JPH03199922A - Coriolis mass flowmeter - Google Patents

Abstract

PURPOSE:To obtain a mass flowmeter which is easy to maintain and clean and having good resistance to vibration by coupling a straight measuring pipe in which a measuring fluid flows with a flat plate and vibrating the same. CONSTITUTION:A straight measuring pipe 13 which has a smaller diameter than a piping passage is fixed to a vibration preventing frame 12. A flat plate 14 having the same minimum resonance frequency as the measuring pipe 13 is provided in parallel to the axis of the pipe. A coupling plate 15 is provided at right angles to the axis of the pipe, thereby coupling the measuring pipe 13 with the flat plate 14. When a measuring fluid is let to flow in the measuring pipe 13 and the flat plate 14 is vibrated by a vibration driving apparatus 16, the measuring pipe 13 is moved in the same direction as the flat plate 14. Although the measuring pipe 13 is deformed by the Coriolis force, the flat plate 14 is not influenced by the Coriolis force. Therefore, if the relative displacement detected by a relative displacement measuring apparatus 18 is divided by the displacement speed of the flat plate 14 obtained by a speed measuring apparatus 17, a mass signal is obtained. Since there is no place for the fluid to accumulate or a branch, it is easy to clean the pipe. Moreover, since the measuring pipe 13 and flat plate 14 are fixed near at the end parts thereof by the vibration preventing frame 12, the pipe is hard to be affected by the outside vibration.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a Coriolis mass flowmeter that is easy to maintain and clean and has good seismic resistance.

<Prior Art> FIG. 9 is an explanatory diagram of the configuration of a conventional example that has been commonly used.

In the figure, 1 is a U-shaped measurement tube attached to piping A at both ends.

2 is a flange for attaching the measuring tube 1 to the conduit A.

3 is a vibrator provided at the tip of the U-shaped measuring tube l.

4.5 are displacement detection sensors provided on both sides of the measuring tube 1, respectively.

In the above configuration, the measurement fluid is flowed through the measurement tube 1, and the vibrator 3 is driven. Angular velocity rω of the vibrator 3 in the vibration direction
'', the flow velocity of the measured fluid rv'' (hereinafter the symbols enclosed in ``'' represent vector quantities), then a Coriolis of Fc = -2mrωJXrVJ acts.If we measure the amplitude of vibration proportional to Coriolis, we can find that the mass flow rate is Can be measured.

However, in general, the amplitude of vibrations proportional to Coriolis is extremely smaller than the amplitude of vibrations caused by excitation, and it is not possible to directly detect the amplitude of vibrations proportional to Coriolis.

Now, when viewed from the second view direction in Fig. 9, the vibration direction is divided into α and β due to the vibration of the vibrator 3, and the flow velocity ryJ
Depending on the orientation, as shown in Figure 10 (A>, (B)),
Since the direction of Coriolis is different, the phase is reversed, and measurement tube 1
vibrates while twisting.

The displacement is detected by the displacement detection sensors 4 and 5, for example, a magnetic sensor, and the phase difference between the displacements of the displacement detection sensors 4 and 5 is (
The mass flow rate can be determined because it is proportional to (amplitude of vibration proportional to Coriolis)/(amplitude of vibration due to excitation).

Since the phase difference can be measured as the difference Δt in time at which the waveform crosses zero, Coriolis can be measured as a result.

FIG. 10 is a diagram illustrating the configuration of another conventional example that has been commonly used.

In this conventional example, the measuring tube 1 is of a two-tube type in order to further reduce noise and increase the signal.

<Problems to be Solved by the Invention> However, even in the device shown in FIG. 10, although the seismic resistance against external vibrations etc. is improved, the measurement flow path is separated into two, and cleaning of the measurement tube is difficult. It has drawbacks such as difficulty in handling and the tendency for deposits to accumulate at the branching part.

The present invention solves this problem.

An object of the present invention is to provide a Coriolis mass flowmeter that is easy to maintain and clean and has good earthquake resistance.

