JPH08338749A - Coriolis flowmeter - Google Patents

Abstract

PURPOSE: To eliminate a zero drift which is caused by the orientation of a mounted Coriolis flowmeter. CONSTITUTION: A sensor 10 for detecting a Corioli's force generated in flow tubes 3 and 4 through which a fluid to be measured flows, by executing alternate driving so that the flow tubes 3 and 4 can come near to or separate from each other, is fitted to the respective faces 8c and 9c of brackets 8 and 9 of a good thermal conductivity which are deposited to the flow tubes 3 and 4 at two places of the opposite ends 8a and 8b, and 9a and 9c, respectively to be opposed to each other. At the time when the fluid of high or low temperature flows through the flow tubes 3 and 4, the heat of the fluid is transmitted to the brackets 8 and 8 with excellent responsiveness and reaches the sensor 10 and the same temperature is maintained. Therefore, the sensor 10 is not affected by the convection at ambient temperature due to a change in the orientation of mounting of a Coriolis flowmeter, but shows a change depending only on the temperature of the fluid, and accordingly, no zero drift takes place.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis flowmeter, and more particularly to the structure of a sensor mounting portion of a Coriolis flowmeter.

[0002]

2. Description of the Related Art As is well known, when a Coriolis flowmeter supports a flow tube through which fluid flows at both ends and is driven by an alternating vibration of angular velocity ω around a support point, a vector of mass flow rate m and angular velocity ω is applied to the flow tube. It is a mass flow meter that obtains the mass flow rate m by measuring the Coriolis force F by utilizing the action of the Coriolis force F proportional to the product. The alternatingly driven flow tube is deformed by this Coriolis force F, and at the symmetrical position of the flow tube from the support position,
Since a phase difference proportional to the Coriolis force F occurs, the mass flow rate m can be obtained by detecting this phase difference.

The flow tube is an essential part of a Coriolis flowmeter for generating a Coriolis force, and can be roughly classified into a straight tube and a curved tube depending on its shape. In any Coriolis flowmeter with any flow tube, by selecting the angular velocity ω of alternating vibration as the natural frequency ω ₀ of the flow tube, it becomes possible to measure the fluid density ρ from the natural frequency ω _0. The driving energy can be minimized and the driving efficiency can be improved.

FIG. 3 is a perspective view for explaining an example of a conventional Coriolis flowmeter. In the figure, 21 is a manifold, 22 is a base, 23 and 24 are flow tubes, 25 is a brace bar, 26 and 27 is a bracket, 28 is a drive part, and 29 is a sensor.

The flow tubes 23 and 24 of the Coriolis flowmeter shown in FIG. 3 are curved tubes of the same shape that are curved in a U shape, and both ends of each are supported by the base 22 and open into the manifold 21. ing. The manifold 21 has connection flanges 21a at both ends, is connected by piping via the connection flanges 21a, and is a partition plate that supports the upstream and downstream of the manifold 21 to the inside so that an equal amount of fluid flows through the flow tubes 23 and 24 ( (Not shown). Also,
A brace bar 25 is provided near both ends of the flow tubes 23 and 24 to form a node of vibration when driven in a tuning fork shape, and further fixed to each other so that the flow tubes 23 and 24 maintain a parallel posture. Has been done.

A bracket 26 axially parallel to the manifold 21 is fixed to the tip end of the flow tube 23 by electron beam welding or the like at a joining position 26a of both legs of the flow tube 23, and similarly, a tip end position of the flow tube 24. A bracket 27 is fixed to both legs of the flow tube 24 at a position facing the bracket 26 by electron beam welding or the like. A drive unit 28 is fixed to the brackets 26 and 27 at a central position, and a pair of sensors 29 is fixed to both end positions.

The drive unit 28 is a core 28a and a bobbin-shaped drive coil 28b, and the sensor 29 is a pickoff coil 2.
9a and a magnet 29b, and the lead wire (not shown) of each coil is led out to the outside via a connector (not shown) provided in the central portion 22a of the base 22.

In the Coriolis flowmeter shown in FIG. 3 described above, the drive unit 28 is driven to cause the flow tubes 23 and 24 to move relative to each other in a so-called tuning fork shape so as to move toward and away from each other. A sinusoidal velocity signal with a phase difference proportional to the force is detected and a mass flow rate proportional to the phase difference is detected. However, the flow tubes 23, 24
The Coriolis force acting on is extremely small compared to the driving force, and therefore the phase difference signal proportional to the Coriolis force is also small, and in order to detect the mass flow rate with high accuracy, the phase difference signal is not affected by disturbance. Stable detection is the first condition.

