Empty container detector.

The present invention relates generally to a system for detecting air in a fluid line, and more particularly to a clamp-on detector apparatus for detecting air in the fluid line between a medication infusion reservoir such as an IV bottle or bag and an IV injection set or a medication infusion pump.

There are two principal techniques used to administer a continuous flow of medication to a patient, with both techniques involving the administration of a therapeutic fluid from a fluid reservoir or container which is typically and IV bottle. First, medication may be delivered through a conventional IV system using a drip chamber with the injection being made into various IV tubes and the associated paraphernalia, with drop counters being used to meter the amount of fluid delivered. Alternatively, medication infusion pumps may be used to administer drugs to a patient in small, precisely metered doses at frequent intervals or, alternatively, in the case of some devices, at a low but essentially continuous rate. Infusion pump therapy is electronically controlled to deliver precise, metered doses at exactly determined intervals.

An essential function of a medication infusion system is to avoid the infusion of fluid containing air bubbles. While a small amount of air may be contained in the fluid to be infused in very small air bubbles, larger air bubbles present a rear danger to the patient if infused. Although steps may be taken to monitor the fluid line downstream before it reaches the patient to ensure that substantially no air bubbles remain in the fluid which is to be infused, it is also essential to minimise the possibility of air bubbles being contained in fluid near the reservoir end of the infusion apparatus. The detection of air bubbles in all fluids which are to be infused is therefore a critical design requirement.

The introduction of air into the infusion system near the reservoir happens principally when the iV bottle is empty. If the system remains unattended when the fluid reservoir or container is empty, air may be allowed to enter the fluid lines from the reservoir or container end. If no air-in-line detection apparatus, is employed, there is a real danger that IV systems could allow air in the infusion lines. In the case of systems using infusion pumps, even if the pump has an air-in-line detection apparatus, it is generally on the patient side of the pump. This would allow air to reach the infusion pump, and many infusion pumps will not pump air but rather will require repriming.

Many air-in-line detectors known in the art will work with either opaque fluids or with transparent fluids, but require a manual control to be set to the type of fluid being infused. Such detectors rely on the operator to set the control properly, and an operator error could result in the system not working and allowing air to pass through the fluid lines without providing an alarm. A detector which will automatically work on either opaque or transparent fluids is disclosed in US patent No. 4, 114, 144 (Hyman). The Hyman detector first detects which type of fluid is in the line, and then provides an alarm if air enters the line.

While the Hyman detector represents an improvement on manual air-in-line detectors, it sacrifices simplicity for its automatic operation, requiring five sets of optical detectors to perform its function. Not only is the Hyman device fairly complex, but it is necessarily relatively larger and more expensive to manufacture than would be desirable. As may be seen from the Hyman reference, the device is a built-in detector rather than an accessory detector, and is used (in the preferred embodiment) downstream of a pump. Due to its size, it is not readily usable as a standalone device, or as an empty container detector.

It is therefore a primary object of the present invention to provide an empty container detection system for use wither in a conventional IV system or in conjunction with an infusions pump unit. The system of the present invention should be simple and easy to use, and should clamp onto a fluid line immediately downstream from the fluid reservoir or container. The empty container detection system of the present invention should be capable of immediately, accurately, and effectively detecting air in the fluid line regardless of whether the fluid being infused is opaque or transparent. The system should be fully automatic, not requiring any setup or intervention by an operator except clipping the device onto a line and plugging it in to the main pump unit or other controller.

Several other additional features are desirable in the design of the empty container detection system. One such feature is the ability to detect air bubbles whether the flow rate of the fluid in the line is fast or slow. In addition to being able to detect air in the fluid line, the system should also be accurate, presenting a high degree of resistance to false alarms. Since the detector of the system is to clip onto the fluid line, it should be small and light in size.

