WO2008104967A2

WO2008104967A2 - Fluid measurement system

Info

Publication number: WO2008104967A2
Application number: PCT/IL2008/000100
Authority: WO
Inventors: Moshe Kline; Yair Yosef Hammer
Original assignee: High Check Control Ltd.
Priority date: 2007-02-26
Filing date: 2008-01-22
Publication date: 2008-09-04
Also published as: WO2008104967A3; IL181568A0

Abstract

Apparatus (20) for measurement of fluid (24) in a container (22) includes a tube (26), which is vertically disposed within the container. A bob (28) is vertically movable within the tube and has a rest position at a location in the tube that is determined by a height of the fluid in the container. A cord (32) extends within the tube and has an upper end and a lower end, which is connected to the bob. A control unit (34) is connected to the upper end of the cord so as to move the bob vertically in the tube between the rest position and a predetermined reference position, above the rest position, while measuring a distance traversed by the bob between the rest and reference positions so as to determine the height of the fluid in the container.

Description

FLUID MEASUREMENT SYSTEM

FIELD OF THE INVENTION

The present invention relates generally to measurement systems and methods, and specifically to measuring fill height and other properties of fluid in a container.

BACKGROUND OF THE INVENTION

In many applications, it is desirable to measure the height of fluid in an opaque container, such as a large tank, without opening or otherwise disturbing the fluid in the container. A variety of devices have been described for this purpose.

For example, U.S. Patent 4,337,656, whose disclosure is incorporated herein by reference, describes a device for measuring the depth and temperature of a liquid stored in a tank. The device includes a hermetically-sealed, vertically-disposed tube, having ultrasonic transmitter/receiver devices at either end thereof. A float encircles the tube and moves up and down with the level of liquid in the storage tank. A reflector inside the tube is magnetically interconnected to the float so that the reflector moves up and down with the float. Other ultrasonic fluid height measurement devices are described in

U.S. Patents 5,076,101 and 5,319,973, whose disclosures are also incorporated herein by reference. Other fluid level measurement devices use optical sensing. For example, U.S. Patent 4,286,464 describes an optical fluid level monitor, which comprises a plurality of prismatic sensors disposed in a linear array for measuring the levels of fluids in closed containers. In use, each of the sensors is sequentially pulsed by an integral light source. If the detector is above the fluid level it appears bright, while if below it appears dark. Counting circuits are provided to determine the number of bright sensors and electronically convert this into a fluid volume for display- purposes. Another optical fill-level indicator is described in U.S. Patent 6,658,933. SUMMARY OF THE INVENTION

Embodiments of the present invention that are described hereinbelow provide devices and methods for measurement of fluid in a container. To measure fluid height, a tube is mounted vertically within the container. The tube contains a bob, which is able to move vertically within the tube. The bob has a rest position at a location in the tube that is determined by the height of the fluid. In one embodiment, the rest position is at the upper surface of fluid that is allowed to flow into the tube. In another embodiment, in which the tube is sealed, the rest position is created by magnetic levitation, using a float coupled to the outside of the tube to create a magnetic field within the tube.

The bob is connected by a cord running upward through the tube to a control unit, which thus moves the bob vertically in the tube between the rest position and a predetermined reference position, above the rest position. The control unit measures the distance traversed by the bob between the rest and reference positions, and thus determines the height of the fluid in the container. In one embodiment, the control unit senses the tension in the cord in order to measure the height precisely.

Embodiments of the present invention may be used in measuring heights of various types of fluids, in both stationary and mobile tanks and other containers. In some embodiments, sensors of other types are mounted at one or more locations along the tube. For example, in one embodiment, temperature sensors are mounted at different heights along the tube in order to measure temperature at different depths within the fluid.

There is therefore provided, in accordance with an embodiment of the present invention, apparatus for measurement of fluid in a container, including: a tube, which is vertically disposed within the container; a bob, which is vertically movable within the tube and has a rest position at a location in the tube that is determined by a height of the fluid in the container; a cord, extending within the tube and having an upper end and a lower end, which is connected to the bob; and a control unit, which is connected to the upper end of the cord so as to move the bob vertically in the tube between the rest position and a predetermined reference position, above the rest position, while measuring a distance traversed by the bob between the rest and reference positions so as to determine the height of the fluid in the container. In some embodiments, the bob is magnetized, and the rest position is defined by magnetic levitation of the bob in the tube. In a disclosed embodiment, the apparatus includes a float, which is coupled to move vertically along an outside of the tube while floating at a surface of the fluid, the float including a magnet, which is configured to generate a magnetic field within the tube so as to cause the bob to levitate at the rest position. Typically, the tube is sealed, so that the fluid cannot enter the tube.

