JP2005106572A - Vibration type measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibration type measuring device uninfluenced by expansion/contraction resulting from a temperature change of a mounting conduit. <P>SOLUTION: A storage case 12 of a mass flowmeter 10 has an inflow side case 22, an outflow side case 24, and a sensor part case 26 interposed between the inflow side case 22 and the outflow side case 24. Both ends of the storage case 12 are held in the displaceable state in the longitudinal direction (X-direction) by a holding mechanism 27. The holding mechanism 27 has an aperture 33 for allowing expansion/contraction in the axial direction of the storage case 12 between the end of the storage case 12 and a step part 28d of the first guide hole 28a or a step part 29d of the second guide hole 29a. Even if the storage case 12 is expanded or contracted by a temperature change, the expansion/contraction quantity can be absorbed by the aperture 33. Hereby, application of a tensile load or a compressive load onto a sensor tube 14 stored inside the storage case 12 is prevented, and a measurement error caused by the temperature change can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vibration type measurement apparatus, and more particularly to a vibration type measurement apparatus configured to measure a flow rate or density by exciting a sensor tube to detect displacement of the sensor tube due to Coriolis force.

  For example, a Coriolis mass flow meter or a vibratory density meter is available as a vibratory measuring device that measures a physical quantity of a fluid by vibrating a pipeline supplied with the fluid. Hereinafter, the Coriolis type mass flow meter will be described.

  In this Coriolis type mass flow meter, a sensor tube through which a fluid to be measured passes is vibrated in a radial direction by a vibrator, and a displacement of the sensor tube due to a Coriolis force proportional to the flow rate is detected by a pickup. The vibration type density meter has the same configuration as the Coriolis type mass flow meter, and the sensor tube vibrates at a frequency corresponding to the density of the fluid to be measured.

  For example, in the case of a Coriolis type mass flow meter, as a conventional vibration type measuring device, a fluid is caused to flow through a pair of sensor tubes, and the pair of sensor tubes are brought close to and away from each other by the driving force of a vibrator (drive coil) It is configured to vibrate.

  Further, the vibrator and the pickup are composed of a magnet and a coil, and when a drive pulse or a positive / negative alternating voltage (AC signal) is input to the drive coil of the vibrator, it is attached to the sensor tube. The sensor tube is vibrated by applying an attractive force or a repulsive force to the drive magnet, and the displacement of the detection magnet attached to the vibrating sensor tube is detected by a detection signal output from the sensor coil (detector) of the pickup. It comes to detect.

  Since the Coriolis force acts in the vibration direction of the sensor tube and is opposite in the inlet side and the outlet side, the sensor tube is twisted, and the twist angle is proportional to the mass flow rate. Accordingly, a pickup (vibration sensor) for detecting vibration is provided at the twisted positions on the inlet side and the outlet side of the pair of sensor tubes, 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. The flow rate is being measured.

  However, when performing the flow measurement by providing the mass flow meter in a gas supply system that feeds compressed natural gas pressurized to a high pressure such as CNG (Compressed Natural Gas) used as a fuel for automobiles, for example, It is necessary to increase the pressure resistance of the sensor tube.

  However, if the thickness of the sensor tube is increased, the driving force of the vibrator that vibrates the sensor tube must be increased, and the resonance amplitude at the time of measurement decreases as the rigidity of the sensor tube increases. There is a problem that the measurement accuracy is deteriorated due to being easily influenced by disturbances, or when the flow rate is measured, the phase difference (twist angle) between the vibration sensors on the inflow side and the outflow side becomes small.

Therefore, in the conventional vibration type measuring device, by supplying the fluid to be measured into the storage case from the pressure supply hole of the sensor tube, the pressure inside and outside of the sensor tube is balanced and the pressure resistance of the sensor tube is increased. High pressure fluid can be measured without increasing the pressure. (For example, refer to Patent Document 1).
JP-A-6-331406

  Further, in the conventional vibration type measuring apparatus, when the high-pressure fluid is measured by filling the measurement case with the fluid to be measured as described above, the vibrator and the pickup are stored in the storage case. When the fluid to be measured is a flammable fluid such as fuel, it is necessary to cover the drive coil of the vibration exciter and the sensor coil of the pickup with an explosion-proof case or the like so as not to contact the fluid to be measured. It was necessary to have a configuration that did not occur.

