JPH0569171B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mass flow meter that measures the mass flow rate of a measurement fluid using Karman vortices.

(Prior Art) It has been known for a long time that when an object is placed in a fluid, vortices are generated alternately and regularly from both rear sides 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 (generation frequency) is proportional to the flow rate of the fluid. Therefore, a vortex generator is placed in the pipe that guides the fluid to be measured, and the vortex generator generates a vortex proportional to the flow velocity. Vortex flowmeters have been put into practical use that measure the flow velocity and flow rate of fluid by detecting it with a sensor and extracting only the frequency of the detection signal. Incidentally, the flow rate that one generally wants to know is often the mass flow rate, not only in processes that involve chemical changes, but also in transactions. Furthermore, when the fluid to be measured is gas or steam, its density changes greatly depending on temperature and pressure, and even when it is a liquid, its density changes considerably depending on temperature. For this reason, the mass flow rate is measured either by installing it in parallel with a vortex flowmeter to measure temperature and pressure, or by measuring the density with a density meter.
However, using a density meter and a vortex flowmeter is complicated and expensive, and a combination of a temperature or pressure gauge and a vortex flowmeter is difficult.
Not only is it complicated and expensive, but it also has poor accuracy and responsiveness because it is difficult to measure the temperature of the fluid.

By the way, as shown in FIG. 5, when the vortex generator 2 is arranged in the pipe line 1 and the measurement fluid is flowed through the pipe line 1, the average drag force F, the fluctuating lift force F, and the pressure acting on the vortex generator 2 are The loss ΔP generally has a relationship expressed by the following equation.

F _D ∝C _D 1/2ρV ² …(1) F _L ∝±C _L 1/2ρV ² …(2) ΔP∝C _P 1/2ρV ² …(3) However, C _D ; Drag coefficient C _L ; Fluctuation lift coefficient C _P ; Pressure loss coefficient ρ ; Density V ; Flow velocity Average drag F _D , fluctuating lift F _L , and pressure loss ΔP are calculated as follows: drag coefficient C _D , fluctuating lift coefficient _CL , and pressure loss coefficient _CP are constants. If there is, it is proportional to ρV ² , so vortex frequency = StV/d = KV (where, St: Strouhal number, d: diameter of vortex generator 2, K = constant at St/d), (1), (2 ), ρV can be obtained by dividing equation (3).

As such, an example of detecting the fluctuating lift force and dividing it by the vortex frequency is shown in JP-A-57-61916 ``Measuring device using Karman vortex''.

JP-A No. 57-61916 will be explained below.

FIG. 6 is an explanatory diagram of the structure of this Japanese Patent Application Laid-Open No. 57-61916. In the figure, 1a is a pipe through which the measurement fluid flows, and 2a is a columnar vortex generator inserted perpendicularly into the pipe 1a, both ends of which are fixed to the pipe 1a. The main body 21a of the vortex generator 2a is made of stainless steel or the like, and has a cross-sectional shape, such as a trapezoid, which produces a Karman vortex street in the measured fluid and stably enhances lift changes. Top part 22a of vortex generator 2a
is made of stainless steel or the like, has a recess 23a, and is integrally formed with the main body 21a by welding or the like.
231a is an outer cylindrical portion formed in the vortex generator 2a by the recess 23a. Reference numeral 41a denotes an element body made of a piezoelectric element, which is sealed to the recess 23a of the vortex generator 2a with an insulating material 3a such as glass, and is formed integrally with the vortex generator. The element main body 41a has a disk shape and is arranged so that its center coincides with the neutral axis of the vortex generator 2a. Furthermore, as shown in FIG. 7, the element body 41a is divided into left and right electrodes 42a and 4 symmetrically on the front and back sides of the element body 41a, respectively.
3a, 44a, 45a are provided, and a first piezoelectric sensor 46a is provided at a portion sandwiched between electrodes 42a and 43a.
A second piezoelectric sensor 47a is formed at a portion sandwiched between electrodes 44a and 45a. Then, the electrodes 42a and 45a and the electrodes 43a and 44a are connected, respectively, so that the charges generated in the first and second piezoelectric sensors 46a and 47a are differential, and lead wires 48a and 48a are connected from the electrodes 42a and 44a, respectively.
49a penetrates the insulating material 3a and is taken out to the outside. 8a is a detection signal processing circuit that converts AC charge q detected by piezoelectric sensors 46a and 47a into AC voltage e. 9a is a comparator for converting the AC voltage e into a pulse signal P of a constant level. 10a is an F/V converter that converts the pulse signal P of the comparator output into a DC voltage proportional to its frequency.
Convert to E ₁ . 11a is a rectifying and smoothing circuit that rectifies and smoothes the AC voltage e and converts it into a DC voltage _E2 proportional to its amplitude. 12a is an arithmetic circuit, F/V
Output of converter 10a and rectifier smoothing circuit 11a
This is to perform a desired calculation on E ₁ and E ₂ and extract a signal related to the density or mass flow rate of the fluid from the output.