Despite the inclusion of all of these features, the system of the present invention should employ a minimum number of parts, all of which should be of inexpensive construction, while yet affording the system the high degree of accuracy which must be retained. The system of the present invention should be able to compete economically with known system, and must provide an ease of use rivalling the best known systems. The system should accomplish all these objects in a manner which will retain and enhance all of the advantages of reliability, durability, and safety of operation, and overcome the limitations of the background art without incurring any relative disadvantage.

According to the present invention, there is provided a device for detecting the presence of air in hollow cylindrical tubing characterised by: a housing including a recessed groove for receiving a portion of the tubing; a light source located on one side of the groove, light from the light source being directed onto the tubing when the tubing is located in the groove; first detecting means for detecting the presence of light passing across the groove; and second detecting means for detecting light from the light source which enters the tubing located in the groove and is reflected off the inside of the tubing and directed onto the second detecting means.

Preferably the first detecting means is a tube/no tube light sensor located in the housing on the other side of the groove from the light source, the tube/no tube light sensor receiving light from the light source when tubing is not located in the groove, the tube/no tube light sensor receiving substantially no light from the light source when tubing is located in the groove; and the second detecting means is a liquid-­in-tube light sensor located in the housing, light from the light source which enters tubing located in the groove being reflected off the inside of the tubing and directed onto the liquid-in-tube light sensor when air is contained in the tubing, while substantially no light entering tubing located in the groove is reflected off the inside of the tubing and onto the liquid-in-tube light sensor when fluid is contained in the tubing, any light entering the tubing instead entering the fluid contained in the tubing. The device may also include an operating characteristic light sensor for monitoring and for producing an output signal indicative of the light produced by the light source, the operating characteristic light sensor preferably monitoring the light source to ensure that the light source is operating properly, and the system preferably additionally comprising means for providing an alarm if the light source is substantially inoperative.

The device preferably includes means for monitoring the output signal from the operating characteristic light sensor, the monitoring means being arranged to measure the relative amounts of light detected by the tube/no tube sensor and the liquid-in-­tube sensor when the level of light output from the light source is at a preselected level, which is preferably below the maximum level of light generated by the light source, and occurs when the level of light generated by the light source has fallen from a higher level to the preselected level. Preferably, the recessed groove is essentially V-shaped, the light source generates infrared (IR) light, and the tube/no tube light sensor and the liquid-in-tube light sensor sense IR light, and a V-shaped filter is located in the groove, the filter allowing only (IR) light to pass, the filter optionally being a polysulphone filter. In a preferred form, the V-shaped filter is so geometrically arranged and configured as to allow the device to work identically for two different predetermined sizes of tubing optionally by the outer diameters of the two different predetermined sizes of tubing generally coinciding at the point at which light would enter the tubing from the filter and at the point at which light would leave tubing containing air and enter the filter on its path to the liquid-in-tube light sensor, and the inner diameters of the two different predetermined sizes of tubing being relatively located so as to reflect light off their inner walls at the same critical angle to direct the light onto the liquid-in-tube light sensor.

The device preferably includes means for retaining tubing in the groove optionally comprising a clamping arm pivotally mounted on the housing, the clamping arm including a clamping segment located over the groove; and means for biasing the clamping segment located over the groove and means for biasing the clamping segment towards the recessed groove, the biasing means optionally comprising a spring. Preferably, the clamping arm also includes a grip portion at the end opposite the clamping segment for opening the clamping arm to allow tubing to be installed into or removed from the groove.

The device may include first alarm means for generating an alarm signal when the tube/no tube light sensor receives substantial light from the light source to indicate that tubing is not located in the groove, and second alarm means for generating an alarm signal when the liquid-in-tube sensor receives substantial light from the inside of the tubing. There may also be means for identifying the device to a main pump unit to which the device is connected, the identifying means optionally comprising a preselected resistance which may be sensed by the main pump unit to identify the device.

