JPH0612281B2 - Mass flow meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mass flow meter for measuring a mass flow rate of a measurement fluid using a Karman vortex.

(Prior Art) It has long been known that when an object is placed in a fluid, vortices are alternately and regularly generated from both rear surfaces of the object and flow in a vortex row downstream. This vortex street is called Karman vortex street, and the number of vortices generated per unit time (generation frequency) is proportional to the flow velocity of the fluid. Therefore, a vortex generator is placed in the conduit that guides the fluid to be measured, and a vortex proportional to the flow velocity is generated by the vortex generator, and changes in lift due to vortex generation are detected by sensors such as piezoelectric elements, strain gauges, and capacitance and inductance. Then
A vortex flowmeter that takes out only the frequency of a detection signal and measures the flow velocity and flow rate of an object has been put into practical use. By the way, in general, the flow rate to be known is often the mass flow rate in the process as well as in the process of causing a chemical change. When the fluid to be measured is gas or steam, its density greatly changes depending on temperature and pressure, and even when it is liquid, its density considerably changes depending on temperature. Therefore, the mass flow rate is measured by installing the vortex flowmeter in parallel 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 and pressure gauge and a vortex flowmeter is not only complicated and expensive, but it is difficult to measure the temperature of the fluid, so accuracy and responsiveness are high. Is also bad.

By the way, as shown in FIG. 3, when the vortex generator 2 is arranged in the conduit 1 and the measured fluid is flown in the conduit 1, the average drag force F _D acting on the vortex generator 2 and the variable lift F _L The pressure loss ΔP generally has a relationship represented by the following equation.

However, C _D ; Drag coefficient C _L ; Fluctuating lift coefficient C _P ; Pressure loss coefficient ρ; Density V; Velocity (1), (2), for example, see “Rheology, Chapter 5, Vortex P.7”.
9, P.87 21 Kutta Zhukovsky's Theorem by Ichiro Tani, Iwanami Shoten ”. (3) is derived from the loss due to separation of the boundary layer from the vortex generator (generation of Karman vortices).

Now, if the drag coefficient C _D , fluctuating lift coefficient C _L , and pressure loss coefficient C _P are constants, the average drag force F _D , fluctuating lift force F _L , and pressure loss ΔP are proportional to ρV ^2; (However, St: Strouhal number, d: Diameter of vortex generator 2, By dividing equations (1), (2), and (3) by (), ρV can be obtained. The values of the drag coefficient C _D , the variable lift coefficient C _L , and the pressure loss coefficient C _P are shown in Fig. 4 for the drag coefficient C _D , published by Maruzen Co., Ltd. As shown in (3), it is required for vortex generators of various shapes.

Also, by dividing the ρV ² detector and the V detector, ρV ²
Obtaining the mass flow rate of / V = ρV is also a technique that has been generally performed conventionally, as described in the flow rate measurement handbook, edited by Hiroo Kawada, P.344, published by Nikkan Kogyo Shimbun.

In the vortex flowmeter, a well-known example of this type is the West German patent.
DE3032578C2 "Dynamic fluid density independent method and device (Mass flow rate measurement by vortex flowmeter)" is available to detect fluctuating lift as strain of strain gauge attached to vortex generator. Alternatively, the mass flow rate is obtained by detecting the torque generated in the vortex generator by a spring, or by detecting the drag force by installing a Pitot tube in front of the vortex generator and dividing the drag force with the vortex frequency.

In Japan, the actual measurement device 54-174359, "Measurement device using Karman vortex", is also equipped with a diaphragm capacity detector on the upstream and downstream sides of the vortex generator to detect the drag force F _D from the DC component of the capacity change. There is a method in which the mass flow rate is obtained by detecting and dividing the eddy frequency from the AC component.

Further, Japanese Patent Application Laid-Open No. 57-61916 “Measuring device using Karman vortex” shows an example in which a variable lift is detected and divided by the vortex frequency.

The following is a description of JP-A-57-61916.

