CA1252009A - Contents gage - Google Patents

Abstract

ABSTRACT

The contents of a closed container, particularly a closed cryogen container, are gauged by lifting the container through a lever arm one end of which acts upon a pressure transducer coupled to indicating means while the other end of the arm is spring biased to suppress the empty or tare weight of the container.

Description

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¦I BACKGROUND OF T~IE INVENTION

¦¦ This invention relates generally to a method and means for gauging I the contents of a closed container.
i In a specific embodiment, this inventlon relates to a ~ethod and ¦ means for gauging the level of lLquid oxygen contained within a I portable, liquid oxygen therapy unlt.

¦I There have been developed a number of comlnercially available ¦~ liqutd oxygen therapy systems, both stationary and portable, to ¦~ provide supplemental oxygen for persons of impaired breathing ability.
1, Capacity of the portable systems is governed primarily by weight '! considerations but they are typically sized to provide about three to ~¦ abou~ Eourteen hours of continuous oxygen supply. This capacity is j~ adequate for a person working normal hours and for shopping, visiting ,¦ and other short trips. In preparation for use, a portable unit is typically filled with liquid oxygen from a larger, stationary ho~e i unit.

It is important to the user o~ such a portable system tllat he be Il able to check at will the oxygen level within the unit. As can be i¦ nppreciated an unexpected exhaustion of the oxygen supply could !I crente a serious problem or even provoke a medlcal crisis for tlle 20 il user. With experience, a user can project with some accuracy the time j a filled unit will last him. However, portable therapy units ¦, typically are arranged for selection of oxygen delivery rates over a rather broad range. If the oxygen de]ivery rate is changed during the ¦ use period, this will throw time projections awry.

li One approach that is used to determine the oxygen level within such portable unic~ is to weigh the entire unit, subtract ~rom the ,I weight obtained the empty, or tare, wei~ht of the container, and thus ..

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¦ obtain the weight of liquid oxygen within the unlt. This technique ls ~¦ cu[nbersome snd requires relatively accurate weight determinations Il because the tare weigllt is a substantial proportion of filled ¦¦ container weight. Yor example, one commercial portable unit has a ¦I capacity of about 1.2 lb of liquid oxygen and weighs about 6.6 lb when j full. A somewhat larger commercial unit has a liquid oxygen capacity of about 3.8 lb and weighs 13 lb when full.

ll Another approach that has been taken in the ~auging of the ¦I contents of a liquid oxy~en therapy unit ls to provlde a spring scale i¦ attachable to the unit and calibrated only over that weight range .! between the tare welght and full weight of the container Such ¦¦ devlces suffer from poor readability and reso]ution and require frequent adjustment. They are also bulky and frequently are carried as a separate device.
il j A varlety of electrical gages have been proposed and used in the past. These electrical gages have employed sensors within the cryogenic container and have included variable resistance sensors, thermistors, variable capacitance sensors and the like capable of I, discriminating between liquid and gaseous oxygen. Appropriate ~1~ circuitry is provLded external to the cryogenic container to activate li the sensors and to provide a read-out of the oxygen level within the i container. As well as being relatively expensive and complicated, such electrical gages re~uire routine battery changes and are prone to ! malntenance proble~s.
, Although the desirabilLty o~ providLng an integral, silnple, accurate and highly read~ble contents gage for use with li(luid oxygen therapy units has long been recognized, no device has yet been developed ~hlch fully satisfie6 these needs.

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:IZ5~009 1i S~RY ~F THI: INVE~T~ON

A contents gage for measuring the a~ount oE material within a closed container, especially the liquid oxygen level wlthin a portable oxygen therapy unit, comprises a lever arm disposed across the top of the container and pivoted intermediate its ends. One end of the arm is spring biased to a tension balancing out the tare weigl1t of the il container while the other arm end ac~s upon a preY6ure cransducer ¦I having a short movement or tl1row over that pressure r~nge developed between an empty and a full container. The pressure transducer is 1l coupled to an indicating means callbrated to provide a direct readout ll of the container contents when the contalner is lifted by handle neans Il attached to the lever arm.
il i1 Hence, it is an object of this invention to provide means for , gauging the contents of a closed container.
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1~ It is a specific object of this invention to provide means for i1 gauging the contents of a cryogen container.

