JPH04276520A - Flowmeter - Google Patents

Abstract

PURPOSE:To realize a flowmeter wherein there is no obstacle in a measuring pipe, pressure loss is small and vibration resistance is excellent. CONSTITUTION:A flowmeter has a measuring pipe 11 wherein fluid to be measured flows through the inside and at least one end is fixed, a circular-motion driving device 13 which drives the pipe 11 so that the device is turned so as to draw a circle with a reference shaft 14 of the measuring pipe 11 as the center at the natural frequency of the measuring pipe 11 under the state wherein a part of the measuring pipe 11 is curved, a displacement measuring device 15 for detecting the natural frequency caused by the turning of the measuring pipe 11 and an operating circuit for operating the flow speed of the fluid to be measured based on the natural frequency detected with the displacement measuring device 15.

Description

[Detailed description of the invention] [Industrial application field]

[0001] The present invention relates to a flow meter that has no obstructions in the measuring tube, has low pressure loss, and has good vibration resistance.

0002

2. Description of the Related Art Conventional flowmeters for minute sizes include volumetric type, area type, etc. These have drawbacks such as large pressure loss and wear of internal parts because there are objects inside that block the flow, such as gears or floats. On the other hand, electromagnetic flowmeters and Coriolis flowmeters have no obstructions to the flow, but each has drawbacks such as being able to measure only conductive fluids and being susceptible to vibrations.

FIG. 14 is an explanatory diagram of the configuration of a conventional example that has been commonly used in the past, and is an example that can be used in a Coriolis mass flowmeter.
MASS FLOW RATE METER”19
It is shown in the application filed on November 3, 1982 and the patent dated January 1, 1985. 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. Reference numeral 3 denotes a vibrator provided at the tip of the U-shaped measuring tube 1. 4 and 5 are displacement detection sensors provided on both sides of the measuring tube 1, respectively.

[0004] In the above configuration, the measurement fluid is flowed through the measurement tube 1, and the vibrator 3 is driven. Assuming that the angular velocity of the vibrator 3 in the vibration direction is "ω" and the flow velocity of the fluid to be measured is "V" (hereinafter, symbols enclosed in "" represent vector quantities), Fc=-
The mass flow rate can be measured by measuring the amplitude of the vibration that is proportional to the Coriolis force of 2m ``ω'' x ``V''. However, in general, the amplitude of vibration proportional to Coriolis force is extremely smaller than the amplitude of vibration due to excitation, and it is not possible to directly detect the amplitude of vibration proportional to Coriolis force.

Now, when viewed from the Z direction in FIG. 15, the vibration directions are divided into α and β due to the vibration of the vibrator 3, and depending on the direction of the flow velocity “V”, the vibration directions shown in FIG. As shown in (B), since the directions of the Coriolis force are different, the phases are reversed, and the measuring tube 1 vibrates while being twisted. 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 (amplitude of vibration proportional to Coriolis force)/(amplitude of vibration due to excitation) Since it is proportional to , the mass flow rate can be determined. Since the phase difference can be measured as the difference Δt in time at which the waveform crosses zero, the Coriolis force can be measured as a result.

FIG. 16 is a diagram illustrating the configuration of another conventional example that has been commonly used. In this conventional example, in order to further reduce noise and increase the signal, the measurement tube 1 is
It is a two-tube system designed to cancel out noise.

[0007]

[Problem to be solved by the invention] However, in such a device, since the magnitude of vibration is measured,
It has the disadvantage of being weak against external vibration noise. The present invention
This problem is solved. An object of the present invention is to provide a flowmeter that has no obstacles in the measuring tube, has low pressure loss, and has good vibration resistance.

[0008]

In order to achieve this object, the present invention provides a measuring tube through which a measuring fluid flows and which is fixed at least at one end, and a part of the measuring tube at the natural frequency of the measuring tube. a circular motion drive device that drives the measurement tube so that it rotates in a circle around the basic axis of the measurement tube while being curved; a displacement measurement device that detects the natural frequency due to the rotation of the measurement tube;
The present invention constitutes a flowmeter characterized by comprising a calculation circuit that calculates the flow velocity of the measured fluid from the natural frequency detected by the displacement measuring device.

