WO2006013312A1

WO2006013312A1 - A fluid detector and alarm system

Info

Publication number: WO2006013312A1
Application number: PCT/GB2005/002074
Authority: WO
Inventors: Andrew Chung-Ming Chu
Original assignee: University College London Hospitals Nhs Foundation Trust
Priority date: 2004-08-04
Filing date: 2005-05-26
Publication date: 2006-02-09
Also published as: GB0503769D0; GB0417337D0; GB2416837A

Abstract

A fluid detector comprising a support, a radiation emitter device mounted on the support and adapted to emit radiation along a first axis, a radiation receiver device mounted on the support and adapted to receive radiation, emitted from the radiation emitter device, along a second axis, the first and second axes being substantially parallel but mutually laterally offset and a detection zone located between the radiation emitter device and the radiation receiver device, the detection zone being arranged to receive therein a tubular conduit containing fluid to be detected whereby, in use, radiation emitted from the radiation emitter device along the first axis may be received by the radiation receiver device along the second axis as a result of a particular degree of refraction of the radiation by the tubular conduit and fluid contained therein.

Description

A FLUID DETECTOR AND ALARM SYSTEM

This invention relates to a fluid detector, and in particular to such a system for detecting the presence of a first fluid phase within an administrative system for a second fluid phase. Most particularly, the invention relates to such a system for detecting the presence of air in a liquid administrative system such as those used in the intravenous infusion of fluid in critically ill patients, or to such a system for detecting the presence of liquid within an air-filled system, and for triggering an alarm if air or liquid is inadvertently present in the system.

In clinical intervention, it is often necessary to infuse fluid such as saline, etc. into a patient intravenously. Care must be taken to exclude air bubbles within the fluid filled system otherwise adverse conditions may arise. For example, a small air bubble may accidentally enter into the bloodstream (e.g. via a vein) and eventually becoming lodged in the fine blood vessels in the lungs (e.g. pulmonary embolism). In most critical care equipment, special air bubble detectors are already incorporated. In other situations whereby air bubble detection is required as an additional safeguard, an independent 'stand-alone' bubble detector system would be very useful. Currently, third party systems are available that use ultrasonic waves to detect the presence of air bubbles, but these are expensive and hence prohibitive for wider applications.

Infra-red light offers a cheaper alternative to ultrasound, and has been used to detect air bubbles within a fluid administrative set in the past, both by using transmission and by reflective method. The detection ability of these systems was very often limited, due to the poor differentiation between air and fluid media. For example, US-A-4366384 discloses an air bubble detector which has a pair of detector heads serially disposed along a transparent conduit through which fluid is passed in use. Each detector head comprises an infra-red radiation source, a first infra-red detector adapted to receive direct infra-red radiation and a second infra-red detector adapted to receive reflected infra-red radiation. A logic circuit compares the signals from the two detectors and when one detects a high level of radiation and the other detects a low level of radiation a signal is emitted to indicate that an air bubble is in the conduit. As well as having poor detection ability, this detector requires plural detectors and complicated electronic circuitry, which increases the cost and complexity of the unit.

FR-A-2660755 discloses an apparatus and method for detecting bubbles in a tube. A light source projects a light beam through the tube and a detector is disposed on the other side of the tube. The light is emitted orthogonal to the tube axis. Analysis of light reaching the detector reveals the presence or absence of bubbles. A second light source/detector pair is provided to yield a reference signal. A mounting block to hold the light source/detector pair in a fixed relative position is disclosed. This system requires plural light source/detector pairs and so is relatively complex. It is also not particularly versatile for medical applications.

WO-A-86/04409 discloses a device for detecting the presence or absence of a liquid in a vessel. A light source projects a light beam through the tube and a detector is disposed on the other side of the tube. The light is emitted orthogonal to the tube axis. Analysis of light reaching the detector reveals the presence or absence of liquid. A platform to hold the light source/detector pair is disclosed. The platform can adjust the positions of the light source and the detector to accommodate tubes of different diameter and to vary the distance between the centre line of the tube and the path of the incident light beam form the light source, thereby to vary the sensitivity of the device. This system is relatively complex to operate so as to obtain accurate results readily for a variety of tubes and is not particularly versatile for medical applications.

WO-A-97/19718 discloses an optical detector for air in a fluid line. The fluid line is shaped as a prism. An optics block with a V-shaped recess and a clamp block cooperatively deform the tube into the prism shape. A photoemitter as a light source projects a light beam through the tube and a photosensor as a detector is disposed on the other side of the tube. The light is emitted orthogonal to the tube axis. The photoemitter and photosensor are mounted on a U-shaped optical interrupter. The clamp block windows the emitted and received light from the interrupter to minimise optical noise. Analysis of light reaching the detector reveals the presence or absence of liquid. This system does not obtain accurate results readily for a variety of tubes and is not particularly versatile for medical applications. US-A-4952055 discloses a differential refractometer for measuring the refractive index of fluid to determine the concentration of solute in the fluid. It is not concerned with bubble detection in the fluid.

US-A-5960129 disclose a bubble detector/direction sensor that like US-A-4366384 has a pair of detector heads serially disposed along a transparent conduit through which fluid is passed in use. The light is emitted orthogonal to the conduit axis.

JP-A-11030547 discloses a liquid level detecting apparatus for a pipeline. This cannot be used to detect the presence of bubbles in a tube for medical applications, e.g. for an IV administration set.

US-A-4857050 discloses an air-in-line detector for an IV administration set which determines the relative intensity of light incident on two sensors. Like US-A-4366384, the system is relatively complicated.

