US3604272A

US3604272A - Soft wall hydrometer

Info

Publication number: US3604272A
Application number: US868564A
Authority: US
Inventors: Homer S Youngs
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-10-22
Filing date: 1969-10-22
Publication date: 1971-09-14
Anticipated expiration: 1988-09-14

Abstract

A specific gravity-sensing instrument in which a closed cell having highly compliant walls is completely filled with a reference liquid and immersed in an ambient liquid, and compensation is made for the difference in compression and thermal expansion of the material comprising the cell walls with either the reference liquid or ambient liquid so that when the cell is immersed, it responds equally to changes in density of the reference liquid and ambient liquid, thereby cancelling the effects of pressure and temperature and so as to measure directly the changes in specific gravity.

Description

United States Patent [72] Inventor Homer S. Youngs 2,094,768 10/1937 Cruse et a] 73/451 8718 Dunaway Dr.. La Jolla, Calif. 92037 2,282,069 5/ l 942 Linebarger. 73/454 [21] Appl. No. 868,564 3,137,158 6/1964 Krueger 73/30 F11d 0C. 22. 1969 FOREIGN PATENTS [45] Patented Sept. 14, 197i continuafianmpafl of application Sen No. 734,684 10/ 1932 France 73/449 583,244, Nov. 30, 1966, now abandoned. OTHER REFERENCES Long Ocean Sciences" 1965, page 141 (copy enclosed) Primary Examiner-Richard C. Quiesser Assistant Examiner-Ellis J. Koch 54 1 SOFT WALL HYDROMETER 5 Claims, 21 Drawing Figs.

[52] U.S. Cl 73/449,

73/30' 73/170, 73/454 ABSTRACT: A specific gravity-sensing instrument in which a [51] Int. Cl G0ln 9/08, dosed Ce having highly compliant walls is completely fill d 9/12 with a reference liquid and immersed in an ambient liquid, and [50] Fleld of Search 73/32, 437, compensation i made f the difference i compression and 450,451, 452,453,454,444, 448, 449, 170. 30 thermal expansion of the material comprising the cell walls 1 5 6 R f C1 ed with either the reference liquid or ambient liquid so that when 1 l e erences I the cell is immersed, it responds equally to changes in density UNITED STATES PATENTS of the reference liquid and ambient liquid, thereby cancelling 794,697 7/1905 Beck et al, 73/449 the effects of pressure and temperature and so as to measure 2,000,308 5/1935 Van Shutz 73/30 directly the changes in specific gravity.

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PATENTED SEP] 4197 3604.272

sum 1 or 4 I N VENTOR. 1 /0415 5. You/v65 rrake/vf ys SOFT WALL ll-IYDROMIETIEIR The present invention is a continuation in part of my copending application, Ser. No. 583,244, filed Sept. 30, 1966, now abandoned entitled Soft Wall Hydrometer.

SUMMARY OF THE INVENTION This invention relates to soft wall hydrometers; more particularly to a hydrometer which is distinguished from previous hydrometers or similar instruments by the fact that the walls which separate the reference fluid from the surrounding fluid are highlycompliant so that the reference fluid is maintained at the same pressure as the surrounding fluid or varies without hysteresis effect in accordance with change in pressure of the surrounding fluid.

Included in the objects of this invention are:

First, to provide a soft wall hydrometer which facilitates the performing of specific gravity measurements under extreme pressures, without sacrifice of precise measurement, and which in fact permits more accurate measurement than has heretofor been feasible or possible except under accurately controlled laboratory conditions.

Second, to provide a soft wall hydrometer which is capable of accurate specific gravity measurement without special thermal control, inasmuch as the necessarily thin and compliant wall offers no appreciable resistance to the transfer of heat between the contained reference fluid and the surrounding or ambient fluid.

Third, to provide a soft wall hydrometer which, although ideally suited for laboratory use, is capable of accurate measurement even under adverse conditions; such as encountered at great depths in the ocean, or those encountered in the continuous or periodic measurement of fluids undergoing treatment in a processing plant or flow in a pipeline.

. Fourth, to provide a hydrometer in which error due to bubble formation is minimized.

Fifth, to provide a hydrometer which facilitates the measurement of highly volatile or inflammable liquids or gases.

Sixth, to provide a soft wall hydrometer which is adaptable to various forms or types corresponding to those of conventional hydrometers; such as, totally immersed angular or linear balances of the float and weight, multiple float, spring-opposed types, whether the direct reading or null balance types; and as well as various forms of emergent stem hydrometers.

Seventh, to provide a soft wall hydrometer wherein the reference liquid may be a particular sample of the surrounding or ambient liquid; for example, in the measurement of sea water at various depths.

Eighth, to provide a soft wall hydrometer with auxiliary counterbalance elements whose functions include net instrumental compressibility and thermal expansivity matching to the reference fluid contained within the soft wall cell.