In another embodiment, the tube has an opening through which the fluid enters and exits the tube, and the bob is configured to float at a surface of the fluid in the tube, thereby defining the rest position of the bob. In a disclosed embodiment, the apparatus includes a sensor associated with the tube for detecting that the bob has reached the reference position.

Typically, the control unit includes a motion assembly for retracting and letting out the cord so as to raise and lower the bob and is configured to measure the distance traversed by the bob by sensing a length of the cord that is retracted or let out between the rest and reference positions. The control unit may include a sensor for detecting a tension in the cord and is configured to determine the length of the cord at the rest position of the bob responsively to a change in the tension detected by the sensor. In one embodiment, the sensor includes a pressure switch, which engages the cord. In some embodiments, the apparatus includes a plurality of sensors distributed along a length of the tube for measuring one or more properties of the fluid, selected from a group of properties consisting of temperature, pH, specific gravity, concentration of a substance in the fluid, electrical properties, and optical properties. In one embodiment, the sensors include multiple temperature sensors, which are deployed at different, respective vertical locations along the tube. The tube may include an inner wall and an outer wall having a space therebetween, wherein one or more of the sensors are deployed in the space between the inner and outer walls.

There is also provided, in accordance with an embodiment of the present invention, a method for measurement of fluid in a container, including: placing a tube vertically within the container, the tube containing a bob, which is vertically movable within the tube and has a rest position at a location in the tube that is determined by a height of the fluid in the container, and which is connected to a lower end of a cord extending within the tube; and moving the bob vertically within the tube, using the cord, between the rest position and a predetermined reference position, above the rest position, while measuring a distance traversed by the bob between the rest and reference positions so as to determine the height of the fluid in the container.

The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic, sectional view of a system for measuring fluid in a container, in accordance with an embodiment of the present invention;

Figs. 2 and 3 are schematic, sectional detail views of lower and upper ends, respectively, of elements of the system of Fig. 1, in accordance with an embodiment of the present invention; and Fig. 4 is a schematic, sectional view of a system for measuring fluid in a container, in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 is a schematic, sectional view of a system 20 for measurement of a fluid 24 in a tank 22, in accordance with an embodiment of the present invention. As described further hereinbelow, the system is capable of measuring not only the height of the fluid, but also other properties, such as temperature and chemical properties. In this example, fluid 24 comprises a potable liquid, such as wine, which is isolated from direct contact with elements of system 20 that actually perform the measurements in question. (In another embodiment, shown below in Fig. 4, certain measurement elements are allowed to come into contact with the fluid being measured. ) The principles of the present invention, however, may be applied to measurement of substantially any type of fluid in any kind of container. Although the figures show systems used to make measurements in stationary tanks, these systems may also be adapted to make measurements in mobile containers, such as tanks mounted on trucks, trains and ships.

System 20 comprises a sealed tube 26, which is disposed vertically in tank 22 and is closed at its lower end 36. The tube may optionally be anchored to the bottom or side of the tank. A bob 28 is suspended from a cord 32 and is able to move vertically within the tube. Although a specific structure of tube 26 is shown in the figures that follow, the tube may alternatively be of any suitable size and profile (not necessarily round) . Cord 32 may comprise any suitable type of material, such as rope, string, filament, cable or ribbon.

A float 30 is coupled to the outer surface of tube 26 and is suspended by its own buoyancy at the upper surface of fluid 24. Typically, float 30 is shaped as a ring, which fits around tube 26 loosely enough so that the float can move up and down with the fluid level. Float 30 generates a magnetic field within tube 26, as described hereinbelow, which causes bob 28 to levitate in a rest position at a location in the tube that is determined by the height of fluid 24 in tank 22. Details of the float and bob are shown in Fig. 2, and the levitation mechanism is described further with reference thereto. The upper end of cord 32 is connected to a control unit 34. To determine the height of fluid 24, the control unit retracts cord 32 so as to lift bob 28 from the rest position to a known reference position higher up in tube 26, typically near the upper end of the tube. The control unit measures the length of cord taken up in retracting the bob up to the reference position (which is equal to the distance between the rest and reference positions) , and thus calculates the height of the fluid. Alternatively or additionally, the measurement may be performed while lowering the bob from the reference position to the rest position.

