JPH0749983B2 - Mass flow meter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter, and more particularly to a mass flow meter configured to eliminate the influence of external vibration from peripheral equipment.

2. Description of the Related Art As a mass flow rate type for measuring the mass flow rate of a fluid to be measured, there is a flow meter that directly measures the mass flow rate by using the Coriolis force generated when a fluid is flown in an oscillating sensor tube.

In this type of mass flowmeter, as described in JP-A-54-52570, a fluid is caused to flow through an approximately U-shaped sensor tube, and the sensor tube is vertically vibrated by the driving force of an exciter (excitation coil). It is configured to let. The Coriolis force acts in the vibration direction of the sensor tube, and since the inlet side and the outlet side are in opposite directions, the sensor tube is twisted, and this twist angle is proportional to the mass flow rate. Therefore, pickups (vibration sensors) that detect vibration are provided at the twisting positions on the inlet side and the outlet side of the sensor tube, and the time difference between the output detection signals of both sensors is measured to measure the twist of the sensor tube, that is, the mass flow rate. is doing.

Problem to be Solved by the Invention The mass flowmeter is usually provided in the middle of a pipe through which a fluid to be measured is fed, and the inflow side and the outflow side are supported by the pipes, respectively. However, a thin tube having a small diameter is used in a piping path through which only a relatively small amount of fluid flows, or a flexible tube (synthetic resin) is used when the pressure is low. When the conduit is formed by such thin tubes and flexible tubes, the mass flowmeter cannot be supported by the conduit, and the mass flowmeter is fixed to the floor or a bracket that is supported at a predetermined height by columns or the like. It will be placed on the base.

However, when the mass flowmeter is placed on the fixed base as described above, various heavy equipments (robots, presses, cranes, forklifts, compressors, machine tools, etc.) are installed in, for example, factories. Therefore, various external vibrations propagate to the mass flowmeter via a fixed base such as a floor or a bracket. On the other hand, since the Coriolis mass flowmeter described above has a structure in which the sensor tube is vibrated vertically to measure the flow rate, external vibration (mainly vertical vibration) is applied to the sensor tube or pickup (vibration sensor). If it is transmitted, accurate flow rate measurement cannot be performed, which causes a problem that the measurement accuracy decreases.

Figure 5 shows 10 to 1000Hz on the floor where the mass flowmeter is installed.
The change in the phase difference between the inflow side and the outflow side detected by the pickup when the flow rate is zero is represented by a signal output (%) when a certain degree of vertical vibration is applied. It can be seen from Fig. 5 that the signal output (phase difference between the inflow side and the outflow side) fluctuates within a maximum of ± 1% in the process of changing the external vibration from 10 to about 1000 Hz. However, since the flow rate is zero, Coriolis force does not act on the sensor tube,
Originally, the signal output should be zero. Therefore, the vibration characteristics as shown in Fig. 5 can be measured by the signal output ±
The range of 1% is set to be measured as zero flow rate, that is, zero flow rate is output even if a signal output of ± 1% or less with respect to zero signal output is obtained during flow rate measurement.
As a result, in the conventional mass flowmeter, the signal output ±
It was not possible to measure a minute flow rate of 1% or less, and as a result, there was a problem that the measurement range of the minute flow rate region was narrowed.

Therefore, an object of the present invention is to provide a mass flowmeter that solves the above problems by making the excitation direction of the sensor tube and the direction of external vibration different and preventing external vibration from propagating to the sensor tube, the pickup, and the like. To do.

Means for Solving the Problems The present invention provides a sensor tube through which a fluid to be measured passes, a vibrator provided to vibrate the sensor tube in a substantially horizontal direction, and a sensor vibrated by the vibrator. A pickup that detects a substantially horizontal displacement of the sensor tube due to a Coriolis force generated according to the flow rate of the fluid to be measured flowing in the tube, and a support member that supports the inflow side and outflow side ends of the sensor tube. A vibration damping member that is provided between the support member and the fixed base and absorbs vibration propagating from the fixed base.

Action Generally, a vertical vibration component is transmitted to external vibration generated by the operation of peripheral devices. On the other hand, in the present invention, since the vibration direction of the sensor tube by the vibration exciter is the horizontal direction orthogonal to the lower part vibration, when the displacement due to the Coriolis force of the sensor tube is detected, it is less susceptible to the external vibration. There is. Furthermore, since the support member that supports the sensor tube is installed on the fixed base via the vibration isolator, the external vibration is absorbed by the vibration isolator and the external vibration is buffered.