DESCRIPTION OF THE FIGURES FIG. 1 is a side view, showing a pair of supporting structures for soft wall hydrometers, adapted particularly for oceanographic studies, the uppermost structure being shown as undergoing a cycle of operation in which the hydrometer is released so as to make a record of the specific gravity of the sea water, whereas the lower structure is shown in the condition prior to its operating cycle.

FIG. 2 is an enlarged fragmentary side view, taken within circle 2 ofFIG. 1.

FIG. 3 is a similar fragmentary side view, taken within circle 3 of FIG. 1.

FIG. 4 is an enlarged fragmentary view of the housing structure, with portions broken away to show the hydrometer and its associated mechanism.

FIG. 5 is a fragmentary sectional view, taken through 5-5 of FIG. 4, showing a window for the admission of sea water, in its open condition.

FIG. 6 is a similar view, showing the window in its closed condition.

FIG. 7 is a fragmentary sectional view, taken through 7-7 of FIG. 4, showing the clutch spring and the clutch-tensioning cam.

FIG. 8 is an essentially diagrammatical perspective view, showing the electrical relationship between the soft wall hydrometer unit and the scale associated therewith.

FIG. 9 is a further enlarged transverse sectional view, taken through 9-9 of FIG. 4, showing the soft wall hydrometer and the scale-supporting structure in their locked condition.

FIG. 10 is a fragmentary sectional view, taken through 10- 10 of FIG. 4, showing the manually operated stop employed to terminate the cycle of operation.

FIG. II is a fragmentary sectional view, taken through ill- II of FIG. 4, showing the electrode pointer and adjacent portion of the scale.

FIG. 12 is a fragmentary sectional view, taken within circle 12 of FIG. 9, showing the clutch in its released condition, wherein the soft wall hydrometer is free to make a record of the specific gravity of the surrounding sea water.

FIG. 23 is an essentially diagrammatical view, illustrating a modified form of the hydrometer, in which the hydrometer is suspended in the ambient liquid and is equipped with a stem projecting into a companion liquid. The location of the stem, with respect to the interface between the ambient fluid and the companion fluid, being indicative of the specific gravity of 4 the companion fluid or the ambient fluid, depending upon which fluid is treated as a variable.

FIG. 14 is a similar essentially diagrammatical view, in which the hydrometer is inverted with respect to the position shown in FIG. 13, for use in conditions in which the companion fluid has a greater density than the ambient fluid.

FIG. I5 is a fragmentary view, showing a further modification of the soft wall hydrometer, immersed in an ambient fluid, and connected to a counterweight chain or flexible linkage, which in turn is connected to a means for vertically adjusting the linkage to facilitate reading of the specific gravity of the ambient liquid.

FIG. I6 is an enlarged fragmentary sectional view, taken within circle 116 of FIG. 15.

FIG. 17 is an enlarged fragmentary sectional view, taken within circle 17 of FIG. I5.

FIG. 18 is an exploded view, showing the parts of a further modified soft wall hydrometer.

FIG. 19 is an enlarged fragmentary sectional view, taken within circle 19 of FIG. I8.

FIG. 20 is a reduced side view of the soft wall hydrometer, shown in FIGS. 18 and I9, and illustrating one manner of its use.

FIG. 21 is an essentially diagrammatical perspective view, illustrating a further modified form of the soft wall hydrometer.

Reference is first directed to FIGS. 1 through 12, which illustrate in detail one embodiment of the invention, especially arranged for oceanographic surveys. In the exercise of this form of the invention, housing structures, each containing a soft wall hydrometer, are mounted on a suspension line I, so that specific gravity readings may be obtained at different levels. Each supporting structure includes a frame 2, having a sleeve 3, through which the line 1 extends. Suitable means, not shown, are employed to secure each sleeve to the line and to allow free rotation of the frame 2 about the sleeve 3 as an axis, to align the frame 2 with possible water currents.

At one side of the sleeve 3, the frame incorporates a counterbalance and battery power supply housing 4. Connected to the other side of the frame 2, is a hydrometer housing 5. The hydrometer housing 5 includes a circular rim 6, to which are secured

opposed sidewalls

7 and 8 in the form of convex disks.

A fixed journal shaft 9 is secured in the sidewall 7 and extends along the axis defined by the rim 6 and through the sidewall 8. Mounted on the shaft 9 is an insulating sleeve 10, which is restrained against rotation. Journaled on the sleeve 10 is a conductor collar II which in turn journals a fulcrum hub 12, which is located intermediate the ends .of a pivot member 13. One arm 14, of the pivot member, is connected by a bracket 15, secured by an adjustment screw 16, to a soft wall hydrometer cell 17.

The soft wall hydrometer cell constitutes the crux of this invention. By reason of the soft wall hydrometer cell, specific gravity measurements of extremely high accuracy may be made.

The soft wall hydrometer cell is a liquid container, having extremely thin or at least highly compliant walls 18. The cell may be in the form of a hollow disk, having circular flat sides. The walls may be formed of plastic material or of thin-gauge metal. In the latter case particularly, the sidewalls may be corrugated so that any resistance to pressure differential across the wall is minimized. It is essential to the operation of the soft wall hydrometer that the chamber formed by the walls be completely filled with a reference liquid 19.

The pivot member 13 includes a second arm 20, on which is mounted a radially adjustable counterbalance 21. The arm terminates in a pointer or marker electrode 22, in the form of a wire offset from the plane of the arm 20, and extending radially, as shown in FIGS. 4, 8 and 11.

The sensitivity of the angular soft wall hydrometer is determined by the angular displacement, about the axis 9, of the centers of buoyancy and of gravity of the rotational unit, including items 12 to 22 inclusive. This adjustment is achieved by positioning the counterbalance 21 along the arm 20 and by angularly positioning the cell 17 with respect to the arm 14 by means of the adjustment screw 16 and the bracket 15.

In the construction illustrated, the reference liquid 19 has a specific gravity greater than the liquid in which the hydrometer cell is immersed. For example, in this case, if the hydrometer cell is immersed in sea water, the reference liquid would have a specific gravity greater than sea water; however, its compressibility would correspond to that of sea water. Consequently, the hydrometer cell tends to rotate the rotational unit counterclockwise, as viewed in FIG. 4, and the counterbalance 21 is a weight.

Should it be desirable to use a reference liquid 19 which has less specific gravity than the ambient liquid, so that the cell 17 would tend to rotate the rotational unit in a clockwise direction, the counterbalance 21 would also be buoyant or, if needed, located on the arm 14. In this case, it would be preferred to position the cell 17 above the pivot member 16.

Also rotatably mounted on the shaft 9 is a scale support 23, having a hub 24. The scale support includes an arcuate rim 25, occupying about one-third of a circle. Occupying a portion of the rim 25, is an arcuate scale 26, removably secured by screw attachments 27. The rim 25 also supports a counterweight 28. In order to provide access to the scale, the sidewall 7 is provided with a removable cover 29.

The rim 6 is provided internally with a set of recesses which receive flanged journaling rollers 30. The rollers rotatably support a timing ring 31. On the axial side of the timing ring 31, facing the sidewall 7, is a ring gear 31a. 1

Supported from the upper portion of the frame 2, and also supported from the periphery of the hydrometer housing 5, is a motor housing 32, which contains a spring-operated drive motor 33, which includes a drive pinion 34, adapted to engage the ring gear 31a.

Secured to the axial side of the timing ring 31, facing the sidewall 8, is a disk 35, conforming to the curvature of the sidewall 8. The disk 35 is provided with a pair of relatively large diametrically disposed openings 36, which in the course of operation of the hydrometer, are caused to register with similar openings 37, provided in the sidewall 8. It is intended that the timing ring 31 and its disk 35 make one-half revolution in the course of operation of the hydrometer. In order to do this, a marker control pin 38, which may be one of the screws connecting the disk 35 to the timing ring 31, protrudes axially toward the sidewall 7.

A manually releasable stop 39 is provided, as shown in FIGS. 4 and 10. This manual stop is released at the time the soft wall hydrometer is cocked and prepared for use, as will become hereinafter evident. In the course of rotation of the timing ring 31, the pin 38 engages a switch 40, mounted in the sidewall 7, which completes a circuit through the marker electrode 22, scale 26 and scale support 23, as will be brought out hereinafter.

Bordering the radially inner sides of the openings 36, is a pair of cam flanges 41, illustrated in FIGS. 4, 7 and 9. A leaf spring 42 bridges between the cam flanges 41 and is mounted on the shaft 9 by means of a clutch collar 43. Theclutch collar is a square in cross section, and fits within a square opening provided at the center of the sidewall 8, so as to slide axially, but be restrained against rotation.

The journal shaft 9 protrudes through the sidewall 8, and is capped by a guide sleeve 44. A spring 45, which is weaker than the leaf spring 42, extends between the sidewalls 8 and the outer extremity of the guide sleeve 44. When the extremities of the leaf spring 42 are engaged with the crest of the cam flanges 44, as shown in FIG. 9, the clutch collar 43 is urged axially against the hub 24 of the scale support 23. The hub 24 in turn presses against a washer 46, of insulating material, which in turn presses against the hub 12 of the pivot member 13, so that the hydrometer and its scale are locked against rotation. When the leaf spring 42 is free of the cam flanges 41, the

clutch collar 43 releases the hydrometer and its scale, as indicated in FIG. 12.

Included in the spring motor 33, is a gear having vanes 47, which, inasmuch as the spring motor is immersed in water during its operation, may serve as a governor. One of the vanes is initially engaged by a latch pin 48, mounted on a slide bar 49. The latch bar is vertically movable through the motor housing. The latch pin is guided in a slot 50, provided in the motor housing. A second pin and slot means51 limits the slide bar 49 to axial movement, as shown in FIGS. 2 and 3. The slide bar 49 extends below the housing 32 and is connected to a rod 52, guided by the frame 2, and provided with a spring 53 so that normally the slide bar 49 occupies an upper position, shown in FIG. 2.

The upper extremity of the slide bar 49 extends above the motor housing 32, and is attached to a lever 54, one end of which is pivotally connected to a bracket 55, extending from the rim 6. The other extremity of the bracket 55 is connected to a link 56 which in turn is connected to a target disk 57, which surrounds the suspension line I. In order to initiate operation of the hydrometer, a messenger 58 is released from a point on the line above the hydrometer and caused to engage the target disk 57, so as to move the slide bar 49 from the position shown in FIG. 2 to the position shown in FIG. 3. For this purpose, each messenger 58 is provided with a retainer strap 59.

It is intended that a series of hydrometers be mounted on the suspension line, and that each hydrometer, except the lowermost hydrometer, initially support a messenger, which will be released when the operation of the hydrometer is initiated. Operation of the uppermost hydrometer is initiated by a messenger released from the ship from which the line 1 is suspended.

Each motor 33 includes a drive spring 33a mounted on a shaft 33b journaled between the two plates forming the motor housing 32. The drive spring tends to rotate the shaft 33b in one direction and drive the gears of the motor in the opposite direction. Each motor housing 32 is provided with a pair of arcuate slots 60, concentric with the shaft 33b. Secured to the shaft is a latch disk 61.

The latch disk is provided with a strap receiving notch 62, which separates two

projections

63 and 64 in angular relation. Edge surfaces of the

projections

63 and 64 confront the slide bar 49, and are so arranged that when the slide bar is in its upper position, shown in FIG. 2, the latch disk is prevented from rotation, but when the slide bar 49 moves downwardly, from the position shown in FIG. 2, to the position shown in FIG. 3, the latch disk is driven counterclockwise to release the retainer strap 59, whereupon the latch disk is locked against further rotation so that the drive spring may drive the pinion gear 34.

Operation of the hydrometer, shown in FIGS. 1 through 12, is as follows:

A series of hydrometers are secured to the suspension line 1, at appropriate intervals. In the conducting of an oceanographic survey, the suspension line may extend to great depths. This has no adverse effect on the hydrometers or the component parts, as all elements may be exposed to the submergence pressure; that is, they need not be contained in pressure-resistant housings. This is true of the batteries, which though forming no part of the present invention, are arranged so that their contents are protected from or subjected to submergence pressures.

Prior to installation on the suspension line, each soft wall cell 17 is completely filled with a reference liquid 19 which may be, if desired, sea water or a selected reference liquid.

When the suspension line has been lowered so as to suspend the series of hydrometers at the desired depths, a messenger, suitably retained at the upper end of the suspension line, is released and engages the target disk 57 of the uppermost hydrometer. This causes the slide bar 49 to be depressed, as indicated in FIG. 3, releasing a second messenger to engage the target disk of the hydrometer located below. Downward movement of the slide bar releases the spring motor so as to cause the ring gear 31a, timing ring 31, and disk 35 to rotate in a clockwise direction, as viewed in FIG. 4. Normally the

openings

36 and 37 are in registry to effect free exchange of the sea water within the hydrometer and the ambient sea water outside the housing 5. Rotation of the diskcloses the openings so that external currents do not disturb the reading. It should be noted that even when the openings are out of registry, the housing need not be watertight.

When the

openings

36 and 37 are closed, the initial rotation of the disk 35 releases the spring 42, clears the cams 41 so that the pivot member 13 and the scale support 23 are free to rotate. As a result, the relative gravitational effect on the hydrometer unit and the scale is constant, irrespective of the angular position occupied by the suspension line, or to the angular position of the housing by reason of the fact that the housing is free to rotate about the axis of the sleeve 3.

The hydrometer unit assumes an angular position relative to the scale that depends upon the relative specific gravity of the reference liquid 19 and the ambient sea water. No compensation need be made for temperature for a reference liquid 19 sufficiently similar to sea water, as the reference liquid is exposed to the same temperature as the ambient sea water. Also, the effect of submergence pressure is cancelled by reason of the fact that the reference liquid is subjected to precisely the same pressure as the ambient sea water. As a result, the angular position of the hydrometer unit is dependent upon the specific gravity of the ambient sea water, due to factors other than submergence pressure and temperature.

In order to make a record of the angular position of the hydrometer, the switch is momentarily closed by the pin 38 so that the current is caused to flow between the marker electrode 22 and the scale support 23, through the scale 26. It has been found feasible to form the scale from paper or similar fibrous material, which has been impregnated with a chemical sensitive to the passage of electric current therethrough, or to the occurrence of minute quantities of electrolytic products in the vicinity of the locations of closest approach of marker electrode 22 and scale 26 at the time of current flow. An example of such material is conventional blueprint paper, which has been previously exposed to light and subsequently developed by water washing. The marker electrode need not contact the paper so that frictional resistance to movement is eliminated. Nevertheless, a momentary current will cause a white mark to appear on the blueprint paper. While blueprint paper is suggested, it should be understood that other suitable electrosensitive materials may be used.

After the record has been made, the disk 35 continues to rotate to complete a half turn; that is, until the pin 38 engages the stop 39. In this final position of the disk 35, the leaf spring 42 has reengaged the cam flanges 41, relocking the hydrometer unit and the scale support, and the

openings

36 and 37 are in registry, to allow free communication of the ambient sea water with that within the hydrometer housing. The hydrometer is now in locked condition, ready for return to the surface by raising the suspension line 1.

While a messenger system is illustrated, other means of operating a series of hydrometers in sequence or simultaneously may be employed. Also, it should be noted that the suspension line may also carry other types of instruments interposed between the hydrometers, depending on the requirements of the oceanographic survey.

The previously described structure illustrated an application of the soft wall hydrometer to the conducting of oceanographic surveys. However, the soft wall hydrometer has many other applications, such as the manual or automatic measurement of specific gravity of liquids in pipelines and various liquid processing plants, where well-known remote reporting or telemetering systems may be used cooperating with angular or linear forms of the soft wall hydrometer, as convenient. The soft wall hydrometer is also adapted to laboratory use for the accurate measurement of specific gravity.

FIGS. 13 to 21 illustrate in essentially diagrammatical form, various other modifications of the soft wall hydrometer.

Reference is first directed to FIG. 13, which illustrates an emergent stem type of my soft wall hydrometer. The hydrometer here illustrated, includes a soft wall cell 71. The walls of the cell may be formed of yieldable plastic material or formed of metal. In the latter case, the configuration being such that the metal offers minimum resistance to the deflection. The cell is completely filled with a reference liquid 72. A stem 73 extends from one end ofthe cell. In FIG. 13, the stem is shown as directed upwardly. Suitably supported over the stem 73, and a portion of the cell 71, is an inverted container 74, connected intermediate its ends to a supply line 75. The container and cell are immersed in an ambient liquid 76, and the upper portion of the container is filled with a comparison liquid 77, of lower density than the ambient liquid. The

fluids

76 and 77 are selected so as to be immiscible and therefore define an interface 78 therebetween. Specific gravity may be measured optically by use of a reference mark 79 on the stem. Movement of the mark may be noted, if the interface 78 is maintained constant, or the interface may be raised or lowered by adding or subtracting comparison fluid through the line 75, so as to maintain the reference mark at a uniform height.

Reference is now directed to FIG. 14. In this case, the stem 73 is directed downward and the cell 71 and its stem are positioned in an upright container 80. In this case, the comparison fluid 81 has higher density than the ambient liquid 76, and preferably the reference fluid 82 has a density equal to or less than the ambient liquid. The position of the hydrometer may be detected in the same manner as that indicated in connection with FIG. 13. Alternatively, the stem 73 may contain an armature 83 and its sensing coils 84 may be immersed in the comparison liquid or surrounding the container 80.

Reference is now directed to FIG. 15. In this embodiment a soft wall cell 85 is illustrated, which as in the previous constructions is highly compliant and offers a little or no resistance to external pressures. As in the previous constructions, the cell 85 is filled with a reference liquid 86. The upper end of the soft wall cell is provided with a low density counterbalance cell 87, whereas the lower end of the soft wall cell is provided with a higher density counterbalance cell 88. Either or both counterbalance cells may be used. The low density counterbalance cell may be filled with a low density liquid, whereas the high density counterbalance cell may be filled with liquid or solid material or a combination of both liquid and solid material. Also the counterbalance cells may be formed of solid material of appropriate density. Either or both counterbalance cells may be used to adjust the net thermal expansivity or compressibility, or both, of the soft wall hydrometer, to desired values.

The soft wall cell is surrounded by ambient liquid 89, contained within a suitable vessel represented by a wall 90. Secured to the lower end of the soft wall cell 85 or to the lower counterbalance cell 88 is a flexible counterbalance link 91, which may be in the form of a chain. The extended end of the link is attached to a traveling nut 92, mounted on an adjustment screw 93, contained within a slotted sleeve 94. The adjustment screw is rotatable by a screw drive 95. A suitable reference mark 96 is provided on the cell and with the adjustment screw fixed, the elevation of the reference mark may be measured optically. Also the reference mark may be maintained at a constant level and the adjustment screw 93 may be moved, the amount of movement being measured by measuring movement of the screw drive 95.

Reference is now directed to FIGS. 18 through 20. This construction lends itself particularly to the laboratory use inasmuch as different reference liquids may be substituted. This construction utilizes a soft wall cell 97 from which extend coaxial integral tubular stems 98. Reference liquid 99 may be drawn into the soft wall cell by immersing one stem in a body of the reference liquid and applying a vacuum to the other stem. One of the stems is closed by a conical pointer tip 100, whereas the other is provided with a seal cap 101, preferably including a screw thread 102 for attachment to an eyelet 103, or other fulcrum means. The eyelet 103 may be freely pivoted on a fulcrum post 104. The hydrometer is immersed in an ambient liquid 105, and an arcuate scale 106 is located for cooperation with the pointer 100.

The soft wall cell 97 may be bridged by a counterweight strap 107, which is provided with a counterweight 108. This simplifies the separation between the centers of gravity and of buoyancy that is required for an angular hydrometer of this type. In this connection, it should be noted that the counterweight may be positive or negative in effect; that is, it may be heavier or lighter than the liquid in which it is immersed.

It should be noted that the cell and stem construction shown in FIGS. 18 through 20 may be employed in the types shown in FIGS. 13 through 17.

Reference is now directed to FIG. 21. In this construction, the force exerted on the hydrometer is opposed by a torsion wire 109, joined at one end to an anchor I and equipped with a dial 111 at its other end, in such a manner that the wire may be placed under tension and twisted about its axis. Mounted on the wire is a connector disk 112, to which is attached, intermediate its ends, a

lever arm

11,3. One end of the lever arm is provided with a counterweight 114, the other end with a soft wall cell 115. In this case the cell is shown as a cylinder with corrugated sidewalls, so as to transmit any outside pressure to the reference liquid contained therein. A pointer 116 and a cooperating scale 117 may be provided so as to measure the position of the cell when immersed in an ambient liquid.

All of the constructions which have been described have in common a soft wall cell which is highly compliant; that is, any external pressure is transmitted to the reference liquid contained within the cell. The reference liquid may correspond to the ambient liquid, such as in the case of the first-described structure, in which the reference liquid is a sample of sea water initially at atmospheric pressure. It is not essential in all cases that the reference liquid be a sample very closely matched to the ambient liquid. It is advantageous, however, to use a sample closely matched to the ambient liquid, particularly if extremely high pressures are involved. If a sample, the chemical composition or physical properties of which is closely matched to the ambient liquid is used, the effect of pressure on the specific gravity of the ambient liquid is compensated or minimized. I

The highly compliant wall of the hydrometer cell offers no appreciable resistance to the flow of heat into or out of the cell, so that the effect of temperature is eliminated 'or minimized.

Heretofore, the measurement of the specific gravity of a liquid, except by the use of elaborate equipment and very careful thermal and pressure control, has been to an accuracy in the vicinity of 1 part in 1000 or a little better. By elaborate instrumentation or precautions and extreme environmental control, hard wall hydrometer procedures can be pushed to accuracies many orders of magnitude better. With the use of the soft wall hydrometer, corresponding accuracies can be achieved without the stringent demands for environmental control imposed by hard wall procedures. For example, a 300 cubic centimeter reference volume soft wall unit essentially in accordance with FIG. 15 was found to have an accuracy of approximately 1 part in 100,000 in measurement of sea water without the requirement for precise thermostatic control. The same accuracy was attained from an angular system of about 30 cubic centimeter reference volume essentially equivalent to that of FIG. 20, also without the requirement for precise thermostatic control. The same measurements performed with hard wall systems would require extreme thermostatic control, to about 001 C. This would be compounded by corresponding precision in equipment standardization and compensation.

In addition, the soft wall hydrometer enables precision measurement under pressures which may be so extreme as to preclude measurements by hard'wall procedures. For example, the in situ measurement of oceanic specific gravity by the apparatus of FIGS. 1 through 12 is intended to be made at an accuracy of 1 part in 100,000. There are no other present specific gravity instruments of corresponding accuracy that may be used under pressures attainable in the ocean, nearly 20,000 p.s.i.

It is to be emphasized that all of the described embodiments measure the specific gravity of the tested fluid, not the density, and that the specific gravity comparison is --made with the reference fluid and the tested fluid at the same temperature and pressure, where the same means identical to the level of accuracy required by the objectives of the measurement. These embodiments do not measure fluid density because they do not measure volume and weight directly. They do not measure specific gravity with respect to water or any other reference fluid at a standard temperature and pressure unless this standard temperature and pressure are among the environmental parameters of the test. The simplest way to describe the measurement performed by any of the described embodiments is to describe it as a measurement of relative buoyancy of a reference quantity of a liquid immersed in the liquid to be tested, or the inverse, a measurement of relative buoyancy of a quantity of a liquid to be tested, immersed in a reference liquid. The critical word is quantity. It is not volume," since this is allowed to vary from the volume when the cell is initially filled to the volume at the time of measurement, under the influence of temperature and pressure changes which occur between the two occasions.