<Means for Solving the Problem> In order to achieve this object, the present invention provides a Coriolis mass flowmeter that measures mass flow rate using Coriolis force, which includes a straight measuring tube through which a measuring fluid flows; a flat plate provided parallel to the tube axis of the measuring tube; a vibration isolation frame to which both ends of the flat plate and the measuring tube are fixed; and a vibration isolation frame provided perpendicular to the tube axis and configured to perform the measurement near the center of the measuring tube. a coupling plate that couples the tube and the flat plate; a vibration drive device that is provided perpendicularly to the tube axis and the flat plate and facing between the coupling plate and the vibration isolation frame and vibrates the flat plate; and the flat plate. a velocity measuring device for measuring the displacement speed of the flat plate, and a relative displacement detecting device for detecting the relative displacement between the measuring tube and the flat plate, the connecting plate being attached near the intermediate portion between the end of the measuring tube and the flat plate. This is a Coriolis mass flowmeter characterized by comprising:

Function> In the above configuration, the measurement fluid is flowed into the measurement tube, and the vibrator is driven. The measuring tube and flat plate are vibrated in the same direction by the vibrator.

If the angular velocity rω1 in the vibration direction and the flow velocity ryJ of the measuring fluid flowing inside the measuring tube are Fc--2m rωI transforms.

However, flat plates are not affected by Coriolika.

Therefore, the relative displacement due to Coriolis is measured by the relative displacement measuring device.

A mass signal is then obtained by dividing the measured relative displacement signal by the velocity measuring device.

On the other hand, with respect to the vibration of the main pipe that acts as noise on the measured values, the measurement pipe and the flat plate are fixed near both ends with vibration isolating frames, so it is difficult to receive external vibrations.

Hereinafter, a detailed explanation will be given based on examples.

<Example> Fig. 1 is an explanatory diagram of the main part configuration of an embodiment of the present invention, Fig. 2 is a cross-sectional view taken along line AA in Fig. 1, and Fig. 3 is a cross-sectional view taken along line B-B in Fig. 1. .

11 is a flange connected to a piping path.

12 is a mouth-shaped anti-vibration frame.

Reference numeral 13 denotes a straight measuring tube through which the measuring fluid flows, and both ends are fixed to a vibration isolating frame. In this case, the tube has a diameter smaller than that of the piping, and is connected to the piping at a reduced portion and an enlarged portion.

14 is a flat plate provided parallel to the tube axis of the measuring tube 13, and both ends are fixed to the vibration isolating frame. The flat plate 14 is the measuring tube 13
The plate thickness is selected so that the minimum resonant frequency and the minimum resonant frequency are the same.

Reference numeral 15 denotes a connecting plate that is provided perpendicularly to the tube axis of the measuring tube 13 and connects the measuring tube 13 and the flat plate 14 near the center of the measuring tube 13.

Reference numeral 16 and 17 denote a vibration drive device which is orthogonal to the tube axis of the measurement tube 13 and the flat plate 14 and is provided facing between the coupling plate 15 and the vibration isolation frame 12, vibrates the flat plate 14, and a vibration drive device which vibrates the flat plate 14, and a vibration drive device which vibrates the flat plate 14. This is a speed measurement device that measures speed.

Reference numeral 18 denotes a relative displacement detecting device that is installed near the intermediate portion between the end of the measuring tube 13 and the connecting plate 15 and detects the relative displacement between the measuring tube 13 and the flat plate 14.

In this case, the relative displacement detection device 18 is a slit 181.
, a light emitting device 182 and a light receiving device 183.

FIG. 4 shows an electric circuit block diagram.

21 is a relative displacement conversion circuit that converts the relative displacement between the flat plate 14 and the measuring tube 13 into voltage.

Relative displacement conversion port v@21 has slit 181 and light emitting device 1
82, a light receiving device W183, and an arithmetic circuit 22.

