GB2041541A - Pendulum densimeter - Google Patents

Abstract

A densimeter for measuring the density of a fluid includes a disc body 12 rotatable about an axis 14. Two open cavities 40, 42 are provided in the body so that the centre of buoyancy of the body is displaced from the axis. The body 12 has a generally homogeneous density and includes a region 44 wherein the density is different from that of the disc. Because of the density anomaly the centre of gravity of the body 12 is displaced from both the centre of buoyancy and from the axis 14. When the densimeter is placed in a fluid, the disc will rotate about its axis. The density of the fluid is determined from the angular position of the disc upon reaching equilibrium. Another embodiment employing weighted arms mounted on a hub is disclosed. <IMAGE>

Description

SPECIFICATION Pendulum densimeter This invention relates to devices for measuring the specific gravity of a fluid, commonly known as densimeters.

Densimeters have been used for many years to measure the specific gravity of fluids. For measuring the specific gravity of liquid in a battery, hydrometers are used which include a float in a hollow tube.

As the fluid is drawn up into the tube the float seeks a level in the fluid proportional to the specific gravity of the fluid. Various types of hydrometers are shown in U.S. Patents 1,898,903; 2,674,119; and 2,674,120. A densimeter for measuring the specific gravity of a moving stream of fluid is shown in U.S.

Patent 2,332,807. There are many applications in which these devices are not suitable.

For example, when the specific gravity of an opaque fluid such as petroleum or milk is needed, the indicator of the device must be such that it can be read without regard to the opacity of the petroleum or milk or through a foam build-up of each. Also the hydrometer of the U.S. Patent No. 1,898,903 is not practical with large, deep containers such as tank cards because it would have to be mounted at the top of the car. Consequently, a densimeter is needed that can be used with a wide range of fluids and in hard to reach locations.

Another problem is involved with moving fluids. The response of the densimeter must not follow the motion of the fluid. The hydrometer of U.S. Patent 2,674,119 has serrated edges which will interact with the stream of fluid. Also, the device of U.S. Patent 2,332,807 could not be used directly in a moving stream of fluid because its response would correspond to the hydrodynamic forces.

The present invention of a pendulum densimeter may be used to measure the specific gravity of a fluid whether in motion or not.

According to the invention there is provided a device for measuring the density of a fluid comprising at least one member supported for rotation about an axis, said at least one member having a centre of gravity and a centre of buoyancy displaced from each other and from the said axis whereby when placed in the fluid the member adopts an equilibrium angular position about said axis which is representative of the density of the fluid.

The densimeter may include one or two members mounted on a shaft so that at least one member is rotatable on or with the shaft.

When the densimeter is placed in a fluid, the member oscillates to an equilibrium position.

The equilibrium position reached is an indication of the specific gravity of the fluid. The outer contours of the rotatable member are preferably rounded so as to minimize the fluid dynamic effects when rotating in the fluid or in a moving fluid.

Another embodiment of the densimeter includes two rotatable members on the same shaft where one of the members rotates counter to the other for more accurate measurements is gases or to amplify the measurement taken.

A preferred feature is that the rotatable member includes two circular holes on one side of a diameter for maximally displacing the centre of buoyancy from the axis as well as minimizing fluid dynamic effects.

Some preferred embodiments of a device according to the present invention are illustrated in the accompanying drawings, and will now be described in detail by way of example.

In the drawings: Figure 1 is an isometric view of one embodiment of the invention; Figure 2 is another isometric view of the embodiment of Fig. 1; Figure 3 is a plan view of a portion of another embodiment of the invention; Figure 4 is a plan view of a portion of another embodiment of the invention; Figure 5 is an enlarged fragmentary sectional view of a modification to Fig. 1; Figure 6 is a plan view of a portion of another embodiment of the invention; Figure 7 is a plan view of a portion of another embodiment of the invention; Figure 8 is a plan view of a portion of another embodiment of the invention; Figure 9 is a vertical sectional view of another embodiment of the invention; Figure 10 is a fragmentary sectional view of another embodiment of the invention; Figure 11 is an enlarged isometric view of a portion of the embodiment of Fig. 10;; Figure 12 is a plan view of a floating bearing embodiment; Figure 13 is a fragmentary vertical sectional view of another embodiment of the invention; Figure 14 is a plan view of another embodiment of the invention; Figure 15 is an elevational view of one means for locking one embodiment.after a reading has been taken; Figure 16 is a side view of the apparatus of Fig. 15; Figure 1 7 is an elevational view of an embodiment of the present invention with one form of telemetering means; Figure 18 is a cross-sectional view taken along the line 18-18 of Fig. 17, and Figure 19 is an elevational view of an embodiment of the present invention with another form of telemetering means.

