Patent ID: 8622713

Claim:
A method of controlling an electrically powered fluid transfer system, the method comprising the steps of: providing a pump configured to displace a fluid, the pump being in one of a first fluid condition wherein a compressible gas is present within the pump and a second fluid condition, wherein the pump has a first frequency response when the pump is in the first fluid condition and a second frequency response when the pump is in the second fluid condition; selecting a frequency range of interest based on differences between the first frequency response and the second frequency response of the pump; monitoring at least one characteristic of a frequency response of the pump within the frequency range of interest while the pump is powered, 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; determining a fluid condition within the pump based on the at least one characteristic of the frequency response of the pump; and altering an operation of the pump when the fluid condition within the pump is the first fluid condition.