JPH09196730A - Vibration-type measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a flow rate of each of a pair of sensor tubes even when natural vibration frequencies of the pair of sensor tubes lose balance as a result of mixing of air bubbles. SOLUTION: In a mass flowmeter 1, a liquid is passed through a pair of sensor tubes 7, 8 vibrated by vibrators 20, 21, and a Coriolis force of a size according to a flow rate, namely a phase difference between the upstream and downstream sides is detected by an upstream pickup unit 22 and a downstream pickup unit 23. A flow rate instrumentation control circuit 30 detects the phase difference of signals of the upstream and downstream sides which is detected by a first pickup 24 when frequencies of the pair of the sensor tubes 7, 8 agree. Moreover, if air bubbles are mixed and natural vibration frequencies of the pair of sensor tubes 7, 8 lose balance, the control circuit 30 vibrates the sensor tubes 7, 8 with the respective natural vibration frequencies, detects the phase differences individually between the upstream and downstream sides of the sensor tubes 7, 8 by second pickups 26, 27 and adds the phase differences.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration type measuring device, and more particularly to a displacement of a pair of sensor tubes between an upstream side and a downstream side while vibrating a pair of sensor tubes through which a fluid to be measured flows at the same natural frequency. The present invention relates to a vibration-type measuring device configured to detect and detect the phase difference.

[0002]

2. Description of the Related Art As a vibrating measuring device for measuring a physical quantity of a fluid by vibrating a pipe line (hereinafter referred to as a "sensor tube") to which a fluid is supplied, there is, for example, a Coriolis mass flowmeter or a vibrating density meter. .

In this type of Coriolis mass flow meter, the displacement proportional to the flow rate between the inflow side and the outflow side of the vibrating sensor tube is detected by a pickup, and the mass flow rate is obtained from the phase difference. Further, in the vibration type densitometer, the density of the fluid is measured from the natural frequency of the sensor tube. Since the Coriolis mass flowmeter and the vibration type density meter have the same configuration, the Coriolis mass flowmeter will be described below.

An example of this type of conventional mass flowmeter is the flowmeter disclosed in Japanese Patent Laid-Open No. 63-30721. In the mass flowmeter of this publication, a pair of linearly extending sensor tubes are vibrated in a radial direction by a vibrator (comprising a drive coil and a magnet) in order to reduce pressure loss when a fluid to be measured passes. Then, the upstream side displacement and the downstream side displacement of the pair of sensor tubes due to the Coriolis force proportional to the flow rate are detected by the pair of pickups (composed of the sensor coil and the magnet).

Since the pair of sensor tubes are formed in the same shape, they have the same natural frequency. Then, the exciter drives and controls the pair of sensor tubes so that the driving force (exciting force) becomes the smallest vibration frequency (natural frequency). Therefore, at the time of measurement, a shaker horizontally placed between the pair of sensor tubes vibrates the middle part of the pair of sensor tubes in the radial direction to vibrate the pair of sensor tubes at the same natural frequency and A pair of pickups arranged on the upstream side and the downstream side of the sensor detects displacement on the sensor tube and on the downstream side. The flow rate flowing through the pair of sensor tubes can be obtained from the phase difference between the detection signals on the upstream side and the downstream side.

[0006]

However, in the conventional vibration type measuring device, since the vibrator is driven so that the pair of sensor tubes vibrate at the natural frequency, the object to be measured flowing inside the pair of sensor tubes. It is necessary that the velocity of the sensor tube containing the fluid be uniform. Especially when the fluid to be measured is a liquid, bubbles may be mixed in the liquid, and it is difficult to make the size and distribution of the bubbles uniform.

Therefore, when measuring a liquid containing bubbles, a large amount of bubbles flow into one of the sensor tubes or a large amount of bubbles into the other sensor tube, so that the amount of aerated air fluctuates irregularly. Therefore, it is impossible to predict the amount of bubbles mixed in each sensor tube.