  Furthermore, depending on the fluid to be measured, it has been necessary to provide a penetrating terminal in the storage case in order to affect the material of the magnet and coil of the vibrator and the insulation coating, or to pass the electrical wiring to the inside.

  In order to solve such a problem, it has been studied to provide a drive coil of a vibrator and a sensor coil of a pickup for inputting and outputting an electric signal outside the storage case.

  In addition, rare earth materials are often used for the magnets attached to the sensor tube, but rare earth metals are likely to combine with hydrogen, and in a hydrogen atmosphere, the magnetic force may be reduced or destroyed. It was difficult to use it in a place where it comes into contact with fluid measurement.

  Therefore, when installing a mass flow meter in the fuel supply path of the filling device that fills the fuel tank of the fuel cell vehicle with high-pressure hydrogen, a storage case that houses the sensor tube in order to reduce the pressure resistance of the sensor tube and increase the measurement accuracy If a configuration in which the fluid to be measured is filled is used, the magnet attached to the sensor tube may come into contact with hydrogen, which may cause a decrease in the magnetic force or destruction of the magnet. It was necessary to cover the magnet with a material (for example, stainless steel).

  Furthermore, in order to increase the measurement sensitivity of the sensor tube, the sensor tube is thinned to the limit that can withstand the pressure pulsation of the fluid to be measured. For this reason, the thinned sensor tube is measured by vibrating a linearly extending portion in a state where it is stored in the storage case, but the both ends are connected to the storage case or a flange coupled to the storage case. It is held so that it is not affected by external force.

However, both ends of the storage case that stores the sensor tube are fastened to the flange of the pipe line by bolts and nuts. Therefore, when axial expansion occurs due to temperature rise, an axial compressive load is applied to the storage case. Is done. As described above, in a state where an external load is applied to the storage case, an axial tensile load or a compressive load acts on the sensor tube, so that the vibration characteristics (natural frequency) of the sensor tube change, For example, this has caused an error in measuring the flow rate of a gas having a small mass such as hydrogen.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a vibration type measuring apparatus that solves the above problems.

  The invention according to claim 1 is a storage case in which a sealed space is formed, a sensor tube that is inserted into the space and through which a fluid to be measured flows, and a driving magnet attached to the sensor tube, Provided on the outer wall of the storage case, and comprising a vibration exciter comprising a drive coil for driving the drive magnet in a vibration direction, a detection magnet attached to the sensor tube, and provided on the outer wall of the storage case; And a pickup comprising a detection unit for detecting displacement of the detection magnet, wherein one end is fitted to at least one end of the storage case in a relatively displaceable manner and the other end is a pipe line A holding mechanism connected to is provided.

  According to a second aspect of the present invention, the holding mechanism includes a first holding portion having a first guide hole that is slidably fitted in one end portion of the storage case in the axial direction, and the other end of the storage case. And a second holding portion having a second guide hole that is slidably fitted in the portion in the axial direction.

  According to a third aspect of the present invention, in the state where the holding mechanism is provided with a gap allowing displacement between the end portion of the storage case and the first guide hole or the second guide hole. It has the supporting member which couple | bonds and supports 1 holding | maintenance part and said 2nd holding | maintenance part, It is characterized by the above-mentioned.

  According to the present invention, even if a pipe line to which the storage case or the vibration measuring device is attached expands or contracts due to a temperature change or the like, the expansion and contraction can be absorbed by the holding mechanism, and thus the sensor stored in the storage case. It is possible to prevent a tensile load or a compressive load from acting on the tube, stabilize the vibration characteristics of the vibration portion of the sensor tube, and suppress measurement errors.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a longitudinal sectional view of a Coriolis mass flow meter as an embodiment of a vibration type measuring apparatus according to the present invention. FIG. 2 is a longitudinal sectional view taken along line AA in FIG.

