JPH0629689Y2 - Mass flow meter - Google Patents

Description

TECHNICAL FIELD The present invention relates to the structure of a curved conduit of a Coriolis mass flowmeter.

Prior Art FIG. 4 is a block diagram for explaining the operating principle of a Coriolis flowmeter. In the figure, 1 is a U-shaped curved conduit through which a fluid to be measured flows, and its inflow and outflow ends are fixed to a support member 2. ing.
A magnet 5 for exciting the curved conduit 1 around the Y-Y 'axis on the support member 2 is arranged via a holding plate 6 at a position where it intersects with the axis of symmetry XX' at the tip of the curved conduit 1. An electromagnetic coil 4, which is opposed to the magnet 5 and gives an electromagnetic force, has one end supported by the support member 2.
It is arranged at the other end on the XX 'axis of the reciprocating member 3 fixed to. Since the reciprocating member 3 and the curved conduit 1 are made equal to the natural vibration around the YY 'axis, the supporting member 2 vibrates in a tuning fork shape. When a flow in the Q direction is given under such vibration, Coriolis force is generated in the fluid flowing through the U-shaped curved conduit 1. The magnitude of this Coriolis force is proportional to the mass flow rate of the fluid flowing in the curved conduit 1. The direction of the force is the vector product direction of the fluid motion direction and the angular velocity around the YY 'axis. Since the flow direction of the fluid is opposite between the inflow side and the outflow side, the Coriolis force is generated as a fluctuating torque having a frequency equal to the vibration frequency in a form superimposed on the amplitude of the drive vibration. Since this torque is applied to the vibration of the curved conduit 1 around the YY 'axis, the position is detected as a light change by the photodetector 7 and the light shielding plate 8 fixed at the symmetrical position of the arm of the U-shaped curved conduit 1. Then, the time difference between the detection signals of both arms passing through the reference surface of the curved conduit 1 is obtained. The curved conduit 1 of the Coriolis flowmeter is usually made of a metal tube having a touch resistance such as stainless steel.

Problems of Prior Art As described above, in the Coriolis mass flowmeter shown in FIG. 4, the Coriolis force is expressed as a vector product of the rotational angular velocity about the YY ′ axis and the mass flow rate, and The Coriolis force imparts an oscillating moment about the axis of symmetry XX 'of the U-shaped curved conduit. This vibration moment also balances the torsional torque of the U-shaped curved conduit. On the other hand, the twisting torque is proportional to the spring constant of the U-shaped conduit and the twisting angle around the axis of symmetry XX '. Therefore, the mass flow rate is proportional to the torsion angle and the spring constant. That is, in the vibration type Coriolis flowmeter, a change in the spring constant of the conduit causes an error in the measured mass flow rate. Also, the spring constant is inversely proportional to the Young's modulus of the U-shaped curved conduit, and the Young's modulus changes almost inversely proportionally to the temperature in a certain temperature range. The temperature of the conduit is detected to correct the change in the spring constant. Further, the U-shaped curved conduit is usually formed by bending stainless steel, but there is a problem that corrosion may occur along the sliding surface of the crystal grain boundary caused by the bending due to an acid, an alkaline liquid or the like. is there. However, although chemically stable synthetic resin is effective as a material that is stable to acids and alkaline liquids, the synthetic resin tends to cause creep, and if used for a long period of time, the supporting part becomes unstable due to deformation, and the measurement accuracy of mass flow rate is high. The other problem that was worsened.

Means for Solving Problems A U-shaped curved conduit that is excited by a natural frequency has a double structure. The U-shaped curved conduit has a metal tube outside and a synthetic resin tube inside. A metal having a small change in temperature, such as an Elinvar alloy such as nickel span C, a synthetic resin tube made of a fluororesin such as Teflon, and a U-shaped curved conduit that has a small change in natural frequency with respect to temperature changes and has high touch resistance. The end of the curved pipe is enlarged to form an enlarged pipe portion, and the enlarged pipe is inserted into the protruding pedestal of the fixing metal fitting that is in close contact with the inner surface of the enlarged pipe portion, and the elastic collar is pressed from the outside of the enlarged pipe portion. By fixing via
The pressure exerted on the synthetic resin pipe is reduced to reduce the amount of creep, and even if the synthetic resin pipe creeps, the elasticity of the holding collar virtually removes the creep, which is stable for a long time, has a wide operating temperature, and is highly active. An object is to provide a flowmeter that is strong in measuring chemical liquids.