The present invention aims to provide a fluid detector that at least partially overcomes the detection problem of known fluid detectors, in particular known air-bubble detectors.

The present invention also aims to provide a fluid detector that is simple in construction and operation, and has a lower cost and complexity than known fluid detectors, in particular known air-bubble detectors, and is portable.

The present invention accordingly provides fluid detector comprising a support, a radiation emitter device mounted on the support and adapted to emit radiation along a first axis, a radiation receiver device mounted on the support and adapted to receive radiation, emitted from the radiation emitter device, along a second axis, the first and second axes being substantially parallel but mutually laterally offset and a detection zone located between the radiation emitter device and the radiation receiver device, the detection zone being arranged to receive therein a tubular conduit containing fluid to be detected whereby, in use, radiation emitted from the radiation emitter device along the first axis may be received by the radiation receiver device along the second axis as a result of a particular degree of refraction of the radiation by the tubular conduit and fluid contained therein, the detection zone having a longitudinal axis along which the tubular conduit is disposed when in the detection zone and the first and second axes being each at an angle of from 15 to 45 degrees to the longitudinal axis, and at least one of the radiation emitter device and the radiation receiver device being movably mounted on the support in a predetermined direction whereby a spacing between the radiation emitter device and the radiation receiver device can be selectively varied, the predetermined direction corresponding to a particular angle of refraction through a tubular conduit containing fluid whereby tubular conduits of different diameter may be selectively disposed in the detection zone between the radiation emitter device and the radiation receiver device.

This angular arrangement between the first and second axes and the tube orientation can provide the improvement, as compared to known structures of the prior art bubble detectors where the incident light is orthogonal to the tube length, of more positive discrimination between liquid and air, particularly when accommodating different tube diameters, and consequently more positive and reliable detection of the presence of a bubble using just one emitter/receiver pair and not requiring a further pair to provide a reference or second reading.

Preferably, the radiation emitter device comprises an infra-red emitter and a first collimator for emitting collimated infra-red radiation along the first axis and the radiation receiver device comprises an infra-red receiver and a second collimator for receiving collimated infra-red radiation along the second axis.

Preferably, the predetermined direction is the first axis for the radiation emitter device when the radiation emitter device is movably mounted on the support and the second axis for the radiation receiver device when the radiation receiver device is movably mounted on the support.

Preferably, each housing has an end face transparent to the radiation from the emitter device, the two end faces are mutually parallel, and between the end faces the tubular conduit may be in use disposed, with the end faces contacting opposed longitudinal sides of the tubular conduit. Preferably, one of the radiation emitter device and the radiation receiver device is fixedly mounted on the support.

The fluid detector may further comprise a holder for holding the tubular conduit in the detection zone, the holder being mounted on the support and comprising first and second holder parts which are mutually relatively movable towards and away from each other, the first holder part containing the radiation emitter device and the second holder part containing the radiation receiver device.

Preferably, one of the first and second holder parts is movable towards and away from the other of the first and second holder parts which is fixed on the support, and further comprising a biasing device for biasing the movable holder part towards the fixed holder part.

The fluid detector may also further comprise a manual actuator for moving the movable holder part away from the fixed holder part against the bias of the biasing device.

Preferably, each of the first and second holder parts has a respective part-cylindrical elongate cavity therein and the two part-cylindrical elongate cavities are mutually opposed so as to define a generally cylindrical cavity for receiving a tubular conduit.

The fluid detector may further comprise an alarm connected to the radiation detection device.

The fluid detector may further comprise a transmitter connected to the radiation detection device for transmitting an alarm signal to a remote receiver.

Preferably, the transmitter is adapted to transmit an identifying signal and the remote receiver is a multi-channel receiver adapted to receive plural identifying signals from respective transmitters of a plurality of fluid detectors.

The fluid detector may further comprise a tube clamp for clamping a tubular conduit so as to prevent fluid flow therethrough, the tube clamp being directly or indirectly operable in response to a signal, or absence of a signal, from the radiation detection device.

Preferably, the tube clamp comprises a pair of clamping elements between which the tubular conduit is, in use, located.

The fluid detector may be in combination with a tubular conduit capable of being received in the detection zone, the tubular conduit comprising at least a part of an intravenous infusion set.

The fluid detector may further comprise control circuitry for operating the radiation emitter device and the radiation receiver device, at least one battery for providing electrical power to the control circuitry, and a switched regulator for increasing the voltage supplied to the control circuitry from the at least one battery.

The present invention also provides a method of detecting fluid in a tubular conduit, the method comprising disposing a tubular conduit containing fluid to be detected into the detection zone of the fluid detector according to any foregoing claim, emitting radiation from the radiation emitter device along the first axis so as to be incident on the tubular conduit containing fluid, and determining whether or not the radiation receiver device receives the radiation along the second axis following refraction of the radiation by the tubular conduit containing fluid, the radiation emitter device and the radiation receiver device being mutually disposed so that the radiation receiver device receives radiation from the radiation emitter device when fluid of a first phase within the tubular conduit is located therebetween and so that the radiation receiver device fails to receive radiation from the radiation emitter device when fluid of a second phase within the tubular conduit is located therebetween.

One preferred method is for detecting gas bubbles in a liquid, wherein the first phase is a liquid and the second phase is a gas. Another preferred method is for detecting liquid drops in a gas, wherein the first phase is a gas and the second phase is a liquid.

In either preferred method, preferably an alarm signal is generated when the radiation receiver device does not receive radiation from the radiation emitter device.

