although this invention is preferably intended to be used for controlling dialysis systems , and will be described below with reference to such an application , it will be obvious to those versed in the art that this invention can also be applied , for example , to other extracorporeal blood treatment systems , and / or for the control , in general , of the flow of different fluids through a tube which can also be connected to such a monitor . refering to the figures , in which like numerals refer to like portions thereof , fig1 thus shows such a tube or tube system which is intended to be used for the withdrawal of blood from a patient . the tube or tube system is normally connected to the front of a control monitor . for the sake of simplicity only certain of the primary components thereof are shown in fig1 . these include an arterial clamp , 3 , which can be used to terminate the flow of blood therethrough , such as in connection with various alarms , an arterial pressure controller , 4 , of a conventional type , a pump , 5 , a combined air detector and holder , 6 , for a drip chamber , 7 , and a conventional venous clamp , 8 . in fig1 there is also shown a dialyzer , 9 , and a detector , 10 , which is an essential component of the present invention . the detector , 10 , is in this case arranged directly connected to the venous clamp , 8 , in a manner such that the tube can be assembled in the detector only when it is also assembled in the venous clamp , 8 . reference numeral 11 designates the outlet end of the tube or tube set , 1 , which in this case is intended to be connected to the patient for return of the blood after dialysis . finally , reference numeral 7a in fig1 designates a venous pressure gauge connected to the drip chamber , 7 . the arterial pressure controller , 4 , and the venous pressure gauge , 7a , are appropriately connected to different pressure gauges , and to a computer included in the monitor , in a manner such that an alarm is activated when certain pressure limits are either exceeded or fail to be reached . referring next to fig2 there is shown the detector , 10 , fitted onto the front face of a monitor , 12 . the actual tube holder is formed by a circular passage or guide 13 , into which the tube can be inserted through a securing device , 14 , which in this case is in the form of a slot which is preferably narrower than the width of the tube . within the front face of the monitor is a transmitter , 15 , preferably for infrared light , which is assembled in conjunction with a receiver , 16 , for the same light . the light is thus passed through a light conductor , 17 , through the circular passage , 13 , and thereby through the tube , 1 , if the tube is in the appropriate location . the light is then refracted by means of angled surfaces , 18 and 19 , so that , after passing through a wavelength filter , 20 , it is directed towards receiver , 16 . reference numeral 21 finally designates means by which the transmitter and the receiver can be connected to the rest of the electronics within the monitor . this electronics pack is described in more detail in connection with fig3 . referring next to fig3 this electronics pack may , of course , be designed in many different ways . in a preferred design , as shown in fig3 a main computer 22 is adapted to put out a signal by means of a driver stage , e . g ., a transistor , 23 , to an infrared light - emitting diode , 24 , which is connected to a positive pole through a resistor , 25 . from the light - emitting diode , 24 , a light beam , 26 , is emitted , which is received by a phototransistor , 27 , which on one side is connected to a positive pole and on the other side , through a resistor , 28 , to ground 29 . the signal which is thus obtained is passed to two comparators , 30 and 31 , each of which receives a reference signal from a so - called safety computer , 34 , by means of two converters , 32 and 33 . the latter two converters convert a digital signal from the safety computer , 34 , to an analogue signal , which can be compared with the analogue signal from the phototransistor , 27 . the upper converter , 32 , transmits a higher reference signal corresponding to a wholly disconnected tube , whereas the lower converter , 33 , transmits a lower signal corresponding to a properly located empty tube , or such a tube filled with a substantially transparent fluid . by means of the comparators , 30 and 31 , it is thus possible to establish whether a tube is installed in the holder , 10 , at all , and whether or not this tube is filled with blood . if blood is present in the tube , the signal , 26 , is practically wholly extinguished , so that the value obtained from the phototransistor , 27 , will be clearly located below the reference signal from the converter , 33 . values obtained from the comparators , 30 and 31 , are transmitted not only to the main computer , 22 , but also to the above - mentioned auxiliary or safety computer , 34 . the plastics from which the above - mentioned tubes are normally manufactured have essentially no absorption peaks within the range of from about 850 nm to 1000 nm . therefore , the wavelength of the infrared light is appropriately selected from within this range . it has thus been found to be particularly suitable to use a wavelength of about 940 nm where these plastic materials have practically no absorption at all . the refractive index of these plastics is normally within the range of from about 1 . 4 to 1 . 6 , depending on the material selected and the wavelength of the light utilized . they may be utilized to detect an empty tube or a tube filled with a substantially transparent fluid . in view of the fact that these tubes are round , they act as a lens , and refract the light . this causes the intensity of the light to diminish on the receiving side . in order to thus obtain the same measured value every time under the same conditions , the tube must not be deformed in the holder , but should be &# 34 ; loose &# 34 ; within the holder , while at the same time it must still be maintained in the desired location . it is also helpful to calibrate the detector before any tube is inserted within the holder . the purpose of doing as is to compensate for any ripples within the light transmission system . if a tube is already incorporated in the holder , 10 , when the system is put into operation , then the computer , 22 , may be adapted so that it is activated from the results of the last such calibration . the smallest opening within the light conductor , 17 , on the transmitter side shall preferably be selected on the basis of the smallest dimension of the tube which is intended to be used therein . in practice , it has thus been found appropriate to use a circular opening of a diameter of about 1 . 5 mm , a square opening of about 1 . 5 mm side length , or a gap of about 1 . 5 mm × 5 mm . the corresponding smallest opening on the receiver side ought to be slightly larger . for example , it may have a corresponding diameter or side of about 2 mm . in this manner , good reliability can be obtained with different tube diameters , down to at least about 1 . 5 mm . such fine - caliber tubes , however , should be fixed in the light beam path in some way . although the invention herein has been described with reference to particular embodiments , it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention . it is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims .
apparatus for monitoring fluid flow in dialysis systems include a tube holder for mounting the tube at a predetermined location on a dialysis monitor , a transmitter for transmitting a signal such as ultraviolet light through that location , a receiver for receiving the signal after it has passed through that location , and a sensor for sensing whether the tube is mounted at that location and whether the fluid is contained within the tube in response to the signal received by the receiver .