referring now to the drawings , an enteral feeding pump ( broadly , “ flow control apparatus ”) constructed according to the principles of the present invention is generally indicated at 10 . the feeding pump 10 may comprise a housing , generally indicated at 12 , that may be constructed to receive an administration feeding set ( broadly , “ a fluid delivery set ”), generally indicated at 14 . it will be understood that although the illustrated flow control apparatus is an enteral feeding pump 10 , the present disclosure has application to other types of flow control apparatus ( not shown ), including medical infusion pumps . moreover , although an administration feeding set 14 is shown , other types of fluid delivery sets ( not shown ) can be used within the scope of the present invention . a user interface , generally indicated at 16 , may be provided on the front of the housing 12 . the user interface 16 may include a display screen 18 that is capable of displaying information about the status and operation of the pump , a plurality of push buttons 20 on one side of the display screen , and a plurality of leds 22 on the other side of the display screen . referring now to fig1 and 2 , the pump 10 may further comprise a rotor 26 that controls the flow of fluid through the feeding set 14 when a cassette , generally indicated at 30 , of the feeding set is loaded on the pump . the cassette 30 may include a valve mechanism 34 and a mounting collar 36 that are releasably securable to the pump 10 . the feeding set 14 may include tubing 11 having a first section of tube 40 ( e . g ., feeding inlet tube ) upstream of the valve mechanism 34 leading to a feeding fluid source 42 , and a second section of tube 44 ( e . g ., flushing inlet tube ) upstream of the valve mechanism leading to a flushing fluid source ( not shown ). the feeding set 14 , more specifically the cassette 30 , may include a third section of tube 46 ( e . g ., cassette tube ) extending between and interconnecting the valve mechanism 34 and the mounting collar 36 . a fourth section of tube 50 ( e . g ., outlet tube ) may extend from the mounting collar 36 toward the patient . the valve mechanism 36 may be operable to selectively permit flow of fluid from the feeding fluid source 42 or a flushing fluid source ( not shown ) into the cassette tube 46 , or prevent any fluid flow communication from the feeding or flushing fluid sources into the cassette tube . when loaded onto the pump 10 , the valve mechanism 34 and the mounting collar 36 may be securely engaged with the pump , and the cassette tube 46 may be placed in a stretched condition around the rotor 26 of the pump . rotation of the rotor 26 , such as by a motor 52 ( fig4 ), compresses the cassette tube 46 and provides a force for driving fluid in the feeding set 30 from the upstream side of the rotor to the downstream side of the rotor for delivery to the patient . referring to fig1 and 2 , at least one fluid sensor associated with the housing 3 may be located in a position to detect a condition of fluid in the feeding set 14 . in the illustrated embodiment , the pump 10 includes two fluid sensors : a first fluid sensor , generally indicated at 56 , is located upstream of the rotor 26 ; and a second fluid detector , generally indicated at 58 , is located downstream of the rotor . it is understood that the pump 10 may include a single fluid sensor or more than two fluid sensors without departing from the scope of the present invention . in one example , the first and second fluid sensors 56 may be ultrasonic sensors for use in detecting a condition of the fluid in the feeding set 14 , although other types of sensors are within the scope of the present invention , including , but not limited to , infrared sensors . the first fluid sensor may be used to detect the presence or absence of fluid in the cassette tube 30 , and the second fluid sensor 58 may be used to detect a downstream occlusion . it is understood that the first and second fluid sensors 56 , 58 may be configured for use in detecting other conditions of the feeding set 14 , such as fluid flow and opaqueness of the fluid . referring now to fig4 , an exemplary block diagram illustrates a control unit 60 of the enteral feeding pump 10 and components that are in communication with the control unit . the control unit 60 may include a processor 60 a ( e . g ., a microprocessor ) and a memory 60 b . it is understood that the control unit 60 may comprise more than one controller , each of which may have at least one processor and at least one memory . as illustrated , the control unit 60 is in communication with the motor 52 and the user interface 16 . referring still to fig4 , the pump 10 includes a fluid monitoring system 62 . the fluid monitoring system 62 may include the first and second fluid sensors 56 , 58 , respectively , the control unit 60 ( e . g ., a fluid monitoring controller of the control unit ), a flow alarm 66 , and a malfunction alarm 70 . the control unit 60 is in communication with the first and second fluid sensors 56 , 58 , respectively , the flow alarm 66 , and the malfunction alarm 70 . each of the flow and malfunction alarms 66 , 70 , respectively , may be audible , visual , vibratory or any combination thereof . in the illustrated embodiment , each of the first and second fluid sensors 56 , 58 , respectively , may include an ultrasonic generator 56 a , 58 a , respectively ( broadly , a sensor signal generator ), and an ultrasonic receiver 56 b , 58 b , respectively ( broadly , a sensor signal receiver ). for each sensor 56 , 58 , the ultrasonic generator 56 a , 58 a and the ultrasonic receiver 56 b , 58 b are on opposite sides of the cassette tube 46 such that the cassette tube is received between the generator and receiver ( see fig3 ). each ultrasonic generator 56 a , 58 a ( e . g ., an ultrasonic transducer ) is configured to receive a drive signal from the control unit 60 ( more specifically , the processor 60 a ), and in response to the drive signal , generate an ultrasonic signal that is transmitted through the cassette tube 46 toward the corresponding ultrasonic receiver 56 b , 58 b . each ultrasonic receiver 56 b , 58 b ( e . g ., an ultrasonic transducer ) is configured to receive the ultrasonic signal and , in response to the received signal , generate an output signal . the control unit 60 ( more specifically , the processor 60 a ) is configured to receive the output signal and determine and analyze a parameter value of the output signal , as described in more detail below . the fluid monitoring system 62 may include a first mode of operation ( e . g ., a fluid monitoring mode ) for determining the condition of the fluid in the cassette tube 46 , such as during operation of the pump 10 for delivering fluid to the patient . by determining the condition of the fluid in the cassette tube 46 , the control unit 60 ( e . g ., the processor 60 a ) may be further configured to determine a condition of the feeding set 14 and the pump 10 in general . fig5 illustrates instructions ( e . g ., software ) stored in the computer readable storage medium ( memory 60 b ) and executed by the processor 60 a of the control unit 60 during the first mode of operation using the first fluid sensor 56 . similar , yet different , instructions may be stored for the second fluid sensor 58 or any additional fluid sensors . at 100 , the control unit 60 ( e . g ., the processor 60 a ) generates a drive signal that is received by the ultrasonic generator 56 a of the first fluid sensor 56 . the drive signal may have a substantially constant frequency matching a resonant frequency of the ultrasonic generator 56 a ( e . g ., between 1 to 3 mhz , and in one example about 2 . 25 mhz ). in response to the drive signal , the ultrasonic generator 56 a resonates , producing an ultrasonic signal that propagates through the cassette tube 46 and toward the ultrasonic receiver 56 b . at 102 , the control unit 60 ( e . g ., the processor 60 a ) receives the output signal from the ultrasonic receiver 56 b of the first fluid sensor 56 . at 104 , the control unit 60 ( e . g ., the processor 60 a ) determines the amplitude of the output signal ( broadly , a parameter value of the output signal ). in other embodiments , other parameter values of the output signal ( e . g ., frequency , phase shift , etc .) may be determined and analyzed by the control unit 60 ( e . g ., the processor 60 a ) to determine the condition of the fluid in the cassette tube 46 . at 106 , the control unit 60 ( e . g ., the processor 60 a ) stores the amplitude of the output signal in the memory 60 b . at 108 , the control unit 60 ( e . g ., the processor 60 a ) compares the stored amplitude to a threshold value that is stored in computer readable storage medium . if the stored amplitude is above the threshold value , indicating that there is fluid in the cassette tube 46 , the control unit 60 ( e . g ., the processor 60 a ) may return to step 100 after a predetermined amount of time and / or communicate to the user , such as by the user interface 16 , that there is fluid in the feeding set 14 . if the determined amplitude is not above ( e . g ., at or below ) the threshold value , indicating that there is air in the cassette tube 46 and / or the tube is empty , then at 110 the control unit 60 ( e . g ., the processor 60 a ) activates the flow alarm 66 and / or shuts off the motor 52 . it is understood that the fluid monitoring system 62 may include additional instructions and / or different instructions for monitoring a flow condition in the feeding set 14 . in another example , turning to the second fluid sensor 58 , the control unit 60 ( e . g ., the processor 60 a ) may analyze the amplitude of the output signal to determine if the amplitude is above a threshold value stored in computer readable storage medium . this may indicate that the pressure in the cassette tube 46 is indicative of a downstream occlusion . the control unit 60 ( e . g ., the processor 60 a ) may activate the flow alarm 66 in response to the detection of an occlusion and / or shut off the motor 52 . the fluid monitoring system 62 may also include a second mode of operation ( e . g ., a malfunction detecting mode ) for determining if the fluid monitoring system is malfunctioning . in one example , the control unit 60 may be configured ( e . g ., the processor 60 a is programmed ) to generate a second drive signal that is different from the first drive signal used in the first mode of operation . in response to the second drive signal , the ultrasonic generator 56 a , 58 a ( broadly , the signal generator ) generates an ultrasonic signal , different from the first ultrasonic signal , that is transmitted through the cassette tube 46 to the ultrasonic receiver 56 b , 58 b ( broadly , the signal receiver ). the ultrasonic receiver 56 b , 58 b generates an output signal in response to the transmitted signal . the control unit 60 ( e . g ., the processor 60 a ) receives the output signal from the ultrasonic receiver 56 b , 58 b , determines a parameter value ( s ) of the received output signal , and analyzes the parameter value ( s ) to determine if it corresponds with an anticipated or expected parameter value ( s ) associated with the second drive signal ( s ). in other words , in the second mode of operation , the fluid monitoring system 62 determines whether the ultrasonic receiver 56 a , 58 a is detecting an anticipated or expected ultrasonic signal in accordance with the second drive signal . if the ultrasonic receiver 56 a , 58 a is not detecting the anticipated or expected ultrasonic signal , then this indicates that the fluid monitoring system 62 is malfunctioning , and the control unit ( e . g ., the processor 60 a ) may activate the malfunction alarm 70 and / or shut off the motor 52 . in one embodiment of the second mode of operation , the control unit 60 ( e . g ., the processor ) generates a second drive signal having a varying parameter ( e . g ., a varying frequency , such as when the first drive signal has a constant frequency ). for example , where the fluid sensor 56 , 58 includes an ultrasonic generator 56 a , 58 a , the control unit 60 ( e . g ., the processor 60 a ) may generate a sweep drive signal having a frequency ( or other parameter ) that varies over time . the sweep signal may have an initial frequency that is one of less than and greater than the frequency necessary for the ultrasonic generator 56 a , 58 a to produce the ultrasonic signal , and an ending frequency that is the other of greater than and less than the frequency necessary for the ultrasonic generator to produce the ultrasonic signal . the control unit 60 ( e . g ., the processor 60 a ) determines and stores amplitudes of the output signal generated by the ultrasonic receiver 56 b , 58 b . the stored amplitudes are analyzed by the control unit 60 ( e . g ., the processor 60 a ) to determine if the output signal had a sufficient change in amplitude that is generally commensurate with the change in frequency of the sweep signal . if the output signal did not have a sufficient change in amplitude that is generally commensurate with the change in frequency of the sweep signal , then this is indicative that the fluid monitoring system 62 is malfunctioning . in response , the control unit ( e . g ., the processor 60 a ) may activate the malfunction alarm 70 ( fig4 ). as non - limiting illustrations , fig6 - 8 are graphs depicting the change in amplitude of the output signal in response to the frequency change of the sweep signal ( from 2 . 2 mhz to 2 . 8 mhz ) delivered to the first fluid sensors 56 of three different fluid monitoring systems 62 . as can be observed from fig6 - 8 , the change in amplitude of the output signal indicative of the sweep signal frequency change in a non - malfunctioning fluid monitoring system 62 ( e . g ., fig6 ) is much greater than the change in amplitude of the output signal indicative of system noise in a malfunctioning fluid monitoring system 62 ( e . g ., fig7 and 8 ). fig6 is a graph depicting the response of a non - malfunctioning fluid monitoring system 62 during the second mode operation . as can be observed from fig6 , there is detectable and constant change in amplitude of the output signal ( from about 0 mv to about 1100 mv ) as the frequency of the drive signal is swept . as illustrated , the amplitude of the output signal undergoes a corresponding change in response to every change in frequency of the swept drive signal . fig7 is a graph depicting a low fail response of a malfunctioning fluid monitoring system 62 during the second mode of operation . as can be observed from fig7 , there is a relatively small change in amplitude of the output signal in a low range ( from about 8 mv to about 15 mv ) as the frequency of the drive signal is swept . this is an indication that the malfunction is related to the output signal ( e . g ., the ultrasonic receiver 56 b is malfunctioning ) or the malfunction is related to the input signal ( e . g ., the ultrasonic generator 56 a is malfunctioning ). moreover , because the amplitude of the output signal is relatively small , during the first mode of operation the fluid monitoring system 62 may give an indication that there is no fluid in the tube , although this is not necessarily the case . fig8 is a graph depicting a high fail response of a malfunctioning fluid monitoring system 62 during the second mode of operation . as can be observed from fig8 , there is a relatively small change in amplitude of the output signal ( from about 208 mv to about 215 mv ) as the frequency of the drive signal is swept . this is an indication that the malfunction is related to the output signal ( e . g ., the ultrasonic receiver 56 b is malfunctioning ) or the malfunction is related to the input signal ( e . g ., the ultrasonic generator 56 a is malfunctioning ). moreover , because the amplitude of the output signal is relatively large , during the first mode of operation the fluid monitoring system 62 would give an indication that there is fluid in the cassette tube , although this is not necessarily the case . one example of steps that may be performed by the control unit 60 ( e . g ., the processor 60 a ) in the second mode of operation to test the first fluid sensor 56 is depicted by a flow chart in fig9 . in particular , fig9 illustrates instructions stored in the computer readable storage medium ( memory 60 b ) of the control unit that are executed or run by the processor 60 a . similar , yet different , instructions may be stored to test the second fluid sensor 58 or any additional fluid sensors . the control unit 60 may perform the second mode of operation as the pump 10 is operating and on a periodic basis . at 200 , the control unit 60 ( e . g ., the processor 60 a ) generates a sweep signal that is received by the ultrasonic generator 56 a of the first sensor 56 . the sweep signal may sweep through a range of drive frequencies . for example , the sweep signal may increase in frequency , at incremental steps , from an initial frequency that is lower than the frequency required to function the ultrasonic generator ( e . g ., 2 . 2 mhz ) to an ending frequency that is higher than the frequency required to function the ultrasonic generator ( e . g ., 2 . 8 mhz ). at 202 , the control unit 60 ( e . g ., the processor 60 a ) receives the output signal from the ultrasonic receiver 56 b of the first sensor 56 . at 204 , the control unit 60 ( e . g ., the processor 60 a ) determines the amplitude of the output signal ( broadly , a parameter value of the output signal ). in other embodiments , other parameter values of the output signal ( e . g ., frequency , phase shift , etc .) may be determined and analyzed by the control unit 60 ( e . g ., the processor 60 a ) to determine the condition of the fluid in the cassette tube 46 . at 206 , the control unit 60 ( e . g ., the processor 60 a ) stores the determined amplitude and the frequency of the sweep signal that produced the determined amplitude in the memory 60 b . the control unit 60 b repeats steps 202 to 206 until the sweep signal has ended . at 208 , the control unit 60 ( e . g ., the processor 60 a ) determines if the amplitude of the output signal changes in accordance with the sweep signal . this step 208 may be accomplished by analyzing the stored amplitudes of the output signal to determine if there was a change in amplitude of the output signal over the frequency sweep . if the amplitude does not change in accordance with the sweep signal , then the control unit 60 ( e . g ., the processor 60 a ) may activate the malfunction alarm 70 at 210 indicating that the fluid monitoring system 62 is malfunctioning . the control unit 60 ( e . g ., the processor 60 a ) may also shut off the motor 52 . if the amplitude does change in accordance with the sweep signal , then the control unit 60 ( e . g ., the processor 60 a ) continues with normal operation ( e . g ., normal pumping according to protocol ) and stops the second mode of operation . embodiments can be implemented in digital electronic circuitry , or in computer hardware , firmware , software , or in combinations thereof . the controller of the compression system can be implemented in a computer program product tangibly embodied or stored in a machine - readable storage device for execution by a programmable processor ; and method actions can be performed by a programmable processor executing a program of instructions to perform functions of the controller of the compression system by operating on input data and generating output . the controller of the compression system can be implemented in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from , and to transmit data and instructions to , a data storage system , at least one input device , and at least one output device . each computer program can be implemented in a high - level procedural or object oriented programming language , or in assembly or machine language if desired ; and in any case , the language can be a compiled or interpreted language . suitable processors include , by way of example , both general and special purpose microprocessors . generally , a processor will receive instructions and data from a read - only memory and / or a random access memory . generally , a computer will include one or more mass storage devices for storing data files ; such devices include magnetic disks , such as internal hard disks and removable disks ; magneto - optical disks ; and optical disks . storage devices suitable for tangibly embodying computer program instructions and data include all forms of non - volatile memory , including by way of example semiconductor memory devices , such as eprom , eeprom , and flash memory devices ; magnetic disks such as internal hard disks and removable disks ; magneto - optical disks ; and cd rom disks . any of the foregoing can be supplemented by , or incorporated in , asics ( application - specific integrated circuits ) or fpgas ( field programmable logic arrays ). when introducing elements of aspects of the invention or the embodiments thereof , the articles “ a ,” “ an ,” “ the ,” and “ said ” are intended to mean that there are one or more of the elements . the terms “ comprising ,” “ including ,” and “ having ” are intended to be inclusive and mean that there may be additional elements other than the listed elements . as various changes could be made in the above constructions , products , and methods without departing from the scope of aspects of the invention , it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense .
detection of fluid conditions in a section of tube of an administration set . a light source is positioned adjacent to the tube to transmit an infrared light through the tube and any fluid therein . a light sensor senses the infrared light transmitted through the tube and generates an output signal . a frequency of the output signal is a function of an intensity of the light transmitted through the tube . a processor receives and determines the frequency of the output signal , and compares the determined frequency to threshold frequency values to determine whether fluid is in the tube . the processor also monitors the generated output signal to determine if the frequency of the output signal changes over a predetermined period of time , and determines whether fluid is flowing in the tube as a function of the determined change in frequency .