The present invention further provides a sensor comprising of an infrared emitter and a detector, accurately positioned on either side of a clear/translucent tube, such that the collimated incident light from the emitter is transmitted into the tube at an angle less than 45 degrees from the normal (i.e. perpendicular), the detector is positioned on the other side of the tube, such that the emerging light beam is in parallel with the incident beam, but slightly offset from the original axis, and the exact geometry and positioning of the emitter and detector pair is such that the detector receives the transmitted beam after it has been refracted by the fluid medium inside the tube.

Preferably, the detector is positioned to detect the light beam only if no refraction takes place inside the tube.

Preferably, either the emitter or the detector is mounted on a spring-loaded actuator, which is mounted at an angle to the tube and maintains correct beam geometry for light detection when different tube sizes are used.

Preferably, the sensor is used together with accompanying signal processing electronics to form an 'air' or 'air-bubble' detection system in a fluid-administrative setup.

Preferably, the sensor is used together with accompanying signal processing electronics to form a 'fluid' detection system.

Preferably, the sensor utilizes the property of the refraction of light within a medium to detect the presence or absence of this medium in a clear or translucent tube or any other suitable vessel.

Preferably, the sensor is used together with accompanying electronic circuits to provide visual and audible warnings when 'alarm' conditions are detected.

Preferably, the sensor sends a warning signal to a remote station during 'alarm' condition by means of electrical wires or wirelessly using optical or radio-frequency signals. Preferably, the sensor is powered by battery and allows portability and ambulatory use.

Preferably, the sensor is self-contained and can be operated independently of other equipment.

In accordance with the invention, an infrared emitter and receiver pair is used to transmit and receive a collimated light beam through an administrative set, except that the light path is arranged so that it is not perpendicular to the tube, as in known configurations, but at an angle away from the normal. Due to the refraction property of light in different media, the light beam within the fluid medium will become refracted and emerges on the other side of the tube into air at an angle similar to the incident beam but with the light path shifted from the incident beam.

By positioning the detector to accept the refracted light beam in a fluid medium, the detection and discrimination of air bubbles in a liquid medium, or liquid drops in a gas such as air, can be much enhanced.

The present invention has particular application for detecting the presence of air bubbles in a liquid administrative system, for example used for the intravenous infusion of fluid to patients. Similarly, the detector system of the invention can be used to detect the presence of liquid within an air-filled tubing in other applications. As an example, one such application is the detection of urine flow in urodynamics/ ambulatory urodynamics, for a male patient wearing a sheath.

An accompanying processing unit senses the air/liquid signal and sets up an alarm condition as necessary, both visually and audibly, to warn users of the condition, or to write the data in recording media for flow synchronisation etc.

The advantage of detector system of the invention is that it is simple but reliable, and low cost. Due to the simplicity in design, the complete system can be packaged into a small portable unit. With low component count and the use of low power devices, the unit can also be made to be battery operated, allowing monitoring to be carried out in most situations.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic drawing of to an infra-red fluid detector and alarm system in accordance with a first embodiment of the present invention;

Figures 2a and 2b illustrate schematically the principle of operation of the infra-red fluid detector and alarm system of Figure 1;

Figure 3 is a schematic drawing which shows the scientific principles on light refraction on which the present invention is predicated;

Figure 4 is a schematic drawing of a tube-clamping device for an infra-red fluid detector and alarm system in accordance with the present invention;

Figure 5 is a schematic side view, partly in phantom, of a further embodiment of an infra-red fluid detector and alarm system in accordance with the present invention which comprises a tube holder, with the tube holder being disposed in a closed position;

Figure 6 is a schematic top view of the infra-red fluid detector and alarm system of Figure 5;

Figure 7 is a schematic side view of the infra-red fluid detector and alarm system of Figure 5 with the tube holder being disposed in an open position;

Figure 8 is a schematic side view of the infra-red fluid detector and alarm system of Figure 5 with the tube holder being disposed in a position holding a tube;

Figure 9 is a schematic view of a voltage regulator, in a first operational half-cycle, for use in a further embodiment of the infra-red fluid detector and alarm system of the present invention; and Figure 10 is a schematic view of the voltage regulator of Figure 9 in a second operational half-cycle.

Referring to Figure 1, there is shown a schematic block diagram of an infra-red fluid detector and alarm system, generally designated as 2, in accordance with a first embodiment of the present invention. An infra-red (IR) radiation emitter 4, comprising a light emitting diode (LED) is connected between ground (0 volts) and a resistor 6, and the resistor 6 is in turn connected to a first terminal 10 of a microcontroller 8. An infra¬ red (IR) radiation receiver 12, comprising an IR sensitive photocell, is connected between ground (0 volts) and a resistor 14, and the resistor 14 is in turn connected to a source 16 of positive voltage (+ volts). A second terminal 18 of the microcontroller 8 is connected between the receiver 12 and the resistor 14. A local alarm 20, capable of generating an audible and/or visual alarm signal to alert the user, is connected to a further terminal 22 of the microcontroller 8. The microcontroller 8 is connected via respective terminals 24, 26 to a remote alarm 28 and to a radio frequency (RF) transmitter 30. The transmitter 30 can transmit a warning signal wirelessly using modern radio frequency techniques to a remote receiver 32. hi a modification of the embodiment, either or both of the remote alarm 28 and the transmitter 30 may be omitted. The local alarm 20 may be omitted if at least one of the remote alarm 28 and the transmitter 30 is provided. The detector and alarm system 2 is powered from a battery 34, via an on/off switch 36. A switched regulator 38, connected between the on/off switch 36 and another terminal 40 of the microcontroller 8, is used to provide the necessary power for normal functioning of the detector and alarm system 2.