Furthermore, when a large amount of air bubbles flow into one of the sensor tubes, the natural frequencies of the pair of sensor tubes deviate from each other, which makes it impossible to accurately measure the flow rate. If the natural frequencies of the pair of sensor tubes do not match in this way, the amplitude of the sensor tubes cannot be obtained sufficiently, so the driving force of the exciter is amplified and the frequency is varied to reduce the vibration of each sensor tube. The numbers are adjusted so that the numbers are the same, but if the frequencies still do not match, the vibrator is stopped due to insufficient driving force of the vibrator.

Therefore, an object of the present invention is to provide a vibration type measuring device which solves the above problems.

[0010]

In order to solve the above problems, the present invention has the following features. The present invention provides a pair of sensor tubes through which a fluid to be measured flows, a pair of vibrators that vibrate the pair of sensor tubes, and a pair of pickup units that individually detect each displacement of the pair of sensor tubes, When the vibration frequencies of the pair of sensor tubes detected by the pair of pickup units are different, the control means controls the pair of vibrators to individually vibrate the pair of sensor tubes at each natural frequency. And is composed of

Therefore, according to the present invention, when the pair of sensor tubes have different frequencies, the pair of exciters controls the pair of sensor tubes to individually vibrate at each natural frequency. Even if the balance of the natural frequencies of the pair of sensor tubes is lost due to the mixture, the flow rates of the pair of sensor tubes can be detected to accurately measure the flow rates of the pair of sensor tubes.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a Coriolis mass flowmeter as an embodiment of the vibration measuring device according to the present invention. still,
FIG. 1 is a vertical sectional view showing the configuration of the mass flowmeter 1.

The mass flowmeter 1 is formed by inserting a pipe 3 through which a fluid to be measured passes in a closed casing 2. Line 3
Is composed of axially displaceable bellows 4A, 4B, an inflow pipe 5, an inflow side manifold 6, a pair of sensor tubes 7, 8, an outflow side manifold 9, and an outflow pipe 10.

The pair of sensor tubes 7 and 8 are made of stainless steel straight pipes linearly extending in the fluid flow direction (X direction), and are parallel to each other between the inflow side manifold 6 and the outflow side manifold 9. It is provided. Support plates 11 and 12 to which the sensor tubes 7 and 8 penetrate and are fixed are laterally provided near both ends of the sensor tubes 7 and 8. Therefore, the sensor tubes 7 and 8 are the support plates 1
It is supported in parallel by 1 and 12, and vibrates with the support plates 11 and 12 as fulcrums during measurement.

The casing 2 is a cylindrical casing body 1.
3 has a closed structure in which both end openings are closed by lid members 14 and 15, and it is possible to prevent dew condensation on the surface of the conduit 3 inserted into the storage chamber 16 in the casing 2. Further, the sealed storage chamber 16 is filled with a dry protective gas (for example, argon gas) at a predetermined pressure.

The inflow pipe 5 has a flange 5a connected to an upstream pipe (not shown) at the inflow end, and the other end of the inflow pipe 5 penetrates the lid member 14 of the casing 2 to form a casing. 2 extends inside. Inflow side manifold 6
The upstream side is connected and fixed to the bellows 4A, and the downstream side is connected and fixed to the upstream end portions of the sensor tubes 7 and 8.

The outflow-side manifold 9 has its upstream side connected to the downstream ends of the sensor tubes 7 and 8, and its downstream side connected to the upstream ends of the bellows 4B. Outflow pipe 10
Has an upstream end connected and fixed to the outflow manifold 9, and a downstream end penetrating the lid member 15 of the casing 2 and projecting to the downstream side (X direction). A flange 10a connected to a downstream pipe (not shown) is provided at the downstream end of the outflow pipe 10.

The bellows 4A on the upstream side has a structure capable of expanding and contracting in the axial direction and absorbs only the expansion and contraction of the sensor tubes 7 and 8 in the longitudinal direction when the sensor tubes 7 and 8 are thermally expanded or contracted. Therefore, the inlet side manifold 6 is provided between the lid member 14 of the casing 2 and the inlet side manifold 6.
An anti-vibration mechanism 17 is provided for holding so as not to vibrate.

