CA1290211C - Enhanced pressure measurement flow control system - Google Patents
Enhanced pressure measurement flow control systemInfo
- Publication number
- CA1290211C CA1290211C CA000576571A CA576571A CA1290211C CA 1290211 C CA1290211 C CA 1290211C CA 000576571 A CA000576571 A CA 000576571A CA 576571 A CA576571 A CA 576571A CA 1290211 C CA1290211 C CA 1290211C
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- Prior art keywords
- pressure
- fluid
- source
- measurement gas
- volume
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000009530 blood pressure measurement Methods 0.000 title description 3
- 239000012530 fluid Substances 0.000 claims abstract description 120
- 238000005259 measurement Methods 0.000 claims abstract description 108
- 230000008859 change Effects 0.000 claims abstract description 38
- 238000004891 communication Methods 0.000 claims abstract description 33
- 238000005086 pumping Methods 0.000 claims abstract description 17
- 230000000694 effects Effects 0.000 claims abstract description 7
- 230000000295 complement effect Effects 0.000 claims abstract description 4
- 230000008867 communication pathway Effects 0.000 claims description 34
- 239000012528 membrane Substances 0.000 claims description 14
- 238000012544 monitoring process Methods 0.000 claims description 12
- 230000004913 activation Effects 0.000 claims description 7
- 230000037361 pathway Effects 0.000 claims description 6
- 238000004537 pulping Methods 0.000 claims description 5
- 238000005304 joining Methods 0.000 claims description 2
- 230000002463 transducing effect Effects 0.000 claims description 2
- 238000006073 displacement reaction Methods 0.000 description 11
- 238000001802 infusion Methods 0.000 description 7
- 238000013459 approach Methods 0.000 description 3
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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
- A61M5/16804—Flow controllers
- A61M5/16813—Flow controllers by controlling the degree of opening of the flow line
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
- A61M5/16804—Flow controllers
- A61M5/16809—Flow controllers by repeated filling and emptying of an intermediate volume
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
- A61M5/16831—Monitoring, detecting, signalling or eliminating infusion flow anomalies
- A61M5/16854—Monitoring, detecting, signalling or eliminating infusion flow anomalies by monitoring line pressure
- A61M5/16859—Evaluation of pressure response, e.g. to an applied pulse
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/36—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests with means for eliminating or preventing injection or infusion of air into body
- A61M5/365—Air detectors
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B43/00—Machines, pumps, or pumping installations having flexible working members
- F04B43/02—Machines, pumps, or pumping installations having flexible working members having plate-like flexible members, e.g. diaphragms
- F04B43/04—Pumps having electric drive
- F04B43/043—Micropumps
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
- F16K31/00—Actuating devices; Operating means; Releasing devices
- F16K31/004—Actuating devices; Operating means; Releasing devices actuated by piezoelectric means
- F16K31/005—Piezo-electric benders
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
- G01F1/34—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P13/00—Indicating or recording presence, absence, or direction, of movement
- G01P13/0006—Indicating or recording presence, absence, or direction, of movement of fluids or of granulous or powder-like substances
- G01P13/0066—Indicating or recording presence, absence, or direction, of movement of fluids or of granulous or powder-like substances by using differences of pressure in the fluid
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M2005/1401—Functional features
- A61M2005/1403—Flushing or purging
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M2205/00—General characteristics of the apparatus
- A61M2205/15—Detection of leaks
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M39/00—Tubes, tube connectors, tube couplings, valves, access sites or the like, specially adapted for medical use
- A61M39/22—Valves or arrangement of valves
- A61M39/26—Valves closing automatically on disconnecting the line and opening on reconnection thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S128/00—Surgery
- Y10S128/13—Infusion monitoring
Landscapes
- Health & Medical Sciences (AREA)
- Engineering & Computer Science (AREA)
- Hematology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Veterinary Medicine (AREA)
- Public Health (AREA)
- Vascular Medicine (AREA)
- Anesthesiology (AREA)
- Biomedical Technology (AREA)
- Heart & Thoracic Surgery (AREA)
- General Health & Medical Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- General Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Emergency Medicine (AREA)
- Fluid Mechanics (AREA)
- Measuring Volume Flow (AREA)
- Infusion, Injection, And Reservoir Apparatuses (AREA)
- Measuring Fluid Pressure (AREA)
Abstract
Abstract of the Disclosure The present invention provides a system for measuring flow of a fluid through a line. In the system, a region of fluid along the line is isolated from pressure effects outside of the region. A source region contains a measurement gas in communication with the isolated region, such that the source means and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the source means with a resulting change in the pressure of the measurement gas contained in the source region. Further provided is a reservoir in communication with the source means for containing a known volume of measurement gas, and means for pumping measurement gas from the reservoir. The pressure of the measurement gas in the reservoir and the source region is monitored. This pressure data is then analyzed to determine the volume of fluid in the isolated region
Description
~290Zll ENHANCED PRESSURE MEASUREMENT FLOW ~ONTROL SYSTEM
Cross-Reference to Related A~lications This application is related to Canadian Patent Application Serial No. 531,004 filed March 3, 1987.
Backqround of the Invention 1. Field of Invention The present invention relates generally to systems for controlling fluid flow, and in particular to medical infusion technology, although other embodiments are discussed below.
Cross-Reference to Related A~lications This application is related to Canadian Patent Application Serial No. 531,004 filed March 3, 1987.
Backqround of the Invention 1. Field of Invention The present invention relates generally to systems for controlling fluid flow, and in particular to medical infusion technology, although other embodiments are discussed below.
2. Description of Related Art The precise and accurate regulation of fluid flow is required in many settings. Precision and accuracy are particularly vital in medical infusion systems, where there can be very narrow tolerances in infusion rates. For example, in chemotherapy, too slow an infusion rate may prove inefficacious, while too rapid a rate may prove toxic to the patient.
However, various elements inherent in medical infusion systems render problematic precise fluid delivery. One factor is the tubing that is used to deliver the fluid. Opening and closing of the line is typically accomplished by clamps, which can distort the walls of the tube leading to irregular flow rates. A second factor is that the 3~
patient receiving medication may move during infusion, producing varying fluid column heights, thereby affecting fluid flow. Third, the fact that fluid i6 delivered from a finite reservoir, such as an intravenous bag or bottle, that gradually empties, also affects the infusion rate.
Numerous approaches are known in the art to compensate for these factors. Certain prior art systems incorporate optical drop counting. Enhanced drop counting ~ystems update drop count data with other measured quantities in order to compensate for varying drop 6ize and splashing.
Other approaches include bag weighing and pumping to regulate flow. However, systemic error is inevitable in most, if not all, of these arrangements.
Summarv of the Invention The present invention provides a system for measuring flow of a fluid through a line. In the system, a region of fluid along the line i6 isolated from pressure effects outside of the region. A ~ource chamber contains a measurement gas in communication with the isolated region, such that the source chamber and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the 60urce chamber with a resulting change in the pressure of the measurement gas contained in the source chamber. Further provided is a reservoir chamber in communication with the source chamber for containing a known volume of measurement gas, and means for pumping measurement gas from the reservoir chamber into the source chamber. The pressure of the measurement gas in the reservoir chamber and the pressure of the measurement fluid in the source chamber are monitored as fluid flows into and out of the region. This pressure data is then analyzed to determine the volume of fluid in the isolated region.
lZgO211 Various aspects of the invention are as follows:
A system for controlling flow of a fluid through a line, the system comprising:
dispensing means (i) for isolating a region of the fluid in the line from effects of pressure in the line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a measurement gas in communication with the isolated region, such that the source means and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the source means with a resulting change in the pressure of the measurement gas contained in the source means;
reservoir means in communication with the source means for containing a known volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas contained in the reservoir means and the measurement gas contained in the source means;
pressure monitoring means for generating data relating to the pressure of the measurement gas in the source means and the measurement gas in the reservoir means; and control means, in communication with the pressure monitoring means, the pulping means, and the dispensing means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
1~9021~
2b A system for controlling flow of a fluid through a line, the system comprising:
dispensing means (i) for isolating a region the first fluid in the line from effects of pressure in the S line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a first volume of measurement gas;
reservoir means in communication with the source means for containing a second volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas in the reservoir means and in the pressure of the measurement gas contained in the source means;
a source communication pathway between the source chamber and the isolated region and a reservoir communication pathway between the reservoir chamber and the isolated region, the source communication pathway and the reservoir communication pathway joining to at some point along each respective pathway to form a joint communication pathway leading to the isolated region;
source valving means for opening and closing the source communication pathway;
reservoir valving means for opening and closing the reservoir communication pathway;
the isolated region, the source means and the reservoir means, and the source communication pathway, the reservoir communication pathway and the joint communication pathway being so disposed in relationship with each other such that they together define a fixed volume, and such that a change in volume of the fluid in the isolated region produces a correlative change in the C
1.29~211 joint communication pathway and in any other enclosure in pressure communication with the joint communication pathway;
pressure transducing means (i) in pressure communication with the source means for generating data relating to the pressure of the measurement gas in the source means, and in any other enclosure in pressure communication with the source means and (ii) in pressure communication with the joint communication pathway for generating data relating to the pressure of the measurement gas in the joint communication pathway, and in any other enclosure in pressure communication with the joint communication pathway; and control means, in communication with the pressure monitoring means, the pulping means, the dispensing means, the source valving means, and the reservoir valving means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
Brief Description of the Drawinas Fig. 1 shows a schematic drawing of a simplified embodiment of the present invention; and Fig. 2 shows a schematic drawing of a preferred embodiment of the present invention.