Embodiment FIG. 1 and FIG. 2 show an embodiment of the mass flowmeter according to the present invention.

In both figures, the mass flowmeter 1 is roughly composed of a flow rate measuring unit 2, a vibration damping table 3 on which the flow rate measuring unit 2 is placed, and a vibration damping member 4 that elastically supports the vibration damping table 3.

The flow rate measuring unit 2 has a sensor tube 5, a pair of vibrators 6a and 6b, and pickups 7a and 7b, which are housed in a cylindrical case 8. A disk-shaped bottom plate 9 is fitted into the lower opening of the case 8, and the case 8 is fitted to the outer periphery of the bottom plate 9 with screws 10.
The lower part of is fastened. The bottom plate 9 is fixed to the anti-vibration table 3 with a fixing bolt 11 inserted from the bottom side of the anti-vibration table 3 screwed thereto and in contact with the upper surface of the anti-vibration table 3.

Further, a disc-shaped lid 12 is fitted in the opening of the case 8 at the obtaining portion. A step portion 12a with which the upper end of the case 8 contacts the outer periphery of the lid 12
The lid 12 is fastened with a screw 13 screwed from the outer periphery of the case 8. Here, the case 8, the bottom plate 9 and the lid 12 constitute a supporting member for supporting the ends of the sensor tube 5 on the inflow side and the outflow side. On the upper surface of the lid 12, an inflow port 14 through which the measured fluid flows and an outflow port 15 through which the measured fluid that has passed through the sensor tube 5 flows out are bored. As shown by the broken line in FIG. 1, an upstream pipe 16 is connected to the inflow port 14 via a joint 17, and a downstream pipe 18 is connected to the outflow port 15 via a bristle 19.

Since the pipes 16 and 18 allow only a small amount of fluid to flow, they are thin pipes having a small diameter and do not have sufficient strength to support the mass flowmeter 1. Therefore, the mass flowmeter 1 is installed on the floor surface (fixed base) 20, and the pipes 16 and 18 are connected to the upper part of the mass flowmeter 1.

The sensor tube 5 is formed in a J shape when viewed from the side and has a straight pipe portion 5a on the inflow side that extends parallel to the hanging direction.
From the straight pipe portion 5b on the outflow side, the curved portions 5c and 5d curved in a U shape from the lower ends of the straight pipe portions 5a and 5b, and the inverted U-shaped connecting portion 5e that connects the curved portions 5c and 5d. Become. Further, the upper end of the straight pipe portion 5a on the inflow side is fitted in the tubular sleeve 21, and the sleeve 21 is fitted in the hole 14a inserted into the inflow port 14. The upper end of the straight pipe portion 5b on the outflow side is fitted into the sleeve 22, and the sleeve 22 has a hole 15 communicating with the outflow port 15.
Mates with a. The sleeves 21 and 22 hold the sensor tube 5 and also function as a sealing material that seals between the holes 14a and 15a.

A connector box 23 is fixed to the upper surface of the lid 12, and a plurality of cords 24 from the vibrators 6a and 6b and the pickups 7a and 7b are drawn therein. The exciters 6a and 6b have substantially the same structure as the electromagnetic solenoid, and the magnets 6a ₁ and 6b ₁ provided at the lower ends of the straight pipe portions 5a and 5b of the sensor tube 5 and the magnets 6a ₁ and 6b ₁ are horizontally arranged. It is composed of coils 6a ₂ and 6b ₂ driven in the (X direction). The pickups 7a and 7b have the same structure as the vibrators 6a and 6b, and are magnets 7a ₁ and 7b ₁ and magnets 7a ₁ and 7b ₁ provided in the middle portions of the straight pipe portions 5a and 5b.
It is composed of coils 7a ₂ and 7b ₂ that generate a voltage according to the relative displacement between the and, and detects the horizontal displacement of the straight pipe portions 5a and 5b.