It may seem that this type of measurement preserves buoyant force in transition of a given pair of fluids, one a reference fluid and the other that which 'is to be measured, from a condition of temperature and pressure A to temperature and pressure B, providing the two fluids are sufficiently similar. Similarity is measured by equality of thermal expansion coefficients and of compressibilities, as modified by the remainder of the assembly, for the two liquids, where equality is defined by effective equality to the level of accuracy that is desired for the specific gravity measurement to be performed.

All of the embodiments described have in common the use of a soft or compliant cell wall for isolating the reference fluid from the tested fluid and for readily communicating pressure and temperature changes between these two liquids. In addition, they all have means for adjustment of the instruments with respect to scale standardization and with respect to net effective reference compressibility and thermal expansion coefficient.

Two means of scale standardization are provided in each construction. The first of these is provided by the selection of the reference liquid for the measurement to be made. The second means for scale standardization is the adjustability for sensitivity. In the case of the angular systems, sensitivity adjustment is achieved by control of the angle between the cen ters of buoyancy and gravity, measured at the axis of rotation of the hydrometer. As illustrated in FIGS. 1 through 12, this is accomplished by angular adjustment of cell 17 with respect to arm 14, through adjustment screw 16 and bracket 15. In the case of linear systems, sensitivity adjustment is achieved by design control of the rate of change of displacement, or of force, with specific gravity. As illustrated in the chain-opposed construction of FIG. 15, this is a function of the ratio between nominal volume of the cell 85 and the displaced weight per unit length of the chain 91. As illustrated in the differential hydrometers of FIGS. 13 and 14, this is a function of the cell volume, stem cross-sectional area and the difference in density of the two companion liquids. The other constructions also have easily recognizable sensitivity control systems.

The materials suitable for selection for cell walls, structural members, counterweights, and other parts of linear and angular forms of the soft wall hydrometer constructions will in general have bulk compressibilities and thermal expansion coefficients that can differ appreciably from those of the reference fluid. For example, a corrosion-resistant steel alloy could be selected as the material to be used for a deep ocean in situ soft wall hydrometer as described in FIGS. 1 through 12. The bulk modulus of the alloy may be in the vicinity of 70 times that of sea water, and the bulk thermal coefficient may be in the vicinity of one-sixteenth of that of sea water. A possible cell volume would be 50 cubic centimeters (measured at room temperature and pressure), with a shape as indicated in FIGS. 1 through 12. Let us assume that the SO-cubic-centimeter reference sea water volume requires 0.25 cubic centimeters of cell wall to contain it. Let us also assume that the bracket 15 is designed so as to position its center of gravity on its axis of rotation by the adjustment screw 16, and that the counterweight 21 has been positioned to align the pointer 22 to the correct position on the scale 26 when the hydrometer has been standardized by immersion in a sea water of known specific gravity after the cell 17 has been angularly positioned with respect to lever 13 to produce the desired instrumental sensitivity. These standardizing operations are performed at room temperature at near-zero effective pressure depth.

Now consider the change that takes place on transport of this assembly from essentially zero-ambient pressure to that at an extreme oceanic depth, say 15,000 pounds per cubic inch, assuming no change in temperature for the purposes of this calculation. The reference water volume will be compressed by almost 4 percent, and the volume of the metal in the remainder of the instrument will be compressed about oneseventieth as much, or about 0.06 percent. Since the greater fraction of the compression of the reference-water will have taken place by movement of the opposing cell walls toward one another, and since we have presumed that one metal was used throughout, the angle between the center of the cell and the lever 13, measured around the axis of the journal shaft 9, will remain constant. The standardizing process had produced an angle between the centers of buoyancy and gravity that would be relatively small for an instrument of oceanographic sensitivity. Thus, the position of the center of gravity relative to the lever 13 is essentially unchanged by the pressure. The far greater contributor to the center of gravity is the cell and its contents, and the center of this cell would move inward about 0.06/3==0.02 percent. The remainder of the assembly would also be compressed inward by about the same fraction, producing an inward shift of the center of gravity by the same percentage. The angle between the centers of gravity and of buoyancy will be decreased by approximately the fractional decrease of the cell volume because of the relatively incompressible metal used in the remainder of the assembly. At the high sensitivities of specific gravity instruments useful in oceanographic work, the angle between these two centers is effectively the same as the sine of the angle (when measured in radians), and the angular specific gravity sensitivity is nearly inversely proportional to the sine of the angle between the centers. This means that at the extreme pressure of this example and with this particular selection of materials, the angular specific gravity sensitivity will be increased by approximately 4 percent. If we consider the measurement to be made in the open ocean, a representative specific gravity change from top to bottom could be from 1.0000 at the top to 1.0023 at the bottom, using the surface ocean water as a reference, a difference of 23 parts per 10,000. This difference includes the effects of temperature, but this may be ignored for the purposes of this particular discussion of materials. If we further desire an accuracy of 1 part per 100,000 in specific gravity, this corresponds to a scale that is at least 230 such parts long, a scale whose sensitivity should remain constant within a little better than 1 percent for the optimal case where the central scale location is halfway between the extremes to be measured, at least if scale corrections are not to be applied, or a little better than 0.5 percent for the case where the central scale location is at an extreme. This calls for some form of compensation, either a passive system through design or selection of materials, or an active system through correction of the measurements that have been made by use of depth or other data associated with the measurements.

