Abstract:
An intravenous system for monitoring the flow of IV fluids to a patient is embodied in a wristwatch sized case for placement on the patient. The device includes a switch uses capable of detecting when flow starts or stops. In one embodiment, the range of flow rates which may trigger a signal is increased using a plurality of sensor elements. The flow indicator switch uses a conical fluid conducting means with a movable stem body which reacts to the motion of the IV fluid. A signal-emitter-sensor arrangement provides a means for converting physical displacement into an electrical signal indicating displacement of the movable member thus detecting when flow starts and stops, as well as the rate of flow. Collected information is stored in a data storage means and may be either displayed on a display means housed within the case, or alternately, the collected data may be uploaded to a computer.

Description:
This application is a continuation in part of application Ser. No. 08/360,994, filed Dec. 20, 1994, now U.S. Pat. No. 5,445,622. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to intravenous (IV) fluid delivery systems and in particular to a monitoring device for providing information on when and if the delivery of an IV fluid to a patient actually occurred. 
     BACKGROUND OF THE INVENTION 
     The rapid rise of health care costs has become an important issue in modern society. To help reduce the costs, professional care givers have begun to seek alternatives, one of which is home health care services. These services not only tend to reduce costs, but are also preferred by the patient wishing to remain in his familiar environment. Among the many types of services provided are: respiratory care, rehabilitation therapy, cardiac monitoring procedures, and infusion therapy. 
     Infusion therapy involves IV administration of drugs. Making this therapy safe and convenient for a home situation allows a great number of patients who would otherwise be hospitalized to remain at home and still receive medication. Currently, over 300,000 patients annually use a home infusion therapy delivery system. Typically, patients include the elderly with chronic diseases like cancer, patients with either Crohns disease, HIV or other immune system disorders, and patients suffering from chronic pain. Many of these patients require infusion treatment over a long duration such as months or even years. 
     One characteristic of home IV drug therapy, in contrast to hospital administered therapy, is that a nurse is not always present or readily available. To provide safe and effective treatment, home infusion therapy usually requires that the patient himself, or other non-professional caregiver, such as a relative, administer IV fluids. Special training is required because many home care patients on IV therapy require multiple drugs or multiple doses of the same drug each day. The average nursing visit to a home infusion therapy patient is typically about 90 minutes including commuting time. The typical patient gets between 1 and 4 nursing visits per week, but has to take IV medications daily. Since the cost of daily care by a nurse is not usually covered by most insurers, the cost of attention by a nurse is most economically applied in training the patent or other amateur caregiver and in monitoring the therapy program. 
     In the home care situation non-compliance, over-medication or under-compliance with the IV therapy protocol is a serious issue and quite prevalent. For instance, non-compliance (not taking a medication) or under-compliance (taking fewer or smaller dosages than prescribed) occurs in up to approximately one-third to one-half of elderly home therapy patients. Typical compliance related problems include forgetting to follow the specified procedure for administration of the IV medication, forgetting to turn on the various devices used to administer the IV medication and forgetting to turn off a medical device which then delivers too much medication (over-medication). Reasons for compliance related problems are varied and include poor communication, confusion or forgetfulness regarding the procedures and/or equipment, or even attempts to avoid the adverse side effects of IV medications and fluids. Misapplication of the home IV therapy protocol can have serious ramifications resulting in greatly increased home health care nursing expenses, re-hospitalization, and reduction in health status of the patient. Thus, there is a strong need for improved monitoring of patient compliance with the health care program. Benefits of such improved monitoring and compliance include, but are not limited to, improved health at a lower cost, while still remaining in the preferred home environment. 
     To properly monitor compliance with an IV therapy protocol, a device may be provided for monitoring the flow of IV medications and fluids. The IV fluids for a single patient are likely to come from several different sources or systems including IV pumps, IV fluid controllers, gravity drips, syringes, and other devices. 
     A typical gravity powered IV may be as simple as an IV bag hanging on a pole in which a nurse or care giver manually adjusts a valve to limit the flow rate, but not control it accurately, or it may use an electronic controller which optically counts the drops of fluid as they pass an optical sensor and then adjusts the flow rate accordingly. However, optical drop counting sensors only provides an indication that the fluid is flowing past the sensor when in a vertical orientation such as hanging from an IV pole. Thus the patient and IV delivery equipment must remain relatively stationary during the administration of the medication or fluid. Optical drop counters also function poorly at higher flow rates and higher line pressures, such as when a syringe is used, because the fluid moving past the drop counter tends to become a continuous stream rather than remaining discrete drops. Therefore, the optical drop counter technique cannot be adapted for use with all fluid sources. 