Referring now to Figs. 1 and 2, there is shown a densimeter comprising a first disc 10 rotatably mounted on a shaft 1 4 through a bore 1 6 that extends through disc 1 0. A second disc 1 2 is mounted on shaft 1 4 through a bore 17. The discs 10, 12 are preferably circular and of a homogeneous material. The discs 10, 1 2 are retained on shaft 14 by means of a retaining washer 1 8 fixedly attached to the shaft. Hollow regions 22 and 24 are formed in disc 10. The hollow regions 22 and 24 are shown as two circular bores, positioned on one side of a diameter of disc 10.The hollow regions 22 and 24 cause the centre of buoyancy of the disc to be displaced from the suspension point at bore 1 6. Another requisite is to make the hollow region on the inside or flat surface of disc 10 so as not to interfere with the fluid dynamic characteristics of disc 1 0. Indentations or recesses with steep entry angles such as a perpendicular bore offer little fluid resistance and are preferred.

Disc 10 also has a mass insert 26 that is placed in a bore 28. Insert 26 is shown as a circular disc but any size or shape of insert may be used which has the effect that the centre of gravity of the disc 10 with insert 26 is displaced from both bore 1 6 and the centre of buoyancy. The insert may be either liquidfilled or solid. Insert 26 is typically flush with the surface of disc 10 so as to minimize its effect on the fluid dynamic characteristics of the disc 10.

Disc 1 2 which is also mounted on shaft 14 has a larger diameter than disc 10. The larger diameter of disc 1 2 allows a density scale 30 to be placed thereon. Disc 10 is provided with an indication marker 31 that co-operates with scale 30 to indicate the specific gravity of the fluid. As shown in Fig. 2, disc 12 has bores 34 therethrough to allow fluid collecting between disc 10 and disc 1 2 to pass through.

Since the primary function of disc 1 2 is to provide a scale 30 thereon, disc 1 2 need not be circular and could be of almost any shape that would not interfere with the rotation of disc 10.

In operation, the densimeter of Fig. 1 is placed in the fluid to be measured so that bore 1 6 has a horizontal component to its orientation. It may be extended into the fluid by shaft 14. If the location of the fluid requires an extremely long shaft, a chain or cable might be more suitable than a shaft.

When the device encounters the fluid, the effect of the displacement of the centre of buoyancy from the centre of gravity of disc 10 and the displacement of both centres from bore 1 6 causes disc 10 to oscillate on shaft 14 until equilibrium is reached when the downward gravity force balances the upward buoyant force. The equilibrium angular position of disc 10 on shaft 14 indicates the density of the fluid. Since disc 1 2 does not rotate, the marker 31 will indicate the density on scale 30.

It is generally not necessary to lock disc 10 to disc 12 because the bores 34 in disc 1 2 allow fluid between the discs to pass through upon removal from the fluid. if care is taken upon removal, the surface tension of the fluid will cause disc 10 to hold its angular position.

Also if the opposing surfaces of discs 10 and 1 2 are rough, the interaction of the two rough surfaces will cause the disc 10 to hold its position. If the fluid is excessively turbulent it might be necessary to mechanically lock disc 10 as will be described hereinafter. An advantage of this densimeter when used with a turbulent fluid is that it is substantially in the shape of a flat circular disc which has very little hydrodynamic interference either with a moving fluid or oscillating in a fluid.