The bracket 15 may be made at least in part of a material whose compressibility and coefficient of thermal expansion differ from those of the reference fluid and the supporting structure, in this way providing the opportunity for compensation by preventing sensitivity change. The objective is to compensate the unbalanced portion of the hydrometer structure with material selected to give it a net compressibility and ther mal expansion coefficient matched to the ambient and reference fluids to the desired level of accuracy. To return to our example, let us assume that in addition to the 0.25 cubic centimeters of cell wall, there is an additional and equal volume of metal to be compensated from the remainder of the structure. If a suitable plastic material is used as a part of or as a protective coating for bracket 15, a relatively small amount can provide the required compressibility For example, if a silicone rubber whose mean compressibility is 3 times that of sea water is used, approximately 0.2 cubic centimeters (at room temperature and pressure) will be sufficient, if it is positioned near the center of gravity of the 0.5 cubic centimeters of metal to be compensated. The same type of calculation and procedure may be used for thermal compensation for cases of extreme instrumental accuracy and reasonably well-known fluids.

The previous discussion has dealt with an angular form of the soft wall hydrometer construction. Essentially the same type of compensation is available in the linear forms, again to the desired level of accuracy, by balance between the weights, densities, compressibilities and thermal expansion coefficients of the structures and counterweights that are identified in FIGS. 13 through 21. If necessary for extreme accuracy and for a particular fluid of known behavior, two or more compensatory materials may be used to improve the degree of matching and to provide a nonlinear compensatory behavior if necessary.

The present embodiments of this invention are to be considered in all respects as illustrative and not restrictive.

lclaim:

l. A specific gravity sensing instrument, comprising:

a. a closed cell filled with a reference liquid, the wall of said cell being highly flexible whereby, when immersed in an ambient liquid, the reference liquid is subjected to the same pressure as the ambient liquid;

b. means for supporting said cell in said ambient liquid for rotation about a horizontal axis, in response to relative change in density of the reference liquid and ambient liquid;

0. means for measuring said rotation;

. means for adjusting said cell on said supporting means to vary the location of the center of buoyancy with respect to said axis of rotation;

e. and a counterweight adjustably mounted on said supporting means to vary the location of the center of gravity with respect to said axis of rotation.

2. An instrument, as defined in claim 1, wherein said measuring means includes:

. an electrode, a confronting-scale element containing a material sensitive to passage of an electric current, and means for establishing a momentary electric current passing between said electrode and said scale element to produce an identifying mark on said scale element.

. An instrument, as defined in claim 1, wherein: said cell is attached to a lever arm pivoted intermediate its ends, and said supporting means includes a shaft journaling said lever arm;

. said measuring means include a pointer on said lever arm and a scale positioned for cooperation with said lever

Claims

1. A specific gravity sensing instrument, comprising: a. a closed cell filled with a reference liquid, the wall of said cell being highly flexible whereby, when immersed in an ambient liquid, the reference liquid is subjected to the same pressure as the ambient liquid; b. means for supporting said cell in said ambient liquid for rotation about a horizontal axis, in response to relative change in density of the reference liquid and ambient liquid; c. means for measuring said rotation; d. means for adjusting said cell on said supporting means to vary the location of the center of buoyancy with respect to said axis of rotation; e. and a counterweight adjustably mounted on said supporting means to vary the location of the center of gravity with respect to said axis of rotation.

2. An instrument, as defined in claim 1, wherein said measuring means includes: a. an electrode, a confronting-scale element containing a material sensitive to passage of an electric current, and means for establishing a momentary electric current passing between said electrode and said scale element to produce an identifying mark on said scale element.

3. An instrument, as defined in claim 1, wherein: a. said cell is attaChed to a lever arm pivoted intermediate its ends, and said supporting means includes a shaft journaling said lever arm; b. said measuring means include a pointer on said lever arm and a scale positioned for cooperation with said lever arm.

4. An instrument, as defined in claim 3, wherein: a. said scale is mounted on a pivotal frame connected to said shaft independently of said cell-supporting lever arm.

5. An instrument, as defined in claim 4, wherein: a. clutch means is provided to secure said lever arm and pivotal frame to said shaft; b. and means is provided to release said clutch for a predetermined interval.