     An alternative to an optical drop counting sensor, or as a stand-alone measuring device, is a single point pressure transducer to measure the fluid pressure in the IV tubing at a selected point of measurement. This type of sensor is common in IV pumps and is used to indicate that the pump is generating a static pressure head and, correspondingly, causing fluid flow or backpressure in the event of an occlusion in the IV line. This type of sensor only determines line pressure at the selected point, and is only useful in monitoring the pressure caused by the IV pumping device and the related backpressure caused by moving fluids into the patient&#39;s body. However, this type of single-point pressure sensor is useful in many IV delivery systems to determine if fluid pressures are at correct levels, and to detect changes in fluid pressure which are indicative of an occluded or collapsed vein. Often, when a certain threshold pressure is detected in a device using this type of sensor, an alarm is sounded to warn of a flow problem. This type of device measures changes in the static line pressure of a fluid line, but is unable to determine if a patient is following proper IV drug administration procedures and cannot differentiate between changes in pressure due to fluid flow versus some other cause, such as an occlusion in which there is actually no fluid flow. 
     Increased backpressure in an IV fluid line causes problems, and, as described above, many IV fluid delivery systems use a sensor to determine when high backpressure develops, i.e., greater than a few inches of water, for instance when an infiltration of tissue occurs or the tubing becomes occluded. Upon the detection of a significant backpressure, the device sounds an alarm and may function to automatically discontinue the delivery of the IV medication and fluids. Therefore, it is important that any device used to monitor whether or not fluid is flowing does not cause a substantial increase in backpressure or a false occlusion alarm might be triggered. 
     Other alternatives use indirect methods to monitor the flow of IV fluids. For instance, the speed and number of rotations in a pump mechanism may be monitored to indirectly determine when fluid flow is occuring. This is useful for flows caused by an IV pump, but is of no value to patients who also receive gravity drips or fluids via syringe. Since nearly all infusion therapy patients must perform venous access device maintenance procedures, such as a heparin flush via syringe to maintain the patency of their IV lines, this pump rotation technique is not of value for monitoring all infusions. 
     The time usage for an IV delivery system may be recorded to prepare bills to patients. Typically, the information is printed or stored in an electronic memory device such as the electronic controls for the drop counter or IV pump. The information may be used to determine which of several patients are using the IV system being monitored, it may be used to coordinate several IV delivery systems with a centrally managed pump, or it may be used to facilitate billing and reimbursement. Unfortunately, none of these systems accommodate tracking of fluid delivered from a variety of sources such as to a patient who receives syringes, gravity drips, and IV pump infusions. The present invention provides an improved flow indicator switch, which overcomes the above-mentioned limitations of the prior art. 
     SUMMARY OF THE DISCLOSURE 
     The present invention is an IV system which provides certain monitoring advantages. An electronic data processing and storage device is used in conjunction with a unique flow indicator switch to record events in the IV infusion process. The processor may be connected in real time or may be used simply as a data recorder for later analysis. If used in real time the processing device is used to interpret signals related to IV flow, to provide instructions on how to properly sense whether fluid flow is occurring, and on when to inform the user to use the IV system or even to take other medications, vis-a-vis, oral or injection therapy, etc. 
     In the preferred embodiment of the present invention, an IV infusion system provides a switch body conducting means having a movable stem body indicator to monitor a flow of fluid through a fluid flow path. The flow indicator includes a switch having a movable stem body that is forced to move by direct viscous forces against it within the flow path, so that it moves in the direction of fluid flow. The movable stem body can sense a change in system flow including positive flow startup from stagnation in order to indicate that fluid flow has stopped or started. A signal emitter-sensor means preferably including an infrared emitter and detector sense the change of position of the movable switch member. A spring element provides a restoring force to return the movable switch member to a null position indicating “no flow” when fluid flow has ceased. The force exerted by the spring element is adjusted to sense flow rates as low as 3.0 milliliters per hour. 
