Dialysis system and valve position detection with reduced valve noise - Patents.com

Abstract

Systems and methods for reducing valve noise and detecting valve position in a medical fluid system are disclosed. One method includes transmitting, by a microcontroller, a control signal to close a valve via a pulse-width modulated (PWM) signal. The valve is configured to control fluid flow within the medical fluid system. The valve may be open at least before the control signal is transmitted. The valve includes a housing, a solenoid coil, and a plunger. The method further includes applying power to the valve to measure a voltage across the valve and monitoring the voltage across the valve based on a sense resistor over a measurement interval. The measurement interval ends when the voltage reaches a predetermined threshold voltage. The method also includes comparing the measurement interval to a reference interval of a normally functioning closed valve and generating an estimate of the valve position based on the comparison.

Description

[Technical Field]

[0001] Technical Field FIELD OF THE DISCLOSURE The present disclosure relates generally to medical fluid treatments, and more particularly to dialysis fluid treatments using valves for medical fluid control. [Background technology]

[0002] background A variety of causes can cause a person's renal system to fail. Renal failure results in several physiological disturbances, such as the inability to balance water and minerals and to excrete the daily metabolic load. Toxic end products of metabolism, such as urea, creatinine, uric acid, and others, can accumulate in the patient's blood and tissues.

[0003]

[0003] Declining kidney function, particularly kidney failure, is treated by dialysis, which removes waste products, toxins, and excess water from the body that normally would be removed by normally functioning kidneys. Kidney replacement dialysis treatment is a potentially life-saving treatment and is therefore very important to many people.

[0004] One type of renal failure therapy is hemodialysis ("HD"), which generally uses diffusion to remove waste products from a patient's blood. Diffusion occurs due to a diffusion gradient across a semipermeable dialyzer between the blood and an electrolyte solution called the dialysate or dialysis fluid.

[0005] Hemofiltration ("HF") is another renal replacement therapy that relies on solute transport associated with the filtration of toxins from the patient's blood. HF is achieved by adding replacement or substitution fluid to the extracorporeal circuit during treatment. The replacement fluid, and fluid accumulated by the patient between treatments, is ultrafiltered during HF treatment, providing a mechanism for solute transport associated with filtration that is particularly useful for removing middle and large molecules.

[0006] Hemodiafiltration ("HDF") is a treatment modality that combines convective and diffusive clearance. HDF uses dialysis fluid flowing through a dialyzer, similar to standard hemodialysis, to provide diffusive clearance. In addition, replacement solution is provided directly to the extracorporeal circuit, thereby providing convective clearance.

[0007] Most HD, HF, and HDF treatments are performed in centers. Today, there is a trend toward home hemodialysis ("HHD"), in part because HHD can be performed daily, offering therapeutic benefits over in-center hemodialysis treatments, which are typically performed twice or three times per week. Studies have shown that more frequent treatments remove more toxins and waste products and result in less interdialytic fluid overload than patients receiving less frequent but potentially longer treatments. Patients receiving more frequent treatments do not experience as much downcycling (fluid and toxin fluctuations) as in-center patients who accumulate two or three days' worth of toxins before treatment. In certain areas, the nearest dialysis facility may be many miles from a patient's home, causing door-to-door treatment times to consume a significant portion of a patient's day. Treatments at facilities closer to the patient's home may also consume a significant portion of a patient's day. In comparison, HHD can be performed at night or during the day when patients are relaxing, working, or otherwise productive.

[0008] Another type of renal failure therapy is peritoneal dialysis ("PD"), in which a dialysis solution, also called dialysis fluid, is infused through a catheter into a patient's peritoneal cavity. The dialysis fluid contacts the peritoneal membrane within the patient's peritoneal cavity. Waste, toxins, and excess water enter the dialysis fluid from the patient's bloodstream through the peritoneal capillaries by diffusion and osmosis, creating an osmotic gradient across the membrane. An osmotic agent in the PD dialysis fluid provides the osmotic gradient. Spent or spent dialysis fluid is pumped out of the patient, thereby removing the waste, toxins, and excess water from the patient. This cycle may be repeated, for example, multiple times.

[0009] There are various types of peritoneal dialysis therapy, including continuous ambulatory peritoneal dialysis ("CAPD"), automated peritoneal dialysis ("APD"), tidal flow dialysis, and continuous flow peritoneal dialysis ("CFPD"). CAPD is a manual dialysis procedure. In this, a patient manually connects an implanted catheter to a drain, allowing used or spent dialysis fluid to drain from the peritoneal cavity. The patient then switches the fluid communication, connecting the patient's catheter to a bag of fresh dialysis fluid and infusing the fresh dialysis fluid into the patient through the catheter. The patient disconnects the catheter from the bag of fresh dialysis fluid, allowing the dialysis fluid to dwell in the peritoneal cavity, transporting waste, toxins, and excess water. After the dwell period, the patient repeats the manual dialysis procedure, for example, four times a day. Manual peritoneal dialysis requires significant patient time and effort and leaves significant room for improvement.

[0010] Automated peritoneal dialysis ("APD") is similar to CAPD in that the dialysis treatment involves drain, fill, and dwell cycles. APD machines, however, perform these cycles automatically, usually while the patient sleeps. APD machines relieve patients of having to manually perform treatment cycles and transport supplies during the day. APD machines are fluidly connected to an implanted catheter, a source or bag of fresh dialysis fluid, and a fluid drain. The APD machine pumps fresh dialysis fluid from the dialysis fluid source through the catheter and into the patient's peritoneal cavity. APD machines also allow the dialysis fluid to dwell within the cavity, allowing for the transfer of waste, toxins, and excess water. The source may contain multiple liters of dialysis fluid, including several solution bags.

[0011] APD devices pump used or spent dialysate from the patient's peritoneal cavity and drain it through a catheter. Similar to the manual process, several drain, fill, and dwell cycles occur during dialysis. A "final fill" may occur at the end of an APD treatment. The final fill fluid may remain in the patient's peritoneal cavity until the start of the next treatment, or it may be manually emptied at some point during the day.

[0012] Each of the dialysis modalities identified above, except for CAPD (which typically does not involve a machine), uses automated valves to control whether dialysis fluid, blood, or other fluids can or cannot flow. Valves also control the direction of fluid flow, such as where the fluid comes from or where it flows to. Different types of valves are used in dialysis systems. One type of valve is typically used with a disposable cassette having a rigid plastic part that defines a fluid flow path and a valve seat, and one or more flexible membranes that cover one or more sides of the rigid plastic part. The disposable cassette is typically loaded into a dialysis machine or cycler, which can close designated portions of one or more plastic sheets against the valve seat to block fluid flow, or force or allow the plastic to move away from the valve seat to allow fluid flow.

[0013] Another type of automated valve is the solenoid pinch valve, which instead pinches closed tubing carrying dialysis fluid, blood, or other fluids to block fluid flow. Here, a hard plastic disposable cassette is not required, saving costs. Generally, there are two types of pinch valves: solenoid pinch valves and motorized pinch valves. Another type of automated valve is the solenoid plunger valve. A solenoid plunger valve uses a plunger (e.g., a metal slug that moves through a solenoid coil by electromagnetic induction) to move a lever that presses against a seat to stop fluid flow (or moves the lever to press the seat to allow fluid flow). One problem with solenoid pinch valves and solenoid plunger valves (collectively referred to herein as "solenoid valves") is noise. For example, solenoid plunger valves typically energize a coil that moves the plunger within a housing. While the coil is energized, the plunger can be moved to open the tubing for fluid flow. When energy is removed from the coil, the compressed spring pushes the plunger in the opposite direction, allowing it to close the tube against a stop or wall located at the opposite end of the tube. As the plunger moves in either direction, it encounters an end of travel, which can involve the plunger contacting a fixed surface, either directly or with the tube between them. When the plunger contacts the end of travel, noise is generated. Noise from a solenoid valve can be annoying and problematic to patients. This is especially true for APD therapy, which is typically administered at night while the patient is sleeping.

[0014] Another problem with solenoid valves is knowing that the valve is open when energized (or closed when de-energized), i.e., knowing that energizing the coil has actually moved the plunger (e.g., in a solenoid plunger valve) or actually unpinched the tubing (e.g., in a solenoid pinch valve) so that the valve no longer blocks tubing or fluid flow. Assuming the valve is open when it may not actually be open creates an undesirable situation.

[0015] Due to each of the above problems, an improved method of operating a solenoid valve is needed. Summary of the Invention [Means for solving the problem]

[0016] overview The present disclosure describes a methodology for operating a solenoid valve for use in a medical fluid system, such as an automated peritoneal dialysis ("PD") system, that improves valve usability. While the system is primarily described in the context of PD, the improved solenoid valve operation of the present disclosure applies to devices used in any dialysis modality described herein, such as online HD, HF, HDF, acute HD, HF, and HDF. The improved solenoid valve operation of the present disclosure also applies to any medical fluid system in which treatment fluid flow, or patient fluid flow, is controlled by one or more valves.

