Apparatus for detecting the fluid condition in a pump

1. An electrically powered fluid transfer system, comprising:

a pump having a fluid inlet and a fluid outlet in fluid communication with the fluid inlet, the pump moving fluid from the fluid inlet through an interior of the pump and onto the fluid outlet when power is provided to a motor of the pump; and

a controller operatively coupled to the pump to control when power is provided to the pump, the controller monitoring at least one characteristic of a frequency response of the pump while the pump is powered to determine a fluid condition within the pump, wherein the at least one characteristic of the frequency response includes one of a magnitude of the frequency response and a phase angle of the frequency response.

2. The system of claim 1 , wherein the at least one characteristic of the frequency response is the magnitude of the frequency response at at least a first frequency.

3. The system of claim 2 , wherein the controller monitors the magnitude of the frequency response of the current drawn by the motor of the pump at the at least the first frequency and compares a relative value to a threshold value to determine the fluid condition within the pump, the relative value being dependent on the magnitude of the frequency response of the current at the at least the first frequency.

4. The system of claim 3 , wherein the controller alters the operation of the pump when the fluid condition within the pump is a first fluid condition, the first fluid condition including the presence of a compressible gas in the interior of the pump.

5. The system of claim 4 , wherein the controller detects the first fluid condition when the relative value crosses the threshold value.

6. The system of claim 5 , further comprising a user input operatively coupled to the controller to adjust the threshold value.

7. The system of claim 4 , wherein the pump is positioned in a reservoir, the pump being configured to move fluid collected in the reservoir to a location outside of the reservoir, the compressible gas being introduced into the interior of the pump when the fluid in the reservoir is at a low fluid level, wherein the compressible gas is air.

8. The system of claim 7 , wherein the controller removes power from the pump upon detection of the first fluid condition.

9. The system of claim 7 , wherein the first fluid condition occurs when air comprises at least about 5% of the fluid within the pump.

10. The system of claim 7 , wherein the first fluid condition occurs when air comprises at least about 15% of the fluid within the pump.

11. The system of claim 7 , further comprising a sensor positioned in the reservoir and operatively coupled to the controller, the controller providing power to the pump upon a detection of a high fluid level in the reservoir with the sensor.

12. The system of claim 7 , wherein the pump is a centrifugal pump, the motor being drivably coupled to an impeller positioned near the fluid inlet in the interior of the pump, the rotation of the impeller drawing the fluid into the pump through the fluid inlet and moving the fluid onto the fluid outlet of the pump.

13. The system of claim 3 , wherein the controller includes an analog circuit having an amplifier for monitoring the current drawn by the motor, a filter for filtering the output of the amplifier to the select frequencies, an integrator for integrating the filtered output of the filter and outputting the relative value of the current drawn by the motor, and a comparator for comparing the relative value of the current to the threshold value for determining the fluid condition within the pump.

14. The system of claim 13 , wherein the relative value is the average magnitude of the frequency response of the current drawn by the motor of the pump at the at least the first frequency over a predetermined time period, each of the relative value and the threshold value being a voltage value.

15. The system of claim 13 , wherein the analog circuit further includes an isolator circuit configured to isolate at least a portion of the analog circuit from the power provided to the motor of the pump.

16. The system of claim 3 , wherein the frequency response of the pump has a first response when the fluid within the pump is substantially a liquid and a second response when the fluid within the pump includes a mixture of the liquid and a compressible gas, the at least the first frequency being selected based on a comparison of the first response and the second response.

17. The system of claim 3 , wherein the controller includes a microprocessor configured to monitor the magnitude of the frequency response of the current drawn by the motor of the pump at the at least the first frequency to determine the fluid condition within the pump.

18. The system of claim 2 , further comprising a pressure transducer positioned in the interior of the pump and configured to detect fluid pressure in the pump, the controller monitoring the magnitude of the frequency response of a signal from the pressure transducer at the at least the first frequency to determine the fluid condition within the pump.

19. The system of claim 2 , further comprising a flexible member positioned in the interior of the pump and configured to resonate upon the introduction of fluid in the pump, the vibration of the flexible member being configured to increase the magnitude of the frequency response of the pump to increase the sensitivity of the controller in the determination of the fluid condition within the pump.

20. The system of claim 2 , wherein the controller determines the fluid condition within the pump based on a detection of a shift in at least one anti-resonance peak of the frequency response of the current signal.

21. The system of claim 1 , wherein the at least one characteristic of the frequency response is a phase angle of the frequency response at least a first frequency.