Optical flow sensor

An optical flow sensor is provided, including a heater configured to heat an aliquot of fluid in an adjacent fluid-delivery channel and a sensor disposed adjacent to the fluid-delivery channel downstream from the heater. The sensor is configured to illuminate fluid in the fluid-delivery channel, to collect reflected light from the illuminated fluid, and to determine when the heated aliquot passes the sensor based upon an amount of the reflected light. A method for determining a flow rate of a fluid is also provided. The method includes heating an aliquot of the fluid at a first position of a fluid-delivery channel, illuminating fluid in the fluid-delivery channel at a second position downstream from the first position, measuring an amount of light reflected from the illuminated fluid to determine a change in the amount corresponding to the heated aliquot passing the second position, and calculating the flow rate of the fluid based upon a distance between the first position and the second position and a time between the heating the aliquot and the heated aliquot passing the second position.

CROSS-REFERENCE TO RELATED APPLICATION

Not applicable.

Not applicable.

FIELD

Embodiments of the present invention generally relate to flow sensors and, in particular, relate to optical flow sensors.

BACKGROUND

Intravenous (“IV”) fluid delivery systems are used to deliver fluids (e.g., medicines, transfusions, etc.) to patients at controlled rates. To accurately control IV fluid delivery, an open-loop control system may be used. An open-loop control system includes a processor that varies the speed of a relatively accurate fluid pump used to infuse a medicinal fluid into a patient based upon a predefined algorithm and as a function of various parameters, such as temperature, fluid type, and desired flow rate. These open-loop, processor-controlled pumping systems are generally expensive and complex. Moreover, compensation for variations in pump accuracy must be employed in such systems to achieve an acceptable level of accuracy. The rate of fluid delivery is also affected by the precision of disposable components used in the fluid path that conveys the fluid to the patient. Open-loop control systems are not capable of compensating for variations in the internal diameter and material hardness of fluid lines and pumping components, which may change over time as the components are repeatedly stressed. As a result, higher cost disposable components with tight tolerances must be used in such systems to avoid a loss of accuracy.

SUMMARY

Embodiments described herein address the foregoing problems by providing a low-cost, low-complexity system for delivery of medicinal fluids utilizing a closed-loop control system that provides high accuracy in the rate of fluid delivery to a patient. The closed loop system measures fluid flow rate using a low cost flow sensor and adjusts an inexpensive fluid delivery pump based upon the measured flow rate to achieve a desired flow rate. An inexpensive pump can be used in such a system, as the accuracy of the pump is not important to achieving a desired delivery rate. Similarly, the tolerance specifications of the disposable components used in the system can be greatly relaxed, as the closed-loop system can easily compensate for a lack of precision in these components. As most of the variables that are considered in algorithms employed for open-loop control can be ignored in a closed-loop controlled infusion system, the process control logic used in a closed-loop infusion system is relatively simple and easy to implement.

Certain embodiments provide an optical flow sensor. The sensor comprises a heater configured to heat an aliquot of fluid in an adjacent fluid-delivery channel, and a sensor disposed adjacent to the fluid-delivery channel downstream from the heater. The sensor is configured to illuminate fluid in the fluid-delivery channel, to collect reflected light from the illuminated fluid, and to determine when the heated aliquot passes the sensor based upon an amount of the reflected light.

Certain embodiments provide a method for determining a flow rate of a fluid. The method comprises heating an aliquot of the fluid at a first position of a fluid-delivery channel, illuminating fluid in the fluid-delivery channel at a second position downstream from the first position, measuring an amount of light reflected from the illuminated fluid to determine a change in the amount corresponding to the heated aliquot passing the second position, and calculating the flow rate of the fluid based upon a distance between the first position and the second position and a time between the heating the aliquot and the heated aliquot passing the second position.

Certain embodiments provide a medicinal fluid administering system. The system comprises a fluid delivery system for administering a fluid to a patient, and an optical flow sensor for measuring a rate of the fluid administered to the patient. The optical flow sensor comprises a laser configured to heat an aliquot of the fluid in an adjacent fluid-delivery channel, and a sensor disposed adjacent to the fluid-delivery channel downstream from the laser. The sensor is configured to illuminate the fluid in the fluid-delivery channel, to collect reflected light from the illuminated fluid, and to determine when the heated aliquot passes the sensor based upon an amount of the reflected light.

It is to be understood that both the foregoing summary and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the embodiments as claimed.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth to provide a full understanding of the disclosed and claimed embodiments. It will be apparent, however, to one ordinarily skilled in the art that the embodiments may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to avoid unnecessarily obscuring the disclosure.