I Another specific object of thls inventLon is to pro.lde a method il and means for accurately ga~ging the liql1id oxygen level withln a 11 portable, liquid oxygen therapy unit.
!l !¦ VESCRIPTION OF THE DRAWING
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ii A specific embodiment of the invention is illustrated in the Il drawing in w11icll:

l l ! Figure 1 is a partially cut away side view of a portable, lLquid oxygen therapy unit and the contents gage of this invention.
'.1 ,1, 4 ¦¦ Figure 2 is a side view of the mounting plate, lever arm and pressure transducer assembly.

¦i Figure 3 ls a partial sectional view of the pressure trsnsducer ! and indicating means sub-assembly.

Figure 4 is a top view of the mounting plate, lever arm and indicating ~eans.

~ DESCRIPTION AND DISCUSSION
il OF THE INVENTION

Il The contents gage oE this invention will be descrlbed in relation ll to its use with a portable, liquid oxygen therapy Ullit. In this embodiment, the contents gage comprises a lever arm disposed across ~ the top of the unit and pivotally attached to a mounting plate at the ,¦ top of the unit. A handle for lifting and carrying the unit is i attached to the lever arm at a point between the lever arm pivot and il the arm end, preferably over the center of gravity of the unit.
lll Consequently, the gage will register whenever the unic is lifted by ,¦ its handle.
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i¦ The empty, or tare, weight of the unit is compensated for by I spring biasing one end of the lever arm. When the container is lifted, the other arm end exerts a force on a pressure transducer proportionate to the weigllt of oxygen within the container. The I pressure transducer, in turn, is coupled to indicating means ,I calibrated to provide a visual indication of the flll level of the container.

Referring now to Figure 1, there is shown an overall view of a ,I portable, liquid oxygen therapy unit including the contents gage of ,~ S

l this lnventlon.
Il The therapy unit, shown generally at 10, comprises a liquid oxygen Il storage container 11 corsistlng of a vacuum insulated flask adflpted to ¦¦ dispense a metered stream of oxygen. Cappi.ng r.he Elask 11 Ls a il clost~re flange 12 which serves also to port three conduits cor~unicating with the lnterior of the flask. One of these conduits 13, is used to flll the flask with liqLid oxygen. Conduit 13 extends downwardly to the side of flask 11 terminating in a quick connect-type I¦ coupling 14 which is connectable to a mating coupling half of a llquid 1¦ oxy~en supply. Preferably, coupling 14 is enclrcled by an open-ended, j cup like shield means lS to prevent freezing of the coupling during liquid oxygen transfer.

A second conduit 16 opens into the top vapor space of flask 11 and ! leads to a tee fitting 17. Tubing 18, connecting with one leg of the ¦ tee fitting, .is directed in a generally ~-shaped path to a leg of a second tee 19. A branch line 20 from tee fitting 19 is coiled around a portion of tubing 18 and terminates in downwardly pointing emergency ¦ relief valve or blow-out plug 21. Plug 21 is adapted to open and vent l! the contents of flask 11 should pressure wlthin the flask increa6e 0 ll above a pre-set level; a pressure level. well below that which would cause rupture of the flask itself. The other leg of tee fitting 1 leads to vent-fill valve assembly 22 having an external handle 23.
I! Valve 22 remains in a normal:Ly closed posit:Lon except durin~ fil.lin~
I of flask 1I with liquid o~ygen. Durlrlg the filling operation, valve jl handle ~3 is placed in ~he open position which vents gas from the interior of fla~;k 11 reduc:ing the pressure therein an~ allowing l.lquid ~¦ oxygen flow into the flaslt. Vented gas is conducted fro~ val~e 22 through tubing 24 and preEerably discllarges i.nto the top interlor of sllield means 1~ as shown.

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'iA second branch condui~ 25 from tee fit~Ln~ 17 lea~s to economizer , 6 1~52009 ¦ valve assembly 26. Tl~e econollllzer valve oper~qtes as a pressure regulator maintaining a positive pressure within flask 11. Low pressure gas dlscharged from economiæer valve 26 i8 led Illto the ll brea~hing circuit in a manner to be described.

¦i A third conduit ports through closure flange 12 at tlle back side Il thereoE and is not shown -ln this Figure. That third conduit is ¦I connected to a liquid withdrawal tube which extends wl~llLn flask 11 to ¦i a point adjacent the bottom thereoF and extends external to the flask jl to a tee fitting. One leg of the tee fitting accepts gas discharged !jj from economizer valve 26 to merge with vapori~ing liquid oxygen fro~
¦ the flask. This merged stream is then directed downwardly through tubing 27 to the bottom of warming coil assembly ~8 whlch warming coil assembly comprises an extension of tubing 27 wrapped in a generally helical fashion around the flask 11. Tlle upper end of w~rming coil 28 termLnates ln a flow rate selector valve (not shown) located in back oE economizer valve 26. Oxygen flowing from the flow rate selector valve is conveyed by way of tubing 29 to outlet fitting 30 which is ! connectable to a breathing mask or cannula supply tube for breathing Il by the user.