The invention also extends to a method for detecting the presence of air in hollow cylindrical tubing characterised by directing light from a light source located in a housing to one side of a recessed groove in the housing, in which groove the tubing may be located; detecting whether or not tubing is properly located in the groove with a tube/no tube light sensor located in the housing on the other side of the groove from the light source, the tube/no tube light sensor receiving light from the light source when tubing is not located in the groove the tube/no tube light sensor receiving substantially no light from the light source when tubing is located in the recessed groove; and detecting whether or not air is contained in the tubing with a liquid-in-tube light sensor located in the housing, light from the light source which enters tubing located in the groove being reflected off the inside of the tubing and directed onto the liquid-in-­tube light sensor when air is contained in the tubing while substantially no light entering tubing located in the groove is reflected off the inside of the tubing and onto the liquid-in-tube light sensor when fluid is contained in the tubing, any light entering the tubing located in the groove instead entering the fluid contained in the tubing.

The disadvantages and limitations of the background art discussed above are overcome by the present invention. In the preferred embodiment, a clamp-on empty container detector device is used to detect the presence of air bubbles in a segment of tubing around which the device is clamped. The device uses a light-emitting diode (LED) which is periodically triggered to produce a burst of light at a desired sampling rate determined by the frequency of the triggering signal. If the tubing is empty of fluid or an air bubble is passing through it, the light is reflected at the inner diameter of the tubing and directed onto a liquid-in-tube sensor. If the liquid-­in-tube sensor detects light, the signal is indicative of air in the tubing, and an alarm will be given.

If there is transparent liquid within the tubing the light will pass through the tubing without being reflected toward the liquid-in-tube sensor, in which case the light will not be directed onto the liquid-in-­tube sensor. Rather, the light will continue in a path through the transparent liquid and through the opposite side of the tubing. Since the liquid-in-tube sensor is not located in line on the opposite side of the tubing, it will not detect the light. This is an indication that there is liquid in the tube.

Similarly, if there is opaque liquid within the tubing, the light will pass through the tubing without being reflected, and again the light will not be directed onto the liquid-in-tube sensor. The light will continue in a path into the opaque liquid, and will be absorbed. Since the liquid-in-tube sensor does not detect the light, an indication is made that there is liquid in the tubing.

The device of the present invention is therefore able to discriminate between air and liquid, regardless of whether the liquid is transparent or opaque. In addition, the inherent design of the present invention requires only a single light source and light sensor. In the preferred embodiment of the present invention, an additional sensor is used to compensate for LED performance degradation caused by temperature and ageing of the LED. This sensor may also be used to verify that the light source (the LED) is in fact operating properly and is emitting light. Another additional sensor is used to verify that the tubing is properly situated in the device. By using these additional sensors, the proper operation of the system is ensured.

The packaging of the system of the present invention is designed to be as size-efficient and easy-­to-use as possible. The system is packaged in a clamp which may be clipped on to the supply tubing near the fluid reservoir. The system of the preferred embodiment is geometrically designed to work on either of two sizes of tubing, both of which are commonly used in medication infusion applications. The detector may easily be clamped onto the tubing using only one hand, and is lightweight to allow the device to be supported by the tubing thereby not requiring additional support apparatus.

The device in the preferred embodiment is designed to be used with a medication infusion pump, and may be plugged into the main pump unit. Accordingly, the empty container detector of the present invention may be driven by the main pump unit, and need not itself contain a power supply or the apparatus to generate the audible or visible alarm from a signal indicating air in the tubing. Such apparatus, of course, could be added to make the detector a stand-alone device. In the preferred embodiment circuitry is included to minimise the power requirements of the detector by operating the system periodically rather than on a continuous basis. Finally, the system may also contain circuitry for compensating for LED degradation or varying ambient light conditions.

