14b. The senna portion 14 is configured to come into contact with the vortex generator 13 only through the underlay 14c and the upper part of the push rod 14g. The piezoelectric sensors 14 a and 14 b are disk-shaped piezoelectric elements PZT 9 and are arranged so that their centers coincide with the neutral axis of the vortex generator 13 . Furthermore, the piezoelectric element PZT is
As shown in the perspective view, electrodes d1. d2. d3°d4 are provided, and the fourth
As shown in Fig.
1142 and the electric charge generated between electrodes d3. The polarization is reversed so that the electric shoulder generated between d4 has the same polarity. Therefore, as shown in Figure 4e, charges of opposite polarity are generated between the two electrodes in response to stress occurring in the same direction.The amount of charge generated by stress in the flow direction of the fluid is the same. The amount of charge that is canceled between the electrodes and generated due to pipe vibration in the flow direction is also canceled between the electrodes and does not come out. The sum of charges of the same polarity generated between d2 and electrodes d4 is set as the output charge q□, and charges of opposite polarity are canceled.Ninthly, electrodes d1 and d3 are connected to a vortex generator in common via a push rod 14g. 13, that is, a reference point, and electrodes d2 and d4 are commonly connected to lead wire e1 via a spacer 14f. The second piezoelectric sensor 14b includes electrodes 61,162 and electrodes d3. The sum of the charges of the same polarity generated between the electrodes d4 is the output charge q2, and the charges of the opposite polarity are cancelled. In order to reverse the polarity of the electrodes d1 and d3, the electrodes d1 and d3 are connected to a common lead wire through the spacer 14d. e2, and the electrodes d2 and d4 are commonly connected to the vortex generator 13, that is, the reference point, via the underlay 14c. Lead wire e1. e2 is the sensor section 14
The vortex flow meter converter 20
connected to. In order to prevent condensation, a gas with a low dew point is filled in a portion of the vortex generator 13 surrounded by the recess 13d and the sensor portion 14, and the push rod 14g is provided with a communication hole 141 for the filled gas. ing. Further, the thickness and material of each component of the sensor section 14 are determined so that the initial pressing stress does not change due to temperature changes.

The eddy flowmeter converter 20 includes two converter amplifiers 21 and 22, an arithmetic unit 23 that adds or subtracts the outputs of these converter amplifiers 21 and 22, and a fixed pump connected to the converter 20 in the conduit 11. Then, the inverting input terminal of the operational amplifier op□ (→
A lead wire r is connected to the inverting input terminal (→) of the operational amplifier OP2, and a lead wire e2 is connected to the inverting input terminal (→) of the operational amplifier OP2.

The arithmetic unit 23 consists of an operational amplifier OP to which feedback is provided by a resistor R3. What is shown is to add the output e2 of the conversion amplifier 22, which is added via a series circuit of R5 and variable resistor R6.

The operation of the vortex flowmeter of the present invention constructed as shown in FIG. 1 will be explained below with reference to FIG. The measurement fluid flows through the vortex generator 13 in the pipe line 11 . , and when a Karman vortex is generated, and %
It undergoes a lift change based on the generation of a single vortex. Vortex generator 13
When the sensor part 14 receives a lift force, a bending moment MY acts on the sensor part 14 due to the lift force, and a substantially linear stress distribution as shown by 5th ICE- is generated inside the sensor part 14. Note that the stress values in FIG. 5 are shown in terms of the amount of charge when detected by a piezoelectric sensor.

The vortex generator 13 also receives a force in the same direction as the lift of the vortex due to disturbance vibrations excited by a pump or the like.

The force due to the disturbance vibration has two modes: a mode due to the vibration of the vortex generator 13 and a mode due to pipe distortion due to the vibration of the loaded object, and a bending moment (Mα12Mα2) acts on the sensor unit 14 depending on each mode.・Se・Su part 1
In 4, there is a mori, a vortex generator, and a moment M due to vibration in 3.
The action of α1 produces a curved stress distribution as shown by a in FIG. 5, and the action of the moment path 20 due to conduit distortion produces a nearly linear stress distribution as shown by b in FIG. As a result, the piezoelectric sensor 14m of the sensor section 14,
In the charges q1sq2 detected at 14b, noise charges due to the vibration of the vortex generator and noise charges due to pipe distortion are superimposed on the signal charge due to the lift of the vortex, respectively, and the amplitude of the signal charge due to the lift of the vortex is 81(・II), 82
(/=su), the amplitude of the noise charge due to the vibration of the vortex generator 13 is A1 (''), A2C (ba), the amplitude of the noise charge due to pipe distortion is B□(ω') * B2 (f,・
1), then 0 q1-81(ω) sin ωt+A1((t)')8in given by the following equations, respectively.
(4t+B1(rt+')81n(&J't+d(ω)(1)q2g+82((c')sin"t+A2(,
co') sin++'t+B2(m') sin(u+'
t+4(u')) (2) However, ω: Angular frequency of signal charge cva: Angular frequency of noise charge 6(・-l): Phase difference between noise charges In equations (1) and (2), the signal Charge amplitude S1
(ω).

B2(ω) varies depending on the lift force of the vortex, that is, the vortex frequency. In addition, the amplitude of the noise charge A1 (ωs* A2
(0・′).

B, (IJ-'), B2 (6') and phase difference 167
') also change depending on the acceleration and frequency of the disturbance brush stroke, but the amplitude ratios A2(,')/A1(ω・) and B2(g')/B1(az') vary depending on the acceleration and frequency of the disturbance vibration. As shown in the S diagram, there are two points where the noise charge distribution curve a due to the vibration of the vortex generator 13 and the noise charge distribution line 1 due to pipe strain intersect. exists, and the mounting of the piezoelectric sensor 14a, 1x, satisfies the relationship of the following equation between the positions M and NJ.

There are various combinations of two points that satisfy equation (S), for example, as shown in Figure 6, the noise charge distribution line due to pipe distortion, the distribution line bI, bI' with different slopes, and the vortex generator. The MI point where the distribution curve a due to vibration of No. 13 intersects with 1
1 point, MII point and 1lII point.

The stress distribution curve due to the vibration of the vortex generator shown in the table shows the stress distribution curve of the vortex generator 1.
3 and the material and shape 1 dimensions of the sensor part 14.
It changes as shown in a□, a□t aS in the figure, but (3
) There are always two points that satisfy the relationship of the equation. In FIG. 7, the stress distribution curve fL1p &2p! The dimensions of the sensor section 14 that generate L3 are Lx # B2 e
Although it is different from B3 (L engineering<B2<B3), it is shown converted to the standard dimension LO for the sake of simplicity. Also, the stress distribution lines due to conduit distortion may vary depending on the weight of the loaded object, etc. in bl, b2, etc. It changes as shown in b3, but the ratio of amplitudes at point M and point N is B21('')/B11((force,
B22GIJ')/B engineering 2(ω') l B23(
t knee) / B13 (ω1) are equal, so equation (5) holds true even if the weight of the loaded object changes.

The output charge q1 of the piezoelectric sensor 14a is applied to the conversion amplifier 21, and the output charge q2 of the piezoelectric sensor 14b is inverted and applied to the conversion amplifier 22, respectively, so that the AC voltage e□T
62 and then added to the arithmetic unit 23. Arithmetic unit 2
3 adds e□t e2, and its output e3 is given by the following equation.

If the gains of the conversion amplifiers 21 and 22 are Kxs K2, then from equations (1) and (2), it becomes e3B3 generation.

1 In equation (5), A2(ωl)/A1(/force and B
2(fII')/B1('...I) is selected to satisfy the relationship of equation (s), so if the variable resistor R6 is adjusted to satisfy the following, the output of the calculator 23 will be e3 becomes, and the influence of noise introduced into the disturbance vibration can be effectively removed. As a result, according to the present invention, the 197N ratio could be improved by more than 10 times compared to the conventional vortex flow rate needle using one piezoelectric cell.

