JPH06147948A - Coriolis mass flow meter - Google Patents

Abstract

PURPOSE:To provide a Coriolis mass flowmeter whereby excitation component in detected signal and Coriolis component, caused by Coriolis farce, can be mechanically separated and detected. CONSTITUTION:Each one end of a pair of supporting tubes 13 and 14 where measured fluid flows is fixed to each fixing end 11 and 12 so that they align themselves on the same axis, and the other end of one supporting tube is connected to that of the other supporting tube for communication, by using a pair of vibration tubes 16 and 17, branching in the direction away from, each other, the said axis so as to from a loop. The vibration tubes 16 and 17 is, by excitation means 18 and 19, excied in the direction orthogonal to the plane formed with respective excitation tubes and vibration tubes, and a distortion detecting plate 15 is fixed between branching points of supporting tubes 13 and 14, and the distortion or stress caused, by the measured fluid, on the distortion detecting plate is detected by a distortion gange 20 as the first signal, a detecting means thus provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis mass flowmeter for measuring a mass flow rate by detecting a Coriolis force generated in a tube to be measured when the fluid to be measured vibrates in the tube. The present invention relates to a Coriolis mass flowmeter improved so that an excitation component and a Coriolis component due to a Coriolis force can be mechanically separated and detected.

[0002]

2. Description of the Related Art FIG. 6 is a conceptual diagram of a first conventional Coriolis mass flowmeter. This Coriolis mass flowmeter is a straight tube type. Reference numeral 1 is a tube through which a measurement fluid can flow, and both ends of the tube 1 are fixed by fixed ends 2 and 3.

A vibrator 4 is installed at the center of the fixed ends 2 and 3, and the tube 1 is vertically vibrated with respect to the central axis of the tube to vertically vibrate. Displacement sensors 5 and 6 for measuring the displacement of the tube 1 are installed between the vibrator 4 and the fixed ends 2 and 3.

Next, the operation of the Coriolis mass flowmeter configured as above will be described with reference to FIG. When vibration is applied from the shaker 4 installed in the center of the tube 1 with the measurement fluid flowing in the tube 1, the tube 1 has a primary mode shape in which the center becomes an antinode of vibration as indicated by M1 and M2. Vibrates.

Considering the upstream side and the downstream side of the tube 1, this vibration can be regarded as a rotational motion centering around the fixed ends 2 and 3, respectively.
When the mass flow rate of the measurement fluid is Q, Coriolis force proportional to the product of ω and Q is generated in each minute section.

As a result, vibration modes M3 and M4 are generated in which the flexural vibrations are symmetrical in the upstream portion and the downstream portion with respect to the center point of the tube 1. The mass flow rate Q can be known by measuring this deformation with the displacement sensors 5 and 6.

On the other hand, the conventional Coriolis mass flowmeter shown in FIG. 8 is constructed as a curved tube type, which is disclosed in, for example, Japanese Patent Publication No. 60-34683. A U-shaped tube 8 is fixed to the supporting portion 7 in a cantilever shape, and a vibrating device 9 is provided on the U-shaped curved pipe portion to vertically vibrate. Further, vibration detectors 10A and 10B are provided on the straight pipe portion of the U-shaped tube 8.

When the U-shaped tube 8 is vibrated up and down as described above, when the mass flow rate Q is applied to the tube 8, the straight tube portions of the pair of tubes 8 are moved in opposite directions by Coriolis force. Since the material is displaced and "twisted", the mass flow rate Q can be known by detecting the resulting displacement with the vibration detectors 10A and 10B.

[0009]

However, in the Coriolis mass flowmeter as described above, the vibration of the tube 8 causes the support member 7 to receive the force of the translational component in the excitation direction, and the vibration isolation is not easy. This means that extra energy is consumed for vibration, which adversely affects sensing, making it more susceptible to external vibration.

Further, also in the cases shown in FIGS. 6 and 8, the displacement sensors 5 and 6 or the vibration detectors 10A and 10B simultaneously detect the excitation vibration and the Coriolis vibration slightly superposed thereon by the same sensor. Is theoretically electrically separated and converted into a mass flow rate Q.