The present invention thus provides an empty container detection system which may be used with a conventional IV system, or (as in the preferred embodiment) in conjunction with an infusion pump unit. The system of the present invention is simple and easy to use, and can be clamped onto a fluid line immediately downstream from the fluid reservoir or container. The system is capable of immediately, accurately, and effectively detecting air in the fluid line regardless of whether the fluid being infused is opaque, translucent, or transparent. The system is fully automatic, not requiring any set up or intervention by an operator except clipping the device onto a line and plugging it in to the main pump unit or other controller.

Several other additional features are available in the design of the empty container detection system. One such feature is the ability to detect air bubbles whether the flow rate of the fluid in the line is fast or slow. In addition to being able to detect air in the fluid line, the system is also accurate, presenting a high degree of resistance to false alarms. It is also small in size and light so that it can be clipped onto the fluid line.

Despite the inclusion of all of the aforesaid features, the system of the present invention employs a minimum number of parts, all of which are of inexpensive construction, yet which afford the empty container detector system of the present invention the high degree of accuracy which must be retained. The system of the present invention is also able to compete economically with known systems, and it provides an ease of use rivalling the best known systems. The system accomplishes all these objects in a manner which will retain and enhance all of the advantages of reliability, durability, and safety of operation, and overcomes the limitations of the background art without incurring any relative disadvantage. All the advantages of the present invention will result in an empty container detector having a number of advantages making it a highly desirable alternative to systems presently available.

The invention may be carried into practice in various ways and one embodiment will now be described by way of example with reference to the accompanying drawings: in which <ul id="ul0001" list-style="none"><li>Figure 1 is a perspective view of the empty container detector of the present invention clamped onto a segment of tubing in the fluid line of a medication infusion system;</li><li>Figure 2 is a side view of the empty container detector shown in Figure 1 with the tubing removed;</li><li>Figure 3 is an end view of the empty container detector shown in Figures 1 and 2;</li><li>Figure 4 is another end view of the empty container detector shown in Figure 1 to 3, partially cut away to illustrate the spring used to bias the clamp arm of the detector onto the tubing to retain the detector in position on the tubing;</li><li>Figure 5 is a sectional view of the empty container detector shown in Figures 1 to 4 without the device being attached to tubing;</li><li>Figure 6 is a view similar to Figure 5, but with a segment of tubing in the fluid line of a medication infusion system being mounted in the device;</li><li>Figure 7 is a partial sectional view of the base portion of the empty container detector shown in Figures 1 to 6 illustrating the geometric design of the device which allows it to work with two different sizes of tubing; and</li><li>Figure 8 is a block diagram of the operation of the system of the present invention.</li></ul>

Figure 1 shows an empty container detector 10 clamped on to a segment of tubing 12. The detector 10 includes a base portion 14, and a clamping arm 6 pivotally mounted onto the base portion 14. The pivot point of the camping arm 16 is at its centre where a pin 18 is used for the pivot mounting as best shown in Figure 2. The clamping arm 16 has a grip portion 20 at one end, and a clamping portion 22 at the other end.

Figure 3 shows the end of the detector 10 where the segment of tubing 12 is gripped. There is a V-­shaped recess 24 in the base portion 14 at that end of the detector 10 into which the segment of tubing 12 is placed. The clamping portion 22 of the clamping arm 16 includes a clamping segment 6 which is located directly over the V-shaped recess 24 and is used to retain the segment of tubing 12 in the V-shaped recess 24.

The clamping arm 16 is spring biased to urge the clamping segment 26 of the clamping arm 16 towards the V-shaped recess 24. Referring to Figure 4, a spring 28 is located between the grip portion 20 of the clamping arm 16 and the base portion 14, and urges the grip portion 20 of the claping arm 16 upwards away from the base portion 14. This bias causes the clamping arm 16 to tend to rotate, with the clamping portion 22 of the clamping arm 16 and the clamping segment 26 being urged downwards towards the V-shaped recess 24.