FIG. 5 is an explanatory view of the construction of this Japanese Patent Laid-Open No. 57-61916.
In the figure, 1a is a pipe through which the fluid to be measured flows, 2a is a columnar vortex generator vertically inserted in the pipe 1a, and both ends of the pipe are 1a.
It is fixed to. 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 that causes a Karman vortex street in the measurement fluid and stably enhances the change in lift. The top 22a of the 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. Reference numeral 41a denotes an element body made of a piezoelectric element, which is sealed in the recess 23a of the vortex generator 2a with an insulating material 3a such as glass and is formed integrally with the vortex generator. Also the element body
41a has a disc shape and is arranged such that its center coincides with the neutral axis of the vortex generator 2a. Further, as shown in FIG. 6, the element body 41a is symmetrically provided with electrodes 42a, 43a, 44a, 45a on the front side and the back side thereof, respectively, and in the portion sandwiched by the electrodes 42a and 43a. The first piezoelectric sensor 46a is formed, and the portion sandwiched by the electrodes 44a and 45a is the second piezoelectric sensor 46a.
Forming 47a. Then, the first and second piezoelectric sensors 46a, 47a
The electrodes 42a and 45a and the electrodes 43a and 44a are connected to each other so that the electric charges generated in the electrodes are differential, and the lead wires 48a and 49a are taken out from the electrodes 42a and 44a through the insulating material 3a to the outside. ing. Reference numeral 8a is a detection signal processing circuit, which converts the AC charges q detected by the piezoelectric sensors 46a and 47a into AC voltage e. Reference numeral 9a is a comparator for converting the AC voltage e into a pulse signal P having a constant level. Reference numeral 10a is an F / V converter which converts the pulse signal P output from the comparator into a DC voltage E ₁ proportional to its frequency. A rectifying / smoothing circuit 11a rectifies and smoothes the AC voltage e and converts it into a DC voltage E ₂ proportional to its amplitude. 12a is an arithmetic circuit performs the desired operation on the output E _1, E ₂ of the F / V converters 10a and the rectifying smoothing circuit 11a, is for taking out the signal related to the density or mass flow rate of the fluid at its output .

In the conventional example of FIG. 5 configured as described above, when the measurement fluid flows in the conduit 1a, the vortex generator 2a generates a Karman vortex and undergoes a lift change due to the generation of the vortex. When the vortex generator 2a receives a change in lift, a stress change in the opposite direction occurs across the neutral axis as shown in the drawing. The stress change generated in the vortex generator 2a is transmitted to the element body 41a integrally attached to the vortex generator 2a by the insulating material 3a. Therefore, in the first and second piezoelectric sensors 46a and 47a, changes in the amount of electric charge in opposite phases occur in response to changes in the lift force. Then, the electric charges generated in the piezoelectric sensors 46a and 47a are differentially taken out, and an alternating electric charge q is generated between the 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, the voltage E ₁ proportional to the vortex frequency, that is, the flow velocity V can be obtained as in the general vortex flowmeter as shown in the equation (4).

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 E ₂ of the rectifying and smoothing circuit 11a is Given by the formula.

E ₂ = K ₂ ρV ² (5) However, since K ₂ is a proportional constant, , The output E _o is Becomes If the cross-sectional area of the conduit 1a is S, the mass flow rate Qm is given by Qm = ρVS (7), so E _o is And the signal becomes proportional to the mass flow rate.

Further, in the arithmetic circuit 12a, if E ₁ is squared and then E ₂ is divided, the output E _o is Therefore, a signal proportional to the fluid density can be obtained.

(Problems to be solved by the invention) However, now, the variable lift E _L due to the Karman vortex, the drag force
F _D and vortex frequency output (volume flow) F _V are F = K ₁ V (12) where F _L ; Fluctuating lift F _D ; Drag F _V ; Vortex frequency output (volume flow) C _L ; Fluctuating lift coefficient C _P ; Drag coefficient ρ; Density V; Velocity d; Vortex generator The diameter D opposite to the flow of the pipe; the diameter K _{1 in the} pipe; K ₃ in equation (6) is Becomes

Here, first, second piezoelectric sensor 46a for detecting a variation lift F _L, 47a is a vortex generator 2a of an insulating material 3a, near attached integrally to the measurement fluid. Therefore, it is directly affected by the temperature of the measuring fluid. This causes a problem in the temperature characteristics of the device, and cannot measure a high-temperature measurement fluid. Also, it is easily affected by corrosive measurement fluid,
There is a problem in corrosion resistance.