23 is a speed value 3 circuit that outputs a voltage signal proportional to displacement from the output of the speed measuring device 17.

24 is a smoothing circuit that smoothes the output of the relative displacement conversion circuit 21.

25 is a smoothing circuit for smoothing the output of the speed signal 1i23.

A dividing circuit 26 divides the outputs of the smoothing circuit 24 and the smoothing circuit 25.

27 is a drive circuit of the vibration drive device 16 consisting of a coil and an iron core, which receives the frequency signal of the speed signal circuit 23 and the smoothing circuit 25.
Control the frequency and magnitude using the smoothed signal.

In the above configuration, the measurement fluid is flowed into the measurement tube 13,
The vibration drive device 16 is driven. The measuring tube 13 and the flat plate 14 are vibrated in the same direction by the vibration drive device j6.

Assuming that the angular velocity in the vibration direction is "ω" and the flow velocity of the measurement fluid flowing inside the measurement tube 13 is fVJ, then Fc--2m'
Due to the direction of the flow velocity "V!" in which the Coriolika of ωJ
However, the flat plate 14 is not affected by Coriolika. Therefore, the relative displacement due to Coriolis is measured by the relative displacement measuring device.

Then, the measured relative displacement signal is transmitted to the speed measuring device 17.
A mass signal is obtained by dividing by Therefore, it is difficult to receive external vibrations.

That is, FIG. 5 shows the movement of the measuring tube 13 and the flat plate 14.

When the vibration drive device 16 is driven, a periodic force is applied to the coupling plate 15, causing it to flex and vibrate as a unit. Figure 7 (A
) shows the case where there is no flow of the measuring fluid, and FIG. 7(B) shows the case where there is a flow of the measuring fluid.

When there is no flow of measurement fluid, the displacement δ of the flat plate 14 and the displacement δ2 of the measurement tube 13 match, as shown in FIG. 5(A). Therefore, the measurement tube 13 seen with the flat plate 14 as a reference.
The displacement δ2-δ1 is zero, as shown in FIG. 6(A).

When there is a flow of measurement fluid, Coriolis proportional to the mass flow rate is applied to the measurement tube 13, as shown in FIG. 5(B), and the measurement tube 13 is distorted in opposite directions in the upstream and downstream directions. Therefore, the displacement δ2-δ of the measuring tube 13 when viewed from the flat plate 14 changes sinusoidally as shown in FIG. 6(B), which is proportional to the Coriolis (ie, mass flow rate).

δ2−δ+=ωM(υ) ω: Angular velocity M(υ) of the measuring tube 13: Mass flow rate Next, FIG. 8 shows the movement of the relative displacement detecting device 18.

FIG. 8(A) shows the case where there is no relative displacement.

The light emitted from the light emitting device 182 is blocked by the slit 181 and a portion reaches the light receiving device 183. The light receiving devices 183 are configured as a pair and receive the same amount of light when there is no relative displacement.

FIG. 8 (A> is the case where there is relative displacement.

In order for the slit 181 to move, a pair of light receiving devices 18
The light reaching 3 becomes unbalanced.

If the respective light amounts are shifted from A + and A 2, A2 A
t is proportional to relative displacement.

Therefore, the output voltage E (At) of the light receiving device 183.

By calculating the difference between E (A2) in the arithmetic circuit 22 and smoothing it in the smoothing circuit 24, a signal proportional to Coriolis can be obtained as shown in the equation below.

Eo −E (A2 > −B (At) = 12
(A2 At) = 12J! 3 (δ2-δ,) A, 12130M (?J) Furthermore, by dividing the above smoothed signal by 4ω to the output Eυ- of the coupling plate 15, which is proportional to the speed from the speed measuring device 17, a signal proportional to the mass signal is obtained. is obtained.

ll:o 11 t -Erl /E1゜”(1+
A2 fi3ωM(υ))/(A4ω) As a result, (1) Since it is composed of - pipes and there are no liquid pools or branch parts, maintenance and cleaning are easy.

