Medical treatment system and methods using a plurality of fluid lines
Improvements in fluid volume measurement systems are disclosed for a pneumatically actuated diaphragm pump in general, and a peritoneal dialysis cycler using a pump cassette in particular. Pump fluid volume measurements are based on pressure measurements in a pump control chamber and a reference chamber in a two-chamber model, with different sections of an apparatus being modeled using a combination of adiabatic, isothermal and polytropic processes. Real time or instantaneous fluid flow measurements in a pump chamber of the diaphragm pump are also disclosed, in this case using a one-chamber ideal gas model and using a high speed processor to obtain and process pump control chamber pressures during fluid flow into or out of the pump chamber.
1. A system for measuring a volume of a pneumatically actuated control chamber of a pneumatically actuated diaphragm pump, comprising:
a fluid inlet valve and a fluid outlet valve connected to a pumping chamber of the pneumatically actuated diaphragm pump;
a diaphragm separating the control chamber from the pumping chamber, the control chamber fluidly connected to a reference chamber of a known volume via a conduit that includes a reference chamber valve;
the control chamber fluidly connected via one or more actuation valves to a source of positive or negative pneumatic pressure;
a controller configured to control the fluid inlet valve and the fluid outlet valve, the reference chamber valve, and the one or more actuation valves, and to receive pressure data from a first pressure sensor connected to the control chamber and a second pressure sensor connected to the reference chamber;
wherein the controller is configured to isolate the pumping chamber by closing the fluid inlet valve and the fluid outlet valve, charge the control chamber with a first control chamber pressure; vent the reference chamber or fix a pneumatic pressure in the reference chamber that is different from the first control chamber pressure: measure the first control chamber pressure and a second reference chamber pressure, connect the control chamber to the reference chamber by opening the reference chamber valve and equalizing pressures between the control chamber and the reference chamber, and measure a third equalized pressure in the control chamber and the reference chamber, and
wherein the controller is configured to compute the volume of the control chamber based on an ideal gas model that assumes an adiabatic pressure equalization process in the reference chamber and a polytropic pressure equalization process in the control chamber, wherein the ideal gas model applied to the control chamber uses a polytropic coefficient and the controller is programed to adjust a value of the polytropic coefficient as a pre-defined function of the volume of the control chamber.
2. The system of claim 1 , wherein the ideal gas model further assumes an isothermal process in the conduit as a gas moves from the control chamber to the reference chamber during the equalizing pressures between the control chamber and the reference chamber.
3. The system of claim 1 , wherein the controller is programmed to compute the polytropic coefficient based on an estimated volume of the control chamber using a model that assumes an adiabatic pressure equalization process in the control chamber.
4. A system for measuring a volume of a pneumatically actuated control chamber of a pneumatically actuated diaphragm pump, comprising:
a fluid inlet valve and a fluid outlet valve connected to a pumping chamber of the pneumatically actuated diaphragm pump;
a diaphragm separating the control chamber from the pumping chamber, the control chamber fluidly connected to a reference chamber of a known volume via a conduit that includes a reference chamber valve;
the control chamber fluidly connected via one or more actuation valves to a source of positive or negative pneumatic pressure:
a controller configured to control the fluid inlet valve and the fluid outlet valve, the reference chamber valve, and the one or more actuation valves, and to receive pressure data from a first pressure sensor connected to the control chamber and a second pressure sensor connected to the reference chamber:
wherein the controller is configured to isolate the pumping chamber by closing the fluid inlet valve and the fluid outlet valve, charge the control chamber with a first control chamber pressure; vent the reference chamber or fix a pneumatic pressure in the reference chamber that is different from the first control chamber pressure: measure the first control chamber pressure and a second reference chamber pressure, connect the control chamber to the reference chamber by opening the reference chamber valve and equalizing pressures between the control chamber and the reference chamber, and measure a third equalized pressure in the control chamber and the reference chamber, and
wherein the controller is configured to compute the volume of the control chamber based on an ideal gas model under a polytropic process, wherein the controller is configured to select a polytropic coefficient for the ideal gas model using a pre-determined function in which a value of the polytropic coefficient depends on and varies with the volume of the control chamber.
5. The system of claim 4 , wherein the pre-determined function is determined by fixing the volume of the control chamber at a known volume, and calculating the polytropic coefficient corresponding to the known volumes of the control chamber and the reference chamber, and the measured first control chamber pressure, the measured second reference chamber pressure, and the measured third equalized pressure; wherein said calculation is repeated a plurality of times, each time of the plurality of times corresponding to fixing the volume of the control chamber at a different known volume.
6. The system of claim 5 , wherein the pre-determined function corresponds to a stored look-up table from which the controller selects the polytropic coefficient corresponding to the volume of the control chamber being computed.
7. The system of claim 5 , wherein the pre-determined function corresponds to an equation that has been fitted to a plurality of calculated polytropic coefficients corresponding to a series of known control chamber volumes.