I Vacuum flask 11 is typically cons-tructed of stainless steel as Ij glass is too fragile for satlsfactory use. As can readily be il appreciated by viewing the constructlon of a portable oxygen therapy i unit as depicted in Figure l, tlle weight of the flask and its ¦ associated coils and controls is large compared to the weight of liquld oxygen which can be accol~modated within the flask. In actual practice, the weight of liquid oxygen ln a portable, llquid oxygen therapy unit comprises some 20~ co 30~ of the total weight of the filled unit. Hence, the difficulties involved in obtainlng an I¦ accurate measure~ent o~ the oxygen level ~ithln ~he flask by I differential weighing is evident.

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1~5 2:0~9 In this embodiment of the invention wherein che contents gage i8 used to provide a measure of the liquid oxygen level within an i insulate(l flask, the gage Inecllanlsm may be arranged as shown. A
i mounting plate 31 is secured to closure Elange 12 as by screw i fasteners 32. Extension brackets 33 and 34 on either end of plate 31 serve to secure the therapy unit within a case (not shown). The gage ,I mechanistn comprises a lever arm 35 pivotally mounted on plate 3l at pivot point 36. A tare spring 37 is attached to one end of arm 35 ,I through spring hanger 38 and exerts a downward tensioll upon that end il of arm 35. Spring 37 must have a configuration such that the spring ¦ exerts an relatively col1stsnt force or tension upon the lever arm over Il a relatively short movelllent or throw of the lever arm. This result il may conveniently be obtained through use of a helically coiled sprLng having a worklng coil length which is long compared to the maximum movement of the lever arm. The bottom end of spring 37 is secured to lower spring hanger assembly 39 which in turn is connected to a spring tension adjustment means which may comprise a threaded adjustment screw 40 threadably inserted lnto bracket member 41 as shown.
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~ pressure transducer 42 and indicating means 43 are mounted on 'l the other end of lever arm 35. Both the transducer and the indicc-ting ¦ means will be described in greater detail in relation to Figures 2-4.
~1 A lift point conveniently comprising handle attachment member 44 is provided lnter-nedl~te the ~are spring end of arm 35 and pivot polnt 36. It is advantageous and preferred thclt handle attachment member 44 I be located at a point on or in close pro~imity to a vertical llne ii passlng through the center of gravity of the unlt. In thls way, a ' carryin~ handle for the unit loay be attached to member 44 by means of a pln inserted through hole 45 thus providing a measure of the oxygen ,¦ level within flask 11 upon llfting of the unlt. Placement of the 0 1¦ handle above the center of gravlty of the unLt allows the unit to hang naturally in a vertical attitude.

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Re~erring now to Figures 2 and 3, Figure 2 is a side view of the ,ll mountlng plate, lever arm and transducer assembly separatetl from the ¦' liquid oxygen therapy Ullit whLle Figure 3 illustrate~ details, oE the , ~; transducer and contents level indicating means sub-assembly. Lever il arm 35 may conveniently comprise a channel member for~ed of sheet i! steel or similar material. It necessarily must be of sufficient ¦¦ stiffness to preclude bending under the loads applied. Indicating ¦ means 43 is rigtdly mounted to arm 35 as by mounting screw 46. Means I1 43 preferably comprises a liquid-filled Bourdon tube gage o~ the type il conventionally used to indicate pressure.
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¦ As shown in partial cross-section in Fi~ure 3, transducer means 42 ~i may comprise a liquid filled, belLows-type load cell or pressurc ~¦ transducer 47 rigidly coupled to and in fluid communication with Bourdon tube ~age 43 through nipple 48. Transducer 47 i8 disposed within a cup-shaped member 49 wt~ich in tum is contained witllln ~i housing 50. Member 49 is free to move vertically withln housing 50 ~~ while housing 50 is rigidly attached as by brazing to plate 31.

1~1 Adjustment means are provlded to remove all backlash or play fr->m the i$ lever arm 35 and pivot point 36. Such adjustment mean~ may comprise a ,20 I screw 51 tllreaded througil a nut 5~ centrally attached to the bottom of ¦I housing 50. The end of screw S1 bears upon the bottom of member 49 ~1~ through plate 53 to provtde vert$cal adjustment thereof.
.1 Figure 4 is a top view of the mounting plate and lever arm ~; assembly. .~s is shown in the Figure, pivot point 36 of arm 35 may be 1~ formed by punching ear member 54 from plate 31 and bending them upward perpendicular to pLate 31. Gage 43 is provided with suitable, callbrated indicia 55 to provide a visual readout of the level of ~1 liquid oxygen within the flask.