In the conventional example shown in FIG. 6 configured as described above, when the measuring fluid flows into the pipe line 1a, the vortex generator 2a generates a Karman vortex and receives a lift change based on the generation of the vortex. When the vortex generating body 2a receives a change in lift, a stress change in the opposite direction is generated inside the vortex generating body 2a across the neutral axis as shown in the figure. This vortex generator 2a
The stress change that occurs is transmitted to the element body 41a, which is integrally attached to the vortex generator 2a, through the insulating material 3a.
Therefore, the first and second piezoelectric sensors 46a, 47
In each case, a change in the amount of charge occurs in opposite phase to each other in response to a change in lift force. and piezoelectric sensor 46
The amount of charge generated on leads a and 47a is taken out differentially, and an alternating charge q is generated between lead wires 48a and 49a. The alternating charge q is converted into an alternating voltage e by the detection signal processing circuit 8a. If the frequency of the AC voltage e is taken out via the comparator 9a and the F/V converter 10a, a voltage _E1 proportional to the vortex frequency f, that is, the flow velocity V, can be obtained as shown in equation (4), similar to a general vortex flowmeter.

E ₁ = K ₁ V ... (4) However, K ₁ is a proportional constant. On the other hand, if the amplitude of the AC voltage e is taken out through the rectifying and smoothing circuit 11a, the output of the rectifying and smoothing circuit 11a
E ₂ is given by the following equation, where ρ is the density of the fluid.

E ₂ = K ₂ ρV ² ...(5) However, K ₂ is a proportionality constant. Therefore, if the calculation circuit 12a performs the calculation E ₂ /E ₁ , the output E ₀ will be E ₀ = E ₂ /E ₁ = K ₂ /K ₁ ρV = K ₃ ρV ...(6). If the cross-sectional area of the pipe 1a is S, then the mass flow rate Qm is given by Qm=ρVS ...(7), so E ₀ is E ₀ =K ₃ /SQm ...(8), and the mass flow rate is The signal is proportional to .

Furthermore, if the arithmetic circuit 12a squares E ₁ and then divides E ₂ , the output E ₀ will be E ₀ = E ₂ /E ₁ ² =K ₂ /K ₁ ² ρ = K ₃ /K ₁ ρ...(9), and a signal proportional to the density of the fluid can be obtained.

(Problem to be solved by the invention) However, now the fluctuating lift due to the Karman vortex
F _L , drag force F _D and vortex frequency output (volume flow rate) F _V are F _L = ±1/2C _L ρV ² dD ……(10) F _D = 1/2C _D ρV ² dD ……(11) F _V =K ₁ V...(12) However, F _L ; Variable lift force F _D ; Drag force F _V ; Vortex frequency output (volume flow rate) C _L ; Variable lift coefficient C _D ; Drag coefficient ρ ; Density V ; Flow velocity d ; Vortex generation Diameter facing the flow of the body D; Internal diameter K ₁ ; Constant Therefore, F _L /F _V = (1/2・_CL d・D/K ₁ ) ρV ……(13) In equation (6) K ₃ is K ₃ = 1/2 C _L dD/K ₁ (14).

Here, the first, which detects the fluctuating lift F _L ,
The second piezoelectric sensors 46a, 47a are made of an insulating material 3a.
and is integrally attached to the vortex generator 2a.

Sensors that detect variable lift include strain, displacement, stress, and the like. For example, as shown in Fig. 8, in the case of a vortex generator with one end fixed and the other end free, if the bending moment due to the fluctuating lift force F _L of the vortex is M, the section modulus is Z, and Young's modulus is E, then M=wx ² /2 ...(15) σ=M/Z=wx ² /2Z ...(16) ε=σ/E=wx ² /2ZE ...(17) However, W=F _L /D=±C _L 1/ 2ρV ² /D x; Distance from fixed end D; Length from fixed end to free end.

From equations (16) and (17), stress σ is not affected by Young's modulus E, but strain ε is affected by Young's modulus.

When a strain gauge is used to detect the fluctuating lift force F _L as strain, if the Young's modulus E of the vortex generator changes due to a temperature change, an error occurs correspondingly.

Furthermore, temperature changes in the gauge factor of the strain gauge cannot be ignored.

On the other hand, in the case of detecting stress σ, if the piezoelectric constant d of _the piezoelectric element changes, the amount of generated charge _Q changes according to the electrode area of the piezoelectric element.