The Coriolis vibration amplitude has an average flow velocity of 1 m / s and is only several hundred to one thousandth of the excitation vibration amplitude. Therefore, it is not easy to separate the Coriolis component, which is a major cause of error. Has become.

Therefore, according to the present invention, by virtue of the axially symmetric structure, the vibration system uses a curved tube having a double-supported beam, so that the translational vibration component is canceled out, the vibration insulation is enhanced, and the stability and vibration resistance are improved. The purpose is to obtain an excellent Coriolis mass flowmeter.

Further, by detecting the shear strain at the central portion, the excitation vibration component is suppressed, and the Coriolis vibration component is detected with priority, facilitating signal processing and achieving a stable Coriolis mass flow rate with a good SN ratio. The purpose is to obtain a total.

[0014]

In order to achieve the above object, the present invention has a main structure in which each one end of a pair of support tubes through which a measurement fluid flows is fixed to each fixed end so as to be aligned on the same axis. The other end of one of the support tubes is fixed, and the other end of the one support tube is branched by a pair of vibrating tubes in directions away from each other to form a loop and connected to the other end of the other support tube. The vibrating tubes are vibrated by vibrating means in a direction perpendicular to the plane formed by the supporting tubes and the vibrating tubes, and the strain detecting plate is fixed between the branch points of the supporting tubes. Coriolis mass flowmeter, comprising a detection means for detecting strain or stress generated in the strain detection plate by the measuring fluid as a first signal by a strain gauge.

[0015]

[Operation] First, a pair of vibrating tubes branched from the support tube and joined together are vibrated by vibrating means in a direction perpendicular to a plane formed by each support tube and each vibrating tube.

In this state, when the measurement fluid flows through the support tube, the measurement fluid branches into the left and right vibrating tubes at the branch portion, and the strain detection plate provided at the branch portion by the Coriolis force generated in the vibrating tube. Rotational forces in opposite directions are applied to the upstream side and the downstream side of the.

Therefore, "strain" occurs in the strain detecting plate, and shear strain or shear stress is generated there. Therefore, the strain gauge provided on the strain detecting plate corresponds to the shear strain or shear stress. Convert to 1 signal.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing an embodiment of the present invention.
For convenience of description, the following description will be given assuming that the horizontal direction is the X axis, the vertical direction is the Y axis, and the vertical direction is the Z axis with respect to the paper surface.

Reference numerals 11 and 12 denote fixed ends of the vibration system, which are fixed to the body of the mass flow meter. These fixed ends 11, 1
2 includes support tubes 13 and 14 through which the measurement fluid flows.
One end of is fixed. The support tubes 13 and 14 are arranged so as to be on the same axis (Y-axis direction).

The other end of the support tube 13 is branched to the left and right by communicating with one ends of vibrating tubes 16 and 17 each having a C shape, and the other ends thereof are connected to the other end of the support tube 14. Are combined. The vibrating tubes 16 and 17 are arranged on the same plane (XY plane) as the support tubes 13 and 14.

A branch point X ₁ branched from the support tube 13 to the vibrating tubes 16 and 17 and a T-shaped branch point X ₂ branched from the support tube 14 to the vibrating tubes 16 and 17. The strain detection plate 15 is fixed between them.

A strain gauge 20, which will be described in detail with reference to FIG. 2, is arranged on the strain detecting plate 15 to detect the Coriolis signal as the first signal e _C and the excitation component as the second signal e _m . Further, at the central portions of the vibrating tubes 16 and 17, vibrating devices 18 and 19 for vibrating in the form of a simple oscillatory motion in the Z-axis direction are provided.

The fluid to be measured flows in from, for example, the support tube 13 and is vibrated at the branch point X ₁ of the T-shape.
To flow out, join at a T-shaped branch point X ₂ , and flow out through the support tube 14.

FIG. 2 is a layout showing a specific layout of the strain detection plate 15 shown in FIG. 2A shows a case where one strain detection plate 15A is provided on the XY plane, FIG. 2B shows a case where the strain detection plate 15B is provided on the YZ plane, and FIG. Support tube 1 on a flat surface
3 shows the case where the strain detection plates 15C ₁ and 15C ₂ are divided into two on the left and right sides with respect to 3 and 14, respectively.