Since the Coriolis flowmeter is a flowmeter that detects a fluid flow rate according to the purpose, like a general flowmeter, it can measure fluids having different temperatures and densities and can be piped horizontally or vertically. It is installed in a posture that suits the conditions. In particular, when the temperature of the fluid has a large temperature difference compared to normal temperature, for example, is high, the sensor 29 is affected by the temperature of the fluid and rises in temperature. Moreover, since the temperature in the vicinity of the flow tubes 23 and 24 changes due to the flow of the outside air due to convection, the temperature of the sensor 29 greatly changes depending on the mounting posture of the Coriolis flowmeter.

FIG. 6 is a diagram showing changes in characteristics when a conventional Coriolis flowmeter is attached to a vertical pipe. The horizontal axis represents temperature, the vertical axis represents the resistance value of a pickoff coil, and a converter (output 4 to 20 mA). ) Output current at zero flow, that is,
It shows the amount of drift for an output of 4 mA.

The resistance value of the pair of pickoff coils 29a increases as the temperature of the fluid to be measured rises, and is lower than the resistance value B on the lower side of the attached Coriolis flowmeter.
The resistance value A of the upper pick-off coil 29a is large. The zero drift amount also changes with the change in the resistance value of the pickoff coil 29a, and when the fluid temperature becomes 80 ° C. as compared with the case where the room temperature is 20 ° C., as indicated by the straight line C, about 0.20.
The mA zero moves.

FIG. 7 is a diagram showing a characteristic change when a conventional Coriolis flowmeter is attached to a horizontal pipe. The resistance values of the pair of pickoff coils 29a increase as the temperature rises, but both have substantially the same inclination. The resistance values A and B do not change at the same temperature. Therefore, the output current is 4 mA ± 0.01 as shown by the straight line C.
At about 0.02 mA, the zero drift amount due to temperature change was negligible.

As described above, the sensor 29 detects the movement of the zero point due to the difference in the mounting posture of the Coriolis flowmeter.
Although the case of a and the magnet 29b has been described, not only a sensor having a coil in which a copper wire is wound but also an optical sensor that detects a change in movement of a slit as a change in light amount,
In other cases, the same drift phenomenon will occur if the type of sensor is affected by heat.

[0014]

Since the sensor 29 is attached to the flow tubes 23 and 24, the bracket 2 interposed between the sensor 29 and the flow tubes 23 and 24 is used.
6 and 27 are plate-shaped, and the fixing portions 26a and 27a joined to the flow tubes 23 and 24 are joined in a circular line shape at one place. Therefore, the thermal resistance from the flow tubes 23 and 24 through which the high and low temperature fluid flows to the sensor 29 is large, and the temperature of the sensor 29 is high.
4 has a long response time to reach the temperature of the fluid flowing in
Therefore, the temperature of the sensor 29 is easily affected by the outside air temperature due to convection, and the mounting posture of the Coriolis flowmeter causes the zero point movement.

In particular, the sensor 29 is the pickoff coil 29.
The equivalent circuit of the pick-off coil of the sensor 29 in which a and the magnet 29b are combined is a circuit having an impedance Z composed of a coil resistance R, a capacitance C between lines, and an inductance L.
Changes, and this is output as a phase change of the detected sine wave signal, which causes a zero point shift.

In order to solve the above-mentioned problems, the present invention reduces the thermal resistance between the sensor and the flow tube so that the temperature of the sensor changes in quick response to the temperature of the fluid flowing through the flow tube, and It is an object of the present invention to provide a Coriolis flowmeter having a sensor mounting structure which makes it possible to ignore the influence.

[0017]

In order to solve the above-mentioned problems, according to the present invention, (1) a flow tube whose both ends are supported by parallel-arranged conduits of the same shape, through which an equal amount of fluid flows, and the flow tube. Drive means for alternately driving around the support position in opposite phases, and a sensor that is mounted symmetrically from the support position of the flow tube and that detects a phase difference proportional to the Coriolis force acting on the flow tube. In a Coriolis flowmeter for obtaining a mass flow rate proportional to the phase difference, each of the sensors is provided at a mounting position of the flow tube, and is attached to a bracket made of a good conductor which is welded to the flow tube at least at two or more places. And (2) in the above (1), the sensor is a bobbin-shaped sensor coil and the bobbin-shaped sensor coil. Constituted by a magnet that is inserted into Le, that the sensor coil shape to a flat shape bonding area is increased relative to the bracket, and further, (3)
In the above (1) or (2), the bracket of the good thermal conductor is made of a non-magnetic material and made of the same material as the flow tube.