Fig. 3 show~ a schematic drawing of the invention claim~d in aforementioned Canadian application Serial No. 5~1,004.
DescriDtion of Preferred~mbodiments The present invention precisely measures discrete volume increments of fluid along a line by taking advantage of the known physical relationship between the pressure and volume of a gas. This is accomplished by isolating a region of the line and housing that region in communication with a measurement gas such that the isolated region of fluid and the measurement gas occupy a fixed and ascertainable volume. Thus, the movement of fluid into and out of the isolated region produces a corresponding change in the pressure of the measurement gas. The pressure of the measurement gas is monitored by a transducer, and the resulting data is used to compute the volume of fluid delivered, usinq methods described below.
In order to function properly, a system of this type must include calibration meanæ for establishing reference quantities against which later measured quantities can be compared. One approach to calibration i8 disclosed in aforementioned Canadian application Serial No. 5~1,004. The systems disclosed therein are calibrated by measuring the pressure of the measurement gas during a calibration cycle, during which the system, in the absence of fluid flow, induces a known decrease in volume of the measurement gas. The system then measures the pressure of the measurement gas during the flow of volume increments of fluid into and out of the isolated region. Using various disclosed physical and mathematical relationships, the system then computes 1~90~11 the volume of fluid delivered using the calibration data together with pressure measurements taken during fluid flow.
Figure 3 is a schematic representation of these systems. The embodiment shown in Figure 3 uses a drip chamber as the isolated region. Figure 3 shows the system having a drip chamber with an upper valve 821 and lower valve 822, which valves are operated by control circuitry 81. Pressure in the interior of the drip chamber 82 is monitored by transducer 83, which is also connected to control circuitry 81. The motor 84 drives piston 85 which compresses air in line 851. The motor 84 is also connected to control circuitry 81.
The earlier device proved to be extremely accurate at low rates of fluid delivery, but was not totally free from error. For example, a certain percentage of error was inherent in the mechanical creation of a precise volume displacement. In an embodiment employing a bellows arrangement to cause the volume displacement, error was found to be caused by a certain bowing out of the folds, which was found to be inevitable. Further, because moving parts are involved in expanding and contracting bellows, any precision could be affected by the aging of system. Other embodiments would still require precise mechanical displacements and generally good seal arrangement along the moving mechanical interface.
Another problem was found to exist in situation where the system is used to deliver relatively large volume increments of fluid, or where the volume increments are being dispensed into a line having significant back pressure. Where there is a significant amount of back pressure, relatively large volume displacements are necessary to produce the delivery of even small quantities of fluid.
The present device solves these problems of the ear~ier device by employing ~ressure displacement instead of the precise volume displacement of the ~X~O~ll - 4a -earlier system. As will be described in greater detail below, the use of pressure displacement solves many of the problems of the earlier device. For example, unlike the volume displacement system, the use of pressure displacement, as described below, does not require a precise mechanical displacement, thus eliminating the errors associated therewith. Further, the system may utilize pressure displacement in such a fashion that the presence of back pressure does not necessitate significantly more pumping than would be the case in the absence of back pressure. Indeed, the system can be configured to compensate for a wide range of bac~
pressures, lncluding 6ituations where back pressure exceeds fluid reservoir head pres6ure.
Fig. 1 ~how~ a 6chematic drawing of A simplified embodiment of the present lnvention. The system includes two chambers, reservoir chamber 11 and source chamber 12 for houeing a measurement gas. The~e chambers may be constructed of a rigid pla6tic using methods known in the art, although a wide variety of other materials, lncluding metals, may also be 6uitable, the principal de6ideratum being that the chambers maintain a fixed volume regardle6s of the pressure of the mea6urement ga~. It is thus conte~plated that the volume of reservoir chamber 11 in this embodiment i~ known, although th~ volume could be determined heuri6tically in the course of initial calibration of the 6y6tem. Each chamb~r has an a6sociated pressure transducer 13, 14. The two chamber~ are connected, but are 6eparated by a pump arrangement 111 that can move measurement gas contained $n reservoir chamber 11 into source chamber 12 with a resulting decrease in pressure in the reservoir chamber and an increase in pressure in the source cha~ber. In this embodiment, the pump arrangement 111~180 serves to prevent bac~flow of measurement gas. Thus, when the pump arrangment is activated, a pressure differential results between the two chambers which 1~ maintained even after the pump arrangment ceases to pump.
The source chamber is in communication with a region 15 of the fluid line 16 that can be isolated by valves 17 and 18 from fluid pressure effects elsewhere in the line.
Communication between the line fluid and the measurement gas is afforded through flexible membrane 19. A bulge 110 is provided in the region. The bulge 6erves two purposes.
First, the bulge allows a greater amount of line fluid to impinge against the measurement gas, thus increasing the pressure communication between the line fluid and the measurement gas. Second, the bulge, because of it6 lX90Zll substantially 6pherical shape, provides maximum radial rigidity, thus preventing the isolated region from becoming distorted as a result of high measurement gas pres6ure.
Thus, it will be seen that when either valve 17 or valve 18 is closed, movement of fluid into or out of the isolated region 15 will, via flexible membrane 19, decrease or increase the volume of the measurement gas in the source chamber, with a resulting change in the pressure of the measurement gas.
For the reasons set forth below, the amount of fluid delivered can be determined by the relationship:
~VS = (~PRVR/APS ) 4~PS/ (PS+~S) ]
where:
~VS = volume increment of fluid delivered ~PR = change in pressure of measurement gas in the reservoir chamber caused by movement of measurement gas from the reservoir chamber to the source chamber VR ' volume of the reservoir chamber (known) QFsO = change in pressure of measurement gas in the source chamber caused by movement of measurement gas from the reservoir chamber to the source chamber (measured before fluid flow) S ~ change in pressure of measurement gas in the source chamber resulting from movement of fluid out of the isolated region PS = pressure of the measurement gas in the source chamber This relationship is derived as follows:
First, assume that valves 17 and 18 are closed with fluid held in the isolated region. Initially, reservoir chamber 11 and source chamber 12 are each isolated. From Boyle's Law it is known that:
( 1 ) PSVS = nSRT
and 1~90X11 (2) PRVR - nRRT
where VS ~ the volume of the source chamber nS ~ the number of moles of measurement gas in the source chamber PR ~ the presS~ of the reservoir chamber nR ~ the number of moles of measurement gas in the reservoir chamber R - a constant T - temperature of the measure~ent gas Adding (1) and (2) ~ields (3) PSVS + PRVR ' (nS + nR)RT
Because thQ ~ourc~ chamber and the reservolr chamber together comprisQ a clo6ed system, (4) nS + nR ~ N, where N is a constant Measurement gas ls then moved from the reservoir chamber to the source chamber. Thi~ results in a change of the respectivQ pressures of the two chambers. Because the chamber~ are rigid and becaus- there i~ no fluid flow lnto or out of the isolated region, the respective volumes remain constant. Thus, (5a) (PSVS + PRVR) ' ~(nS + nR)RT]
which yields (5b) (PS+~ S )VS + (PR~PR)VR ' NRT
Subtractin~ (3) from (5) yields:
(6) ~ PsVs + APRVR - 0 Solving for Vs yields:
(7) VS ~ - ~PR VR /~Ps At this point, the pump arrangment is then closed off, thus cutting off any communication between the two chambers. BY BOY1Q 's ~aw, it is known that at constant temperature, with respect to the source chamber volume:
(8) PSVS ' XS ; KS ~ constant Now valve 18 is opened, and fluid flows out of the isolated reglon. The outflow of fluid results in an increase in the volume of measurement gas housed in the source chamber, with a resulting decrease in pressure. By 1290~11 Boyle's Law lt is known that the product of the ~easurement gas pressure in the source chamber volume and the source chamber volumes remain constant. Thus, ~g) (Ps + ~s) (Vs +AVs) - Psvs - ~s Solving eguation (9) for ~Vs yields (lOa) ~Vs 8 Psvs/(ps +~S) - Vs or (lOb) ~Vs ' -~Psvs/(ps+~ps) ~ ecause we are assuming that some fluid has indeed flowed out of the isolated region, PS i6 not egual to the initial pressure Ps~
Using the relation of eguation (7) to remove the Vs term ~n eguation (lO) yields:
(11) ~VS ~ PS/(PS +~ PS) ~ ~- A~PR VR / ~PS]
This equation can be rewritten ~B:
(12) ~Vs ~ ~PRovR /~PS ]t~s/~Ps + ~PS)]
which 16 the final eguation.
