Dialysis system having reduced valve noise
Systems and methods are disclosed for reducing noise in solenoid valve activation and deactivation in peritoneal dialysis (“PD”) systems. In at least one embodiment, the PD system operates with solenoid valves under the control of a control unit. The control unit takes measures to control the movement of the solenoid valve to minimize the amount of sound that occurs at impact during activation and deactivation of the valve. The measures include the slowing of the movement of the valve plunger within the valve coil. In one aspect, the valve plunger may be slowed down by applying voltage to the valve coil through pulse width modulation (“PWM”).
1 . A medical fluid system comprising:
a control unit;
a plurality of metal oxide semiconductor field effect transistors (“MOSFETs”) configured to control a plurality of valves, in response to control signals received from the control unit; and
a plurality of valves,
wherein each valve comprises a housing, a coil, and a plunger, and
wherein each valve is configured to allow a flow of medical fluid through a tube by applying, via an associated MOSFET of the plurality of MOSFETs, a voltage to the corresponding coil to move the corresponding plunger within the corresponding housing,
the control unit comprising at least one processor and at least one memory, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the at least one processor to:
transmit, to one of the MOSFETs, a high digital control signal,
wherein the MOSFET, responsive to the high digital control signal, causes a corresponding valve to ramp up the voltage applied to a corresponding coil until the voltage reaches a predetermined input voltage, Vin, and
wherein the ramping up of the voltage applied to the corresponding coil causes the corresponding plunger to move in a manner in which sound generated by the corresponding plunger is reduced in comparison to operation without the MOSFET.
2 . The medical fluid system of claim 1 , wherein each valve is configured to close the flow of medical fluid through the tube by un-applying, via the corresponding MOSFET, the voltage to the corresponding coil so that the corresponding plunger moves in an opposite direction to occlude the corresponding tube.
3 . The medical fluid system of claim 2 , wherein the instructions, when executed by the at least one processor, further cause the at least one processor to:
transmit, to the MOSFET of the plurality of MOSFETs, a low digital control signal,
wherein the MOSFET, responsive to the low digital control signal, causes the corresponding valve to ramp down the voltage applied to the corresponding coil until the voltage reaches 0 volts, and
wherein the ramping down of the voltage applied to the corresponding coil causes the corresponding plunger to move in an opposite direction and in a manner in which sound generated by the corresponding plunger is reduced in comparison to operation without the MOSFET.
4 . The medical fluid system of claim 3 , further comprising:
at least one resistor serially arranged between the control unit and the MOSFET,
wherein a duration of the ramping up of the voltage applied to the corresponding coil is based on at least one resistance value of the corresponding at least one resistor, and
wherein a duration of the ramping down of the voltage applied to the corresponding coil is based on the at least one resistance value of the corresponding at least one resistor.
5 . The medical fluid system of claim 4 , further comprising:
at least one capacitor serially arranged between the control unit and the MOSFET,
wherein the duration of the ramping up of the voltage applied to the corresponding coil is further based on capacitance values of the corresponding at least one capacitor, and
wherein the duration of the ramping down of the voltage applied to the corresponding coil is further based on the capacitance values of the corresponding at least one capacitor.
6 . The medical fluid system of claim 1 , further comprising an initial ramp offset circuit comprising a feedback resistor.
7 . The medical fluid system of claim 6 , wherein the instructions, when executed, further cause the processor to:
apply, via the initial ramp offset circuit, an offset voltage set below the voltage applied to the corresponding coil when ramping up the input current to the MOSFET.
8 . A medical fluid system comprising:
a control unit;
a plurality of input/output (“I/O”) nodes configured to control a plurality of valves via pulse width modulation (“PWM”) signals, in response to control signals received from the control unit; and
a plurality of valves,
wherein each valve comprises a housing, a coil, and a plunger, and
wherein each valve is configured to allow a flow of medical fluid through a tube by applying, via an associated I/O node of the plurality of I/O nodes, a voltage to the corresponding coil to move the corresponding plunger within the corresponding housing,
the control unit comprising at least one processor and at least one memory, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the at least one processor to:
transmit, to an I/O node of the plurality of I/O nodes, a control signal causing the I/O node to apply and ramp up a PWM signal to the corresponding coil, and
wherein the ramping up of the PWM signal causes the corresponding plunger to move in a manner in which sound generated by the corresponding plunger is reduced in comparison to operation without the PWM signal.
9 . The medical fluid system of claim 8 , wherein ramping up of the PWM signal comprises ramping up a duty cycle of a pulsed application of the voltage to the corresponding coil from 0% to 100% during 50 ms.
10 . The medical fluid system of claim 8 , wherein the instructions, when executed, further cause the processor to:
after the plunger reaches an end position, transmit, to the I/O node, a second control signal causing the I/O node to ramp down the PWM signal to the corresponding coil to a duty cycle that is at least 25%.
11 . The medical fluid system of claim 10 , wherein the second control signal causes the I/O node to ramp down the PWM signal to the corresponding coil to a duty cycle that is at least 50%.
12 . The medical fluid system of claim 10 , wherein each valve is configured to close the flow of medical fluid through the tube by un-applying, via the corresponding I/O node, the voltage to the corresponding coil so that the corresponding plunger moves in an opposite direction to occlude the corresponding tube.
13 . The medical fluid system of claim 12 , wherein the instructions, when executed by the at least one processor, further cause the at least one processor to:
transmit, to the I/O node, a third control signal causing the I/O node to ramp down the PWM signal to the corresponding coil to a duty cycle of 0%,
wherein the ramping down of the PWM signal to the corresponding coil causes the corresponding plunger to move in an opposite direction and in manner in which sound generated by the corresponding plunger is reduced in comparison to operation without the PWM signal.
14 . The medical fluid system of claim 13 , wherein the ramping down of the PWM signal to the corresponding coil to the duty cycle of 0% occurs during a time between 25 to 75 ms.
15 . The medical fluid system of claim 13 , further comprising:
at least one resistor serially arranged between the control unit and the I/O node,
wherein a duration of the ramping up of the PWM signal is based on resistance values of the corresponding at least one resistor, and
wherein a duration of the ramping down of the PWM signal is based on the resistance values of the corresponding at least one resistor.
16 . The medical fluid system of claim 13 , further comprising:
at least one capacitor serially arranged between the control unit and the I/O node,
wherein the duration of the ramping up of the PWM signal is further based on capacitance values of the corresponding at least one capacitor, and
wherein the duration of the ramping down of the PWM signal is further based on the capacitance values of the corresponding at least one capacitor.