JPH0593640A - Coriolis mass flow meter - Google Patents

Abstract

(57) [Summary] [Purpose] By increasing the displacement due to Coriolis force,
Realizes a Coriolis mass flowmeter with a high SN ratio. [Structure] A measuring fluid is caused to flow in an oscillating measuring tube, and due to the flow and the Coriolis force generated by the angular vibration of the measuring tube,
In a Coriolis mass flowmeter that deforms and vibrates the measuring tube,
The section of the measuring tube which is the driving mode is constrained through an elastic material so that the natural frequency of the driving mode and the natural frequency of the Coriolis vibration mode are substantially the same. Is a Coriolis mass flowmeter characterized by.

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a Coriolis mass flowmeter having a high S / N ratio by increasing displacement due to Coriolis force.

[0002]

2. Description of the Related Art FIG. 6 is an explanatory view of the configuration of a conventional example that has been generally used in the past. It is an example used in a Coriolis mass flowmeter, for example, US Pat. PATH CORIOLIS MASSFLOW RATE METER
No. 3, filed Nov. 3, 1982, and filed on Jan. 1, 1985. In the figure, reference numeral 1 is a U-shaped measuring pipe having both ends attached to a pipe A. Reference numeral 2 is a mounting flange of the measuring pipe 1 to the pipe line A. Reference numeral 3 is a vibrator provided at the tip of the U-shaped measuring tube 1. Reference numerals 4 and 5 are displacement detection sensors provided on both sides of the measuring tube 1.

In the above structure, the measuring fluid is flown through the measuring tube 1 to drive the vibrator 3. Assuming that the angular velocity “ω” in the vibration direction of the vibrator 3 and the flow velocity “V” of the measured fluid (hereinafter, the symbol enclosed in “” represents a vector amount), Fc = −2 m “ω” × “V” The mass flow rate can be measured by measuring the amplitude of vibration that is proportional to the Coriolis force acting on the Coriolis force. However, in general, the amplitude of vibration proportional to the Coriolis force is much smaller than the amplitude of vibration due to excitation, and the amplitude of vibration proportional to the Coriolis force cannot be directly detected.

Now, when viewed from the Z direction in FIG. 6, considering the vibration directions of α and β by vibrating the vibrator 3,
As shown in FIGS. 7 and 8, the direction of the Coriolis force is different depending on the direction of the flow velocity “V”, so that the phases are opposite to each other and the measuring tube 1 vibrates while being twisted. This is detected by the displacement detection sensors 4, 5, for example, magnetic sensors, and the displacement detection sensors 4, 5 are detected.
Since the phase difference of the displacement of is proportional to (amplitude of vibration proportional to Coriolis force) / (amplitude of vibration due to excitation), the mass flow rate can be obtained. Since the phase difference can be measured as the time difference Δt at which the waveform crosses zero, the Coriolis force can be measured as a result.

FIG. 9 is a diagram for explaining the structure of another conventional example which is generally used in the past. In this conventional example, in order to further reduce noise and increase the signal, the measuring tube 1 is set to 2
It is a tube type that cancels noise.

[0006]

However, in such a device, the displacement due to the Coriolis force is about 1/1000 smaller than the displacement due to driving. When disturbance vibration is applied, it is overlapped with the displacement due to the Coriolis force, and the output is greatly disturbed. The present invention solves this problem. An object of the present invention is to provide a Coriolis mass flowmeter having a high S / N ratio by increasing displacement due to Coriolis force.

[0007]

In order to achieve this object, the present invention allows a measuring fluid to flow in an oscillating measuring tube, and the Coriolis force generated by the flow and the angular vibration of the measuring tube causes the measuring tube to deform and vibrate. In the Coriolis mass flowmeter to be operated, the node of the drive mode of the measuring tube is constrained via an elastic material, and the natural frequency of the drive mode and the natural frequency of the Coriolis vibration mode are This is a Coriolis mass flowmeter which is characterized in that they are made to substantially coincide with each other.

