KR820001268B1 - Pressure measuring aparatus using vibratable wire - Google Patents

Abstract

The appts. comprises a main body(20) with a pair of diaphragms(22,24) each subject to a respective fluid press. The diaphragms are mounted on support plates(42,44) on an intermediate member(94) which holds the diaphragms so that they are normal to the direction of fluid flow. Between the support plates is stretched an oscillating wire(50) surrounded by a tube(52). The right-hand end of the wire is clamped in the closed end of the tube, whilst the other end is directly coupled to the left hand diaphragm. The elastic characteristics of the diaphragms are different and thus, under pressure changes, the wire tension and hence its oscillating frequency varies.

Description

Pressure measuring device using vibration line

1 is a partial cutaway perspective view of an instrument according to the present invention.

2 is a vertical sectional view of the central body of the instrument shown in FIG.

3 is a partially cut away perspective view illustrating the internal elements of the two diaphragm subassemblies of the instrument shown in FIG.

4 is a perspective view of a device used to transmit tension to a vibrating line.

5 is a perspective view of a tubeless magnetic component surrounding a vibrating line.

6 is a front view of a magnetic component showing, in cross section, a vibrating line and a tubing enclosure surrounding it.

7 is a partial detail view showing the arrangement of the force-transmitting member carried by the range diaphragm.

8 is a cross-sectional view of the bent support for the closed end of the tube surrounding the vibration line.

9 is an enlarged longitudinal sectional view of a vibrating wire and tubing components.

10 is a vertical sectional view of a second embodiment of the present invention.

The present invention relates to a measuring instrument responsive to fluid pressure. More specifically, the present invention relates to a measuring instrument in the form of using vibration lines as basic force-sensing elements.

Instrument systems for use in industrial processes have used various types of devices to measure the differential pressure generated across the orifice plate of a flow pipe for many years to represent fluid pressure, especially fluid flow signals. Typically, such a device consists of a differential-pressure cell in force-balanced form as shown in US Pat. No. 3,564,923. These instruments have been in use for many years, but conventional devices have not met modern industrial process instrumentation systems. For example, modern systems must make things like temperature more stable and accurate than in conventional devices.

The use of electric wires as basic sensing elements for pressure-response instruments has long been proposed by those skilled in the art. Such proposals are based on the fact that the frequency of wire vibration is closely related to the tension in the wire, which in turn is controlled by the differential pressure to be measured. Therefore, the frequency of wire vibration can be represented as a measurement signal in response to differential pressure. In addition, in theory such an instrument can be implemented with high accuracy.

There are several patents relating to conventional vibratory devices, some of which include US Pat. Nos. 2,447,817, 2,455,021, and 3,047,789. U. S. Patent No. 3,393, 565 describes a number of vibrating line instruments that attempt to measure differential pressures, and shows a device in which wires are formed in a container filled with liquid in FIG. The structure of FIG. 2 includes a pivoting lever 26 for connecting an input to a wire, suggesting a variant in which the lever is removed below 15 rows of the third column of this patent specification and the wire is directly attached to one side of the diaphragm. did.

The instruments proposed in the process using vibrating line detectors are not acceptable for process instrumentation technology, mainly because they cannot be operated correctly under the required operating conditions. Therefore, these early proposals did not actually solve the problem and did not progress to the stage where the results achieved were available to the process industry.

The pressure-response mechanisms have recently developed accurate and practical electric-line gauges for measuring differential gas pressures. A description of this instrument is described in US Patent Application No. 732,130, filed October 13, 1976 by E.O. Olsen et al. Electronic transmitters suitable for use in this vibrating line instrument are described in US Patent Application No. 732,129 filed on October 13, 1976 by E.O.Olson et al.

Although the differential-gas-pressure gauge described above has an execution force suitable for its intention, it cannot be used as a differential pressure gauge for a versatile industrial process. In particular, the device cannot measure the various differential liquid pressures that must be measured in most commercial processes today.