Referring now to Fig. 3, there is shown another embodiment of disc 1 2 that is rotatably mounted on shaft 14 through bore 1 7 as in Figs. 1 and 2. Disc 10 is not shown for clarity. Disc 12 is made of the same homogeneous material as disc 10 and includes hollow regions 40 and 42 and an insert 44 which are similar in size, shape, location, and density to those of disc 10.When placed on shaft 14, disc 1 2 is oriented so that its insert 44 and hollow regions 40, 42 cause it to rotate in the opposite direction to disc 1 0. This is accomplished by mounting disc 1 2 on shaft 1 4 so that insert 44 is in a quadrant of disc 1 2 adjacent the quadrant container insert 26 in disc 1 0. This can be seen by comparing Figs. 1 and 3.

In this embodiment the densimeter is placed in the fluid to be measured and both discs 10 and 1 2 rotate to an equilibrium position on shaft 1 4. Disc 1 2 is mounted on shaft 14 so as to rotate in the opposite direction to disc 1 0. Thus, a much more accurate scale 30 may be used on disc 1 2 since the same fluid density will cause twice the total angular rotation on shaft 14. if hollow regions 40, 42 are bored completely through disc 12, the bores 34 as shown in Fig. 1 will not be needed to drain the fluid between the discs so that the discs 1 0,1 2 lock together- by surface tension of the fluid and by roughening their opposing surfaces.

Again if care is exercised this densimeter may be used without a locking mechanism.

Referring now to Fig. 4 there is shown another embodiment of disc 1 2 wherein scale 30 is placed on a ring 31 of a density different from ring 12. Ring 31 is attached to disc 12, and attachment may be accomplished by screws or bolts or by cooling disc 12 until ring 31 fits therearound. The addition of ring 31 of density different from disc 1 2 provides the feature of changing the density of disc 1 2. If the device were to fall completely into the fluid being measured, ring 31 could act as a buoy to float the densimeter on the surface for easy retrieval. A similar ring 31 might be mounted around disc 10 so that disc 10 will also float. On the other hand, by adding a ring 31 of sufficient weight to disc 10, the locking of the angular position of disc 10 will be augmented if the device is removed from the liquid so that a heavy disc 10 bears against disc 1 2.

Referring now to Fig. 5, there is shown an enlarged view of an insert 50 which is similar to the insert 26 of disc 10. Insert 50 is shown as a flat disc although any size or shape may be used. The insert 50 has a bore 52 therein in which another insert 54 is carried. Insert 54 is preferably made of metal.

A bimetallic strip 56 tyically in the form of a helical spring attaches at one end to the insert 50 and at the other end to the metal insert 54.

This form of insert 50 is used to provide for temperature compensation. As the temperature of the fluid may vary, the centre of buoyancy of the disc 10 will vary due to contraction or expansion. Since the coefficient of expansion of the material of disc 10 may differ from that of the fluid being measured, the density measured will be incorrect due to temperature variation. The temperature- compensating means of metal insert 54 and bimetallic spring 56 acts to change the centre of gravity of disc 10 by moving insert 54 in correlation with change in temperature. This change in the centre of gravity affects the rotation of the discs about shaft 14 and thereby compensates for changes in temperature. If the dual rotating disc device of Fig. 3 is used, an insert 50 also replaces insert 44 of disc 12.

Another important design factor of insert 50 is the angle of the bore 52 to the vertical. As discs 10 and 1 2 rotate on the shaft, the angle of the bore 52 to the vertical will also change.

The pull of gravity on metal insert 54 and bimetallic spring 56 will affect the temperature compensation of spring 56. Consequently, the initial angle of the bore 52 with respect to the vertical must be predetermined for each instrument depending upon the desired density range of each. Insert 50 could, however, be rotatably mounted in discs 10, 1 2 so that the angle of bore 52 to the vertical will not change upon rotation of discs 10, 12.

Referring again to Fig. 1, the angular displacement of disc 10 on shaft 14 does not vary linearly with density of the surrounding fluid. Telemetry means, hereinafter described, such as linear differential transformers, piezoelectric devices or any other suitable devices may be used to transmit a signal corresponding to the angular position of disc 10 on shaft 1 4 and thus the specific gravity of the surrounding fluid may be monitored. The electronic signal, without providing for linearization, will correspond to the angular position of disc 10 on shaft 14, and non-linearities of up to 9% for a rotation of 180 may result. If a telemetry receiver expects a linear input, which is desirable, inaccuracies of up to 9% for a rotation of 180 may therefore result.

