JPS5855816A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To remove the influence of disturbing vibration effectively and to improve an S/N ratio, by arranging two sensors at two points where the ratio of the noise components due to the vibration of the vortex yielding body and the ratio of the noise component due to the strain of a pipe are substantially equal. CONSTITUTION:The vortex yielding body 13 yields K arm an vortex and receives buoyancy when fluid to be measured flows in the pipe which is not shown in the Figure. The piezoelectric sensors 14a and 14b are arranged on the two point M and N, where the ratio of the amplitudes of noise charges due to the vibration of the vortex yielding body 13 and the ratio of the amplitudes of the noise charges due to the strain of the pipe are substantially equal; i.e. a distribution curve (a) of the noise charges due to the vibration of the vortex yielding bldy 13 intersects a distribution curve (b) of the noise charges due to the strain of the pipe. The output charges q1 and q2 from the sensors 14a and 14b are applied to conversion amplifiers 21 and 22, converted into AC voltages e1 and e2, respectively, and added in an operator 23. Then a voltage e3, wherein influence of the noises due to the vibration of the vortex yielding body 13 is removed, is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex flow meter that uses Karman vortices to measure the flow velocity or flow rate of a fluid.

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 as a vortex train. This vortex street 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, sensors such as piezoelectric elements, strain gauges, capacitances, and inductances are installed in the vortex generator (t or force receiving body) by placing a vortex generator in the pipe that guides the fluid to be measured, and changes in lift due to the generation of the vortex. Vortex flowmeters have been put into practical use that measure the flow velocity and flow rate of fluid by detecting the flow rate and converting the signal. However, this type of vortex flow needle has six disadvantages: it is affected by external vibrations such as pipe vibrations excited by pumps, etc., and the 8/N ratio deteriorates especially at low flow speeds. When the force is applied, the vortex generating body (t or force receiving body) vibrates, and the equipment attached to the pipe, such as a transducer, also vibrates. When the vortex generating body (or 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, and this distortion As a result, a moment acts on the 4bill1 generating body (the receiving force body). As a result, Senna has
The signal component due to the bending moment based on the lift of the vortex is superimposed with the noise component due to the bending moment based on the vibration of the vortex generating body (t or force receiving body) and the noise component due to the bending moment due to pipe distortion. Detected. For this reason, conventional measures have been taken, such as experimentally finding a point where the sum of the noise component due to vibration of the vortex generator (or force receiving body) and the noise component due to pipe strain is small, and installing a sensor at that point. However, the magnitude and phase difference of both noise components 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 changes depending on the magnitude of the acceleration and frequency of the disturbance vibration, so it is sufficient No surface effect has been achieved.0 The present invention is capable of determining the ratio of noise components due to the vibration of the vortex generating body (or force receiving body) at any two points of the sensor section provided on the vortex generating body (or force receiving body); Focusing on the fact that the ratio of noise components due to pipe distortion is constant regardless of the acceleration and frequency of disturbance vibration, two cells are placed at two points where the ratio of both noise components is substantially close. By converting each signal and performing calculations, the influence of disturbance vibration is effectively removed, and a vortex flow rate needle with a good 8/N ratio OJL is realized.

Fig. 1 is an external view of one embodiment of the vortex flowmeter of the present invention, 0) is a front view, ←) is a side view, Fig. 2 is a configuration explanatory diagram showing the detection section in section, and Fig. 3 The figure is an electrical connection diagram showing an embodiment of the vortex flowmeter of the present invention. 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 generator is made of stainless steel or the like, and its upper end 13a 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 vortex generator in contact with the measurement fluid has a cross-sectional shape such as a trapezoid, for example, so as to generate a Karman vortex street in the measurement fluid and stabilize and strengthen lift changes, and a recess 1 is provided on the upper end 13a side.
The stone has 3D.