Referring generally to Figures 1 to 4, it will be appreciated that to clamp the empty container detector 10 onto the segment of tubing 12, the grip portion 20 of the clamping arm 16 is squeezed towards the base portion 14, forcing the clamping segment 26 away from the V-shaped recess 24. A portion of the segment of tubing 12 is placed in the V-shaped recess 24, and the grip portion 20 of the clamping arm 16 is released, allowing the spring 28 to force the clamping segment 26 down onto the top of the portion of tubing located in the V-shaped recess 24. The force with which the clamping segment 26 is urged onto the tubing 12 is great enough to retain it in position as shown in Figure 1, although if a cord 30 containing wires (not shown) to carry electrical signals to and from the empty container detector 10 is pulled sharply, the detector 10 will slide on the segment of tubing 12.

In the preferred embodiment, since the detector 10 is used to detect when fluid from a reservoir (not shown) is exhausted, the segment of tubing 12 that the empty container detector 10 would be mounted onto would be located as close as possible to the reservoir (not shown). However, since the detector 10 of the present invention could be used at any location as a bubble detector, it will be appreciated that the detector 10 could be located on tubing at various locations in the wide variety of different infusion setups possible.

Figure 5 shows some of the electronic components located inside the base portion 14. The bottom of the base portion 14 is closed with a back 32 to seal and protect the electronic components located therein. Located near the bottom of the inner portion of the base portion 14 is a circuit board 34, which contains a number of electrical components. Located near the top of the base portion 14 is an LED mounting block 36 having an LED 38, which is a light source, and three sensors.

The LED 38 is located on one side of the V-shaped recess 24, and will shine light through a channel 40 in the LED mounting block 36 across the V-shaped recess 24. Located beside the LED 38 is is an LED sensor 42 with a channel 44 in the block 36 allowing light from the LED 38 to reach the LED sensor 42. Located directly across the V-shaped recess 24 from the LED 38 is a tube/no tube sensor 46, with a channel 48 in the block 36 allowing light shining directly across the V-­shaped recess 24 from the LED 38 to reach the tube/no tube sensor 46. Located below the tube/no tube sensor 46 is a liquid-in-tube sensor 50, with a channel 52 leading downwards from the V-shaped recess 24 to the liquid-in-tube sensor 50.

Located at the V-shaped recess 24 and mounted onto the block 36 is a V-shaped filter 54, which acts to filter out extraneous light frequencies. In the preferred embodiment, the V-shaped filter 54 is a polysulphone filter, which allows only infrared (IR) light to pass, the LED 38 generates IR light, and the LED sensor 42, the tube/no tube sensor 46, and the liquid-in-tube sensor 50 all sense IR light. The LED mounting block 36 is supported above the circuit board 34 by a pair of leads 56 extending from the LED 38 to the circuit board 34, a pair of leads 58 extending from the LED sensor 42 to the circuit board 34, a pair of leads 60 extending from the tube/no tube sensor 46 to the circuit board 34, and a pair of leads 62 extending from the liquid-in-tube sensor 50 to the circuit board.

The basic operation of the empty container detector 10 of the present invention may be described with reference to Figure 6. The segment of tubing 12 is located in the V-shaped recess 24. The LED 38 generates light, which is detected by the LED sensor 42, which is used to compensate for fluctuations in the light level from the LED 38 caused by temperature variations and other factors including degradation in performance of the LED 38 due to ageing. In the preferred embodiment this is accomplished by using the LED sensor 42 to detect a particular light level which is less than the maximum light level, and by taking a reading at that time of the output of the liquid-in-­tube sensor 50. By doing so, it is ensured that the measurement of light taken by the liquid-in-tube sensor 50 will always be taken at a constant light level, which in the preferred embodiment occurs at a point when the light impulse from the LED 38 is falling off. In the preferred embodiment, the LED sensor 42 may also be used to confirm that the LED 38 is indeed generating light. If the LED 38 were to suddenly suffer a catastrophic failure, an alarm could then be provided.