The present invention solves this problem.

An object of the present invention is to provide a mass flowmeter having good temperature characteristics, capable of measuring even high temperature measurement fluids, and good corrosion resistance.

(Means for Solving the Problems) In order to achieve this object, the present invention detects the variable lift and the vortex frequency by using the Karman vortex signal acting as an alternating force on the force receiving body to detect the mass flow rate. In a mass flowmeter for measuring, a pipe through which a fluid to be measured flows, and a force receiving body that is inserted at a right angle to the pipe, has one end fixed to the pipe and the other end outside the pipe, and receives a torque due to a Karman vortex. , One end of which is connected to the other end of the force receiving body and the other end of which is connected to the conduit and is provided outside the other end of the force receiving body concentrically with the force receiving body. A mass flowmeter comprising a torque tube arranged and a torque detector provided on the torque tube for detecting the torque.

(Operation) In the above configuration, when the measurement fluid flows, Karman vortices are generated. Due to this Karman vortex, torque acts on the force receiving body. This torque is detected as an electric signal in the torque detector via the torque tube. The mass flow rate can be measured by processing the electric signal.

Examples will be described below.

(Embodiment) FIGS. 1 (A) and (B) are configuration explanatory views of an embodiment of the present invention.
(A) is a front view and (B) is a plan view.

In the figure, 1 is a pipe through which the fluid to be measured flows, and 2 is a force receiving body that is inserted at a right angle to the pipe 1 and receives a torque due to a Karman vortex. Reference numeral 3 is a torque tube provided between the force receiving body 2 and the conduit 1. 4 is a torque tube 3 and force receiving body 2
Strain gauges that are placed opposite to each other. Reference numeral 5 is a temperature measuring element attached to the torque tube 3.

FIG. 2 is a block diagram of the electric circuit 6 (not shown in FIG. 1) of FIG.

Reference numeral 61 is a strain detection circuit, which is a circuit for detecting the strain detected by the strain gauge 4. A first amplifier circuit 62 amplifies the signal from the strain detection circuit 61. 63 is a rectification detection circuit, which rectifies and detects the signal from the first amplification circuit 62. A filter circuit 64 removes low-frequency or high-frequency noise included in the output of the strain detection circuit 61. A second amplifier circuit 65 amplifies the output from the filter circuit 64. A Schmitt trigger circuit 66 converts the AC voltage from the second amplifier circuit 65 into a pulse signal of a constant level. 67 is an F / V converter that converts the pulse signal from the Schmitt trigger circuit 66 into a DC voltage proportional to its frequency. Reference numeral 68 denotes a division circuit, which performs a desired calculation on the outputs of the rectification detection circuit 63 and the F / V converter 67, and extracts a signal related to the density or mass flow rate of the fluid at the output. Reference numeral 71 denotes a temperature conversion circuit, which is a circuit for converting a detection signal of the temperature sensing element 5 into an electric signal. Reference numeral 72 denotes a temperature correction circuit, which corrects the temperature of the signal from the division circuit 68 by the signal from the temperature conversion circuit 71 and outputs it as an output signal E _o .

In the above configuration, the stress τ generated in the torque tube 3
Is τ; Shearing force generated in the torque tube T; 〃 〃 Torque Z _t ; Torsional section modulus of 〃 ρ; Fluid density V; Fluid flow velocity L; Lifting force acting on the force receiving body 2 D; Torque tube outer diameter d; The strain output detected by the strain gauge 4 on the inner diameter torque tube 3 of 〃 is calculated using the equations (1) to (3). R: Resistance of strain gauge K _G : Gauge factor σ ₁ ; Principal stress generated in torque tube (= τmax) E; Young's modulus of 〃 〃 Mass flow rate ρv by circuit operation processing shown in Fig. ² ρv ² ÷
The output E _o (∝ρv) is K _T; K-factor f _v in the case of the fluid temperature T; vortex frequency Therefore, the output E _o can be obtained by (5).

