JPS58169029A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To obtain the flowmeter having an excellent S/N ratio, by arranging two sensors at two points, where the ratio of the noise component due to the vibration of a force receiving body is substantially equal to the noise component due to the strain of a pipe, performing signal conversion, and thereafter performing computation. CONSTITUTION:In a detector 10 of the vortex flowmeter, a tubular nozzle 12 is provided at a right angle with the pipe 11 wherein fluid to be measured flows. The pillar shaped force receiving body 13 is inserted at a right angle with the pipe passage 11 through the nozzle 12. The first piezoelectric sensor 14a and the second piezoelectric sensor 14b are compressed and fixed to the inside of a concave part 13 of the force receiving body 13 with a specified interval being provided. Electric charges q1 and q2 are detected by the piezoelectric sensors 14a and 14b. The noise electric charge due to the vibration of the force receiving body 13 and the noise electric charge due to the strain of the pipe are superimposed on the signal electric charges obtained from the lift of the vortex in the q1 and q2, respectively. They are computed in an operator through an operation amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex flowmeter that measures the flow velocity or flow rate of a fluid using Karman vortices.◎When an object is placed in a fluid,
It has been known for a long time that vortices are generated alternately and regularly from the sides of objects after rain, and flow downstream in the form of a full moon.

This full moon is called a Karman vortex street, and the number of vortices generated per unit time ah (vortex frequency) is proportional to the flow velocity of the fluid. Therefore, a K1 generator is placed in the pipe that guides the measured fluid to generate vortices. A vortex flow meter has been put into practical use that detects the change in lift caused by a piezoelectric element, strain gauge, capacitance, or inductance sensor installed in the receiving body, and then converts the signal after the round to measure the flow velocity and flow rate of the fluid.

However, this type of vortex flowmeter is affected by external vibrations such as piping vibrations excited by pumps, etc.
In particular, there was a drawback that the 87N ratio at low flow speeds deteriorated.

That is, when external vibration is applied, the force receiving body vibrates, and the mounted objects such as the converter 6 attached to the conduit also vibrate. When the force-receiving body vibrates, a bending moment based on its mass distribution etc. acts on the force-receiving body, and when the loaded object vibrates, pipe distortion occurs, and this distortion also causes a bending moment to act on the force-receiving body. . As a result, the sensor detects bending based on the vibration of the force receiving body in the signal component due to the bending moment based on the lift of the vortex. For this reason, countermeasures have been taken in the past, such as experimentally finding a point where the sum of the noise component due to the vibration of the force receiving body and the noise component due to pipe distortion is small, and installing a sensor at that point. The magnitude and phase difference change independently depending on the acceleration and frequency of the disturbance vibration, and the point where the sum of both noise components is small also corresponds to the magnitude of the acceleration of the disturbance vibration and MILtiIL#! Since it changes depending on the value of i, it is not sufficiently effective.

Furthermore, in order to increase the sensitivity of the device, it is effective to reduce the rigidity of the force receiving body, but this has the disadvantage of lowering the natural frequency of the force receiving body. Furthermore, when the functions of the device are improved and the measurable range is expanded, the upper limit of the measurable range approaches the natural frequency of the force receiving body.

The present invention solves these problems.The present invention solves these problems by determining the ratio of the noise component due to the vibration of the force receiving body and the pipe distortion K at any two points of the sensor section provided on the force receiving body.
Focusing on the fact that the ratio of the noise components is constant regardless of the acceleration and frequency of the disturbance vibration, two sensors are placed at two points where the ratio of both noise components is substantially equal, and the signals are converted. By calculating K, the influence of disturbance vibration is effectively removed, and the force receiving body is configured so that the ratio of resonance noise when the force receiving body resonates due to the vortices is almost equal to the noise ratio due to vibration, This realizes a vortex flowmeter with a good 8/N ratio.

Figure 1 is an external view of one embodiment of the vortex flowmeter of the present invention, (a)
2 is a front view, ←) is a side view, FIG. 2 is a configuration explanatory diagram showing the detection section in cross section, and FIG. 5 is an electrical connection diagram showing one embodiment of the vortex flowmeter of the present invention. In the figure, 10 vortex flowmeter detectors and 20 are vortex flowmeter converters.

In the vortex flowmeter 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 nozzle inserted perpendicularly into the pipe 11 through the nozzle 12. It is a force receiving body, and its upper end 1 is from the stainless steel town.
3iL is fixed to the nozzle 12 (by screws or welding),
The lower end 13b is supported by the conduit 11.

The portion 13c of the force-receiving body 13 that is in contact with the constant fluid has a cross-sectional shape such as a trapezoid, for example, to produce a carmine column in the measured fluid and to stabilize and strengthen changes in lift, and the upper end 13
a Ill #IC has a recess 13d l-. So, when the force receiving body 13 resonates due to the vortex, is it a resonant electric sensor of KF51r? 14m and the 1st! The piezoelectric sensors 14b are suppressed and fixed at regular intervals. In the sensor part 14, the underlay 14c made of stainless steel or the like is connected to the second piezoelectric sensor 14.
b and the bottom of the recess 13d.
This is to compensate for the difficulty in controlling the roughness of the bottom surface of 3D. A first spacer 14d made of stainless steel, an insulating plate 14e made of ceramic or the like, and a first spacer made of stainless steel or the like! The spacer 14f is used to determine the distance between the first piezoelectric sensor 14m and the second piezoelectric sensor 14b, and to insulate them. A push rod 14g made of stainless steel or the like presses the senna 14m and 14b, and in good condition presses the upper end 1 of the force receiving body 13.
3a K @ is in contact 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 sensor is worn out. Furthermore, piezoelectric element pz
As shown in the perspective view of Fig. 4 (0), electrodes d are arranged symmetrically on the front and back sides of the electrodes divided into right and left sides with respect to the flow direction of the fluid to be measured (direction of the arrow in the figure), d2. d3. d
4 is provided, and the arrow direction (
Stress (compressive stress and tensile stress) generated in mutually opposite directions across the neutral axis due to the bending moment caused by the force (in the direction of the lifting force of the vortex)
Electrode d3. The polarization is reversed so that the electric charges generated between the terminals d4 and d4 have the same polarity. Therefore, as shown in FIG. 4, charges of opposite polarity are generated between the two electrodes in response to stresses occurring in the same direction. The amount of electric charge generated by the stress in the flow direction of the measured fluid is canceled between the electrodes and does not come out, and the amount of electric charge generated by pipe vibration in the flow direction is also canceled out between the electrodes and does not come out. The first piezoelectric sensor 14a includes electrodes d, d2 and electrodes d.
3. In order to make the sum of charges of the same polarity generated between the electrodes d and 63 the output charge q1 and cancel the charges of opposite polarity, the electrodes d□ and 63 are connected to the force receiving body 1 in common via the push rod 14g.
3, that is, the reference point, and the electrodes d2 and d are commonly connected to the lead 1IIe1 via the spacer 14f.