A first slit collimator 42 is disposed adjacent the infra-red (IR) radiation emitter 4 and is configured to collimate IR radiation therethrough. A housing (not shown) may be provided to prevent IR radiation emission from other than through the first collimator 42. Correspondingly, a second slit collimator 44 is disposed adjacent the infra-red (IR) radiation receiver 12 and is configured to receive collimated IR radiation therethrough emitted from the first slit collimator 42. A housing (not shown) may be provided to prevent IR radiation reception from other than through the first collimator 42 The two collimators 42, 44 are juxtaposed so as to define therebetween a detection zone 46. The detection zone 46 is arranged to receive and support a portion of a tubular conduit 48, the fluid contents 50 of which are periodically inspected using the IR radiation. The collimators 42, 44 are parallel to each other, but their axes 52, 54 are offset.

The principle of operation of the detector will now be described with reference to Figures 2a and 2b and Figure 3.

Referring to Figures 2a and 2b, a liquid medium 56 is carried along a clear, IR transparent, tubular conduit 48 which may be flexible and may form part of a standard clinical fluid administrative set or a collecting tube. The slit collimators 42, 44 are located in front of the infrared emitter 4 and the infrared receiver 12 respectively. The infrared emitter 4 and first slit collimator 42 are disposed in an emitter housing 58 having an end face 60 which permits transmission of IR radiation therethrough. The end face 60 is inclined at an acute angle x degrees to the direction of radiation emission from the collimator 42. The infrared receiver 12 and second slit collimator 44 are disposed in a detector housing 62 having an end face 64 which permits transmission of IR radiation therethrough. The end face 64 is inclined at the same acute angle x degrees to the direction of radiation reception by collimator 42. The two end faces 60, 64 are therefore parallel. In this embodiment, the end faces 60, 64 are configured to squeeze a portion 66 of the tubular conduit 48 therebetween, so as to ensure a high degree of radiation coupling between the end faces 60, 64 and the wall 70 of the tubular conduit 48.

The angle x degrees between the optical axis of each collimator 42, 44 and the axis of the tubular conduit 48 is selected so that it is less than the angle which would otherwise cause total internal reflection of the infra-red radiation in the wall of the tubular conduit 48. Typically, the angle is from 15 to 45 degrees, most typically from 30 to 40 degree. The slit of each collimator 42, 44 typically has a width of from 0.5 to 1 mm. Typically, the emitter housing 58 and the detector housing 62 are mutually spaced so as to be able to receive therebetween a tubular conduit 48 having an external diameter of from 4 to 8 mm, most typically 6 mm, with a corresponding internal diameter of from 3 to 7 mm, and a wall thickness of about 0.5 mm. These dimensions may be varied. The emitter housing 58 and the detector housing 62 may be configured so as to be relatively movable so as to be able to accommodate different diameter tubular conduits. Figure Ia shows the IR radiation beam 68 from the infrared emitter 4, collimated by the collimator 42, then refracted by the liquid medium 56 in, and flowing through, the administration set, and then falling onto the infrared receiver 12. Accordingly, the exiting light beam 74 passes through the second collimator 42 and consequently is detected by the infrared receiver 12. This generates a radiation detection signal. Therefore the presence of liquid in the tubular conduit 48 between the two end faces 60, 64 results in a positive detection signal.

However, in contrast when air, in the form of a bubble 72 for example, is present between the two end faces 60, 64 as shown in Figure Ib, refraction of the IR radiation beam 68 by the air bubble 72 within the tubular conduit 48 is much reduced as compared to refraction by the liquid medium 52. Accordingly, the exiting light beam 76 misses the second collimator 42 and consequently is not detected by the infrared receiver 12. A detection signal is therefore not generated by the infrared receiver 12.

The theory of operation of the present invention is described below.

The refractive index for a given pair of materials ('A' and 'B') is a constant, and is defined as the ratio:

Speed of light in 'A'

Speed of light in 'B'

In vacuum, the refractive index is by definition to be 1. In air, the refractive index is very close to 1, and in other materials such as water, the refractive index is 1.33, and in glass, 1.5, etc.

Referring to Figure 3, when a beam of light enters from air into a second medium, such as water, there is a significant change in the speed of light (refraction). Depending on the angle of incidence (i) of the light beam entering the water, the angle of the refracted light beam (r) within the water will be different. Similarly, refraction of light occurs when the light beam emerges from water into air, and the angle of the emerging beam into air will be the same as the incident beam before entering into the water, but the path of the light beam will become shifted (s).

For a beam of light in air entering a medium at an angle of incidence (i), the direction of the beam will become refracted according to the equation:

sin i = n x sin r where n = refractive index of the medium i = angle of incidence r = angle of the refracted beam

At an incidence angle of 40 degrees in air, the refracted beam angle will be just under 29 degrees for water. On exit from water to air, the emerging beam will be similarly refracted, with the angle of refraction (in air) equal to 40 degrees, parallel to the beam before entering water, but shifted by a distance (s). Similarly, in accordance with the present invention, refraction also occurs at the interface between air and the plastic material of the tubular conduit of an infusion set, but due to the thin wall thickness, the overall change is negligible.

The overall optical path shift increases with the increase in the thickness T of the liquid medium, which depends on the diameter of the tubular conduit. In the absence of liquid inside the tubular conduit, the shift will be reduced to the effect of the wall thickness of the tubular conduit of the infusion set only, and the optical path shift will be very small.