[0018]

[Operation] A bracket having good heat conductivity is welded to each position of the flow tube to which a pair of sensors for detecting the Coriolis force are attached, and the temperature of the bracket is adjusted to the temperature of the fluid flowing through the flow tube. The temperature of the sensor fixed to the bracket depends on the temperature flowing through the flow tube so that the sensor temperature is not affected by the external environment even when the mounting posture of the Coriolis flowmeter changes and the zero point Prevent drift.

[0019]

1 is a perspective view for explaining an example of a Coriolis flowmeter according to the present invention, in which 1 is a manifold, 2 is a base, 3 and 4 are flow tubes, 5 is a brace bar, 6 is a drive unit, 7 is a sensor unit, 8 and 9 are brackets, and 10 is a sensor.

The Coriolis flowmeter shown in FIG. 1 differs from the Coriolis flowmeter shown in FIG. 3 in that the drive unit 6 and the sensor unit 7 are attached to the flow tube, and the manifold 1, base 2, The flow tubes 3 and 4 and the brace bar 5 are the manifold 21, the base 22, and the flow tubes 23 and 2 of the conventional Coriolis flowmeter shown in FIG.
Since this is the same as the main structure of the Coriolis flowmeter composed of 4 and the brace bar 25, description of this part will be omitted.

The drive unit 6 comprises a columnar core 6a and an annular drive coil 6b. The core 6a and the drive coil 6b are perpendicular to the U-shaped flow tubes 3 and 4 from the axis of the manifold 1. Are attached to the positions on the line of symmetry extending through the mounting brackets 6c and 6d, respectively.

The sensor portion 7 is composed of brackets 8 and 9 and a sensor 10, and is attached to the left and right leg portions of the flow tubes 3 and 4 which are symmetrical from the drive portion 6 in pairs.

FIG. 2 is a sectional view taken along the line B--B of FIG. 1 for explaining the details of the sensor section, and portions having the same functions as those in FIG. 1 are designated by the same reference numerals as in FIG. It is attached.

The bracket 8 is a rectangular plate-like member made of a non-magnetic metal material having good heat conductivity, and the opposing sides 8a and 8b are bent in parallel at an angle θ, and the opposing side 8a and 8b are axially parallel to the flow tube 3. It is welded to the flow tube 3 at two points 8b. Like the bracket 8, the bracket 9 is a rectangular plate-shaped body made of a non-magnetic metal material with good heat conduction, and the opposite side 9
a and 9b are bent in parallel at an angle θ, and are welded to the flow tube 4 at two points of opposing sides 9a and 9b which are axially parallel to the flow tube 4. At this time, the opposing surfaces 8c and 9c of the brackets 8 and 9 which are bent and welded are parallel to each other.

On the surface of the bracket 8c, one end of a column 10c made of a non-magnetic material is fixed at a right angle, and a bar magnet 10b having magnetic poles at both ends is fixed to the other end. On the other hand, on the surface of the bracket 9c, an annular sensing coil 10a is fixed at a position where the central bar magnet 10b is inserted on the axis. The sensing coil 10a has the same number of turns as the conventional one, and the resistance value is reduced by increasing the wire diameter to reduce the influence of thermal resistance and increase the shape to increase the mounting area.

Since the brackets 8 and 9 are bent at an angle θ and are welded to the flow tubes 3 and 4 at the two sides 8a, 8b, 9a and 9b at both ends, the thermal resistance is small and the flow tube 3 is small. When a high or low temperature fluid flows through the brackets 4 and 4, the brackets 8 and 9 are rapidly heated or cooled to the fluid temperature, and the sensing coil 10a is also heated or cooled to a temperature close to the fluid temperature, ignoring the influence of the outside air temperature. As a result, the pair of sensors 10 maintain the same temperature, and as a result, the zero point movement due to the change in the mounting posture of the Coriolis flowmeter also disappears.

However, the tube materials of the flow tubes 3 and 4,
If the materials of the brackets 8 and 9 are different from each other, even if the brackets 8 and 9 are good conductors of heat, the flow tube 3,
4 causes thermal strain due to a difference in thermal expansion between the bracket 8 and
Since the zero point movement occurs due to the thermal strain of 9 itself, the material of the brackets 8 and 9 is selected to be the same material as the flow tubes 3 and 4, for example, when the flow tubes 3 and 4 are non-magnetic stainless steel pipes, 9 also uses the same stainless steel plate. Further, as a matter of course, the heat distortion of the welded portion when the Coriolis flowmeter is assembled and constructed by welding is removed by heating and cooling in a vacuum furnace (corresponding to claim 3).