Total fluid delivered can be calculated by 6umming each individual ~Vsl ~hich can be expressed by the following formula:
~1 ~ S ~PR VR / PSi]L~PS-/(pBi+aP i)]
The operation ot the device depict-d ln Fig. l can be summariz~d by th- ~ollowing steps:
A. Initlalize the y-tem - valve~ 17 and 18 are closed with fluid held ln the isolated region.
B. Mea~ure the pres~ure of the measurement gas in the reservoir chamber and the 60urce chamber.
C. Mov- ~ome measurement gas from the reservolr chamber into the source chamber, and close off the source chamber from the reservoir chamber.
D. Measure the new pressures of the measurenent gas in the reservoir chamber and the source chamberO
E. Open valve 18, which allows fluid to flow out of the isolated region 15.
F. Measure the pressure of the measurement gas in the source chamber, which is presumably decreasing as the 1290~11 volume increa~e~ ln re~pons- to fluid leaving the lsolated region G Compute the volume of fluid delivered u~ing equation (12) It is contemplated that the data from the pressure transducers 13 and 14 will be interpreted by a microprocessor, or other computing unit 112, which would also activate the pumping arrangment 15 and valves 17 and 18 It can be 6een that the foregoing cycle i8 only exemplary, and that other cycles may be employed that can utilize the essential relationships described above For example, steps E, F, and G may be repeated a desired number of times as a subcycle within larger cycle of steps B through G
Fig 2 6hows a schematic diagram of a preferred embodiment of th- present invention This embodiment involve~ a ~lightly dlfferent arrangement for placing the reservoir chambér 11 and the source chamber 12 in communication with each other and with the i601ated region of the fluid lin- Th- mbodiment of Fig 2 provides a communicatlon pathway 21, gated by valve 22, to the isolated region The pathway 23 between the source chamber 12 and th- i601ated region 15 i6 gat-d by valv- 24 In one mode of operatlon of thi- e~bodlm~nt, lt 18 po~ible to circulate measursment fluld around ~ closed clrcuit, namely from reservolr chamb-r 11 to source chamber 12 into the bulge 110 and th-n bac~ to the reservoir chamber 11, with a resultlng economy o~ operatlon ln operatlon, assume, for xample, that a measurement gas, such as air, i~ at one atmosphere ln chamber~ 11 and 12, and that valv-- 17, 18, 22 and 24 are closed Valves 17 and 22 are then opened The opening of valve 17 allows fluid to flow into the isolated region The opening of valve 22 defines two separate volumes One of these volu~es is the sum of the volumes of the reservoir chamber 11 and communication pathway 21 up to flexible membrane 19 The second is the volume of source chamber 12 plus the volu~e of that portion of communication pathway 23 up to 1~90~11 valve 24. The pressure of measurement gas associated with these two volumes are then measured and recorded.
Valve 17 is then closed. Pump 25 is then run to create a pressure differential between the reservoir chamber and the source chamber. Then valve 22 is closed. At this point, because fluid flow has been stopped~ the pressure of tha mea~urement gas is the same on either side of valve 22, now closed. Thus, either pressure quantity could be measured. In the depicted embodiment transducer 13 measures the pressure between the valve and the flexible membrane.
Th- pr-~-ur- PS f th- ourc- cha~b-r up to valv- 24, whic~ 1- clo--d, and tho pr---uro P~R+Dj ~ th- r---rvoir chamb-r, includlng com~unication pathway 21 up to fl~xible membran- 19, ar~ m~a~ur-d b-for- and att~r activation of pump 25 to calculat- ~Ps and ~P(R+D):
14) ~Ps ' PSs ~ P
(15) ~P(R+D)o - P(R+D)f ~ P(R+D)~
' chang- in pr-~-ur- of m-a~ur-m-nt ga~
ln th- ourc- chamb-r re~ultlng from activatlon of pu~p 2S
Psf - pr-~-ur- of ~-a-ur~m-nt ga~ in th-ourc- chaib-r aft-r tha actlvatlon of pu~p 25 PSl ' pr---ur- Or m-a~ur-m-nt ga- in th-ourc- ch~mb-r b-for- th- actlvatlon of pump 25 ~P(R+D~ - chang- in pr-~-ur- of m-a~ur~m-nt ga~ in th- r-~-rvoir chamb-r (up to fl-xibl- m-~bran- 19) r-~ultlng from activation of pump 25 P(R+D)f - pr-~-ur- of m-a~ur-m~nt ga~ in th- r---rvoir chamb-r (up to flexibl- membran- 19) after th-activation of pump 25 P(R+D~i - pressur- of m-asurement gas in th- res-rvoir chamb-r (up to l~90Xll flexible membrane 19) before the activation of pump 25 From the Boyle' 6 Law relationship, (16) ~P(R+Dl V(R+D) ' ~ APS0VS0 V(R+D) ~ volume of re~ervoir chamber (up to flexible membrane 19) before fluid flow (thi6 quantity changes because flexible membrane 19 moves in response to fluid flow into or out of the isolated region) Vs = volume of source chamber it i~ known that (17) V(R+D) ' ~ ~ S VS / ~P(R+D) V(R+D) = volume of reservoir chamber (up to flexible ~embrane 19) during fluid flow But, it is also known that (18) VD = v(R+D)o ~ VR
VD = volume from valve 22 to flexible membrane 19 VR = known volume of the reservoir chamber 60:
(19) VD ~ ~ ~ sVs / ~ P(R+D)0 - VR
This volume VD can be checked by an alternative calculation. It will be 6een that when valve 24 is opened, that the change in vol~me of fluid in the isolated region will be reflected in a change in pressure in the measurement gas in the source chamber up to the flexible membrane 19.
~ hus, PSi, which is the pressure of the source chamber before opening valve 24, is remeasured. If there has been no leak in the system, or other error, P
should be equal to Psf, which was the pressure measured after activation of pump 25 but before fluid flow. Valve 24 is then opened- PScal~ which is the resulting pressure of the measurement gas in the source chamber up to flexible membrane 19, is then measured and 1~90~1~
u~-d to calculat- ~Seal~ th- r--ultlng ch~ng- ln pr~s~ur-(20) ~Seal ' PSeal ~ PSl Sub~ituting ~oure- eha~b-r valu-~ for r---rvolr eha~ber valu-s ln ~quat- 19 yi~ld- th- followlng guatlon (21) VD = ~PScal Vs /a P(R + D) s Th$s VD should, lf th- y-t-n 1- op-ratlng prop-rly, bQ qual to VD abov- If th- two valu-- for VD
ar- not qual, thl~ eould lndleat- varlou- y-t-n rror-, lnc~uding l-akag- of ~-a-ur-~-nt ga-Aft-r v~lv- 24 ha- b~-n op-n-d, valv- 18 1- th-n op-ned to ~llow ~luld ~low Valv-- 18 and 24 ar- th-n elo--d, and Psf i- ~-a-ur-d ~PS 1- ealeul-t-d by ubtr~etlng PSl fro~ Psf, ~nd ~Vs 1- ealeulat-d for th- elo--d y~t-~
(22) PSlVSl-(Psl+l~Ps)(VSl+~VS) by using th- foruula (23)aVS- (PSivs~) / (Ps~+.~ps) -VS~'~VD
(b-eaus- VSO 1- a eon-tant and Vs ~ Vs+VD~
Th- op-r~tlon of th- d-vle- d-plet-d ln Flg 2 and doserlb-d abov- ean b- um~-d up ln th- ~ollowlng t-ps A Inltl~llz- th- y-t-u - m-a-ur-u-nt ga~ should b-at on- atmo-ph-r- ln th- r---rvo~r and soure- ehamb-r- and valv-~ 17, 18, 2~ and 24 hould b- elo--d B M-a-ur- th- pr---ur- o~ ~-a-ur-u-nt ga~ ln th-r---rvolr eha~b-r up to th- fl-xlbl- n-~bran- 19, and th-pr-s-ur- of th ~-a-ur-~-nt ga- in th- oure- eha~b-r C op-n valv-- 17 and 22, allowlng fluld to ~low $nto tho lsolat-d r-glon D. Close valve 17.
E. Activate pump 25 to create a pressure differential between the reservoir chamber and the s ce chamber, and then stop the pump.
F. Close valve 22.
G. Measure the new pressure of the souroe chamber, and the new pressure of either the reserv~ir chamber or the portion of communication pathway 21 between valve 22 and flexible membrane 19.