By using a collimated beam and arranging the geometry of the IR emitter 4 and the IR receiver 12 in the way described hereinabove, a radiation signal is positively obtained whenever there is liquid 52 present in the tubular conduit 48, and no signal when liquid is absent in the portion 66 of the tubular conduit 48 between the IR emitter 4 and the IR receiver 12.

In contrast, if the IR receiver 12 is configured to detect the undesired presence of liquid, for example in the form of drops, in a tubular conduit 48 containing air, then the IR emitter 4 and IR receiver 12 and their respective collimators 42, 44 would be configured to provide a positive radiation signal when air is present, and no signal when liquid is present. This would be achieved by modifying the relative orientation of the IR emitter 4 and IR receiver 12 and their respective collimators 42, 44 as compared to the arrangement in Figures 1 and 2.

The emitter and detector would be mutually oriented in either case so as to provide a failsafe warning signal should the emitter and/or the detector fail, thereby providing a "no" signal.

Referring back to Figure 1, in operation, the infra-red (IR) radiation emitter 4 is periodically powered to emit IR radiation in a succession of detection cycles. The infra¬ red (IR) radiation emitter 4 is powered on by the microcontroller 8 just before a measurement sample is taken. The signal from the receiver 12 is processed and fed into the microcontroller 8, which monitors for the presence or absence of the radiation signal, and determines whether air or liquid is present inside the tubular conduit 48. In air bubble detection, the presence of air in the tubular conduit 48 represents an 'alarm' condition, and the microcontroller 8 then correspondingly generates an audible and/or visual alarm by local alarm 20 to alert the user, i.e. the patient to whom the infusion set is connected. As well as providing the alarm locally by local alarm 20, the microcontroller 8 may also transmit the 'alarm' signal as a warning signal to a remote alarm 28 at a nurses' station either via a cable, or wirelessly using modern radio frequency techniques, i.e. using a RF transmitter 30 and complementary receiver 32.

Discrimination between the presence of air or liquid within the tube is by the presence or absence of the radiation signal. Therefore, this is a much more positive and reliable way of detection compared to some other previous methods using infra-red components.

A tube-clamping device may also be incorporated, either locally together with the detector and alarm system, or remotely positioned but receives the warning signal from the transmitter and clamps the fluid administrative tube whenever the 'alarm' condition is triggered. Such a tube-clamping device is illustrated in Figure 4.

In the embodiment illustrated, the receiver 32 is connected to a microcontroller 80. The microcontroller 80 is driven by a power supply 82 and is connected to an audio and/or visual local alarm 84. The microcontroller 80 is also connected to a further alarm 86 at a nurses or control station. The microcontroller 80 is further connected to a tube-clamping device 88 comprising two mutually spaced clamping elements 90, 92, at least one of which is reciprocably movable towards the other. The two clamping elements 90, 92 have the tubular conduit 48 disposed therebetween.

When the receiver 32 receives a signal from the transmitter 30 that air is inadvertently present in the liquid-containing tubular conduit 48 (or conversely that liquid is inadvertently present in the air-containing tubular conduit 48), the microcontroller 80 actuates the tube-clamping device 88 so that the tubular conduit 48 is squeezed between the two clamping elements 90, 92. This clamps the tubular conduit 48 so as to prevent any further fluid flow therethrough.

The tube-clamping device 88 is configured so that the two clamping elements 90, 92 are urged automatically to a closed clamping position when the tube-clamping device 88 is turned off. This provides a failsafe clamping action in the event that the tube-clamping device 88 fails. The two clamping elements 90, 92 may also be urged automatically to a closed clamping position when the tube-clamping device 88 fails to receive a signal from the infra-red fluid detector and alarm system 2. When the tube-clamping device 88 is turned on, the two clamping elements 90, 92 mutually separate to a preset separation distance, which is larger than the diameter of a desired tubular conduit 48, by movement of one or both of them so that the tubular conduit 48, if not already present, may be disposed between two clamping elements 90, 92.

Preferably, the receiver 32 is adapted to constitute a multi-channel device which supports a plurality of, for example eight, individual infra-red fluid detector and alarm systems 2. Each individual infra-red fluid detector and alarm system 2 is provided with a dedicated channel, for example selected using a series of dual inline (DIL) switches. The signal emitted from the respective RF transmitter 30 therefore includes a coded identifier of the respective infra-red fluid detector and alarm system 2. In this way, medical personnel monitoring the receiver 32 are able to monitor plural systems simultaneously, for example for a number of patients on a single ward, and when a warning signal is emitted, this can readily be associated with the correct system. The receiver 32 may be provided with a set of lights for each system, for example an ON light indicating that the respective system is switched on and functioning, and transmitting, properly, and a WARNING ALARM light indicating an alarm state of a respective system.

The infra-red fluid detector of Figures 1 and 2 may be incorporated into a tube holder for holding the tubular conduit. An embodiment of such a tube holder is illustrated in Figures 5, 6, 7 and 8.

Figure 5 is a schematic side view, partly in phantom, of the tube holder disposed in a closed position and Figure 6 is a top view of the tube holder of Figure 5. The tube holder 100 comprises a casing 102 on which is mounted a fixed tube holding element 104 and a movable tube holding element 106. The two tube holding elements 104, 106 are adjacent and face each other with respective tube holding faces 108, 110. Each tube holding face 108, 110 has an elongate part-cylindrical cavity 112 extending therealong. The two elongate part-cylindrical cavities 112 are aligned and together define a generally cylindrical cavity 114 between the two tube holding elements 104, 106. As shown in phantom, the infra-red emitter 4 and collimator 42 are mounted in the fixed tube holding element 104 and the infra-red receiver 12 and collimator 44 are mounted in the movable tube holding element 106. Each tube holding face 108, 110 is either infra-red transparent or has a window (not shown) through which infra-red radiation can pass from the infra¬ red emitter 4 to the infra-red receiver 12. A sliding push button 116 extends out of a side of the casing 102. The sliding push button 116 is connected to the movable tube holding element 106, and is biased towards an outward orientation (as shown by arrow A) by means of a biasing element such as a helical tension spring 118, also shown in phantom, which is disposed within the casing 102. In this way, the movable tube holding element 106 is biased towards the fixed tube holding element 104, so that the bias acts to minimise the cross-section of the generally cylindrical cavity 114. The other electronic component of the infra-red fluid detector, such as the microcontroller, the power source (such as a battery), an alarm, a transmitter, etc. are received within the casing 102. This makes the device small in dimensions and light in weight, and consequently very portable. The casing may be provided with a clip 120 for clipping to a support.

The angle y degrees of the direction of movement of the movable tube holding element 106 relative to the longitudinal axis z of the tube holding cavity is selected so as substantially to correspond to the angle of refraction of the radiation at the interface of the tubular conduit and the fluid therein. For example, for water the angle is 29 degrees. In contrast, the angle, relative to the longitudinal axis z, of the radiation emitted by and received by the emitter 4 and receiver 12 respectively may be different. For example, in a preferred embodiment the angle of the axes of the infra-red emitter 4 and the infra-red receiver 12 relative to the longitudinal axis z is 40 degrees whereas the angle of the direction of movement of the movable tube holding element 106 relative to the longitudinal axis z is 29 degrees. By providing that at least one of the radiation emitter 4 and the radiation receiver 12 which is movably mounted on the casing 102, constituting a support, is movable in a predetermined direction corresponding to a particular angle of refraction through a tubular conduit 48 containing fluid, this provides the advantage that tubular conduits 48 of different diameter may be selectively disposed in the detection zone between the radiation emitter 4 and the radiation receiver 12.

Referring to Figure 7, the push button 116 can be pushed manually by medical personnel against the action of the biasing element 118 (as shown by arrow B) so as to open up the generally cylindrical cavity 114 and permit a tubular conduit to be received therein. As shown in Figure 8, when the push button 116 is released, the biasing element 118 urges the movable tube holding element 106 towards the fixed tube holding element 104 so as securely to hold the tubular conduit 48 between the tube holding faces 108, 110 within the generally cylindrical cavity 114. The tubular conduit 48 is securely received in the tube holder 100 so that the infra-red emitter 4 and the infra-red receiver 12, and their respective associated collimators 42, 44, are correctly disposed in the required position and orientation on opposed sides of the tubular conduit 48.

The rube holder can readily be used by medical personnel and reliably ensures correct positioning and optical coupling between the infra-red emitter 4, the infra-red receiver 12, their respective associated collimators 42, 44, and the tubular conduit 48. The tube holder 100 can easily be secured to a tubular conduit 48 and removed therefrom using simple manual operation of the push button 116. The bias applied by the helical spring 118 is sufficient to ensure secure holding of the tube holder 100 on the tubular conduit 48, for example so that the tubular conduit 48 can support the weight of the tube holder 100 if necessary, yet without being so large as to deform the tubular conduit 48 or require a large manual pressure to move the push button 116 to open up the generally cylindrical cavity 114 to receive the tubular conduit 48. The tube holder 100 can readily accommodate a range of different tube diameters in the generally cylindrical cavity 114, providing secure holding of the tube holder 100, containing the infra-red fluid detector, onto the tubular conduit 48, and also effective optical coupling between the infra-red emitter and detector and the tubular conduit 48.

In order to maximize the power available from the battery 34 so that monitoring can be carried out continuously over a long period, a sufficiently large battery will be required, but this would increase the weight and the size of the detector unit. The detector unit is ideally to be as small and light-weight as possible, hence a compromise is required between the power available and the duration of use.

In order to get maximum power conversion efficiency from the battery voltage to the required operating voltage, a switched regulator 38 is used which has higher efficiency compared to an analogue regulator. As a compromise, and also for maximum power capacity, typically 2 'AAA' size batteries are used. Such batteries provide a high power storage capacity (up to about 65OmAh) and provide a sufficiently high current of about 10mA to drive the detector unit. The switched regulator 38 is therefore used to 'boost' the battery input voltage (Vj_n) from 3 volts to the required 5 volts operating voltage (V₀Ut)- This enables the required current to be achieved, without compromising on battery power.

Refering to Figures 9 and 10, the switched regulator 38 consists of a charge pump capacitor (C_pump) and several electronic switches, SWl -4, which open and close according to an internal control signal. The control signal consists of an oscillating (clock) waveform with a roughly 50% duty cycle. The duty cycle as well as the frequency of the oscillation varies according to the voltage at the output (V_out).

During the first half-cycle (Fig. 9), SWl and SW4 are turned off, while SW2 and SW3 are turned on, allowing the capacitor (C_pUmp) to be charged via currents I₁ and I₂. During the second half-cycle (Fig. 10), switches SW2 and SW3 are turned off, while SWl and SW4 are turned on, with the voltage on C_pump added to V_out • By oscillating at a sufficiently high frequency, as well as by skipping the clock as necessary, a constant output voltage is hence maintained.

The switched regualtor 38 therefore permits high power storage capacity batteries to be used and the voltage to be increased to a higher operating voltage very efficiently and in a controlled manner. This provides the advantage that the infra-red detector and alarm system can be battery powered, and so be readily portable, using inexpensive batteries yet still provide a long operating time for a given battery life cycle.

Although the use of infrared light to detect the presence of fluid is not new, by critical geometrical positioning of the emitter and detector, distinction between air and fluid within a clear tube can be made both reliably and with high sensitivity. For the given circuit simplicity and low component count, a low cost and low power consumption system can be realised. Portability and ambulatory use of the device is also made possible. The device can readily accommodate different tube diameters.

In accordance with the preferred embodiments of the invention, a simple detector/alarm system using infra-red emitter and detector has been developed which detects and discriminates the presence of air or fluid within a clear or translucent tube system, such as those used for intravenous fluid administration in critical patient care. The described system utilizes the refraction property of light in the medium and provides a much improved detection and discrimination between air and the fluid medium.

Due to the simplicity of design and low component cost, the system can be made to be small and portable. The equipment can also be made to be low power, i.e. can be powered by battery for ambulatory use. Signals from the detector unit may be sent to remote monitoring stations using a 'wired' or a 'wireless' system such as optical or radio-frequency waves.

The detector system can be used to detect the presence of air in a normally fluid- filled system, and conversely, to detect the presence of clear or translucent fluid in a normally dry environment. In the air-bubble detection, an optional 'tube-clamp' system can be added to clamp the administrative set and stop the flow of fluid whenever an alarm condition is detected.

The complete detection and alarm system can operate as a 'stand-alone' unit and can be used in any applications, simultaneously and independently from other equipment, providing new information as well as safeguarding against adverse infusion incidents.

The present invention therefore provides a system for detecting air-in-line (also fluid-in¬ line) during administration of fluid (or air) using a simple but reliable way of detection using infra-red light. The system and the detection method are not restricted to IV tubes used in clinical applications, but also industrially, such as the food industry, and for automobiles, for example in fuel lines.

For example, the present invention contemplates 'air-in-line' bubble detection with audible and visual (LED) alarm. The unit is battery operated, and clips onto the IV set (clear plastic tube) during use.

For example, the present invention also contemplates 'air-in-line' bubble detection with audible and visual (LED) alarm locally similar to that described above, but in addition, each unit also has an identification ID and during 'alarm' conditions, transmits the alarm signal to a remote monitoring station. The mode of transmission can be wirelessly using radio-frequency (RF) waves, or for longer distances via cables. Typically, up to 8 such devices can be used within the locality.

For example, the present invention further contemplates a monitoring unit which receives the alarm signal from the above detector wirelessly, decodes the channel ID, and generates the alarm signals for that particular unit. The alarm signal is 'cleared' by resetting the detector unit by switching the unit 'off and then 'on' again.

For example, the present invention yet further contemplates a receiver unit which responds to a specific detector unit (eg with preset IDs). During 'alarm' condition of its corresponding detection unit, this device actuates a tube clamping mechanism and stops further infusion of fluid to take place. TV infusion can only resume after this unit is reset. As this receiver unit is separate from the detector unit, one can position the detector and the clamping unit at different locations, eg with the detector close to the source of possible air intake, and the clamp unit close to the patient for protection.

For example, the present invention also contemplates a combined detector and a tube- clamping device within the same unit. Once 'alarm' condition is triggered, the tube- clamping action is initiated and stopping the IV infusion process immediately.

For example, the present invention additionally contemplates that the detector is integrated into a bottle, an outlet, a tube and/or a fluid giving or administration unit. Therefore the respective bottle, outlet, tube and/or fluid giving or administration unit can be sold to a user with an integrated bubble detection system.

Claims

1. A fluid detector comprising a support, a radiation emitter device mounted on the support and adapted to emit radiation along a first axis, a radiation receiver device mounted on the support and adapted to receive radiation, emitted from the radiation emitter device, along a second axis, the first and second axes being substantially parallel but mutually laterally offset and a detection zone located between the radiation emitter device and the radiation receiver device, the detection zone being arranged to receive therein a tubular conduit containing fluid to be detected whereby, in use, radiation emitted from the radiation emitter device along the first axis may be received by the radiation receiver device along the second axis as a result of a particular degree of refraction of the radiation by the tubular conduit and fluid contained therein, the detection zone having a longitudinal axis along which the tubular conduit is disposed when in the detection zone and the first and second axes being each at an angle of from 15 to 45 degrees to the longitudinal axis, and at least one of the radiation emitter device and the radiation receiver device being movably mounted on the support in a predetermined direction whereby a spacing between the radiation emitter device and the radiation receiver device can be selectively varied, the predetermined direction corresponding to a particular angle of refraction through a tubular conduit containing fluid whereby tubular conduits of different diameter may be selectively disposed in the detection zone between the radiation emitter device and the radiation receiver device.

2. A fluid detector as claimed in Claim 1, wherein the radiation emitter device comprises an infra-red emitter and a first collimator for emitting collimated infra¬ red radiation along the first axis and the radiation receiver device comprises an infra-red receiver and a second collimator for receiving collimated infra-red radiation along the second axis.

3. A fluid detector as claimed in Claim 2, wherein the predetermined direction is the first axis for the radiation emitter device when the radiation emitter device is movably mounted on the support and the second axis for the radiation receiver device when the radiation receiver device is movably mounted on the support.

4. A fluid detector as claimed in any one of Claims 1 to 3, wherein each housing has an end face transparent to the radiation from the emitter device, the two end faces are mutually parallel, and between the end faces the tubular conduit may be in use disposed, with the end faces contacting opposed longitudinal sides of the tubular conduit.