Various approaches to fluid delivery employ different methods for measuring fluid flow rates. For example, one method, referred to as a thermal “time of flight” method, involves measuring the motion of a small heated volume of fluid down a flow path to determine a flow rate of the fluid. An aliquot of fluid is heated at a first position in the flow path, and at a predetermined second position downstream from the first, the passage of the heated aliquot of fluid is detected by a sensor. The sensor may measure different parameters of the fluid in the flow path to determine when the heated portion passes the sensor. For example, the sensor may shine a light through a fluid-delivery channel through which the fluid flows to determine when the heated aliquot passes. Because the temperature of a fluid changes the index of refraction thereof, the amount of light entering a photodetector will change as a heated fluid passes. For fluids whose index of refraction is a function of temperature, a measured change in index of refraction at the sensor indicates the passage of the heated aliquot of fluid. Such an approach may not work, however, with less-than-transparent fluids (e.g., translucent and opaque fluids such as lipids, packed cells, total parenteral nutrition (“TPN”), blood, breast milk, etc.).

According to certain embodiments, an optical flow sensor provides accurate measurement of flow rate for any fluid, whether opaque or transparent, at a relatively low cost. A block diagram illustrating an exemplary optical flow sensor according to certain embodiments is illustrated inFIG. 1. Optical flow sensor100includes a heater101configured to heat an aliquot102of fluid103in a fluid-delivery channel104adjacent to heater101. According to one exemplary embodiment, heater101may be a laser. In accordance with certain other embodiments, heater101may be any one of a number of other heating devices, including electrical heaters, resistors, etc. Optical flow sensor100further includes a sensor105disposed adjacent to fluid-delivery channel104downstream a predetermined distance d from heater101. Sensor105is configured to illuminate fluid103in fluid-delivery channel104. According to certain embodiments, sensor105may illuminate fluid103with an LED106. In accordance with certain other embodiments, sensor105may illuminate fluid103with any one of a number of other light sources, including, for example, a laser, an incandescent filament, a fluorescent bulb, etc. Moreover, sensor105may illuminate fluid103with radiation of any wavelength, including visible light, infrared, ultraviolet, etc.

Sensor105is further configured to collect reflected light from the illuminated fluid103, and to determine when heated aliquot102passes sensor105based upon an amount of the reflected light. In this regard, sensor105may include a photodetector107optically coupled to fluid-delivery channel104with a polished fiber, a lens, a prism, or the like. In the present exemplary embodiment illustrated inFIG. 1, sensor105includes a first highly polished fiber108that optically couples LED106to fluid-delivery channel104, and a second highly polished fiber109that optically couples photodetector107to fluid-delivery channel104. According to certain embodiments, photodetector107may be an optical photodetector. In accordance with certain other embodiments, photodetector107may be any one of a number of other light or radiation sensors, including a photoresistor, a photovoltaic cell, a photodiode, etc.

As can be seen with reference toFIG. 1, both LED106and photodetector107are disposed on the same side of fluid-delivery channel104. This arrangement allows optical flow sensor100to determine the flow rate of fluids not previously suitable for time-of-flight rate sensing, such as opaque fluids, non-homogenous fluids, non-Newtonian fluids and the like.

FIG. 2is a block diagram illustrating an optical flow sensor200according to another exemplary embodiment. Optical flow sensor200includes a heater201configured to heat an aliquot202of fluid203in a fluid-delivery channel204adjacent to heater201. Optical flow sensor200further includes a sensor205disposed adjacent to fluid-delivery channel204downstream a predetermined distance d from heater201. Sensor205is configured to illuminate fluid203in fluid-delivery channel204with an LED206optically coupled to fluid-delivery channel204with a lens208. Sensor205is further configured to collect reflected light from the illuminated fluid203, and to determine when heated aliquot202passes sensor205based upon an amount of the reflected light. In this regard, sensor205includes a photodetector207optically coupled to fluid-delivery channel204with a lens209.

As can be seen with reference toFIG. 2, both LED206and photodetector207are disposed on the same side of fluid-delivery channel204. This arrangement allows optical flow sensor200to determine the flow rate of fluids not previously suitable for time-of-flight rate sensing, such as opaque fluids, non-homogenous fluids, non-Newtonian fluids and the like.

FIG. 3illustrates a medicinal fluid administering system in accordance with one exemplary embodiment. Medicinal fluid administering system300includes a fluid delivery system for administering a fluid to a patient and optical flow sensor200, which is configured to measure a rate at which the fluid is administered to the patient. The fluid delivery system includes a fluid reservoir301, from which fluid313is pumped by a pump302through a fluid delivery path303ato the optical flow sensor310and on (via delivery path303b) to the patient. The optical flow sensor310includes a heater311configured to heat an aliquot312of fluid313in a fluid-delivery channel314adjacent to heater311. Optical flow sensor310further includes a sensor315disposed adjacent to fluid-delivery channel314downstream a predetermined distance d from heater311. Sensor315is configured to illuminate fluid313in fluid-delivery channel314with an LED316optically coupled to fluid-delivery channel314with a lens. Sensor315is further configured to collect reflected light from the illuminated fluid313, and to determine when heated aliquot312passes sensor315based upon an amount of the reflected light. In this regard, sensor315includes a photodetector317optically coupled to fluid-delivery channel314with a lens.