The strain detecting plate 15A is arranged at an angle of ± 45 degrees with respect to the X-axis, and shear strain or shear stress generated by the Coriolis force is applied to the strain detecting plate 15A as the first signal e.
Strain gauges A, C and, X-axis or the second signal the excitation component by the expansion and contraction strain produced is vibrated in the Z-axis direction by vibrating unit 18, 19 in the direction parallel to the Y-axis e _m for detecting a _C Strain gauges B for detecting as are respectively arranged.

Further, the strain detecting plate 15B is arranged at an angle of ± 45 degrees with respect to the Z axis, and shear strain or shear stress generated by the Coriolis force is applied to the strain detecting plate 15B.
Strain gauges A and C for detecting the signal e _C are arranged. In this case, providing a detection means such as detecting gauge B for detecting the excitation component by the expansion and contraction strain produced is vibrated in the Z direction vibrating device 18, 19 as the second signal e _m.

Further, the strain detecting plates 15C ₁ and 15C ₂
The strain gauge A for detecting shear strain or shear stresses generated by the Coriolis force on the strain sensing plate 15C _1, 15C ₂ are arranged to be inclined ± 45 degrees with respect to the X axis as the first signal e _C, C And strain gauges A'and C'are either X-axis or Y
The excitation component is generated by the second signal e due to the expansion and contraction distortion generated by the vibration devices 18 and 19 in the direction parallel to the axis in the Z-axis direction.
Strain gauges B and B ′ for detecting _m are respectively arranged.

Next, the operation of the mass flowmeter configured as described above will be described with reference to the explanatory view shown in FIG. FIG. 3 (a) shows the excited state when the measurement fluid is not flowing,
FIG. 3B shows how the Coriolis force generated by the flow of the measurement fluid acts in the excited state.

In FIG. 3, the solid line indicates the reference position of the vibration system, and the dotted line indicates the deformed state of the vibration tubes 16 and 17 at a certain time. The arrow shows the direction of vibration,
In particular, the support tubes 13 and 14 show the axial twist direction. The direction of excited vibration at a certain moment is indicated by the solid arrow m, and the Coriolis force generated at that time is indicated by the dotted arrow c.

As shown in FIG. 3, when the measurement fluid flows in from the support tube 13 and flows out from the support tube 14 via the left and right vibrating tubes 16 and 17, the vibrating tubes 16 and 17 in the Y-axis direction. The arm portions (upstream side and downstream side) of the tubes spaced apart from each other are displaced in opposite directions to each other, and the arm portions of the vibrating tubes 16 and 17 are opposite to each other with respect to the axis connecting the support tubes 13 and 14. Therefore, the strain detection plate 15 is “twisted” and shear strain or shear stress is generated.

The shear strain or shear stress generated in the strain detection plate 15 (15A, 15B, 15C ₁ , 15C ₂ ) due to this "twist" is detected by the strain gauge 20 as the first signal.

In this case, FIG. 2 (a), (b), (c)
With the arrangement of the strain gauges shown in (1), since the central portion connecting the support tubes 13 and 14 of the strain detection plate 15 has an axially symmetric vibration system, shear strain does not occur due to the excitation vibration. In particular, the strain gauge arrangement shown in FIG. 2B does not cause any strain.

However, it is also possible to detect a Coriolis component by detecting it as a mixed signal in which these components are mixed and separating it by a conversion circuit which will be described later due to a slight asymmetry problem in manufacturing or intentionally. .

FIG. 4 is a block diagram showing the configuration of the signal processing unit 22 which processes the signal from the sensor unit 21 shown in FIG. Although the following signal processing will be described as a configuration in which the first signal is divided by the second signal, the division is not always necessary when the signal processing is performed only by the first signal.

The sensor section 21 outputs a first signal (a signal including a Coriolis signal) e _c and a second signal (excitation signal) e _m to the preamplifiers 23 and 24 of the signal processing section 22, respectively.

Excitation signal e output from the preamplifier 24
_m1Is input to the drive circuit 25, where it is amplified and driven.
A current is passed through the exciters 18, 19. This result is the second
Issue e _mAnd is output to the preamplifier 24. this
Repeatedly vibrating tube with resonance frequency of constant amplitude
16, 17 are vibrated up and down.