The vibration-proof mechanism 17 has a plurality of support columns 1 having one end fixed to the lid member 14 and the other end extending into the casing 2.
7a, and a metal diaphragm 17b that is connected across the other ends of the plurality of columns 17a and is connected to the inflow side manifold 6. Therefore, the inflow-side manifold 6 is supported by the anti-vibration mechanism 17 so as to be movable in the axial direction, and its lateral movement is restricted.

The bellows 4B on the downstream side also has an expandable structure like the bellows 4A on the upstream side, and when the sensor tubes 7, 8 are thermally expanded or contracted, the expansion and contraction of the sensor tubes 7, 8 in the longitudinal direction is absorbed. To do. Therefore, a vibration isolation mechanism 18 that holds the inflow side manifold 9 so as not to vibrate is provided between the lid member 15 of the casing 2 and the outflow side manifold 9.

The vibration isolating mechanism 18, like the vibration isolating mechanism 17, has one end fixed to the lid member 15 and the other end fixed to the casing 2.
It is composed of a plurality of pillars 18a extending inward, and a metal diaphragm 18b which is laterally bridged between the other ends of the plurality of pillars 18a and connected to the outflow side manifold 9. Therefore, the outflow-side manifold 9 is supported by the anti-vibration mechanism 18 so as to be movable in the axial direction, and its lateral movement is restricted.

Reference numeral 19 denotes a vibration exciter unit, which comprises a vibration exciter 20 for vibrating the intermediate portion of one sensor tube 7 and a vibration exciter 21 for exciting the intermediate portion of the other sensor tube 8. FIG. 2 is a diagram showing the configuration of the vibrator unit 19, which is a vertical cross-sectional view taken along the line II-II in FIG.

The pair of exciters 20 and 21 includes magnets 20b, 21a, and 21c on excitation coils 20a, 21a to which excitation signals are input, respectively.
21b has a configuration similar to that of a substantially electromagnetic solenoid, and the excitation coils 20a and 21a have casing main body 13
The magnets 20b and 21b are in contact with the outer circumferences of the sensor tubes 7 and 8, respectively.

Therefore, when the excitation coils 20a and 21a are excited, the vibrators 20 and 21 press the sensor tubes 7 and 8 in the radial direction (Y direction) by the electromagnetic force of the excitation coils 20a and 21a, so that the sensor tubes 7 and 8 are moved. Vibrate in the proximity or separation direction.
The vibrators 20 and 21 are usually drive-controlled so that the pair of sensor tubes 7 and 8 have a frequency (natural frequency) at which the driving force (excitation force) becomes the smallest.

Further, when bubbles are mixed in the liquid to be measured and the densities of the pair of sensor tubes 7 and 8 are not uniform, the natural frequencies of the sensor tubes 7 and 8 are out of balance. Will not match. In that case, the drive control of the vibrators 20 and 21 is switched so that the sensor tubes 7 and 8 are individually vibrated and the respective natural frequencies are obtained, as described later.

Reference numeral 22 denotes an upstream pickup unit which has two pairs of pickups which output a detection signal corresponding to the upstream amplitude of the sensor tubes 7 and 8, and is located at a position upstream of the vibrator unit 19. It is installed in. Reference numeral 23 denotes a downstream pickup unit, which has a configuration including two pairs of pickups that output detection signals according to the downstream amplitudes of the sensor tubes 7 and 8. That is, the downstream pickup unit 23 has the same configuration as the upstream pickup unit 22, and the vibrator unit 19
It is arranged at a more downstream position.

FIG. 3 is a view showing the structure of the downstream pickup unit 23, which is a vertical sectional view taken along the line III-III in FIG. The upstream pickup unit 22
Has the same configuration as the downstream pickup unit 23. The pickup units 22 and 23 have first pickups 24 and 25 that detect relative displacement between the sensor tubes 7 and 8, and second pickups 26 and 27 that individually detect amplitudes of the sensor tubes 7 and 8. Have and. The pickups 24 to 27 respectively include the sensor coil 2
The structure is substantially the same as the electromagnetic solenoid in which magnets 24b to 27b are inserted into 4a to 27a.