The embodiment of Fig. 6 linearizes such angular non-linearities. In this embodiment disc 10 is modified to include an arcuate groove 60 in which is disposed a mass 62.

Mass 62 may be spherical or cylindrical or any suitable shape to allow'it to roll in groove 60. The modified disc 10 is then rotatably mounted to shaft 14 as in Fig. 1 or Fig. 3.

Upon rotation of disc 10, mass 62 will roll in groove 60 and the position of mass 62 will vary with the angle of rotation of disc 10.

Thus, the centre of gravity of disc 10 will vary with rotation. By this manner linearity is possible with rotations of + 150 .

The particular shape of arcuate groove 60 is not limited. Fig. 6 shows a circular arc groove 60; however, Fig. 7 shows a spiral groove 70 that is closer to the axis of suspension of the disc at one end of the groove than at the other. Mass 72 is carried by groove 70 and rolls in groove 70 as disc 10 rotates on shaft 14. The output (position) of disc 10 will be linearized by the change of the centre of gravity of disc 10 due to the position of mass 72 in groove 70. The shape of groove 70 will have to be determined for each type model.

Referring now to Fig. 8 there is shown another embodiment of the linearizing arcuate groove. A cavity 80 in disc 90 having an arcuate inner perimeter surrounds the axis of suspension, i.e. bore 16, and may be filled with a liquid and contain a mass 82 herein which may roll on the perimeter thereof. Hollow regions 84 and 86 in disc 90 function like regions 22, 24 of disc 10 in Fig. 1 to displace the centre of buoyancy; however, the insert 26 of disc 10 in Fig. 1 has been replaced by mass 82. The density of the liquid used in the cavity and the coefficient of expansion thereof should preferably match that of the disc material. The mass 82 may be of any suitable mass that will roll on the perimeter of the cavity, typically a ball bearing or a cylindrical disc.

Instead of using a mass 62, 72 or 82, the embodiments of the linearity devices of Figs.

6 to 8, respectively, might have groove or cavity 60, 70 or 80, respectively, filled with a liquid of density different from that of the disc 10 or 90, such that an air bubble is trapped within the groove or cavity 60, 70, or 80. As disc 10 or 90 rotates, the air bubble will shift due to the downward gravitational force thereby effectively shifting the centre of gravity of the fluid in the groove. Thus the centre of gravity of disc 10, 90 will be shifted and linearity may be achieved.

Referring now to Fig. 9, there is shown another embodiment of the densimeters of Figs. 1 to 8 that may be used with liquids such as drilling mud having solids which tend to settle out and adhere to any devices encountered thereby. The discs 10 and 1 2 are similar to discs 10 and 12 of Fig. 1 except there are no right angle corners or edges for mud or solids to collect thereon. All surfaces are at steep angles of inclination to the vertical including, for example, the perimeters of hollow regions 22 and 24 of disc 10 and the holes 34 of disc 1 2 of Fig. 1. Since drilling mud generally undergoes irregular motion, the inertial qualities of the disc 10 are designed so that the effects of the motion of the mud on the rotation of discs 10 and 1 2 will be minimized.

Referring now to Fig. 10, there is shown another embodiment of a densimeter. Spokes 100, 102 are connected to a bearing 104 rotatably mounted on a shaft 1 06. Threadedly connected to each outer end of spokes 100, 102 are masses 108 and 110, respectively.

Masses 108 and 110 and spokes 100, 102 combine to provide a first configuration that has its centre of gravity and the centre of buoyancy displaced from each other and from the centre of suspension at bearing 104. A second configuration similar to the first is composed of masses 11 2 and 114 threadedly connected to the ends of spokes 116, 118, respectively. As shown in Figs. 10 and 11, spokes 116, 118 are then connected to a bearing 1 20 that is also rotatably mounted to shaft 106. Bearings 104 and 120 are locked together through splines 1 22 on bearing 104 and grooves 1 24 on bearing 1 20. It is desirable that the first set and second set are similar in size and design characteristics.An advantage of a four-spoke device is that the first set of spokes, masses, and bearings can be made identical to the second set. Since each bearing interlocks with the other, the first set of spokes and masses can be calibrated separately from the second set. Then when both sets have been adjusted, which may be accomplished by changing the position of the masses on the threads of their respective spokes, they are interlocked through the bearings onto shaft 106.