[0017] In the PD example, the system includes a PD device or cycler. The PD device is described herein primarily as a durable system that attempts to limit disposable waste as much as possible, for example, by using an electromechanical piston pump to pump medical or PD fluid through the body of the pump. The PD fluid pump may also be an electromechanically driven gear, peristaltic, or centrifugal pump. In further alternative embodiments, a pneumatically driven PD fluid pump may be used. Any of the above pumping scenarios may be used in combination with the electromechanically actuated solenoid valves of the present disclosure. In one embodiment, the PD device or cycler can deliver unused, heated PD fluid to the patient at, for example, 14 kPa (2.0 psig) or greater. The PD device can remove used PD fluid or effluent from the patient at, for example, negative pressures of -9 kPa (-1.3 psig) or even greater. The unused PD fluid delivered to the patient may first be heated to body fluid temperature, for example, 37°C.

[0018] A PD device or cycler may also include multiple valves, any one, more, or all of which may be solenoid valves. The solenoid valves described herein may be of any type. For example, one type of solenoid valve uses an internal fluid path that opens or closes depending on whether a coil is energized. This type of solenoid valve is well suited to durable or reusable versions of a PD device or cycler. Another type of solenoid valve operates by opening or closing flexible tubing depending on whether a coil is energized. This type of solenoid valve is well suited to versions of a PD device or cycler that operate with disposable sets, but may also be used in durable versions of a PD device or cycler that have internal flexible tubing for operation with the solenoid valve.

[0019] The disclosed system and associated methodology automatically determines the position or state of a solenoid valve, which can be used to detect stuck valves and other valve faults. Automatically detecting valve position allows for automatic self-calibration of the solenoid valve hardware, in addition to detecting faults. Self-calibration also aids in implementing the noise reduction methods described herein. The system includes electrical hardware and software and is configured to control an electromechanical device, such as a solenoid valve.

[0020] Noise Reduction The PD device or cycler of the system operates in conjunction with a solenoid valve under the control of a control unit. In various embodiments, the control unit controls the operation of the solenoid valve to minimize the amount of noise generated during shocks during valve activation and deactivation. The control involves the use of a PWM drive waveform provided via a microcontroller programmed to increase the PWM duty cycle from 0 to 100% (closing the valve) and then decrease from 100 to 0% over a curved profile, as opposed to a momentary jump or drop-off. The curved profile becomes more horizontal toward the end of plunger travel, thereby reducing the shock force generated by the valve lever and reducing the sound or noise associated with the end of the solenoid valve opening and closing. In one embodiment, the curved profile is electrically implemented in the valve coil by a metal-oxide semiconductor field-effect transistor (MOSFET) and a diode.

[0021] Determining the position of the solenoid valve As described herein, solenoid valves generally open by energizing a coil that moves a plunger within the solenoid valve housing (e.g., in the case of a solenoid plunger valve) and / or releases a pinched tube (e.g., in the case of a solenoid pinch valve). It is desirable and necessary to assess the position of a solenoid valve in a medical fluid device or cycler (e.g., a PD, HD, HF, HDF, and / or CRRT device or cycler) to ensure the valve does not stick or otherwise become compromised. Furthermore, in the noise reduction systems and related methodologies disclosed herein, valve lever position detection is useful to ensure that the noise-reducing PWM drive waveform is initiated when the valve lever is in the fully open or fully closed position, as appropriate.

[0022] In one embodiment, an analog signal is sent from a point electrically upstream from the MOSFET along a position detection line that extends to a multiplexer that allows multiple solenoid valves to be analyzed sequentially. The output from the multiplexer is sent to a comparator that compares each valve's analog signal to a threshold. The comparator outputs a signal when a valve's analog signal reaches the threshold. The comparator outputs a signal to a microcontroller that is programmed to determine the valve lever position of a particular valve from the timing at which the signal was received.

[0023] In light of the disclosure described herein, and which does not limit the disclosure in any way, but which may be combined with any other aspect or portion thereof, a first aspect of the present disclosure is disclosed, which includes a drive circuit, a valve, and a microcontroller. The drive circuit is configured to control the valve via a pulse-width modulation (PWM) signal in response to a control signal received from the microcontroller. The valve is configured to control the flow of fluid within the medical fluid system. The valve includes a housing, a solenoid coil, and a plunger. The valve is configured to actuate the flow of fluid through a tube by applying a voltage to the solenoid coil via the drive circuit to move the plunger within the housing.

[0024] In a second aspect of the present disclosure, which may be combined with any other aspects or portions thereof, the instructions, when executed by a processor, further cause the processor to apply power to the valve via a drive circuit to measure a voltage across the valve; monitor the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; compare the measurement interval to a reference interval of a normally functioning closed valve; and generate an assessment of the valve position based on the comparison of the measurement interval and the reference interval.

[0025] In a third aspect of the present disclosure, which may be combined with any other aspect or a portion thereof, the valve is further configured to close the flow of medical fluid through the tube by de-energizing the solenoid coil via the drive circuit to move the plunger in the opposite direction from the housing to occlude the tube. Furthermore, the instructions, when executed by the processor, cause the processor to send a second control signal to the drive circuit, causing the drive circuit to lower the PWM signal to the solenoid coil to a 0% duty cycle. The lowering of the PWM signal moves the plunger in the opposite direction and such that the sound generated by the corresponding plunger is reduced compared to operation without the PWM signal.

[0026] In a fourth aspect of the present disclosure, which may be combined with any other aspects or portions thereof, the instructions, when executed by a processor, further cause the processor to apply a second power to the valve via the drive circuit to measure a second voltage across the valve; monitor the second voltage across the valve based on a sense resistor associated with the valve and via the drive circuit over a second measurement interval, the second measurement interval ending when the voltage reaches a predetermined threshold voltage; compare the second measurement interval to a second reference interval of a normally functioning open valve; and generate a second assessment of the valve position based on a comparison of the second measurement interval with the second reference interval.

[0027] In a fifth aspect of the present disclosure, which may be combined with any other aspect or a portion thereof, a method for determining a valve position in a medical fluid system is disclosed. The method includes: sending, by a microcontroller having a processor, a control signal to close a valve configured to control fluid flow in the medical fluid system, the valve being open at least before the control signal is sent, the valve including a housing, a solenoid coil, and a plunger; applying power to the valve via a drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measurement interval to a reference interval of a normally functioning closed valve; and generating an estimate of the valve position based on the comparison.

[0028] In a sixth aspect of the present disclosure that may be combined with any other aspect or portion thereof, the method further includes setting a power level to zero for a predetermined period of time to cause desaturation of the solenoid coil for the predetermined period of time before applying power to the valve.

[0029] In a seventh aspect of the present disclosure that may be combined with any other aspect or a portion thereof, the predetermined period is 5 milliseconds.

[0030] In an eighth aspect of the present disclosure that may be combined with any other aspect or portion thereof, monitoring the voltage across the valve includes receiving an indication from a comparator connected to the drive circuit of when the voltage reaches a predetermined threshold voltage.

[0031] In a ninth aspect of the present disclosure, which may be combined with any other aspects or portions thereof, the method further includes: sending, by the microcontroller, a second control signal to open the valve; applying a second power to the valve via a drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve over a second measurement interval based on the sense resistor and via the drive circuit, wherein the second measurement interval ends when the second voltage reaches a second predetermined threshold voltage; comparing the second measurement interval to a second reference interval of a normally functioning open valve; and generating a second assessment of the valve position based on the comparison of the second measurement interval with the second reference interval.

[0032] In a tenth aspect of the present disclosure that may be combined with any other aspect or portion thereof, any of the features, functionality, and alternatives described in association with one or more of Figures 1-16 may be combined with any of the features, functionality, and alternatives described in association with any other of Figures 1-16.

[0033] In light of the above aspects and the disclosure described herein, it is an advantage of the present disclosure to provide a medical fluid system with improved solenoid valve operation.

[0034] Another advantage of the present disclosure is to provide a medical fluid system having a solenoid valve methodology that reduces noise caused by valve operation.

[0035] A further advantage of the present disclosure is to provide a medical fluid system having a solenoid valve methodology that allows for determining the position or state of a solenoid valve, which can be used to detect when the solenoid valve is stuck or otherwise faulty.

[0036] Yet another advantage of the present disclosure is to provide a medical fluid system having a solenoid valve methodology that allows for determining the position or state of the solenoid valve using information from the solenoid valve itself, thereby reducing the required hardware.

[0037] Yet another advantage of the present disclosure is to provide a medical fluid system having a solenoid valve methodology that allows the solenoid valve to self-calibrate.

[0038] Yet another advantage of the present disclosure is to provide a medical fluid system having a solenoid valve methodology that enables the position or state of the solenoid valve to be determined with high accuracy and high resolution (e.g., better than 0.01 millimeters).

[0039] Yet another advantage of the present disclosure is to provide a medical fluid system with a solenoid valve methodology that uses common, low-cost electrical components.

