WO2012095827A1

WO2012095827A1 - Methods, apparatus and systems for metering fluid flow

Info

Publication number: WO2012095827A1
Application number: PCT/IB2012/050189
Authority: WO
Inventors: Shachar Rotem; Boaz Eitan
Original assignee: Q-Core Medical Ltd.
Priority date: 2011-01-16
Filing date: 2012-01-16
Publication date: 2012-07-19

Abstract

Disclosed is a fluid flow meter for measuring fluid flowing through a conduit associated with a medical device which may include: an inducer to selectively and contactlessly alter an ion distribution within a volume of the fluid in proximity of the inducer, wherein the altering may include exposure of the volume to an electrical field, a sensor located at a known distance downstream from the inducer to sense a physical parameter associated with the ion distribution induced by the inducer, and a controller functionally associated with the inducer and the sensor, to estimate a fluid flow rate based on an output of the sensor.

Description

PATENT APPLICATION

FOR:

Methods, Apparatus and Systems for Metering Fluid Flow

Inventors: Shachar Rotem; Dr. Boaz Eitan

FIELD OF THE INVENTION

[001] The present invention relates generally to the field of fluid flow metering and control in medical devices. More specifically, the present invention relates to methods, apparatus and systems for performing fluid flow metering.

BACKGROUND

[002] Medical devices operate for therapeutic and/or diagnostic uses. Some exemplary medical devices may be: blood pressure monitors which may monitor a patient's blood pressure and heart rate, electrical thermometers which may measure a patient's body temperature and many more.

[003] Some medical devices may administer fluid to a patient via a conduit such as a flexible tube. Some medical devices may monitor fluid flowing through its system and connected to one or more of a patient's bodily fluids. For example a peristaltic pumps which may be used to infuse medicines into a vein. In another example, a dialysis machine may pass a patient's blood through the machine to filter and get rid of toxins and excess fluids.

[004] Some medical devices administering fluid or monitoring fluid may want to control the rate at which the fluid is flowing within the system. In some medical devices a flow rate may be achieved by carrying out preliminary tests on the medical device to correlate an expected flow rate to secondary features of the medical device such as motor rate and more. [005] A medical device may be used in a hospital, doctor or nurse's office or other medical treatment centers. Medical devices may also be used at patient's homes or personal environments.

SUMMARY OF THE INVENTION

[006] The present invention includes methods, apparatus and systems for metering fluid flow and controlling fluid flow.

[007] According to some embodiments of the present invention, there may be provided a fluid flow metering assembly including: (1 ) a fluid conduit or fluid tube (hereinafter "conduit") through which fluid may flow; (2) an inducer adapted to modify a characteristic of a volume of fluid flowing through the conduit in proximity with the inducer, and (3) a fluid characteristic sensor positioned downstream from the inducer in a predetermined/known distance from the inducer and adapted to sense a characteristic of fluid passing through the conduit in proximity with the sensor.

[008] According to further embodiments, there may be provided a controller adapted to intermittently activate the inducer for a period of time (e.g. duty cycle) sufficient to measurably modify a characteristic of a volume of fluid in proximity with the inducer. Concurrently or shortly after activating the inducer the controller may monitor output from the sensor so as to determine when the volume of fluid whose characteristics have been modified by the inducer reaches a portion of the conduit in proximity with the sensor. The controller may utilize the output from the sensor to calculate, determine or detect fluid flow conditions such as: flow rate, conduit occlusion, fluid free flow, air bubbles within the conduit, disturbances and/or back flow of fluid. According to some embodiments, the controller may also include or receive additional information which may be used to calculate, determine or detect fluid flow condition such as diffusion information, expected received signals at a sensor, an expected flow rate and more.

[009] According to some embodiments, the inducer may also function as a sensor.

[0010] According to some embodiments, the controller may calculate or determine a flow rate regardless of flow pressure changes for example, stemming from changes/fluctuations in a fluid destination connected to the conduit.

[001 1 ] According to some embodiments, the inducer may take the form of an electric field source. The modified fluid characteristic may be a localized ion density or concentration of the fluid volume. The sensor may take the form of a capacitance or electric field sensor.

[0012] According to some embodiments the modified characteristic of fluid passing through the conduit may be considered a characteristic that does not medically affect the fluid flowing within the conduit. For example, the modified or changed characteristic may not affect composition of a drug administered through the conduit or may not substantially change the temperature of the fluid. The modified or changed characteristic may not change the chemical characteristic(s) of the fluid

[0013] According to further embodiments, the sensor may relay a feedback or control data to a medical device regarding the fluid flow conditions or parameters, to cause the medical device to adjust its operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: [0015] Figs. 1A-1 C schematically depict a side view of an exemplary conduit with saline flowing within it in accordance with some embodiments of the invention;

[0016] Fig. 2 is a functional block diagram of an exemplary fluid flow metering system and assembly according to embodiments of the present invention;

[0017] Figs. 3A-3I are exemplary inducers usable as suitable inducers depicted relative to a cross section of a fluid conduit in according to embodiments of the present invention;

[0018] Figs. 4A-4F are exemplary sensors usable as suitable inducers depicted relative to a cross section of a fluid conduit in according to embodiments of the present invention;

[0019] Figs. 4G-4H are perspective views of an exemplary flow metering assembly according to some embodiments of the invention;

[0020] Figs. 5A-5B are side views of exemplary conduits according to some embodiments of the invention;

[0021 ] Fig. 5C is a block level exemplary conduit assembly system according to some embodiments of the invention;

[0022] Figs. 5D-5E are a cross section of a conduit having a variable cross section in accordance with embodiments of the invention;

[0023] Figs. 5F-5H are a cross section of a conduit including internal channels according to some embodiments of the invention;

[0024] Fig. 6A is a functional block diagram of an exemplary controller and ancillary circuitry according to some embodiments of the invention;

[0025] Fig. 6B is a circuit diagram of an exemplary electrical circuitry which may be used with either a sensor or an inducer in accordance with some embodiments of the invention;

[0026] Figs. 7A-7B are exemplary graphs showing signals associated with some embodiments of the invention; [0027] Fig. 8 is a functional block diagram of an exemplary medical device system and assembly in accordance with some embodiments of the invention including a flow metering feedback;

[0028] Fig. 9 is a functional block diagram of an exemplary fluid flow metering system and assembly with multiple sensors, in accordance with some embodiments of the invention.