Embodiment FIG. 1 is a block diagram showing an outline of the present invention. The parts having the same functions as those of the conventional example shown in FIG. In FIG. 1, 9 is a fixed portion of a U-shaped curved conduit, 11 is a U-shaped compound curved conduit according to the present invention, and the fixed portion 9 is shown in an enlarged sectional view in FIG. As shown in FIG. 2, the U-shaped compound curved conduit 11 has a double structure, and the outer tube of the U-shaped compound curved conduit 11 is composed of a metal tube 111 made of an Erinver alloy such as nickel span C. The inner tube is composed of a synthetic resin tube 112 such as 4-fluorine resin. The metal tube 111 and the synthetic resin tube 112 are in close contact with each other and have an integrated structure. The metal pipe 111 and the synthetic resin pipe 112 are joined by an adhesive, but the synthetic resin pipe 1
Especially when 12 is 4 fluororesin, 4 fluororesin has extremely high chemical stability, so that there is no suitable adhesive and it cannot be adhered without surface treatment of 4 fluororesin.
Surface treatment methods include the sodium-ammonia method and the sodium-naphthalene-tetrahydrofuran method. The former utilizes the fact that 4 fluororesin is slightly eroded by a liquid in which metallic sodium is dissolved in liquid ammonia. Metal sodium is added to cooled liquid ammonia at a weight ratio of 1% and dissolved therein. The fluororesin is immersed for a short time, washed with water and dried. The latter utilizes the fact that a solution of a sodium-naphthalene complex compound in tetrahydrofuran erodes tetrafluororesin. Dissolve naphthalene in tetrahydrofuran and add metal sodium or sodium disversion in the same mole as naphthalene. The resin is immersed for about 15 minutes, washed with acetone, washed with water and dried. In the present invention, the outer wall surface of the 4 fluororesin tube having an outer diameter slightly smaller than the inner diameter of the Erinba tube such as nickel-span C is treated by any one of the above-mentioned methods, and the epoxy adhesive is mainly applied. After being inserted into the Elimba tube, it is curved and fixed to be integrated. As another method, one end of a 4 fluororesin tube that is slightly thicker than the Erinba tube is sealed, the other end is joined to a vacuum pump to make the inside of the tube a vacuum, and it is compressed by external pressure to be miniaturized and inserted into the Erinba tube. It is pressed into the Erinva pipe by opening the rear seal. Even in this case, if it is bonded by the above-mentioned treatment, a stronger integrated composite pipe is obtained.
In this case, the spring constant of the composite pipe is dominated by the Elinvar pipe, and the 4-fluorine resin pipe merely serves as a corrosion resistant material. Therefore, the secular change due to the internal strain does not occur even after the bending process after the integration. The end portion 114 of the composite curved equal tube 11 manufactured as described above is enlarged for fixing. The end portion 114 having the enlarged portion 113 is a portion fixed to the support member 2, and the fixing portion 9 is fixed. The fixing portion 9 includes a fixing metal fitting 91 and a packing 9.
2, consisting of a presser fitting 93 and a presser collar 94. The fixing bracket 91 is a cylindrical pedestal 91 having a through hole 913 formed in the center.
1, and the synthetic resin pipe 112 of the enlarged portion 113 of the composite curved conduit 11 is inserted into the pedestal 911. Packing 9
2 is made of 4 fluororesin and has a fixing bracket 91 and an end 1
It is sandwiched and sealed with 14. External metal tube 1 of expansion section 113
A holding collar 94 made of hard rubber, resin, or metal is attached to the outer wall portion of 11, and is covered with a holding tool 93, and a screw 931 threaded on the outer wall of the holding tool 93 and an inner screw 912 of a fixing bracket 91 are provided. The enlarged portion 113 is pressed against the pedestal 911 and fixed in a liquid-tight manner by screwing. In addition, at least the through hole 91 that comes into contact with the liquid
In order to have the same corrosion resistance as that of the synthetic resin pipe 112, 3 is subjected to corrosion resistance treatment such as inserting the same synthetic resin pipe. The composite curved conduit 11 configured as described above forms a tuning fork with the reciprocating member 3 with respect to the support member 2 as in the prior art shown in FIG. Light generated by being electromagnetically driven at a frequency and being blocked by the light shielding plate 8 is used as a reference surface by the photodetector 7 to form a complex curved tube 11
The Coriolis force is detected as the time difference of passing by.

