JPH0454894B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Industrial Application Field The present invention relates to a mass flowmeter using Coriolis force.

(2) Prior art When vibration is applied to a fluid flow flowing through a flow tube,
It is known that a Coriolis force is generated in a direction perpendicular to the direction of the fluid flow and the vibration axis, and that the Coriolis force is proportional to the vibration frequency and the mass flow rate of the fluid. For example, U.S. Patent No. 3355944 (corresponding to Japan, Japanese Patent Publication No. 43-26009), U.S. Patent No. 4127028 (corresponding to Japan, Japanese Patent Publication No. 1987-26009),
Mass flowmeters such as those disclosed in US Pat. No. 4,187,724 (Japanese version, JP-A-54-52570) determine the mass flow rate by measuring the Coriolis force.

The device disclosed in the above-mentioned Japanese Patent Publication No. 43-26009 is a member having an inlet and an outlet located on the same axis, an intermediate section and a straight member having an axis concentric with the axis of the inlet. a flow passageway having a curved bend of less than 180 degrees, comprising a curved inlet compartment portion having an end and a curved outlet compartment portion having a straight end having an axis concentric with the axis of the outlet; a connecting conduit between the inlet and the outlet having a flexible device for connecting the end of the conduit with the member; and a device for moving the conduit relative to a flow passageway. This mass flow meter utilizes the Coriolis force couple to
However, in order to increase the detection sensitivity of the Coriolis couple, it is necessary to increase the arm length of the Coriolis couple. However, since the conduit is connected to the inlet and outlet via a flexible device, the fluid inside the conduit is also susceptible to external vibrations, making it difficult to detect mass flow signals with a high S/N ratio. .

On the other hand, in the method disclosed in JP-A-54-52570, an attempt was made to reduce the influence of external vibrations by attaching a U-shaped conduit to a support member in a cantilevered manner in the form of a beam. A reciprocating member having a natural frequency substantially equal to that of the U-shaped conduit is fixed to the support member in a cantilever manner in the same way as the U-shaped conduit, and is driven based on the tuning fork principle to prevent external vibrations other than the natural frequency. Efforts are being made to desensitize people to this. Furthermore, in the method disclosed in JP-A No. 54-4168, the distance between the parallel paths of the U-shaped conduit is made larger than the distance between the fixed portions on the inlet and outlet sides of the U-shaped conduit with respect to the support member. We aim to increase the detection sensitivity of Coriolis couples.

(3) Problems to be Solved by the Invention The above-mentioned conventional examples all employ a U-shaped conduit as a means for detecting Coriolis force with a high S/N ratio. In the above conventional example, when the drive shaft connecting the inlet and outlet of the U-shaped conduit with respect to the support member is the first axis, and the neutral axis of the conduit, that is, the axis of the Coriolis couple, is the second axis, the drive energy is In order to detect a sufficiently small Coriolis signal with high sensitivity, it is a basic requirement to increase the moment arms in the detection sections of the first axis and the second axis. Meeting this requirement inevitably leads to an increase in the length of the conduit. Furthermore, since the stationary surface of the U-shaped conduit is parallel to the main pipe from which the conduit is drawn out, that is, the piping, it is susceptible to vibrations that occur in the piping system in a direction of low rigidity, that is, in a direction perpendicular to the piping, and this is caused by the Coriolis force. There is a problem that the detection signal is added as noise. In other words, in conventional examples, in order to effectively realize a highly sensitive flowmeter, the flowmeter body becomes long and requires a large installation area, and in order to reduce the influence of external vibrations, the installation location and posture must be adjusted. There were inconveniences such as having to take into account the following.

(4) Means for solving the problem The present invention was made in order to solve the above-mentioned problem, and the conduit that generates the Coriolis force is made into a coil spring shape and is arranged coaxially so as to surround the main pipe (piping). By adopting an insertion structure, the flow tube is blocked by a blocking means such as a branch plate, and the blocked fluid flow is allowed to flow through the conduit, thereby reducing the size of the main body. Furthermore, although the Coriolis force is generated and detected in the conduit, the driving direction of the conduit is in the axial direction of the flow tube.
For this reason, even if the flow tube receives the vibration because the flow tube is easily affected in the lateral direction of the flow tube,
The influence of this vibration on the vibration of the flow type conduit is sufficiently small.

(5) Embodiment FIG. 1 shows the main body of a flowmeter according to an embodiment of the present invention. Figure A is a plan view, Figure B is a side view, and Figure C is a front view viewed in the flow direction.