[0029] Fig. 10 is a flowchart including the exemplary steps which may be performed by the exemplary controller shown in Fig. 6A in accordance with some embodiments of the invention;

[0030] Fig. 1 1 is a flowchart including the exemplary steps which may be performed by the exemplary flow metering controller shown in Fig. 8 in accordance with some embodiments of the invention.

[0031 ] Fig. 12 is a flowchart including the exemplary steps which may be performed by the exemplary medical device controller shown in Fig. 8 in accordance with some embodiments of the invention.

[0032] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION

[0033] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.

[0034] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing", "computing", "calculating", "determining", or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.

[0035] According to some embodiments, a fluid flow meter for measuring fluid flowing through a conduit associated with a medical device, may include: an inducer to selectively and contactlessly alter an ion distribution within a volume of the fluid in proximity of the inducer, wherein the altering may include exposure of the volume to an electrical field, a sensor located at a known distance downstream from the inducer to sense a physical parameter associated with the ion distribution induced by the inducer, and a controller functionally associated with the inducer and the sensor, to estimate a fluid flow rate based on an output of the sensor.

[0036] According to some embodiments, the physical parameter may be a capacitance, and the sensed capacitance of the volume may be associated with a second ion distribution resulting from a first ion distribution induced by the inducer and passively altered along a conduit path between the inducer and the sensor.

[0037] According to some embodiments, the controller may estimate a fluid flow rate based on: an initiation time of the first ion distribution, a detection time of a unique point within the second ion distribution and the known distance and a cross section area of the conduit.

[0038] According to some embodiments, the controller may estimate a fluid flow rate based on two or more of the initiation times and two or more of the detection times to improve accuracy of the estimation of the fluid flow rate.

[0039] According to some embodiments, the controller may receive a target flow rate.

[0040] According to some embodiments, the inducer may modulate an ion distribution in the form of a pattern.

[0041 ] According to some embodiments, the controller may identify one or more fluid flow conditions (such as: an occlusion, free flow, presence of air bubbles and/or back flow) based on an output of the sensor.

[0042] According to some embodiments, a medical device system associated with a fluid meter assembly including a conduit, may include: a medical device assembly which may administer a treatment to a patient; and a first controller functionally associated with the medical device assembly which may receive an output indicative of an achieved flow rate from the fluid meter assembly.

[0043] According to some embodiments, a second controller may be configured to estimate a fluid flow rate based on an output of a contactless sensor.

[0044] According to some embodiments, the second controller may be embedded within the first controller.

[0045] According to some embodiments, the medical device may administer fluid through the conduit at a target flow rate, and the first controller may compensate for deviations from the target flow rate using the output indicative of an achieved flow rate. [0046] According to some embodiments, the output indicative of an achieved flow rate may include fluid flow condition information.

[0047] According to some embodiments, the fluid flow condition may be: an occlusion, free flow, presence of air bubbles and/or back flow.

[0048] According to some embodiments, the medical device may administer fluid through the conduit at a target flow rate, and the first controller may trigger an appropriate alarm to the fluid flow condition information.

[0049] According to some embodiments, a method of metering fluid flowing within a conduit associated with a medical device, may include: selectively inducing an electrical field at a predetermined segment of the conduit, contactlessly altering a localized ion distribution within a volume of the fluid, contactlessly sensing a localized ion distribution alteration downstream from the predetermined area of the conduit, and estimating an actual fluid flow rate of the fluid flowing within the conduit.

[0050] According to some embodiments, the method may further include generating an error signal indicative of a difference between the estimated actual flow rate and a target flow rate.

[0051 ] According to some embodiments, the method may further include using the error signal to compensate for the difference between the estimated actual and the target flow rates.

[0052] According to some embodiments, the method may further include identifying at least one fluid flow condition of the fluid within the conduit such as: an occlusion, free flow, presence of air bubbles and/or back flow.

[0053] According to some embodiments, the method may further include triggering an alarm in response to the fluid flow condition. [0054] According to some embodiments, accurately monitoring flow of fluid and associated parameters within a system associated with a medical device may be considered advantageous. Some medical devices, such as pumps, heart and lung machines, dialysis machines and more may administer drugs or treatments to a patient and accurate monitoring of the amount of fluid being administered or passing through the system may be crucial to the medical treatment of a patient. Thus, accurate detection of fluid flow conditions may be advantageous or, at times, crucial, for the safe functioning of a medical device.

[0055] According to some embodiments, some medical devices may operate in a wide range of treatments and thus a wide range of flow rates may be applicable in a given medical device. Thus an accurate flow metering system or apparatus operable at a wide range of flow rates may be desirable, or a flow metering system designed for predefined range of flow rates which may be selectively coupled to a medical device based on the desired or expected flow rate.

[0056] According to some embodiments, feedback of information or data associated with accurate fluid flow metering may enable replacing or substituting at least some of the complex mechanical systems within a medical device, designed to assist in producing accurate flow, with mechanical, or electronic circuits or systems or a combination of the two. These circuits and systems may be considered easier to design and may produce more accurate flow rates.

[0057] According to some embodiments, medical treatments may include saline within the treatment- for example, mixed with medication and administered intravenously. Saline is an ionic fluid typically comprised of water and about 0.9% Sodium Chloride (NaCI). Turning now to Figs. 1A-1 C, depicted is a conduit such as conduit 101 , in which Saline is flowing, in accordance with some embodiments. Fig. 1A schematically depicts the conduit 101 in which Saline is flowing in its natural or steady state, the ionic concentration in the saline solvent/ solution may be substantially homogenous. Turning now to Fig. 1 B, an exemplary electrical field is applied across the flow at point or area approximate the flow such as points 102 and 104, the electrical field may propel ion motion and cause a local uneven ion distribution within the saline solvent.

[0058] According to some embodiments, the exposure to an electrical field may cause ions with a positive charge to move in one direction and the ions with a negative charge to move in a substantially opposite direction. Fig. 1 C depicts the conduit 101 after the electrical field is no longer applied. The ion distribution will travel and can be detected downstream, although diffusion may cause the distribution to change or fade over time (not shown here). Furthermore, it is understood that the electrical field may cause only a portion of the ions to reach the conduits edges - depending on the force of the electrical field. While this example depicts saline, it is understood that it is exemplary and can be substituted with a different ionized fluid such as saline combined with a drug, human bodily fluids and more.

