Abstract:
An integrated multi-function sensor system has a head having a slot to accept a tube of a deformable material and a plurality of sensor elements mounted in the walls of the head slot to confront a tube in the slot, each sensor element being for affecting sensing of a condition relating to a liquid in the tube. An integrated electronic circuit including a microprocessor operates to determine the various conditions of a liquid flowing in the tube sensed by the sensor elements, which conditions include detection of air bubbles and/or particles by ultrasonic sensing elements, detection of an occlusion in the liquid flow by sensing the deformation of the tube wall by a force sensing element, determining the temperature of the liquid by an infrared temperature sensing element, and determining the color of the liquid by optical elements.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to a sensor system utilizing a multi-function sensor head having sensor elements that can perform non-invasively multiple functions such as sensing the temperature of a liquid flowing in a tube, sensing and characterizing air bubbles and/or particles present in the liquid as well as sensing the type of the liquid and sensing an occlusion in the liquid flow. 
       BACKGROUND OF THE INVENTION 
       [0002]    In certain applications in medical equipment such as kidney dialysis machines, infusion pump blood analyzers, transfusion systems, cardio-pulmonary bypass machines and the like, an attempt is made to ensure patient safety. In these applications flexible plastic tubes are used to for tasks such as to supply the patient with medication, supply saline solution, extract fluid such as blood from the patient&#39;s body and supply it back after cleansing or purification, as well as for other functions. For example, during a kidney dialysis process tubes are connected to both the vein and artery of the patient for the blood extraction and return after cleansing. Another tube is used for infusion of medicine. 
         [0003]    For each tube connected to the patient&#39;s body it is desirable and even necessary to monitor different conditions relative to the liquid flowing in the tube and even conditions concerning the tube itself. For example, it might be required or desirable to sense the temperature of the liquid flowing in the tube, sense the presence of air bubbles and/or particles present in the liquid and to characterize these as to size and quantity. Sensing of other conditions include that of the type of liquid, such as blood or a clear saline solution, flowing in the tube as well as sensing an occlusion in the flow. It is even desirable to sense that a required tube is connected to the patient. 
         [0004]    In the prior art, a separate sensor and an associated electronic circuit is used to perform each of the sensing functions. This complicates the use of the medical equipment in that each of the sensors has to be mounted to the one or more tubes. For example, several different sensors are separately mounted to a single tube to sense conditions that are supposed to be monitored relative to the liquid flowing in that tube. This requires a selection process by the medical technician. It also makes use of the medical equipment more cumbersome in terms of operation, size and also makes it more costly. Also, since a different sensor and its associated electronic circuit is required to monitor each of the different conditions, the reliability of the entire system of the medical equipment and sensors decreases because the failure mode possibility increases due to the use of multiple and separate sensors each having a dedicated electronic circuit. Further, the user of the equipment often needs to coordinate with multiple vendors to purchase different sensors and different electronic circuits for different functionality. Accordingly, a need exists for apparatus that can overcomes these many problems and disadvantages. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    The present invention is directed to a system that can perform a plurality of sensing functions and that includes an integrated multifunction sensing module to eliminate the above problems. In the invention, the module has a head that has a slot into which the tube is to be placed. The head incorporates a plurality of sensor elements such as those needed for air bubble detection, temperature sensing and pressure sensing for use in sensing occlusions in the fluid flow in the tube and to also to give an indication of the tube being positively connected to the head. The head also includes a light emitting device, such as an LED, that transmits a light beam into the tube in the slot and a photodetector that receives the light. This permits a determination of wether the fluid in the tube is blood or a more clear liquid, such as saline solution or a flow of medicament. The module head is formed of a block of material, such as a clear polycarbonate plastic, that has a slot with opposing side walls on which the various sensor elements are mounted. The tube is laid in the slot and is contacted by those of the sensing elements that need physical contact to perform its function. The leads from the various sensor elements mounted in the head are connected to an electronic circuit that includes a microprocessor that is programmed to perform the various functions related to the sensor elements mounted in the head. The electronic circuit preferably includes a multiplexer so that a single microprocessor can be used to control all sensing functions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings in which: 
           [0007]      FIG. 1  is a perspective view of the integral multi-function sensor head; 
           [0008]      FIG. 2  is a cross section of the head of  FIG. 1 ; 
           [0009]      FIG. 3  is a block diagram of the electronic circuit of the system; 