  The vibration type measuring device can be used as a vibration type density meter and a Coriolis type mass flow meter because the mass flow rate can be obtained using the density and density of the fluid to be measured. Since the vibration type density meter and the Coriolis type mass flow meter have the same configuration, this embodiment will be described in detail when used as a mass flow meter.

  As shown in FIGS. 1 and 2, the mass flow meter 10 vibrates one sensor tube 14 inserted into a sealed storage case 12 and an intermediate portion in the longitudinal direction of the sensor tube 14. The vibrator unit 16 includes an inflow side pickup unit 18 that detects displacement on the inflow side of the vibrating sensor tube 14, and an outflow side pickup unit 20 that detects displacement on the outflow side of the vibrating sensor tube 14.

  The storage case 12 includes an inflow side case 22, an outflow side case 24, and a sensor part case 26 interposed between the inflow side case 22 and the outflow side case 24.

  The storage case 12 is held in a state in which both ends can be displaced in the longitudinal direction (X direction) by the holding mechanism 27. The holding mechanism 27 includes a first holding portion 28 that holds the inflow side end portion 12a of the storage case 12 so as to be slidable in the axial direction (X direction), and an outflow side end portion 12b of the storage case 12 in the axial direction (X And a plate-like base (support member) 31 that supports the first holding unit 28 and the second holding unit 29. The base 31 is formed of the same metal material (for example, stainless steel) as the storage case 12 so that the thermal expansion coefficient is the same as that of the storage case 12.

  The base 31 prevents the first holding part 28 and the second holding part 29 from being separated from the storage case 12, and may be a resin having low rigidity. However, by increasing the rigidity, it is possible to prevent the expansion and contraction due to the heat of the pipe line from being transmitted to the storage case 12.

  The first holding portion 28 includes a first guide hole 28a in which the inflow side end portion 12a is slidably fitted in the axial direction (X direction), and a first guide communicated with the first guide hole 28a. It has a pipe connection port 28b having a smaller diameter than the hole 28a and connected to the pipe, and a leg portion 28c fastened to the base 31 by a bolt 31a. Further, a step portion 28d serving as a stopper for the inflow side end portion 12a is provided at the boundary between the first guide hole 28a and the pipe connection port 28b.

  The second holding portion 29 is communicated with the second guide hole 29a and the second guide hole 29a in which the outflow side end portion 12b of the storage case 12 is slidably fitted in the axial direction (X direction). A pipe connection port 29b having a smaller diameter than the second guide hole 29a and connected to the pipe line, and a leg portion 29c fastened to the base 31 by a bolt 31b. Further, a step portion 29d serving as a stopper for the outflow side end portion 12b is provided at the boundary between the second guide hole 29a and the pipe connection port 29b.

  A seal member (O-ring) 35 that seals between the inner periphery of the first guide hole 28a and the second guide hole 29a on the outer periphery of the inflow side end 12a and the outflow side end 12b of the storage case 12. , 37 are provided.

  The holding mechanism 27 is a gap that allows the storage case 12 to expand and contract in the axial direction between the end portion of the storage case 12 and the step portion 28d of the first guide hole 28a or the step portion 29d of the second guide hole 29a. 33. In the present embodiment, a gap 33 is formed between the step portion 28 b formed inside the first guide hole 28 a and the inflow side end portion 12 a of the storage case 12. This is because the storage case 12 is pressed to the downstream side (outflow side) by the pressure of the fluid to be measured supplied to the flow path 28 c of the first holding unit 28.

  Further, the dimension of the gap 33 in the axial direction is set to a value larger than the displacement amount of the storage case 12 that contracts within the range between the upper limit temperature and the lower limit temperature of the fluid to be measured. Therefore, even if the storage case 12 expands and contracts due to a temperature change, the expansion and contraction amount can be absorbed. Furthermore, when the rigidity of the base 31 is low, expansion and contraction of the pipe line to which the mass flow meter 10 is attached can be absorbed. As a result, a tensile load or a compressive load is prevented from acting on the sensor tube 14 stored in the storage case 12, and the vibration characteristics of the vibration portion of the sensor tube 14 are stabilized regardless of the temperature change, and the temperature change. Measurement errors due to can be suppressed.

  Further, the sensor tube 14 is formed to be thin and extend in the longitudinal direction (X direction) so as to maintain measurement sensitivity even with a fluid having a relatively small specific gravity (for example, hydrogen). The thermal expansion amount tends to be relatively large with respect to the temperature change. On the other hand, the storage case 12 that holds both ends of the sensor tube 14 has an increased pressure resistance so as to withstand the fluid pressure, and has a relatively small amount of thermal expansion with respect to a temperature change.

  Furthermore, since the storage case 12 can expand and contract in the axial direction between the first holding portion 28 and the second holding portion 29, a tensile load or a compressive load due to thermal expansion of the storage case 12 does not act, Further, since an external force due to thermal expansion or the like of the pipe line to be attached does not act, measurement errors due to temperature changes or the like can be suppressed.

  The inflow side case 22 is made of an austenitic non-magnetic stainless steel (SUS316L), a sliding portion 22a is provided on the outer periphery of the inflow side end portion 12a, and the other end of the sensor portion case 26 is provided at the other end. Is provided with a female screw portion 22b. The sliding portion 22a is formed in a cylindrical shape when viewed from the axial direction, and an inflow port 22c into which the fluid to be measured flows is provided inside the sliding portion 22a.

  The inflow side case 22 is provided such that a through hole 22d penetrating between the female screw portion 22a and the inflow port 22c extends along the center line. The through hole 22d is fitted with a flange 30 fixed to one end of the sensor tube 14 to regulate the mounting position of the sensor tube 14. The flange 30 is fastened by a bolt 34 to a fixed plate 32 fixed to the wall surface of the inflow port 22c.

  The fixing plate 32 is provided with a central hole 32 a that communicates with the inflow side end of the sensor tube 14. Further, a minute passage (not shown) for supplying a fluid to be measured is penetrated through the flange 30 in the through hole 22d and inside the sensor portion case 26 in the axial direction.

  Like the inflow side case 22, the outflow side case 24 is made of austenitic nonmagnetic stainless steel (SUS316L), and has a sliding portion 24a on the outer periphery of the outflow side end 12b. A female screw portion 24b into which the end portion of the sensor portion case 26 is screwed is provided at the end. The sliding portion 24a is formed in a cylindrical shape when viewed from the axial direction, and an outlet 24c through which the fluid to be measured flows out is provided inside the sliding portion 24a.

  The outflow side case 24 is provided such that a through hole 24d passing through between the outflow port 24c and the female screw portion 24b extends along the center line. The through-hole 24d is fitted with a flange 38 fixed to the other end of the sensor tube 14 to regulate the mounting position of the sensor tube 14.

  Further, the rotation of the flange 38 is restricted by the pin 42 of the fixing plate 40 that is formed on the inner wall of the outlet 24c and is screwed into the screw 24e. The fixing plate 40 is provided with a central hole 40 a that communicates with the outflow side end of the sensor tube 14.

  The sensor part case 26 is formed of a non-magnetic stainless steel material (SUS316L) made of austenite, and has a sensor tube insertion hole 50 extending along the center line. The sensor tube 14 is mounted at the center of the sensor tube insertion hole 50.

  Further, one end of the sensor part case 26 is provided with a male thread part 26a that is screwed into the female thread part 22b of the inflow side case 22, and the other end of the sensor part case 26 is provided with a female thread of the outflow side case 24. A male screw portion 26b to be screwed into the portion 24b is provided. The sensor case 26 is provided with vibrators 52 and 54, inflow side pickups 56 and 58, and outflow side pickups 60 and 62. The vibrators 52 and 54 are attached so as to face an intermediate position in the longitudinal direction (X direction) of the sensor tube 14, and the inflow side pickups 56 and 58 and the outflow side pickups 60 and 62 include the vibration exciter. They are arranged symmetrically on the inflow side and the outflow side which are separated from each other by a predetermined distance.

