Liquid level sensing assembly and method for measuring using same

Abstract

A sensing assembly ( 10 ) senses a level ( 24 ) of a liquid ( 22 ) in a reservoir ( 12 ). The sensing assembly ( 10 ) includes a first input port ( 32 ) for receiving a first input voltage signal. The sensing assembly ( 10 ) also includes a second ( 32 ) input port ( 36 ) for receiving a second input voltage signal. An excitation circuit ( 40 ) is electrically ( 36 ) connected to the first ( 32 ) and second ( 34 ) input ports for receiving the first ( 34 ) and second ( 38 ) input voltage signals and for generating a first excitation signal and a second excitation signal. A receiving circuit ( 50 ) is disposed adjacent the excitation circuit ( 40 ) and defines a variable capacitance with the excitation circuit ( 40 ). The receiving circuit ( 50 ) produces an output voltage variable with the level ( 24 ) of the liquid ( 22 ) in the reservoir ( 12 ) due to capacitance changes between the excitation circuit ( 40 ) and the receiving circuit ( 50 ). The receiving circuit ( 50 ) includes a first receiving electrode ( 54 ) extending through a sine wave form and a second receiving electrode ( 56 ) extending through a cosine wave form. The capacitance changes are due to dielectric changes created by the presence of the liquid ( 22 ) adjacent at least a portion of the sensing assembly ( 10 ).

1 . A sensing assembly for sensing a level of liquid in a reservoir, said sensing assembly comprising: 
 a first input port for receiving a first input voltage signal;    a second input port for receiving a second input voltage signal;    an excitation circuit electrically connected to said first and second input ports for receiving the first and second input voltage signals and for generating a first excitation signal and a second excitation signal, said excitation circuit includes first and second excitation electrodes extending along a portion of the reservoir, said first and second excitation electrodes disposed adjacent to and separated by said first receiving electrode; and    a receiving circuit disposed adjacent said excitation circuit defining a variable capacitance with said excitation circuit, wherein said receiving circuit includes first and second receiving electrodes extending along a portion of the reservoir and a first trace connected to ground and extending between said first receiving electrode and said first and second excitation electrodes, wherein said first receiving electrode extends along a first non-linear path and said second receiving electrode extends along a second non-linear path differing from said first non-linear path, said receiving circuit producing an output voltage signal variable with the level of liquid in the reservoir due to capacitance changes between said excitation circuit and said receiving circuit due to dielectric changes created by the liquid.    
   
   
       2 . A sensing assembly as set forth in  claim 1  wherein said first non-linear path extends along a sine wave shape.  
   
   
       3 . A sensing assembly as set forth in  claim 2  wherein said second non-linear path extends along a cosine wave shape.  
   
   
       4 . (canceled).  
   
   
       5 . A sensing assembly as set forth in claim wherein said excitation circuit includes third and fourth excitation electrodes extending along a portion of the reservoir, said third and fourth excitation electrodes disposed adjacent to and separated by said second receiving electrode.  
   
   
       6 . (canceled).  
   
   
       7 . A sensing assembly as set forth in  claim 1  including a second trace extending between said second receiving electrode and said third and fourth excitation electrodes, said second trace connected to ground.