A Novel PQCR-L Circuit for Inductive Sensing and Its Application in Displacement Detection

A novel circuit for inductive sensing that was constructed using a quartz crystal resonator and an inductance element in series was proposed. Resonant frequency expression of equivalent model of the circuit was derived. The experimental results of the resonant frequency responses versus inductance changes of the circuit were coincident with the theoretical derivation, which proved that resonant frequency of the circuit could be tuned by inductance element. A quartz crystal inductive displacement sensor utilizing a planar spiral inductor was developed based on the earlier theories. The measurement results of the displacement sensor exhibited a highly sensitive response of 1 Hz/
$\mu \text{m}$
in the wide distance range 0–2000
$\mu \text{m}$
and a good stability with 0.043-Hz standard deviation of the output frequency. Furthermore, the fundamental frequency dependence of quartz crystal inductive displacement sensor was also discussed. The experimental results showed that the maximum sensing range of the sensor with 10-MHz fundamental frequency was 18 mm. The best advantage of the proposed method in this paper was the convenient implementation of a high-sensitivity inductive sensor with stable digital frequency output.