           [0010]      FIG. 4  is a cross-sectional view showing tube deformation; and 
           [0011]      FIG. 5  is a view that explains operation of the infrared sensor used to measure temperature of a liquid in the tube. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring to  FIGS. 1 and 2 , the integral multi-function sensor of the invention has a head  10  that is a block of a plastic material such as UDEL polysulfone resin manufactured by Solvay Advanced Polymers. The head  10  is illustratively shown as being a generally rectangular shape and can be molded by any suitable technique. In the head  10  there is a longitudinal slot  12  that has opposing side walls  14  and  16 . A tube  20  of flexible and elastically outwardly expansible plastic material having a liquid flowing in it is to be placed in the slot  12 . The tube  20  is to have one end connected to the body of a patient and the other end connected to a liquid supply, such as a medicine or saline solution, or to a machine such as a dialysis machine. In the molding of the head  10  a number of depressions are formed in the opposing slot side walls  14  and  16 . Different types of sensor elements, to be described below, are mounted in the depressions and each depression is of a shape to accommodate the particular type of sensor element that is to be mounted in it. The slot side wall thickness is typically 0.30″ to 0.050″ depending upon plastic material and the sensor elements used. A hole is drilled through the outside wall of the head  10  to each of the depressions in the slot sidewall  14  and  16  to accommodate a respective lead wire or wires connected to the respective sensor element. 
         [0013]    Considering the sensor elements, near one end of the head  10  is a pair of piezoelectric elements  26   a  and  26   b  mounted opposing each other in the slot opposing slot side walls  14  and  16 . Near the center of the head  10  a temperature sensor  20  is mounted in one of the slot side walls  14  and a force sensor  30  is mounted in the other sidewall  16 . Near the other end of the head  10  a light emitting element  32 , such as an LED, is mounted in the side wall  14  and a photodetector  34  is mounted opposing it in the side wall  16 . The representation of the shapes of the various sensor elements are in schematic form and the shape will depend upon the specific sensor element that is used. The placement of the various sensor elements also can be varied. Each of the sensor elements is held in its respective depressions by a suitable adhesive, such as an epoxy, and the lead wires for each sensor element pass out through the walls of the head that form the slot to be exterior of the head so as to be able to be connected to an electronic circuit, to be described below. 
         [0014]    In the operation of the system of the invention, the plastic tube  12  is laid in the slot  12  of the head  10 . The width of the slot  12  is slightly less than the outer diameter of the plastic tube  20  so that the faces of the sensor elements  26 ,  28  and  30  mounted in the opposing slot side walls  14  and  16  that need to be in contact with the tube  20  makes such contact. A typical deformation or squeeze of the tube in the slot would be 15% to 20% of the tube outer diameter. The light emitting element  32  and photo transistor  34  optical elements need not necessarily make contact with the wall of the plastic tube but one or both of these elements can make such contact. A description of individual sensor elements and their respective functions follows. 
         [0015]    The piezoelectric elements  26   a  and  26   b  are of any suitable material used in ultrasonic technology, such as PZT or PVDF material. In the integral multi-function sensor system of the invention, the piezoelectric elements  26   a  and  26   b  operate as part of an air bubble detection and characterization apparatus. In such an apparatus, ultrasonic energy is supplied to one of the piezoelectric elements  26  and is transmitted though the tube  20  to be received by the other element. A circuit of this type is described in U.S. patent application Ser. No. 11/703,025, filed Feb. 7, 2007 for “Ultrasonic System for Detecting and Quantifying of Air Bubbles/particles in a Flowing Liquid”, which is assigned to the assignee of this application and whose disclosure is incorporated herein by reference. This system is briefly described below with reference to  FIG. 3 . Other ultrasonic type systems also can be used to detect air bubbles. 
         [0016]    The temperature sensor element  28  preferably is an infrared thermocouple, an example being P/N: 150042, Model No C UIRT-K-98.6f/37C manufactured by Exergen, Watertown, Mass. This device has the ability to measure the internal temperature of the liquid in the tube  20  non-invasively by measuring both tube surface temperature and the ambient temperature. It is preferred that the sensor element  28  is mounted in the head  10  so as to converge the sensor infrared beam at a focus point in the middle of tube  20  to measure fluid temperature accurately. 
         [0017]    The operation of the temperature sensor element  28  is described referring to  FIG. 5 . As seen in  FIG. 5 , a liquid L flowing in a tube such as the tube  20  having a temperature T L  which is represented by thermal resistance R L  transfers heat by conduction to the tube inside surface T IW , which in turn conducts heat to the tube external surface T OW . This transfer is represented by the thermal resistance R T . The heat on the tube outer wall is transferred to the environment via radiation and convection as represented by thermal resistance Ro. Using the method of thermal analysis with electrical analogs: current=heat flow and voltage=temperature, the heat transfer equation may be written as follows: 
         [0000]    
       
         
           
             Q 
             = 
             
               
                 1 
                 
                   
                     R 
                     L 
                   
                   + 
                   
                     R 
                     T 
                   
                   + 
                   
                     R 
                     O 
                   
                 
               
                
               
                 ( 
                 
                   
                     T 
                     L 
                   
                   - 
                   
                     T 
                     A 
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    where
 
Q=Heat transfer, and
 
         [0000]      R L   +R   T   =R   O    
         [0000]    For heat balance: 
         [0000]    
       
         
           
             Q 
             = 
             
               
                 1 
                 
                   R 
                   O 
                 
               
                
               
                 ( 
                 
                   
                     T 
                     OW 
                   
                   - 
                   
                     T 
                     A 
                   
                 
                 ) 
               
             
           
         
       
     
       Accordingly, 
       [0018]    
       
         
           
             
               T 
               L 
             
             = 
             
               
                 
                   
                     
                       R 
                       L 
                     
                     + 
                     
                       R 
                       T 
                     
                     + 
                     
                       R 
                       O 
                     
                   
                   
                     R 
                     o 
                   
                 
                  
                 
                   ( 
                   
                     
                       T 
                       OW 
                     
                     - 
                     
                       T 
                       A 
                     
                   
                   ) 
                 
               
               + 
               
                 T 
                 A 
               
             
           
         
       
     
         [0019]    The infrared sensor  28  measures both T OW  and T A . The output lead of sensor  28  is connected to a suitable circuit that includes an analog to digital converter and other necessary circuit for converting the change in temperature measured by the sensor  28  into a digital value and a suitably programmed microprocessor or similar device to automatically solve the equation for the liquid temperature T L . The technique used has been found to be able to measure the liquid temperature with an accuracy of ±0.2° C. The measurement is done non-invasively and provides a highly accurate method of monitoring the temperature of interest. The measured value of the liquid temperature can be used for control purposes, such as turning on and off heating and cooling units or to advise the system operator of changes in temperature. 
         [0020]    Sensor element  30  is a force/pressure sensor that accomplishes non-invasive measurement of the internal pressure of the elastic tube  20 . During dialysis or infusion of a medicine, the internal pressure of the liquid in the tube  20  exerts force on the inner wall of the tube which is transmitted to the tube outside wall. The force exerted on the tube outer wall has a linear relationship with the tube internal pressure. As shown in  FIG. 4 , a tube  20  placed in the slot  12  with no liquid flowing in it has a somewhat elliptical shape. Liquid flowing through the tube causes it to expand to a more circular shape a shown by the dash lines. The outer tube wall expansion is measured using a force or strain gauge pressure sensor  30  which is commercially available. A suitable force sensor element is P/N: DEL 2239 equivalent and manufactured by Strain Measurement Device, Meriden Conn. The face of the sensor element  30  contacts the outer wall of the tube laid in the slot  12 . Such force or strain gauge devices produce a change in resistance as a measurement of the force sensed. 
         [0021]    The force sensor  30  is used to perform several functions. It detects an occlusion in the tube by sensing a sudden change in pressure of the liquid in the tube  20 . There also will be drop in pressure in the case of a pump failure occurs. The sensor  30  also detects the presence of a tube in sensing slot  12 . That is, insertion of the tube  20  in the slot  12  exerts a force against the sensor element  30 . The sensor  30  differentiates between dry and liquid presence conditions in the tube. That is, when liquid flows in the tube  20  the force on the tube outer wall will be greater than if there is no liquid flowing in the tube. 
         [0022]    The sensor elements  32  and  34  provide for detection of the type of liquid flowing in the tube  20 . A typical use would be in detecting if there is blood, or a similar dark liquid, or a clear liquid, or a saline solution, which is relatively clear. Another use is to detect if there is any liquid in the tube or if it is dry. The light emitting element  32  is a suitable device, such as an Infrared emitting diode, and the light receiving element  34  a suitable device, such as a silicon photo transistor. The light emitting element  32 , which can be an infrared energy emitting diode, is positioned so as to have its output beam focused in the center of the tube  20 . A constant current source is used to drive infrared emitting diode. The photo transistor  34  receives the light energy transmitted through the tube  20 . The optical transmission through the tube and a liquid flowing through it is amplified and an amplified analog signal is digitized and analyzed by a microprocessor, as described below. 
         [0023]    The optical elements  32  and  34  accomplish a number of functions. There is a detection of blood vs saline solution since the amount of light passing through the liquid will be of different amplitudes. Different amplitudes of light will be detected by the detector  34  when there is no tube in the slot, tube with a clear liquid flowing in it, and a tube with blood inside the tube. All of these different conditions can be recognized and different indications given to the operator of the equipment. 
         [0024]    In certain applications it is important to detect presence of a tube in the slot before fluid is injected. Buy combining the pressure and optical sensing techniques described above, the system of the invention provides added reliability to sense tube presence or absent conditions. 
         [0025]      FIG. 3  is a block diagram of an electronic circuit that can be used with the multi-function sensor of the invention. The circuit of  FIG. 3  is integral in that one microprocessor is used to control all of the measuring functions for all of the sensors mounted in the head. While this is preferred, other circuits can be used, for example, a separate circuit with its own microprocessor and display for each different type of sensor. Also, it is not necessary to utilize all of the sensor elements of the head  10 . For example, in a particular use it might not be necessary to measure one of the conditions measured by one of the sensor elements. 
         [0026]    Referring to  FIG. 3 , there is a microprocessor  50  that is suitably programmed to perform all of the functions described below. That is, the microprocessor  50  outputs the necessary signals to control the operation of each of the several sensor elements to perform its intended function and to produce an output measurement. The microprocessor  50  also has an output on line  51  that controls operation of a bi-directional multiplexer  52  that is gated by the microprocessor to sequentially apply the signals from the microprocessor  50  to control operation of an air bubble detection and characterization circuit  60  associated with the piezoelectric sensor elements  26   a  and  26   b , a temperature sensing circuit  70  associated with sensor element  28 , a pressure sensing circuit  80  associated with the force sensor  30 , and a liquid detection circuit  90  associated with the optical elements  32  and  34 . An analog to digital converter  54  digitizes an analog output signal from any of the circuits  60 ,  70 ,  80  and  90  and applies it to the microprocessor  50  for processing for producing the proper output depending upon the sensor element that is active. The microprocessor  50  drives a visual display device  56  to display measurement results, warnings, and other information. The microprocessor also can produce outputs to other devices such as printers, audio alarms, RS  232  output, etc. All of this is conventional in the art. 
         [0027]    The air bubble and particle sensing circuit  60  is gated on for operation by the multiplexer  52  for a predetermined time by the microprocessor  50 . Considering the air bubble detection and characterization circuit  60 , as described in the aforesaid patent application Ser. No. 11/703,025, energy in the ultrasonic frequency range, for example 2-5 MHz, is supplied by a generator  62  to the element  26   a  or  26   b  that is to be the transmitter element to be transmitted to the opposing other element which serves as a receiver element. The received ultrasonic energy is amplified in an amplifier  64  and detected and preferably split by a suitable circuit into a steady state (DC) component and a varying or transient (AC) component, the components respectively being indicative of the absence and the presence of an air bubble or a particle in the liquid. The two components of the signal are applied to the A/D converter  56  whose output is supplied to microprocessor  50  which uses the digital data that corresponds to the presence of a varying transient component to indicate the presence of an air bubble and/or a particle and to determine its characteristics. When liquid is flowing through the tube  20  the presence of the steady-state component indicates that the system is operating properly to provide a continuous self check against system malfunction. 
         [0028]    The temperature sensing circuit  70  is any suitable conventional circuit used to measure temperature based on infrared (IR) energy. Such circuits are well known in the art. When gated on by the microprocessor  50  through the multiplexer  52 , the temperature sensing circuit  70  electronics  72  produces the IR beam of energy that heats the wall of the tube  20  in the manner described with respect to  FIG. 5 . and produces an analog output voltage that is amplified by an amplifier  74 . The analog output is applied to the analog to digital converter  54  and the digital output applied to the microprocessor for processing and display. 
         [0029]    The force sensing circuit  80  that uses the sensor element  30  has a circuit, such as a bridge circuit, that converts the change of resistance of the sensor element in response to the force or pressure into a voltage that is applied to an amplifier  84  and then through the multiplexer  52  to the analog to digital converter  54 . The measured force represented by the analog voltage is converted into digital format to be used by the microprocessor  50  and to be displayed on the display  56 . 
         [0030]    The liquid color sensing circuit  90  has a drive circuit  92  for the light emitting element  92  which preferably is left on at all times when the system is operating. An amplifier  94  that is gated on by signals from the microprocessor  50  permits the signal generated from the light passing through the tube  20  and/or liquid that is received by the photo transistor  34  to pass through the multiplexer  52  to the analog to digital converter  54 . As explained above, the amplitude of the signal produced by the photo transistor corresponds to the absence of liquid in the tube and the color of the liquid. After processing of the digital signal by the microprocessor the results are displayed on the display  56 . 
         [0031]    Specific features of the invention are shown in one or more of the drawings for convenience only, as each feature may be combined with other features in accordance with the invention. Alternative embodiments will be recognized by those skilled in the art and are intended to be included within the scope of the claims. Accordingly, the above description should be construed as illustrating and not limiting the scope of the invention. All such obvious changes and modifications are within the patented scope of the appended claims.