5. A fluid detector as claimed in any foregoing Claim, wherein one of the radiation emitter device and the radiation receiver device is fixedly mounted on the support.

6. A fluid detector as claimed in any foregoing Claim, further comprising a holder for holding the tubular conduit in the detection zone, the holder being mounted on the support and comprising first and second holder parts which are mutually relatively movable towards and away from each other, the first holder part containing the radiation emitter device and the second holder part containing the radiation receiver device.

7. A fluid detector as claimed in Claim 6, wherein one of the first and second holder parts is movable towards and away from the other of the first and second holder parts which is fixed on the support, and further comprising a biasing device for biasing the movable holder part towards the fixed holder part.

8. A fluid detector as claimed in Claim 7, further comprising a manual actuator for moving the movable holder part away from the fixed holder part against the bias of the biasing device.

9. A fluid detector as claimed in any one of Claims 6 to 8, wherein each of the first and second holder parts has a respective part-cylindrical elongate cavity therein and the two part-cylindrical elongate cavities are mutually opposed so as to define a generally cylindrical cavity for receiving a tubular conduit.

10. A fluid detector as claimed in any foregoing Claim, further comprising an alarm connected to the radiation detection device.

11. A fluid detector as claimed in any foregoing Claim, further comprising a transmitter connected to the radiation detection device for transmitting an alarm signal to a remote receiver.

12. A fluid detector as claimed in Claim 11, wherein the transmitter is adapted to transmit an identifying signal and the remote receiver is a multi-channel receiver adapted to receive plural identifying signals from respective transmitters of a plurality of fluid detectors.

13. A fluid detector as claimed in any foregoing Claim, further comprising a tube clamp for clamping a tubular conduit so as to prevent fluid flow therethrough, the tube clamp being directly or indirectly operable in response to a signal, or absence of a signal, from the radiation detection device.

14. A fluid detector as claimed in Claim 13, wherein the tube clamp comprises a pair of clamping elements between which the tubular conduit is, in use, located.

15. A fluid detector as claimed in any foregoing Claim, in combination with a tubular conduit capable of being received in the detection zone, the tubular conduit comprising at least a part of an intravenous infusion set.

16. A fluid detector as claimed in any foregoing Claim, further comprising control circuitry for operating the radiation emitter device and the radiation receiver device, at least one battery for providing electrical power to the control circuitry, and a switched regulator for increasing the voltage supplied to the control circuitry from the at least one battery.

17. A method of detecting fluid in a tubular conduit, the method comprising disposing a tubular conduit containing fluid to be detected into the detection zone of the fluid detector according to any foregoing claim, emitting radiation from the radiation emitter device along the first axis so as to be incident on the tubular conduit containing fluid, and determining whether or not the radiation receiver device receives the radiation along the second axis following refraction of the radiation by the tubular conduit containing fluid, the radiation emitter device and the radiation receiver device being mutually disposed so that the radiation receiver device receives radiation from the radiation emitter device when fluid of a first phase within the tubular conduit is located therebetween and so that the radiation receiver device fails to receive radiation from the radiation emitter device when fluid of a second phase within the tubular conduit is located therebetween.

18. A method as claimed in Claim 17, which is for detecting gas bubbles in a liquid, wherein the first phase is a liquid and the second phase is a gas.

19. A method as claimed in Claim 17, which is for detecting liquid drops in a gas, wherein the first phase is a gas and the second phase is a liquid.

20. A method as claimed in any one of Claims 17 to 19, wherein an alarm signal is generated when the radiation receiver device does not receive radiation from the radiation emitter device.

21. A sensor comprising of an infrared emitter and a detector, accurately positioned on either side of a clear/translucent tube, such that the collimated incident light from the emitter is transmitted into the tube at an angle less than 45 degrees from the normal (i.e. perpendicular), the detector is positioned on the other side of the tube, such that the emerging light beam is in parallel with the incident beam, but slightly offset from the original axis, and the exact geometry and positioning of the emitter and detector pair is such that the detector receives the transmitted beam after it has been refracted by the fluid medium inside the tube.

22. A sensor as claimed in Claim 21, but with the positioning of the detector to detect the light beam only if no refraction takes place inside the tube.

23. A sensor as claimed in Claims 21 or 22, but with either the emitter or the detector mounted on a spring-loaded actuator, which is mounted at an angle to the tube and maintains correct beam geometry for light detection when different tube sizes are used.

24. A sensor as claimed in any of Claims 21 to 23, used together with accompanying signal processing electronics to form an 'air' or 'air-bubble' detection system in a fluid-administrative setup.

25. A sensor as claimed in any one of Claims 21 to 23, used together with accompanying signal processing electronics to form a 'fluid' detection system.

26. A sensor as claimed in any one of Claims 21 to 25, that utilizes the property of the refraction of light within a medium to detect the presence or absence of this medium in a clear or translucent tube or any other suitable vessel.

27. A sensor as claimed in any one of Claims 21 to 26, used together with accompanying electronic circuits to provide visual and audible warnings when 'alarm' conditions are detected.

28. A sensor as claimed in any one of Claims 21 to 27, which sends a warning signal to a remote station during 'alarm' condition by means of electrical wires or wirelessly using optical or radio-frequency signals.

29. A sensor as claimed in any one of Claims 21 to 28, which is powered by battery and allows portability and ambulatory use.

30. A sensor as claimed in any one of Claims 21 to 29, which is self-contained and can be operated independently of other equipment.