14 is a senna part, and a first
The piezoelectric sensor 14a and the second piezoelectric center t14b are suppressed and fixed at a constant interval. In the sensor section 14, the underlay 14c made of stainless steel or the like is connected to the second piezoelectric sensor 14b.
serves as a buffer between the bottom surface of the recess 13d and the recess 13d.
This is to compensate for the difficulty in controlling the roughness during machining of the bottom surface of d. The first (D spacer 14d made of stainless steel, etc.), the insulating plate 14e (made of ceramic etc.), and the second spacer 14f (made of stainless steel, etc.) determine the distance between the first piezoelectric sensor 14a and the second piezoelectric sensor 14b, and also maintain the insulation between them. It is meant to be done.

Push rods 14g made of stainless steel etc. are Senna 14a and 14b.
While pressed, the upper end 13a of the vortex generator 13 is welded to press and fix 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 14a and 14b are disk-shaped piezoelectric elements pz, and are arranged so that their centers coincide with the neutral axis of the vortex generator 13. Furthermore, as shown in the perspective view of FIG. 4(A), the piezoelectric element pz has electrodes d1. d2. d3. d4 is provided,
As shown in Fig. 4←), the stress (compressive stress and tensile stress) generated in opposite directions across the neutral axis due to the bending moment due to the force in the direction of the arrow (in the lifting force direction of the vortex) K corresponds to the electrode d□, The charge generated between electrodes d2 and electrodes 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(c)K, charges of opposite polarity are generated between the two electrodes in response to stresses occurring in the same direction. Further, the amount of electric charge generated due to 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 due to pipe vibration in the flow direction is also canceled out between the electrodes and does not come out. The first piezoelectric sensor 14a has electrodes d1. d2 question and electrode d3. In order to use the sum of the charges of the same polarity generated between the electrodes d4 as the output charge q1 and cancel the charges of opposite polarity, the electrodes d1 and d3 are commonly connected to the vortex generator 13 via the push rod 14g, that is, the reference point. The electrodes d2 and d4 are commonly connected to the lead wire 61 via a spacer 14f. The second piezoelectric sensor 14b is connected between electrodes d and d2 and between electrodes d3 and d3. d2
Electrodes d1 and d3 are connected to a common lead wire through a spacer 14d in order to use the sum of charges of the same polarity generated between them as an output charge q2, cancel charges of opposite polarity, and invert the polarity of q. connected to e2, electrodes d2 and d4
and are commonly connected to the vortex generator 13, that is, the reference point Km via the underlay 14c. The leads IIe□, -2 are connected to the through holes and holes provided in each part of the sensor section 14,
It is taken out to the outside via the seal 14h and connected to the vortex flow meter converter 20.

Note that a gas with a low dew point is filled in the area surrounded by the concave portion 13d of the vortex generator 13 and the sensor portion 14 for dew condensation cutting, and the push rod 14gK is the communication hole 14 for the filled gas.
1 is provided. Further, the thickness of each component of the sensor section 14 and the material L1 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 and subtracts the outputs of these converter amplifiers 21 and 22, and a converter 20 for fixing the converter 20 to the pipe line 11. It has a bracket 24 of. Conversion amplifier 21
(22) is an operational amplifier op□ (OP2) and O
A capacitor connected to the feedback circuit of P (OP)
2 A charge amplifier consisting of a parallel circuit of C1 (C2) and a resistor R (R2) is shown, and the lead 11 is connected to the inverting input terminal (→) of the operational amplifier Op1.
A lead wire e2 is connected to the inverting input terminal (-) of No.2. The arithmetic unit 23 is fed back by a resistor R3 and consists of nine operational amplifiers OP, and the output voltage e1 of the converter 21 is applied to the inverting input terminal ← of OP3 via the operational resistor R4.
, and the output @2 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 vortex flow needle of the present invention constructed as described above will be explained below with reference to FIG. When the measuring fluid flows into the pipe 11, the vortex generator 13 generates a Karman member and receives a lift change based on the generation of the vortex. When the vortex generating body 13 receives a lift force, a bending moment MY due to the lift force acts on the senna portion 14, and a substantially linear stress distribution as shown by S in FIG. 5 is generated inside the senna portion 14. Note that the stress values in FIG. 5 are shown as the amount of charge when detected by a piezoelectric sensor.