     Further, the conducting means has a variable orifice positioned in a shaped fluid passageway in the form of an annulus. The orifice changes in cross-sectional size depending upon the position of the movable stem body. The cross-sectional area of the orifice is designed to enhance sensitivity to low fluid flows when the orifice has a smaller cross-sectional area, as well as to limit backpressure generated by higher fluid flow when the orifice has a larger cross-sectional area. In the preferred embodiment, the increase in backpressure is limited to about  4  inches of water with flow rates as high as 3600 milliliters per hour. In the preferred embodiment, the flow indicator switch functions equally well at line pressures from a fraction of an inch of water to over 60 pounds per square inch pressure because no occlusion of the flowpath occurs. Therefore, the flow indicator switch is not an occlusive device and does not react to changes in static pressure. 
     The processor is preferably operationally coupled to the flow indicator switch, to monitor the time and date of starts and stops of IV fluid flow in the system. One preferred embodiment of the present invention provides for the processor to be housed in a case about the size of a wrist watch so that it is highly portable for wearing on the person. This provides several key advantages and benefits to the infusion patient which would not otherwise become possible. 
     The processor and the flow indicator may be operationally coupled by fluid conduits, electrical conductors, wireless transmitters and receivers, or the like. The processor includes a memory storage device which retains information related to the programmed IV protocol and the actual time of start and stop events. The processor may of course be interconnected with a computer or other high speed data device for data archiving purposes and for further data analysis. In the preferred embodiment, the processor is serially coupled with a notebook PC that downloads prescribed IV protocols and uploads actual fluid flow start/stop events for comparison. The downloaded and uploaded data may include fluid flow events from any or all sources of fluid including, but not limited to, IV pumps, gravity drips, and syringes. 
     The flow indicator switch may operate in any attitude providing an advantage over prior apparatus. Moreover, the flow indicator switch housing is formed with a fluid flow path that is easily de-aired by a flow of fluid through the device housing. The flow indicator switch is a passive device, in which the movable switch member is actuated by the fluid flow through the tube. It can have a sensitivity to low fluid flows of less than or equal to 3.0 milliliters per hour and a backpressure limited to less than or equal to 4.0 inch of water line pressure at higher flow rates common to intravenous drug therapy, such as 3600 milliliters per hour. The flow indicator switch can work well with pulsed fluid flows without triggering a false alarm in the fluid delivery equipment. 
     Another advantage is that the small size and portability of the flow indicator switch precludes the necessity of having the patient attach and detach the device each time it is used. It may be attached to the patient&#39;s IV catheter for long periods of time. Also, since it is a passive device, it requires less electrical power and maintenance, thereby reducing health care costs. It may be connected to a catheter or IV tubes by standard connectors typically used on common IV equipment, or it may be an integral part of the IV catheter tube assembly. 
    
    
     Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of the several embodiments of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of embodiments of the invention will be made with reference to the accompanying drawings, wherein like numerals designate corresponding parts in the several figures, in such drawings: 
     FIG. 1 particularly showing a signal emitter-sensor means and fluid conducting means with a stem body in a first position against a proximal shoulder is a perspective view showing on overview of the present invention in a general orientation as applied to a patient in a wrist or arm mounted embodiment; 
     FIG. 2 is a schematic representation of a first prefered embodiment of the present invention of FIG. 1 shown as the simple flow indicator switch held within the case shown in FIG. 1, wherein some dimensions are shown exaggerated for better understanding of the principles involved, and particularly showing a flow conduit, inlet and outlet orifices, stem body, and light emitter and detector of the preferred embodiment; 
     FIG. 2A is a cross-section view of the flow indicator switch taken along lines  2 A— 2 A of FIG.  2  and particularly showing the preferred relationship between a proximal shoulder, the fluid conductor and an end of the stem body, wherein some dimensions are shown exaggerated for better understanding of the principles; 
     FIG. 2B is a schematic representation similar to that of FIG. 2 showing an alternate position of the stem body of the invention; 
     FIG. 3 is a schematic representation of a second prefered embodiment of the present invention of FIG. 1 shown as a flow rate indicator held within the case shown in FIG. 1, wherein some dimensions are shown exaggerated for better understanding of the principles involved, and particularly showing a flow conduit, inlet and outlet orifices, stem body, and light emitter and detector of the preferred embodiment; 
     FIG. 3A is a cross-section view of the flow indicator switch taken along lines  3 A— 3 A of FIG.  3  and particularly showing the preferred relationship between a proximal shoulder, the fluid conductor and an end of the stem body, wherein some dimensions are shown exaggerated for better understanding of the principles; 
     FIG. 3B is a schematic representation similar to that of FIG. 2 showing an alternate position of the stem body of the invention; 
     FIG. 4 is a general block diagram of an electronic circuit of the invention showing the preferred interconnections of various electrical elements of the invention; and 
     FIG. 5 is a view of the preferred layout of the face of a wrist watch sized event monitor housing of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a fluid flow device for monitoring the flow of a fluid such as is used in medical applications such as infusion therapy where an IV fluid is monitored for providing information on the delivery of the IV fluid to a patient. Other fluids, and other applications both within medicine and outside of the medical field may be suitable for advantageously applying the device. Preferably, the device has a wristwatch sized case  80  that attaches to a patient&#39;s arm or that may be taped to the patient&#39;s chest depending upon the site of the IV catheter. The case  80  provides a visual display means  85  that is easily viewed by the patient. As shown more clearly in FIG. 5, the display  85  preferably displays a variety of different pertinent information such as the current time and date; the time and date of the next IV infusion process including which drugs to use; and the time and date of the last IV infusion process performed. 