Reference numeral 25 denotes a first support plate, the upper end portion of which penetrates the straight pipe portions 5a and 5b, and which is fixed to the outer periphery of the straight pipe portions 5a and 5b by brazing or the like. 26 is a second support plate, which is the connecting portion 5e and the bending portion 5
It is mounted between c and 5d and is fixed so as to hold both ends of the connecting portion 5e. Therefore, the straight pipe portions 5a, 5b are
When the lower end of is vibrated, the straight pipe portions 5a and 5b vibrate in the horizontal direction with the first support plate 25 as a fulcrum and the curved portions 5c and 5d with the second support plate 26 as a fulcrum. In this way, the straight pipe portions 5a, 5b of the sensor tube 5 vibrate in the direction orthogonal to the external vibration in the vertical direction, and thus are less susceptible to the external vibration. Then, the pickups 7a and 7b are vibrated straight pipe portions 5a and 5b.
Since the horizontal displacement due to the Coriolis force proportional to the flow rate flowing inside is detected, the vertical component of external vibration is not detected, and the displacement of the straight pipe portions 5a, 5b is accurately detected according to the flow rate.

27 is the sensor tube 5, the vibrators 6a and 6b, and the pickup 7
It is a column that supports a and 7b, and is provided so as to extend vertically between the bottom plate 9 and the lid 12. That is, the column 27 is the upper end
27a is press-fitted into a hole 12b provided on the lower surface of the lid 12, and the lower end 27a
The b is fitted into the hole 9a of the bottom plate 9 and is held in the horizontal direction without play. Further, the male thread portion of the bolt 28 inserted from the lower surface side of the bottom plate 9 is screwed into the female thread portion provided at the lower end of the column 27, and the column 27 is pulled downward by a predetermined tension by tightening the bolt 28. ing.

Flat portions 27c and 27d are provided on both sides of the pillar 27, and the flat portion 27c
Pedestals 27e and 27f are in contact with c and 27d. 28a to 28d are brackets for supporting the coil portions 6a ₂ and 6b _{2 of} the exciters 6a and 6b and the coils 7a ₂ and 7b ₂ of the pickups 7a and 7b, and the bases 27e and 27f, respectively.
It is stopped by screws 29. Each screw 29 penetrates through the pedestals 27e, 27f and is screwed into a screw hole (not shown) provided in the flat surface portions 27c, 27d of the support column 27.

30 is a bracket for supporting the sensor tube 5, the base end side of which is screwed to a pedestal 27g projecting forward from the column 27,
The tip side is fixed to the second support plate 26.

The flow rate measuring unit 2 having the above-described configuration is mounted so as to stand upright on the vibration isolation table 3 supported by the four vibration isolation members 4.
The anti-vibration member 4 is made of elastic rubber and has an upper surface flange.
4a, a lower surface flange 4b that abuts on the floor surface 12, and a tapered neck portion that surrounds between the upper surface flange 4a and the lower surface flange 4b.
It consists of 4c. An engaging recess 4d is provided at the center of the upper surface flange 4b, and an opening 4e is provided on the bottom surface side of the lower surface flange 4b. The outer diameter of the lower surface flange 4b is larger than the outer diameter of the upper surface flange 4a, and the vibration damping member 4 is formed in a bell shape. A disc 31 having a small hole 31a is fitted in the opening 4e.

Therefore, the space 32 formed inside the vibration isolation member 4 is
However, the air in the space 32 can be supplied and exhausted through the small holes 31a. Therefore, anti-vibration member
14 has an air spring structure, and elastically absorbs the vibration propagated from the floor surface 12 due to the elasticity of the material itself and the pressure of the air in the space 32.

33 is a mounting plate, which is a circular hole that fits on the bottom of the vibration isolator 33
It has a and is integrally fixed to the vibration isolator 4.
Further, the mounting plate 33 has a square shape when viewed from above, and bolts that are screwed into nuts 34 (shown by broken lines in FIG. 1) embedded in the floor 12 at the four corners protruding from the outer periphery of the vibration isolator 4. 35 is inserted.

Therefore, each vibration isolation member 4 is fixed to the floor surface via the mounting plate 33. In addition, a pressing plate is attached to the upper surface flange 4a of the vibration isolation member 4.
36 comes into contact, and a washer 37 is provided between the holding plate 36 and the vibration isolation table 3.
Intervenes. Then, a hexagon bolt 38 (not shown in the hexagon head) inserted from the upper surface of the vibration isolator 3 is screwed into the center of the holding plate 36, and the vibration isolator 4 is integrally attached to the vibration isolator 3. There is.