1 ~ 9~ 13 -H. Calculate the volume of fluid in the isolated region using equations (14) - (21).
I. Open valve 24, and measure the pressure of the measurement gas in the source chamber.
J. Open valve 18, with resulting change in volume of fluid in the isolated region (normally outflow).
K. Close valves 18 and 24, and measure the resulting pressure of the measurement gas in the source chamber.
L. Calculate the volume of fluid delivered using equation (23).
It will be seen that measurement gas follows a cyclical travel pattern. Measurement gas is pumped from the reservoir chamber into the source chamber. The repeated opening and closing of valves 22 and 24 result in the migration of measurement gas from the source chamber back into the reservoir chamber. It will thus be seen that the system displays an innovative economy of design, since no venting or other means of pressure balancing is required.
Further, various modes of operation are possible.
For example, the present invention can be configured to operate as a pump. There i8 a point in the operation cycle when valves 18 and 24 are both open. Because the measurement gas in source chamber 12 is at a relatively high pressure, fluid will tend to be pushed out of the isolated region. If a high enough pressure differential is created between the measurement gas in the source chamber and the measurement gas in the reservoir chamber, significant pumping action will result.
The pressure differential can also be used to solve the problem of back pressure. It will be seen that the system will provide data as to fluid flow through the line even if back pressure results in no flow at all, or in backflow.
1 ~ 90 ~ 11 These phenomena will produce a correspondlng change in measurement ga6 pre66ure, whlch in turn will yl-ld a zero or negative volume increment using th- calculcatlons disclosed ~bove Thls lnformatlon can be used to compensate for downstream pres6ur- condltion~ The microprocessor, or other controlling device 112, ~ be programmed to increase the pre6sure differéntial where small or negative flows are detected The pressure differential would bs increa~ed by activating pump 25 as needed It should al60 be noted that th- detectlon of aberrant down~tream lin- pressure condltlon~ could al60 be used to detect infiltration, or oth-r unde~lrabl- condltions, all ln a manner 61mllar to that dlsclo~ed ln my copending Unlted States application Sor No 021,294, filed March 3, 1987, which i~ hereby incorporatod by refer-nce Similarly, the approachQs descrlb-d in my Unit-d States application Ser No 022,167, filed March 5, 1987, can be used to determine when an upstream reservoir 1~ reaching a near empty condition, to det-ct the pres-nce of air in the fluid line, and to purgo air from tho fluid llne As ln th- cas- of Flg 1 ~bov-, th- for-goinq cy~l- is only exQmplary and oth-r cycl-- may b- mploy-d that can utillze th- o-~ential relatlon~hlp~ d-~crlbed abov- Thus, for xample, et-p~ J through L may b- rep-ated a desired number Or tlm-- a~ a ~ubcycl- within a larger cycle of steps B through L Furthermor-, if the operating pressure of source chamber 12, ls kept at approximately that of the line pressure at valve 17, the system may be operated in a controller mode It is contemplated to construct the em~odiment of Fig 2 out of rigid plastic, arranging the chambers and pathways in 6uch a way that the final structure can be housed in a block configuration, although other materials, including metal, and configurations, known to practitioners of ordinary 6kill in the art, are also be within the spirit of the present invention
However, various elements inherent in medical infusion systems render problematic precise fluid delivery. One factor is the tubing that is used to deliver the fluid. Opening and closing of the line is typically accomplished by clamps, which can distort the walls of the tube leading to irregular flow rates. A second factor is that the 3~
patient receiving medication may move during infusion, producing varying fluid column heights, thereby affecting fluid flow. Third, the fact that fluid i6 delivered from a finite reservoir, such as an intravenous bag or bottle, that gradually empties, also affects the infusion rate.
Numerous approaches are known in the art to compensate for these factors. Certain prior art systems incorporate optical drop counting. Enhanced drop counting ~ystems update drop count data with other measured quantities in order to compensate for varying drop 6ize and splashing.
Other approaches include bag weighing and pumping to regulate flow. However, systemic error is inevitable in most, if not all, of these arrangements.
Summarv of the Invention The present invention provides a system for measuring flow of a fluid through a line. In the system, a region of fluid along the line i6 isolated from pressure effects outside of the region. A ~ource chamber contains a measurement gas in communication with the isolated region, such that the source chamber and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the 60urce chamber with a resulting change in the pressure of the measurement gas contained in the source chamber. Further provided is a reservoir chamber in communication with the source chamber for containing a known volume of measurement gas, and means for pumping measurement gas from the reservoir chamber into the source chamber. The pressure of the measurement gas in the reservoir chamber and the pressure of the measurement fluid in the source chamber are monitored as fluid flows into and out of the region. This pressure data is then analyzed to determine the volume of fluid in the isolated region.
lZgO211 Various aspects of the invention are as follows:
A system for controlling flow of a fluid through a line, the system comprising:
dispensing means (i) for isolating a region of the fluid in the line from effects of pressure in the line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a measurement gas in communication with the isolated region, such that the source means and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the source means with a resulting change in the pressure of the measurement gas contained in the source means;
reservoir means in communication with the source means for containing a known volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas contained in the reservoir means and the measurement gas contained in the source means;
pressure monitoring means for generating data relating to the pressure of the measurement gas in the source means and the measurement gas in the reservoir means; and control means, in communication with the pressure monitoring means, the pulping means, and the dispensing means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
1~9021~
2b A system for controlling flow of a fluid through a line, the system comprising:
dispensing means (i) for isolating a region the first fluid in the line from effects of pressure in the S line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a first volume of measurement gas;
reservoir means in communication with the source means for containing a second volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas in the reservoir means and in the pressure of the measurement gas contained in the source means;
a source communication pathway between the source chamber and the isolated region and a reservoir communication pathway between the reservoir chamber and the isolated region, the source communication pathway and the reservoir communication pathway joining to at some point along each respective pathway to form a joint communication pathway leading to the isolated region;
source valving means for opening and closing the source communication pathway;
reservoir valving means for opening and closing the reservoir communication pathway;
the isolated region, the source means and the reservoir means, and the source communication pathway, the reservoir communication pathway and the joint communication pathway being so disposed in relationship with each other such that they together define a fixed volume, and such that a change in volume of the fluid in the isolated region produces a correlative change in the C
1.29~211 joint communication pathway and in any other enclosure in pressure communication with the joint communication pathway;
pressure transducing means (i) in pressure communication with the source means for generating data relating to the pressure of the measurement gas in the source means, and in any other enclosure in pressure communication with the source means and (ii) in pressure communication with the joint communication pathway for generating data relating to the pressure of the measurement gas in the joint communication pathway, and in any other enclosure in pressure communication with the joint communication pathway; and control means, in communication with the pressure monitoring means, the pulping means, the dispensing means, the source valving means, and the reservoir valving means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
Brief Description of the Drawinas Fig. 1 shows a schematic drawing of a simplified embodiment of the present invention; and Fig. 2 shows a schematic drawing of a preferred embodiment of the present invention.
Fig. 3 show~ a schematic drawing of the invention claim~d in aforementioned Canadian application Serial No. 5~1,004.
DescriDtion of Preferred~mbodiments The present invention precisely measures discrete volume increments of fluid along a line by taking advantage of the known physical relationship between the pressure and volume of a gas. This is accomplished by isolating a region of the line and housing that region in communication with a measurement gas such that the isolated region of fluid and the measurement gas occupy a fixed and ascertainable volume. Thus, the movement of fluid into and out of the isolated region produces a corresponding change in the pressure of the measurement gas. The pressure of the measurement gas is monitored by a transducer, and the resulting data is used to compute the volume of fluid delivered, usinq methods described below.
In order to function properly, a system of this type must include calibration meanæ for establishing reference quantities against which later measured quantities can be compared. One approach to calibration i8 disclosed in aforementioned Canadian application Serial No. 5~1,004. The systems disclosed therein are calibrated by measuring the pressure of the measurement gas during a calibration cycle, during which the system, in the absence of fluid flow, induces a known decrease in volume of the measurement gas. The system then measures the pressure of the measurement gas during the flow of volume increments of fluid into and out of the isolated region. Using various disclosed physical and mathematical relationships, the system then computes 1~90~11 the volume of fluid delivered using the calibration data together with pressure measurements taken during fluid flow.
Figure 3 is a schematic representation of these systems. The embodiment shown in Figure 3 uses a drip chamber as the isolated region. Figure 3 shows the system having a drip chamber with an upper valve 821 and lower valve 822, which valves are operated by control circuitry 81. Pressure in the interior of the drip chamber 82 is monitored by transducer 83, which is also connected to control circuitry 81. The motor 84 drives piston 85 which compresses air in line 851. The motor 84 is also connected to control circuitry 81.