[0059] Thus, in accordance with some embodiments, an inducer within proximity to a conduit can induce a change in a characteristic of a fluid flowing within a conduit, which can be subsequently detected downstream by a fluid characteristic sensor. Induction of the characteristic may be selective, preplanned and/or controlled.

[0060] Turning now to Fig. 2, depicted is a functional block diagram of an exemplary fluid flow metering system and assembly such as flow metering assembly 200, in accordance with some embodiments of the invention. Flow metering assembly 200 may include an inducer such as inducer 202 configured to induce or stimulate a change in a characteristic of a volume of fluid in proximity to inducer 202 flowing within a conduit such as conduit 204. Conduit 204 may be configured to allow or enable fluid flow to pass through it, for example, from a fluid source such as fluid source 206 to a fluid destination such as fluid destination 208. Fluid source 206 and fluid destination 208 may be external to the flow metering assembly 200 and are depicted for clarity. At a different point on or near the conduit 204 a sensor such as fluid characteristic sensor 210 may be configured to detect a change in a fluid flow characteristic. A controller such as controller 212 may be configured to control inducer 202 and fluid characteristic sensor 210 as well as receive information from fluid characteristic sensor 210 to determine or calculate a fluid flow condition.

[0061 ] According to some embodiments, inducer 202 may be configured so that it enables sensing a change in a fluid flow characteristic as well as inducing a change in a fluid flow characteristic.

[0062] According to some embodiments, inducer 202 may alter the characteristic of a volume of fluid contactlessly. Contactless alteration of a characteristic may include an alteration of the ion distribution without changing chemical parameters of the fluid. Exemplary processes that may include change of chemical parameters include: reduction, oxidation, adding additives and more. Contactless alteration may be achieved by using contactless sensors and/or inducers such as: isolated inducers and sensors and configuring elements not isolated from the fluid so that no chemical reaction such as electrolysis may occur, for example, if non-isolated elements have a voltage potential substantially identical to the fluid.

[0063] Turning to Figs. 3A-3I depicted are exemplary inducers such as inducers 302-321 usable as suitable inducers in flow metering assembly 200 of Fig. 2 depicted relative to a cross section of a fluid conduit in accordance with some embodiments of the invention. Inducers 302-321 may include inducer elements such as substantially flat plate electrodes such as electrodes 322-329, mesh electrodes such as electrodes 330-334, cylindrical electrodes such as electrodes 336-341 and more. Inducers 302-321 may include contacts such as contacts 342- 374 to enable controller 212 of Fig. 2 to activate the inducers. Inducers 304, 306 and 321 may further include an additional electrodes such as electrode plates 331 and 333 and cylindrical electrode 338 configured to be placed within the conduit causing a smaller or reduced gap between the electrode plates (for example, the distance of electrode plate 331 to electrode plate 324 or 325 may be smaller than the difference between electrode plate 324 and 325) which may enhance or strengthen the electrical field, also depending on the supplied source connected to the electrodes. Although a single internal electrode is depicted in inducers 304, 306 and 321 it is to be understood that multiple plates may be included. Although contacts 362 364 and 368 cross one or more electrodes it is to be understood that they may not be electronically connected to the crossed over electrodes (for example, contact 364 may be electronically connected to electrode 343 but not electrodes 342 and 344).

[0064] In accordance with some embodiments, electrode plates 331 and 333 may be ground or earthing plates. Inducer elements such as electrodes 322-341 may be configured to induce an electrical field across a cross section of a conduit causing positively charged ions of the fluid within the conduit to move in the direction of one of the electrodes and negatively charged ions to move in the direction of the other electrode (depending on the direction of the induced electrical field). For example, electrode 322 may be connected via connecter 342 to a positive side of a power source and electrode 323 may be connected via connector 343 to a negative or ground side of the power source. In another example, electrode 324 may be connected via connecter 344 to a positive side of a power source and electrode 325 may be connected via connector 345 to a negative side of the power source and electrode 331 may be connected via connector 372 to a ground connection. In another example, electrode 324 may be connected via connecter 344 to a negative side of a power source and electrode 325 may be connected via connector 345 to a grounded side of a power source and electrode 331 may be connected via connector 372 to a negative side of the power source. [0065] In accordance with some embodiments, mesh electrodes 330-334 may be stainless steel covered in gold and isolation. The isolation is discussed in more detail below.

[0066] In accordance with some embodiments, mesh electrodes 330-334 may be characterized by relatively strong electrical fields and strong surface contact with the fluid.

[0067] In accordance with some embodiments, inducer 202 of Fig. 2 may be isolated from the fluid. One example for achieving isolation is by coating the inducer elements with high dialectical strength. Exemplary coating materials include: 1 um to 3um of: AI3O2, Zi0₂, Ti0₂ Si0₂, Si3N₄, Nb₂05, Ta₂Os_, and more or 1 um to 25um of organic coatings like Parylene or Teflon (PTFE).

[0068] In accordance with some embodiments, the coating may be configured to: provide substantial protections against anodic and cathodic reactions, substantially preventing electrolysis of the fluid within conduit 204 of Fig. 2. Furthermore, the coating may be configured so that it has sufficient adhesion to the inducer elements surface, minimal thickness to allow maximal effect of inducer 202 of Fig. 2 on fluid characteristic, a predefined dielectric strength to prevent electrical breakdown (for example 20V per coating thickness), a strong micro structure and minimal sensitivity to pitting problems, minimal surface energy to prevent accumulation of air bubbles on the inducer elements surface and further configured to undergo Ethylene Oxide (ETO) sterilization

[0069] In accordance with some embodiments, the coating may include galvanic coating coupled with another coating, as erosion within the fluid stemming from the contact with the galvanic coating may be undesirable for medical reasons. However, for inducer elements such as electrode plates 331 and 333 positioned within the conduit having a ground potential, the coating may be strictly galvanic as erosion may not be a concern when no substantial electrical current is being produced. [0070] In accordance with some embodiments, inducer 202 of Fig. 2 may be placed in proximity, adjacent, on or within conduit 204 of Fig. 2. The exact location and placement of inducer 202 of Fig. 2 may be configured to achieve: minimal disturbance to fluid flow within conduit 204 of Fig. 2, minimal effect on flow turbulence, maximal effectively of inducer 202 of Fig. 2 (for example, nominal electric or magnetic field), dimensional stability and more.

[0071 ] Turning to Fig. 4A-4F depicted are exemplary fluid characteristic sensors usable as suitable sensors in flow metering assembly 200 of Fig. 2 in accordance with some embodiments of the invention, depicted relative to a cross section of a fluid conduit. The fluid characteristic sensors such as sensors 402-420 may include sensor elements such as substantially flat plate electrodes such as electrodes 422-429; mesh electrodes such as electrodes 430-434 or cylindrical electrodes such as electrodes 438-439 or other. Sensors 402-420 may include contacts such as contacts 442- 459 to enable controller 212 of Fig. 2 to activate the sensor(s) 402-420 or receive information or signals from the sensor(s) 402-420. Although contact 459 is depicted as crossing over electrodes 438 it may not be electronically connected to the electrode 438.

[0072] Turning now to Fig. 4G, depicted is a perspective view 4501 of a conduit such as conduit 451 1 in accordance with some embodiments of the invention suitable with any of the sensors and/or inducers described in Fig. 3A and Fig. 4A. Conduit 451 1 may further include an inducer including electrodes such as inducer electrodes 4521 and 4541 and a sensor including electrodes such as sensor electrodes 4561 and 4581 . Sensor electrodes 4561 and 4581 may be identical or of a different plate area than inducer electrodes 4521 and 4541 . Turning now to Fig. 4H, depicted is a perspective view of a conduit such as conduit 4502 in accordance with some embodiments of the invention suitable with the sensors and/or inducers described in Fig. 3H and Fig. 4F. Conduit 4502 may include an external surface such as surface 4512 and an internal surface such as surface 4510. Conduit 4502 may further include an inducer including electrodes such as inducer electrodes 4522 and 4542 and a sensor including electrodes such as sensor electrodes 4562 and an additional internal electrode not viewable in this view. Sensor electrodes 4562 may be identical or of a different cylinder height than inducer electrodes 4562.

[0073] According to some embodiments, controller 212 of Fig. 2 may be configured to receive information from a medical device system such as expected flow rate, selected medical treatment and more. Controller 212, may control timing of inducer actuating signals, may control timing and activation of sensing circuits, may store conduit 204 cross section area and store the distance between inducer 202 and fluid characteristic sensor 210. Controller 212 may calculate the fluid flow rate based on the above received and controlled parameters and more. Controller 212 may detect or calculate flow deviations from acceptable ranges (such as occlusion, free flow, air bubbles etc.).

[0074] Turning now to Fig. 5A-5B, depicted are side views of exemplary conduits such as conduit configurations 500 and 501 usable as suitable conduits in flow metering assembly 200 of Fig. 2 in accordance with some embodiments of the invention. It is to be understood that conduit 5041 -5044 may be substantially interchangeable with conduit 204 and fluid sources 5061 -5064 may be interchangeable with fluid source 206 and fluid destination 5081- 5084 may be interchangeable with fluid destination 208.

[0075] According to some embodiments, conduit 5041 may be a conduit designed or configured to work at substantially low flow rates, for example, 0.1 -0.6ml fluid per hour, for use in systems where a high accuracy may be required at these rates while at higher rates less accuracy may be required causing a metering assembly to be redundant.

[0076] According to some embodiments, a conduit plurality such as dedicated conduits 5042-5044 may each be designed or configured to work at different flow rate ranges, for example, 0.1 -0.6 ml fluid per hour (ml/h), 0.6-4.0 ml/h, 4.0-25.1 ml/h, 25.1-158.5ml/h and 158.5-1000ml/h. Dedicated conduits may each be of a different cross section. A dedicated conduit 5042, 5043 or 5044 may be inserted, applied to a metering assembly based on the predefined expected flow rate or flow rate range. Furthermore, each conduit may have a dedicated flow metering assembly where the dimension of the electrodes associated with the sensor and/or inducer may vary between conduits and depend on the expected flow rate.

[0077] Turning now to Fig. 5C, depicted is a side view of an exemplary conduit assembly system such as conduit assembly system 502 usable as a suitable conduit in flow metering assembly 200 of Fig. 2 in accordance with some embodiments of the invention. It is to be understood that fluid source 5065 may be interchangeable with fluid source 206 and fluid destination 5085 may be interchangeable with fluid destination 208. A conduit assembly such as conduit assembly 504 may be configured to receive fluid from fluid source 5065 and transfer the fluid to fluid destination 5085. Fluid source 5065 and fluid destination 5085 may be external to the conduit assembly, and are depicted for clarity. Conduit assembly 504 may be comprised of a plurality of conduits such as conduits 5045, 5046 and 5047 which may each be designed or configured to work at different flow rate ranges and may each be of a different cross section. A fluid router such as fluid router 507 may be configured to receive fluid from fluid source 5065 and determine which conduit: conduit 5045, 5046 or 5047 to relay or transfer the fluid to. Fluid router may include a switch to determine which conduit to transfer the fluid to based on: a manual decision by a user, an electro-mechanical input based on an associated medical device configuration (expected flow rate, specific treatment and more) or may include a detector to internally route the flow to the appropriate conduit (5045, 5046 or 5047). Although 3 conduits have been depicted it is to be understood that any number of combinations with any range of flow rates (overlapping or not) may be utilized. Furthermore, each conduit 5045, 5046 and 5047 may have a dedicated inducer and/or sensor. Fluid router 507 may be re-usable or configured to be disposable with the plurality of conduits 5045-5047.