     The monitoring apparatus for the intravenous fluid delivery is a system comprised of two primary components, the first being a processor circuit  60  housed within the case - 80 , used to store and record electronic data pertaining to fluid flow. The second component is a signal emitter-sensor means  52 , for detecting fluid stop and start events as well as potentially monitoring of fluid flow rate. 
     Referring now to FIGS. 2,  2 A and  2 B, an important component of the fluid flow monitoring device is shown as fluid conducting means  20 . Preferably, the conducting means  20  is a conductor that has a clear conical wall  22  for advantageously visually ensuring that air is removed from the IV fluid path. In one preferred embodiment, the fluid conductor  20  extends between proximal and distal fluid conduits  30 P and  30 D. The case includes an inlet fluid conductor means  87 P that connects the proximal conduit  30 P to a source of intravenous fluid, preferably an IV bag  84 , or a syringe (not shown) or an IV pumping device (not shown) well known to the field. An outlet fluid conductor means  87 D connects the distal conduit  30 D to an intravenous discharge device  88  that discharges the IV fluid to the patient&#39;s vein. 
     The conductor wall  22  has a conical shape having a slight wall divergence of approximately between 0.03 to 2.0 degrees, so that it is larger at its distal end. Preferably, a proximal and distal circular shoulders  33 P and  33 D are provided at the ends respectively of the conductor  20 , the proximal shoulder  33 P defining an inlet fluid orifice  35 P, and the distal shoulder  33 D defining an outlet orifice  35 D. 
     In the preferred embodiment, an opaque stem body  40  for use with optically clear fluids, is a movable piston or plug element, and is provided within the the conductor  20 . An alternate embodiment, to be discussed later, uses an optically clear stem body  40  for use with opaque fluids. 
     In the preferred embodiment the body  40  has a volume of 6.8586×10 −3  cubic centimeters and a density of approximately 1.25 grams per cubic centimeter. As shown in FIG. 2, the stem body  40  preferably has a circular cross section and is slightly smaller in diameter than the conductor  20 . When the stem body  40  is positioned at the proximal end of the conductor  20  abutting the proximal shoulder  33 P, the stem body  40  does not engage any portion of the conical wall  22 . The stem body  40  has a generally flat surface  42  at the end that contacts the proximal annular shoulder  33 P, but does not form a tight seal with the shoulder. The stem body  40  may have a relatively smooth (FIG. 2A) or a ridged (FIG. 3A) outer surface  44  that provides a series of fluidic pathways  46  for conducting the fluid between the stem body  40  and the conical wall  22 , thus providing improved conductance of the fluid. The surface  44  and fluid pathways  46  are shown in FIGS. 3 and 3A in an exaggerated manner. The preferred dimensional clearance between stem body  40  and the proximal shoulder  33 P is about 0.0015 inches and this effective gap may often be accomplished by virtue of the natural texture or roughness of the surface of the materials without having to especially provide for grooved fluid pathways as shown in the aforementioned figures. The stem body is biased, preferably by means of a stem body biasing means  45  such as a spring, so that the surface  42  of the stem body  40  is urged in position against the proximal shoulder  33 P, thus partially, but not fully, closing the fluid conductor  20  under static conditions. This partial closure allows at least some of the fluid to pass out of the conductor  20  in the direction away from the patient in the event that blood must be drawn from the patient or fluid must be removed from the line. It also allows for instantaneous equilibrium between pressure changes upstream or downstream of the stem body  40  in that upstream and downstream fluids are not mutually isolated. Occlusion of the flow path does not occur. 