The excitation signal e _m1 amplified by the preamplifier 24 is input to a phase locked loop circuit (PLL circuit) 26, where it is generated as a timing signal e _T1 whose phase is shifted by 90 degrees.

The Coriolis signal e _{c1 obtained} by amplifying and outputting the first signal e _c in the preamplifier 23 is input to the synchronous rectification circuit 27, where the Coriolis signal e _c2 is synchronously rectified by using the timing signal e _T1. Are output separately.

Further, the excitation signal e _{m1 obtained} by amplifying the second signal e _m by the preamplifier 24 and outputting it is the effective value circuit 28.
, The effective value of the excitation signal e _m1 is calculated, and is output as the excitation signal e _m2 . The division circuit 29 divides the Coriolis signal e _c2 by the excitation signal e _m2 to remove the fluctuation of the vibration amplitude of the vibration tubes 16 and 17, and outputs it as a flow rate signal e _f1 proportional to the mass flow rate Q of the measured fluid. To do.

FIG. 5 is a block diagram showing the configuration of another signal processing section 30 for processing the signal from the sensor section 21 shown in FIG. In the following description, parts having the same functions as those of the components shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

From the sensor section 21, the first signal e _c and the second signal e _c
The signal e _m is the preamplifier 23 of the signal processing unit 30,
24 is output. The excitation signal e _m1 amplified by the preamplifier 24 is input to the PLL circuit 26, where the phase is 9
A timing signal e _T2 that is in phase with the timing signal e _{T1 that} is shifted by 0 degrees is generated.

The Coriolis signal e _c1 is input to the synchronous rectification circuit 31, which is synchronously rectified using the timing signals e _T1 and e _T2 to separate the Coriolis signal e _c3 and the excitation signal e _m3 and the division circuit 29. Output to.

The division circuit 29 divides the Coriolis signal e _c3 by the excitation signal e _m3 to remove the fluctuation of the vibration amplitude of the vibrating tubes 16 and 17, and to obtain a flow rate signal e proportional to the mass flow rate Q of the fluid to be measured. Output as _f2 .

In the above description, the strain gauge is mainly used as the detection gauge for detecting the signal.
The present invention is not limited to this, and for example, a piezoelectric element may be used as a detection gauge to detect stress. Since this excitation vibration vibrates axisymmetrically about the fixed axis connecting the two fixed ends 11 and 12, the translational motion component of the entire vibration system is canceled.

[0045]

As described above in detail with the embodiments, the present invention has various effects described below. In the invention described in claim 1, since the axially symmetric vibration is performed around the fixed axis connecting the two fixed ends, the translational motion component of the entire vibration system is canceled, and the vibration insulation with the outside is improved, Vibration can be efficiently and stably continued, and the influence of external vibration noise is reduced.

Further, since the excitation vibration component can be suppressed and the Coriolis vibration component can be detected with priority, the signal processing can be simplified, the SN ratio is good, and the detection can be performed with high accuracy and stability with a simple circuit. Ideally, the excitation vibration component becomes zero and only the Coriolis vibration component can be detected.

Usually, when measuring displacement with a single tube, since a relative displacement between a certain reference point, for example, the body and the tube is measured, not only the vibration of the tube but also the mounting base of the displacement sensor (reference position) Is affected by position variations. On the other hand, in the strain measurement by the strain detection plate according to the present invention, since the absolute strain or displacement of the tube vibration can be measured, it is stable against external vibration.

Furthermore, since the conventional Coriolis flowmeter reacts to all vibrations at the measurement point, noise other than the vibrations of the excitation mode and Coriolis mode, which are the necessary vibrations, is detected. In the flow meter,
Since it has sensitivity only to a specific vibration mode, it has good vibration resistance.

In the inventions according to claims 3 and 5, since the strain gauge can be integrated in one place as a detection sensor, not only the structure can be simplified, but also variation in temperature conditions due to the position of the strain gauge can be eliminated. You can
A flowmeter that is stable against temperature fluctuations can be constructed.