This embodiment of the densimeter of Figs.

10 to 11 is useful to measure the density of gases. Since gases have very low densities, the densimeters of Figs. 1 to 8 would not be responsive enough for accurate measurement because of manufacturing difficulties due to accuracy considerations and friction generated during rotation of the discs 10, 1 2. A fourspoke densimeter, as shown in Fig. 10, can be much more responsive and sensitive to gas densities. By varying the length of the spokes and the masses, this four-spoke device can also be made responsive to a wide range of gas densities.

For measuring gas density, the bearings 104, 1 20 may, however, have too much friction when rotating on a shaft such as shaft 14 to be responsive to a general range of gas densities. Figure 1 2 shows a substitute bearing system for bearings 104, 1 20 wherein shaft 14 is mounted on a fixed bearing 1 30 that is placed in a container 1 32 of mercury 1 34. Bearings 1 30 float on the mercury 1 34 so that there is very little friction.The material of the container 1 32 should be of a material that will form an amalgam on the inside edge with the mercury 1 34 in the container 1 32 so that a conventional meniscus will form and the mercury 1 34 does not stick ta the inside of container 1 32. This floating bearing is sufficiently low in friction loss to be useful in gas density measurement, however, other types of low friction bearings such as air bearings or magnetic bearings may be used.

Referring now to Fig. 13, there is shown an embodiment of the densimeter of Fig. 10 that is designed for use with flowing gases. A housing 200 is joined at one end to an inlet conduit 202 and at the other end to an outlet conduit 204. Housing 200 provides a plenum chamber 206 in which is disposed a front dome-like shield 208 centrally located in the chamber 206. Orifices 210 in front shield 208 allow gas flowing from inlet conduit 202 to outlet conduit 204 to pass through shield 208 A back shield 212 is also disposed in the plenum chamber 206 downstream of the front shield 208. Between the front and back shields 208, 212, a chamber 230 is formed, and the four-spoke device 214 of Fig. 10 is rotatably mounted therein on shaft 216. Shaft 216 is coaxially disposed in the housing 200 and is mounted on bearings 218, 220 to struts 222 which are connected to housing 200.Shaft 216 extends through both front shield 208 and back shield 212. An electronic readout device may then be used to monitor the angular position of the shaft 21 6.

In this embodiment, the gas sample flows from inlet conduit 202 into plenum chamber 206. Most of the gas flows around front shield 208 and back shield 212 and into outlet conduit 204. Orifices 210 in front shield 208 allow the gas to enter chamber 230 between front shield 208 and back shield 212. Upon encountering the gas in chamber 230, the four spoke device 214 will rotate with shaft 216 to an equilibrium position so that the buoyant forces and gravitational forces are equalized. The angular equilibrium position of shaft 21 6 will thus correspond to the specific gravity of the gas. An electronic readout device then will monitor the shaft 216 position to a recording station. The back shield 212 is arcuately contoured at 240 so as to shield the four-spoke device 214 from turbulence resulting from the gas flowing around front shield 208.

The embodiment of Fig. 1 3 is a highly sensitive device for making gas density measurements in a flowing gas stream. By making the measurements in chamber 230 the gas will be substantially at rest and the fluid dynamic effects on the four-spoke device 214 will be negligible.

Referring now to Fig. 14, there is shown another embodiment of a densimeter for measuring gas densities in which accurate measurements are necessary and friction losses are important. A disc device such as disc 10 shown in Fig. 1, consisting of circular disc 300, hollow regions 302, 304, and heterogeneous insert 306, is disposed on a platform 308. Platform 308, which may be straight or curved, is tilted by means of screws 310. Disc 300 has an indication marker 312 pointing downwardly.

Typically in this embodiment, the disc 300 and platform 308 are surrounded by the fluid.

The platform 308 is then tilted so that the disc 300 will roll thereon until the marker 312 points downwardly. By calibrating the angle of tilt for a known gas, the angle of tilt for a gas sample will correspond to the density of the gas. This device alleviates some of the problems with friction because the only friction involved is rolling friction between disc 200 and platform 208, and rolling friction is small compared to the sliding friction encountered with bearings.