In a preferred embodiment of the invention described hereinafter, the multipurpose differential-pressure measuring instrument consists of a main body part having a pair of diaphragms, each responding to fluid pressure. The power plate includes a sealed chamber filled with liquid-liquid surrounding a non-magnetic vibration line that is tensioned according to an applied differential pressure. The magnetic field passes transversely through the wire and current is supplied to the wire by the electronic circuit arrangement to create a vibratory force on the wire as a result of the interaction between the current and the magnetic field.

According to one embodiment of the present invention, the vibrating line is a closed tubular passage having an extremely small cross section to reduce the internal liquid volume, to work closely with the magnet, and to vibrate the wire without interference from walls or boundary effects. It is effectively contained within. The pole pieces are arranged on opposite sides of this passage, creating a high intensity magnetic field to vibrate the wires strongly and generate a high power signal. According to another embodiment of the present invention, the wire surrounding the tubing is closed at one end, and the wire is stuck to the closed end, providing several important advantages as described later.

In another embodiment of the present invention, specific means are provided to substantially minimize the effect on the operation of the instrument with respect to changes in external conditions such as temperature and static pressure. Another important aspect of the present invention involves the selective orientation of vibration lines with respect to the magnetic field to allow stable vibrations with appropriate amplitudes. The instrument also includes a unique device that prevents damage to wires or other elements of the device in the case of pressure-excess conditions.

Therefore, the main object of the present invention is to provide a vibrating linear commercially viable pressure measuring instrument. Other important objects, forms and advantages of the present invention will become apparent from the following description in detail with reference to the accompanying drawings.

Referring to FIGS. 1 and 2, the differential-pressure measuring instrument is shown as consisting of a bottom body 20 and diaphragms 22, 24 on opposite sides. The left diaphragm 22 is a range vibration plate having a predetermined modulus of elasticity, for example about 40 pounds / inch (7.2 kg / cm), while the other diaphragm 24 is a loose diaphragm having an extremely low elastic modulus.

The two fluid pressures to be measured are transmitted separately to each diaphragm by a device (not shown) commonly used in differential-pressure gauges.

On top of the body part 20 is formed a stem 26 which acts as a protective conduit for the electrical connector wire which is led to the electronic closure 28, which is the longitudinal center member 30 and the two cylindrical side ends. (32,34). This closure includes a number of electrical components and connections needed to operate the instrument. Primarily, these parts include a solid-state transmitter as described in US Patent Application No. 732,129, which will not be described in detail herein. In short, the transmitter includes a device for inducing a vibration of a taut wire at a frequency corresponding to the wire tension and a device for generating a d-c measurement output signal whose magnitude represents the vibration frequency.

The cutout in FIG. 1 shows one of the two connectors guided to the transmitting circuit by 36 behind the diaphragm 24.

As shown in FIG. 2, the body part 20 includes a central body member 40 to which solid support plates 42 and 44 for the diaphragms 22 and 24 are fixed. A vibrating line 50 of round cross-section having a predetermined small diameter (0.020 inches (about 0.051 cm) or less in an embodiment of the present invention, preferably 0.010 inches (about 0.025 cm)) is provided with an internal space and support within the body member. It extends through the plate to the center. Surrounding the wire by its length is an elongated tubing 52 of small diameter (see also FIG. 3). The right end of this tubing is closed and the corresponding end of the wire is fixed to this closed end. The left end of the tube is supported by a cylindrical insulator sleeve 54, for example made of ceramic, which in turn is fixed to the left support plate 42 through the joined portion.

The left end of the wire 50 is fixed to a movable end piece 60 of button type (see FIG. 4) having a peripheral flange 62 and a center hub 64 for attaching the wire by soldering or the like. A spacer ring 66 with three radial ribs for stable placement presses on the right surface of the buttoned flange 62 to apply tension to the wire to the left. This force is applied to the spacer ring 66 via an over-range spring 68 that includes two sets of interconnected Belleville type washer elements (or sometimes referred to as conical disc springs). Is passed to.

The over-range spring 68 is prestressed with a force of about 11 pounds by the element of the diaphragm hub component indicated by 70 (see FIG. 8). This part has a circular plate 72 pressing the right end of the spring 68 and a button-shaped flange 62 which restrains the left movement of the spacer ring 66 and a ring-shaped element 74 formed integrally with a part thereof. ). Therefore, the hub part keeps the spring 68 in a predetermined pressing state during normal machine operation.