If the segment of tubing 12 is properly located in the V-shaped recess 24, the light from the LED 38 will be refracted by the tubing 12, and will not reach the tube/no tube sensor 46. If the segment of tubing 12 is not located in the V-shaped recess 24, the light will reach the tube/no tube sensor 46, indicating that the segment of tubing 2 is not properly located in the V-­shaped recess 24. It should be noted that the presence or absence of fluid in the segment of tubing 12 is not relevant to whether or not the light from the LED 38 reaches the tube/no tube sensor 46. As will become apparent below, either way, if the segment of tubing 12 is properly located in the V-shaped recess 24, light from the LED 38 will not reach the tube/no tube sensor 46, thereby indicating that the segment of tubing 12 is properly located in the V-shaped recess 24.

When the segment of tubing 12 is properly located in the V-shaped recess 24, light from the LED 38 will be refracted by the other wall of the segment of tubing 12 in an upward direction through the wall of the segment of tubing 12 as shown in Figure 6. If this light encounters air (the term "air" is used generically to indicate an air bubble or greater quantities of air) in the segment of tubing 12, the light will be reflected off the inner wall of the segment of tubing 12 in a downward direction, with the light then being directed onto the liquid-in-tube sensor 50. It should be noted that a small proportion of the light will be refracted by the segment of tubing 12, and reflected off the opposite side of the inner diameter of the tubing 12, but this proportion is not significant in the sense that it is insufficient to operate the liquid-in-tube sensor 50. The angle at which light is reflected off of the inner wall of the tubing 12 is critical, since it must be selected to direct the light so that it will reach the liquid-in-­tube sensor 50. Accordingly, if the liquid-in-tube sensor 50 detects light it is an indication that air is contained in the segment of tubing 12.

If transparent fluid is contained in the segment of tubing 12, light from the LED 38 which is refracted by the outer wall of the segment of tubing 12 in an upward direction through the wall of the tubing 12 will continue in that direction as indicated by the dotted line. In this case, the light will not reach the liquid-in-tube sensor 50, indicating that there is liquid in the segment of tubing 12. If opaque fluid is contained in the segment of tubing 12, light from the LED 38 which is refracted by the outer wall of the segment 12 in an upward direction through the wall of the tubing 12 will be directed into the opaque fluid, and will be substantially absorbed. Again, the light will not reach the liquid-in-tube sensor 50, indicting that there is liquid in the segment of tubing 12. In the case of a translucent fluid, of course, part of the light will be absorbed by the fluid and part will pass through the fluid, but substantially no light will reach the liquid-in-tube sensor 50.

Clearly, therefore, the direction of reflection (and refraction) of the light in tubing containing air is dependent upon the geometry of the device. In other words, the geometry of the device is designed to direct light onto the liquid-in-tube sensor 50 when air is contained in the segment of tubing 12. Referring now to Figure 7, two sizes of tubing are illustrated in dotted lines namely, a larger tubing 12A and a smaller tubing 12B, with the two sizes 12A and 12B representing the two sizes of tubing used most frequently in the field of medication infusion. By designing the configuration and size of the V-shaped recess 24, the thickness of the V-shaped filter 54, and the relative locations of the LED 38 and the liquid-in-tube sensor 50, the empty container detector 10 will work indentically for the two different sizes of tubing 12A and 12B. It may also be noted that the clamping action of the clamping segment 36 (Figures 1 to 6) may act to distort somewhat the shape of the segment of tubing 12, and this factor may enter into the geometric design of the device.

It is apparent from Figure 7 that the outer diameters of the tubing 12A and the tubing 12B largely coincide at the points at which light would enter the tubing from the V-shaped filter 54 and at the point at which light would leave tubing containing air and enter the V-shaped filter 54 on is way to the liquid-in-tube sensor 50. Similarly, the inner diameters of the tubing 12A and the tubing 12B are relatively located so as to reflect light off their inner walls at the same critical angle to direct the light onto the liquid-in-­tube sensor 50.