[0040] Additional features and advantages are described in and will be apparent from the following detailed description and drawings. The features and advantages described herein are not all-inclusive, and in particular, many additional features and advantages will be apparent to those skilled in the art in view of the drawings and description. Also, it is not necessary for any particular embodiment to have all of the advantages enumerated herein, and it is expressly contemplated that each advantageous embodiment may be separately claimed. Furthermore, it should be noted that the language used herein has been chosen primarily for readability and descriptive purposes, and not to limit the scope of the inventive subject matter. For example, the present invention provides the following items: (Item 1) 1. A medical fluid system comprising: a valve configured to control fluid flow within the medical fluid system, the valve comprising a housing, a solenoid coil, and a plunger, the valve configured to actuate fluid flow through a tube by applying a voltage to the solenoid coil to move the plunger within the housing; a drive circuit configured to control the valve of the medical fluid system via a pulse width modulated (PWM) signal in response to a control signal; a microcontroller having a processor and a memory; Equipped with The memory stores instructions that, when executed by the processor, cause the processor to: causing the drive circuit to send a control signal to the drive circuit, causing the drive circuit to apply and raise a PWM signal to the solenoid coil of the valve; the rising edge of the PWM signal slowly moves the plunger until it reaches an end position within the housing; A medical fluid system, wherein the slow movement of the plunger reduces sound generated by the plunger. (Item 2) The instructions, when executed by the processor, further cause the processor to: applying power to the valve via the drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating an estimate of the valve position based on the comparison of the measurement interval to the reference interval; and Item 1. The medical fluid system according to item 1, (Item 3) The valve is further configured to close the flow of medical fluid through the tube by de-energizing the solenoid coil via the drive circuit to move the plunger in an opposite direction from the housing to occlude the tube, and the instructions, when executed by the processor, further cause the processor to: sending a second control signal to the drive circuit that causes the drive circuit to reduce the PWM signal to the solenoid coil to a 0% duty cycle; 3. The medical fluid system of claim 1, wherein the descending of the PWM signal causes the plunger to move in the opposite direction and such that the sound produced by the corresponding plunger is reduced compared to operation without the PWM signal. (Item 4) The instructions, when executed by the processor, further cause the processor to: applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a second measurement interval, the second measurement interval ending when the second voltage reaches the predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating a second estimate of the valve position based on the comparison of the second measurement interval to the second reference interval; and 4. The medical fluid system according to item 3, (Item 5) Item 1, wherein the valve, the drive circuit, and the microcontroller are contained within a peritoneal dialysis machine or a hemodialysis machine. (Item 6) 1. A method for determining a valve position in a medical fluid system, the method comprising: sending, by a microcontroller having a processor, a control signal to close a valve, the valve configured to control fluid flow in the medical fluid system, the valve being open at least prior to sending the control signal, the valve comprising a housing, a solenoid coil, and a plunger; applying power to the valve via a drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating information indicative of whether the valve is closed based on the comparison; and A method comprising: (Item 7) 7. The method of claim 6, further comprising setting a power level to zero for a predetermined period of time to cause desaturation of the solenoid coil for the predetermined period of time before applying the power to the valve. (Item 8) 8. The method of claim 7, wherein the predetermined period is 5 milliseconds (ms). (Item 9) 7. The method of claim 6, wherein monitoring the voltage across the valve includes receiving an indication from a comparator connected to the drive circuit of when the voltage reaches the predetermined threshold voltage. (Item 10) sending, by the microcontroller, a second control signal to open the valve; applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on the sense resistor over a second measurement interval, the second measurement interval ending when the second voltage reaches a second predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating second information indicative of whether the valve is open based on the comparison of the second measurement interval with the second reference interval; and Item 7. The method of item 6, further comprising: (Item 11) 1. A medical fluid system comprising: a valve configured to control fluid flow within the medical fluid system, the valve comprising a housing, a solenoid coil, and a plunger, the valve configured to actuate fluid flow by applying a voltage to the solenoid coil to move the plunger within the housing; a drive circuit configured to control the valve of the medical fluid system via a pulse width modulated (PWM) signal in response to a control signal; a microcontroller having a processor and a memory; Equipped with The memory stores instructions that, when executed by the processor, cause the processor to: transmitting a control signal to close the valve, the valve being open at least prior to transmitting the control signal; applying power to the valve via the drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating information indicative of whether the valve is closed based on the comparison; and A medical fluid system that performs the above. (Item 12) The instructions, when executed by the processor, further cause the processor to: 12. The medical fluid system of claim 11, wherein a power level is set to zero for a predetermined period of time to cause desaturation of the solenoid coil for the predetermined period of time before applying the power to the valve. (Item 13) Item 13. The medical fluid system of item 12, wherein the predetermined period is 5 milliseconds (ms). (Item 14) Item 12. The medical fluid system of item 11, wherein monitoring the voltage across the valve includes receiving an indication from a comparator connected to the drive circuit of when the voltage reaches the predetermined threshold voltage. (Item 15) The instructions, when executed by the processor, further cause the processor to: sending a second control signal to open the valve; applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on the sense resistor over a second measurement interval, the second measurement interval ending when the second voltage reaches a second predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating second information indicative of whether the valve is open based on the comparison of the second measurement interval with the second reference interval; and Item 12. The medical fluid system according to Item 11, (Item 16) Item 12. The medical fluid system of item 11, wherein the valve, the drive circuit, and the microcontroller are contained within a peritoneal dialysis machine or a hemodialysis machine. (Item 17) 1. A method of controlling a valve, the method comprising: sending a control signal by a microcontroller having a processor to a drive circuit to apply and raise a PWM signal to a solenoid coil of the valve; the valve is configured to actuate fluid flow by applying a voltage to the solenoid coil to move a plunger within a housing; the rising edge of the PWM signal slowly moves the plunger until it reaches an end position within the housing; The method wherein the slow movement of the plunger reduces sound produced by the plunger. (Item 18) applying power to the valve via the drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating an estimate of the valve position based on the comparison of the measurement interval to the reference interval; and Item 18. The method of item 17, further comprising: (Item 19) the valve is further configured to close the flow of medical fluid by de-energizing the solenoid coil via the drive circuit to move the plunger in an opposite direction from the housing to occlude the tube; The method further includes sending, by the microcontroller, a second control signal to the drive circuit that causes the drive circuit to reduce the PWM signal to the solenoid coil to a 0% duty cycle; 19. The method of claim 17 or 18, wherein the descending of the PWM signal causes the plunger to move in the opposite direction and such that the sound produced by the corresponding plunger is reduced compared to operation without the PWM signal. (Item 20) applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a second measurement interval, the second measurement interval ending when the second voltage reaches the predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating a second estimate of the valve position based on the comparison of the second measurement interval to the second reference interval; and 20. The method of claim 19, further comprising: [Brief explanation of the drawings]

[0041] [Figure 1] FIG. 1 is a schematic diagram of one embodiment for an automated PD system having solenoid valves, according to a non-limiting embodiment of the present disclosure.

[0042] [Figure 2] FIG. 2 is a cross-sectional elevation view of one embodiment for a two-way valve usable in the disclosed system and associated methodology, according to a non-limiting embodiment of the present disclosure.

[0043] [Figure 3] FIG. 3 is a cross-sectional elevation view of one embodiment for a three-way valve usable in the disclosed system and associated methodology, according to a non-limiting embodiment of the present disclosure.

[0044] [Figure 4] FIG. 4 is an exemplary solenoid valve drive circuit for the disclosed system and associated methodology that may be used to reduce operating noise associated with a solenoid valve, according to a non-limiting embodiment of the disclosure.

[0045] [Figure 5] FIG. 5 is a pulse width modulation ("PWM") plot showing a noisy valve without using the PWM drive waveform of the present disclosure, in accordance with a non-limiting embodiment of the present disclosure.

[0046] [Figure 6] FIG. 6 is a PWM plot showing a quiet valve using the PWM drive waveforms of the present disclosure for both energizing and de-energizing, in accordance with a non-limiting embodiment of the present disclosure.

[0047] [Figure 7] FIG. 7 is an expanded exemplary solenoid valve drive circuit for multiple valves that multiplexes the outputs from multiple valve circuits, which may be used to reduce operating noise associated with solenoid valves, in accordance with a non-limiting embodiment of the present disclosure.

[0048] [Figure 8] FIG. 8 is an electrical schematic diagram illustrating a drive circuit for determining the position of a valve lever in a given solenoid valve, according to an exemplary embodiment of the present disclosure.

[0049] [Figure 9A] FIG. 9 is a graphical output from a valve lever position test setup showing valve position based on inductance, according to a non-limiting embodiment of the present disclosure. [Figure 9B] FIG. 9 is a graphical output from a valve lever position test setup showing valve position based on inductance, according to a non-limiting embodiment of the present disclosure.

[0050] [Figure 10A] FIG. 10 is a data output from a valve lever position test setup showing the position of the plunger within the valve over time, in accordance with a non-limiting embodiment of the present disclosure. [Figure 10B] FIG. 10 is a data output from a valve lever position test setup showing the position of the plunger within the valve over time, in accordance with a non-limiting embodiment of the present disclosure. [Figure 10C]FIG. 10 is a data output from a valve lever position test setup showing the position of the plunger within the valve over time, in accordance with a non-limiting embodiment of the present disclosure. [Figure 10D] FIG. 10 is a data output from a valve lever position test setup showing the position of the plunger within the valve over time, in accordance with a non-limiting embodiment of the present disclosure.