In the invention according to the fourth aspect, distortion due to excitation vibration does not occur. In the conventional shear strain detection method, it is unavoidable that bending strain or expansion / contraction strain occur at the same time. In any case, the same excitation component as the Coriolis component was mixed, but in this invention, the mixture of the excitation component is greatly reduced. Can be made.

In the invention according to claim 5, since the strain detecting plate is divided into two parts and the fixed end and the fixed end are not directly connected by the structure, the tube bends to absorb the thermal expansion. be able to. Therefore, it has good temperature characteristics and can be used in a wide temperature range.

According to the sixth aspect of the invention, since the Coriolis component contained in the first signal is divided by using the excitation component, the influence of the excitation voltage can be removed.

According to the invention described in claim 7, since the division is performed using the Coriolis component and the excitation component contained in the first signal, the temperature characteristic of the strain gauge is canceled and the temperature characteristic is canceled. A Coriolis mass flowmeter with stable characteristics can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a layout diagram showing a specific layout of the strain detection plate shown in FIG.

FIG. 3 is an explanatory diagram explaining an operation of the embodiment shown in FIG.

FIG. 4 is a block diagram showing a configuration of a signal processing unit connected to the sensor unit shown in FIG.

5 is a block diagram showing the configuration of another embodiment of the signal processing unit shown in FIG. 1. FIG.

FIG. 6 is a conceptual diagram showing a configuration of a first conventional Coriolis mass flowmeter.

FIG. 7 is an explanatory diagram illustrating an operation of the Coriolis mass flowmeter shown in FIG.

FIG. 8 is a perspective view showing a configuration of a second conventional Coriolis mass flowmeter.

[Explanation of symbols]

11, 12 Fixed end 13, 14 Support tube 15, 15A, 15B, 15C ₁ , 15C ₂ Strain detection plate 16, 17 Vibration tube 18, 19 Vibration device 20 Strain gauge 21 Sensor part 23, 24 Preamplifier 25 Drive circuit 27, 31 Synchronous rectification circuit 29 Division circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenta Mikita 2-9-32 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd.

Claims (7)

[Claims] 1. A pair of support tubes, through which a measurement fluid flows, each one end of which is fixed to each fixed end so as to be aligned on the same axis,
The other end of the one support tube is branched by a pair of vibrating tubes in directions away from each other to form a loop, and is connected to the other end of the other support tube so as to communicate therewith. Vibrating means vibrates in a direction perpendicular to the plane formed by each supporting tube and each vibrating tube, the strain detecting plate is fixed between the branch points of each supporting tube, and the strain is detected by the measuring fluid on the strain detecting plate. A Coriolis mass flowmeter, characterized in that the strain or stress generated is detected as a first signal by a strain gauge. 2. The Coriolis mass flowmeter according to claim 1, further comprising detection means for detecting an excitation signal generated by the vibrating means as the second signal by the strain detecting plate or the vibrating means. 3. The Coriolis mass flowmeter according to claim 1, wherein the strain detection plate is arranged on the same plane as the plane. 4. The Coriolis mass flowmeter according to claim 1, wherein the strain detection plate is arranged on a plane perpendicular to the plane. 5. The strain detecting plate is arranged on the same plane as the plane and is divided into two parts on the side of the pair of vibrating tubes with respect to the axis. Coriolis mass flow meter. 6. A first phase locked loop circuit for pulse-shaping the second signal to generate a timing signal with a 90 degree phase shift, and a first synchronous rectification for synchronously rectifying the first signal using the timing signal. A means and an effective value calculation means for calculating an effective value of the second signal, wherein the output of the synchronous rectification means is divided by the effective value to obtain a mass flow rate. Coriolis mass flowmeter described in. 7. A second phase locked loop circuit for pulse-shaping the second signal to generate a 90 ° timing signal with a 90 ° phase shift and an in-phase timing signal in phase with the second signal, and the first signal. Second synchronous rectification means for synchronously rectifying and separating the first signal into the Coriolis signal component using the 90-degree timing signal into the excitation signal component using the in-phase timing signal, and the Coriolis signal component into the excitation signal. The Coriolis mass flowmeter according to claim 2 or 3 or 4 or 5, further comprising: a dividing unit that divides by the component to calculate the mass flow rate.