Systems and methods for control of pumps employing electrical field sensing

1. A system for pumping a fluid comprising

a pump chamber,

a flexible diaphragm on the pump chamber and responsive to applied pressures to convey fluid through the pump chamber,

an electrode in electrical conductive contact with fluid in the pump chamber coupled to an electrical source and configured to generate an electrical field in the pump chamber that varies according volume of fluid in the pump chamber, and

a sensing circuit coupled to the electrode and configured to register variations in the electrical field as fluid is conveyed through the pump chamber.

2. A system according to claim 1

wherein the sensing circuit includes a processor operating to process variations in the electrical field and generate an output.

3. A system according to claim 2

wherein the processor includes a function operating to derive, based upon the output, a value indicating volume of fluid conveyed by the pump chamber.

4. A system according to claim 2

wherein the processor includes a function operating to derive, based upon the output, a value indicating a flow rate of fluid conveyed by the pump chamber.

5. A system according to claim 2

wherein the processor includes a function operating to derive, based upon the output, a value indicating presence of air in the pump chamber.

6. A system according to claim 2

wherein the processor includes a function operating to derive, based upon the output, a value indicating an occlusion of flow through the pump chamber.

7. A system according to claim 2

wherein the processor includes a function operating to calibrate the output according to stroke volume of the pump chamber.

8. A system according to claim 2

further including a controller coupled to the processor operating to vary the applied pressures based, at least in part, upon the output.

9. A system according to claim 2

wherein the processor includes a function operating to register variation of the output over time.

10. A system according to claim 9

wherein the processor includes a function operating to compare the output to a set value to derive a deviation.

11. A system according to claim 10

wherein the processor includes a function operating to register variation of the deviation over time.

12. A system according to claim 1

wherein the sensing circuit registers variations in capacitance due to variations in the electrical field.

13. A system according to claim 12

wherein the sensing circuit includes a processor operating to process variations in capacitance and generate an output.

14. A system according to claim 1

further including tubing communicating with the pump chamber to couple the pump chamber in-line between a source of blood and a blood separation device.

15. A system for pumping a fluid comprising

a pump chamber having a known stroke volume, which is essentially constant,

a flexible diaphragm on the pump chamber and responsive to applied pressures to convey fluid through the pump chamber,

an actuator interacting with the flexible diaphragm during a stroke interval to pump fluid through the pump,

an electrode in electrical conductive contact with fluid in the pump chamber coupled to an electrical source to generate an electrical field within the pump chamber that varies according volume of fluid in the pump chamber,

a sensing circuit coupled to the electrode and configured to register variations in the electrical field as fluid is conveyed through the pump chamber, and

a controller coupled to the sensing circuit and including a control function operating to command a desired flow rate by deriving an actual flow rate based upon the variations in the electric field over a sample time period and adjusting the stroke interval so that the desired flow rate is achieved.

16. A system according to claim 15

wherein the actuator provides the stroke interval comprising a time interval component to draw fluid into the pump, a time interval component to expel the fluid from the pump, and an idle time interval component, and

wherein the controller adjusts one or more of the time interval components to achieve the desired flow rate.

17. A system according to claim 15

wherein the controller includes a diagnostic function operating to detect abnormal operating conditions based upon the variations in the electric field and to generate an alarm output.

18. A system according to claim 15

wherein the sensing circuit registers variations in capacitance due to variations in the electrical field.

19. A system according to claim 15

further including tubing communicating with the pump chamber to couple the pump chamber in-line between a source of blood and a blood separation device.

20. A system for pumping a fluid comprising

a pump chamber having a known stroke volume, which is essentially constant,

a flexible diaphragm on the pump chamber and responsive to applied pressures to convey fluid through the pump chamber,

an actuator interacting with the flexible diaphragm during a stroke interval to pump fluid through the pump,

an electrode in electrical conductive contact with fluid in the pump chamber coupled to an electrical source and configured to generate an electrical field within the pump chamber that varies according volume of fluid in the pump chamber,

a sensing circuit coupled to the electrode and configured to register variations in the electrical field as fluid is conveyed through the pump chamber, and

a controller coupled to the sensing circuit and including a diagnostic function operating to detect abnormal operating conditions based upon variations in the electrical field and to generate an alarm output.

21. A system according to claim 20

wherein the diagnostic function operates to derive a value indicating presence of air in the pump chamber.

22. A system according to claim 20

wherein the diagnostic function operates to derive a value indicating an occlusion of flow through the pump chamber.

23. A system according to claim 20

wherein the sensing circuit registers variations in capacitance due to variations in the electrical field.

24. A system according to claim 20

further including tubing communicating with the pump chamber to couple the pump chamber in-line between a source of blood and a blood separation device.

25. A system for pumping a fluid comprising

a pump chamber,

a flexible diaphragm on the pump chamber and responsive to applied pressures in a draw cycle to draw fluid into the pump chamber and in an expel cycle to expel fluid from the pump chamber,

an electrode in electrical conductive contact with fluid in the pump chamber coupled to an electrical source and configured to generate an electrical field in the pump chamber that varies according volume of fluid in the pump chamber, and

a sensing circuit coupled to the electrode and configured to register changes in capacitance due to variations in the electrical field during draw and expel cycles, the capacitance having a high signal magnitude when the pump chamber is filled with liquid, a low signal magnitude when the pump chamber is empty of fluid, and has a range of intermediate signal magnitudes when the pump chamber is neither full nor empty of fluid.

26. A system according to claim 25

wherein the sensing circuit includes a function operating to calibrate the difference between the high and low signal magnitudes to stroke volume of the pump chamber.

27. A system according to claim 25

wherein the sensing circuit includes a function operating to relate a difference between sensed maximum and minimum signal values during successive draw and expel cycles to fluid volume drawn and expelled through the pump chamber.

28. A system according to claim 27

wherein the sensing circuit includes a function operating to sum fluid volumes pumped over a sample time period to yield a flow rate.

29. A system according to claim 28

wherein the sensing circuit includes a function operating to register a deviance between the flow rate and a desired flow rate.

30. A system according to claim 29

further including a controller operating to vary pressures applied to the flexible diaphragm to minimize the deviance.

31. A system according to claim 25

wherein the sensing circuit includes a function operating to register an increase in the magnitude of the low signal magnitude over time and generates an alarm signal reflecting presence of air inside a pump chamber.

32. A system according to claim 25

wherein the sensing circuit includes a function operating to derive a derivative of the changes in the capacitance over time and to generate an alarm signal reflecting occlusion of the pump chamber based upon changes in the derivative or absence of a derivative.

33. A system according to claim 25

further including tubing communicating with the pump chamber to couple the pump chamber in-line between a source of blood and a blood separation device.