The earlier device proved to be extremely accurate at low rates of fluid delivery, but was not totally free from error. For example, a certain percentage of error was inherent in the mechanical creation of a precise volume displacement. In an embodiment employing a bellows arrangement to cause the volume displacement, error was found to be caused by a certain bowing out of the folds, which was found to be inevitable. Further, because moving parts are involved in expanding and contracting bellows, any precision could be affected by the aging of system. Other embodiments would still require precise mechanical displacements and generally good seal arrangement along the moving mechanical interface.
Another problem was found to exist in situation where the system is used to deliver relatively large volume increments of fluid, or where the volume increments are being dispensed into a line having significant back pressure. Where there is a significant amount of back pressure, relatively large volume displacements are necessary to produce the delivery of even small quantities of fluid.
The present device solves these problems of the ear~ier device by employing ~ressure displacement instead of the precise volume displacement of the ~X~O~ll - 4a -earlier system. As will be described in greater detail below, the use of pressure displacement solves many of the problems of the earlier device. For example, unlike the volume displacement system, the use of pressure displacement, as described below, does not require a precise mechanical displacement, thus eliminating the errors associated therewith. Further, the system may utilize pressure displacement in such a fashion that the presence of back pressure does not necessitate significantly more pumping than would be the case in the absence of back pressure. Indeed, the system can be configured to compensate for a wide range of bac~
pressures, lncluding 6ituations where back pressure exceeds fluid reservoir head pres6ure.
Fig. 1 ~how~ a 6chematic drawing of A simplified embodiment of the present lnvention. The system includes two chambers, reservoir chamber 11 and source chamber 12 for houeing a measurement gas. The~e chambers may be constructed of a rigid pla6tic using methods known in the art, although a wide variety of other materials, lncluding metals, may also be 6uitable, the principal de6ideratum being that the chambers maintain a fixed volume regardle6s of the pressure of the mea6urement ga~. It is thus conte~plated that the volume of reservoir chamber 11 in this embodiment i~ known, although th~ volume could be determined heuri6tically in the course of initial calibration of the 6y6tem. Each chamb~r has an a6sociated pressure transducer 13, 14. The two chamber~ are connected, but are 6eparated by a pump arrangement 111 that can move measurement gas contained $n reservoir chamber 11 into source chamber 12 with a resulting decrease in pressure in the reservoir chamber and an increase in pressure in the source cha~ber. In this embodiment, the pump arrangement 111~180 serves to prevent bac~flow of measurement gas. Thus, when the pump arrangment is activated, a pressure differential results between the two chambers which 1~ maintained even after the pump arrangment ceases to pump.
The source chamber is in communication with a region 15 of the fluid line 16 that can be isolated by valves 17 and 18 from fluid pressure effects elsewhere in the line.
Communication between the line fluid and the measurement gas is afforded through flexible membrane 19. A bulge 110 is provided in the region. The bulge 6erves two purposes.
First, the bulge allows a greater amount of line fluid to impinge against the measurement gas, thus increasing the pressure communication between the line fluid and the measurement gas. Second, the bulge, because of it6 lX90Zll substantially 6pherical shape, provides maximum radial rigidity, thus preventing the isolated region from becoming distorted as a result of high measurement gas pres6ure.
Thus, it will be seen that when either valve 17 or valve 18 is closed, movement of fluid into or out of the isolated region 15 will, via flexible membrane 19, decrease or increase the volume of the measurement gas in the source chamber, with a resulting change in the pressure of the measurement gas.
For the reasons set forth below, the amount of fluid delivered can be determined by the relationship:
~VS = (~PRVR/APS ) 4~PS/ (PS+~S) ]
where:
~VS = volume increment of fluid delivered ~PR = change in pressure of measurement gas in the reservoir chamber caused by movement of measurement gas from the reservoir chamber to the source chamber VR ' volume of the reservoir chamber (known) QFsO = change in pressure of measurement gas in the source chamber caused by movement of measurement gas from the reservoir chamber to the source chamber (measured before fluid flow) S ~ change in pressure of measurement gas in the source chamber resulting from movement of fluid out of the isolated region PS = pressure of the measurement gas in the source chamber This relationship is derived as follows:
First, assume that valves 17 and 18 are closed with fluid held in the isolated region. Initially, reservoir chamber 11 and source chamber 12 are each isolated. From Boyle's Law it is known that:
( 1 ) PSVS = nSRT
and 1~90X11 (2) PRVR - nRRT
where VS ~ the volume of the source chamber nS ~ the number of moles of measurement gas in the source chamber PR ~ the presS~ of the reservoir chamber nR ~ the number of moles of measurement gas in the reservoir chamber R - a constant T - temperature of the measure~ent gas Adding (1) and (2) ~ields (3) PSVS + PRVR ' (nS + nR)RT
Because thQ ~ourc~ chamber and the reservolr chamber together comprisQ a clo6ed system, (4) nS + nR ~ N, where N is a constant Measurement gas ls then moved from the reservoir chamber to the source chamber. Thi~ results in a change of the respectivQ pressures of the two chambers. Because the chamber~ are rigid and becaus- there i~ no fluid flow lnto or out of the isolated region, the respective volumes remain constant. Thus, (5a) (PSVS + PRVR) ' ~(nS + nR)RT]
which yields (5b) (PS+~ S )VS + (PR~PR)VR ' NRT
Subtractin~ (3) from (5) yields:
(6) ~ PsVs + APRVR - 0 Solving for Vs yields:
(7) VS ~ - ~PR VR /~Ps At this point, the pump arrangment is then closed off, thus cutting off any communication between the two chambers. BY BOY1Q 's ~aw, it is known that at constant temperature, with respect to the source chamber volume:
(8) PSVS ' XS ; KS ~ constant Now valve 18 is opened, and fluid flows out of the isolated reglon. The outflow of fluid results in an increase in the volume of measurement gas housed in the source chamber, with a resulting decrease in pressure. By 1290~11 Boyle's Law lt is known that the product of the ~easurement gas pressure in the source chamber volume and the source chamber volumes remain constant. Thus, ~g) (Ps + ~s) (Vs +AVs) - Psvs - ~s Solving eguation (9) for ~Vs yields (lOa) ~Vs 8 Psvs/(ps +~S) - Vs or (lOb) ~Vs ' -~Psvs/(ps+~ps) ~ ecause we are assuming that some fluid has indeed flowed out of the isolated region, PS i6 not egual to the initial pressure Ps~
Using the relation of eguation (7) to remove the Vs term ~n eguation (lO) yields:
(11) ~VS ~ PS/(PS +~ PS) ~ ~- A~PR VR / ~PS]
This equation can be rewritten ~B:
(12) ~Vs ~ ~PRovR /~PS ]t~s/~Ps + ~PS)]
which 16 the final eguation.
Total fluid delivered can be calculated by 6umming each individual ~Vsl ~hich can be expressed by the following formula:
~1 ~ S ~PR VR / PSi]L~PS-/(pBi+aP i)]
The operation ot the device depict-d ln Fig. l can be summariz~d by th- ~ollowing steps:
A. Initlalize the y-tem - valve~ 17 and 18 are closed with fluid held ln the isolated region.
B. Mea~ure the pres~ure of the measurement gas in the reservoir chamber and the 60urce chamber.
C. Mov- ~ome measurement gas from the reservolr chamber into the source chamber, and close off the source chamber from the reservoir chamber.
D. Measure the new pressures of the measurenent gas in the reservoir chamber and the source chamberO
E. Open valve 18, which allows fluid to flow out of the isolated region 15.
F. Measure the pressure of the measurement gas in the source chamber, which is presumably decreasing as the 1290~11 volume increa~e~ ln re~pons- to fluid leaving the lsolated region G Compute the volume of fluid delivered u~ing equation (12) It is contemplated that the data from the pressure transducers 13 and 14 will be interpreted by a microprocessor, or other computing unit 112, which would also activate the pumping arrangment 15 and valves 17 and 18 It can be 6een that the foregoing cycle i8 only exemplary, and that other cycles may be employed that can utilize the essential relationships described above For example, steps E, F, and G may be repeated a desired number of times as a subcycle within larger cycle of steps B through G
Fig 2 6hows a schematic diagram of a preferred embodiment of th- present invention This embodiment involve~ a ~lightly dlfferent arrangement for placing the reservoir chambér 11 and the source chamber 12 in communication with each other and with the i601ated region of the fluid lin- Th- mbodiment of Fig 2 provides a communicatlon pathway 21, gated by valve 22, to the isolated region The pathway 23 between the source chamber 12 and th- i601ated region 15 i6 gat-d by valv- 24 In one mode of operatlon of thi- e~bodlm~nt, lt 18 po~ible to circulate measursment fluld around ~ closed clrcuit, namely from reservolr chamb-r 11 to source chamber 12 into the bulge 110 and th-n bac~ to the reservoir chamber 11, with a resultlng economy o~ operatlon ln operatlon, assume, for xample, that a measurement gas, such as air, i~ at one atmosphere ln chamber~ 11 and 12, and that valv-- 17, 18, 22 and 24 are closed Valves 17 and 22 are then opened The opening of valve 17 allows fluid to flow into the isolated region The opening of valve 22 defines two separate volumes One of these volu~es is the sum of the volumes of the reservoir chamber 11 and communication pathway 21 up to flexible membrane 19 The second is the volume of source chamber 12 plus the volu~e of that portion of communication pathway 23 up to 1~90~11 valve 24. The pressure of measurement gas associated with these two volumes are then measured and recorded.