[0008]

[Operation] In the above configuration, the node of the driving mode of the measuring tube is restrained by the elastic material, and the natural frequency of the driving mode and the natural frequency of the Coriolis vibration mode are determined. Since they are made to substantially coincide with each other, the vibration mode due to the Coriolis force becomes close to the resonance state, and a large signal amplitude can be obtained. Hereinafter, detailed description will be given based on examples.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the essential structure of an embodiment of the present invention, and FIG. 2 is a side view of FIG. In the figure, the same symbols as those in FIG. 6 represent the same functions. Only parts different from FIG. 6 will be described below. Reference numeral 11 denotes a pair of oscillators, which generate forces having mutually opposite phases, and in this case, the measuring tube 1 acts so as to resonate in a twist mode. Reference numeral 12 is a spring that connects the base 13 and the measuring tube 1. The spring 12 has a spring constant such that the natural frequency of the bending mode of the measuring tube 1 and the natural frequency of the twisting mode of the measuring tube 1 substantially match.

In the above structure, as shown in FIG. 3, when the measuring fluid flows in the measuring tube 1 vibrating at the natural frequency of the twist mode by the vibrator 11, Coriolis force acts. Since the Coriolis force is distributed as shown in FIG. 4, the vibration of the measuring pipe 1 has a bending mode waveform as shown in FIG. Since the natural frequency of the bending mode of the measuring tube 1 and the natural frequency of the twisting mode of the measuring tube 1 are substantially matched by the spring 12, the vibration of the bending mode which is the displacement vibration due to the Coriolis force also resonates. It is close to the state and a large signal amplitude is obtained.

As a result, the displacement due to the Coriolis force is almost in resonance, and a large displacement is obtained, so that the SN ratio to the disturbance vibration is excellent.

In the above embodiment, the measuring tube 1
The U-shaped one has been described above, but the present invention is not limited to this, and may be, for example, an arbitrary bent pipe or a straight pipe, as long as the Coriolis force can be detected. Also,
The measuring tube 1 may be composed of two parallel tubes. Further, although one oscillator 11 is arranged at the node of the drive mode, it may be installed at two symmetrical points of the node of the drive mode.

[0013]

As described above, the present invention provides a Coriolis mass flowmeter which causes a measuring fluid to flow in an oscillating measuring tube and which causes the measuring tube to deform and vibrate by the Coriolis force generated by the flow and the angular vibration of the measuring tube. , The position of the driving tube of the measuring tube is restrained through an elastic material so that the natural frequency of the driving mode and the natural frequency of the Coriolis vibration mode are substantially equal to each other. A Coriolis mass flowmeter was constructed that was characterized.

As a result, the displacement due to the Coriolis force is almost in the resonance state and a large displacement is obtained, so that the SN ratio to the disturbance vibration is excellent.

Therefore, according to the present invention, it is possible to realize a Coriolis mass flowmeter having a high SN ratio by increasing the displacement due to the Coriolis force.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is an operation explanatory view of the measuring tube vibrating at the natural frequency of the twist mode.

FIG. 4 is an explanatory view of the action of Coriolis force on a measuring tube.

FIG. 5 is an operation explanatory view of a measuring tube.

FIG. 6 is an explanatory diagram of a configuration of a conventional example that is generally used in the past.

FIG. 7 is an operation explanatory diagram of FIG. 6;

8 is an explanatory diagram of the operation of FIG.

FIG. 9 is a configuration explanatory view of another conventional example that is generally used conventionally.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Measuring tube 4 ... Displacement detection sensor 11 ... Oscillator 12 ... Spring 13 ... Base

Claims (1)

[Claims] 1. A Coriolis mass flowmeter for deforming and vibrating a measuring tube by virtue of a Coriolis force generated by flowing a measuring fluid into an oscillating measuring tube and causing angular flow of the measuring tube and the vibration of the measuring tube. A Coriolis mass flowmeter characterized in that the natural frequency of the drive mode and the natural frequency of the Coriolis vibration mode are made to substantially coincide with each other by constraining the nodes as nodes through an elastic material.