  In the recesses 26e and 26f provided on the upper surface 26c and the lower surface 26d of the sensor case 26, the drive coils 52a and 54a of the vibrators 52 and 54, the inflow side pickups 56 and 58, and the sensors of the outflow side pickups 60 and 62 are provided. Coils 56a, 58a, 60a and 62a are fitted. Therefore, the drive coils 52a and 54a and the sensor coils 56a, 58a, 60a, and 62a are attached so as to be close to the magnets 52b, 54b, 56b, 58b, 60b, and 62b. Furthermore, since the drive coils 52a and 54a and the sensor coils 56a, 58a, 60a and 62a are provided outside the storage case 12, the storage case 12 is filled with a combustible gas such as CNG or hydrogen. However, since there is no possibility of sparks from the electrical system, safety is ensured.

  The magnets 52b, 54b, 56b, 58b, 60b, and 62b of the vibrators 52 and 54, the inflow side pickups 56 and 58, and the outflow side pickups 60 and 62 are attached to the outer periphery of the sensor tube 14. Therefore, the intermediate portion in the longitudinal direction of the sensor tube 14 is driven in the Z direction by the electromagnetic force from the drive coils 52a and 54a. The phase difference between the inflow side and the outflow side of the sensor tube 14 that vibrates in the Z direction is proportional to the flow rate, and the sensor coils 56a, 58a, 60a, A detection signal is output by 62a.

  The vibrators 52 and 54 have a configuration in which drive coils 52a and 54a and magnets 52b and 54b are combined, and a magnetic field generated by alternately applying positive and negative alternating voltages (AC signals) to the drive coils 52a and 54a. On the other hand, when the magnets 52b and 54b are attracted or repelled, the middle portion of the sensor tube 14 is vibrated in the lateral direction (Z direction). In addition, the inflow side pickups 56 and 58 and the outflow side pickups 60 and 62 have a configuration in which sensor coils 56a, 58a, 60a, and 62a and magnets 56b, 58b, 60b, and 62b are combined in the same manner as the vibrators 52 and. When a relative displacement occurs between the sensor coils 56a, 58a, 60a, 62a and the magnets 56b, 58b, 60b, 62b, a detection signal corresponding to (displacement speed) is output.

  Each coil 52a, 54a, 56a, 58a, 60a, 62a is held by a coil holder 64, and each coil holder 64 is fixed to the sensor case 26 by a bolt 66. Furthermore, cover members 68 and 70 for protecting the coils 52a, 54a, 56a, 58a, 60a, and 62a are attached to the upper surface 26c and the lower surface 26d of the sensor case 26.

  In addition, the inflow side case 22, the outflow side case 24, and the sensor unit case 26 have sufficient pressure resistance so that they can withstand pressure even when a high pressure fluid is supplied. Further, high-pressure fluid is introduced into the through holes 22c and 24c through which the sensor tube 14 is inserted and the sensor tube insertion hole 50, so that there is almost no pressure difference between the inside and the outside of the sensor tube 14. Yes.

  Therefore, in the mass flow meter 10, the fluid to be measured is filled in the space on the outer peripheral side of the sensor tube 14 as described above, and the pressure difference between the inside and the outside of the sensor tube 14 becomes small. By reducing the thickness, the driving force of the vibrator 16 can be reduced, and the current value flowing through the drive coils 52a and 54a of the vibrators 52 and 54 can be reduced to save power consumption. it can. Further, the sensor tube 14 vibrates in the Z direction by the exciting force of the vibrators 52 and 54.

  Furthermore, since the sensor tube 14 is made of a thin metal pipe, deformation and displacement of the sensor tube 14 due to Coriolis force is increased, and a larger output than the inflow side pickups 56 and 58 and the outflow side pickups 60 and 62 is obtained. The SN ratio can be improved and the measurement accuracy is improved.

  The drive coils 52a, 54a and the sensor coils 56a, 58a, 60a, 62a are connected to a flow rate measurement control circuit 72. The flow rate measurement control circuit 72 includes an intrinsically safe explosion-proof barrier circuit, an excitation / time difference detection circuit, a Young's modulus / A V / F conversion circuit, an output circuit, a power supply circuit, an attenuation rate detection circuit, a discrimination circuit, a control circuit (each not shown), and the like are included.

  When the flow rate is measured, in the mass flow meter 10 configured as described above, the vibrators 52 and 54 are driven by the flow rate measurement control circuit 72, and the sensor tube has a period and amplitude according to the vibration characteristics (natural frequency) of the sensor tube 14. 14 is vibrated in the vertical direction (Z direction).