[0078] Turning now to Fig. 5D and 5E, depicted is a cross section of a conduit having a variable cross section to support selection of variable flow rates in accordance with some embodiments of the invention. In a first configuration 5100, conduit cross section 5127 may be in an "open" state allowing maximal fluid flow through a cross section of the conduit and flat plate electrodes such as electrodes 5128 and 5129 emit an electrical field on a fluid flowing through the conduit. In a second configuration 5101 , conduit cross section 5127 may be in a "compressed" state allowing less fluid to flow through a cross section of the fluid and thus maintaining an appropriate, suitable and/or detectable speed of the fluid flowing through the cross section at low flow rates. It is also to be understood that electrodes 5128 and 5129 may have a larger effective contact with the conduit and cross section may be reduced and thus the electrical field felt by the fluid within the conduit may be greater, enhancing a localized ion concentration. Transition between configuration 5100 and configuration 5101 may be controlled by a controller associated with electrodes 5128 and 5129 such as controller 212 of Fig. 2, or may be carried out mechanically, manually or electromechanically either automatically or manually by a user.

[0079] According to some embodiments, conduit 204 of Fig. 2 may be configured to improve turbulence disturbances which may improve flow metering assembly 200 of Fig.2 performance or accuracy. Turning now to Fig. 5F depicted is a cross section 5102 of a conduit such as conduit 5227 with reduced turbulence disturbances according to some embodiments. Internal channels within conduit 5227 such as channels 5230-5236 may prevent or lessen turbulence within the conduit. Channels 5230-5236 may be in a substantially horizontal, substantially vertical or any other angle compared to conduit 5227. Channels 5230-5236 may be parallel to each other, arranged in a fan like configuration or otherwise. Conduit 5227 may include two or more channels such as any two of channels 5230-5236 and more. In embodiments utilizing mesh electrodes (such as electrodes 330-334 of Figs. 3E-3G) the electrodes mesh architecture may decrease turbulence disturbances.

[0080] Turning now to Fig. 5G depicted is a top view 5103 of a conduit such as conduit 5301 with reduced turbulence disturbances in accordance with some embodiments of the invention. Internal channels within conduit 5301 such as channels 5302-5306 may prevent or lessen turbulence within the conduit. Channels 5302-5306 may be in a substantially horizontal, substantially vertical or any other angle compared to conduit 5301. Channels 5302-5306 may be parallel to each other, arranged in a fan like configuration or otherwise. Conduit 5301 may include two or more channels such as any two of channels 5302-5306 and more. Channels 5302-5306 may be placed before an inducer, between an inducer and a subsequent sensor or otherwise.

[0081 ] Turning now to Fig. 5H depicted is a cross section of a conduit such as conduit 5600 characterized by reduced turbulence disturbances in accordance with some embodiments of the invention. Conduit 5600 may include an external surface such as surface 5602 and external surface 5603 and internal surfaces of the conduit such as 5604 and 5605. Internal spacers or plates to divide the flow cross section within conduit 5600 such as spacers 5620- 5649 and the additional unmarked channels may prevent or lessen turbulence within the conduit. Spacers 5620-5649 may be in a substantially horizontal, substantially vertical or any other angle compared to conduit 5600 and may be parallel to each other, arranged in a fan like configuration or otherwise. Conduit 5600 may include two or more channels such as any two of spacers 5620-5649 and more. Spacers 5620-5649 may be placed before an inducer, between an inducer and a subsequent sensor or otherwise.

[0082] According to some embodiments, conduit 204 of Fig. 2 may further connect to an additional conduit. Conduit 204 may have a different cross section than the additional conduit but still supply an accurate flow rate measurement for the additional conduit alone, as the flow rate may be proportional to a nominal or requested flow rate and the cross section of a conduit.

[0083] Turning now to Fig. 6A, depicted is a functional block diagram of an exemplary controller, and ancillary circuitry such as controller and ancillary circuitry (CA) 600 in accordance with some embodiments of the invention, usable with the inducers and sensors of Figure series 2 and 3.

[0084] According to some embodiments, CA 600 may include a controller such as controller 602. It is to be understood that controller 602 may be substantially interchangeable with controller 212 of Fig. 2. Controller 602 may include a control logic circuitry such as control logic 604. Control logic 604 may be connected to an inducer through actuation driver circuits such as inducer interface circuits 606. Control logic 604 may be connected to one or more sensors via a sensor interface circuits such as sensor interface 608.

[0085] According to some embodiments, information and algorithms associated with such factors may be stored in a flow estimation logic such as flow estimation logic 610. Additional external information such as expected flow rate, system configuration, administered treatment and more may be relayed to the controller via an external interface such as external interface 612. For example, if the flow is configured to be pulsatic to avoid inaccurate readings, control logic 604 may not try to measure flow speed at pointes between pulses.

[0086] According to some embodiments, control logic 604 may utilize the sensed signal received via sensor interface circuits 608 as well as information from flow estimation logic 610 and external interface 612 to calculate a fluid flow rate or detect flow conditions.

[0087] According to some embodiments, control logic 604 may be configured to monitor or detect a breakdown or electrical failure of an inducer and/or sensor which may cause an electrical current to flow through the fluid. Control logic 604 may output this information to a medical device via external interface 612 to enable a medical device to deactivate or trigger an alarm if a breakdown or fault has been detected. In accordance with some embodiments, the control unit may include a galvanic connection with the fluid, controlled in a way to prevent any voltage buildup that may harm a patient connected to the flow meter via a conduit.

[0088] According to some embodiments, in order to calculate a flow rate or detect flow conditions, control logic 604 may await detection of a change or shift or maximal point in a sensed signal indicating arrival of the fluid characteristic at the sensor.

[0089] According to some embodiments, controller 602 may initiate the actuating signal synchronously or asynchronously to the sensed signal. In an asynchronous configuration, the controller may initiate an actuating signal based on a predetermined frequency dependent on system requirements and characteristics as well as expected flow rate received from external interface 612. The controller may initiate sensor sensing at a rate associated with the actuating signal rate. In a synchronous configuration, the controller may initiate an actuating signal once the previous signal was detected at the sensor.

[0090] According to some embodiments, CA 600 may further include a power supply such as power supply 644. Controller 602 may enable power supply 644 to supply power to the metering apparatus such as inducer and sensor(s).