Valve 17 is then closed. Pump 25 is then run to create a pressure differential between the reservoir chamber and the source chamber. Then valve 22 is closed. At this point, because fluid flow has been stopped~ the pressure of tha mea~urement gas is the same on either side of valve 22, now closed. Thus, either pressure quantity could be measured. In the depicted embodiment transducer 13 measures the pressure between the valve and the flexible membrane.
Th- pr-~-ur- PS f th- ourc- cha~b-r up to valv- 24, whic~ 1- clo--d, and tho pr---uro P~R+Dj ~ th- r---rvoir chamb-r, includlng com~unication pathway 21 up to fl~xible membran- 19, ar~ m~a~ur-d b-for- and att~r activation of pump 25 to calculat- ~Ps and ~P(R+D):
14) ~Ps ' PSs ~ P
(15) ~P(R+D)o - P(R+D)f ~ P(R+D)~
' chang- in pr-~-ur- of m-a~ur-m-nt ga~
ln th- ourc- chamb-r re~ultlng from activatlon of pu~p 2S
Psf - pr-~-ur- of ~-a-ur~m-nt ga~ in th-ourc- chaib-r aft-r tha actlvatlon of pu~p 25 PSl ' pr---ur- Or m-a~ur-m-nt ga- in th-ourc- ch~mb-r b-for- th- actlvatlon of pump 25 ~P(R+D~ - chang- in pr-~-ur- of m-a~ur~m-nt ga~ in th- r-~-rvoir chamb-r (up to fl-xibl- m-~bran- 19) r-~ultlng from activation of pump 25 P(R+D)f - pr-~-ur- of m-a~ur-m~nt ga~ in th- r---rvoir chamb-r (up to flexibl- membran- 19) after th-activation of pump 25 P(R+D~i - pressur- of m-asurement gas in th- res-rvoir chamb-r (up to l~90Xll flexible membrane 19) before the activation of pump 25 From the Boyle' 6 Law relationship, (16) ~P(R+Dl V(R+D) ' ~ APS0VS0 V(R+D) ~ volume of re~ervoir chamber (up to flexible membrane 19) before fluid flow (thi6 quantity changes because flexible membrane 19 moves in response to fluid flow into or out of the isolated region) Vs = volume of source chamber it i~ known that (17) V(R+D) ' ~ ~ S VS / ~P(R+D) V(R+D) = volume of reservoir chamber (up to flexible ~embrane 19) during fluid flow But, it is also known that (18) VD = v(R+D)o ~ VR
VD = volume from valve 22 to flexible membrane 19 VR = known volume of the reservoir chamber 60:
(19) VD ~ ~ ~ sVs / ~ P(R+D)0 - VR
This volume VD can be checked by an alternative calculation. It will be 6een that when valve 24 is opened, that the change in vol~me of fluid in the isolated region will be reflected in a change in pressure in the measurement gas in the source chamber up to the flexible membrane 19.
~ hus, PSi, which is the pressure of the source chamber before opening valve 24, is remeasured. If there has been no leak in the system, or other error, P
should be equal to Psf, which was the pressure measured after activation of pump 25 but before fluid flow. Valve 24 is then opened- PScal~ which is the resulting pressure of the measurement gas in the source chamber up to flexible membrane 19, is then measured and 1~90~1~
u~-d to calculat- ~Seal~ th- r--ultlng ch~ng- ln pr~s~ur-(20) ~Seal ' PSeal ~ PSl Sub~ituting ~oure- eha~b-r valu-~ for r---rvolr eha~ber valu-s ln ~quat- 19 yi~ld- th- followlng guatlon (21) VD = ~PScal Vs /a P(R + D) s Th$s VD should, lf th- y-t-n 1- op-ratlng prop-rly, bQ qual to VD abov- If th- two valu-- for VD
ar- not qual, thl~ eould lndleat- varlou- y-t-n rror-, lnc~uding l-akag- of ~-a-ur-~-nt ga-Aft-r v~lv- 24 ha- b~-n op-n-d, valv- 18 1- th-n op-ned to ~llow ~luld ~low Valv-- 18 and 24 ar- th-n elo--d, and Psf i- ~-a-ur-d ~PS 1- ealeul-t-d by ubtr~etlng PSl fro~ Psf, ~nd ~Vs 1- ealeulat-d for th- elo--d y~t-~
(22) PSlVSl-(Psl+l~Ps)(VSl+~VS) by using th- foruula (23)aVS- (PSivs~) / (Ps~+.~ps) -VS~'~VD
(b-eaus- VSO 1- a eon-tant and Vs ~ Vs+VD~
Th- op-r~tlon of th- d-vle- d-plet-d ln Flg 2 and doserlb-d abov- ean b- um~-d up ln th- ~ollowlng t-ps A Inltl~llz- th- y-t-u - m-a-ur-u-nt ga~ should b-at on- atmo-ph-r- ln th- r---rvo~r and soure- ehamb-r- and valv-~ 17, 18, 2~ and 24 hould b- elo--d B M-a-ur- th- pr---ur- o~ ~-a-ur-u-nt ga~ ln th-r---rvolr eha~b-r up to th- fl-xlbl- n-~bran- 19, and th-pr-s-ur- of th ~-a-ur-~-nt ga- in th- oure- eha~b-r C op-n valv-- 17 and 22, allowlng fluld to ~low $nto tho lsolat-d r-glon D. Close valve 17.
E. Activate pump 25 to create a pressure differential between the reservoir chamber and the s ce chamber, and then stop the pump.
F. Close valve 22.
G. Measure the new pressure of the souroe chamber, and the new pressure of either the reserv~ir chamber or the portion of communication pathway 21 between valve 22 and flexible membrane 19.
1 ~ 9~ 13 -H. Calculate the volume of fluid in the isolated region using equations (14) - (21).
I. Open valve 24, and measure the pressure of the measurement gas in the source chamber.
J. Open valve 18, with resulting change in volume of fluid in the isolated region (normally outflow).
K. Close valves 18 and 24, and measure the resulting pressure of the measurement gas in the source chamber.
L. Calculate the volume of fluid delivered using equation (23).
It will be seen that measurement gas follows a cyclical travel pattern. Measurement gas is pumped from the reservoir chamber into the source chamber. The repeated opening and closing of valves 22 and 24 result in the migration of measurement gas from the source chamber back into the reservoir chamber. It will thus be seen that the system displays an innovative economy of design, since no venting or other means of pressure balancing is required.
Further, various modes of operation are possible.
For example, the present invention can be configured to operate as a pump. There i8 a point in the operation cycle when valves 18 and 24 are both open. Because the measurement gas in source chamber 12 is at a relatively high pressure, fluid will tend to be pushed out of the isolated region. If a high enough pressure differential is created between the measurement gas in the source chamber and the measurement gas in the reservoir chamber, significant pumping action will result.
The pressure differential can also be used to solve the problem of back pressure. It will be seen that the system will provide data as to fluid flow through the line even if back pressure results in no flow at all, or in backflow.