The second piezoelectric sensor 14b has electrodes d1. Let Wakura output charge q2 be the charge of the same polarity generated at d2 and electrode ds+%, cancel the charge of opposite polarity, and ql
In the ninth step of reversing the polarity, electrodes d and d3 are commonly connected to the lead wire e2 through the spacer 14d, and electrodes d2 and d4 are commonly connected to the force receiving body 1 through the underlay 140.
3, that is, connected to the reference point. Lead wire e, 1
2 is taken out to the outside through a through hole provided in each part of the sensor section 14 and a hermetic seal 14h, and connected to a vortex flowmeter converter 20. Note that a gas with a low dew point is filled in the area surrounded by the recess 13d of the force receiving body 13 and the sensor part 14 to prevent condensation.
K is provided with a communication hole 141 for the sealed gas. In addition, the thickness and material of each part of the sensor section 14 are determined so that the initial pressing stress does not change due to temperature adjustment.
1.22, an arithmetic unit 23 that adds or subtracts the outputs of these conversion amplifiers 21.22, and a converter 2o are connected to the pipe 11.
It has a placket 24 for fixing to. The conversion amplifier 21 (22) is an operational amplifier 0p1 (O
20) and a charge amplifier consisting of a parallel circuit of a capacitor C (C2) and a resistor R (R2) connected to the feedback circuit of Op (0P2) are shown, and the inverting input terminal of operational amplifier Op is shown. ←) Lead wire l! 1 is connected, operational amplifier 1 □・
The inverting input terminal of Op2 is connected to the KIJ-do line e2.

The operation @23 consists of an operational amplifier op which is fed back by a resistor R3, and the output voltage of the converter 21 is applied to the inverting input terminal (-) of O20 via the operational resistor R4.
, and the output e2 of the conversion amplifier 22, which is added through a series circuit of a resistor R5 and a variable resistor R6.

The operation of the nine inventive vortex flow needles constructed in this manner will be described below with reference to FIG. When the measuring fluid flows into the pipe line 11, the force receiving body 13 generates a Curl vortex and K,
It undergoes lift changes based on the generation of vortices. When the force receiving body 13 receives a lift force, bending moment due to the lift force is applied to the senna section 14)
MV acts, and a nearly linear stress distribution as shown at 8 in FIG. S is generated inside the MV. Note that the stress values in FIG. 5 are shown in terms of the amount of charge when detected by a piezoelectric sensor.

Furthermore, the force receiving body 13 receives a force in the same direction as the lifting force of the vortex due to disturbance vibrations excited by a pump or the like. The force due to this disturbance vibration has a mode due to the vibration of the force receiving body 13 and a mode due to the pipe distortion K based on the vibration of the loaded object, and a bending moment yα19Mα2 acts on the sensor section 14 depending on each mode. Inside the sensor section 14,
The action of the moment Mα1 caused by the vibration of the force-receiving body 13 causes a curved stress distribution as shown in Figure Km, and the action of the moment Mα2 due to pipe distortion creates a nearly linear stress distribution as shown in Figure 5 Kb. . As a result, the charges qtt q2 K detected by the piezoelectric sensors 14a and 14b of the sensor unit 14 are composed of a signal charge due to the lift of the vortex, a noise charge due to the vibration of the force receiving body 13, and a noise charge due to pipe distortion. The amplitude of the signal charge due to the lift of the vortex is 81 (ω)! 32 (ω), the amplitude of the noise charge due to the vibration of the force receiving body 13 is A1 (ω), and Mu2 (ω).
, the amplitude of noise charge due to pipe distortion is B1 (ω), B2
(ω) are given by the following equations.

q1■81(ω)1i1nM+A 1(ω)sln4'
t+81(ω豐)sin(ω't+4(ω轡))
(1)q21j! 32 (”) sin61t+
A2 ((1))81nω't+82(u') sin(
ω't-1n(m')) (2) However, ω:
Angular frequency ωI of signal charge: Angular frequency 4 (ω1) of noise charge: Phase difference between noise charges In equations (1) and (2) 2, amplitude S1 of signal charge
(ω).

B2(ω) varies depending on the lift force of the vortex, that is, the vortex frequency. Also, the amplitude of the noise charge is □ (ω snow).

A2(ω1), B(6J), B2(ω) and phase difference φ(L,...) also change depending on the acceleration and frequency of the disturbance vibration, but the amplitude ratio 2(ω')/A Engineering (
H) and B2(ω')/B□(ωI) are constant without being affected by the acceleration and frequency of disturbance vibration, and as shown in FIG. There are two points where - and the noise charge distribution tab due to pipe distortion intersect, and piezoelectric sensors 14m and 14b intersect.
The following equation is satisfied at the position M and NA.

