Method and apparatus for sensing the natural frequency of a cantilevered body

An apparatus for measuring a natural frequency of movement of a spring element, the apparatus comprising:

• a first transducer coupled to the spring element;
• means for causing vibratory movement of the spring element;
• a second transducer for converting movement of the spring element to an electrical output signal;
• a phase detector for detecting a phase difference between the electrical input signal and the electrical output signal, wherein said phase difference represents an oscillation frequency of the spring element due to accumulation of chemical substances on a surface thereof;
• and
• a voltage controlled oscillator for adjusting the frequency of the electrical input signal until a phase difference is obtained that corresponds to a natural oscillating frequency for vibratory movement of the spring element due to accumulation of chemical substances on a surface thereof;
• an integrator for integrating the phase difference to provide the input to the voltage controlled oscillator.