Apparatus and method for determining the linear position of a hydraulic cylinder

An apparatus for detecting a position of a piston and a piston rod being movable within a housing, said piston, piston rod and housing defining first and second coaxial resonant cavities, the first and second coaxial resonant cavities being on opposite sides of the piston, comprising:

• means for producing a first electromagnetically radiated signal and delivering said first electromagnetically radiated signal into said first resonant cavity, said electromagnetically radiated signal having a frequency varying between predetermined minimum and maximum values;
• means for sensing an electromagnetic wave signal within said first coaxial cavity, comparing said first electromagnetic wave signal with a first predetermined threshold, and producing a first frequency signal in response to the magnitude of said first electromagnetically radiated signal being greater than said first predetermined threshold;
• means for producing a second electromagnetically radiated signal and delivering said second electromagnetically radiated signal into said second resonant cavity, said electromagnetically radiated signal having a frequency varying between predetermined minimum and maximum values;
• means for sensing an electromagnetic wave signal within said second coaxial cavity, comparing said second electromagnetic wave signal with a second predetermined threshold, and producing a second frequency signal in response to the magnitude of said second electromagnetically radiated signal being greater than said second predetermined threshold;
• and
• means for receiving said first and second frequency signals and responsively determining a first position of said piston and piston rod as a function of said first frequency signal, determining if said first determined position is valid, and determining a second position of said piston and piston rod as a function of said second frequency signal if said first determined position is valid.

An apparatus for detecting a position of a piston and a piston rod being movable within a housing, said piston, piston rod and housing defining first and second coaxial resonant cavities, comprising:

• means for determining the resonant frequency of said first coaxial cavity and responsively producing a first resonant frequency signal;
• means for determining the resonant frequency of said second coaxial cavity and responsively producing a second resonant frequency signal;
• and
• means for receiving said first and second resonant frequency signals and responsively determining a first position of said piston and piston rod as a function of said first frequency signal, determining if said first determined position is valid, and determining a second position of said piston and piston rod as a function of said second frequency signal if said first determined position is invalid.

A method for detecting a position of a piston and a piston rod being movable within a housing, said piston, piston rod, and housing defining first and second coaxial resonant cavities, including the steps of:

• determining the resonant frequency of one of said first and second coaxial resonant cavities and responsively producing a first resonant frequency signal;
• receiving said first resonant frequency signal and responsively determining a first location of said piston;
• determining if said first determined location is valid;
• and
• determining the resonant frequency of the other of said first and second coaxial resonant cavities and responsively determining a second location of said piston, if said first determined location is not valid.