[0009]

[Function] In the above configuration, when the measurement fluid does not flow into the measurement tube, by driving the circular motion drive device, the measurement tube remains partially bent at the natural frequency of the measurement tube. Rotates in a circle around the basic axis. When the measurement fluid is flowing through the measurement tube, a part of the measurement tube remains curved due to the natural frequency of the measurement tube and the measurement fluid, and rotates in a circle around the basic axis of the measurement tube. A displacement measurement device detects the natural frequency due to the rotation of the measurement tube. In the arithmetic circuit,
The flow velocity of the measured fluid is calculated from the natural frequency detected by the displacement measuring device. Hereinafter, a detailed explanation will be given based on examples.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of the main part of an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA in FIG. Reference numeral 11 denotes a measuring tube through which a measuring fluid flows, and both ends of which are fixed to the case 12. Reference numeral 13 indicates the natural frequency of the measuring tube 11, and a circular motion drive device drives the measuring tube 11 so that it rotates in a circle around the basic axis 14 of the measuring tube 11 while keeping a part of the measuring tube 11 curved. It is. Here, the basic axis 14 of the measurement tube 11 is
It is assumed that this is the central axis when the measuring tube 11 is not bent. 15 is a displacement measuring device that detects the natural frequency due to the rotation of the measuring tube 11. 16 is an arithmetic circuit that calculates the flow velocity of the measurement fluid from the natural frequency detected by the displacement measuring device 15. The arithmetic circuit 16 will be described later.

FIG. 3 shows a block diagram of the electrical circuit of FIG. 13 is a drive device, and 15 is a displacement measuring device. The displacement measuring device 15 outputs a voltage proportional to the displacement of the measuring tube 11. 16 is a frequency measuring circuit that converts periodic changes in the displacement measuring device 15 into a frequency. A switch 17 is turned on when recording the zero point, and is normally turned off. A memory 18 records the frequency when the switch 17 is on. 19 is an arithmetic circuit that measures the flow rate from the output of the memory 18 and the output of the frequency measurement circuit 16. 21 is a drive circuit that supplies current to the circular motion drive device 13.

In the above configuration, (1) When the measuring fluid does not flow through the measuring tube 11, by driving the circular motion drive device 13, a part of the measuring tube 11 is moved by the natural frequency of the measuring tube 11. Measurement tube 1 remains bent.
It rotates in a circle around the basic axis 14 of 1. That is, as shown in FIG. 4, the circular motion drive device 13
is pulled outward in the radial direction with a force F. Therefore, the force F is F
1, F2, F3, and F4, it sequentially moves and rotates around the measuring tube 1. In the end, while the force F attracts the measuring tube 1,
It rotates around the measuring tube 1. Thus, the measuring tube 1 is rotating at its natural frequency. As shown in FIG. 5, when rotating at this natural frequency, the bending rigidity B of the measuring tube 1 and the centrifugal force C are in balance. Since both ends of the measuring tube 1 are fixed, they rotate as shown in FIG. 6.

(2) When the fluid to be measured is flowing through the measuring tube 1, as shown in FIG. 7, a centrifugal force D is applied by the fluid to be measured, and the centrifugal force as a whole changes. At this time, the natural frequency of the measuring tube 1 changes so as to balance the bending rigidity. Eventually, due to the natural frequency of the measurement tube 1 and the fluid to be measured, a part of the measurement tube remains curved and rotates in a circle around the basic axis of the measurement tube. Then, the displacement measuring device 15 detects the natural frequency due to the rotation of the measuring tube 1. The arithmetic circuit 15 calculates the flow velocity of the fluid to be measured from the natural frequency detected by the displacement measuring device 15.

FIG. 8 shows a diagram of the principle. The equivalent equation of motion in this case is Mo rω 2=rk−M1 (v 2/R)

(1) Here, Morω 2: Centrifugal force caused by rotation in the E direction rk: Restoring force due to the spring M1 (v 2/R): Centrifugal force caused by the fluid flowing in the F direction Mo: Measuring tube 1 and mass of the measured fluid r: radius of rotation of the bending part ω: angular velocity k: constant M1 : mass of the measurement fluid v: flow velocity of the measurement fluid R: radius of curvature of the bending part

From equation (1), ω 2 = (k/Mo ) - (M1 / (Mo
r)) (v 2/R) (2)
=(k/Mo)(1-(M1/k
)(v 2/(rR))) If R is proportional to 1/r in equation (2), then Rr=const, so e=1
/Rr, ω 2 = ω 0 2(1-(
M1 /k)ev 2)
(3) In equation (3), M1 is proportional to the density, and v is the flow velocity of the measuring fluid. You can ask for 2. Here, ρ
represents density.