In the figure, fluid is assumed to flow in the direction of the arrow. A dividing plate 2 is fixed in the flow tube 1 so as to block the flow. The blocked fluid flow is conducted through a conduit 3 having an inlet 4 and an outlet 5 opening in the upstream and downstream walls of the dividing plate 2, respectively. The conduit 3 is flexible and surrounds the outer periphery of the flow tube by more than one and a half pitches as shown in the figure in the form of a coiled spring. There are points A, A' and E on ZZ' on the diameter of the flow tube which constitute the axis of symmetry for the inlet 4 and outlet 5 of the conduit. In this case, the line AA' connecting points A and A' is offset by a predetermined pitch angle with respect to the conduit axis near points A and A', and point E is the midpoint between the inlet 4 and the outlet 5. In the vicinity of A and A' of the conduit, drive means (not shown), such as an electromagnetic type, which repeats attraction and repulsion at a predetermined amplitude and frequency in a direction perpendicular to the conduit axis are respectively installed. The operation when the fluid flows in the direction of the arrow in FIG. 1 and the conduit is driven near A and A' will be explained. The fluid flows spirally through the inlet 4 of the conduit and exits from the outlet 5. The center point E of the conduit does not vary with respect to the flow tube 1;
In the drive section of the conduit, there are an inlet 4 and an outlet 5, respectively.
are twisted in opposite directions about the axis. This causes a Coriolis force to act on the fluid within the conduit 3. Coriolis force acts as a vector in the direction of the product of the rotation vector around the axis and the mass flow vector in the conduit, so in diagram C, the force is in the repulsion direction on the diameter Y side, and in the suction direction on the Y' side. arise. Since this force appears as a vector sum with the drive vector, the mass flow rate component must be separated and extracted. As a method of separation and extraction, the relative displacement of the conduit on the Y side in Figure C is detected as a time delay between the change that occurs with respect to the position in the static state and the same change on the Y' side, or the inlet 4 and the outlet 5 It can be detected as the difference in the change in torsional torque in the vicinity of Note that when detecting the Coriolis force as a time delay, detecting it as a displacement or velocity provides the highest sensitivity. Inlet 4, point A and outlet 5
Considering the intermediate points B and C′ between and point A′,
It is better to install detectors at points B' and C corresponding to these, respectively, and when detecting torsional torque, it is better to install detectors near the inlet and outlet, respectively.

Note that if the moment of inertia around the Z-axis in the absence of fluid is I ₀ , the natural frequency around the Z-axis is f ₀ = α√ ₀ . Here, α and K are constants. If density ρ
When the conduit is filled with fluid, the natural frequency is β with ₀ as a constant. becomes. In other words, when the vibration of the conduit is caused to self-oscillate at its natural frequency, the self-oscillation frequency becomes a function of density, so it is possible to measure not only the mass flow rate but also the density, and the flow rate can be measured with the influence of density removed. .

Figure 2 shows two pipes with the same shape as the conduit in Figure 1.
2 shows another embodiment in which the two conduits are arranged with inlets and outlets each parallel to the flow tube axis and separated by a half-pitch for parallel flow. Figure A is a perspective view of the main body, Figure B is a front view of the flow tube as seen from the flow direction.
Figure C is an explanatory view seen from above the main body. Furthermore, the first
The same numbers as in the figures indicate the same structural elements. Second
Conduit 31 in the figure is conduit 3 of FIG. 1 described above.
It is added so that it is parallel to the inlet 41.
The outlet 51 opens in the wall of the flow tube 1 in the same phase as the inlet 4 and the outlet 5 of the conduit 3 with respect to the central axis ZZ' of the flow tube 1. The fluid blocked by the dividing plate 2 flows out in the conduits 3 and 31 as spiral parallel flows. Each conduit surrounds the flow tube 1 by at least 1.5 pitches.

The central parts of these conduits are designated A and A', respectively, and the A,
When A' are moved toward each other, the conduits are twisted in opposite directions about their respective openings. Now, assuming that the intermediate points from intermediate points A and A' to the conduit inlet are B and B', respectively, and the intermediate points from the outlet to C and C', respectively, the fluid flow in the conduit,
That is, the flow vectors that create the Coriolis force are in opposite directions at points B and B' and points C and C'. Since the Coriolis force is given by the vector product of the flow vector and the rotation vector, points B and B' point in a direction away from each other, and points C and C' point in a direction close to each other. Also, if you move in the direction of separating points A and A',
B, B', C, C' are each close to each other, opposite to the above motion,
Separate. Since the amount of this approach and separation is proportional to the Coriolis force, if the driving frequency of the approach and separation of points A and A' is constant, it is proportional to the mass flow rate of the fluid. Detection of proximity and separation is based on optical, electrical, and magnetic means, and by arranging them at positions B, B' and C, C', the time difference B, when the detection element passes the reference position when it is stationary, is determined by It can be determined by measuring the time deviation of B', C, and C'. In the above case, the conduit openings 4, 41 and 5, 51, which are fixed axes, are connected to A and A', which are drive parts and intermediate points.
Although there is an advantage that the arm length is longer and the driving energy can be reduced, the Coriolis force on the side where the conduit is fixed relative to the detection position is in the opposite direction to the above Coriolis force, which reduces the signal. /N ratio decreases. In order to eliminate this, it is better to fix the axially symmetrical positions l and m of the flow tubes A and A' at their resting positions. In addition, when the conduits are driven, stress concentrates on the part of the conduit where the flow pipe is fixed, so damage accidents are likely to occur in this part.To prevent this, it is necessary to In some cases, points P and Q are preferably fixed to each other, and points R and S are preferably fixed to each other in the vicinity of the outflow conduits 5 and 51.