Referring now to Figs. 1 5 and 16, there is shown another embodiment of a densimeter, a single disc similar to the disc 10 shown in Fig. 2 consisting of a circular disc 400, circular hollow regions 402 and 404 which are positioned on one side of a diameter of the disc 400 for shifting the centre of buoyancy away from the axis of the disc 400 for obtaining maximum buoyancy while at the same time minimizing dynamic resistance. A heterogeneous insert 406 is provided in the disc 400 for positioning the centre of gravity of the disc 400 away from both the axis of the disc 400 and the centre of buoyancy of the disc 400. The disc 400 is supported on its axis by a support such as shaft 408 whereby the disc 400 may oscillate when it is placed in a liquid to be measured until it reaches its equilibrium.While the disc 400 may suitably measure specific gravity of a fluid which can be measured and indicated by markings 410 as they are positioned relative to the shaft 408, it may be desirable in some instances to provide a locking means to lock the disc 400 in position so that it can be retrieved from the fluid and its rotational position observed for measurement purposed. One suitable locking means may be a float 41 2 which is slidably positioned on the shaft 408. Thus, when the disc 400 is positioned in a fluid, the float 412 will move up the shaft 408 and out of contact with the disc 400.Once the disc 400 has reached its equilibrium position which is a measurement of the specific gravity of the fluid in which it is immersed, the support 408 is raised and the float 41 2 will slide down the upper portion of the shaft 408 to rest against the outer periphery of the disc 400 to prevent its rotation as it is removed from the fluid.

Preferably, the interconnection between the float 41 2 and the shaft 408 is non-circular to prevent rotation of the float 412 relative to the shaft 408 which could also rotate the disc 400 causing erroneous readings. If desired, a stop 414 can be placed on the shaft 408 to limit the distance of travel of the float 41 2 away from the disc 400.

Referring now to Figs. 1 7 and 18, a single disc embodiment is shown utilizing telemetering for measuring the rotational position of the disc and thus the specific gravity of the fluid in which it is immersed. The disc 500 is a circular disc including circular hollow regions 502 and 504 and a heterogeneous insert 506 and is rotatable about its axis on a support 508. For telemetering a circular groove 510 is positioned around the disc 500 and contains two parallel resistance conductors 512 and 514. Also positioned in the groove 510 is a movable electrical conductor such as mercury blob 516 which maintains its position in the bottom part of the groove 510 as the disc 500 moves.The conductor 516 will short out between the parallel conductors 51 2 and 51 4 and a measurement of the resistance by leads 518 and 520 would be a measurement of the rotational position of the disc 500 and thus of the specific gravity of the fluid. Of course, the leads 518 and 520 should be sufficiently slack so as not to interfere with the rotation of the disc 500 during measurement.

Referring now to Fig. 19, another suitable means for telemetering the rotational position of a single disc is shown. The circular disc 600 having circular hollow regions 602 and 604 and a weighted insert 606 is rotatable about its axis on a support 608 which may be suitably supported such as on a float 61 0. A shaft 61 2 is secured to and rotates with the disc 600. Pivotally connected to each end of the shaft 612 are identical rods 614 and 616 which extend upwardly. A suitable measuring means such as a linear differential transformer measures the vertical position of the rod 614 and thus of the rotational position of the disc 600. If desired, the other rod 61 6 may pass through an electromagnetic vibrator 618 for applying vibrations to the rods 616, the shaft 61 2 and the disc 600 which is advantageous in some instances when the disc 600 is attempting to measure specific gravity of highly viscous fluids such as drilling muds.

Claims (3)

1. A device for measuring the density of a fluid comprising at least one member supported for rotation about an axis, said at least one member having a centre of gravity and a centre of buoyancy displaced from each other and from the said axis whereby when placed in the fluid the member adopts an equilibrium angular position about said axis which is representative of the density of the fluid.

2. A device according to Claim 1, comprising a shaft, a first member having an axis, said first member having means for rotatably mounting said first member to said shaft along said axis, a second member having an axis, said second member having means for rotatably mounting said second member to said shaft along said second member axis, said first member having means for displacing the centre of buoyancy of said first member from said first member axis, said second member having means for displacing the centre of buoyancy of said second member from said second member axis, said first member further including means for displacing the centre of gravity of said first member from said first member centre of buoyancy and from said first member axis, and said second member further including means for displacing the centre of gravity of said second member from said second member centre of buoyancy and from said second member axis.

