Method and circuit for detecting a change in inductance

Abstract

A method and circuit for detecting a change in inductance of a variable inductance element. An oscillating signal has a frequency that varies with inductance of the element. An intermediate voltage is produced at a level that varies according to frequency of the oscillating signal. The intermediate voltage is scaled to produce an output voltage.

1 . A method for detecting changes in inductance of a variable inductance element comprising the steps of: 
 a) producing an oscillating square wave signal having a frequency that varies in proportion to variations in inductance of the variable inductance element;    b) inputting the oscillating square wave signal to a phase-locked loop circuit and producing an intermediate analog voltage that varies in proportion to variations in frequency of the oscillating square wave signal of step a);    c) scaling the intermediate analog voltage of step b) to produce an output analog voltage; and    d) detecting changes in inductance of the variable inductance element based upon changes in the output analog voltage of step c).    
   
   
       2 . The method of  claim 1 , wherein the variable inductance element comprises an inductive sensor.  
   
   
       3 . The method of  claim 2  where the inductive sensor includes at least one coil located adjacent a magnetostrictive object.  
   
   
       4 . (canceled)  
   
   
       5 . The method of  claim 1 , wherein step d) includes inputting the output analog voltage to an analog to digital converter.  
   
   
       6 . (canceled)  
   
   
       7 . The method of  claim 1 , wherein step a) involves connecting the variable inductance element in a feedback path of an oscillator circuit.  
   
   
       8 . The method of  claim 1  wherein the scaling of step c) involves offsetting and amplifying the intermediate analog voltage.  
   
   
       9 . A circuit for producing a voltage level substantially proportional to inductance of a variable inductance element, the circuit comprising: 
 an oscillator stage having a feedback path and the variable inductance element connected therein and producing an oscillating signal having a frequency that varies with inductance of the variable inductance element;    a conversion stage comprising a phase-locked loop circuit operatively connected to receive the oscillating signal and producing an intermediate analog voltage that varies in proportion to variations in the frequency of the oscillating signal; and    an amplification stage operatively connected to receive the intermediate analog voltage and operating to offset and amplify the intermediate analog voltage to produce an output analog voltage with a voltage level proportional to inductance of the variable inductance element.    
   
   
       10 . (canceled)  
   
   
       11 . (canceled)  
   
   
       12 . The circuit of  claim 9  wherein the amplification stage includes an adjustable offset control component.  
   
   
       13 . The circuit of  claim 12  wherein the adjustable offset control component comprises a potentiometer.  
   
   
       14 . The circuit of  claim 12  wherein the adjustable offset control component comprises an automated control component.