FIG. 3 is a view showing another embodiment of the present invention. In this embodiment, the flow tube 2 is held by a flange 22 in a pipe (not shown).
The inside of 1 is partitioned by a partition plate 23, and the partitioned liquid is divided into the complex curved conduits 25 and 26. Like the composite conduit 11 shown at 11 in FIG. U consisting of 4 fluororesin pipes inserted and joined in the Erinba pipe
The letter-shaped compound curved conduits 25 and 26 are fixed to the flow pipe 21 by the fixing portion 9 shown in FIG.
6, each conduit is supported by the support plate 27 in the vicinity of the fixed portion 9 of 6,
The support plate 27 can be vibrated like a tuning fork. The vibration drive is a U-shaped compound curved conduit 25,2.
Drive magnets 5 arranged at the centers of the respective magnet brackets 28 and coil brackets 29 mounted near the tips of the magnets 6.
And a driving coil 4 are driven by a power source (not shown) at a natural frequency with a constant amplitude. The detection magnet 32 and the sensor coil 33 use the Coriolis force generated in the direction of the vector product of the fluid flow and the vibration angular velocity as the time difference when the composite bending pipes 25, 26 pass through the stationary reference plane of the composite bending pipes 25, 26. It is a sensor for detecting.

In the above, the example in which the composite curved conduit is composed of elinvar and 4 fluororesin has been described, but 3 fluororesin or other oily resin may be used as long as it is corrosion-resistant, and the metal tube also expands such as amber. A metal having a small coefficient may be used. However, even in this case, the spring constant must be dominated by the metal conduit.

Effect The compound curved conduit in the mass flowmeter of the present invention described above is resonantly driven substantially by the natural frequency dominated by the spring constant of the metal conduit and the fluid, and does not decrease Q, and is efficient. Since it can be driven and there is no change in Young's modulus or length due to temperature, it becomes a stable vibration system with respect to temperature, and temperature error is suppressed to a minimum. Therefore, temperature compensation of highly accurate mass flow rate measurement in a wide range of temperature It is possible without complicated methods, and the use of 4 fluororesin makes it possible to measure aqua regia, hot nitric acid, hot concentrated sulfuric acid, concentrated caustic soda solution, etc. Further, the connection between the composite curved conduit and the flow pipe opening to the supporting member is performed by enlarging the end of the composite curved conduit so as to reduce the surface pressure acting on the synthetic resin pipe on the inner surface of the expanded pipe. Since the expansion pipe portion is pressed and supported from the outside by the elastic pressing collar, the pipe is stably supported even if the synthetic resin pipe is creep-deformed, and the accuracy is maintained for a long time.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an example of a mass flowmeter according to the present invention, FIG. 2 is a detailed diagram of the fixing portion 9 shown in FIG. 1, and FIG. 3 is an overall configuration showing another embodiment. FIG. 4 and FIG. 4 are views for explaining a conventional technique. 1 ... Curved conduit, 2 ... Support member, 3 ... Reciprocating member, 4
...... Drive coil, 5 ...... Drive magnet, 7 ...... Photodetector, 8 ...... Light shield, 11,25,26 …… Complex curved conduit, 21 …… Flow tube, 111 …… Metal tube, 112 …… Synthetic resin tube.

Claims (1)

[Scope of utility model registration request] 1. A support having a fluid inlet and a fluid outlet arranged apart from each other, and an end portion connected to and supported by the inlet and the outlet of the support and perpendicular to a surface of the support. An axially symmetric curved conduit, drive means for driving the curved conduit in a single direction in a direction perpendicular to the curved conduit surface, and detection means for detecting the Coriolis force acting on the curved conduit by driving the drive means. In the mass flowmeter for detecting the mass flow rate proportional to the Coriolis force, the curved conduit is made of a metal having an enlarged tube portion with an enlarged end and an outer side made of metal and a chemically resistant synthetic resin. A composite curved tube, the expansion tube portion is fitted and inserted into the pedestal of a fixing member fixed to the support body having a pedestal of substantially the same shape as the inner surface of the expansion tube portion, and the elasticity is fitted and inserted into the outer surface near the expansion portion. For a retainer that retains the expansion tube through a retaining collar with Ri mass flow meter of the composite bending tube and fixed to the fixing bracket, characterized in that the connection support to the support.