2. A device according to Claim 1, comprising a shaft, a first member having an axis, said first member having means for rotatably mounting said first member to said shaft along said axis, a second member having an axis, said second member having means for rotatably mounting said second member to said shaft along said second member axis, said first member having means for displacing the centre of buoyancy of said first member from said first member axis, said second member having means for displacing the centre of buoyancy of said second member from said second member axis, said first member further including means for displac ing the centre of gravity of said first member from said first member centre of buoyancy and from said first member axis, and said second member further including means for displacing the centre of gravity of said second member from said second member centre of buoyancy and from said second member axis.

3. A device according to Claim 2 wherein said means for displacing the centre of buoyancy in said first and second members includes hollow regions having at least one opening in the outer surfaces of said first and second members, respectively.

4. A device according to Claim 3, wherein said means for displacing the centre of gravity in said first and second members includes recessed regions in said first and second members, respectively, said regions being filled with material heterogeneous with respect to the first and second members, respectively.

5. A device according to Claim 2, wherein said first and second members have smooth and continuous outer peripheral edges.

6. A device according to Claim 5 wherein said first and second members are circular discs.

7. A device according to Claim 5, wherein said means for displacing the centre of gravity in said first member is located to cause said first member to rotate in an angular direction on said shaft opposite the direction of rotation of said second member on said shaft.

8. A device according to Claim 1, comprising a shaft, a first member rotatably mounted on said shaft along the axis of said first member, a second member fixedly mounted to said shaft and adjacent said first member, said first member having means for displacing the centre of buoyancy of said first member from said first member axis, said first member further including means for displacing the centre of gravity of said first member from the centre of buoyancy of said first member and from said first member axis, and said second member having means for passing fluid between the first and second members through the second member.

9. A device according to Claim 1, comprising a shaft, a disc having a non-interrupted outer periphery and an axis and rotatably mounted to said shaft through said axis, first means for displacing the centre of buoyancy of said disc from said axis, and second means for displacing the centre of gravity of said disc from both said centre of buoyancy and said axis.

1 0. A device according to Claim 9, wherein said first displacing means includes a hollow region having at least one opening on the surface of said disc, and said second means includes weight means for altering the mass distribution of said disc.

11. A device according to Claim 10, wherein said weight means includes a recessed region in said disc and a mass mounted in said recessed region.

1 2. A device according to Claim 9, wherein said second means includes weight means for altering the mass distribution of said disc, said weight means including temperature compensation means for altering the centre of gravity of the disc to compensate for changes in temperature of the fluid.

1

3. A device according to Claim 9, wherein said second means includes both weight means for altering the mass distribution of said disc and temperature compensation means for altering the centre of gravity of the disc to compensate for changes in temperature of the fluid, and said disc further has means for compensating for the angular position of the disc on the shaft to maintain the change in density with respect to the change in angular position substantially constant over a typical range of fluid specific gravity.

14. A device according to Claim 1 3 wherein said angularity compensating means includes a mass rollable along a track included in said disc.

1 5. A device according to Claim 14, wherein said track has arcuate contours and is located inside the disc.

1 6. A device according ot Claim 14, wherein said mass includes a liquid with an air bubble trapped therein.

17. A device according to Claim 14, wherein said track comprises a smooth cavity inside the disc.

1 8. A device according to Claim 1 comprising a circular disc having an axis and an axial bore therethrough, a shaft extending through said bore and rotatably mounting the disc thereon, a cavity in said disc with at least one opening on the surface of the disc for displacing the centre of buoyancy of the first disc from said axis, a first material mounted in said disc for displacing the centre of gravity of said disc from said centre of buoyancy and from said axis, reference means for indicating a reference angular position of said disc on said shaft, and means for indicating the angular position of said disc on said shaft relative to said reference angular position.