When measuring the flow rate, the vibrators 6a and 6b vibrate the straight pipe portions 5a and 5b of the sensor tube 5 in the horizontal direction as described above, and the pair of straight pipe portions 5a and 5b are vibrated.
It vibrates in the horizontal direction (X direction) so that a and 5b come close to or away from each other. The fluid to be measured from the upstream pipe 16 flows into the straight pipe portion 5a of the sensor tube 5 that vibrates in this way, and then enters the curved portion.
It passes through 5c, the connecting portion 5e, the curved portion 5d, and the straight pipe portion 5b, and flows out from the outflow port 15 to the downstream side pipe 18. A Coriolis force having a magnitude proportional to the flow rate is generated in the straight pipe portions 5a and 5b, and opposite Coriolis forces are generated on the inflow side and the outflow side.

This causes a time delay between the straight pipe portions 5a and 5b,
This is detected as a phase difference between the output signal of the pickup 7a and the output signal of 7b. The details of the principle of flow rate measurement can be found, for example, in Japanese Patent Application Laid-Open No.
Since it is the same as that of −262526, it is omitted here.

However, when the mass flowmeter 1 having the above-mentioned configuration is installed on the floor surface of a factory, for example, vibration from peripheral equipment causes the floor surface to vibrate.
Propagated through 12.

However, in this embodiment, since the vibration isolator 4 having the air spring structure is provided at the bottom of the flow rate measurement unit 2, external vibration from the floor 12 causes the air pressure in the space 23 of the vibration isolator 4 and the vibration isolator. 4 is elastically absorbed by the elasticity of itself. Therefore, the external vibration (mainly the vertical vibration component) does not propagate to the flow rate measurement unit 2, and the vibration isolation member 4 effectively insulates the external vibration.

In addition, the vertical component of the external vibration is transmitted through the vibration-proof base 3 to the case.
Even if it propagates to the support members such as 8, the bottom plate 9, the lid 12, the straight pipe portions 5a and 5b of the sensor tube 5 are excited in the horizontal direction orthogonal to the vibration component, and the pickups 7a and 7b are generated in the horizontal direction. Since the displacement of the straight pipe portions 5a and 5b due to the Coriolis force is detected, the flow rate can be measured with almost no influence of external vibration. Therefore, the mass flowmeter 1 can accurately measure the flow rate even when the mass flowmeter 1 is installed on the floor surface where external vibration is likely to propagate.

FIG. 3 shows a floor surface 12 on which the mass flowmeter 1 according to the present invention is installed.
Inflow side straight pipe part 5a detected by a pickup at zero flow rate when external vibration of about 10 to 1000 Hz is applied to
The signal output (%) represents the displacement of the phase difference between the outflow side straight pipe portion 5b. From the experimental results shown in FIG. 3, it can be seen that even if the external vibration is continuously changed from 10 to 1000 Hz, the signal output during that period is substantially zero. Therefore, the external vibration from the floor surface 12 is hardly propagated to the flow rate measurement 2, and the dead zone of the signal output is minute but can be regarded as substantially zero.

Further, it is apparent from FIG. 3 that the dead zone measured when the flow rate is zero is much narrower than the conventional experimental result shown in FIG. Therefore, in the mass flowmeter 1, the measurement range can be expanded to the minute flow rate range, and the flow rate measurement accuracy can be further improved.

Although the sensor tube is formed in a J shape in the above embodiment, it goes without saying that a sensor tube having a shape other than this may be used. For example, instead of the sensor tube 5 shown in FIGS. 1 and 2, the U-shaped sensor tube of the above-mentioned Japanese Patent Laid-Open No. 54-52570 described above in the prior art has a lid 12 at the inflow side and outflow side ends. Mounted on the sensor tube, the straight pipe part of this sensor tube is extended in parallel in the vertical direction, and the U-shaped tip bend part is horizontally excited by a shaker. The phase difference due to the horizontal displacement from the straight pipe portion may be detected by the pickup. Further, the straight pipe portion of the sensor tube may be extended not in the vertical direction but in other directions such as the horizontal direction.