[0051] [Figure 11] FIG. 11 illustrates various waveforms from a valve lever position test showing measured voltage over time to determine valve position when the valve is open and when the valve is closed, in accordance with a non-limiting embodiment of the present disclosure.

[0052] [Figure 12] FIG. 12 shows average waveforms from multiple valve lever position tests showing characteristic transition points for the valve, in accordance with a non-limiting embodiment of the present disclosure.

[0053] [Figure 13] 13 and 14 show valve lever 170, 210 position test data taken after the gate drive was desaturated, according to a non-limiting embodiment of the present disclosure. [Figure 14A] 13 and 14 show position test data of the valve levers 170, 210 taken after the gate drives were desaturated, in accordance with a non-limiting embodiment of the present disclosure. [Figure 14B] 13 and 14 show position test data of the valve levers 170, 210 taken after the gate drives were desaturated, in accordance with a non-limiting embodiment of the present disclosure.

[0054] [Figure 15] FIG. 15 illustrates recorded valve lever position test data showing the valve lever stuck closed, the valve lever functioning normally, and the valve lever stuck open when the valve is commanded to transition from an open to a closed state, in accordance with a non-limiting embodiment of the present disclosure.

[0055] [Figure 16] FIG. 16 illustrates recorded valve lever position test data showing the valve lever stuck closed, the valve lever functioning normally, and the valve lever stuck open when the valve is commanded to transition from a closed to an open state, in accordance with a non-limiting embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0056] Detailed Description System Overview Referring now to the drawings, and in particular to FIG. 1 , an exemplary system 10 incorporating solenoid valve operation of the present disclosure is illustrated. System 10 includes a dialysis machine 20, such as an automated peritoneal dialysis ("PD") machine, a control unit 100 having one or more processors 102, one or more memories 104, a video controller 106, and a user interface 108. Control unit 100 controls all electrical, fluid flow, and heating components of system 10 and receives outputs from all sensors in system 10. System 10 in the illustrated embodiment includes durable, reusable components that come into contact with medical fluids, such as PD fluids, requiring the PD machine or cycler 20 to be disinfected between treatments, e.g., by thermal disinfection.

[0057] System 10 of FIG. 1 includes an in-line resistance heater 56, reusable supply lines or tubing 52a1-52a4 and 52b, an air trap 60 operating in conjunction with upper and lower level sensors 62a and 62b, respectively, an air trap valve 54d, a vent valve 54e located along vent line 52e, reusable line or tubing 52c, a dialysis fluid pump 70, temperature sensors 58a and 58b, and pressure sensors 78a, 78b1, 78b2 and 78c. The system includes reusable patient tubing or lines 52f and 52g with respective valves 54f and 54g, dual lumen reusable patient line 28, hose reel 80 for retracting patient line 28, reusable drain tubing or line 52i extending to drain line connector 34 and having drain line valve 54i, and first and second reusable recirculation or disinfection tubing or lines 52r1 and 52r2 operating with respective disinfection valves 54r1 and 54r2. A third recirculation or disinfection tubing or line 52r3 extends between disinfection connectors 30a and 30b for use during disinfection. A fourth recirculation or disinfection tubing or line 52r4 extends between disinfection connectors 30c and 30d for use during disinfection.

[0058] System 10 further includes PD fluid containers or bags 38a-38c (e.g., holding the same or different formulations of PD fluid) that connect to distal ends 24d of reusable PD fluid lines 24a-24c, respectively. System 10d further includes a fourth PD fluid container or bag 38d that connects to distal end 24d of reusable PD fluid line 24e. Fourth PD fluid container or bag 38d may hold the same or a different type of PD fluid (e.g., icodextrin) as provided in PD fluid containers or bags 38a-38c. Reusable PD fluid lines 24a-24c and 24e, in one embodiment, extend through openings (not shown) defined or provided by housing 22 of cycler 20.

[0059] In the illustrated embodiment, system 10 includes four disinfection connectors 30a-30d for connecting to distal ends 24d of reusable PD fluid lines 24a-24c and 24e, respectively, during disinfection. System 10 also provides a patient line connector 32 including an internal lumen, e.g., a U-shaped lumen, that directs fresh or used dialysis fluid from one PD fluid lumen to the other PD fluid lumen of dual-lumen reusable patient line 28. Reusable supply tubes or lines 52a1-52a4 communicate with reusable supply lines 24a-24c and 24e, respectively. Reusable supply tubes or lines 52a1-52a3 operate with valves 54a-54c, respectively, to allow PD fluid to be drawn into cycler 20 from desired PD fluid containers or bags 38a-38c. Three-way valve 94a in the illustrated example allows control unit 100 to select between (i) 2.27% (or other) glucose dialysis fluid from container or bag 38b or 38c and (ii) icodextrin from container or bag 38d. In the illustrated embodiment, icodextrin from container or bag 38d is connected to a normally closed port of three-way valve 94a.

[0060] 1 also shows that system 10 includes and uses a disposable filter set 40 in fluid communication with the unused and used PD fluid lumens of dual lumen reusable patient line 28. Disposable filter set 40 includes a disposable connector 42 that connects to distal end 28d of reusable patient line 28. Disposable filter set 40 includes a connector 48 that connects to a patient transfer set. Disposable filter set 40 further includes a sterilizing-grade filter membrane 46 that further filters the unused PD fluid.

[0061] System 10, in one embodiment, is configured such that during filling, drain line 52i is fluidly connected downstream of dialysis fluid pump 70. In this manner, if drain valve 54i fails or somehow leaks during patient filling of patient P, unused PD fluid is forced into disposable drain line 36 instead of potentially drawing used PD fluid into pump 70. Disposable drain line 36, in one embodiment, is removed for disinfection while drain line connector 34 is capped by cap 34c.

[0062] System 10 further includes a leak detection pan 82 located at the bottom of housing 22 of cycler 20 and a corresponding leak detection sensor 84 that outputs to control unit 100. In the illustrated example, system 10 is provided with an additional pressure sensor 78c located upstream of dialysis fluid pump 70, which allows measurement of the suction pressure of pump 70 and helps control unit 100 more accurately determine pump volume. The additional pressure sensor 78c in the illustrated embodiment is located along vent line 52e, which may be filled with air or a mixture of air and PD fluid, but which should nevertheless be at the same negative pressure as the PD fluid located in PD fluid line 52c.

[0063] 1 includes redundant pressure sensors 78b1 and 78b2, one output of which is used for pump control as described herein, and the other pressure sensor output is a safety or watchdog output to ensure the control pressure sensor is reading accurately. Pressure sensors 78b1 and 78b2 are located along a line that includes third recirculation valve 54r3. In yet another example, system 10 may use one or more crosses, marked with an X in FIG. 1, which may (i) reduce the overall amount and volume of reusable internal tubing, (ii) reduce the number of valves required, and (iii) minimize the portion of the fluid circuit shared by both unused and used PD fluid.

[0064] 1 further includes an acid source, such as a citric acid container or bag 66. The citric acid container or bag 66 is in selective fluid communication with a second three-way valve 94b via a citric acid valve 54m located along a citric acid line 52m. The citric acid line 52m, in one embodiment, is connected to a normally closed port of the second three-way valve 94b to provide a redundant valve between the citric acid container or bag 66 and the PD fluid circuit during treatment. The redundant valve ensures that citric (or other) acid does not reach the treatment fluid line during treatment. Instead, citric (or other) acid is used during disinfection.

[0065] It should be understood that system 10 is not required to (i) be a dialysis system or (ii) use redundant or durable components that are sanitized between uses in order to employ the sensor thermoelectric heating of the present disclosure. Instead, system 10 may be any type of medical fluid system and may use a disposable set having disposable pump portions that contact the corresponding medical fluid. In the primary examples described herein, solenoid valves are described as operating in a PD device or cycler 20.

[0066] Any one or more or all of valves 54a-54h, 54m, and 54r1-54r4, 94a, and 94b may be solenoid valves, which may be of a type that uses an internal fluid path that opens or closes depending on whether a coil is energized. This type of solenoid valve is well suited to durable or reusable versions of PD devices or cyclers. Another type of solenoid valve for valves 54a-54h, 54m, and 54r1-54r4 operates by opening or closing flexible tubing depending on whether a coil is energized. This type of solenoid valve is well suited to versions of PD devices or cyclers that operate with disposable sets, but may also be used in durable versions of PD devices or cyclers that have internal flexible tubing for operation with the solenoid valve.

[0067] Referring now to FIG. 2, one suitable two-way solenoid valve 154 is shown for two-way valves 54a-54h, 54m, and 54r1-54r4. Valve 154 of FIG. 2 is of the type that uses an internal fluid path that opens or closes depending on whether a coil is energized. Valve 154 includes two main sections: a solenoid section 160 and a valve section 180. Solenoid section 160 includes a solenoid housing 162. Solenoid housing 162 supports a coil 164 that extends around an inner wall 162i of housing 162 and is energized to move or translate a solenoid plunger 166. A compression spring 168 is provided and positioned to bias plunger 166 to a closed position when energy is removed from coil 164.