As a result, (1) The natural frequency of the measuring tube 1 changes depending on the flow rate of the fluid to be measured, so by measuring this natural frequency, the flow rate of the fluid to be measured can be easily measured. (2) Since the measured value is the natural frequency, a flowmeter that is resistant to disturbance vibrations, that is, has good noise resistance characteristics, can be obtained.

FIG. 9 is an explanatory diagram of the main part of another embodiment of the present invention. In this embodiment, at one end of the measuring tube 1,
A bellows 21 is provided, and one end of the measuring tube 1 vibrates as a free end. FIG. 10 is an explanatory diagram of the main part configuration of another embodiment of the present invention. In this embodiment, a bent tube is used as the measurement tube 1, and both ends are fixed.

FIG. 11 is an explanatory diagram of the main part of another embodiment of the present invention. In this embodiment, a bent tube is used as the measurement tube 1, and the center of the measurement tube 1 is fixed, and both ends are configured as free ends. FIG. 12 is an explanatory diagram of the main part configuration of another embodiment of the present invention. In this embodiment, a parallel tube is used as the measurement tube 1, and both ends are fixed. FIG. 13 is an explanatory diagram of the main part configuration of another embodiment of the present invention. In this embodiment, a parallel tube is used as the measuring tube 1, and one side of the measuring tube 1 is configured as a free end.

[0019]

[Effects of the Invention] As explained above, the present invention provides a measuring tube through which a measuring fluid flows and at least one end of which is fixed;
a circular motion drive device that drives a part of the measuring tube to rotate in a circle around the basic axis of the measuring tube while being curved at the natural frequency of the measuring tube; A flowmeter has been constructed, which is characterized by comprising a displacement measuring device that detects a natural frequency, and an arithmetic circuit that calculates the flow velocity of a fluid to be measured from the natural frequency detected by the displacement measuring device.

As a result, (1) The natural frequency of the measuring tube changes depending on the flow rate of the fluid to be measured, so by measuring this natural frequency, the flow rate of the fluid to be measured can be easily measured. (2) Since the measured value is the natural frequency, a flowmeter that is resistant to disturbance vibrations, that is, has good noise resistance characteristics, can be obtained.

Therefore, according to the present invention, it is possible to realize a flowmeter with no obstructions in the measuring tube, low pressure loss, and good vibration resistance.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a 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 block diagram of the electric circuit in FIG. 1;

FIG. 4 is an explanatory diagram of the operation in FIG. 1;

FIG. 5 is an explanatory diagram of the operation in FIG. 1;

FIG. 6 is an explanatory diagram of the operation in FIG. 1;

FIG. 7 is an explanatory diagram of the operation in FIG. 1;

8 is a diagram illustrating the operating principle of FIG. 1. FIG.

FIG. 9 is an explanatory diagram of the main part configuration of another embodiment of the present invention.

FIG. 10 is an explanatory diagram of the main part configuration of another embodiment of the present invention.

FIG. 11 is an explanatory diagram of the main part configuration of another embodiment of the present invention.

FIG. 12 is an explanatory diagram of the main part configuration of another embodiment of the present invention.

FIG. 13 is an explanatory diagram of the main part configuration of another embodiment of the present invention.

FIG. 14 is a diagram illustrating the configuration of a conventional example that has been commonly used.

FIG. 15 is an explanatory diagram of the operation in FIG. 14;

FIG. 16 is a diagram illustrating the configuration of another conventional example that has been commonly used.

[Explanation of symbols]

11...Measuring tube 12...Case 13...Circular motion drive device 14...Basic axis 15...Displacement measuring device 16...Frequency measurement circuit 17...Switch 18...Memory 19... Arithmetic circuit 21...Drive circuit 22...Bellows

Claims (1)

[Claims] Claim 1: A measuring tube in which a measuring fluid flows inside and has at least one end fixed, and a circle is drawn around the basic axis of the measuring tube while a part of the measuring tube is curved at the natural frequency of the measuring tube. a circular motion drive device that rotates the measurement tube; a displacement measurement device that detects the natural frequency due to the rotation of the measuring tube; and a displacement measurement device that calculates the flow velocity of the measurement fluid from the natural frequency detected by the displacement measurement device. A flowmeter characterized by comprising an arithmetic circuit.