[0091 ] According to some embodiments, controller 602 may be configured to calculate a flow rate. The controller may receive/include information associated with the metering assembly such as: the distance between an inducer and a sensor, the conduit's cross section area, an expected flow rate, the difference in time between initiating the actuating signal and arrival of a detected maximum or shift at the sensor, and secondary information such as additional information stored in the flow estimation logic and determine or calculate a flow rate of fluid within the conduit of a metering apparatus. [0092] According to some embodiments, control logic 604 may control or initiate the actuation signal_configured to activate the inducer. Turning now to Fig. 7A and 7B, depicted are exemplary graphs to describe signals associated with some embodiments of the invention. Graph 701 depicts an exemplary actuation such as a step function. An additional example of an actuation signal may be step function 701 multiplied by a sinus. Additional exemplary actuation signals may include modulated marker patterns/codes whose detection may be resilient to spreading due to diffusion and/or turbulence. In an embodiment in which the inducer is a plate electrode (such elements 328 and 329 depicted in Fig. 3D) configured to change a localized ion density, T_c may indicate a length of time in which the inducer may be activated to "trap" ions at the plate electrodes. At a certain point the actuation signal may be reversed for a length of time indicated by T_mark causing the ions to substantially immediately be released into the flow causing a substantial change in a localized ion concentration. In some configurations such as the plate electrodes it may be preferable that T_mark be substantially shorter than T_c. The "trapping" and "releasing" of the ions within the fluid in proximity to the inducer is depicted in graph 702. It is to be understood in this configuration that the total amount of trapped ions (marked as Area A) may be substantially equal to the amount or density of released ions (marked as Area B). Graph 701 may repeat itself after a sufficient length (indicated by Taxation) of time so that the ions may return to a substantial steady state before initiating the next actuation signal, other configurations are also possible depending also on if the configuration is synchronous or asynchronous.

[0093] According to some embodiments, control logic 602 of Fig. 6A may control, initiate, or enable the sensor to detect a sensed signal. Graph 703 of Fig. 7B depicts an exemplary sensed signal (7032) following an exemplary induced signal (7031 ) associated with some embodiments of the invention which may be substantially identical to the signal of graph 702. Sensed signals 7032 depicts the change in the signal at the sensor compared to the inducer 7031. Various factors such as fading factors, diffusion factors, thermal factors, environmental factors and more may cause the sensed signal to be passively altered from the actuating signal. Thus, the time it took for the fluid flow ion change to reach the sensor may be identified when a maximum or minimum in the function is reached. The difference in times used to calculate a flow rate is indicated by TOF in Fig. 7B. A specific point inside the inducing signal, pattern or code may be designated as the reference for calculating TOF for the pattern, for example the end of T_mark in graph 701 of Fig. 7A, the maximal or minimal value of induced signal 7031 and more.

[0094] Turning now to Fig. 6B, depicted is a circuit diagram of an exemplary electrical circuitry 6000 suitable to be embedded or associated with controller 602 of Fig 6A to be used with either a sensor or an inducer in accordance with some embodiments of the invention. A voltage source such as voltage source 662 may be configured to supply a sinus wave voltage input. An additional voltage source such as voltage source 664 may input a step function. A resistor such as resistor 660 may be utilized to measure a voltage on the resistor via a voltage detector such as voltage detector 666. Contact/Connection Points A1 and B1 may be utilized as an interface to input or output electrical signals associated with a sensor or an inducer. Thus, electrical circuitry 6000 may function as voltage source for an inducer, for example, with voltage source 664 producing a step function similar to graph 701 of Fig. 7A, voltage detector 666 may be turned off or not utilized and A1 and B1 may be connected to inducer elements such as contacts 342 and 343 of Fig. 3A. Electrical circuitry 6000 may further function with a sensor, for example, with voltage source 664 producing a flat function (i.e. 0V); A1 and B1 may be connected to sensor elements such as contacts 442 and 443 of Fig 4A. Voltage detector 666 may be utilized to measure the voltage falling on resistor 660 which may be proportional to the capacitance falling between A1 and B1 (which in this example may be connected to the sensor) and thus may supply a sensed input associated with the ion distribution which may also be proportional or associated with the detected capacitance across the sensor. It is to be understood that the described circuitry is exemplary and that alternative circuitry including RC and RLC circuits can replace the described circuit.

[0095] Turning now to Fig. 8, depicted is a functional block diagram of an exemplary medical device system and assembly such as system 800 in accordance with some embodiments of the invention including a flow metering feedback. It is to be understood that elements 802- 810 may be substantially similar to elements 202-210 of Fig. 2 (accordingly). System 800 further includes a flow metering controller such as flow metering controller 812 understood to include the elements and functionalities as described with regard to Fig. 6A controller 602. Flow metering controller 812 may be configured to connect to and be associated with a medical device such as medical device 814. Medical device 814 may include fluid source 806, a motor such as motor 816, a medical device (MD) controller such as MD controller 818 and additional apparatus to support in the functioning of the medical device. Medical devices 814 may be a pump such as a peristaltic pump, a heart-lung machine, a dialysis machine and more. MD controller 818 and flow metering controller 812 may be combined or embedded within one another or may be separate as depicted in Fig. 8. Flow metering controller 812 may be connected (electronically, wirelessly or otherwise) to allow information from flow metering controller 812 to and from medical device 814 such as a requested flow rate, power control signals and more.

[0096] According to some embodiments, flow metering controller 812 may further relay an assembly feedback or control data associated with information regarding the detected or calculated achieved flow rate or flow conditions to medical device 814. Medical device 814 may adjust its operation based on the feedback. For example, in a pump, an error signal may be indicative of a difference between an estimated actual flow rate and a target flow rate, the pump may correct its motor pace to achieve the target flow rate. In another example, in a pump if free flow is detected then the pump may stop or close flow from the fluid source and initiate an alarm. In a different example, a dialysis machine may amend its motor rate if too many or too little fluid is detected as exiting a patient's body. Thus, a medical device configured with direct flow control may be achieved (for example, where the flow is corrected/calibrated with actual measurements of the fluid flow) and may be advantageous to medical devices with indirect flow control (for example, mechanical systems configured to estimate the actual flow with secondary parameters, or systems configured to create a desired flow rate based on statistical information such as expected flow rate at specific motor operating points and more).