[0068] FIG. 2 shows that the plunger 166 has a contact end 166e. The core portion 162c of the solenoid housing 162 is also provided with a stopper 162s. When the coil 164 is energized, a magnetic field is induced, causing the solenoid plunger 166 to translate from right to left within the inner wall 162i of the housing 162 until the contact end 166e of the plunger 166 abuts the stopper 162s, providing an end of travel for the plunger 166 in the valve-open position. The abutment of the contact end 166e with the stopper 162s causes noise, which can be problematic for PD patients, especially when the patient is trying to sleep. Described herein are structures and related methodologies that help reduce noise caused by the abutment of the contact end 166e with the stopper 162s.

[0069] 2 shows the two-way solenoid valve 154 in a no-fluid, or closed, state. Here, the coil 164 is de-energized, causing the compression spring 168 to urge the contact end 166e of the plunger 166 away from the stopper 162s provided on the core portion 162c of the solenoid housing 162. The lever end 166l of the plunger 166 is translated such that the lever 170, rotatably held on the lever end 166l of the plunger 166, tilts to close the fluid path located within the valve portion 180 of the valve 154.

[0070] The valve portion 180 of the valve 154 includes a valve housing 182. The valve housing 182 defines a fluid inlet 184 and a fluid outlet 186. Attached to the portion of the lever 170 that extends into the valve housing 182 is a membrane or stopper 188, which may be made of a medically safe, compressible (sealable) rubber, such as silicone. In the closed position shown in FIG. 2, with the coil 164 de-energized and the compression spring 168 extended, the lever 170 pivots the membrane or stopper 188 to contact the interior of the outlet 186, e.g., against the tilted port 186p, sealing it closed and thereby preventing fluid flow. When the coil 164 is energized, the plunger 166 moves left, compressing the spring 168 and pivoting the lever 170 until the membrane or stopper 188 stops in a substantially vertical position, away from the tilted port 186p of the outlet 186. Here, a fluid, such as water or a PD fluid, can flow from a fluid inlet 184 , around a membrane or stopper 188 , and through a fluid outlet 186 .

[0071] When the valve 154 is closed and the membrane or stopper 188 is sealed against the tilted port 186p of the fluid outlet 186, the fluid pressure downstream of the outlet 186 is lower than the fluid pressure upstream of the fluid inlet 184. The pressure differential helps seal the membrane or stopper 188 against the tilted port 186p, so that the compression spring 168 does not need to provide the force necessary (or all of the force necessary) to keep the membrane or stopper sealed against the tilted port. The primary function of the compression spring 168 is to translate the plunger 166 when the coil 164 is de-energized. However, it should be understood that the pressure differential that helps seal the membrane or stopper 188 against the tilted port 186p when the valve 154 is to be closed also counters the magnetic force induced when the coil 164 is energized. Structures and associated functions for ensuring that the valve 154 opens properly when commanded to open are described herein.

[0072] Referring now to FIG. 3, a three-way solenoid valve 194 suitable for the three-way valves 94a and 94b is shown. The valve 194 of FIG. 3 is of a type that uses an internal fluid path that opens or closes depending on whether a coil is energized. Similar to valve 154, the valve 194 includes two main sections: a solenoid section 200 and a valve section 220. The solenoid section 200 is essentially the same as the solenoid section 160 of valve 154. The solenoid section includes a solenoid housing 202 that supports a coil 204 that is energized to move or translate a solenoid plunger 206. A compression spring 208 is provided and positioned to bias the plunger 206 to a closed position when energy is removed from the coil 164. A contact end 206e of the plunger 206 abuts a stopper 202s provided on a core portion 202c of the solenoid housing 202 when the coil 204 is energized. The abutment of the contact end 206e and the stopper 202s causes noise, which can be problematic for PD patients, especially when the patient is trying to sleep. Described herein are structures and related methodologies that help reduce the noise caused by the abutment of the contact end 206e and the stopper 202s.

[0073] 3 shows the three-way solenoid valve 194 in a normally closed state. Here, the coil 204 is not energized, and the compression spring 208 urges the contact end 206e of the plunger 206 away from the stopper 202s provided on the core portion 202c of the solenoid housing 202. The lever end 206l of the plunger 206 is translated such that the lever 210, which is rotatably held on the lever end 206l of the plunger 206, tilts to close the fluid path located within the valve portion 220 of the valve 194.

[0074] Valve portion 220 is where three-way valve 194 differs from two-way valve 154. Valve portion 220 includes a valve housing 222 that defines a fluid inlet 224, a normally closed fluid outlet 226, and a normally open fluid outlet 228. Attached to the portion of lever 210 that extends into valve housing 222 is a membrane or stopper 230, which again may be made of a medically safe, compressible (sealable) rubber such as silicone. In the normally closed position of FIG. 3, with coil 204 de-energized and compression spring 208 extended, lever 210 pivots membrane or stopper 230 to contact the interior of normally closed fluid outlet 226, e.g., against angled port 226p, sealing the closed state, thereby preventing fluid flow through the normally closed outlet. When coil 204 is energized, plunger 206 moves to the left, compressing spring 208 and pivoting lever 210, causing membrane or stopper 230 to move away from angled port 226p of normally closed fluid outlet 226 and instead contact and seal against angled port 228p inside normally open fluid outlet 228, for example, thereby preventing fluid flow through the normally open outlet. In the normally closed state, three-way valve 194 allows fluid, such as water or PD fluid, to flow from fluid inlet 224 through normally open fluid outlet 228. In the normally open state, three-way valve 194 allows fluid, such as water or PD fluid, to flow from fluid inlet 224 through normally closed fluid outlet 228.

[0075] The higher fluid pressure through fluid inlet 224 serves to seal membrane or stopper 230 against both normally closed port 226p and normally open port 228p, where the pressure is lower at normally closed fluid outlet 226 and normally open fluid outlet 228. However, it should be understood that the pressure differential that serves to seal membrane or stopper 230 against angled ports 226p, 228p also counters (i) the magnetic force induced when coil 164 is energized to open normally closed fluid outlet 226, and (ii) the force of compression spring 208 when coil 164 is de-energized to open normally open fluid outlet 226. Structures and associated features are described herein to ensure that the valve opens properly when normally closed fluid outlet 226 is commanded to open.

[0076] Solenoid valve methodology for noise reduction As previously mentioned, a reliable methodology for reducing noise caused by solenoid valves in medical fluid delivery operations is desirable and needed. Noise reduction is particularly relevant for peritoneal dialysis systems, which operate in close proximity to patients and may occur at night while the patient is asleep, making noise reduction important. A desirable PD system may be one that maintains noise levels below 33 decibels. Figure 4 illustrates an exemplary solenoid valve drive circuit 110 for the disclosed system and associated methodology that may be used to reduce operational noise associated with the solenoid valve.

[0077] The drive circuit 110 includes a programmable microcontroller 112 provided as part of the control unit 100 ( FIG. 1 ). The microcontroller 112 includes a pulse-width modulated (“PWM”) channel output 114, which in one embodiment is greater than 20 kHz. The PWM drive waveform is sent along line 116 to a metal-oxide semiconductor field-effect transistor (“MOSFET”) 120. In the illustrated example, the MOSFET 120 may be an IRF640 MOSFET; however, the MOSFET 120 may alternatively be any N-channel logic-level gate MOSFET capable of handling currents in excess of 323 mA. The MOSFET 120 operates in combination with a diode 130 to power the coil 164 of the two-way valve 154 or the coil 204 of the three-way solenoid valve 194. The diode 130 in the illustrated example may be a 1N400X diode; however, similar diodes may be used instead. Notably, the MOSFET 120 and diode 130 may be standard and relatively inexpensive components.

[0078] 5 illustrates the operation of the solenoid valves 154, 194 without the driver circuit 110, where the PWM signal transitions from 0 to 100% instantaneously to energize the coil 164, 204, and from 100% instantaneously to 0% instantaneously to de-energize the coil 164, 204. In both cases, a loud click or noise is generated. Here, the PWM frequency is greater than 20 kHz, e.g., 78.1 kHz in one test.

[0079] FIG. 6 illustrates the operation of the solenoid valves 154, 194 using a drive circuit 110 programmed by software to follow a first curved PWM profile 132 from 0 to 100% and a second curved PWM profile 134 from 100%. In both cases, loud clicks or noises are eliminated. In the illustrated embodiment, the first curved PWM profile 132 executes over 256 steps at 5 milliseconds per step, taking a total of 1.28 seconds to fully energize the coils 164, 204. Furthermore, in the illustrated embodiment, the second curved PWM profile 134 executes over 120 steps at 40 milliseconds per step, taking a total of 4.8 seconds to fully de-energize the coils 164, 204. Again, the PWM frequency is greater than 20 kHz, e.g., 78.1 kHz in one test. It should be understood from FIG. 6 that the drive circuit 110 does not require position feedback, and both actuation and de-actuation are silent. 5. Also, the solenoid valves 154, 194 are actively opened and closed without the use of the drive circuit 110, similar to FIG.