The first pickups 24 and 25 are mounted between brackets 28 and 29 fixed to the sensor tubes 7 and 8 and detect the displacement of the sensor tubes 7 and 8 in the vibration direction (Y direction). It is provided in parallel so that it can be done. That is, the sensor coil 25 a and the magnet 24 b are attached to the bracket 28 fixed to the sensor tube 7, and the sensor coil 24 a and the magnet 25 b are attached to the bracket 29 fixed to the sensor tube 8.

Therefore, when the sensor tubes 7 and 8 are vibrated by being excited in the Y direction, the relative displacement of the sensor tubes 7 and 8 and the sensor coils 24a and 25a and the magnets 24b,
Since 25b is relatively displaced, a voltage corresponding to the amplitude of the sensor tubes 7 and 8 is excited in the sensor coils 24a and 25a and output as a sensor signal.

When measuring the flow rate, the mass flowmeter 1 having the above configuration
In, the pair of sensor tubes 7 and 8 are
It is vibrated in the direction (Y direction) of approaching and separating by 21. The fluid to be measured supplied from an upstream pipe (not shown) reaches the manifold 6 through the bellows 4A on the upstream side of the inflow pipe 5, passes through the flow path of the manifold 6, and vibrates. Flows in. Then, the fluid that has passed through the sensor tubes 7 and 8 passes through the bellows 4B on the downstream side of the flow path of the manifold 9, and flows out from the outflow pipe 10 to a downstream side pipe (not shown).

In this way, the vibrating sensor tube 7,
When the fluid flows through 8, a Coriolis force having a magnitude corresponding to the flow rate is generated. Therefore, an operation delay occurs on the inflow side and the outflow side of the straight tubular sensor tubes 7 and 8, which causes the pickup 24 and the pickup 24 of the upstream pickup unit 22, respectively.
There is a phase difference between the output signal of 25 and the output signals of the pickups 24 and 25 of the downstream pickup unit 23.

Since the phase difference between the inflow side and the outflow side is proportional to the flow rate, the flow rate measurement control circuit 30 outputs the output signal from the upstream pickup unit 20 and the output signal from the downstream pickup unit 21. The flow rate is calculated based on the phase difference between Further, when air bubbles are mixed in the liquid to be measured and the flow rates do not flow evenly to the pair of sensor tubes 7 and 8, the natural frequencies of the sensor tubes 7 and 8 do not match. A pair of sensor tubes 7,
If the natural frequencies of No. 8 do not match, the amplitudes of the sensor tubes 7, 8 cannot be obtained sufficiently, so the shakers 20, 21
Amplify the driving force of. If the frequencies still do not match, the vibrators 20 and 21 are stopped due to insufficient driving force.

Therefore, in the present embodiment, each vibrator 20,
The drive frequency of each vibrator 20, 21 is switched so that 21 vibrates each sensor tube 7, 8 at each natural frequency. At this time, the second pickups 26 and 27 individually detect the amplitudes of the sensor tubes 7 and 8, and the sensor signals output from the second pickups 26 and 27 are added to calculate the flow rate.

Here, the configuration of the flow rate measurement control circuit 30 will be described. FIG. 4 is a block diagram showing the configuration of the flow rate measurement control circuit 30. The output signals from the pickups 24 and 25 are integrated by the integrator 31, and the flow rate calculation unit 3
It is accumulated by 2. The output signals from the pickups 26 and 27 are integrated by integrators 33 and 34, respectively, and integrated by the flow rate calculators 35 and 36. Then, the flow rate calculation unit 32
Alternatively, the signals output from the flow rate calculation units 35 and 36 are determined by the output calculation determination unit 37, and the signal from the flow rate calculation unit 32 is output as it is. However, the flow rate calculation units 35, 36
The signals output from are added and output.