The hub component 70 is secured to the inner end of the range diaphragm 22 to receive the force exhibited by the range diaphragm according to the differential pressure to be measured. During normal operation of the instrument, e.g., within a selected wire force adjustment range of up to about 9 pounds (about 4.08 kg), the over-range spring 68 causes the hub part 70 to end up at the end of the wire 50. The force exhibited by the range diaphragm 22 is applied directly to the wire because it effectively acts as a solid (infinitely rigid) force-transmitting element to functionally connect it to.

The hub component 70 is also subjected to "zero-set" forces from the initial wire-tension or zero spring 80 in addition to the forces from the range diaphragm 22. The spring includes a pair of interconnected washers that are nearly flat and surround the wire and can be formed, for example, by spiral cutting (not shown) to increase their flexibility. In the above-described embodiment, these spring elements generate about two pounds of force to measure the wire tension without any force from the range diaphragm 22.

When the length of the wire changes, the interconnected spring elements 80 that are secured together to the inner edge of the spring element 80 move in the form of a parallelogram, causing the spring force to act concentrically with the wire axis. Since the total amount of change in wire length is about 0.0015 inches, the spring force does not change significantly when the diaphragm 22 strokes through the full range of instrument spans.

The support plates 42 and 44 are carefully formed to have a vibrating support surface that accurately matches the shape of the combined diaphragm, so that the diaphragm is stable against the diaphragm in the case of an over-range pressure condition in which the diaphragm presses its support plate. Provide support. When the meter is within the normal operating range, these plates define a closed area of small volume adjacent to each diaphragm, which is filled with other internal cavity areas within the body part (including the interior of the tub 52). Forming an internal hermetic chamber filled with liquid 84.

The two closed zones behind each of the diaphragms 22 and 24 are a first tubular member 90 (see FIG. 3) fixed to the first support plate 42 and a second fixed to the other support plate 44. Liquid contact with each other through the passage consisting of the tubular member (92). The diaphragms are usually arranged on corresponding support plates by respective welding rings 94 and 96 of the structure.

When using the instrument to measure the difference between two fluid pressures, a low pressure is applied to the range diaphragm 22 having a predetermined modulus of elasticity of, for example, about 40 pounds / inch (about 7.2 kg / cm). Higher fluid pressure is applied to the right diaphragm 24, which is a loose diaphragm with a much lower modulus than that of the range diaphragm. The elasticity of the wire 50 is considerably higher than that of the range diaphragm 22, for example about 4000 pounds / inch (about 720 kg / cm).

As shown in the accompanying drawings, the diaphragms 22 and 24 combine important features. According to one of these features, the elastic modulus of the relaxed vibration plate 24 becomes almost zero during normal instrument operation. Under these conditions, the pressure in the fill-liquid 84 in the sealed chamber is essentially equal to the higher of the two applied pressures, ie the pressure applied to the relaxation diaphragm 24.

Thus, the range diaphragm 22 exhibits a net force proportional to the differential pressure to be measured, which is the tension on the wire 50 [of course, from the zero spring 80 as described above. In addition to the initial fixed force. This pure force controls the oscillation frequency of the wire 50 in accordance with established physical laws, so that the oscillation frequency is the magnitude of the differential pressure to be measured.

In order to cause the wire 50 to vibrate, its end is connected to a vibratory circuit having positive feedback characteristics (see US Patent Application No. 732,129 described above) and arranged to generate an alternating current in the wire. By creating a stable magnetic field through the wire in a direction perpendicular to the wire axis, the interaction between the oscillating line current and the magnetic flux creates a lateral force on the wire. Wire 50 and tubing 52 are made of a nonmagnetic material to adequately exhibit lateral vibration forces.

In this embodiment, a very strong magnetic field is generated through the wire 50 by the magnetic structure 100 (see in particular FIGS. 5 and 6), which is a two-sided permanent magnet 102, 104, which is connected to opposite V-shaped pole pieces 106, 108 disposed on opposite sides of the closely spaced tubing. These magnets must be made of materials that provide the strongest magnetic field. Magnetic materials are suitable for rare-earth / cobalt combinations, such as samarium-cobalt magnets, which produce a magnetic flux density of about 18,000 Gauss in the wire. The magnetic structure 100 is placed in a suitable place by the magnet retaining spring 110.

