Volume Measurement Using Gas Laws
First Claim
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1. A method of measuring a volume of liquid in a flexible container, comprising:
- placing the flexible container within a first rigid container of known volume, the first rigid container containing an inflatable bladder;
pressurizing the inflatable bladder with a gas;
pressurizing a second rigid container of known volume with a gas, the pressure of the gas in the bladder being approximately equal to the pressure of the gas in the second rigid container;
delivering a first molar quantity of gas to the bladder to cause a measurable increase in pressure in the bladder;
delivering a second molar quantity of gas to the second rigid container to cause a measurable increase in pressure in the second rigid container, the first molar quantity of gas being approximately equal to the second molar quantity of gas;
measuring the increase in pressure in the bladder;
measuring the increase in pressure in the second rigid container;
calculating the volume of gas in the bladder using the known volume of the second rigid container, the measured increase in pressure in the bladder, and the measured increase in pressure in the second rigid container; and
calculating the volume of liquid in the flexible container by subtracting the calculated volume of gas in the bladder from the known volume of the first rigid container.
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Abstract
A system and method for measuring fluid volume and changes in fluid volume over time, using a simple, low cost architecture is described.
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Citations
14 Claims
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1. A method of measuring a volume of liquid in a flexible container, comprising:
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placing the flexible container within a first rigid container of known volume, the first rigid container containing an inflatable bladder; pressurizing the inflatable bladder with a gas; pressurizing a second rigid container of known volume with a gas, the pressure of the gas in the bladder being approximately equal to the pressure of the gas in the second rigid container; delivering a first molar quantity of gas to the bladder to cause a measurable increase in pressure in the bladder; delivering a second molar quantity of gas to the second rigid container to cause a measurable increase in pressure in the second rigid container, the first molar quantity of gas being approximately equal to the second molar quantity of gas; measuring the increase in pressure in the bladder; measuring the increase in pressure in the second rigid container; calculating the volume of gas in the bladder using the known volume of the second rigid container, the measured increase in pressure in the bladder, and the measured increase in pressure in the second rigid container; and calculating the volume of liquid in the flexible container by subtracting the calculated volume of gas in the bladder from the known volume of the first rigid container. - View Dependent Claims (2, 3, 4, 6, 7)
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5. The method of claim 5, wherein said pump is not a precise metering device.
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8. A method for calculating a flow rate of liquid exiting a flexible container contained within a rigid container of known volume, the rigid container containing an inflatable bladder, the inflatable bladder pressurized with a gas to urge the liquid out of the flexible container, said method comprising:
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calculating the volume of gas in the inflatable bladder; determining the initial pressure in the inflatable bladder; monitoring the pressure decay in the inflatable bladder over time until the change in pressure reaches some preselected threshold value; calculating the rate of pressure decay; and calculating the flow rate using the rate of pressure decay, the calculated volume of gas in the inflatable bladder, and the initial pressure in the inflatable bladder.
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9. A fluid delivery system, comprising:
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a pressure frame (10) of known total volume; an inflatable bladder (20) within said pressure frame; said pressure frame adapted to receive a flexible bag (30) containing a liquid to be infused (40); a calibration tank (60) of known volume; a pump (50) fluidically coupled to said bladder and said calibration tank for selectively delivering a gas to said bladder and said calibration tank; a first pressure sensor (202) coupled to said bladder for sensing the pressure of a gas in said bladder; a second pressure sensor (204) coupled to said calibration tank for sensing the pressure of a gas in said calibration tank; a processing unit (700) coupled to said first and second pressure sensors and said first and second temperature sensors for storing pressure and temperature information from said first and second pressure sensors and said first and second temperature sensors; said processing unit coupled to said pump for controlling operation of said pump; and said processing unit further including means for calculating one or both of; a volume of liquid in the flexible container; and a flow rate of fluid exiting the flexible container. - View Dependent Claims (10, 11, 12, 13, 14)
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Specification