Further, the signals output from the integrators 31, 33 and 34 are also supplied to the first, second and third amplitude control sections 38, 39 and 40, respectively, and the amplitude control sections 38 and 39 are also provided. , 40, integrators 31, 33, 34
Generate a drive signal based on the signal from. Then, at the time of normal flow rate measurement, the drive signal from the first amplitude control unit 38 is amplified by the amplifiers 41 and 42, and the vibration exciter 2
0,21. Further, the first amplitude control unit 38 drives the vibrators 20 and 21 so that the sensor tubes 7 and 8 vibrate at the same frequency.

However, when air bubbles flow into the sensor tubes 7 and 8 and the natural frequencies of the sensor tubes 7 and 8 do not match, the drive signal from the first amplitude controller 38 is further fed to the amplifiers 41 and 42. Is amplified. At this time, the sensor tubes 7 and 8 vibrate at the same frequency, that is, the average frequency of their natural frequencies.

Then, when the amplifiers 41 and 42 are saturated, the control mode switching signal from the first amplitude control section 38 is transmitted to the second and third amplitude control sections 39 and 4.
Output to 0. Therefore, the output of the drive signal from the first amplitude control unit 38 is stopped, and the drive signals from the second and third amplitude control units 39 and 40 are amplified by the amplifiers 41 and 42, respectively, and the shaker 20 , 21 are supplied.

As a result, the respective vibrators 20 and 21 are individually drive-controlled by the drive signals from the second and third amplitude control sections 39 and 40, and the sensor tubes 7 and 8 are respectively driven with different natural frequencies. Excite each to vibrate. FIG. 5 is a flowchart for explaining the processing executed by the flow rate measurement control circuit 30.

In step S1 (hereinafter, "step" is omitted), the flow rate measurement control circuit 30 amplifies the drive signal from the first amplitude control section 38 by the amplifiers 41 and 42 and outputs the drive signals to the shakers 20 and 21. Supplied, sensor tube 7,
8 is vibrated at a natural frequency (frequency determined by the sensor tubes 7, 8 and the mass of the fluid to be measured flowing through the sensor tubes 7, 8).

At the next step S2, it is determined whether the amplifiers 40 and 41 are in the saturated state. When the amplifiers 40 and 41 are not in the saturated state, the process proceeds to S3 and the drive signal from the first amplitude control unit 38 is supplied to the exciters 20 and 21 to control the drive of the exciters 20 and 21.

Then, in S4, the phase difference between the output signals of the first pickups 24 and 25 of the upstream pickup unit 22 and the output signals of the first pickups 24 and 25 of the downstream pickup unit 23 is read, and the sensor tube is read. The flow rate flowing through the sensor tubes 7 and 8 is calculated from the phase difference between the upstream side and the downstream side of 7 and 8.

However, when the amplifiers 40 and 41 are saturated in step S2, for example, when the bubbles are mixed in the fluid to be measured flowing through the sensor tubes 7 and 8 and a stronger driving force is required, the amplifiers 40 and 41 are saturated. Since the driving force of the devices 20 and 21 is insufficient, the process proceeds to S5, the drive signals from the second and third amplitude control units 39 and 40 are waveform-shaped from a sine wave to a rectangular wave, and the vibration exciter 20, While strengthening the driving force of 21,
The vibrators 20 and 21 are individually driven and controlled. Therefore, the vibrators 20 and 21 can vibrate the sensor tubes 7 and 8 with a stronger force.

In S6, the amplifiers 40 and 41 are again used.
Is saturated. When the drive signals from the second and third amplitude control units 39 and 40 are shaped into rectangular waves and the amplifiers 40 and 41 are not in the saturated state, the process proceeds to S3 and the processes of S3 and S4 are executed.

However, in S6, the second, third
When the amplifiers 40 and 41 are in a saturated state and the driving force of the vibrators 20 and 21 is insufficient even though the drive signals from the amplitude control units 39 and 40 of FIG. Proceeding to S7, drive control is switched to the second and third amplitude control sections 39, 40. That is, the drive signals from the second and third amplitude control units 39 and 40 are supplied to the shakers 20 and 21 to individually drive the shakers 20 and 21. As a result, the sensor tubes 7, 8
Is excited by each of the exciters 20 and 21 at its natural frequency.