An important advantage of using a small amount of liquid passages for wire 50, as provided by tubing 50, is that the magnetic pole pieces 106, 108 can be mounted very close to the wire, leading to good magnetic field strength. To make the wire vibrate powerful. In a preferred embodiment, the cap between the pole pieces is about 0.045 inches (about 0.11 cm). The tub 52 has an outer diameter of 0.041 inches (about 0.10 cm), an inner diameter of 0.026 inches (about 0.07 cm), and a wire diameter of 0.010 inches (about 0.025 cm).

The current for the wire is supplied to the right end of the vibration line 50 by the connecting portion 36 (see FIGS. 1 and 2) guided to the electron closure portion 28. The return line for the vibrating wire current is connected from the left wire end to the mechanism chassis (ie, electrical ground) through the button-type movable end piece 60, the spacer ring 66, the hub part 70, and the range diaphragm 22. And an electronic closure through a wire (not shown).

At low wire tension (about 2 pounds measured by zero spring 80), the vibration frequency in the preferred embodiment was about 1750 Hz. In the high operating range with a wire tension of about 9 pounds (about 4.08 kg), the oscillation frequency was about 3100 Hz.

One of the more important problems with instruments of the type described above is the error caused by changes in ambient temperature. In other words, the frequency of wire vibration is a function of the temperature of the instrument. There are several factors that contribute to this temperature error. A particularly important factor among these is caused by the change in viscosity of the fill-liquid 84 inside the enclosure.

The viscosity of the fill-liquid is typically temperature dependent, i.e. increases with decreasing temperature. Increasing the viscosity decreases the wire oscillation frequency, and as they become more viscous, as in the case of liquid molecules, they attach more strongly to the wire, increasing the effective weight of the wire. Since the oscillation frequency is inversely proportional to the weight of the wire, increasing the viscosity results in a decrease in the frequency of the wire oscillation (others become equal).

In terms of viscosity, it is suitable to use a fill-liquid having a relatively low viscosity in order to minimize the change caused by temperature. It has been found to be beneficial to use fill-liquids having room temperature viscosities on the order of about 1 centistoke.

Also important is the use of fill-liquids with low viscosity temperature coefficients. The most significant effect on viscosity change was found commercially in the low temperature region of -40F to 180 ° F, which is an important temperature range. For example, the liquid viscosity can vary from 200% to 300% when the temperature drops from room temperature to -40 ° F. The fill-liquid should therefore be chosen to have a minimum viscosity temperature coefficient in the cold zone. In particular, it is preferable to use a liquid having a coefficient of less than or equal to 0.05 cm stoke of 1 ° F at 0 ° F. Filled-liquids having this property and room temperature viscosity on the order of one centistoke are sold by Dow Corning as a silicone oil designated as DC 200.

By selecting the fill liquid 84 according to the above criteria, problems caused by the temperature-induced viscosity change can be reduced. However, in most applications it is desirable to further minimize the effect of viscosity change. According to another aspect of the invention, this is taken by compensating means for changing the tension on the wire 50 with a change in temperature in order to avoid a change in viscosity.

In particular, compensation in the preferred embodiment described above is achieved using a zero spring 80 having a negative thermal effect. That is, the force of the spring 80 decreases with increasing temperature. Therefore, the spring force is increased in order to compensate for the effect of the corresponding temperature-induced viscosity change in wire vibration when the temperature is lowered, thereby increasing the vibration frequency.

This negative heat springing property is achieved by selecting for the zero spring 80 a material with increasing modulus of elasticity as the temperature decreases and the spring force increases. In a preferred embodiment, the spring material was a product called "Carpenter Custom 445" in the form of stainless steel manufactured by Carpenter Steel Co.

It has also been found that good viability of the vibratory line instrument is obtained by providing a large density difference between the wire 50 and the fill-liquid 84. This ratio is suitably in excess of 20 for running the entire operation well but should be at least 10. In a preferred embodiment, the density of the wire (made of iridium) was 21 g / cm 3 of liquid, and the density of the silicone oil fill-liquid was about 0.818 g / cm 3 at 77 ° F., giving a good ratio of about 25. Because of the iridium wire, it is suitable to make the tube 52 made of tantalum, because it has a coefficient of temperature expansion that is approximately equal to iridium.

Iridium is also excellent as a vibrating line because it has a high modulus of elasticity, which makes the stretching of the wire extremely small and also the electrical resistance low. Also, it can be easily fixed to the joined parts by a method such as welding or soldering.

Regardless of the ratio of wire-to-liquid density, the density of the wire must be sufficiently high in either case, at least 10 g / cm 3 being suitable, and at least 20 g / cm 3 preferred.

As mentioned above, iridium is advantageous in this respect and has a density of 21 g / cm 3. Tungsten wire is of moderately high density and has good performance in the instrument.

Another important factor due to temperature error is the change in liquid volume caused by temperature changes.

Silicone oils of the type described above have an expansion coefficient of about 6% / 100 ° F. This liquid expansion creates a force that pushes the diaphragm outwards, increasing the pressure in the fill-liquid, thus correspondingly changing the wire tension and the measured output signal.

In order to minimize the effects of liquid volume changes with temperature changes, it is first important to design the instrument so that the volume of fill-liquid is very small. Therefore, the space between the diaphragms 22 and 24 and their supporting plates 42 and 44 should be as small as the other parts of the instrument containing the connecting passage therebetween and the filling-liquid. An important advantage of using a tubular passage having a small cross-sectional area for the wire 50 is that only a very small amount of liquid is filled in this passage (essentially comprising the tube 52 in this embodiment). By using this tubular passageway and the instrument described above, the total liquid volume in the interior hermetic chamber of the instrument was maintained at about 0.06 cubic inches in the preferred unit described above.

Even with the minimum amount of fill-liquid amount, there is a slight effect on the liquid expansion.

This expansion can be controlled by inflating the diaphragms 22, 24, but if the diaphragm is of the conventional type with typical modulus of elasticity, the diaphragm motion causes additional-pressure to be applied to the fill-liquid, thus changing the wire tension and correspondingly This causes a measurement error. Therefore, it is preferable to reduce this error to form the right vibration plate 24 as a so-called relaxation vibration plate so that the elastic modulus of the diaphragm is much lower than the elastic modulus of the range diaphragm 22.

Although the relaxation diaphragm expands as the liquid expands, the pressure change of the fill-liquid remains low and correspondingly has a small effect on the frequency of wire vibration.

Another important problem with this type of instrument is that a change in the static pressure correspondingly changes the measurement signal. When the external pressure on the two diaphragms 22, 24 increases, for example, the diaphragm moves inwardly by a small distance due at least in part to the compressibility of the fill-liquid. When the range diaphragm 22 moves inward (right), since there exists a tendency to loosen the wire 50, the vibration frequency is reduced and it appears as an error at the time of a measurement. However, according to another embodiment of the present invention, this static pressure error can be significantly reduced by the compensation arrangement described later.

Static pressure compensation is achieved by forming a closed end in the tubing 52 surrounding the wire in the aforementioned instrument and attaching the wire 50 to this end. Therefore, as the liquid pressure increases with increasing static pressure (eg from 2000 psi to 3000 psi), the force for pressing the closed end of the tubing also increases correspondingly. This increase in force will correspondingly increase the force on the closed end of the tube. This increase in force effectively extends the tubule in small amounts, thus separating the right end of the wire from the support plate 42. Thus, moving the range diaphragm 22 to the right, where the boosted static pressure tends to pull the wire, the same pressure increase moves the distal end of the wire to the right, which tends to increase the wire tension. By properly balancing the relative sizes of the components involved, these two opposing effects almost cancel each other out, resulting in extremely small variations in the output signal resulting from changes in the static pressure.