Furthermore, as another modification, a mass flowmeter 41 shown in FIG. 4 can be considered. In FIG. 4, the mass flowmeter 41 has a flow measurement unit 44 provided laterally from a U-shaped sensor tube 43 on a vibration isolation table 42 supported by a vibration isolation member 4. 45
Is a disk-shaped base having an inflow port 45a and an outflow port 45b. The sensor tube 43 includes an inflow side straight pipe part 43a located at a lower side connected to the inflow port 45a, and an outflow side straight pipe part located directly above the inflow side straight pipe part 43a and connected to the outflow port 45b. 43b
And a curved portion 43c connecting the straight pipe portions 43a and 43b.

A cylindrical case 47 that constitutes a support member together with the base 45 is provided between the bases 45 and 46 on both sides, and a pair of pickups 48, 49 and a vibrator 50 are supported in the case 47. . The vibrator 50 vibrates the curved portion 43c of the sensor tube 43 in the horizontal direction (X direction), and the pickups 48 and 49 detect the displacement of the straight pipe portions 43a and 43b which vibrate in the same direction. Incidentally, since the Coriolis force is generated in the opposite direction between the inflow side straight pipe portion 43a and the outflow side straight pipe portion 43b, the signal outputs of the pickups 48 and 49 have a phase difference, which is proportional to the flow rate.

As described above, even in the mass flowmeter 41 that vibrates the straight pipe portions 43a and 43b in the same direction, accurate flow rate measurement can be performed without being affected by external vibration, as in the above-described embodiment.

Further, in the above-mentioned embodiment, the description was made using the vibration isolating member having the air spring structure, but the present invention is not limited to this, and any vibration isolating member having another configuration may be used as long as it is a configuration that absorbs external vibration well. Of course it's good.

Although the mass flowmeter 1 is mounted on the floor surface 12 in the above embodiment, the mass flowmeter 1 is mounted on the fixed base (bracket or stand) fixedly provided on the floor surface 12. The present invention can be applied even when it is attached.

It should be noted that in the above-described embodiment, the vibrator is provided so as to horizontally vibrate the straight tube portion of the sensor tube, and the horizontal displacement of the sensor tube is detected by the pickup. The same effect can be obtained by vibrating the pipe section.

EFFECTS OF THE INVENTION As described above, in the mass flowmeter according to the present invention, since the vibration direction of the sensor tube by the vibrator is the horizontal direction orthogonal to the vertical external vibration, the displacement of the sensor tube due to the Coriolis force is also horizontal. The output signal of the pickup can be prevented from being affected by external vibration. Further, since the support member that supports the sensor tube is supported by the vibration isolator, even if the external vibration propagates to the fixed base, the vibration isolator can absorb the external vibration, and the external vibration is the above-mentioned support member or the like. It is possible to satisfactorily prevent the measurement accuracy from being deteriorated by being transmitted to the user. Further, since the flow rate can be measured in a minute flow rate range and the measurable range can be further widened, the flow rate measurement accuracy can be further improved.

[Brief description of drawings]

FIG. 1 is a front vertical sectional view of an embodiment of a mass flowmeter according to the present invention, FIG. 2 is a side vertical sectional view thereof, and FIG. 3 is a signal when an external vibration is applied to the mass flowmeter of the present invention. FIG. 4 is a diagram showing a change in output, FIG. 4 is a perspective view of a modified example of the present invention, and FIG. 5 is a diagram showing a change in signal output when external vibration is applied to the conventional mass flowmeter. 1,41 ... Mass flow meter, 2 ... Flow rate measuring unit, 3 ... Vibration isolation table, 4 ...
Anti-vibration member, 5,43 ... Sensor tube, 6a, 6b, 50 ... Vibrator,
7a, 7b, 48, 49 ... Pickup, 8, 47 ... Case, 9 ... Bottom plate, 12 ... Lid, 16 ... Upstream piping, 18 ... Downstream piping, 20 ... Floor, 27 ... Struts, 31 ... Disc, 32 ... Space, 33 ... Mounting plate, 45, 4
6 ... Base.

Claims (1)

[Claims] 1. A sensor tube through which a fluid to be measured passes, an exciter provided to vibrate the sensor tube in a substantially horizontal direction, and an object to be measured flowing in the sensor tube vibrated by the exciter. A pickup that detects a displacement of the sensor tube in a substantially horizontal direction due to a Coriolis force generated according to a flow rate of a fluid, a support member that supports an inflow side end and an outflow side end of the sensor tube, and a support member fixed to the support member. A mass flowmeter, comprising: a vibration damping member provided between the fixed base and the base for absorbing vibration propagating from the fixed base.