(2) Since the difference in vibration between the measurement tube 13 and the flat plate 14 is used to detect @ motion, it is difficult to receive external vibrations.

In addition, when driving the speed measuring device 17 so that the speed is constant, the division circuit 26 may be omitted.

The relative displacement detection device 18 is not an optical type, but may be a capacitance type, an electromagnetic induction type, a strain gauge type, or a PZT type.

1. The speed measuring device 17 is not an electromagnetic induction type, and may be a method of differentiating the output of a displacement sensor or a method of integrating the output of an acceleration sensor.

Although a pair of relative displacement detection devices 18 are installed at symmetrical positions on the coupling plate 15, the S/N ratio can be improved by processing the pair of displacement signals after picking them up.

Calculation accuracy can be improved by A/D converting the sensor signal.

<Effects of the Invention> As explained above, the present invention provides a Coriolis mass flowmeter that measures mass flow rate using the Coriolis force, which includes a straight measuring tube through which a measuring fluid flows, and a tube axis of the measuring tube. A flat plate provided in parallel, a vibration isolation frame to which both ends of the flat plate and the measurement tube are fixed, and a vibration isolation frame provided perpendicular to the tube axis and connecting the measurement tube and the flat plate near the center of the measurement tube. a coupling plate to be coupled, a vibration drive device that is provided perpendicularly to the tube axis and the flat plate and facing between the coupling plate and the vibration isolation frame and vibrates the flat plate; and a vibration drive device that vibrates the flat plate; A speed measuring device for measuring speed, and a relative displacement detecting device for detecting relative displacement between the measuring tube and the flat plate, the measuring device being provided near the intermediate portion between the end of the measuring tube and the connecting plate. A Coriolis mass flowmeter featuring the following features was constructed.

As a result, (1) It is composed of -1 piping, and there are no liquid pools or branching parts, so maintenance and cleaning are easy.

<2> Vibration detection uses the difference in vibration between the measurement tube and the flat plate, so it is difficult to detect external vibrations.

Therefore, according to the present invention, it is possible to realize a Coriolis mass flowmeter that is easy to maintain and clean and has good earthquake resistance.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the main part configuration of an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA in FIG. 1, FIG. 3 is a sectional view taken along BB in FIG. 1, and FIG. 1 is an electric circuit block diagram, FIGS. 5 to 8 are operation explanatory diagrams of FIG. 1, FIG. 9 is an explanatory diagram of the configuration of a conventional example commonly used, and FIG. FIG. 11 is a diagram illustrating the configuration of another conventional example that has been commonly used. DESCRIPTION OF SYMBOLS 11...Flange, 12...Vibration isolation frame, 13...Measuring tube, 14...Flat plate, 15...Joining plate, 16...
Vibration drive device, 17... Measurement measuring device, 18... Relative displacement detection device, 181... Slit, 182...
Light emitting device, 183... Light receiving device, 21... Relative displacement circuit, 22... Arithmetic circuit, 23... Speed signal circuit,
24.25...Smoothing circuit, 26...Division port m= Fig. 5 Trees S1 Fig. Sz4+ 5z-5;+

Claims (1)

[Claims] A Coriolis mass flowmeter that measures mass flow rate using the Coriolis force, comprising: a straight measuring tube through which a measuring fluid flows; a flat plate provided parallel to the axis of the measuring tube; a vibration isolation frame to which a flat plate and both ends of the measuring tube are fixed; a coupling plate provided perpendicularly to the tube axis and connecting the measuring tube and the flat plate near the center of the measuring tube; and the tube axis. and a vibration drive device that is provided perpendicularly to the flat plate and facing between the coupling plate and the vibration isolation frame to vibrate the flat plate, and a speed measuring device that measures the displacement speed of the flat plate; A Coriolis mass flowmeter characterized by comprising a relative displacement detection device that is provided near an intermediate portion between an end portion and a mounting portion of a coupling plate and detects a relative displacement between the measurement tube and the flat plate.