(Concrete Example) FIG. 4 is a characteristic diagram for explaining an example of the temperature characteristic of the Coriolis flowmeter according to the present invention in vertical piping, in which the horizontal axis represents temperature (° C.) and the vertical axis represents zero drift ( mA) and the sensing coil resistance (Ω). The brackets 8 and 9 are the flow tubes 3 and 4, respectively.
Same as stainless steel.

As shown in FIG. 4, even in the case of vertical piping, the resistance value B of the lower sensing coil 10a is changed with respect to the change of the resistance value A of the upper sensing coil 10a at the same temperature.
Change is so small that it can be ignored, and the zero drift value C that accompanies this change is about 0.01 mA, which is about 1/20 of the conventional zero drift value of 0.2 mA shown in FIG.

FIG. 5 is a diagram for explaining an example of the temperature characteristic of the Coriolis flowmeter according to the present invention when horizontal piping is used. The horizontal and vertical axes are the same as those in FIG.

The temperature characteristic in the horizontal piping shown in FIG. 5 is similar to the temperature characteristic in the vertical piping shown in FIG. 4, and the resistance values of the left and right sensing coils 10a show substantially the same value at the same temperature. The zero point drift was ± 0.01 mA or less, which was substantially the same as in the case of vertical piping.

[0032]

As is apparent from the above description, the present invention has the following effects. Effect corresponding to claim 1: A pair of sensors for detecting the Coriolis force are welded to the flow tube at at least two points respectively, and a highly heat-conductive bracket is fixed, so that the sensor temperature flows in the flow sensor. It changes with good response to the fluid temperature. For this reason, the temperature influence on the sensor due to the convection of the outside air generated in the vicinity of the flow tube due to the mounting posture of the Coriolis flowmeter is ignored, and it is possible to perform measurement without zero-point fluctuation. Effect corresponding to claim 2: The sensor mounted on the bracket is composed of a ring-shaped sensing coil and a magnet coaxial with the ring-shaped sensing coil, and the wire diameter of the sensing coil is increased to make the mounting area relatively. Since the resistance value was small, the resistance value was small and the thermal response was good, and the amount of change in resistance value could be small. A Coriolis flow meter can be provided. Effect corresponding to claim 3: Since the material of the bracket for mounting the sensor is the same non-magnetic material as the material of the flow tube, thermal distortion does not occur in the bracket due to temperature change, and zero drift is prevented in a wide temperature range. be able to.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating an example of a Coriolis flowmeter according to the present invention.

FIG. 2 is a sectional view taken along the line BB of FIG. 1 for explaining the details of the sensor unit.

FIG. 3 is a perspective view for explaining an example of a conventional Coriolis flowmeter.

FIG. 4 is a characteristic diagram for explaining an example of the temperature characteristic of the Coriolis flowmeter according to the present invention during vertical piping.

FIG. 5 is a diagram for explaining an example of temperature characteristics of a Coriolis flowmeter according to the present invention when horizontal piping is used.

FIG. 6 is a diagram showing a change in characteristics when a conventional Coriolis flowmeter is attached to a vertical pipe.

FIG. 7 is a diagram showing characteristic changes when a conventional Coriolis flowmeter is attached to a horizontal pipe.

[Explanation of symbols]

1 ... Manifold, 2 ... Base, 3, 4 ... Flow tube, 5 ... Brace bar, 6 ... Drive part, 7 ... Sensor part,
8, 9 ... Bracket, 10 ... Sensor.

Claims (3)

[Claims] 1. A flow tube whose both ends are supported by parallel-arranged conduits of the same shape through which an equal amount of fluid flows, drive means for alternately driving the flow tube around the support position in opposite phases, and the flow tube of the flow tube. A Coriolis flowmeter that is mounted at a symmetrical position from the support position and that comprises a sensor that detects a phase difference proportional to the Coriolis force acting on the flow tube, and that determines a mass flow rate proportional to the phase difference. The Coriolis flowmeter, wherein the sensor is provided at a mounting position of the flow tube, and is mounted on a bracket made of a good conductor which is welded to the flow tube at least at two or more locations. 2. The sensor comprises a bobbin-shaped sensor coil and a magnet inserted into the bobbin-shaped sensor coil,
2. The sensor coil has a flat shape in which a joint area with respect to the bracket is large.
Coriolis flowmeter described in. 3. The Coriolis flowmeter according to claim 1, wherein the thermal conductive bracket is made of a non-magnetic material and made of the same material as the flow tube.