Furthermore, when the piezoelectric element is sealed with an insulating material such as glass as shown in Figure 6, the temperature change in the Young's modulus of glass is significantly different from the temperature change in the Young's modulus of stainless steel. The stress σ applied to varies significantly.

That is, the eddy signal stress σ detected in the element main body 41a is approximately expressed as σ∝E ₃ I ₃ /E ₃ I ₃ +E ₂₃ I ₂₃ ·F _L. However, here, E ₂₃ ; Young's modulus of outer cylinder portion 23a I ₂₃ ; Moment of inertia of 〃 〃 E ₃ ; Young's modulus of inertia 3a I ₃ ; Moment of inertia of 〃 F _L ; Lifting force Errors occur due to changes in the d constant due to the temperature of the piezoelectric element. In the vortex flowmeter, since the target is the output frequency, the piezoelectric sensors 46a and 47
Although the change in sensitivity of a to temperature is not a problem,
In the case of a mass flowmeter, since the absolute value of the lift force is required, sensitivity changes due to temperature changes in the piezoelectric sensors 46a and 47a have a large effect on measured values, resulting in large measurement errors.

The present invention solves this problem.

The purpose of the present invention is to perform temperature compensation to
The object of the present invention is to provide a highly accurate mass flowmeter with good temperature characteristics.

(Means for Solving the Problems) In order to achieve this object, the present invention detects the fluctuating lift force and vortex frequency using Karman vortex signals that act as an alternating force on the force receiving body, and detects the mass flow rate. In a mass flowmeter that measures This is a mass flowmeter that is characterized by:

(Function) In the above configuration, when the measurement fluid flows into the pipe, the vortex generator generates a vortex proportional to the flow velocity of the measurement fluid. This vortex causes an alternating force to act on the force receiving body. As for this alternating force, the vortex frequency and the absolute value of the fluctuating lift signal are detected by the detection sensor, and the mass flow rate is detected.

In this case, a temperature change occurs in the force receiving body due to the high temperature measurement fluid or the like. This temperature change is detected by a temperature sensor.

Examples will be described below.

(Embodiment) FIG. 1 is a diagram illustrating the configuration of an embodiment of the present invention.

In the figure, reference numeral 1 denotes a pipe through which a fluid to be measured flows, and reference numeral 2 denotes a columnar vortex generator inserted perpendicularly into the pipe 1, with one end fixed to the pipe 1. 21 is the vortex generator 2
This is a recess provided on one end side. 3 is the recess 21
This is a strain gauge installed in the 4 is a temperature sensor provided in the recess 21 near the strain gauge 3, and in this case a temperature measuring body is used. A detection signal processing circuit 5 converts the signal detected by the strain gauge 3 into an electric signal corresponding to the mass flow rate. 51 is a distortion measurement circuit, and 52 is an amplifier circuit, which amplifies the signal from the distortion measurement circuit. 5
3 is a detection/rectification circuit that detects/rectifies the signal from the amplifier circuit 52; A filter circuit 54 removes low-frequency or high-frequency noise contained in the signal from the distortion measurement circuit 51. 55 is an amplifier circuit that amplifies the signal from the filter circuit 54. 5
6 is a Schmitt trigger circuit that converts the signal from the amplifier circuit 55 into a pulse signal of a constant level.
57 is an F/V converter that converts the pulse signal from the Schmitt trigger circuit 56 into a DC voltage proportional to its frequency. 58 is a division circuit,
A desired calculation is performed on the outputs of the F/V converter 57 and the detection/rectification circuit 53, and the output is extracted as a signal related to the mass flow rate of the measured fluid. 59 is a temperature conversion circuit that converts the temperature measurement signal from the temperature measuring element 4 into an electric signal. Reference numeral 61 denotes a temperature correction circuit 61 that performs temperature correction on the output signal from the division circuit 58 using a signal from the temperature conversion circuit 59.

In the above configuration, in the strain measurement circuit 51, ΔR/R=K _G・x ² /2ZE・D・(±C _L )・1/2ρ・V ² ...(19) R; Resistance K _G ;Measure the value called gauge factor and convert it to AC voltage e ₁ . This is amplified, detected, and rectified to obtain a DC voltage _E1 .

E ₁ =∝C _L x ² ／4ZD K _G ／E ρV ² ＝K ₁ K _G ／EρV ² ……(20
) K ₁ ; Constant On the other hand, the signal of AC voltage e ₁ is filtered and amplified,
Obtain the vortex frequency f _v using the Schmitt circuit.

F _v = StV/d St; Strouhal number d; diameter of the vortex generator 2 This vortex frequency _v is converted by the F/V converter 57.
Convert to a DC voltage of _E2 .