1 9. A device according to Claim 18 further including a second circular disc having an axis and an axial bore therethrough and rotatably mounted on said shaft adjacent said first disc, said second disc including a cavity therein with at least one opening on the surface of said second disc for displacing the centre of buoyancy of said second disc from said second disc axis, and a second material mounted in said second disc for displacing the centre of gravity of said second disc from said second disc centre of buoyancy and from said second disc axis.

20. A device according to Claim 19, wherein said first material is added to at least one quadrant of the flat face of said first disc and said second material is added to at least one quadrant of the flat face of said second disc, said second disc quadrant being a quadrant adjacent to said first disc quadrant.

21. A device according to Claim 20, wherein the outer peripheral edges of said first and second disc are bevelled and the peripheral edges of said cavities are also bevelled.

22. A device according to Claim 1 comprising bearing means having an axis and a bore therethrough along said axis, a shaft extending through said bore and said bearing means being rotatably mounted thereon, said bearing means being partable and having spokes extending therefrom, and weights threadedly connected to said spokes for adjusting the centre of gravity and centre of buoyancy of said device.

23. A device according to Claim 1 comprising bearing means having an axis, a shaft extending from said bearing means and being fixedly mounted thereto, spokes attached to said bearing means, weights threadedly connected to said spokes for adjusting the centre of gravity and centre of buoyancy of the combination of said bearing means, shaft, spokes and weights, and a container containing mercury, said bearing means floating on said mercury in said container.

24. A device according to Claim 1, comprising a housing, an inlet conduit and an outlet conduit in communication through said housing, a fluid supply connected to said inlet conduit so that a fluid stream flows from said inlet conduit to said outlet conduit, front shield means mounted to said housing for diverting said fluid stream, back shield means mounted to said housing for limiting turbulent backflow, said front shield means defining a chamber therebetween, said front shield means having at least one fluid passageway to permit some of said fluid stream to enter said chamber, a shaft mounted in said housing, bearing means having an axis and a bore therethrough along said axis, said bearing means being rotatably mounted on said shaft, spokes connected to said bearing means and extending therefrom, and weights threadedly connected to said spokes for adjusting the centre of gravity and centre of buoyancy of said bearing means.

25. A device according to Claim 1, comprising a platform, tilt means for tiltably moving said platform, and a circular disc carried by said platform, said disc including means for displacing the centre of gravity and the centre of buoyancy thereof.

26. A device as defined by Claim 9, further comprising density means for changing the density of said disc.

27. A device according to Claim 26, wherein said density means includes a ring having an inner diameter being substantially equal to the diameter of said disc and connected to said disc, said ring having a density different from said disc.

28. A device according to Claim 1, comprising a circular disc having an axis and an axial bore therethrough, a shaft extending through said bore and rotatably mounting said disc, said disc including two circular holes therein both positioned on one side of a diameter of the disc for displacing the centre of buoyancy of the disc from said axis, a material mounted in said disc for displacing the centre of gravity of said disc from said centre of buoyancy and from said axis, and means for measuring the angular position of said disc relative to said shaft.

29. A device according to Claim 28 including electrical means for measuring the angular position of said disc.

30. A device according to Claim 29, wherein the electrical means includes a circular body having first and second circular resistance wires therein and a movable conductive body.

31. A device according to Claim 29, wherein the electrical means includes a shaft connected to the disc and a transducer connected to the shaft for measuring the position of the shaft.

32. A device according to Claim 29, wherein the electrical means includes a shaft extending through the axis of the disc, a rod connected to each end of the shaft, a transducer connected to one of the rods, and a vibrator connected to the other rod.

33. A device according to Claim 28 including locking means for locking the disc in position after a measurement.

34. A device according to Claim 33, wherein the locking means includes a float slidably connected to the shaft and positioned above the disc for disengaging the disc when the disc is inserted in a fluid, but which engages the disc when the disc is removed from the fluid.

35. A device for measuring the density of a fluid substantially as hereinbefore described with reference to the accompanying drawings.

CLAIMS (7 Nov 1979)

1. A device for measuring the density of a fluid comprising at least one circular member supported for rotation about an axis, said member including a recessed region therein for displacing the centre of buoyancy from the said axis, and having a material mounted in said member for displacing the centre of grav ity from the said axis and from said centre of buoyancy, whereby when placed in the fluid the member adopts an equilibrium angular position about said axis which is representative of the density of the fluid.