     The spring constant of the biasing means  45  is preferably approximately 0.06 pounds per inch of deflection which means that the stem body  40  is displaced by a very slight flow of fluid into inlet  35 P and out of outlet orifice  35 D. It should be noted, however, that other spring constants and stem body masses may be selected for similar performance. 
     In one preferred embodiment shown in FIG. 2, the signal emitter-sensor means  52  consists of a signal emitter  50  positioned outside of the conductor  20 , lateral to the stem body  40 , and a single signal detector  55  positioned directly across from the emitter  50 , on the opposite side of the conductor  20 . As shown in FIG. 2, the left-hand side edge of the detector  55  is aligned with the proximal shoulder  33 P and the base of the stem body  40 . A masking means is positioned between the emitter-sensor means  52  and the stem body  40 . In one preferred embodiment, the masking means  52  consists of one mask  56 A positioned between the signal emitter  50  and the stem body  40 , and another mask  56 B placed between the detector  55  and the opposing side of the stem body  40 . Preferably, both masks  56 A and  56 B have tiny openings that are aligned in corresponding pairs in opposition across the fluid conductor. In the preferred embodiment, these openings are between 0.003 to 0.030 inches in diameter depending upon the power of the emitter  50  and the sensitivity of the detector  55  These openings in the masks  56 A and  56 B restrict signal travel from the emitter  50 , to a narrow signal path  58  across the fluid conductor  20 , thereby focusing the signal. As seen in FIG. 2, when the stem body  40  is in position against the proximal shoulder  33 P, the signal path  58  between the emitter  50  and the detector  55  is fully blocked by the opaque stem body  40 , the signal is prevented from fully reaching the signal detector  55 . However, as seen in FIG. 3, when the stem body  40  moves away from the proximal shoulder  33 P, the signal path  58  is provided. Thus, any change in position of the stem body  40  within fluid conductor  20  is easily determined by whether the signal path  58  is blocked or not. 
     Although FIGS. 2 and 2B show an embodiment with a single signal detector  55 , the signal emitter-sensor  52  may also consist of a linear sequence of independent signal emitters  50  and sensors  55  as shown in FIG.  3 . In this alternative manner, an IV line with a constant flow, such as those used for KVO or “Keep Vein Open” applications, may be monitored for a meaningful change in flow rate. In the preferred embodiment, the signal emitter-sensor means  52  preferably emits and senses light signals in infrared wavelengths, although it is by no means limited to such use. 
     As mentioned previously, in the preferred embodiment the stem body  40  is opaque in order to block the passage of the signal from the emitter  50  to the detector  55  when used with optically clear fluids. In certain instances however, a patient may receive IV fluids such as blood products or feeding solutions, that are not optically clear. The optical properties of these opaque solutions naturally attenuate light passing through them. This attenuation is proportional to the length of distance that the light must pass through the fluid. Therefore, an alternative embodiment of the stem body  40  uses a clear plastic which then limits the attenuation to that which occurs over a few thousandths of an inch. In this manner, the electronics may be modified to receive an optical signal for “no-flow” conditions and an opaque or blocked signal for “flow” conditions. 
     The processor circuit  60  of the intravenous system may use a digital microprocessor chip to provide a logic program for interfacing the device into a therapeutic program of IV infusion and other medications. The circuit  60  preferably provides a means for using electrical signals from the detector  55  to store IV fluid flow event information. Intermittently, it is possible that non-fluidic events, such as the motion of a patient, may cause spurious signals due to minor displacements of the stem body  40 . Testing has shown that these spurious signals are of short duration, such as a fraction of a second. The case  80  houses the processor circuit  60  which also includes logic for determining minimum “Flow On” time periods and intervals to remove most spurious signals from the log of flow events stored in memory. 