  Thus, when a fluid flows through the vibrating sensor tube 14, a Coriolis force having a magnitude corresponding to the flow rate is generated. Therefore, an operation delay occurs between the inflow side and the outflow side of the straight tubular sensor tube 14, thereby causing a phase difference in output signals between the inflow side pickups 56 and 58 and the outflow side pickups 60 and 62.

  Since the phase difference between the inflow side output signal and the outflow side output signal is proportional to the flow rate, the flow rate measurement control circuit 72 calculates the flow rate based on the phase difference. Therefore, when the displacement of the sensor tube 14 is detected by the inflow side pickups 52 and 54 and the outflow side pickups 56 and 58, the phase difference due to the vibration of the sensor tube 14 is converted into a mass flow rate by the flow rate measurement control circuit 72. The

  As described above, in this embodiment, the influence of the thermal expansion of the attachment pipe line is received by the base 31 and can be absorbed by the gap 33 even if the storage case 12 expands or contracts due to a temperature change or the like. It is possible to prevent a tensile load or a compressive load from acting on the sensor tube 14 accommodated in the sensor tube, stabilize the vibration characteristics of the vibration portion of the sensor tube 14, and suppress measurement errors.

  In the above embodiment, an example in which the base (support member) 31 is provided as the holding mechanism of the present invention has been shown. However, the first holding unit 28 and the second holding unit 29 are connected to the first holding unit 28 from the storage case 12. If a retaining mechanism is provided, the base (support member) 31 may not be provided. In this case, the thermal expansion of the attachment pipe line is absorbed by the gap 33.

  In the above embodiment, the first holding portion 28 and the second holding portion 29 are provided at both ends of the storage case 12, but only the first holding portion 28 is provided at one end of the storage case 12. It is also possible to provide a joint for attaching the pipe line directly on the other end side.

  In the above-described embodiment, the flow rate measurement is performed using a combustible gas such as CNG as the fluid to be measured. However, the present invention is not limited to this, and the present invention can be applied to measurement of other high-pressure and high-temperature fluids. Of course.

It is a longitudinal cross-sectional view of the Coriolis type | mold mass flowmeter as one Example of the vibration type measuring apparatus which becomes this invention. It is a longitudinal cross-sectional view which follows the AA line in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Mass flow meter 12 Storage case 14 Sensor tube 16 Exciter unit 18 Inflow side pickup unit 20 Outflow side pickup unit 22 Inflow side case 24 Outflow side case 26 Sensor part case 27 Holding mechanism 28 1st holding part 29 2nd Holding part 31 Base 50 Sensor tube insertion holes 52, 54 Exciters 52a, 54a Drive coils 52b, 54b, 56b, 58b, 60b, 62b Magnets 56, 58 Inflow side pickups 56a, 58a, 60a, 62a Sensor coils 60, 62 Outlet pickup 68, 70 Cover member 72 Measurement control circuit

Claims (3)

A storage case in which a sealed space is formed;
A sensor tube that is inserted into the space and through which the fluid to be measured flows;
A vibration exciter comprising a drive magnet attached to the sensor tube and a drive coil provided on an outer wall of the storage case and driving the drive magnet in a vibration direction;
A pickup comprising a detection magnet attached to the sensor tube, and a detection unit provided on an outer wall of the storage case and detecting a displacement of the detection magnet;
In a vibration measuring device having
A vibration type measuring apparatus, wherein a holding mechanism is provided in which one end is fitted to at least one end of the storage case in a relatively displaceable manner and the other end is connected to a pipe line. The holding mechanism is
A first holding portion having a first guide hole fitted to one end portion of the storage case so as to be slidable in the axial direction;
A second holding portion having a second guide hole that is slidably fitted in the other end portion of the storage case in the axial direction;
The vibration type measuring apparatus according to claim 1, comprising: The holding mechanism is
The first holding part and the second holding part are coupled in a state where a gap allowing displacement is provided between an end of the storage case and the first guide hole or the second guide hole. The vibration type measuring apparatus according to claim 2, further comprising a supporting member for supporting.

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