3 and 4 show other embodiments of the present invention shown in FIG. 2, respectively. In FIG. 3, the inlet 4 of the conduit 3 opens near the horizontal diameter wall of the flow tube 1, goes around the flow tube 1 for 1.5 times, and has an outlet on the wall surface symmetrical to the inlet 4 with respect to the flow tube 1 axis. Open 5.
The inlet 4 and the outlet 5 are separated by a dividing plate 2, and the flow within the flow tube flows through the conduit 3.
The conduit 31 has the same shape as the conduit 3, and the inlet 4
1. The outlet 51 is arranged symmetrically with respect to the middle loop of the conduit, reducing the distance between the loops. The length of the intermediate portions BAC, B'A'C' of the conduit loop is slightly longer than the loop portion located on the opposite side of the flow tube 1. As in FIGS. 1 and 2, the driving means is driven by electromagnetic means (not shown) to intermediate positions A and A' with respect to the inlet and outlet of the conduit.
The detection means is detected in the conduit loops B, B' and C, C' by detection means (not shown) as in FIG. In addition, P, Q, P', Q', R, S, R', S', R'',
Join at the S'' position.The reason for joining is the second above.
As in the case shown in the figure, this is to improve the S/N ratio and reinforce the fatigue of the conduit.

Figure 4 shows a loop-shaped conduit 3 having an inlet 4 and an outlet 5 that goes around the flow tube 1, and a conduit 31 having the same shape as the conduit 3, which are arranged in parallel. The plate 2 separates the inlets 4, 41 and the outlet 5, 51, respectively, as in FIG. 3, and is sine-driven at a predetermined frequency and a predetermined amplitude by a driving means (not shown) at the intermediate portions A, A' of the conduit. Conduit B, B', C,
At section C', the magnitude of the Coriolis force is detected by a detection means (not shown) as in the case of FIG.

(6) Effects As described above, according to the present invention, the conduit that generates the Coriolis force has a structure that surrounds the flow tube, so the flow meter body composed of the flow tube and the conduit becomes small and easy to install. It also becomes easier. Furthermore, when looking at the characteristics of the flowmeter, one of the technical problems with this type of flowmeter is to prevent noise effects caused by pipe vibration. Since the flowmeter is configured so that the direction in which the Coriolis force is detected is perpendicular to the direction in which the pipe vibrates easily, the influence of pipe vibration on the detection signal can be reduced.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the principle of the present invention, and A is a plan view.
B is a side view, C is a front view seen from the flow direction, and
Figures 3 and 4 show other embodiments, respectively. In the figure, reference numeral 1 represents a flow tube, 2 represents a branch plate, 3 and 31 represent conduits, 4 and 41 represent an inlet, and 5 and 51 represent an outlet.

Claims (1)

[Scope of Claims] 1. A flow tube, a blocking means for blocking a fluid flow flowing in the flow tube, and an inlet and an outlet opening in walls of the flow tube on the upstream and downstream sides with respect to the blocking means, respectively. a main body consisting of a flexible conduit that surrounds the outer periphery of the flow tube and communicates the fluid flow blocked by the blocking means; a drive means that vibrates the conduit in a direction perpendicular to the conduit surface; What is claimed is: 1. A mass flowmeter comprising: detection means for detecting the Coriolis force exerted on a flowing fluid stream due to vibration; and determining a mass flow rate of the fluid proportional to the Coriolis force. 2. The mass flowmeter according to claim 1, wherein the blocking means comprises a dividing plate that substantially obliquely divides the inside of the flow tube. 3. The mass flowmeter according to claim 1 or 2, wherein the conduit surrounding the flow tube is in the shape of a coiled spring of 1.5 pitch or more and has an axis parallel to the axis of the flow tube. 4 A plurality of conduits having substantially the same shape and dimensions are arranged such that the inlet and outlet are parallel to the flow tube axis and separated by a half-pitch, and the fluids flowing through the plurality of conduits flow in parallel. A mass flowmeter according to any one of claims 1 to 3, characterized in that: 5. A plurality of annular conduits of the same size and shape are arranged substantially in parallel, and the inlet and outlet of the conduit surrounding the flow tube are each opened in the flow tube wall parallel to the flow tube axis. A mass flowmeter according to claim 1 or 2. 6. Claim 4 or 4, characterized in that a support member is provided that integrally supports the conduits arranged in parallel at a position slightly separated from the inlet and outlet of each of the conduits. The mass flow meter according to item 5. 7 At each inlet and outlet side of the conduit,
6. The mass flowmeter according to claim 4, further comprising a support that integrally supports the conduits arranged in parallel.