1 ~ 90 ~ 11 These phenomena will produce a correspondlng change in measurement ga6 pre66ure, whlch in turn will yl-ld a zero or negative volume increment using th- calculcatlons disclosed ~bove Thls lnformatlon can be used to compensate for downstream pres6ur- condltion~ The microprocessor, or other controlling device 112, ~ be programmed to increase the pre6sure differéntial where small or negative flows are detected The pressure differential would bs increa~ed by activating pump 25 as needed It should al60 be noted that th- detectlon of aberrant down~tream lin- pressure condltlon~ could al60 be used to detect infiltration, or oth-r unde~lrabl- condltions, all ln a manner 61mllar to that dlsclo~ed ln my copending Unlted States application Sor No 021,294, filed March 3, 1987, which i~ hereby incorporatod by refer-nce Similarly, the approachQs descrlb-d in my Unit-d States application Ser No 022,167, filed March 5, 1987, can be used to determine when an upstream reservoir 1~ reaching a near empty condition, to det-ct the pres-nce of air in the fluid line, and to purgo air from tho fluid llne As ln th- cas- of Flg 1 ~bov-, th- for-goinq cy~l- is only exQmplary and oth-r cycl-- may b- mploy-d that can utillze th- o-~ential relatlon~hlp~ d-~crlbed abov- Thus, for xample, et-p~ J through L may b- rep-ated a desired number Or tlm-- a~ a ~ubcycl- within a larger cycle of steps B through L Furthermor-, if the operating pressure of source chamber 12, ls kept at approximately that of the line pressure at valve 17, the system may be operated in a controller mode It is contemplated to construct the em~odiment of Fig 2 out of rigid plastic, arranging the chambers and pathways in 6uch a way that the final structure can be housed in a block configuration, although other materials, including metal, and configurations, known to practitioners of ordinary 6kill in the art, are also be within the spirit of the present invention
Claims (17)
1. A system for controlling flow of a fluid through a line, the system comprising:
dispensing means (i) for isolating a region of the fluid in the line from effects of pressure in the line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a measurement gas in communication with the isolated region, such that the source means and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the source means with a resulting change in the pressure of the measurement gas contained in the source means;
reservoir means in communication with the source means for containing a known volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas contained in the reservoir means and the measurement gas contained in the source means;
pressure monitoring means for generating data relating to the pressure of the measurement gas in the source means and the measurement gas in the reservoir means; and control means, in communication with the pressure monitoring means, the pulping means, and the dispensing means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
dispensing means (i) for isolating a region of the fluid in the line from effects of pressure in the line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a measurement gas in communication with the isolated region, such that the source means and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the source means with a resulting change in the pressure of the measurement gas contained in the source means;
reservoir means in communication with the source means for containing a known volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas contained in the reservoir means and the measurement gas contained in the source means;
pressure monitoring means for generating data relating to the pressure of the measurement gas in the source means and the measurement gas in the reservoir means; and control means, in communication with the pressure monitoring means, the pulping means, and the dispensing means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
2. A system according to Claim 1, wherein the measurement gas is air.
3. A system according to Claim 1, wherein the dispensing means includes an input valve at the fluid input to the region and an output valve at the fluid output from the region.
4. A system according to Claim 3, wherein the isolated region includes a flexible interface surface defining a boundary between the fluid and the measurement gas contained in the source means.
5. A system according to Claim 4, wherein the isolated region includes a rigid enclosure with an input, an output, and a window, the flexible interface surface covering the window.
6. A system according to Claim 3, wherein the control means includes means for controlling first fluid flow in accordance with a calibration and dispensing cycle as follows:
(A) closing the input and output valves with fluid in present in the isolated region;
(B) measuring the pressure in the reservoir means and the source means;
(C) actuating the pumping means to move measurement gas from the reservoir means to the source means;
(D) measuring the resulting pressure in the reservoir means and the source means;
(E) closing off the pumping means, such that any communication between the reservoir means and the source means is cut off;
(F) opening the output valve, thereby allowing fluid to flow out of the isolated region;
(G) measuring the resulting change in pressure of the measurement gas contained in the source means;
(H) calculating the volume of fluid delivered based on data from steps (B), (D) and (G);
(I) closing the output valve;
(J) opening the input valve, thereby allowing fluid to flow into the isolated region;
(K) closing the input valve;
(L) repeating subcycle (F) - (K) until a desired amount of fluid has been delivered.
(A) closing the input and output valves with fluid in present in the isolated region;
(B) measuring the pressure in the reservoir means and the source means;
(C) actuating the pumping means to move measurement gas from the reservoir means to the source means;
(D) measuring the resulting pressure in the reservoir means and the source means;
(E) closing off the pumping means, such that any communication between the reservoir means and the source means is cut off;
(F) opening the output valve, thereby allowing fluid to flow out of the isolated region;
(G) measuring the resulting change in pressure of the measurement gas contained in the source means;
(H) calculating the volume of fluid delivered based on data from steps (B), (D) and (G);
(I) closing the output valve;
(J) opening the input valve, thereby allowing fluid to flow into the isolated region;
(K) closing the input valve;
(L) repeating subcycle (F) - (K) until a desired amount of fluid has been delivered.
7. A system according to Claim 6 further including in the pumping cycle:
(M) monitoring the rate of fluid delivery, and if the rate of fluid delivery has dropped below a desired level, increasing the pressure difference between the reservoir means and the source means, and resuming the cycle from step (D).
(M) monitoring the rate of fluid delivery, and if the rate of fluid delivery has dropped below a desired level, increasing the pressure difference between the reservoir means and the source means, and resuming the cycle from step (D).
8. A system according to Claim 6, wherein the volume of fluid delivered is determined by the relationship:
.DELTA.VS = (.DELTA.PR°VR/.DELTA.PS°) [.DELTA.PS/(PS+.DELTA.PS)]
where:
.DELTA.VS = volume increment of fluid delivered;
.DELTA.PR° = change in pressure of measurement gas in the reservoir chamber caused by movement of measurement gas from the reservoir chamber to the source chamber;
VR = known volume of the reservoir chamber;
.DELTA.PS° = change in pressure of measurement gas in the source chamber caused by movement of measurement gas from the reservoir chamber to the source chamber, measured before fluid flow;
.DELTA.PS = change in pressure of measurement gas in the source chamber resulting from movement of fluid out of the isolated region;
PS = pressure of the measurement gas in the source chamber.
.DELTA.VS = (.DELTA.PR°VR/.DELTA.PS°) [.DELTA.PS/(PS+.DELTA.PS)]
where:
.DELTA.VS = volume increment of fluid delivered;
.DELTA.PR° = change in pressure of measurement gas in the reservoir chamber caused by movement of measurement gas from the reservoir chamber to the source chamber;
VR = known volume of the reservoir chamber;
.DELTA.PS° = change in pressure of measurement gas in the source chamber caused by movement of measurement gas from the reservoir chamber to the source chamber, measured before fluid flow;
.DELTA.PS = change in pressure of measurement gas in the source chamber resulting from movement of fluid out of the isolated region;
PS = pressure of the measurement gas in the source chamber.
9. A system for controlling flow of a fluid through a line, the system comprising:
dispensing means (i) for isolating a region the first fluid in the line from effects of pressure in the line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a first volume of measurement gas;
reservoir means in communication with the source means for containing a second volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas in the reservoir means and in the pressure of the measurement gas contained in the source means;
a source communication pathway between the source chamber and the isolated region and a reservoir communication pathway between the reservoir chamber and the isolated region, the source communication pathway and the reservoir communication pathway joining to at some point along each respective pathway to form a joint communication pathway leading to the isolated region;
source valving means for opening and closing the source communication pathway;
reservoir valving means for opening and closing the reservoir communication pathway;
the isolated region, the source means and the reservoir means, and the source communication pathway, the reservoir communication pathway and the joint communication pathway being so disposed in relationship with each other such that they together define a fixed volume, and such that a change in volume of the fluid in the isolated region produces a correlative change in the joint communication pathway and in any other enclosure in pressure communication with the joint communication pathway;
pressure transducing means (i) in pressure communication with the source means for generating data relating to the pressure of the measurement gas in the source means, and in any other enclosure in pressure communication with the source means and (ii) in pressure communication with the joint communication pathway for generating data relating to the pressure of the measurement gas in the joint communication pathway, and in any other enclosure in pressure communication with the joint communication pathway; and control means, in communication with the pressure monitoring means, the pulping means, the dispensing means, the source valving means, and the reservoir valving means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
dispensing means (i) for isolating a region the first fluid in the line from effects of pressure in the line outside of the region, the region having an input and an output for the first fluid, and (ii) for repetitively dispensing into and out of the region volume increments of the fluid;
source means for containing a first volume of measurement gas;
reservoir means in communication with the source means for containing a second volume of measurement gas;
pumping means for moving a quantity of measurement gas between the reservoir means and the source means, thereby producing changes in the pressure of the measurement gas in the reservoir means and in the pressure of the measurement gas contained in the source means;
a source communication pathway between the source chamber and the isolated region and a reservoir communication pathway between the reservoir chamber and the isolated region, the source communication pathway and the reservoir communication pathway joining to at some point along each respective pathway to form a joint communication pathway leading to the isolated region;
source valving means for opening and closing the source communication pathway;
reservoir valving means for opening and closing the reservoir communication pathway;
the isolated region, the source means and the reservoir means, and the source communication pathway, the reservoir communication pathway and the joint communication pathway being so disposed in relationship with each other such that they together define a fixed volume, and such that a change in volume of the fluid in the isolated region produces a correlative change in the joint communication pathway and in any other enclosure in pressure communication with the joint communication pathway;
pressure transducing means (i) in pressure communication with the source means for generating data relating to the pressure of the measurement gas in the source means, and in any other enclosure in pressure communication with the source means and (ii) in pressure communication with the joint communication pathway for generating data relating to the pressure of the measurement gas in the joint communication pathway, and in any other enclosure in pressure communication with the joint communication pathway; and control means, in communication with the pressure monitoring means, the pulping means, the dispensing means, the source valving means, and the reservoir valving means, for causing the dispensing means to dispense first fluid in determinable increments based on data from the pressure monitoring means taken at predetermined points during a calibration and dispensing cycle.