Optionally, tube 26 comprises additional sensors for measuring other properties of fluid 24. For example, temperature sensors 38 may be distributed along the length of the tube, so as to measure the fluid temperature at different heights within the tank. This sort of differential measurement can be important in monitoring the progress of reactions occurring in the tank, such as fermentation of wine. Other properties that may be measured by sensors in tube 26 include, for example, pH; concentration of various chemicals, gases and particulates (particularly Brix, which is a measure of sugar content) ; specific gravity; electrical properties, such as conductivity; and optical properties, such as color and turbidity. The sensors may be mounted either inside or outside tube 26, or between inner and outer walls of the tube, as described hereinbelow.

Control unit 34 outputs readings of fluid height and other sensor parameters to a console 35, which typically comprises a computer. The connection between the control unit and console may be either wired or wireless. The console reports on these parameters to a user, who may thus track and adjust the fill level and other properties of the fluid in tank 22. Additionally or alternatively, console 35 may automatically generate records and adjust the fill level and other properties based on the readings . Further additionally or alternatively, the console may detect and report on leaks in tank 22 when the fluid level in the tank drops unexpectedly.

Fig. 2 is a schematic, sectional view of the lower end of tube 26, showing details of bob 28 and float 30, in accordance with an embodiment of the present invention. Tube 26 in this embodiment comprises an inner wall 44 and an outer wall 46, with a space 48 therebetween. The outer wall may be made from stainless steel, for example, or any other suitable material that is compatible with fluid 24. The inner wall may be made from the same material as the outer wall, or it may alternatively comprise a different material, such as PVC or other plastic. In the pictured embodiment, inner wall 44 comprises tubing, which is sealed at its lower end and rests on a spacer 47 on lower end 36 of tube 26. Bob 28 is magnetized. As shown in the figure, for example, the bob may comprise a permanent magnet 42, which is held by guides 40, which are designed to slide freely within inner wall 44. Alternatively, the bob may comprise an electromagnet, which may be driven, for instance, by a current carried by a conductor in cord 32.

Float 30 comprises a suitable buoyant material 52, which is lighter than fluid 24. For example, the float may comprise an inert plastic. Alternatively, the float may simply contain air within a sealed outer shell, which may be made from stainless steel or other inert metal or plastic.

The upper end of the float, adjacent to outer wall 46 of tube 26, may be pointed, as shown in the figure, to permit the float to move easily through sediments or other particulates that may accumulate around the tube. The float contains a magnet or magnets 54, which surround tube 26 and create a magnetic field inside the tube. Magnets 54 and 42 are oriented so that the magnetic field of magnets 54 repels magnet 42, which is located above magnets 54 as shown in the figure. The balance between the upward repulsive magnetic force and the downward gravitational force on bob 28 causes the bob to levitate at a certain rest position relative to the height of float 30.

Since the height of the float is determined by the level of fluid 24, and the rest position is determined by the location of magnets 54 in the float, the rest position of bob 28 gives an exact indication of the level of the fluid in tank 22. Optionally, a stop 55 prevents float 30 from falling off the lower end of tube 26 when tank 22 is empty.

Lower end 36 optionally comprises one or more additional sensors, such as a magnetic sensor 56, which senses the magnetic field of magnets 42 and/or 54 and thus generates a signal when tank 22 is nearly empty. Additionally or alternatively, lower end 36 may comprise a sensor 58, such as a temperature sensor and/or a pH sensor or other chemical sensor. It may be advantageous to place such a sensor at the bottom of tube 26 so that the property of interest is measured regardless of the quantity of fluid remaining in tank 22. Sensors 56 and 58 may be connected to control unit 34 by wires 50 running through space 48 between inner and outer walls 44 and 46.

Space 48 may also contain other sensors that are distributed along the length of tube 26, such as temperature sensors 38 (shown in Fig. 1). Space 48 may be filled with a suitable liquid, such as purified water, or other material to enhance the convection or conduction of heat between outer wall 46 and the temperature sensors.

Fig. 3 is a schematic, sectional view of the upper end of tube 26 and control unit 34, in accordance with an embodiment of the present invention. Tube 26 opens at its upper end into control unit 34, which is held by a hatch 60 over an opening in the upper end of tank 22. Hatch 60 may contain one or more ports 64 for filling space 48, as described above.

Control unit 34 comprises a motion assembly 66, which comprises a drum on which cord 32 is wound, driven by a suitable motor and transmission. The motion assembly retracts and lets out cord 32 over a pulley 70 or a suitable hook or peg in order to move bob 28 up and down within tube 26. Assembly 66 also comprises a rotary encoder, which senses the revolutions of the drum (or of the motor shaft) , and thus measures the length of cord 32 that has been taken up or let out. Alternatively, the encoder may be separate from the motion assembly, and may either be associated with pulley 70 or may be a separate unit. Further alternatively, other types of sensors may be used to measure the length of cord taken up or played out. For example, cord 32 may be marked with gradations at regular intervals, and a camera or other optical sensor may be used to sense the passing gradations as the cord is extended and retracted.