E ₂ = K ₃ V ……(21) K ₃ ; constant Divide equation (20) by equation (21), E ₃ = E ₁ /E ₂ = K ₁ /K ₃ K _G /EρV… (22) In equation (22), K _G and E have temperature coefficients and change depending on temperature, so a temperature error occurs in E ₁ /E ₂ . A temperature measuring element 4 is installed at approximately the same position as the strain gauge 3, and the temperature of the measured fluid is detected, and the value to be corrected by the temperature conversion circuit 59.
Output E ₄ .

E ₄ =K ₄ 1+βt/1+αt≒K ₄ [1+(β-α)t]...
(23) α: Temperature coefficient of gauge factor K _G β: Temperature coefficient of Young's modulus E The output E ₃ of the divider circuit 58 is E ₃ = E ₃₀ 1+αt/1+βt≒E ₃₀ [1+(α−β)t] ...(24) E ₃₀ ; Value in standard state In the temperature correction circuit 61, E ₃ is multiplied by E ₄ .

E ₅ =E ₃ ×E ₄ =K ₁ /K ₃ ×K ₄ ×ρQ ...(25) As a result of the above, the mass flow rate ρQ is obtained.

Note that the sensitivity of the strain gauge 3 is proportional to the supplied current, so using the output _E4 of the temperature conversion circuit 59, instead of multiplication in the temperature correction circuit 61,
This supply current may be controlled.

FIG. 2 is a configuration explanatory diagram of another embodiment of the present invention.

In this embodiment, the strain generated in the flexible portion 221 provided on the flange portion 22 of the vortex generator 2 is extracted as a differential output by strain gauges 31 and 32. As shown in FIG. 3, a strain gauge 33 for detecting temperature is provided at the center or outer peripheral portion of the flange 22 where no distortion occurs. The principle circuit diagram is shown in Figure 4.
In the figure, strain gauges 31 and 32 and fixed resistors 34 and 35 constitute a bridge, and the supply voltage (supply current) E of this bridge is controlled by the correction output of strain gauge 33.

In the above-described embodiment, a strain gauge was used as a detection sensor, but the present invention is not limited to this, and a stress detection method using a piezoelectric element, for example, may be used.

Further, although the vortex generator 2 has been described as having one end free and the other end fixed, the vortex generator 2 is not limited to this, and it goes without saying that the vortex generator 2 may be supported or fixed to the conduit 1. be.

Furthermore, in the above embodiment, an explanation has been given of a structure that serves both as a vortex generating body and a force receiving body, but it is also possible to provide a vortex generating body separately and receive an alternating force due to vortex generation with a force receiving body. Of course.

(Effects of the Invention) As explained above, the present invention provides a mass flowmeter that measures mass flow rate by detecting fluctuating lift and vortex frequency using Karman vortex signals that act as alternating force on a force receiving body. , a mass flowmeter comprising a temperature sensor disposed at a position where the temperature is the same as that of the detection sensor so as to compensate for changes in detection sensitivity caused by temperature changes in Young's modulus of the detection part and temperature changes of the detection sensor. With this configuration, the temperature sensor can correct errors due to temperature changes in the Young's modulus of the detection section and changes in detection sensitivity due to temperature changes of the detection sensor.

As a result, a highly accurate mass flowmeter with good temperature characteristics can be realized.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of one embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the main part configuration of another embodiment of the present invention.
Figure 4 is an explanatory diagram of the main part configuration of Figure 2, Figure 5 is an explanatory diagram of the lifting force etc. when a vortex generating body is arranged in the pipe, and Figure 6 is a diagram of the conventional system generally used. FIG. 7 is an explanatory diagram of the components of FIG. 6, and FIG. 8 is an explanatory diagram of the operation of FIG. 6. 1... Pipeline, 2... Vortex generator, 21... Recessed part,
3, 31, 32, 33...Strain gauge, 3
4, 35...Fixed resistance, 4...Temperature sensor, 5...
...Detection signal processing circuit, 51...Distortion measurement circuit, 5
2...Amplification circuit, 53...Detection/rectification circuit, 54
...Filter circuit, 55...Amplification circuit, 56...
Schmitt trigger circuit, 57...F/V converter, 58...divider circuit, 59...temperature conversion circuit, 61...temperature correction circuit.

Claims (1)

[Claims] 1 In a mass flowmeter that measures mass flow rate by detecting fluctuating lift and vortex frequency using Karman vortex signals that act as alternating force on a force receiving body, temperature changes in Young's modulus of the detection part and temperature of the detection sensor A mass flow meter characterized by comprising a temperature sensor placed at a position where the temperature is the same as that of the detection sensor so as to compensate for changes in detection sensitivity due to changes.