FIG. 4illustrates a medicinal fluid administering system utilizing a closed-loop control system in accordance with one exemplary embodiment. Medicinal fluid administering system400includes a fluid delivery system for administering a fluid to a patient and optical flow sensor200, which is configured to measure a rate at which the fluid is administered to the patient. The fluid delivery system includes a fluid reservoir401, from which fluid413is pumped by a pump402through a fluid delivery path403ato the optical flow sensor410and on (via delivery path403b) to the patient. The optical flow sensor410includes a heater411configured to heat an aliquot412of fluid413in a fluid-delivery channel414adjacent to heater411. Optical flow sensor410further includes a sensor415disposed adjacent to fluid-delivery channel414downstream a predetermined distance d from heater411. Sensor415is configured to illuminate fluid413in fluid-delivery channel414with an LED416optically coupled to fluid-delivery channel414with a lens. Sensor415is further configured to collect reflected light from the illuminated fluid413, and to determine when heated aliquot412passes sensor415based upon an amount of the reflected light. In this regard, sensor415includes a photodetector417optically coupled to fluid-delivery channel414with a lens. System400further includes a controller418configured to calculate a flow rate of fluid413based by dividing the time between heater411heating aliquot412and heated aliquot412being detected by sensor415. Controller418may be further configured to adjust a pumping rate of pump402based upon a difference between the calculated flow rate and a desired flow rate (e.g., by reducing or increasing the pump speed).

FIG. 5is a flow chart illustrating a method for determining a flow rate of a fluid in accordance with one embodiment of the present invention. The method begins in step501, in which an aliquot of fluid is heated at a first position of a fluid-delivery channel. In step502, fluid in the fluid-delivery channel is illuminated at a second position, downstream from the first position. The amount of light reflected from the illuminated fluid is measured in step503to determine a change in the amount corresponding to the heated aliquot passing the second position. In step504, the flow rate of the fluid is calculated based upon a distance between the first position and the second position, and upon a time between heating the aliquot and the heated aliquot passing the second position.

FIG. 6is a block diagram that illustrates a computer system600upon which certain embodiments may be implemented. Computer system600includes a bus602or other communication mechanism for communicating information, and a processor604coupled with bus602for processing information. Computer system600also includes a memory606, such as a random access memory (“RAM”) or other dynamic storage device, coupled to bus602for storing information and instructions to be executed by processor604. Memory606may also be used for storing temporary variables or other intermediate information during execution of instructions by processor604. Computer system600further includes a data storage device610, such as a magnetic disk or optical disk, coupled to bus602for storing information and instructions.

Computer system600may be coupled via I/O module608to a display device (not illustrated), such as a cathode ray tube (“CRT”) or liquid crystal display (“LCD”) for displaying information to a computer user. An input device, such as, for example, a keyboard or a mouse may also be coupled to computer system600via I/O module608for communicating information and command selections to processor604.

According to certain embodiments, determining a flow rate of a fluid is performed by a computer system600in response to processor604executing one or more sequences of one or more instructions contained in memory606. Such instructions may be read into memory606from another machine-readable medium, such as data storage device610. Execution of the sequences of instructions contained in main memory606causes processor604to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in memory606. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement various embodiments. Thus, embodiments are not limited to any specific combination of hardware circuitry and software.

The term “machine-readable medium” as used herein refers to any medium that participates in providing instructions to processor604for execution. Such a medium may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as data storage device610. Volatile media include dynamic memory, such as memory606. Transmission media include coaxial cables, copper wire, and fiber optics, including the wires that comprise bus602. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency and infrared data communications. Common forms of machine-readable media include, for example, floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.

The foregoing description is provided to enable any person skilled in the art to practice the various embodiments described herein. While the foregoing embodiments have been particularly described with reference to the various figures and embodiments, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the invention.

There may be many other ways to implement the invention. Various functions and elements described herein may be partitioned differently from those shown without departing from the spirit and scope of the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made to the invention, by one having ordinary skill in the art, without departing from the spirit and scope of the invention.

A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the invention, and are not referred to in connection with the interpretation of the description of the invention. All structural and functional equivalents to the elements of the various embodiments of the invention described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the invention. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.