The right end of tubing 52 moves only in the longitudinal direction to achieve this compensation. The flexural support 120 (see FIG. 9) is fixed to the end of the tube for axial movement and axial movement in order to make this movement structurally stable and also to prevent the wire vibration from shaking the tube. Restrain. The support comprises two bends 122, 124 parallel at regular intervals, bolted to the central body member 40 at its upper and lower ends. In their central area, these bends are fixed to a metal ring 126 that separates these two bends at even intervals.

Ring 126 forms part of a metal-to-glass sealing structure (see FIG. 7), including insulating ring 128 and inner metal sleeve 130. The metal sleeve described above is fitted into and secured to another sleeve 132 of Invar having a layered inner surface. The right end of this layered sleeve is fixed to a Monel pin 134 to which the end of the wire 50 is fixed. The left end of the layered sleeve is fixed to tantalum tubing 52. Therefore, the flex support 120 restrains axial movement at this end of the tube, while causing it to move axially in response to a pressure change of the fill-liquid or to a temperature change of the tubing material.

The inner sleeve 130 receives the electrical connector 36 from the electronic transmitter circuit 28. This sleeve is electrically connected to the ends of the wire 50 and the tubing 52 via the layered sleeve 132. These wires and tubing both have different voltages than ground (ie instrument chassis).

As mentioned above, the left end of the tube is electrically insulated from ground by the ceramic insulator sleeve 54. The outer surface of the tube is well covered with a Mylar insulating layer.

As a result of testing with the above-described instrument, it was found that there was a slight anomaly in the resonant vibration frequency of the wire. In particular, for some instruments, the wires under fixed tension alternately resonate at two different frequencies, for example 2000 Hz and 2002 Hz. This double-resonance characteristic makes for a commercially unreliable instrument of course.

However, this problem has been solved based on the finding that the double resonance phenomenon arises from the following fact: the wire 50 is not uniform, and the irregularity or unevenness around the wire axis. Therefore, the resonant frequency in one plane through the axis can vary considerably from the resonant frequency of the other plane through the wire axis. More specifically, the wire will have two suitable vibration planes with different resonant frequencies.

These two planes are usually perpendicular to each other, and the vibration width in one plane becomes larger than the vibration width in the other plane.

Based on this finding, a method was developed to determine the vibration plane to create the maximum amplitude and to position the wire in the instrument along the direction of the magnetic field so that the wire would cause vibration in the maximum amplitude plane. According to this method, the wire 50 is placed under tension in air, and vibrates in a conventional manner by the above-described electric circuit. Since the magnetic field through the wire is generated by a magnet mounted to rotate around the wire axis, the magnetic field can change the direction of the magnetic field through the wire without changing its size. As the magnetic field rotates around the wire, it rotates around the axis of the top view of the vibration wire.

By observing the amplitude of the high current electrical signal generated by the wire as the magnet rotates, a two-amplitude inter-vertical vibration plane is found, so that one of the larger vibrations can be selected. Then, the selected good vibration plane is displayed on the fixture holding the wire, and when the wire is assembled as its gauge, the wire is placed so that the selected vibration plane is perpendicular to the direction of the magnetic field.

Referring to the other problem of the instrument described above, if the over-range condition occurs on the high pressure side, the range diaphragm 22 will not exceed 11 pounds of force on the hub component 70 (the force from the zero spring 80). Includes the over-range spring 68 is pressed to absorb an additional force exceeding its preload of 11 pounds.

The hub component moves correspondingly to the left when the over-range spring is pressed, but there is no corresponding movement of the end piece 60. If the over-range condition is stringent, the loose vibration plate 24 comes under its support plate 44 before the over-range spring 68 reaches its pressing limit. Therefore, the wire is protected from excessive deformation and damage.

When the over-range condition occurs on the low pressure side, the range diaphragm 22 moves to the right and falls below the support plate 42, and the button 60 is ringed from the spacer ring 66. This causes the wire 50 to relax, but does not cause any damage to the wire. The amount of diaphragm stroke allowed is very small, about 0.055 inches (0.2397 cm).

The support plates 42 and 44 are preferably formed of a magnetic material such as a stainless steel seal called E-Brite.

Therefore, the support plate additionally acts as a magnetic shield of the magnets 102 and 104 to reduce magnetic flux in the region of the diaphragm 22 and 24 and minimize the chance of sucking particles from the process fluid.