There are various combinations of two points that satisfy equation (3).

For example, as shown in FIG. 6, the soi N1 point, the MII point, and the N" electric point may be generated due to distortion of one pipe. Note that the stress distribution curve due to the vibration of the force receiving body is the same as that of the force receiving body 13 and the ax e in Figure 7 depending on the material and shape 1 dimension.
lL2 * aaK varies as shown, but there are always two points that satisfy the relationship in equation (3). In FIG. 7, the dimensions of the sensor section 14 that produce the stress distribution tB 111 a□H62g B3 are L□#L2#L, respectively.
3 (t, < L2 < L3) is shown in terms of the rounding standard dimension LoK to simplify the explanation. Also, the stress distribution line due to conduit distortion may vary depending on the weight of the loaded object, etc. as shown in Figure 8.

B2. The ratio of amplitudes at point M and point N varies as shown in B3.
j) lB12(ω1).

Since B23(ω')lB13(ω') is steep, equation (5) holds true even if the weight of the loaded object changes.

The output charge q□ 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, and the AC voltage e□+
After being converted into 82, it is added to the arithmetic unit 23.・Arithmetic unit 2
3 adds el, @2, and the output 3 is given by the following equation.

If the gains of the conversion amplifiers 21 and 22 are expressed as tB2, 63 becomes the following equation from equations (1) and (2).

(5) Formula 'f, A2('d)/A1(a+''
) k X and B2 (m')/Bl (U) is (
Since it is selected to satisfy the relationship of equation s), if the variable resistor R6 is adjusted to satisfy the following, the output of the arithmetic unit 23 becomes e3, which effectively eliminates the influence of noise caused by external vibration. So B1 stone.

Now, it has been explained that noise caused by one or more piping vibrations is removed by circuit processing using the difference between the signal ratio and noise ratio of two piezoelectric elements.

The influence of piping noise is felt when the vortex frequency is relatively low and the signal level is small. On the other hand, when the vortex frequency becomes high, it approaches the natural frequency of the force receiving body 13. For example, if the diameter of the conduit 11 is D-50 mm.

d/D-0,28 (d is the diameter of the force receiving body) Flow velocity 70 m/s
K varies, but it is about 2 to 3 kHz. When the vortex frequency approaches the natural frequency fn, the element becomes difficult to excite noise at the natural frequency fn, and the signal processing becomes difficult. , the upper limit of the measured flow velocity is effectively determined by the signal processing of the resonant noise of this vortex generator.

The noise at the time of resonance of the force receiving body 13 is K, as shown in the figure.
This results in noise in the form of a load acting on the center of gravity of the force receiving body 13.

Noise generated in the piezoelectric element placed at point M and N, aK (5)
If it is equal to λ in the formula, this resonance noise will not appear in the output 3 of the arithmetic unit.

Therefore, considering the position of the center of gravity and the position of the piezoelectric element, if λ in equation (5) is roughly equal to the ratio of the former two, the signal level is sufficiently large, so there is no problem in practice.

It should be noted that although the value of λ does not seem to match in Figure 9 #i, this is due to the convenience of explanation.Actually, the curve between points M and N is based on the base line 0- OK, if the lines are close to parallel, the values of 13 will be the same or approximately equal.

However, in curve C, the center of gravity of the force-receiving body is still too high and does not satisfy equation (8). For example, the center of gravity may be lowered like a 0 curve, and K may be set so as to satisfy equation (8).

As a result, according to the present invention, the 87N ratio could be improved by more than 10 times compared to the conventional vortex flowmeter using one piezoelectric sensor.