10. A system according to Claim 9, wherein the measurement gas is air.
11. A system according to Claim 9, wherein the dispensing means includes an input valve at the fluid input to the region and an output valve at the fluid output from the region.
12. A system according to Claim 11, wherein the isolated region includes a flexible interface surface defining a boundary between the fluid and the measurement gas contained in the source means.
13. A system according to Claim 12, wherein the isolated region includes a rigid enclosure with an input, an output, and a window, the flexible interface surface covering the window.
14. A system according to Claim 11, wherein the control means includes means for controlling first fluid flow in accordance with a pumping cycle as follows:
(A) initializing the system by estabilishing a pressure of one atmosphere of the measurement gas in the reservoir means, the source means, and all of the communication pathways, and closing the input valve, the output valve, the source valve, and the reservoir valve;
(B) taking pressure readings at the pressure transducer means;
(C) opening the input valve and the reservoir valve, thereby allowing fluid to flow into the isolated region;
(D) actuating the pulping means to create a pressure differential between the reservoir means and the source means, and then stopping the pump;
(E) closing the fluid input valve and the reservoir valve;
(F) taking a new pressure reading at the pressure transducer means;
(G) calculating the volume of fluid in the isolated region based on the data obtained in steps (B) and (F);
(H) opening the source valve;
(I) taking a pressure reading at the pressure transducer of the pressure of the measurement gas in the source means;
(J) opening the fluid output valve, thereby causing a change in the volume of fluid in the isolated region;
(K) closing the fluid output valve and the source valve, and measuring taking a pressure reading at the pressure transducer means of the pressure of the measurement gas on the source means;
(L) calcuting the volume of fluid delivered using data obtained from (G), (I), and (K);
(M) repeating steps (F) - (L) until a desired volume of fluid has been delivered.
(A) initializing the system by estabilishing a pressure of one atmosphere of the measurement gas in the reservoir means, the source means, and all of the communication pathways, and closing the input valve, the output valve, the source valve, and the reservoir valve;
(B) taking pressure readings at the pressure transducer means;
(C) opening the input valve and the reservoir valve, thereby allowing fluid to flow into the isolated region;
(D) actuating the pulping means to create a pressure differential between the reservoir means and the source means, and then stopping the pump;
(E) closing the fluid input valve and the reservoir valve;
(F) taking a new pressure reading at the pressure transducer means;
(G) calculating the volume of fluid in the isolated region based on the data obtained in steps (B) and (F);
(H) opening the source valve;
(I) taking a pressure reading at the pressure transducer of the pressure of the measurement gas in the source means;
(J) opening the fluid output valve, thereby causing a change in the volume of fluid in the isolated region;
(K) closing the fluid output valve and the source valve, and measuring taking a pressure reading at the pressure transducer means of the pressure of the measurement gas on the source means;
(L) calcuting the volume of fluid delivered using data obtained from (G), (I), and (K);
(M) repeating steps (F) - (L) until a desired volume of fluid has been delivered.
15. A system according to Claim 14 further including in the dispensing cycle:
monitoring the rate of fluid delivery, and if the rate of fluid delivery has dropped below a desired level, increasing the pressure difference between the reservoir means and the source means, and resuming the cycle from step (E).
monitoring the rate of fluid delivery, and if the rate of fluid delivery has dropped below a desired level, increasing the pressure difference between the reservoir means and the source means, and resuming the cycle from step (E).
16. A system according to Claim 14, wherein the volume calculated in step (G) is determined by the following relationship:
Vf = VT - VD°
where Vf = volume of fluid in the isolated region;
VT = known total volume of fluid and measurement gas contained in the isolated region and in enclosures in pressure communication with the isolated region;
VD° = volume of measurement gas contained in enclosures in pressure communication with the isolated region;
wherein VD° is determined by the following relationship:
VD° = - PS°VS° / .DELTA.P(R+D) °-VR
where:
.DELTA.Ps° = change in pressure of measurement gas in the source chamber resulting from activation of the pumping means;
Vs° = volume of source chamber;
.DELTA.P(R+D)° = change in pressure of measurement gas in the reservoir means (up to flexible membrane) resulting from activation of the pumping means;
VR = known volume of the reservoir chamber; and wherein the volume calculated in step (L) is determined by the relationship:
.DELTA.V = - .DELTA.VD
where:
.DELTA.V = change in volume of the fluid in the isolated region;
.DELTA.VD = change in volume of the measurement gas in the isolated region;
and where DVD is determined by the following relationship;
.DELTA.VD = (PSiVsi) / (PSi+ .DELTA.PS) - VSi where:
PSi = pressure of the measurement gas in the source means before opening the source valve;
Vsi = volume of the measurement gas in the source means before opening the source valve;
.DELTA.PS = change in pressure in the measurement gas in the source means resulting from the opening of the source valve;
Vf = VT - VD°
where Vf = volume of fluid in the isolated region;
VT = known total volume of fluid and measurement gas contained in the isolated region and in enclosures in pressure communication with the isolated region;
VD° = volume of measurement gas contained in enclosures in pressure communication with the isolated region;
wherein VD° is determined by the following relationship:
VD° = - PS°VS° / .DELTA.P(R+D) °-VR
where:
.DELTA.Ps° = change in pressure of measurement gas in the source chamber resulting from activation of the pumping means;
Vs° = volume of source chamber;
.DELTA.P(R+D)° = change in pressure of measurement gas in the reservoir means (up to flexible membrane) resulting from activation of the pumping means;
VR = known volume of the reservoir chamber; and wherein the volume calculated in step (L) is determined by the relationship:
.DELTA.V = - .DELTA.VD
where:
.DELTA.V = change in volume of the fluid in the isolated region;
.DELTA.VD = change in volume of the measurement gas in the isolated region;
and where DVD is determined by the following relationship;
.DELTA.VD = (PSiVsi) / (PSi+ .DELTA.PS) - VSi where:
PSi = pressure of the measurement gas in the source means before opening the source valve;
Vsi = volume of the measurement gas in the source means before opening the source valve;
.DELTA.PS = change in pressure in the measurement gas in the source means resulting from the opening of the source valve;
17. A system according to Claim 16, further including the step of testing the system by alternatively calculating the volume calculated in step (G) by the following relationship:
(21) VD° = .DELTA.Pscal°VS°/.DELTA.P(R+D)° - VS
where .DELTA.PScal° = the change in pressure of measurement gas in the source chamber up to the flexible membrane resulting from the opening of the source valve;
.DELTA.P(R+D)° = change in pressure of measurement gas in the reservoir means (up to flexible membrane) resulting from activation of the pumping means;
Vs° = volume of source chamber.
(21) VD° = .DELTA.Pscal°VS°/.DELTA.P(R+D)° - VS
where .DELTA.PScal° = the change in pressure of measurement gas in the source chamber up to the flexible membrane resulting from the opening of the source valve;
.DELTA.P(R+D)° = change in pressure of measurement gas in the reservoir means (up to flexible membrane) resulting from activation of the pumping means;
Vs° = volume of source chamber.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US07/092,481 US4826482A (en) | 1986-03-04 | 1987-09-03 | Enhanced pressure measurement flow control system |
US092,481 | 1987-09-03 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1290211C true CA1290211C (en) | 1991-10-08 |
Family
ID=22233431
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000576571A Expired - Lifetime CA1290211C (en) | 1987-09-03 | 1988-09-06 | Enhanced pressure measurement flow control system |
Country Status (6)
Country | Link |
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US (1) | US4826482A (en) |
EP (1) | EP0332690B1 (en) |
JP (1) | JP3092070B2 (en) |
CA (1) | CA1290211C (en) |
DE (1) | DE3882966T2 (en) |
WO (1) | WO1989001795A1 (en) |
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- 1988-09-01 EP EP88908607A patent/EP0332690B1/en not_active Expired - Lifetime
- 1988-09-01 JP JP63507766A patent/JP3092070B2/en not_active Expired - Lifetime
- 1988-09-01 DE DE88908607T patent/DE3882966T2/en not_active Expired - Lifetime
- 1988-09-01 WO PCT/US1988/003079 patent/WO1989001795A1/en active IP Right Grant
- 1988-09-06 CA CA000576571A patent/CA1290211C/en not_active Expired - Lifetime
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WO1989001795A1 (en) | 1989-03-09 |
DE3882966D1 (en) | 1993-09-09 |
JPH02501198A (en) | 1990-04-26 |
EP0332690A4 (en) | 1990-09-26 |
EP0332690A1 (en) | 1989-09-20 |
JP3092070B2 (en) | 2000-09-25 |
DE3882966T2 (en) | 1993-11-25 |
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