The six-member 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 this disturbance vibration has a mode due to the vibration of the vortex generator 13,
There are modes due to pipe distortion caused by vibrations of the loaded object, and bending moments Mα1t Mα2 act on the sensor section 14 depending on the respective modes. Inside the sensor part 14, a stress distribution of a curve as shown in FIG. A nearly linear stress distribution as shown by b in FIG. 5 occurs. As a result, a charge q is detected by the piezoelectric sensors 14a and 14b of the sensor section 14.

In q2, a noise charge due to the vibration of the vortex generating body and a noise charge due to pipe distortion are superimposed on the signal charge due to the lift of the vortex9, and the amplitude of the signal charge due to the lift of the vortex is expressed as S□(', I), 52(-j+), the amplitude of the noise charge due to the vibration of the vortex generator 13 is expressed as A□(ω'), A2(・
)I'), the amplitude of the noise charge due to pipe distortion is B1(o
+), B2('・1), then 0 q1-i91(ω)sin'++t+A1(ω+)6 given by the following equations, respectively.
1nω't+B1(ωsu8in(b+ 't+i(ω
) (1) q2IIIS2(lsin ・
, t+A2(14+')81fb++kan t+B2(,
,1')Sin(r,+'t+d(ta'))
(2) However, ω: Angular frequency of signal charge ω1: Angular frequency of noise charge d(61'): Phase difference between noise charges In equations (1) and (2), amplitude of signal charge 8x
G) J) tS2(ω) varies depending on the lift force of the vortex, that is, the vortex frequency. Also, the amplitude A of the noise charge
□ (0 houses).

A2 Co door), B1(ω')p B2(z+')
The phase difference t<ω'> 4 varies depending on the acceleration and frequency of the disturbance vibration, but the amplitude ratio A2 (W
')/A□(rs') and B2Coz")/B
y(rr) is constant without being affected by the acceleration and frequency of the disturbance vibration, and as shown in FIG. There are two points where the charge distribution lines intersect,
The piezoelectric sensor 14a, 14b O mounting satisfies the following relationship at the positions y point and N point.

There are various combinations of two points that satisfy equation (3). For example, as shown in Figure 6, the noise charge distribution line due to pipe distortion has a distribution with a different slope @b+,b" and a vortex generator. The point M' where the distribution curve a due to vibration of No. 13 intersects with N1
The stress distribution curve due to the vibration of the vortex generator 13 and the sensor section 14 may be the alt point in FIG.
IL2. Although it changes as shown in B3, there are always two points that satisfy the relationship in equation (5). In FIG. 7, the stress distribution curve a1. a2. The dimensions of the sensor section 14 that produce a3 are Ll, B2. Different from B3 (L□<
B2 and B3 are standard dimensions for ease of explanation. The figure is converted to . In addition, the stress distribution lines due to pipe distortion may vary depending on the weight of the loaded object, etc. in Fig. 8, b□, B2. The amplitude ratio at point M and point N varies as shown in B3.
□('d')lB□□(ωI), B22(011)lB
12(ω'), n23(r,,+')lB13(a+
') are the same, so even if the weight of the loaded object changes, (5
) formula holds true.

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□t is respectively
After being converted into B2, it is added to the arithmetic unit 23. Arithmetic unit 2
3 adds e-tB2, and its output e3 is given by the following equation.

If the gain of the conversion amplifier 21 and 22 is set to 2, then
From equations (1) and (2), 03 becomes as shown in the following equation.

In equation (5), A2(・!l1)lA1(c・door)
and B2 (0 weight) lB□ (er door) are selected to satisfy the relationship of equation (3), so adjust the variable resistor R6 and set 1 to R4N2 1-□・λ--〇R5+R6 If (6) is satisfied, the output e3 of the arithmetic unit 23 is as follows, and the influence of noise due to disturbance vibration can be effectively removed. As a result, according to the present invention, the S/N ratio could be improved by more than 10 times compared to a conventional vortex flowmeter using one piezoelectric sensor.