Figure 8 is a block diagram of the circuit used by the empty container detector 10 of the present invention. It will be appreciated that the electronic components 10 not already specifically described are all mounted on the circuit board 34. A main pump unit 64 is used in conjunction with the detector 10 of the present invention. (It will be appreciated by those skilled in the art that the electronic components could alternatively be mounted in the main pump unit 64 instead of inside the detector 10 on the circuit board 34). The main pump unit 64 supplies power to the detector 10 via a V wire and a ground or earth connection. It should be noted that the various components of Figure 8 are connected to +V and ground, although these connections are not expressly shown in Figure 8.

Other connections between the main pump unit 64 and the empty container detector 10 include a trigger signal, an I.D. signal, and an alarm signal. These five connections between the main pump unit 64 and the empty container detector 10 would be contained in the cord 30 (Figures 1 and 2) extending from the empty container detector 10. The I.D. Signal is optional and in the preferred embodiment I.D. circuitry 66 is used to indicate to the main pump unit 64 either that the cord 30 from the detector 10 is properly connected to the main pump unit 64, or the type of device which is plugged in to the main pump unit 64.

In the former case, the I.D. circuitry 66 need only feed the +V signal back to the main pump unit 64 as the ID signal to indicate that the detector 10 is properly connected to the main pump unit 64. As such, if the main pump unit 64 does not detect +V on the I.D. Signal line, it will be an indication that the detector 10 is not properly connected to the main pump unit 64. In the latter case, the I.D. Circuitry 66 includes a resistor (not shown), with the size of the resistor indicating to the main pump unit 64 (by the returning current) which particular device is plugged into the main pump unit 64. For example, three different resistances could be used in three different devices which may be plugged into the main pump unit 64, with one of these three different devices being the detector 10 of the present invention.

Firing circuitry 68 is included in the empty container detector 10 to conserve power. Rather than having the LED 38 on all the time, it may be strobed periodically by the firing circuitry 68 in response to the trigger signal from the main pump unit 64. The rate at which the LED 38 is strobed depends upon several factors, including tubing size and maximum flow rear. In the preferred embodiment, the rate is sufficiently fast to prevent an air bubble from moving through the segment of tubing 12 without being detected.

The tube/on tube sensor 46 supplies an output to an inverting amplifier 70, which in turn provides an output which is the Data (D) input to a first D flip-­flop 72. The Direct Reset (R) and Direct Set (S) inputs of the first D fli+p-flop 72 are both inactive (tied to ground). The LED sensor 42 supplies an output to an inverting amplifier 74, which in turn provides an output which is the Clock signal for both of the first D flip-flop 72 and a second D flip-flop 76. In the preferred embodiment the Clock signal occurs when the signal from the LED sensor 42 has decayed to a predetermined light level which is less than the maximum light level. This is accomplished by using the inverting amplifier 74 to provide the CLock signal when the decaying signal from the LED sensor 38 has dropped to the predetermined level, causing the system to take a reading of the liquid-in-tube sensor 50 at that time. This operation ensures that the measurement of light taken by the liquid-in-tube sensor 50 will always be taken at constant light level, which in the preferred embodiment is the point at which the light impulse from the LED 38 has fallen off to the predetermined level. The Q output from the first D flip-flop 72 is supplied to the second D flip-flop 76 as the R input. The liquid-in-tube sensor 50 supplies an output to an inverting amplifier 78, which in turn provides an output which is the D input to the second D flip-flop 76 . The S input to the second D flip-flop 76 is inactive (grounded). Finally, the Q output of the second D flip-flop 76 is supplied to the main pump unit 64 as the alarm signal.