A pressure sensor 68, in the form of a spring-loaded pressure switch that engages cord 32 (via a roller, for example) , senses the tension in the cord. Alternatively, other sorts of pressure and tension sensors, as are known in the art, may be used for this purpose.

A controller 78, such as a microprocessor with suitable interfaces and software, controls and receives signals from motion assembly 66 and sensor 68, as well as from other sensors along tube 26. To measure the height of fluid 24 in container 22, controller 78 instructs the motion assembly to let out cord 32 until bob 28 reaches the rest position defined by float 30, as explained above. When the bob is in the rest position, suspended by magnetic levitation, the tension in cord 32 is low, so that the switch in sensor 68 is released. The controller then instructs the motion assembly to begin retracting the cord, while measuring the amount of cord taken up. When the cord lifts the bob above the rest position, sensor 68 is actuated and indicates to controller 78 that the bob has begun to move. Sensor 68 thus eliminates uncertainty that would otherwise enter the measurement on account of the flexibility of cord 32.

Motion assembly 66 continues to retract cord 32 until bob 28 reaches a point near the top of tube 26. This stop defines a reference position. A magnetic sensor 74 detects the field of magnet 42 in bob 28 and indicates to controller 78 that the bob has reached the reference position, at which point the controller instructs the motor to stop.

Optionally, a second magnetic sensor 76 may be used for backup, in case sensor 74 fails. (In such a case, upon receiving the signal from sensor 76, controller 78 may determine that sensor 74 has failed.)

Controller 78 determines the length of cord taken up by motion assembly 66 between the rest position of bob 28 (when sensor 68 was actuated) and the reference position (as detected by sensor 76) . As noted earlier, this length is egual to the distance between the rest and reference positions of the bob. Since the location of the reference position relative to the bottom of tank 22 is known, controller 78 or console 35 can determine the height of the fluid 24 based on the distance traversed by the bob. Alternatively or additionally, controller 78 may measure the length of cord 32 that is played out in lowering the bob from the reference position to the rest position. For accurate measurement, the controller may instruct motion assembly 66 to let out the cord until sensor 68 indicates that the tension has dropped, meaning that the bob has reached the reference position. The controller then instructs the motion assembly to begin retracting the cord slowly until the pressure sensor is again actuated. The difference between the length of cord let out and the small length that is then taken up in retracting the cord provides an accurate reading of the location of the rest position.

If it becomes necessary to replace or service parts of the system inside tube 26, bob 28 and control unit 34 may be removed, and inner wall may then be pulled up and out of outer wall 46. Replacement after service proceeds in the opposite fashion.

Fig. 4 is a schematic, sectional view of a system 80 for measuring a fluid 84 in a tank 82, in accordance with another embodiment of the present invention. The principles of operation of this embodiment are similar to those of the preceding embodiment, and some elements in Fig. 4 are labeled with the same reference numbers as the corresponding elements in Figs. 1-3. As in the preceding embodiment, system 80 uses a bob 90 that is contained in a vertical tube 86 within tank 82. In the present embodiment, however, fluid 84 is allowed to enter tube 86 through an opening in the bottom of the tube. (A baffle 88 or other aperture may be used in the opening to damp waves and other rapid changes in the fluid level within the tube.) This arrangement is suitable for fluids, such as oil and other types of fuel, whose purity and sterility will not be substantially affected by permitting them to flow into and out of tube 86. Bob 90 is of appropriate buoyancy to float at the surface of fluid 84. The bob may comprise, for example, a suitable inert plastic or an inert metal shell containing air. Thus the rest position in this case is determined by the buoyant force exert by fluid 84, rather than magnetic force as in the preceding embodiment. A proximity sensor 100, such as a pressure sensor or optical sensor or a mechanical switch, may be used to determine when the bob has reached the reference position at the top of tube 86.

The operation of system 80 is controlled by a control unit 94. In this embodiment, for the sake of illustration, the control unit comprises a separate motion assembly 96 and encoder 98. The control unit raises and lowers bob 90 on a cord 92 between the reference and rest positions in order to measure the height of fluid 84, as described above. Although the embodiments described above relate to certain types of containers and fluids that may be held in such containers, the principles of the present invention may similarly be applied to containers and fluids of other types, such as hazardous (flammable or explosive) fluids and other non-potable fluids (such as raw or processed sewage) . It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Claims

1. Apparatus for measurement of fluid in a container, comprising: a tube, which is vertically disposed within the container; a bob, which is vertically movable within the tube and has a rest position at a location in the tube that is determined by a height of the fluid in the container; a cord, extending within the tube and having an upper end and a lower end, which is connected to the bob; and a control unit, which is connected to the upper end of the cord so as to move the bob vertically in the tube between the rest position and a predetermined reference position, above the rest position, while measuring a distance traversed by the bob between the rest and reference positions so as to determine the height of the fluid in the container.