[0080] FIG. 7 shows a driver circuit 110 expanded to drive multiple coils 164, 204 of multiple solenoid valves 154, 194. The driver circuit 110 of FIG. 7 also includes a programmable microcontroller 112 provided as part of the control unit 100 (FIG. 1). The driver circuit 110 of FIG. 7 includes multiple, e.g., two, PWM channel outputs 114. The PWM drive waveforms are sent from the PWM channel outputs 114 along line 116 to a shift register 118. The shift register 118 includes cascaded flip-flops sharing a single clock signal to shift the PWM drive waveform from one MOSFET 120, diode 130, and solenoid valve 154, 194 to the next, e.g., nth, MOSFET 120, diode 130, and solenoid valve 154, 194. FIG. 7 shows that the drive circuit 110 may include a limited number of PWM channel outputs 114 to drive multiple solenoid valves 154, 194 to significantly reduce noise output. Determining the position of the solenoid valve

[0081] As previously mentioned, a reliable methodology for verifying the position of the levers 170, 210 within the solenoid valves 154, 194 to ensure the valves are not stuck or otherwise compromised is desired and needed. Knowing the position of the levers 170, 210 also enables self-calibration of the noise-reduced PWM drive waveforms described above, such that (i) the fully closed or 0% PWM position of the levers 170, 210 may be verified by the microcontroller 110 before sending the noise-reduced PWM drive waveform 132 to the solenoid valve, and (ii) the fully open or 100% PWM position of the levers 170, 210 may be verified by the microcontroller 110 before sending the noise-reduced PWM drive waveform 134 to the solenoid valve. To obtain the position of the levers 170, 210 within the solenoid valves 154, 194, respectively, a resistor 136, e.g., a 0.1 ohm resistor, is placed between the MOSFET 120 and ground 138. Additionally, for each valve 154, 194, a position sense line 142 extends from a point between the MOSFET 120 and the resistor 136 to an analog multiplexer 140. The multiplexer 140 selects between multiple analog signals traveling along the position sense line 142 for output on a single output line 144 extending from the multiplexer 140. The multiplexer 140 allows multiple valves 154, 194 to share a single comparator 150.

[0082] The comparator 150 is configured to compare an analog position sense signal traveling along a position sense line 142 from one of the solenoid valves 154, 194 with a threshold signal 152. The comparison by the comparator 150 provides an output indicative of the position of the lever 170, 210 in the solenoid valve 154, 194, which is sent along a comparator output line 146 to a general purpose input / output (GPIO) port 148 of the programmable microcontroller 110, which uses programmed software to analyze the comparator output, thereby knowing / verifying the position of the lever 170, 210 in the solenoid valve 154, 194 by sampling each valve via the multiplexer 140.

[0083] FIG. 8 is an electrical schematic diagram illustrating a drive circuit 110 for determining the position of a valve lever in a given solenoid valve, according to an exemplary embodiment of the present disclosure. As shown in FIG. 8, the drive circuit 110 includes a solenoid inductor coil 802 that drives the valve. A current for driving the solenoid inductor coil 802 may be provided by a voltage source 804 (e.g., 24 V). A sense resistor 806 may be used to measure the current 820 driving the solenoid inductor coil 802 (e.g., by dividing the voltage by the resistance of the sense resistor 806). For example, the current 820 passing through the sense resistor 806 may be substantially the same as the current passing through the solenoid coil inductor 802 (e.g., to trigger the solenoid valve). Thus, if a voltage is to be measured across the sense resistor 806, the voltage is proportional to the current 820. In the exemplary drive circuit 110 shown in FIG. 8, the sense resistor 806 exhibits a resistance of 0.1 ohms.

[0084] A current 820 for driving the solenoid coil may pass through a transistor 808 (e.g., a MOSFET (IRF640)) in response to commands from a microcontroller (e.g., microcontroller 112). For example, a pulse-width modulated (PWM) waveform may be generated by associated PWM hardware within the microcontroller. The PWM waveform may drive a gate 810 of the transistor 808. The current 820 entering the solenoid coil valve 802 may be measured using a sense resistor 806. In some embodiments, the current 820 may be filtered using an RC filter 816 (e.g., a low-pass filter) including, for example, a capacitor and a resistor. The current 820 may enter a comparator 812. The comparator 812 is configured to compare a voltage associated with the current 820 to a threshold voltage provided by a threshold voltage source 814. For example, as shown in FIG. 8, the threshold voltage may be 0.7 V. When the voltage associated with the current 820 passing through the solenoid coil transistor 802 is higher than the threshold voltage 814, the comparator 812 is configured to generate a digital output (e.g., a “high” or “1” signal) that is sent to a microcontroller (e.g., the microcontroller 112) via a GPIO line 818. The voltage associated with the current 820 may be used to generate waveforms described herein, for example, in connection with subsequent figures. In some embodiments, the threshold voltage may be configured to suit an expected voltage range of the current 820, which may depend on the resistance value of a sense resistor 806 disposed within the drive circuit 110.

[0085] FIG. 9 is a graphical output from a position test configuration of the valve lever 170, 210, showing the valve position based on inductance, according to an exemplary embodiment of the present disclosure. Specifically, FIG. 9 shows two graphs: an upper graph 900a shows voltage 902 on the y-axis, which is based on current 820 sensed in the drive circuit 110 (e.g., based on the resistance of the sensor resistor 806) over time 904 shown on the x-axis; and a lower graph 900b shows the digital output of the comparator 812 over the same time range. The position of the plunger (e.g., a metal slug) within the solenoid coil, which indicates the valve position, is believed to reflect the inductance of the solenoid coil. Therefore, by measuring the inductance of the solenoid coil, the extent to which the plunger is within the solenoid coil (e.g., whether the plunger is fully in, fully out, or somewhere in between) can be determined. For example, a plunger fully inside the solenoid coil may result in a higher inductance than a plunger that is outside or not fully inside. When the valve is open (e.g., and not actuated), less of the plunger is inside the magnetic field induced by the solenoid coil (because the plunger may be partially outside the solenoid coil), and the inductance may be lower. However, because the inductance is lower, the magnetic field increases more quickly, and the current through the solenoid coil may change more quickly over time. Because the current is correlated with the voltage (e.g., based on the sense resistor 806), the voltage changes more quickly over time, causing the voltage to reach a given threshold voltage (e.g., 30 mV) relatively quickly. In contrast, when the solenoid valve is closed, more of the plunger may be located inside the solenoid coil, and therefore more inside the magnetic field induced by the solenoid coil. This presence increases the inductance and may cause the current to change more slowly. Because the current is correlated with the voltage (e.g., based on the sense resistor 806), the voltage changes more slowly over time, causing the voltage to reach a given threshold voltage (e.g., 30 mV) relatively slowly.

[0086] As shown in graph 900a, curve 910 represents the voltage over time for a scenario in which the valve is open (e.g., and not actuated), while curve 912 represents the voltage over time for a scenario in which the valve is closed. As noted above, curve 910 shows that the voltage associated with an open valve reaches a given threshold voltage of 30 mV at time 906, much earlier than time 908, when curve 912 reaches the same threshold voltage. This difference is therefore the result of a difference in the position of the plunger within the solenoid coil, which results in different inductance levels and a difference in the time it takes for the solenoid coil to reach the threshold voltage. Therefore, the difference between times 906 and 908 may reflect a change in inductance. For the particular valve associated with the graph results shown in FIG. 9, when the valve is open (e.g., the plunger is not completely inside the magnetic field of the solenoid coil), the inductance of the valve is 113 mH. However, when the valve is closed (e.g., the plunger is pulled further inside the solenoid coil), the inductance of the valve is 128 mH. Therefore, the difference between times 906 and 908 may correspond to the difference between these inductances (113 mH and 128 mH). By accurately measuring the time, it may be possible to distinguish between an open and a closed valve.

[0087] As shown in graph 900b, the digital output of the comparator of the drive circuit 110 associated with the valves described above exhibits curves 914 and 916, corresponding to curves 910 and 912, respectively. Curve 914 of graph 900b, representing the digital output of the comparator for an open valve, shows that the comparator provides a high signal (e.g., a true or "1" signal) when the voltage associated with the open solenoid coil crosses the voltage threshold. Curve 916 of graph 900b, representing the digital output of the comparator for a closed valve, shows that the comparator provides a low signal (e.g., a false or "0" signal) when the voltage associated with the open solenoid coil crosses the voltage threshold. However, because there is a difference in the inductance associated with an open valve versus a closed valve (e.g., 113 mH vs. 128 mH, respectively), resulting in a difference in the time it takes for the applied voltage to reach the voltage threshold, there is a difference in the time (e.g., as shown in graph 900b) by which the digital output of the comparator shifts its signal for each curve.

[0088] FIG. 10 illustrates data output from a position test configuration of a valve lever 170, 210 showing the position of a plunger within a valve over time, according to a non-limiting embodiment of the present disclosure. For example, graph 1002 in FIG. 10 illustrates data output showing the position of the plunger after the valve has been conventionally opened or conventionally closed, and graph 1004 in FIG. 10 illustrates data output showing the position of the plunger after the valve has been opened or closed using the systems and methodologies described above to reduce noise. In these graphs 1002, 1004, the vertical axis represents time, and the horizontal axis represents plunger position (e.g., 0 mm to 1.8 mm). The graphs illustrate with high resolution that the plunger can move a distance of 1.8 mm to actuate the valve. Each line is a sample point at a given time, and the displacement is represented numerically. As illustrated by the graphs in FIG. 10, the systems and methods presented herein may enable the position of a valve (e.g., by the position of the plunger within the valve) to be determined with high resolution (e.g., better than one-hundredth of a millimeter).