In the next step S8, the output signals of the second pickups 26 and 27 of the upstream pickup unit 22 and the second pickup 2 of the downstream pickup unit 23 are output.
The flow rate is calculated from the phase difference with the output signals of 6 and 27, and the respective flow rates of the sensor tubes 7 and 8 obtained by the respective pickups 26 and 27 on the upstream and downstream sides are added.

As described above, when the amplifiers 40 and 41 are not in the saturated state, the normal drive control is performed by the first amplitude control section 38, and the vibrators 20 and 21 are simultaneously driven to drive the first pickup 24, 41. The displacement between the upstream side and the downstream side of the sensor tubes 7 and 8 is detected by 25, and the flow rate is obtained from the phase difference of this output signal.

Further, air bubbles flow into the sensor tubes 7 and 8 to increase the driving force of the vibrators 20 and 21 to increase the amplifier 40,
When 41 becomes saturated, the control mode is switched by the second and third amplitude control units 39 and 40 so as to individually drive and control the vibrators 20 and 21, and the Coriolis of the sensor tubes 7 and 8 is changed. The phase difference between the output signals of the second pickups 26 and 27 of the upstream pickup unit 22 and the output signals of the second pickups 26 and 27 of the downstream pickup unit 23, which is proportional to the force, is obtained. Since the phase difference between the upstream side and the downstream side of each of the sensor tubes 7 and 8 is proportional to the flow rate, the bubbles are mixed in the fluid to be measured, but these are added and the sensor tube 7 is added. , 8 can be obtained.

Therefore, even when the flow rate is measured in a state where the flow rates of the flow through the sensor tubes 7 and 8 due to the inflow of air bubbles are not equal, the vibration operation of the vibrators 20 and 21 is stabilized by switching the control mode as described above. Therefore, the measurement error can be reduced and the flow rate can be accurately measured regardless of the presence or absence of bubbles.

Since the vibration type density meter has the same structure as the mass flowmeter of the above-mentioned embodiment, its explanation is omitted. Further, in the above embodiment, the vibration exciter and each pickup are configured to have the same configuration as the solenoid utilizing the electromagnetic force, but the vibration exciter and the sensor having other configurations are used. Of course, it may be done.

[0050]

As described above, according to the present invention, when the pair of sensor tubes have different frequencies, the pair of exciters controls the pair of sensor tubes to individually vibrate at each natural frequency. Therefore, even if the natural frequencies of the pair of sensor tubes are unbalanced due to the inclusion of air bubbles, the flow rates of the pair of sensor tubes can be detected to accurately measure the flow rates of the pair of sensor tubes. Therefore, it is possible to prevent the vibration operation of the vibrator from stopping even if air bubbles are mixed, and stabilize the vibration operation of the vibrator to reduce the measurement error.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a Coriolis mass flowmeter as one embodiment of a vibration type measuring apparatus according to the present invention.

FIG. 2 is a vertical cross-sectional view showing a mounted state of a vibrator unit.

FIG. 3 is a vertical cross-sectional view showing a mounted state of a pickup unit.

FIG. 4 is a vertical cross-sectional view showing the configuration of a downstream pickup unit.

FIG. 5 is a flowchart for explaining processing executed by a flow rate measurement control circuit.

[Explanation of symbols]

 1 Mass Flowmeter 7, 8 Sensor Tube 19 Exciter Unit 20, 21 Exciter 22 Upstream Pickup Unit 23 Downstream Pickup Unit 24, 25 First Pickup 26, 27 Second Pickup 30 Flow Measurement Control Circuit 37 Output calculation determination unit 38 First amplitude control unit 39 Second amplitude control unit 40 Third amplitude control unit

Claims (1)

[Claims] 1. A pair of sensor tubes through which a fluid to be measured flows, a pair of vibrators for vibrating the pair of sensor tubes, and a pair of pickup units for individually detecting each displacement of the pair of sensor tubes. When the frequencies of the pair of sensor tubes detected by the pair of pickup units are different from each other, the pair of vibrators controls the pair of sensor tubes to individually vibrate at each natural frequency. A vibration type measuring device comprising: