Abstract:
The patent discloses a method of verifying that a dialysis machine audio alarm has been sounded. The method senses a waveform of electric power, such as a waveform of the current or voltage that drives a speaker. When the speaker produces sound, power consumption changes the waveform in a manner that is detectable by electrical and electronic sensors. The amplitude envelope and frequency or period of the waveform is specific to the electrical and mechanical characteristics of the speaker. The waveform may be detected by a current-sensing resistor in series with the speaker power source, by a non-contact current transformer or hall-effect sensor, or may be sampled by an ADC. A computer program then compares this resulting signal to an expected signal or waveform and verify the speaker is working. If the speaker is not working, the machine sends a visual alarm or places itself in a safe state.

Description:
BACKGROUND 
       [0001]    The present patent relates to verification that an audio alarm has been sounded by a speaker upon activation of the alarm from a controller or other device. The verification particularly relates to patients using medical machines, such as dialysis machines, and even more particularly extracorporeal blood machines, such as hemodialysis machines, apheresis machines, and heart-lung operation machines. 
         [0002]    Modem medical machines perform a variety of life-sustaining and life-preserving tasks, from peritoneal dialysis and hemodialyis, to plasmapheresis, and even performing blood circulation and oxygenation that allows surgeons to perform medical procedures during a heart-bypass operation. Of course, machines are not perfect and conditions can arise during their use that threatens the completion or the quality of the procedure. For example, if a peristaltic pump is used to convey blood within tubing, the pump head could break, the motor could stall, and the tubing could develop leaks. Sensors on the instrument would detect these conditions in at least one way, such as a loss of blood pressure or a drop in motor current. 
         [0003]    If one of these failures occurred, for example, during a coronary artery bypass procedure, an alert operator on the medical team would immediately detect the condition and would take action to substitute a back-up machine or otherwise correct the situation. Other procedures, however, may have only a single operator, such as a caregiver, or may have only the patient present while the procedure is performed. An example is plasmapheresis. Plasmapheresis typically takes place at a medical center, with a head nurse or other professional to supervise one or more patients undergoing the procedure. If a machine failure occurs, or an unsafe condition develops, the plasmapheresis machine may flash a warning light or a warning on a video screen, or more likely, sound an audio alarm, such as a buzzer. The audio alarm alerts the patient or a nurse or other caregiver, or both, that attention is needed. If for any reason the audio alarm does not sound, the patient or nurse may notice the visual alarm or alert and is then motivated to correct the situation. 
         [0004]    The audio alarm may not sound if there is an alarm fault, such as a connectivity fault, in the chain between the machine fault or failure and the audio speaker that is intended to sound an alarm or alert as a result of the machine fault or failure, or other condition for which an alarm is desired. For example, an electrical wire may become disconnected from a speaker connection, or the wire may break, thus preventing an audio signal from reaching the speaker. Other electrical or physical problems could also result in a failure of the speaker to emit audible sound, such as failure of a relay within the control system, disconnection of power to an audio amplifier, or disconnection of a ground from the circuit. 
         [0005]    If an audio alarm fails to sound through the speaker, as noted above, corrective action is needed but personnel may not be alerted to the need. There are several ways to detect the failure of the sound. For example, the machine of which the speaker is a part may be equipped with a local microphone for detection of sound from the speaker. If the machine control system attempts to sound an audio alarm, but the alarm is not detected by the microphone, the failure to detect is interpreted as a speaker or other system failure and corrective action can be taken. Examples are depicted in U.S. Pat. No. 5,736,927 and U.S. Pat. No. 6,094,134. However, this method requires a separate microphone near the speaker, an amplifier and tuner for the microphone, as well as tuning of the microphone, and additional programming to perform the analysis and then to follow up. In addition, this system would be subject to interference from nearby noise, possibly including interfering noise that would mask the speaker output from detection by the microphone. 
         [0006]    What is needed is a way to ensure that when a medical device or machine sounds an alert or an alarm, that the intended speaker has actually sounded the alert or alarm. If the alarm has not been sounded, the medical device or machine is then programmed to take additional steps, such as sending a visual alert or alarm, or placing the machine in a safe mode. 
       SUMMARY 
       [0007]    One embodiment is a method for verifying operation of a speaker for a dialysis machine. The method includes steps of generating an audio alarm for the dialysis machine by sending electric power to a speaker, sensing a waveform of the electric power, and verifying the waveform is consistent with power consumption by the speaker. For instance, this may be accomplished by comparing the waveform to a waveform from a known good speaker. 
         [0008]    Another embodiment is a method for verifying speaker operation. The method includes steps of generating an audio alarm in a medical therapy machine by sending electric power to a speaker, sensing a waveform of the electric power, and verifying the waveform is consistent with power consumption by the speaker of the medical therapy machine by comparing an amplitude or a period of the waveform to a desired amplitude or period. 
         [0009]    Another embodiment is a method of verifying speaker operation. The method includes steps of generating an audio alarm by sending electric power to a speaker for a medical therapy machine, sensing a current or a voltage of the electric power, and verifying with a computer program that the current or the voltage is consistent with power consumption by a known good speaker by comparing an amplitude portion or a period portion of the current or the voltage to a desired amplitude portion or desired period portion. 
         [0010]    Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]      FIG. 1  depicts a dialyzer with a controller and an audio alarm; 
           [0012]      FIG. 2  is a schematic diagram of a circuit for verifying speaker operation during an alarm; 
           [0013]      FIG. 3  depicts waveforms for electric power for detecting speaker operation; 
           [0014]      FIGS. 4-9  depict diagrams of alternate circuits for verifying speaker operation; and 
           [0015]      FIG. 10  is a flowchart depicting a method for operating a dialysis machine and verifying speaker operation. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    It is very important, and may be life-preserving, to note quickly when a medical instrument, such as a dialyzer or other extracorporeal instrument, sounds an alarm or sends a signal indicating that an operating parameter has been exceeded. There may be danger to the machine, or more importantly, a condition may exist that indicates a threat to the health or life of the patient using the machine. 
         [0017]    An example of such a medical instrument is disclosed in  FIG. 1 . Medical instrument  10  may be a dialyzer or other medical instrument, including an operating portion  11  with fluid lines  12  for connection to a patient. An operating section  11  may perform dialysis or other therapeutic or diagnostic function for the patient under the supervision of a control section or computer  13 . Control section or computer  13  has at least an input keypad  14 , a video screen  14   a,  which may be a touch screen, an input number pad  14   b,  and a mouse  14   c.  The computer will also include input drive  15   a,  which may be suitable for a floppy drive or for a CD drive. 
         [0018]    The computer is configured with a port for Internet access  15   b,  as well as additional inputs and outputs, including ports  16 . The additional input ports may be any combination of serial ports, such as USB ports, or parallel ports. In some embodiments, the computer will be adapted to receive commands from a remote control unit, and will include an infrared receiver  15   c  for a hand-held remote. Inputs/outputs may include an optical input or output  15   d  and other digital or analog inputs. Control portion  15   e  includes a series of controls knobs or switches for operating the medical machine. There is also at least one lamp  15   f,  such as an LED, or flashing a visual alert. In order to sound an audio alarm, the instrument includes at least one speaker  17   a,  or alternately or in addition, headphones  17   b  or earbuds  17   c.  The instrument optionally includes a microphone connection  18 , and an antenna  19  for receiving at least remote commands or information. The antenna may be used for wireless (WiFi) internet access or may be used for remote, but closer, commands. 
         [0019]    The medical instrument depicted in  FIG. 1  is under the control of at least one microcontroller. The video screen  14   a  may also output a visual alarm. As noted, the instrument includes a speaker for sounding an audio alarm. One circuit for sounding the audio alarm or tone is depicted in  FIG. 2 . Alarm circuit  20  includes a microcontroller  21 , which includes pulse-width modulation (PWM) module  22  and an analog-to-digital converter (ADC)  23 . A voltage-signal output of the PWM module is sent to an audio power amplifier  24 , which is connected to additional power Vcc. The amplifier amplifies the input PWM voltage signal and sends the amplified signal to speaker  25 , when instructed to do so by the microcontroller. In order to detect current to the speaker, a current-sensing resistor  26  is placed between the speaker leads and ground  27 . The current-sensing resistor is a very low value, such as a few milliohms. The signal produced by resistor  26  is then sent to ADC  23 . The microcontroller  21  a memory or has access to a memory with a computer program or software algorithm for determining whether the waveform detected is a match with an expected waveform from the speaker. 
         [0020]    The upper portion of  FIG. 3  depicts a square wave signal as it is sent to the amplifier, and the lower portion of  FIG. 3  depicts the signal as it looks after it is amplified and sent to speaker  25 . The speaker produces tones whose fundamental frequency equals that of the input square wave. The speaker produces a back electromotive force (EMF), as seen in the lower portion of  FIG. 3 , and each pulse is changed, acquiring a slight ringing or oscillation on the leading edge and trailing edge of the pulse. This ringing or oscillation is caused by the step-change nature of a square wave and its interaction with the speaker. Each step produces a ringing of amplitude A and period T, imposed atop the waveform. The ringing or oscillation in this example has about three cycles, each cycle with diminishing amplitude, before the waveform resumes a relatively constant value. As noted above, the waveforms of  FIG. 3  depict current over a period of time. If, for example, the square wave is cycling at about 5 kHz, the period of each square wave is about 200 microseconds long, and the ringing in this instance lasts for about 25 microseconds per pulse, a frequency of about 40 kHz. Within reasonable limits, in the work done to date, the period T and the amplitude A are not affected by the frequency or duty cycle of the input square wave. The amplitude envelope and frequency or period of this waveform ringing are specific to the mechanical and electrical characteristics of the speaker, rather than of the input signal. 
         [0021]    This system will detect several failure modes of the speaker. For example, if the speaker fails open, due to a broken wire in the speaker&#39;s voice coil, no current will flow and no current will be detected. No current will flow, no power will be delivered to the speaker, and no sound will be heard. As a result, no ringing or oscillation is possible because there is no current and no power. The system disclosed herein will detect the lack of current and will also detect the lack of ringing or oscillation. If the speaker fails shorted, excessive current will flow to the speaker, and this will also be detected. The disclosed system will note the lack of current or the high current as a failure and will respond with appropriate actions, such as using a visual alarm or placing the machine in a safe mode automatically. Furthermore, more subtle damage to the speaker, e.g., speaker cone damage, can also be detected since such damage will also cause a change in the ringing waveform. 
         [0022]    Other circuits may also be used to detect a ringing or oscillation in the power for a positive indication that the speaker is operable and is working, i.e., converting electrical energy into acoustical energy. As noted, if there were an open in the circuit, no power would be consumed, and no current or voltage waveform would appear in certain parts of the circuit. If there is a disconnect between the PWM module and the amplifier, there is no signal to amplify and no current (or voltage) would appear on the outputs of the amplifier. If the connection between the power amplifier and the speaker is broken, no power will be applied to the speaker. If the speaker internal wiring (which may be modeled as a resistor and inductor in series) is severed or otherwise broken, the speaker will be inoperable and will not consume electricity. Of course, if there is a short circuit in any portion of the circuitry, the speaker may also be inoperable and will also not yield the desired or expected waveform. This method will also detect mechanical failures of the speaker itself, such as a damaged speaker cone or stuck speaker coil, and so forth, as well as the electrical failures discussed above. The circuit and technique described herein may be used to determine the condition of the speaker or alarm circuit of a dialyzer or other extracorporeal blood treatment machine. 
         [0023]    Other circuits, as shown in  FIGS. 4-8  below, may also be used.  FIG. 2  took advantage of the fact that electricity must complete a “current loop” or circuit in order for the circuit to function.  FIGS. 4 and 5  use a different detection method, employing differential current or voltage detection and a differential ADC to detect the resultant waveform. In  FIG. 4 , waveform detection circuit  40  includes a microcontroller  41 , a PWM module  22 , and a differential ADC  43 . The differential ADC accepts two inputs as shown from resistor  46 , which is connected in series between the audio power amplifier  44  and the speaker  25 . ADC  43  determines the differences between the inputs. This data is then used by a software program in microcontroller  41  to determine whether the waveform detected is indicative of a speaker that is working or of a speaker that is not working. The software program may be the same as the program in microcontroller  21  or may be different, tailored for differential inputs. In this example, the current-sensing resistor  46  is placed in series with one of the speaker leads. Since neither end of the resistor is referenced to ground, the differential ADC is needed. In the example of  FIG. 5 , detector circuit  50  includes a current sensing resistor  56  placed in series with the amplifier power source, Vcc. This differential circuit will function in a manner very similar to that of  FIG. 4 . Note that if the speaker is not operating, Vcc will not be called upon to supply power to the amplifier and the speaker, and the current or voltage sensed will be only quiescent current or voltage. 
         [0024]    Other variations of an alarm circuit  60  may also be used, as depicted in  FIG. 6 , which uses a grounded speaker  65  and resistor  66 , which is configured as a voltage input to ADC  63 . Microcontroller  61  also includes a PWM module  62 . Audio amplifier  64  utilizes Vcc as a power input and both the amplifier and the voltage-input resistor  66  are grounded with chassis ground  27 .  FIG. 7  and speaker detection circuit  70  is yet another variation on this theme, with precision low resistance resistor  76  in series between power source Vcc and amplifier  74 . The microprocessor  71  may be the same as other microprocessors mentioned above, or it may include a different software program attuned to the specific circuit of  FIG. 7 . PWM module  72  and ADC  73  may also be the same or may be different from the PWM modules in other examples discussed above. Speaker  75  receives power from amplifier  74 , which is connected to chassis ground  77 . 
         [0025]    Yet another technique is disclosed in the circuit of  FIG. 8 . In detection circuit  80 , an audio signal  81  is input into amplifier  83 , with an amplifier power supply  82 . Differential voltage probe  84  is connected between the leads to speaker  85  to detect the voltage to the speaker. Current transformer (CT) probe  86  is also used to detect the current flowing in the circuit. The voltage and current readings are then sent to an ADC or other signal processing circuitry, such as a digital signal processor (DSP), to determine a voltage, current, or power waveform for the speaker  85 , in the same manner used in the previous methods described. The detection circuit  90  of  FIG. 9  is similar. Audio signal  91  is input to power amplifier  93 , which is powered by DC power supply  92 . The voltage on each lead to speaker  95  is monitored by a grounded voltage probe  94 . Each probe is equipped with a current limiting resistor and a small capacitor, e.g., 47 pf, in addition to a voltage sensor  97 . Voltage sensor  97  may be a precision resistor or other voltage measuring device and may have a direct input to an ADC connected to the microprocessor or microcontroller. Current probe  96  detects the current in circuit  90  and sends a signal indicative of the current to a microprocessor or DSP for calculation of the waveform and a decision on whether the speaker is operational. 
         [0026]    The circuits described above can be used in a method of operating a dialysis machine, such as a peritoneal dialysis machine or a hemodialysis machine. The circuits described above may be incorporated as part of the dialysis machine. In other methods, the circuits described above, or other audio speaker operation detection circuits, may be made a part of an extracorporeal blood processing machine, such as a hemodialysis machine or an apheresis machine. One method of operating these machines is depicted in the flowchart of  FIG. 10 . The first step  101  of the method is to furnish a signal detector to detect, current, voltage or power to an alarm speaker. The signal detector does not necessarily require additional parts, in that the microprocessor may have sufficient memory for the required software, an analog-to-digital converter (ADC) may already be available in the machine control section, and so forth. Even the current-measuring or voltage-measuring resistor may already be available by using a spare resistor or trace already present in circuitry of the machine. 
         [0027]    In operation, the control system then sends  102  power to the audio speaker to detect current, voltage, or power with the detector. The detector circuit then sends  103  signals indicative of speaker consumption of current, voltage, or power to signal processing circuitry. The signal processing circuitry converts the analog signals of a speaker to digital signals useful for comparison, and a computer program then compares  104  the detected signals to the signal waveforms previously detected in operation of speakers that are known to be operating properly. A look-up table of such expected signals and their characteristics or parameters may be stored in memory of the microcontroller or in a memory accessible to the microcontroller. 
         [0028]    Using guidelines and logic from the program, the microcontroller and the computer program then determine  105  whether the waveform is indicative or characteristic of an operational speaker or whether the speaker appears inoperable. If the waveform conforms to the expected model, the sampling of data may be repeated periodically, as in a “test cycle” or start-up procedure. Alternatively, if the waveform conforms to expectations, no action need be taken. If the waveform appears to be consistent with damage or non-operation of the speaker, the microcontroller may cause  106  any therapy to cease, or may not allow therapy to begin if it fails a power-on self test (POST). The microcontroller may then send a visual alarm to alert operators or caregivers. The visual alarm may take the form of a alert message or sequence on a computer screen or by illuminating LEDs or flashing lights on a therapy machine. The machine may also be shut down or placed into a “safe” state if the waveform comparison or other check is not consistent with a correctly-functioning speaker. 
         [0029]    In addition to the ways discussed above to discern an incorrectly-functioning speaker, there are many other ways. For example, rather than looking at ringing or oscillation in the waveform, spectrum analysis of the sensed waveform may be used. This could include FFT (Fast Fourier Transform) or other spectrum analysis. As with the other techniques used, a FFT transform or other spectrum of the resultant current waveform may be made and compared with a reference spectrum, or known good spectrum, to determine whether the speaker is functioning correctly. 
         [0030]    Before any detection or sampling, the signal may first be filtered, such as by sending the signal through a high-pass filter. For example, if the fundamental frequency of the input voltage waveform is from about 100-200 Hz, a high pass filter that removes the fundamental components would allow easier detection of the ringing features of the resultant waveform. The high pass filter may be used for type A and B amplifiers. For type D, differential amplifiers, a low-pass filter for eliminating noise may yield better performance. In testing to date, the circuits described herein have worked for types A, B and D amplifiers. 
         [0031]    Other ways of processing the signals may be used to detect power consumption by the speaker. It is understood that a square wave is a composite signal made of a fundamental sinusoid and the odd sinusoid harmonics. It is more convenient, in some cases, to think of a square wave as merely a simple square or trapezoidal signal in the time domain (rather than the frequency domain). By subtracting the input waveform from the output waveform, the result is a distinctive signal that is indicative of the speaker&#39;s mechanical and electrical characteristics. The resultant waveform may be easier to detect and process. 
         [0032]    Other techniques may also be used in the detection circuit. For example, the waveform may be sensed as a current or a voltage by sensing the waveform across the terminals of the speaker, or by using a current-sensing resistor in series in the circuit. A non-contact sensor may be used, such as an inductively-coupled current transformer, or a hall-effect sensor, to detect the waveform. Alternatively, the resultant waveform may be sensed by capacitively coupling to the speaker wires or circuit board traces. 
         [0033]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.