     The processor circuit  60  preferably includes a processor means  62 , clock means  90  and a data storage means  95  interconnected so as to enable the processor circuit  60  to gather and record information concerning the infusion such as the time of day at start, time of day at stop, and time of day at change in IV flow rate with each associated flow rate change. The processor circuit  60  also preferably includes a parameter measuring instrument signal receiving means  130 , which, in one preferred embodiment, consists of an analog-to-digital circuit, an amplifier and a jack. A variety of different measuring instruments (not shown), such as a scale or a thermometer, may be quickly and easily interconnected with the instrument signal receiving means  130  so that parameters pertinent to the patient&#39;s (pulse, blood pressure, body temperature, weight, etc.) condition may be easily and effectively monitored. The data received by the signal receiving means  130  is stored in the data storage means  95 . 
     All data stored in the data storage means  95  may either be visually accessed by the patient at the display means  85  of the processor circuit  60  contained within the case  80 , or, alternately, the circuit  60  may also include a communication means  100  that enables communication between the circuit  60  and a computer system  110 . The communication means  100  may be either a hardwire or a wireless device of the type well known in the art. From the computer system  110 , recorded data may be quickly uploaded and viewed. 
     A variety of pertinent information, such as oral medication schedule, may also be programmed into the computer  110  as desired. The processor circuit  60  of the present invention preferably includes an alerting means  120  for reminding the patient when to take oral medications or begin an IV infusion, for alerting the patient when the recorded body temperature is too high, fluid flow rate is too low, etc. To accomplish this, the desired information, as for example the times of day at which infusions should begin, is programmed into the computer  110 . When the time recorded by the clock means  90  corresponds with the preprogrammed infusion times, the alerting means  120  alerts the patient by producing an audible alarm, vibrating or any other such means. In the same manner, a range of preferred fluid flow rates may be preprogrammed into the computer  110 , and when the recorded flow rate during a infusion does not fall within the specified range, the alerting means is actuated. 
     Thus, in use, the proximal conduit  30 P is connected to an IV bag or other fluid source, and the distal conduit  30 D connects to an intravenous discharge device interconnected with a vein. Both conduits  30 P and  30 D and the conductor  20  are filled with IV fluid and deaired prior to attaching to the patient, and the stem body  40  is nominally positioned against the proximal shoulder  33 P indicating a no flow condition. The system remains static until flow from the IV bag or other fluid source is activated and the stagnation pressure due to fluid motion against the stem body  40  increases. The force on stem body  40  overcomes the restoring force of the biasing means  45 , causing stem body  40  to move away from the proximal shoulder  33 P. This allows fluid which flows from the conduit  30 P and through the inlet orifice  35 P to be immediately sensed. The force of the fluid flow moves stem body  40  to a position within the fluid conductor  20  where a state of dynamic equilibrium is achieved between the force of fluid against stem body  40  and the restoring force. As stem body  40  moves further toward the distal end of the fluid conductor  20 , as is typical at higher flow rates, the annular flow path area between the stem body  40  and the conical conductor wall  22  becomes larger, thereby increasing flow conductance in the conductor  20 . Therefore a nonlinear relationship is developed between stem body displacement and conductance such that backpressure is minimized very quickly. 
     In particular, when the stem body  40  is positioned against the proximal shoulder  33 P, as shown in FIG. 2, it blocks the signal from arriving at the leftmost edge of sensor  55 . This leftmost edge of sensor  55  is particularly of interest in establishing if fluid in the system is static, or is flowing. Further, the signal reaching the leftmost edge of sensor  55  does not have to saturate the photodector means in signal sensor  55 . In the preferred embodiment, a signal of about 300 millivolts is generated when the sensor  55  is fully saturated when both tiny openings  56 A and  56 B are fully exposed. However, an almost minuscule change in position of stem body  40  will cause a smaller change in voltage from 0.0 millivolts (totally opaque) to 0.5 millivolts because the leftmost edge of sensor  55  is partially illuminated. This smaller change is voltage is used to determine that fluid motion has commenced or ceased. Thus the signal induced by the leftmost edge of sensor  55  is used in the preferred embodiment to determine the “flow ON/OFF” time periods. The detector  55  signals are used in the processor circuit  60 , thereby to log start and stop of fluid flow. 
     While the invention has been described with reference to a preferred embodiment, it is to be clearly understood by those skilled in the art that the invention is not limited thereto. Rather, the scope of the invention is to be interpreted only in conjunction with the appended claims.