Method and apparatus for controlling a medical fluid heater

1. A method of controlling a medical fluid heater comprising the steps of:

determining a first heater control output based on a number of measured inputs for the heater and at least one mathematical relationship between at least two of the measured inputs;

determining a second heater control output based on at least one fuzzy logic membership function and at least one fuzzy logic rule; and

determining a third heater control output based on the first and second outputs and using the third heater control output to control the heater.

2. The method of claim 1 , which includes the further step of determining the significance of the second heater control output with respect to determining the third heater control output.

3. The method of claim 1 , wherein determining the first heater control output includes measuring and inputting a signal selected from the group consisting of: a measured number of pump stroke intervals, a heater input voltage and a measured fluid temperature.

4. The method of claim 1 , wherein determining the first, second and third heater control outputs includes determining a first, second and third duty cycle, respectively.

5. The method of claim 1 , wherein determining the first heater control output includes calculating a flow rate based on a measured number of stroke intervals and a pump chamber volume.

6. The method of claim 1 , wherein determining the first heater control output includes calculating a total heater power based on a heater input voltage and a heater plate resistance.

7. The method of claim 1 , wherein determining the first heater control output includes calculating a duty cycle based on a difference between a desired temperature and a measured temperature.

8. The method of claim 1 , wherein determining the second heater control output includes: (i) determining a plurality of fuzzy logic membership functions; (ii) converting a difference between a desired temperature and a measure temperature into fuzzy sets based on the membership functions; (iii) applying a plurality of fuzzy logic rules; and (iv) converting an output of the rules to a fuzzy logic based duty cycle.

9. The method of claim 8 , wherein the first heater control output is a first duty cycle and which includes the further step of determining how much weight to place on the fuzzy logic based duty cycle with respect to the first duty cycle.

10. The method of claim 8 , wherein the membership functions include at least one triangular membership function and at least one trapezoidal membership function.

11. The method of claim 8 , wherein the fuzzy logic rules yield at least one of a large decrease output, a decrease output, a neutral output, a small increase output and a large increase output.

12. The method of claim 1 , which includes the further step of setting a heater temperature limit and preventing the third heater control output from raising a heater temperature above the heater temperature limit.

13. The method of claim 1 , wherein determining the first and second heater control outputs includes updating the first heater control output at a different frequency than a frequency at which the second heater control output is updated.

14. The method of claim 1 , which includes the step of updating the second heater control output about 8.5 to about 9.5 times per second and at a frequency unevenly divisible into an input power frequency.

15. A method of controlling a medical fluid heater comprising the steps of:

determining a first heater control output using a first mathematical relationship between a number of heater inputs and updating the first output at a first frequency;

determining a second heater control output using a second mathematical relationship between a number of heater inputs and updating the second output at a second frequency, wherein the second mathematical relationship includes a measured fluid temperature feedback at the second frequency; and

determining a third heater control output based on the first and second outputs and using the third heater control output to control the heater.

16. The method of claim 15 , wherein updating the first output includes updating a number of measured heater input signals into the first mathematical relationship.

17. The method of claim 15 , wherein determining the second heater control output using the second mathematical relationship includes applying at least one fuzzy logic principle.

18. The method of claim 15 , wherein determining the second heater control output includes inputting a difference between a desired fluid temperature and an actual temperature, at the second frequency, into the second mathematical relationship.

19. A method of controlling a medical fluid heater comprising the steps of:

determining a first heater control output using a first mathematical relationship between a number of heater inputs;

determining a second heater control output using a second mathematical relationship between a number of heater inputs;

weighting the relative importance of the first and second outputs and determining a third heater control output based on the first output, second output and the weighting; and

controlling the heater using the third heater control output.

20. A method of controlling a medical fluid heater comprising the steps of:

determining a first heater duty cycle based on at least one input signal selected from the group consisting of: a measured number of pump stroke intervals, a heater input voltage and a measured fluid temperature;

determining a second heater duty cycle by: (i) determining a plurality of fuzzy logic membership functions; (ii) converting a difference between a desired temperature and a measure temperature into fuzzy sets based on the membership functions; (iii) applying a plurality of fuzzy logic rules; and (iv) converting an output of the rules to the second duty cycle; and

determining a third heater duty cycle based on the first and second heater duty cycles and using the third heater duty cycle to control the heater.

21. An automated dialysis system comprising:

a pump operable to pump medical fluid;

a heater operable to heat the medical fluid; and

a controller that operates with the medical fluid heater to:

determine a first heater control output based on a number of measured inputs for the heater and at least one mathematical relationship between at least two of the inputs;

determine a second heater control output based on at least one fuzzy logic membership function and at least one fuzzy logic rule; and

determine a third heater control output based on the first and second outputs and use the third heater control output to control the heater.