[0097] According to some embodiments, a flow metering assembly including, for example, flow metering controller 812, inducer 802, fluid characteristic sensor 810 and a conduit such as conduit 804 may be configured to be partially disposable and partially re-usable. In many medical devices, apparatus and systems parts coming in contact with human fluids may be commonly disposable to avoid contamination or the need to carry out sterilization of the parts. Thus the conduit and parts coming in contact with the fluid within the conduit 804 may be designated as disposable and the flow metering assembly may be configured to allow easy replacement of these parts. In some embodiments, inducer 802 and/or fluid characteristic sensor 810 may also be in contact with the fluid and may also be designated as disposable. As the distance between fluid characteristic sensor 810 and inducer 802 may be required to be accurate it may further be advantageous for the fluid characteristic sensor 810 and inducer 802 to be disposable to avoid calibration of the metering system to confirm the distance between these elements. The controller may also be reusable or disposable.

[0098] According to some embodiments, a configuration of sensor 810 and inducer 802 may be configured to mechanically snap on or latch to conduit 804. Optionally, the configuration may further include controller 812. [0099] Turning now to Fig. 9, depicted is a functional block diagram of an exemplary fluid flow metering system and assembly with multiple sensors such as flow metering assembly 900, in accordance with some embodiments of the invention. It is to be understood that elements 902-912 may be substantially similar to corresponding elements 202-212 of Fig. 2. Inducer 902 may be configured to operate as both an inducer and a sensor. Flow metering assembly 900 further comprises additional sensors such as fluid characteristic sensors 914-920. Fluid characteristic sensor 914 may be located upstream from inducer 902. Fluid characteristic 916 may be located downstream of and near fluid characteristic sensor 910. Fluid characteristic 918 and 920 may be located farther downstream from inducer 902 and adjacent one another.

[00100] According to some embodiments, Controller 912 may receive a sensed signal from fluid characteristic sensor 916 to supply additional information. For example, resampling of the received signal may improve flow metering calculations.

[00101 ] According to some embodiments, Controller 912 may receive a sensed signal from fluid characteristic sensor 918 or 920 which may be located substantially downstream of inducer 902 to supply additional information. For example, confirming that the characteristic of a volume of fluid flowing through conduit 904 has dissolved before reaching the fluid destination which may be a patient, or to detect additional statistical information to be used in flow metering calculations such as the fluid's steady state characteristics.

[00102] According to some embodiments, Controller 912 may receive a sensed signal from inducer 902 to detect occlusion of conduit 904. The controller may take into account the expected fluid characteristic at inducer 902, if the fluid characteristic is greater than expected it may indicate an occlusion. For example, in a system wherein the induced fluid characteristic change may be a localized ion concentration the capacitance at inducer 902 may exceed the expected amount if an occlusion prevents the fluid from flowing downstream. Furthermore, sensor 914 may sense a characteristic change in the fluid upstream indicating an occlusion downstream. Sensors 910, 916, 918 and 920 may supply additional information regarding fluid flow to aid in detecting an occlusion within conduit 904, or in line with conduit 904 if it is connected to a further conduit. For example, if sensor 910 does not detect an expected characteristic change this may indicate an occlusion.

[00103] According to some embodiments, Controller 912 may receive a sensed signal from fluid characteristic sensor 918 or 920 which may be located downstream and in proximity to fluid characteristic sensors 910 and 916 to supply additional information. For example, analyzing detection of a fluid characteristic change between the fluid characteristic sensors may indicate the direction of the flow. A fluid flowing downstream may be detected first by fluid characteristic sensor 910 then fluid characteristic sensor 916 then by fluid characteristic sensor 918. If the flow is reversed before reaching fluid characteristic sensor 916 then fluid characteristic sensor 918 may detect a fluid characteristic change before sensor 916 indicating that the previous signal has traveled upstream and that flow may be reversed.

[00104] According to some embodiments, Controller 912 may receive a sensed signal from fluid characteristic sensor 914 while expecting to receive a sensed signal from fluid characteristic signal 910 which may indicate that the fluid is flowing upstream.

[00105] According to some embodiments, in some medical devices back flow or flow upstream may be configured to occur periodically and controller 912 may store such associated information to determine if the upstream flow is scheduled or not.

[00106] According to some embodiments, Controller 912 may receive one or more sensed signals from fluid characteristic sensors 910, 916-920 and may detect if there is free flow of the fluid within the conduit. For example, a sensed signal may have different characteristics than expected due to the quicker than expected flow of the fluid, or the flow rate may be substantially higher than expected which may indicate free flow. In an additional example the controller may receive indication that no flow is expected (for example if an associated medical device is turned off), if a flow rate is detected it may indicate free flow within the conduit.

[00107] According to some embodiments, Controller 912 may receive a sensed signal from fluid characteristic sensor 910 with characteristics different than expected such as localized ion density or concentration of the detected signal or other and combined with additional information, the controller may detect a disturbance such as air bubbles or residue within conduit 904.

[00108] According to some embodiments, controller 912 may be configured to detect an occlusion within the conduit of a metering apparatus. The controller may receive/include information associated with the metering assembly such as: the distance between an inducer and a sensor, the conduit's cross section, an expected flow rate, the difference in time between initiating the actuating signal and it's expected arrival at the sensor, and secondary information such as additional information stored in the flow estimation logic and detect an occlusion of fluid within the conduit of a metering apparatus.

[00109] Turing now to Fig. 10, depicted is a flowchart 1000 including the exemplary steps which may be performed by the exemplary controller shown in Fig. 6A in accordance with some embodiments of the invention. A change in a characteristic of a volume of fluid may be induced at a point of induction and the time of induction or initiation time, referred to as T1 , may be stored (step 1002). A change in the characteristic of a volume of fluid may be detected downstream from the point of induction and the detection time, referred to as T2, may be stored (step 1004). The induced change in characteristic may be configured so that it is resilient to diffusion and/or turbulences when detected downstream. For example, if inducing a signal including a unique point such as a maximal or minimal point, the sensed signal downstream may be a maximal or minimal point within the change of the fluid, since the unique point (for example maximum/minimum point) may not be affected by diffusion and/or turbulence and may be resilient to them (note that the amplitude of the maximum/minimum may be effected by diffusion and/or turbulence). Additional system parameters and information such as an expected or target flow rate, functionality of the medical device, distance between point of induction and downstream detection (referred to as X), conduit cross section (referred to as A) may be received or stored (step 1006). A flow rate and/or flow conditions may then be calculated and/or detected (step 1008). For example the following equation: A^*X (T2-T1 ) may be suitable to calculate the flow rate. The difference between T2 and T1 may also be referred to as time of flight (TOF).