FIG. 10 shows another embodiment of the present invention incorporating other arrangements to compensate for temperature-induced changes in the fill-liquid volume. This instrument is as shown in the previous figures, but includes a range and relaxation oscillation plates 150 and 152 for sealing the sealed chamber containing the fill-liquid. The range diaphragm carries an end piece 154 connected to one end of the vibration line 156 and applies tension thereto. The other wire end is fixed to the ceramic insulator in the form of a glass bead 158, which in turn is attached to the central body member 162 by a cantillever over-range spring 160 fixed to its upper end. maintain.

The rightward movement of the cantilever spring 160 is suppressed by the front portion 164 of the bolt 166 in engagement with the body member 162. During normal instrument operation, the spring 160 presses the bolt portion 164, thereby fixing the glass beads 158 in place against the tensile force applied to the wire by the range diaphragm 150.

The small diameter tubing 170 surrounds the wire 156, and both ends thereof are fixed to the central body member 162. This tubing forms part of an interior enclosure, which also includes a closed area between the diaphragms 150, 152 and their respective support plates 172, 174, and from the right diaphragm region through a large block 178. A connection passage 176 is guided to the area of the glass bead 158.

The large block 178 is disposed in the corresponding space inside the enclosure of the instrument. This space is almost identical in size to the block, and the fill-liquid takes up a small space around the block. Since the block is not physically fixed to the body member 162, it is effectively suspended inside the sealed chamber. Block 178 is made of Invar, which has an extremely low coefficient of thermal expansion close to the material. However, the other part of the instrument containing the sealed chamber for the fill-liquid has a coefficient of expansion temperature of normal (relatively high). As the temperature of the instrument rises, the other parts of the instrument expand, increasing the size of the enclosure. However, block 178 is essentially unchanged in size. By appropriately selecting the volume of block 178 in relation to the total volume of the sealed chamber, the temperature-induced increase in the pure volume of the chamber (less than block 178) is proportional to coincide with the capacity expansion of the filling liquid. Significant influence on the pressure of the fill-liquid due to capacity expansion will be prevented.

The embodiment of FIG. 10 also includes a modification of the over-range protection mechanism. When a high pressure over-range occurs, the range diaphragm 150 moves to the left as before, and exhibits excessive force on the wire 156. However, when the normal wire force is exceeded, the cantilever spring 160 is bent and moved to the left to lift from the top of the bolt 164, thereby preventing excessive deformation of the wire. Under stringent over-range conditions, the oscillating vibration plate 152 comes under its support plate to prevent other pressures from occurring in the fill-liquid. This bottoming on the support plate occurs before the cantilever spring reaches the point where the cantilever spring engages with the body member 162 so that the wire is not damaged from over-range conditions.

Although the specific preferred embodiment of this invention was described in detail so far, this is for demonstrating the principle of this invention, and does not limit this invention to this.

Those skilled in the art can make various modifications without departing from the scope of the present invention.

Claims (1)

A vibrating line instrument for generating a measurement signal corresponding to an applied differential pressure, the vibrating line instrument comprising: first and second vibrating plate support members which provide an internal cavity and closely displace an inner surface of a corresponding diaphragm; A body forming a second hermetic zone, the first and second spatial diaphragms, the first and second spatial diaphragms, fixed to the body and arranged to seal the cavity and to receive respective fluid pressures on the outer surface of the diaphragm to measure the difference in pressure A vibrating line connected to one end of the vibrating plate, a fixing member for fixing the other end of the vibrating line to the body, and the vibrating line providing an elongated passage having a small cross section disposed adjacent to each other and guided from a first sealing region adjacent to the first vibrating plate. An enclosed tubular passage, between the interior of the tubular passage and the first and second sealed regions adjacent the first and second diaphragms Energy for supplying energy to the vibrating line to vibrate a delivery member, a hermetically sealed chamber constituent member comprising the enclosed area and the elongated tubular passage and the delivery member, the fill-liquid and the vibrating line in the hermetic chamber at a frequency related to its tension. Vibration line using pressure measuring device, characterized in that consisting of a supply member.

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