2. The apparatus according to claim 1, wherein the bob is magnetized, and wherein the rest position is defined by magnetic levitation of the bob in the tube.

3. The apparatus according to claim 2, and comprising a float, which is coupled to move vertically along an outside of the tube while floating at a surface of the fluid, the float comprising a magnet, which is configured to generate a magnetic field within the tube so as to cause the bob to levitate at the rest position.

4. The apparatus according to claim 2, wherein the tube is sealed, so that the fluid cannot enter the tube.

5. The apparatus according to claim 1, wherein the tube has an opening through which the fluid enters and exits the tube, and wherein the bob is configured to float at a surface of the fluid in the tube, thereby defining the rest position of the bob.

6. The apparatus according to any of claims 1-5, and comprising a sensor associated with the tube for detecting that the bob has reached the reference position.

7. The apparatus according to any of claims 1-5, wherein the control unit comprises a motion assembly for retracting and letting out the cord so as to raise and lower the bob and is configured to measure the distance traversed by the bob by sensing a length of the cord that is retracted or let out between the rest and reference positions.

8. The apparatus according to claim 7, wherein the control unit comprises a sensor for detecting a tension in the cord and is configured to determine the length of the cord at the rest position of the bob responsively to a change in the tension detected by the sensor.

9. The apparatus according to claim 8, wherein the sensor comprises a pressure switch, which engages the cord.

10. The apparatus according to any of claims 1-5, and comprising a plurality of sensors distributed along a length of the tube for measuring one or more properties of the fluid, selected from a group of properties consisting of temperature, pH, specific gravity, concentration of a substance in the fluid, electrical properties, and optical properties.

11. The apparatus according to claim 10, wherein the sensors comprise multiple temperature sensors, which are deployed at different, respective vertical locations along the tube.

12. The apparatus according to claim 10, wherein the tube comprises an inner wall and an outer wall having a space therebetween, and wherein one or more of the sensors are deployed in the space between the inner and outer walls.

13. A method for measurement of fluid in a container, comprising: placing a tube vertically within the container, the tube containing a bob, which is vertically movable within the tube and has a rest position at a location in the tube that is determined by a height of the fluid in the container, and which is connected to a lower end of a cord extending within the tube; and moving the bob vertically within the tube, using the cord, between the rest position and a predetermined reference position, above the rest position, while measuring a distance traversed by the bob between the rest and reference positions so as to determine the height of the fluid in the container.

14. The method according to claim 13, wherein the bob is magnetized, and wherein the rest position is defined by magnetic levitation of the bob in the tube.

15. The method according to claim 14, and comprising generating a magnetic field within the tube using a float, which comprises a magnet and is coupled to move vertically along an outside of the tube while floating at a surface of the fluid, so as to cause the bob to levitate at the rest position.

16. The method according to claim 14, wherein the tube is sealed, so that the fluid cannot enter the tube.

17. The method according to claim 13, wherein the tube has an opening through which the fluid enters and exits the tube, and wherein the bob is configured to float at a surface of the fluid in the tube, thereby defining the rest position of the bob.

18. The method according to any of claims 13-17, wherein moving the bob comprises detecting that the bob has reached the reference position using a sensor associated with the tube.

19. The method according to any of claims 13-17, wherein moving the bob comprises measuring a length of the cord that is retracted or let out in raising the bob from the rest position to the reference position or lowering the bob from the reference position to the rest position.

20. The method according to claim 19, wherein measuring the length comprises detecting a tension in the cord and determining the length of the cord at the rest position of the bob responsively to a change in the tension.

21. The method according to claim 20, wherein the detecting the tension comprises sensing actuation of a pressure switch, which engages the cord.

22. The method according to any of claims 13-17, and comprising measuring one or more properties of the fluid using a plurality of sensors distributed along a length of the tube, wherein the one or more properties are selected from a group of properties consisting of temperature, pH, specific gravity, concentration of a substance in the fluid, electrical properties, and optical properties.

23. The method according to claim 22, wherein the sensors comprise multiple temperature sensors, which are deployed at different, respective vertical locations along the tube.

24. The method according to claim 22, wherein the tube comprises an inner wall and an outer wall having a space therebetween, and wherein one or more of the sensors are deployed in the space between the inner and outer walls.