[001 10] According to some embodiments, inducing a change (step 1002) may be re- executed periodically or intermittently regardless of detection of change downstream from point of induction (step 1004), this may be referred to as an asynchronous method. The frequency in which a change may be induced (step 1002) may be dependent on expected flow rate or other parameters and may vary.

[001 1 1 ] According to some embodiments, inducing a change (step 1002) may be re- executed after a change in a characteristic of a volume of fluid may be detected (step 1004) and may be referred to as a synchronous method.

[001 12] Turing now to Fig. 1 1 , depicted is a flowchart 1 100 including the exemplary steps which may be performed by the exemplary flow metering controller shown in Fig. 8 in accordance with some embodiments of the invention. A change in a characteristic of a volume of fluid may be induced at a point of induction and the time of induction (step 1 102). A change in the characteristic of a volume of fluid may be detected downstream from the point of induction (step 1 104). Additional system parameters and information such as an expected flow rate, functionality of the medical device, distance between point of induction and downstream detection, conduit cross section and more may be received or stored (step 1 106). A flow rate and/or flow conditions may then be calculated and/or detected (step 1 108). The flow rate/flow condition may then be returned to an associated medical device so that the medical device may modify a function of the medical device (step 1 1 10).

[001 13] Turning now to Fig. 12, depicted is a flowchart 1200 including the exemplary steps which may be performed by the exemplary medical device controller shown in Fig. 8 in accordance with some embodiments of the invention. The medical device (MD) controller may signal to an associated flow meter (FM) to measure an instantaneous or continuous flow rate (step 1202). The MD controller may receive control data from the FM (step 1204). If the detected fluid flow condition is undesirable (step 1206) for example if presence of air bubbles is detected, free flow and more, the MD controller may issue an alarm and/or stop operation of the MD (step 1208). If a flow rate, different than the nominal or requested flow rate is detected (step 1210) the MD controller may adjust operation of MD to achieve the requested flow rate (step 1212).

[001 14] In several figures above fluid flow has been depicted via arrows (such as Fig. 1 , 2, 5A-C and more). These arrows are for clarity only and do not limit the embodiments to fluid flowing in that direction. It is to be understood that fluid may be designed to flow in the opposite direction, may flow in the opposite direction as an error in the system (back flow), may flow in additional directions (due to turbulence etc.) and more.

[001 15] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

Claims What is claimed:

1. A fluid flow meter for measuring fluid flowing through a conduit associated with a medical device, said meter comprising:

an inducer to selectively and contactlessly alter an ion distribution within a volume of said fluid in proximity of said inducer, wherein said altering includes exposure of the volume to an electrical field;

a sensor located at a known distance downstream from said inducer and adapted to sense a physical parameter associated with the ion distribution induced by said inducer; and

a controller functionally associated with said inducer and said sensor, said controller configured to estimate a fluid flow rate based on an output of said sensor.

2. The fluid flow meter according to claim 1 , wherein said physical parameter is a capacitance, and wherein the sensed capacitance of the volume is associated with a second ion distribution resulting from a first ion distribution induced by said inducer and passively altered along a conduit path between said inducer and said sensor.

3. The fluid meter according to claim 1 , wherein said controller estimates a fluid flow rate based on: an initiation time of said first ion distribution, a detection time of a unique point within said second ion distribution and said known distance and a cross section area of the conduit.

4. The fluid meter according to claim 3, wherein said controller is adapted to estimate a fluid flow rate based on two or more of said initiation times and two or more of said detection times to improve accuracy of said estimation of the fluid flow rate.

5. The fluid meter according to claim 1 , wherein said controller is further configured to receive a target flow rate.

6. The fluid meter according to claim 1 , wherein said inducer is configured to modulate an ion distribution in the form of a pattern.

7. The fluid meter according to claim 1 , wherein said controller is further configured to identify one or more fluid flow conditions based on an output of said sensor, wherein said one or more fluid flow conditions are selected from the group consisting of: an occlusion, free flow, presence of air bubbles and back flow.

8. A medical device system associated with a fluid meter assembly including a conduit, said medical device comprising:

a medical device assembly adapted to administer a treatment to a patient; and a first controller functionally associated with the medical device assembly and adapted to receive an output indicative of an achieved flow rate from the fluid meter assembly.

9. The medical device system according to claim 8, further comprising a second controller configured to estimate a fluid flow rate based on an output of a contactless sensor.

10. The medical device system according to claim 9, wherein said second controller is embedded within said first controller.

1 1 . The medical device according to claim 8, wherein said medical device is adapted to administer fluid through the conduit at a target flow rate, and said first controller is adapted to compensate for deviations from the target flow rate using said output indicative of an achieved flow rate.

12. The medical device according to claim 8, wherein said output indicative of an achieved flow rate includes fluid flow condition information.

13. The medical device according to claim 8, wherein said fluid flow condition is selected from the group consisting of: an occlusion, free flow, presence of air bubbles and back flow.

14. The medical device according to claim 10, wherein said medical device is adapted to administer fluid through the conduit at a target flow rate, and said first controller being adapted to trigger an appropriate alarm to the fluid flow condition information.

15. A method of metering fluid flowing within a conduit associated with a medical device, said method comprising:

selectively inducing an electrical field at a predetermined segment of the conduit;

contactlessly altering a localized ion distribution within a volume of said fluid;

contactlessly sensing a localized ion distribution alteration downstream from the predetermined area of the conduit; and estimating an actual fluid flow rate of the fluid flowing within the conduit.

16. The method according to claim 15, further comprising generating an error signal indicative of a difference between the estimated actual flow rate and a target flow rate.

17. The method according to claim 16, further comprising using the error signal to compensate for the difference between the estimated actual flow rate and the target flow rates.

18. The method according to claim 15, further comprising identifying at least one fluid flow condition of the fluid within the conduit, wherein said at least one fluid flow condition is selected from the group consisting of: an occlusion, free flow, presence of air bubbles and back flow.

19. The method according to claim 18, further comprising triggering an alarm in response to the fluid flow condition.