~I Pressure transducer 42 has been illustrated and described as 'I comprisin~ a liquid-fllled, be11Ows-type load cell ~7 connected to anL1 ~,1 5~ g Ij co~municating with a liquid filled Bourdon tube pressure gnge. Other ¦I types of llquid-filled load cells may be used as well including those ¦ f the flat or corrugaced diaphram type, those of the aneroid type conslsting of two corrugated diaphrams sealed togetller, and load cells of other configuration which produce an equivalent result. Pressure Il transducers of the capacitive, resistive, inductive and pie~oeleetric ¦I types can be used as well. ~lowever, these last named pressure 1 transducers are less preEerred for use with liq~id oxygen containers I¦ because they require adAitional eLectronic circuitry thus increaslng ~ the cost, colDplexity and, in some instance3 the hazards, of the lil gauging system.
,1 1~ One property that all appropriate pressure transducers ~ust have !l in common is that of translating Q s~all vertical movement of the end of lever arm 35 into a full scale lndication of the contents of flask 11; that is, from e~pty to full. As can be appreciated fro~n the drawing, particularly Figure 2, lifting tile container through handle ! attach~ent means 44 produces an upward force on lever arm 35 at that point. Tare spring 37 is adjusted to exert a downward ~orce on one il end of arm 35 equal to the upward force applied when lifting the 20 ll container in an e~pty state through attachment means 44. The geometry ¦ of lever arm 35, in par~icular the location of pivot point 36, is set !I to provide a full scale reading of gage 43 when flask 11 i6 full and the unit is lifted through means l~4. Ur,der these conditions, the tare spring end of arm 35 Ls caused to move upwardly a short distance whlle the opposite end of the arm moves downwardly placing a compressive force upon the load cell. Compression of the liquid within the loacl cell in turn causes the ~ourdon tube gage to regJster a value which is ¦~ a direct measure of the differential weight of the unit attributable il to the weight of liquid oxygen within flask 11.

30 1, In order to ohtain an accurate and linear readout of the contents j weigilt, it is necessary that tare spring 37 have a very low spring il .

520~119 r~te or iorce con~t~lt Thi6 r~quirement con beeCer be underscood hy ¦¦ conslderation of ~looke's law which, when applled to a spring under ¦! tension, scates that the force exerted by the spring is equal to the l extension of the spring multiplied by a constant referred to as the I force constant of the spring. As can be seen from this mathematlcal Il relationship, if one were to extend a spring having a low or small j, iorce constant for a short distance, the force exerted by the sprinK
would remain ~ubstantially constant. By proper choice of the pressure I trans~ucer and gage, it i8 possible to obtain a full scale defLection i of the gage with a very small movement of the lever arm. Thus, the ¦I distance that tare spring 37 is extended between an empty and a full l! condition of the flask can be made very small. A low ~pring force u constant can be obtained through use oE a relatively long coiled j spring. In practical tenns, working length of the tare spring sho-lld be at least about 10 times lcs extension from an empty to a full I condition of the flask an~l preferably should have a length to !~ extension ratio of 30 or more.
iil '~ The contents gage oE tllis Lnvention as described and Ll1l3strated j allows the gauging or measurement of the contents withLn a closed 0 ii container through simple mechanica] means whi:le automatically compensating for the tare weight of the container. It provides an expanded scale or visual readout of the contents compared to other gauging systems, ls light in weight and is ea~ily adaptable as an integral incluston with portable cryogen containers. No external power i8 required to operate the gage and it is comp]etely safe with liquld oxygen systems.

While the contents gage of this invention has b ~:n described ~¦ speclfically in relatlon to portable, liquid oxygen therapy systems, ¦j its use is not so limited. Many other applications of thi~ gauging !¦ system will be .~pparent to Chose skilled in the art includillg use with I other cryogens or with toxic or ha~ardous liquids dispensed from a 1 11 , closed container. Such other appllcatlons may be einr)loyed witl~out departing fro~ the spirit and scope of thLs lnven~ion as defined by the ~ppendea claims.