[0089] FIG. 11 illustrates various waveforms from a position test of a valve lever 170, 210 showing measured voltages over time to determine the position of the valve when the valve is open and when the valve is closed, in accordance with a non-limiting embodiment of the present disclosure. For example, graphs 1102 and 1104 illustrate the voltage measured at the intersection of the drive circuit 110 (e.g., current 820 in FIG. 8 ) combined with the voltage 810 provided to the gate of transistor 808 (e.g., gate drive). Graph 1102 illustrates the voltage measured over time to determine the actual position of the valve when the valve is reportedly in an open state, while graph 1104 illustrates the voltage measured over time to determine the actual position of the valve when the valve is reportedly in a closed state. Additionally, graph 1106 superimposes graph 1104, which illustrates the actual voltage measured over time for a valve that is reportedly closed, with a reference waveform 1108 of a reference voltage over time for a valve that is actually closed. Graph 1110 superimposes a reference waveform of the reference voltage measured over time for the valve in an actual open state with a reference waveform 1108 of the reference voltage over time for the valve in an actual closed state. For each of these graphs, the measured voltage may be based on the sense resistor 806 used in the drive circuit 110. In some aspects, the waveform may be measured or output by a processor or microprocessor (e.g., in the microcontroller 112).

[0090] The time difference between edge 1112 and edge 1114 (e.g., the difference in the time it takes to reach the threshold voltage) indicates that the valve is open or closed, respectively. As previously described, when the valve is open (e.g., when the plunger is partially outside the magnetic field of the solenoid coil associated with the valve), the inductance of the solenoid coil may be at its lowest point, causing the current level entering the valve to rise more quickly until it reaches the threshold voltage. Because the current is proportional to the measured voltage (e.g., based on sense resistor 806), the waveform of an open valve shows a faster rise in the measured voltage to the threshold voltage. This faster rise is shown, for example, in graph 1102 and edge 1112. When the valve is closed, the plunger is located further into the magnetic field of the solenoid coil, causing the current to rise more slowly. Therefore, as shown in graphs 1104 and 1106, the measured voltage (e.g., across sense resistor 806) may take longer to reach the same threshold voltage.

[0091] For valves whose actual state (e.g., open or closed) or position of the plunger has not yet been determined or confirmed, the voltage may similarly be measured (e.g., using a sense resistor 806 as used in the drive circuit 110). The microcontroller 112 may search for a transition in the measured voltage (e.g., edges 1112 and 1114) in the measured voltage waveform. The transition may be the point at which the measured voltage reaches a threshold voltage. The microcontroller 112 may determine the time it takes for the valve to reach that transition (e.g., threshold voltage). The position of the plunger within the valve, and therefore the state of the valve, may be determined by determining whether the time to reach the transition is closer to the time it takes to reach edge 1114 (e.g., in this case, the valve may be closer to a closed state) or closer to the time it takes to reach edge 1112 (e.g., in this case, the valve may be closer to an open state). Thus, the exact point of the plunger may be determined based on the time it takes the valve to reach the threshold voltage, and that time may be compared to the known times for reaching the threshold voltage in the closed and open states. For example, if the time it takes for the measured voltage at the valve to reach the threshold voltage is halfway between the time it takes to reach edges 1112 and 1114, then the position of the plunger in the valve is halfway between fully inside and fully outside, and the valve is neither open nor closed (i.e., the valve is stuck). In some embodiments, the microcontroller 112 may perform image processing on the measured voltage of the valve to obtain a clearer waveform to better identify transition points (e.g., the time it takes for the measured voltage to reach the threshold voltage).

[0092] The microcontroller 112 is configured to provide information indicating whether the valve is in the commanded position. In some embodiments, the microcontroller 112 may generate an alert (e.g., via the user interface 108) after detecting that the valve is not in the commanded position. Additionally or alternatively, the microcontroller 112 may pause the dialysis treatment. In some cases, the microcontroller 112 may attempt to re-actuate the valve several times to move it to the recommended position. If the valve position is still incorrect, the microcontroller 112 may then generate an alert.

[0093] FIG. 12 shows an average waveform from multiple valve lever 170, 210 position tests performed on a valve, showing a characteristic transition point 1202 for that valve. The transition point 1202 may indicate the average time at which the average measured voltage from the valve reaches a threshold voltage. As shown in FIG. 12, averaging multiple waveforms results in a very noisy averaged waveform. For example, individual pulses of various duty cycles in the averaged waveform may not be distinguishable. Even so, the transition point 1202 may be readily distinguishable and can be used to determine valve position to a high resolution (e.g., at least better than 0.01 mm). Furthermore, the various duty cycles may determine how much total power is supplied to the valve to generate the measured voltage waveform.

[0094] As described herein in connection with the following figures, measuring the position of a valve when the valve is not actuated (e.g., when the valve is not powered) may involve different pre-processing steps than when the valve is actuated because the solenoid coil associated with the valve may saturate, which may affect the waveform of the measured voltage.

[0095] 13 and 14 show position test data of the valve lever 170, 210 recorded after the gate drive is desaturated, according to a non-limiting embodiment of the present disclosure. In some embodiments, to effectively evaluate the valve's measurement voltage waveform output, the microcontroller 112 may need to temporarily turn off the pulse width modulation (PWM) and reduce the power supplied to the drive circuit 110 to zero for a predetermined period of time (e.g., 5 ms). The plunger associated with the valve may be prevented or rendered unable to move anywhere within that predetermined period (e.g., due to the plunger's mass). Additionally, the microcontroller 112 may turn off power for a predetermined period of time to desaturate the solenoid coil associated with the valve. The predetermined period may be long enough to allow the solenoid coil to make useful measurements during the measurement interval by minimizing noise caused by saturation, but not long enough to release the valve or cause the valve to chatter. After a predetermined period of time has elapsed, the microcontroller 112 may reapply power to the valve (eg, by applying current to the gate of transistor 808).

[0096] Thus, as shown in FIG. 13 , when a given valve state and position of a plunger associated with the valve is measured, the microcontroller 112 may zero the power applied by the gate drive 1302 from a previous phase 1304 in which power may be applied to drive the valve via pulse width modulation. As described in connection with FIG. 14 , the exact power previously applied to the valve may vary, resulting in a different waveform in phase 1304. The gate drive may then decelerate the valve and / or apply zero power during a desaturation phase 1306, which lasts a predetermined period of time (e.g., 5 ms). After the predetermined period has elapsed, the valve may be ready (e.g., desaturated) for its voltage to be measured (e.g., over a measurement interval 1308). A corresponding waveform 1310 of the measured voltage, including a transition point 1312, is also shown. Thus, the measurement interval 1308 may be the time it takes for the measured voltage of the valve to reach the transition point 1312 (i.e., the threshold voltage).

[0097] FIG. 14 shows position test data for the valve lever 170, 210 recorded after the gate drive was desaturated, and the valve had previously had different levels of power applied. For example, graph 1402 shows the resulting waveform when the microcontroller 112 applied 1% PWM, graph 1404 shows the resulting waveform when the microcontroller 112 applied 50% PWM, and graph 1406 shows the resulting waveform when the microcontroller 112 applied 99% PWM. The yellow traces in graphs 1402-1406 and throughout FIG. 13 may represent the measured voltage across the valve (e.g., based on the measured voltage across sense resistor 806) and therefore the current flowing through the valve. For each existing PWM level (e.g., graphs 1402-1406), the applied current went to 0 amps during the respective desaturation phase (e.g., desaturation phase 1306) and then rose during the respective measurement interval (e.g., measurement interval 1308).

[0098] When the rising current causes the voltage applied across the valve to reach a threshold voltage, the comparator 812 may provide a signal indicating this transition point (i.e., the point at which the measured voltage reaches the threshold voltage). Thus, the microcontroller 112 may measure the time it takes for the voltage to reach the voltage threshold by determining the time the comparator 812 sends a signal after the measurement interval 1308 begins. For example, the comparator 812 may send a low / high digital signal to the microcontroller 112 via IO line 818 when the valve reaches the transition point, and the microcontroller 112 may detect the low / high signal and, in response, terminate a timer to mark the time elapsed during the measurement interval. The microcontroller 112 may then return to driving whatever PWM duty cycle was previously set to drive the valve (e.g., in the previous stage 1304).

[0099] 15 and 16 show recorded position test data for the valve levers 170, 120, showing the valve levers 170, 210 stuck closed, the valve levers 170, 120 functioning normally, and the valve levers stuck open. Specifically, FIG. 15 shows the three position test data described above for a valve commanded to transition from an open to a closed state, but only one of the three (i.e., position test data 1504) shows the valve actually operating normally in response to the command. Similarly, FIG. 16 shows the three position test data described above for a valve commanded to transition from a closed to an open state, but only one of the three (i.e., position test data 1604) shows the valve actually operating normally in response to the command. Such position test data is based on inductance measurements of the valve when commanded to operate.