Furthermore, the noise charge caused by the vibration of the vortex generator 13 becomes zero at two points (P) as shown in the distribution curve tL2 in FIG.
IQ) exists. Moreover, there are two points (P, Q) that are zero.
The position of does not change depending on the acceleration and frequency of the disturbance vibration. Hence the piezoelectric sensor 14a.

If 14b is placed in the sensor section 14 at two points (p, Q) where the noise charge due to the vibration of the vortex generator 13 is zero, only the noise charge due to the pipe distortion becomes the noise component, □, and the piezoelectric sensors 14m and 14b. Output charge q1 +
'Q2 F' are given by linear equations. - q 1 □81(ω) sinr++t+8l-(61'
) sin('6 't+6<')! >)
(a) q2xs2(r++)s
inrot+B2(r)sin(ω't+d(u>tsu)(9) Therefore, the output e3 of the arithmetic unit 23 is expressed as
') is constant (A1), so if the variable resistor R6 is adjusted to satisfy the expression e3, the output e3 of the arithmetic unit 23 becomes, which effectively eliminates the influence of noise caused by external vibration.

In addition, in the above description, the case where the output e of the conversion amplifier 21 and the output e2 of the conversion amplifier 22 are added by the arithmetic unit 23 was exemplified, but the output charges q□, q2 of the piezoelectric sensors 14a and 14b
If the noise components are in phase, the arithmetic unit 23 may perform subtraction. Moreover, although the above-mentioned example f uses the output charges of the piezoelectric sensors 14a and 14b, it is also possible to use the output voltage. □In this case, a voltage amplifier is used as the conversion amplifier 21, 22 instead of the charge amplifier 6. In the above, the case where a piezoelectric element with reverse polarization is used as a pressure wax cell 14m and 14b is illustrated, but when using a piezoelectric element that cannot be reversely polarized, such as linium niobate, piezoelectric The element may be divided into left and right parts, and one side may be mounted upside down to form a substantially reverse polarization type.

Furthermore, in this embodiment, the sensor section 14 is provided in the recess 13d of the vortex generator 13 as the vortex positioning needle detector 10. A body may be provided, and a senna portion may be provided within the recessed portion of the force receiving body.

As explained above, in the vortex flowmeter of the present invention, the stress distribution of the signal component due to the lift of the vortex generated in the sensor section provided in the recess of the vortex generating body (or force receiving body), and the stress distribution of the noise component due to disturbance vibration. Based on the difference in distribution, the first. Since the second inverted polarization type piezoelectric sensor is used and its output is converted into signals and then calculated, the influence of noise caused by disturbance vibration is effectively removed, so a good 87N ratio can be achieved.
In addition, the structure of the sensor section can be simplified since only two lead wires are needed from the sensor section.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the configuration of one embodiment of the vortex flowmeter of the present invention;
The figure is a cross-section diagram of the detector part, FIG. 5 is an electrical connection diagram showing one embodiment of the vortex flowmeter of the present invention, 111481 is a configuration explanatory diagram showing an example of the piezoelectric sensor used in the present invention, FIG. ~
FIG. 6 is a characteristic curve for explaining the operation of the vortex flow needle of the present invention. 10...Eddy current positioning needle detector, 11...Pipe line, 13...
...Vortex generator, 13d...Concavity of vortex generator, 14...
-Sensor part, 14a...first piezoelectric kyt, 14b
... second piezoelectric sensor, 2o... eddy current positioning needle transducer,
21.22... Conversion amplifier, 23... Arithmetic unit. Figure 1 (a) Invitation 3 (b) 3 Atsushi 6 illustration 7 times

Claims (1)

[Claims] In a vortex flow rate needle, a sensor section is provided in a recess of a vortex generator that generates a Karman vortex according to the flow velocity of the fluid to be measured, or in a recess of a force receiving body disposed downstream of the vortex generator. is a metal underlay, a second inverted polarization type piezoelectric sensor, a second metal spacer, an insulating plate, a first metal spacer, and a first inverted polarization type piezoelectric sensor, which are stacked in order in the recess. A vortex flowmeter characterized by having a polarized piezoelectric sensor and a metal push rod for suppressing and fixing these stacked parts.