Claims (26)

I claim:

1. A portable, liquid oxygen therapy unit having integral contents gauging means comprising:
flask means adapted to contain and store a quantity of liquid oxygen;
means to vaporize and deliver a metered stream of oxygen to a user;
a mounting plate attached to the top of said flask means;
a lever arm pivotally attached to said plate at a point intermediate the arm ends;
spring means extending between one lever arm end and an attachment point in the lower portion of said unit, said spring means adapted to bias said lever arm end in a downward direction;
pressure transducer means disposed at the other lever arm end and adapted to indicate an increased pressure upon downward movement of said other arm end;
indicating means operatively connected to said pressure transducer and calibrated to show the level of liquid oxygen within said flask as a function of pressure indicated by said transducer, and handle means attached to said lever arm at a point intermediate the spring-attached lever arm end and the pivot point of said lever arm.

2. The unit of claim 1 wherein said spring means comprise a helically coiled spring having a working length substantially greater than ten times its extension from an empty to a full flask condition.

3. The unit of claim 1 wherein said pressure transducer means comprise a hydraulic pressure transducer.

4. The unit of claim 3 wherein said hydraulic pressure transducer comprise a liquid-filled load cell.

5. The unit of claim 4 wherein said indicating means comprise a liquid-filled, Bourdon tube pressure gage.

6. The unit of claim 5 wherein said load cell is coupled to and is in fluid communication with said Bourdon tube pressure gage.

7. The unit of claim 6 wherein said load cell is a bellows-type load cell.

8. The unit of claim 3 wherein said pressure transducer is disposed within a cup-shaped member placed within a housing, said housing rigidly attached to said plate member.

9. The unit of claim 8 wherein said cup-shaped member is free to move vertically within said housing and wherein means are provided to adjust the position of said cup-shaped member within said housing.

10. The unit of claim 2 wherein the tension on said spring member is adjustable and is set to a level whereat said indicating means register a zero value when said flask is empty and said unit is lifted by said handle means.

11. The unit of claim l wherein said handle means are attached to said lever arm at a point on, or in close proximity to, a vertical line passing through the center of gravity of said unit.

12. A means for gauging a relatively small weight of fluid contained in a relatively heavy container comprising:
a lever arm disposed across the top of said container and pivoted at a point intermediate its ends;

spring means attached to and biasing one end of said lever arm;
lifting means for said container attached to said lever arm at a point intermediate its ends but removed from said pivot point;
pressure transducer means disposed at the other end of said lever arm, said transducer means arranged to indicate an increased pressure when said container is lifted, and indicating means displaying a visual measure of the contents of said container as a function of said increased pressure.

13. The means of claim 12 wherein said transducer means is an electrical transducer.

14. The means of claim 13 wherein said electrical transducer is selected from the group consisting of capacitative, resistive, inductive and peizoelectric transducers.

15. The means of claim 12 wherein said lever arm is pivoted to a mounting plate attached to said container.

16. The means of claim 15 wherein said spring means downwardly bias said lever arm end and wherein said lifting means are attached to said lever arm at a point intermediate said spring biased end and said pivot point.

17. The means of claim 16 wherein said transducer means comprise a hydraulic load cell.

18. The means of claim 17 wherein said load cell is disposed within a cup-shaped member placed within a housing, said housing rigidly attached to said mounting plate.

19. The means of claim 18 wherein said cup-shaped member is movable vertically within said housing and wherein means are provided to adjust the position of said cup-shaped member within said housing.

20. The means of claim 17 wherein said indicating means comprise a liquid-filled, Bourdon tube pressure gage.

21. The means of claim 20 wherein said load cell is coupled to and is in fluid communication with said Bourdon tube pressure gage.

22. The means of claim 12 wherein said spring means comprise a helically coiled spring having a working length substantially greater than ten times the spring extension from an empty to a full condition of the container.

23. The means of claim 21 wherein the force exerted by said spring is set to a level whereat said indicating means register a zero value when said container is empty and is lifted by said lifting means.

24. The means of claim 12 wherein said container is adapted to hold and to store a cryogen.

25. A method for gauging a relatively small weight of liquid confined within a relatively heavy container, comprising:
pivoting a lever arm across the top of said container at a point intermediate the arm ends;
providing a substantially constant biasing force acting downwardly upon one end of said arm;
lifting said container by said lever arm at a point on that arm intermediate the downwardly biased arm end and the pivot point of said arm;
sensing the force exerted by the other end of said arm when said container is lifted, and translating said sensed force into visual indicia representative of the liquid level in said container.

26. The method of claim 24 wherein said biasing force is set to a level whereat the force exerted by the other arm end is essentially zero when said container is empty and is lifted through said lever arm.