A DEVICE FOR DETECTING THE PRESENCE OR ABSENCE OF LIQUID IN A VESSEL

Abstract: A device for detecting the presence or absence of liquid in a translucent vessel or tube which consists of a light source (11) and a light sensor (12) adjustably mounted on a platform (16) on which a tube (10) through which a fluid substance is to pass, is located. If the tube (10) contains no liquid then the sensor (12) receives the light beam and produces a signal for indication. However, if the tube (10) is filled with a translucent or opaque liquid, the light beam is deflected by refraction or scattered to prevent it from activating the sensor (12).

Description: A DEVICE FOR DETECTING THE PRESENCE OR ABSENCE OF LIQUID IN A VESSEL THIS INVENTION concerns a device for detecting the presence or absence of liquid in a translucent vessel or tube, and has particular appl ication in the detection of air bubbles in pipelines carrying a stream of liquid. In medical appl ications, for example, during infusions and transfusions where the presence of a large air bubble in the blood supply can present a danger to l i fe, it i s most important that the continuity of the liquid stream i s monitored to detect the presence of any air bubbles in the stream, if large enough to be dangerous. The invention is based upon the principle that a beam of light passing into a translucent tube containing no liquid, will be sufficiently diffused for at least some of the light to pass through the tube in a generally straight line substantially al igned wi th the incident light beam, whilst a similar beam pas sed through a clear or largely translucent liquid within the tube would be deflected by refraction ? and that the presence of an opaque liquid in the tube would caus e the inc ident l i ght beam to be re flected thus preventing it from pas sing through the liquid. An object of the present invention is to provide a simple device for detecting the present or absence of liquid in a translucent vessel or tube and accordingly the device comprises a light source adapted to transmit a beam of light through said vessel or tube to a photo-electric sensor, the light source and the photo-electric sensor being so disposed relative to one another and to the vessel or tube, that when the latter contains an opaque liquid the incident light path is obstructed thereby; when it contains a translucent liquid the incident light path is deflected by refraction away from said sensor? and when it contains air or other gas so that the incident light path is not obstructed or deflected, a signal is produced by the photo¬ electric sensor to provide an indication of the absence of liquid in the vessel or tube. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which:- Fig. 1 illustrates in cross-section, a translucent tube through which a fluid substance is to pass, and a light system for detecting the presence or absence of liquid in the tube; Fig. 2 shows the tube containing a translucent liquid; and Fig. 3 shows the tube containing an opaque liquid. Referring now to the drawings it will be seen in Fig. 1 that a tube 10 having a translucent material wall contains no liquid and a beam of light transmitted by a light source 11 effectively passes in a straight path through the tube wall to be received by a photo-electric sensor 12. The sensor 12 is adapted under these conditions to produce an electrical signal which can be used to drive a visual or audible indicator or a meter. The distance 'X' between the centre line 'Y' of tube 10 and the path of the incident light beam from light source 11 is equal to about one quarter of the internal diameter of tube 10. Referring to Fig. 2, wherein the tube 10 now contains a clear or translucent liquid 13 the path of the incident light beam entering the liquid 13 is deflected by refraction and emerges on the opposite side of the centre line of the tube 10 as indicated at 14. In this case the light beam is not received by sensor 12 and no signal is produced. Referring to Fig. 3, wherein the tube 10 now contains an opaque liquid 15, the incident light beam is substantially prevented from passing through the 1 liquid and is thus scattered, and again is not received by sensor 12, so that no signal is produced. With the arrangement described therefore, the presence or absence of liquid in the tube can be detected since no signal will be produced by the sensor unless the liquid level in the tube falls below that of the incident light beam from source 11. By varying the distance 'X', the sensitivity of the device can be adjusted to ensure that the sensor receives no refracted light when the tube is filled or substantially filled with liquid. The device can be produced by placing the light source 11 and sensor 12 on a small platform 16 across which the tube 10 can be placed, and preferably the positions of source 11 and sensor 12 on platform 16 are adjustable to accommodate tubes of different diameter and to vary the distance 'X'. The device can be applied to existing pipelines provided that at least a portion of the pipe where it passes between the source 11 and sensor 12 is transparent or at least translucent. An advantage of the device in accordance with the invention when used in conjunction with toxic, corrosive or contaminatable liquids, is that no parts are caused to come into contact with the liquid within the tube, and it is simple and inexpensive to produce and maintain when compared with systems using, for example, ultrasonics. If the device is exposed to ambient light its sensitivity and reliability can be effected. Therefore, it is preferable in some cases for the light source 11 to emit a beam of infra-red light and for the sensor to detect same, so that ambient light cannot interfere with its operation. The invention has particular application in the medical field for the delivery of blood or other fluids to patients for introduction intravenously where the injection of a large air bubble might be dangerous. However, the device can be applied to monitoring the flow of liquid in many forms of apparatus, for example, in sight glasses on tanks, in manometers, and it might be used in some instances to replace the conventional ball cock in a liquid storage tank.

Claims: CLAIMS 1. A device for detecting the presence or absence of liquid in a translucent vessel or tube, comprising a light source adapted to be disposed with respect to said vessel or tube to transmit a beam of light through same, a sensor to detect said beam of light, the light source and the sensor being so positioned relative to one another and to the vessel or tube, that when the latter contains an opaque liquid the incident light beam is obstructed thereby; when it contains a translucent liquid the incident light path is deflected by refraction away from said sensor; and when it contains air or other gas or vapour such that the incident light beam is not obstructed or deflected, a signal is produced by the sensor to provide an indication of the absence of liquid in the vessel or tube. 2. A device according to Claim 1, wherein the relative disposition of said light source and said vessel or tube is adjustable. 3. A device according to Claim 1, or Claim 2, wherein the relative disposition of said sensor and said vessel or tube is adjustable. 4. A device according to Claim 1, wherein said light source and said sensor are mounted on a platform and are adjustable thereon to accommodate different sizes of vessel or tube and to adjust the sensitivity of the device. 5. A device according to any preceding claim, in which said light source is adapted to transmit a beam of infra-red light. 6. A device according to any preceding claim, in which said sensor is adapted to drive a visual or audible indicator. 7. A device according to any preceding claim, wherein sai d s ensor i s adapted to dr ive a mete r to g ive an indication of the absence of liquid in the vessel or tube. 8. A device for detecting the presence or absence of liquid in a translucent vessel or tube, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings .

Inventors: PLATT ANTHONY HOLDEN, PLATT, ANTHONY, HOLDEN
Applicants: UNIV MANCHESTER, THE VICTORIA UNIVERSITY OF MANCHESTER
Application year: 1986
Main classification: G01F23
IPC codes: G01F23