In the above description, the case where the output e1 of the conversion amplifier 21 and the output e2 of the conversion amplifier 22 are added by the arithmetic unit 23 has been illustrated, but the output charges q1y q of the piezoelectric sensors 14a and 14b
If the two noise components are in phase, the arithmetic unit 23 can subtract them. Although the above example uses the output charges of the piezoelectric sensors 14a and 14b, the output voltage may also be used. In this case, a voltage amplifier is used as the conversion amplifier 21, 22 instead of a charge amplifier. Moreover, although the case where piezoelectric elements with reverse polarization are used as the piezoelectric sensors 14a and 14b is illustrated above, piezoelectric elements without reverse polarization may be used. 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 piezoelectric sensor 14a of the building 1 and the push rod 1
4g and between the second piezoelectric sensor 14c, electrodes d1 and d3 and electrodes d2 and d4 of the piezoelectric element pz are connected, and lead wires are connected to the electrodes d□ and d3, respectively. All you have to do is connect. Also number 1. Second
In this example, the piezoelectric sensor is pressed and fixed in the recess of the vortex generator by a push rod, but it may also be sealed and fixed with glass or the like. In the above, the case where the recess of the vortex generator is provided on the upper end side is illustrated, but it is also provided on the lower end side, and the first recess is provided on the upper end side.
A second piezoelectric sensor may be disposed in a recess on the lower end side of the piezoelectric sensor.

Further, in this embodiment, the sensor section 14 is provided in the recess 13d of the vortex generator 13 as the vortex flowmeter detector 10, but the receiving force on the downstream side of the vortex generator 13 receives the lift force due to the generation of the vortex. A body may be provided, and the sensor portion may be provided within the recess of the force receiving body. Furthermore, the sensor of 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. When using an elongated piezoelectric sensor, there is an advantage that stress changes caused by bending moment (K) can be directly detected in the sensor section.

As explained above, in the present invention, 2Il sensors are arranged at two points where the ratio of noise due to vibration of the vortex generator (or force receiving body) and noise due to pipe distortion are substantially equal. If the outputs are converted into signals and then calculated, the influence of disturbance vibrations is effectively removed, so a vortex flowmeter with a good Six ratio can be obtained.

[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;
3 is an electrical connection diagram showing one embodiment of the eddy flow needle of the present invention, FIG. 4 is a configuration explanatory diagram showing an example of the piezoelectric sensor used in the present invention, and FIG. 8 are characteristic curves for explaining the operation of the vortex flowmeter of the present invention. 10...Vortex flow meter detector, 11...Pipeline, 13...
- Vortex generator, 13d... Concavity of vortex generator, 14...
Sensor section, 14a...first piezoelectric sensor, 14b...
- Second piezoelectric sensor, 20... Vortex flow meter converter, 21
．． 22... Conversion amplifier, 23... Arithmetic unit. Figure 731 (a) 5m2 diagram 3 (b) Stress 3 6th factor

Claims (2)

[Claims] (1) A conduit through which the fluid to be measured flows, a vortex generator attached to the conduit to generate a vortex in the measured fluid according to the flow velocity, and a vortex generator fixed in a recess provided in the vortex generator. 1st. a second sensor, a first conversion amplifier to which a signal from the first sensor is added, a second conversion amplifier to which a signal from the second sensor is added, and an output of the first conversion amplifier and a second conversion amplifier; and an arithmetic unit that adds or subtracts the output of the conversion amplifier, and the first sensor and the second sensor are configured based on the disturbance vibration. A vortex flowmeter characterized in that the vortex flowmeter is arranged at two points where the ratio of noise due to distortion is substantially equal. (2) A conduit through which the measurement fluid flows, a vortex generator installed in this conduit that generates a Karman vortex in the measurement fluid according to its flow velocity, and a Karman vortex generated by this vortex generation decoy. a first force-receiving member fixed in a recess provided in the force-receiving member; a second sensor, a first conversion amplifier to which a signal from the first sensor is added, a second conversion amplifier to which a signal from the second sensor is added, an output of the first conversion amplifier and a second conversion amplifier; and an arithmetic unit that adds or subtracts the output of the conversion amplifier of A vortex flowmeter characterized in that the vortex flowmeter is arranged at two points where the ratio of noise to noise is substantially sharply expressed.