Flow Sensor Calibrated by Volume Changes

1 . An inline flow sensor, comprising:

a conduit defining a flow passageway between a fluid inlet and a fluid outlet;

a ball member movable within said flow passageway;

a spring for urging said ball member in a direction opposite a direction of fluid flow through said conduit; and

an optical sensor for determining a position of said ball member within said

conduit.

2 . The inline flow sensor of claim 1 , wherein said conduit comprises:

a housing defining a cavity having an axis and which is tapered in the direction of said axis; and

optionally, means within said cavity for restricting movement of said ball member to movement along said axis.

3 . The inline flow sensor of claim 2 , wherein said optical sensor comprises:

an optical transmitter positioned on a first side of said housing; and

an optical receiver positioned on a second side of said housing opposite said first side.

4 . The inline flow sensor of claim 3 , wherein an optical path is created through said ball member.

5 . The inline flow sensor of claim 3 , wherein said optical receiver comprises a linear photosensor array extending in a direction parallel to said axis.

6 . The inline flow sensor of claim 5 , wherein said photosensor array is selected from the group consisting of a photodiode array, a CCD array, and a CMOS digital detector array.

7 . The inline flow sensor of claim 5 , wherein said optical transmitter comprises a linear LED array.

8 . The inline flow sensor of claim 3 , further comprising:

said optical transmitter comprises a light source having a light source wavelength selected from a wavelength in the IR, visible, or UV region; and

said housing and ball member are formed of a material that optically transmits light in said light source wavelength.

9 . The inline flow sensor of claim 1 , further comprising:

means for adjusting a preload force of said spring on said ball member.

10 . A flow control system for a fluid delivery system of a type for delivering a volume of fluid from a container, the fluid control system comprising:

an inline flow sensor fluidically coupled to an output of the fluid delivery system for generating a signal representative of a sensed flow rate of the fluid;

means for calculating volume of the liquid remaining in the container; and

a computer-based information handling system including:

means for monitoring the signal from the inline flow sensor;

means for calibrating said inline flow sensor using the signal from the inline flow sensor and successive calculations of volume of the liquid remaining in the container; and

means for determining a flow rate of the fluid using one or both of: the successive calculations of volume of the liquid remaining in the container; and the signal from the inline flow sensor.

11 . A method of determining an absolute flow rate of a fluid to be delivered in a fluid delivery system, comprising:

sensing a relative flow rate using an inline flow sensor fluidically coupled to an output of the fluid delivery system for generating a signal representative of the sensed relative flow rate of the fluid; and

determining the absolute flow rate of the fluid from the sensed relative flow rate of the fluid.

12 . The method of claim 11 , wherein determining the absolute flow rate of the fluid comprises:

calculating volume of the liquid to be delivered;

monitoring the signal from the inline flow sensor;

calibrating the inline flow sensor using the signal from the inline flow sensor and one or both of:

successive calculations of volume of the liquid to be delivered; and

a pressure decay of a pressurized bladder bearing against the liquid to be delivered; and

determining the absolute flow rate of the fluid using one or more of:

the successive calculations of volume of the liquid to be delivered;

the signal from the inline flow sensor; and

a pressure decay of a pressurized bladder bearing against the liquid to be

delivered.

13 . The method of claim 11 , wherein determining the absolute flow rate of the fluid comprises one or more of:

comparing the sensed relative flow rate of the fluid to previously stored sensed relative flow rates for known absolute flow rates; and

converting the sensed relative flow rate of the fluid to an absolute flow rate using an algorithmic formula mapping sensed relative flow rates to absolute flow rates.

14 . The method of claim 11 , wherein the inline flow sensor includes:

a conduit defining a flow passageway;

a ball member movable within said flow passageway;

a spring for urging said ball member in a direction opposite a direction of fluid flow through said conduit; and

an optical sensor for determining a position of said ball member within said

conduit.

15 . The method of claim 14 , wherein determining the absolute flow rate of the fluid comprises comparing known absolute flow rates for ball member positions within said flow passageway.

16 . The method of claim 15 , wherein comparing known absolute flow rates for ball member positions within said flow passageway comprises looking up the known absolute flow rates in a look up table.

17 . The method of claim 11 , further comprising:

independently calculating an absolute flow rate of the fluid as it exits a primary fluid source of the fluid delivery system; and

comparing the independently calculated absolute flow rate to the absolute flow rate determined using the inline sensor.

18 . The method of claim 17 , further comprising using differences between said independently calculated absolute flow rate of the fluid as it exits the primary fluid source and said absolute flow rate determined using the sensed relative flow rate to identify one or more of:

fluid delivered from a secondary fluid source of the fluid delivery system; and

a quantity of gas leaving the fluid delivery system.

19 . The method of claim 17 , further comprising:

placing a flexible bag containing the liquid to be infused within a rigid container of known total volume and containing an inflatable bladder, said inflatable bladder fluidically coupled to a pneumatic system for inflating said bladder;

using one or both of volume measurements in said bladder over time and pressure measurements of said bladder over time to calculate said independently calculated absolute flow rate.

20 . The method of claim 19 , further comprising using differences between said independently calculated absolute flow rate of the fluid as it exits the primary fluid source and said absolute flow rate determined using the sensed relative flow rate to identify one or more of:

fluid delivered from a secondary fluid source of the fluid delivery system;

a quantity of gas leaving the fluid delivery system; and

a leak in the pneumatic system.

21 . The method of claim 19 , wherein said independently calculated absolute flow rate is calculated using a rate of pressure decay of a volume of gas in the inflatable bladder.