[0100] As shown in FIGS. 15 and 16 , each position test data 1502-1506, 1602-1606 slopes downward as a result of saturation of the solenoid coil associated with the valve. It should be understood that if the valve had not been actuated at all, such position test data 1502-1506, 1602-1606 could be approximately horizontal (e.g., with little or no slope). However, because position test data was received when the valve was commanded to actuate (e.g., from an open state to a closed state in FIG. 15 and from a closed state to an open state in FIG. 16 ), the solenoid coil associated with the valve began to saturate, causing the position test data 1502-1506, 1602-1606 to slope downward. As previously mentioned, the microcontroller 112 can mitigate noise caused by saturation during the measurement interval 1308 by undergoing a desaturation phase 1306 in which the power applied to the valve is set to zero for a predetermined period of time. However, even with the downward slope caused by saturation, FIGS. 15 and 16 very clearly show when the valve is operating normally (e.g., position test data 1504 and 1604) as opposed to when the valve is stuck open (e.g., position test data 1502 and 1602) or stuck closed (e.g., position test data 1506 and 1606). Furthermore, FIG. 15 shows the actual transition 1508 of the valve from an open state to a closed state when the valve is operating normally in both scenarios, and FIG. 16 shows the actual transition 1508 of the valve from a closed state to an open state. However, when the valve is commanded to close, the position test data should be traced from left to right in FIG. 15, whereas when the valve is commanded to open, the position test data should be traced from right to left in FIG. 16. Thus, each transition point 1508 and 1608 may occur at different locations and / or times depending on whether the valve is commanded to open (e.g., FIG. 15) or to close (e.g., FIG. 16). Additionally, each transition point 1508 and 1608 may vary based on the particular characteristics of the valve (e.g., the batch in which it was manufactured) or may change over time as the valve wears.

[0101] Thus, in some embodiments, a generic waveform may be used to compare the measured voltage of the valve (e.g., based on the sense resistor 806) to a generic threshold voltage. The generic waveform may be customized so that the transition point of the measured voltage from the valve asymptotically aligns with the threshold voltage.

[0102] 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. Accordingly, such changes and modifications are intended to be covered by the appended claims. For example, while MOSFETs and NPN transistors have been described as transistors used to assist in noise reduction during activation and deactivation of solenoid valves, other transistors may similarly be used to slow down the plungers of solenoid valves to similarly reduce noise. In another example, while different valve embodiments have been described primarily in connection with peritoneal dialysis ("PD"), valve embodiments may also be used with other medical fluid systems and associated devices, such as those for hemodialysis ("HD"), hemofiltration ("HF"), hemodiafiltration ("HDF"), and continuous renal replacement therapy ("CRRT").

Claims

1. 1. A medical fluid system comprising: a valve configured to control fluid flow within the medical fluid system, the valve comprising a housing, a solenoid coil, and a plunger, the valve configured to actuate fluid flow through a tube by applying a voltage to the solenoid coil to move the plunger within the housing; a driver circuit configured to control the valve of the medical fluid system via a pulse width modulated (PWM) signal in response to a control signal; a microcontroller having a processor and a memory; Equipped with The memory stores instructions that, when executed by the processor, cause the processor to: causing the drive circuit to send a control signal to the drive circuit that applies and raises a PWM signal to the solenoid coil of the valve; the rising edge of the PWM signal slowly moves the plunger until it reaches an end position within the housing; A medical fluid system, wherein the slow movement of the plunger reduces sound generated by the plunger.

2. The instructions, when executed by the processor, further cause the processor to: applying power to the valve via the drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating an estimate of the valve position based on the comparison of the measurement interval to the reference interval; and The medical fluid system according to claim 1 ,

3. The valve is further configured to close the flow of medical fluid through the tube by de-energizing the solenoid coil via the drive circuit to move the plunger in an opposite direction from the housing to occlude the tube, and the instructions, when executed by the processor, further cause the processor to: sending a second control signal to the drive circuit that causes the drive circuit to reduce the PWM signal to the solenoid coil to a 0% duty cycle; 3. The medical fluid system of claim 1, wherein the decline of the PWM signal causes the plunger to move in the opposite direction and such that the sound produced by the corresponding plunger is reduced compared to operation without the PWM signal.

4. The instructions, when executed by the processor, further cause the processor to: applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a second measurement interval, the second measurement interval ending when the second voltage reaches the predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating a second estimate of the valve position based on the comparison of the second measurement interval with the second reference interval; and The medical fluid system according to claim 3 , wherein the

5. The medical fluid system of claim 1 , wherein the valve, the drive circuit, and the microcontroller are contained within a peritoneal dialysis machine or a hemodialysis machine.

6. 1. A method for determining a valve position in a medical fluid system, the method comprising: sending, by a microcontroller having a processor, a control signal to close a valve, the valve configured to control fluid flow in the medical fluid system, the valve being open at least prior to sending the control signal, the valve comprising a housing, a solenoid coil, and a plunger; applying power to the valve via a drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating information indicative of whether the valve is closed based on the comparison; and A method comprising:

7. 7. The method of claim 6, further comprising setting a power level to zero for a predetermined period of time to cause desaturation of the solenoid coil for the predetermined period of time before applying the power to the valve.

8. The method of claim 7 , wherein the predetermined period is 5 milliseconds (ms).

9. 7. The method of claim 6, wherein monitoring the voltage across the valve includes receiving an indication from a comparator connected to the drive circuit of when the voltage reaches the predetermined threshold voltage.

10. sending, by the microcontroller, a second control signal to open the valve; applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on the sense resistor over a second measurement interval, the second measurement interval ending when the second voltage reaches a second predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating second information indicative of whether the valve is open based on the comparison of the second measurement interval with the second reference interval; and The method of claim 6 further comprising:

11. 1. A medical fluid system comprising: a valve configured to control fluid flow within the medical fluid system, the valve comprising a housing, a solenoid coil, and a plunger, the valve configured to actuate fluid flow by applying a voltage to the solenoid coil to move the plunger within the housing; a driver circuit configured to control the valve of the medical fluid system via a pulse width modulated (PWM) signal in response to a control signal; a microcontroller having a processor and a memory; Equipped with The memory stores instructions that, when executed by the processor, cause the processor to: transmitting a control signal to close the valve, the valve being open at least prior to transmitting the control signal; applying power to the valve via the drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating information indicative of whether the valve is closed based on the comparison; and A medical fluid system that performs the above.

12. The instructions, when executed by the processor, further cause the processor to:

12. The medical fluid system of claim 11, wherein a power level is set to zero for a predetermined period of time to cause desaturation of the solenoid coil for the predetermined period of time before applying the power to the valve.

13. The medical fluid system of claim 12 , wherein the predetermined period of time is 5 milliseconds (ms).

14. 12. The medical fluid system of claim 11, wherein monitoring the voltage across the valve includes receiving an indication from a comparator connected to the drive circuit of when the voltage reaches the predetermined threshold voltage.

15. The instructions, when executed by the processor, further cause the processor to: sending a second control signal to open the valve; applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on the sense resistor over a second measurement interval, the second measurement interval ending when the second voltage reaches a second predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating second information indicative of whether the valve is open based on the comparison of the second measurement interval with the second reference interval; and The medical fluid system of claim 11 ,

16. The medical fluid system of claim 11 , wherein the valve, the drive circuitry, and the microcontroller are contained within a peritoneal dialysis machine or a hemodialysis machine.

17. 1. A method of controlling a valve, the method comprising: sending a control signal by a microcontroller having a processor to a drive circuit to apply and raise a PWM signal to a solenoid coil of the valve; the valve is configured to actuate fluid flow by applying a voltage to the solenoid coil to move a plunger within a housing; the rising edge of the PWM signal slowly moves the plunger until it reaches an end position within the housing; The method wherein the slow movement of the plunger reduces sound produced by the plunger.

18. applying power to the valve via the drive circuit to measure a voltage across the valve; monitoring the voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a measurement interval, the measurement interval ending when the voltage reaches a predetermined threshold voltage; comparing the measured interval to a reference interval for a normally functioning closed valve; generating an estimate of the valve position based on the comparison of the measurement interval to the reference interval; and 20. The method of claim 17, further comprising:

19. the valve is further configured to close the flow of medical fluid by de-energizing the solenoid coil via the drive circuit to move the plunger in an opposite direction from the housing to occlude the tube; The method further includes transmitting, by the microcontroller, a second control signal to the drive circuit that causes the drive circuit to reduce the PWM signal to the solenoid coil to a 0% duty cycle; 19. The method of claim 17 or 18, wherein the descending of the PWM signal causes the plunger to move in the opposite direction and such that the sound produced by the corresponding plunger is reduced compared to operation without the PWM signal.

20. applying a second power to the valve via the drive circuit to measure a second voltage across the valve; monitoring the second voltage across the valve via the drive circuit based on a sense resistor associated with the valve over a second measurement interval, the second measurement interval ending when the second voltage reaches the predetermined threshold voltage; comparing the second measurement interval to a second reference interval for a normally functioning open valve; generating a second estimate of the valve position based on the comparison of the second measurement interval with the second reference interval; and 20. The method of claim 19, further comprising:

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