Although those skilled in the art will readily understand the operation of the system described above, it may be helpful to add a brief description of the operation of the circuit of Figure 8. First, with regard to to the output of the inverting amplifier 74, which is the Clock input to the first D flip-flop 72 and the second D flip-flop 76, when the LED 38 is pulsed and the light is detected by the LED sensor 42, the output of the inverting amplifier 74 will go low. When the light from the LED 38 diminishes, the output of the inverting amplifier 74 will go high, causing the first D flip-flop 72 and the second D flip-flop 76 to cycle. The Clock pulse from the inverting amplifier 74 will go high when the light level from the LED 38 has dropped to the preselected level. By operating the Clock in this manner, the circuit will be operational with the light level at a uniform, preselected level, thereby eliminating problems due to ambient light, thermal and age degradation of the LED 38, and supply voltage variations.

If the output from the tube/no tube sensor 46 is high (indicating that the segment of tubing 12 is not properly installed), the output from the inverting amplifier 70 and the D input to the first D flip-flop 72 will be low. If the D input to the first D flip-­flop 72 is low, then the Q output from the first D flip-flop 72 will be high . The Q output from the first D flip-flop 72 is the R input to the second D flip-flop 76, and if the R input to the second D flip-­flop 76 is active (high), the Q output of the second D flip-flop 76 is always inactive (low). For the preferred embodiment of the present invention, a low Q output from the second D flip-flop 76 will cause an alarm. It is therefore apparent that if the output of the tube/no tube sensor 46 is high, an alarm will be sounded regardless of the state of the liquid-in-tube sensor 50.

The reasons for having a low Q output from the second D flip-flop 76 cause an alarm instead of a high level causing an larm is that if the connection between the empty container detector 10 and the main pump unit 64 were broken, the alarm signal input to the main pump unit 64 would be low. It is therefore a sound design to use a low output from the second D flip-flop 76 as an alarm state.

If the output of the tube/no tube sensor 46 is low (indicating the segment of tubing 12 is properly installed), the output Q of the first D flip-flop 72 will be inactive (low). In this case, the state of the liquid-in-tube sensor 50 will determine whether or not an alarm is sounded. If the output of the liquid in the tube sensor 50 is high (indicating that air is in the segment of tubing 12), the output of the inverting amplifier 78 will then be low. The output of the inverting amplifier 78 is the D input to the second D flip-flop 76, and if the D input to the second D flip-­flop 76 is low, the Q output of the second D flip-flop 76 will be low, causing an alarm.

If, with the output of the tube/no tube sensor 46 still low (indicating the segment of tubing 12 is properly installed), the output of the liquid-in-tube sensor 50 is high (indicating that no air is contained in the segment of tubing 12), the output of the inverting amplifier 78 is high. Accordingly, the D input to the second D flip-flop 76 is high, and the Q output of the second D flip-flop 76 will be high, and no alarm will be sounded.

Of course, it will be appreciated by those skilled in the art that the circuit of Figure 8 represents only one of a number of different circuits which could be used to achieve the same result. The important thing is that; 1. wherever the output of the tube/no tube sensor 46 is high, an alarm be sounded (indicating that the segment of tubing 12 is not properly installed); and 2. when the output of the tube/no tube sensor 46 is low, an alarm is sounded when the output of the liquid-­in-tube sensor 50 is high.

It will be appreciated that a visual alarm mechanism and/or an audible alarm mechanism is contained in the main pump unit 64. For example, the visible alarm mechanism could be a flashing light or a word on a screen indicating an alarm, and the audible alarm mechanism could be a buzzer, horn, or electrically generated tone. These mechanisms could of course alternatively be contained in the empty container detector 10 itself. Likewise, the power supply and oscillator means to generate the trigger signal could also be contained in the empty container detector 10 itself. These modifications are considered to be within the scope of the present invention, although they are not the preferred embodiment.

It may be perceived that the present invention provides an empty container detection system which is simple and easy to use, clamping onto a fluid line immediately downstream from the fluid reservoir container. The system is capable of quickly, accurately and effectively detecting air in the fluid line regardless of whether the fluid being infused is opaque, translucent, or transparent.