In addition, in the above description, the case where the output of the conversion amplifier 21 and the output e2 of the conversion amplifier 22 are added by the arithmetic unit 23 was illustrated, but the output charge q11 of the piezoelectric cells y t 14a, 14b
If the noise components of q2 are in phase, the arithmetic unit 23 may subtract them. Further, although the above example uses the output charges of the piezoelectric sensors 14m and 14b, it is also possible to use the output voltage. In this case, voltage amplifiers are used instead of charge amplifiers as the conversion amplifiers 21 and 22.In addition, in the above example, a piezoelectric element with inverted polarization is used as the piezoelectric sensor 14a, but it is also possible to use a piezoelectric element without inverted polarization. ◎In this case, the piezoelectric element may be divided into left and right parts, and one side may be mounted upside down to form a substantially inverted polarization type, or the first piezoelectric sensor 14a and pusher 1
An insulating plate is provided between 4g and the second piezoelectric sensor 14c, and the electrodes d and d3 and the electrodes d2 and d4 of the piezoelectric element pz are connected respectively, and the electrodes d□ and d3 are connected to each other.
Just connect the lead wires to each. Also number 1. Although the case where the second piezoelectric sensor is pressed and fixed in the recess of the force receiving body 13 with a push rod has been illustrated, it may be sealed and fixed with glass or the like. Furthermore, although the case where the recessed portion of the force receiving body 13 is provided with upper-side pressure is illustrated above, it is also provided at the lower end 11, and the first piezoelectric sensor is placed in the recessed portion on the upper end side, and the second piezoelectric sensor is placed in the recessed portion on the lower end side. In this embodiment, as the vortex ftt tt detector 10, the sensor part 14 is provided in the recess 13d of the force receiving body 13. A separate vortex generator may be provided. Note that the sensor in the sensor section is not limited to a piezoelectric sensor, and various sensors such as a strain gauge, capacitance, inductance, etc. can be used as required. However, when a piezoelectric sensor is used, there is an advantage that changes in stress caused by bending moments in the sensor can be directly detected.

As explained above, in the present invention, the ratio of noise due to vibration of the force receiving body and the ratio of noise due to pipe strain K are substantially equal to 2%! The shadow I# caused by external vibration can be effectively removed by arranging several sensors and converting their outputs into signals and then calculating them. In this way, it is possible to effectively eliminate the resonance of the force receiving body itself when the frequency of the hook signal is high.

As a result, according to the present invention, it is difficult to realize a vortex flow meter with a good S/N ratio.

[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 sectional view of the detection wheel portion, Figure S is an electrical connection diagram showing an embodiment of the vortex flow meter of the present invention, Figure 4 is a configuration explanatory diagram showing an example of a piezoelectric sensor used in the present invention, and Figure 5 9 to 9 are characteristic curves for explaining the operation of the vortex flowmeter of the present invention. 10...Vortex flowmeter converter, 11...Pipe line, 13...
・Force receiving body, 13d... Concavity of force receiving body, 14... Senna portion, 14 &... First piezoelectric sensor, 14b... Second piezoelectric sensor, 20... Eddy flowmeter conversion Vessel, 21.
22... Conversion amplifier, 23... Arithmetic unit 〇', Vire%/[! 1 (/l) Kaya zrB Yuu 31!1! J4 Figure (a) d. Stress No. fl! l lj 1g41!1 Bud 7 Figure Z Bud 3 m 99[! 1

Claims (1)

[Claims] A conduit through which a measurement fluid flows, a force receiving body inserted and fixed in the conduit, and a first force receiving body fixed in a recess provided in the force receiving body.
$2 sensor and a first sensor to which a signal of movement is applied.
0 conversion amplifier, a second conversion amplifier to which an O signal is added, and an arithmetic unit that adds or subtracts the output of the first conversion amplification SO output and the output of the second conversion amplifier, The senna and the second senna are placed at two points where the ratio of noise due to vibration of the force-receiving body based on external vibration is equal to the ratio of noise due to pipe distortion due to external vibration, and A vortex flowmeter comprising a force receiving body configured such that a ratio of resonance noise detected by the two sensors during resonance is approximately equal to a ratio of noise caused by the disturbance vibration.