Next, in equation (5), the fluid temperature is t, the flow coefficient is K _M , the temperature coefficient of the gauge factor K _G is α, the Young's modulus E of the torque tube 3 is β, the torque tube 3 and the line of the conduit 1 are If the expansion coefficient is γ, the output E _o is Therefore, the temperature error ΔE _o of the output E _o is the temperature coefficient (α-β-
6γ).

Therefore, the temperature of the detecting portion is measured by the temperature measuring element 5, and the second
As shown in the figure, if temperature correction is performed by circuit calculation processing,
Further, it is possible to obtain a device with good accuracy.

Since the torque can be measured at a distance from the measurement fluid by the torque tube 3, the measurement fluid is relatively unaffected by the temperature of the measurement fluid, has good temperature characteristics, and can measure even high-temperature measurement fluid. Even a highly corrosive fluid can be obtained that is not affected by it.

As a result, it is possible to obtain a mass flowmeter having good temperature characteristics, capable of measuring even a high temperature measurement fluid, and good corrosion resistance.

Although the strain gauge 4 is used as the torque detector in the above-described embodiment, the torque detector is not limited to this. For example, a piezoelectric element may be used as long as the torque can be measured.

(Effects of the Invention) As described above, the present invention relates to a mass flowmeter that detects a variable lift and a vortex frequency using a Karman vortex signal acting as an alternating force on a force receiving body to measure a mass flow rate. A pipe through which the measurement fluid flows, a force receiving body which is inserted at a right angle to the pipe, one end of which is fixed to the pipe and the other end of which is arranged outside the pipe and which receives a torque due to Karman vortex, and the other of the force receiving body. A torque tube, one end of which is connected to the other end and the other end of which is connected to the conduit, is provided outside the other end of the force receiving body concentrically with the force receiving body, and is disposed outside the conduit. A mass flowmeter comprising a torque detector provided on the torque tube for detecting the torque is configured.

As a result, the torque tube can be used to easily measure the torque at a position distant from the measurement fluid, so that the temperature characteristic of the measurement fluid is relatively unaffected by the temperature of the measurement fluid.
Even a high temperature measurement fluid can be measured, and even if the measurement fluid is a highly corrosive fluid, a fluid that is not affected by the measurement fluid can be obtained.

Therefore, according to the present invention, it is possible to realize a mass flowmeter having excellent temperature characteristics, capable of measuring even a high temperature measurement fluid, and good corrosion resistance.

[Brief description of drawings]

1 (A) and (B) are explanatory views of the configuration of an embodiment of the present invention.
(A) is a front view, (B) is a plan view, FIG. 2 is a block diagram of the electric circuit of FIG. 1, and FIG. 3 is an explanatory view of the lift force and the like when a vortex generator is arranged in the pipeline, FIG. 4 is an explanatory view of the drag coefficient, and FIG.
FIG. 6 is a structural explanatory view of a conventional example which is generally used from the conventional art, and FIG. 6 is a component explanatory view of FIG. 1 ... Pipe line, 2 ... Force receiver, 3 ... Torque tube, 4
...... Strain gauge, 5 ...... Temperature sensor, 6 ...... Electrical circuit, 61 …… Strain detection circuit, 62 …… First amplifier, 63 …… Rectification detection circuit, 64 …… Filter circuit, 65 …… Second Amplifier circuit,
66 …… Schmidt circuit, 67 …… F / V converter, 68 ……
Division circuit, 71 ... Temperature conversion circuit, 72 ... Temperature compensation circuit.

Claims (1)

[Claims] 1. A mass flow meter for measuring a mass flow rate by detecting a variable lift and a vortex frequency by utilizing a Karman vortex signal acting as an alternating force on a force receiving body, and a pipe through which a measurement fluid flows, A force receiving body which is inserted at a right angle to the pipe line, one end of which is fixed to the pipe line and the other end of which is arranged outside the pipe line and which receives the torque due to the Karman vortex; A torque tube connected to the pipe line and provided outside the other end side of the force receiving body concentrically with the force receiving body and arranged outside the pipe line; and a torque tube provided on the torque tube for detecting the torque. A mass flowmeter, comprising: