Patent ID: 8427138
Filing Date: 2013-04-23
Classification: G01B

Abstract:
1. A position sensor comprising: a moving member configured to be displaced in response to displacement of a measurement target; a resonant unit including a detection coil arranged to have inductance varied corresponding to displacement of said moving member, said resonant unit being configured to have a resonant frequency determined by the inductance of said detection coil; an oscillation unit configured to output an oscillation signal having its magnitude oscillating at a frequency corresponding to the resonant frequency; a signal processing unit configured to determine the displacement of said measurement target on a basis of the oscillation signal; an output unit configured to output an output signal indicative of the displacement of said measurement target determined by said signal processing unit; a signal absence detection unit configured to judge whether or not the oscillation signal is output from said oscillation unit, said signal absence detection unit being configured to, upon judging that the oscillation signal is not output from said oscillation unit, output a malfunction detection signal to said signal processing unit; and a low-pass filter interposed between said oscillation unit and said signal absence detection unit, wherein said signal processing unit is configured to, upon receiving the malfunction detection signal, issue occurrence of malfunction, said low-pass filter being configured to have a cut-off frequency which passes the oscillation signal corresponding to the resonant frequency of said resonant unit in a normal condition, but blocks the oscillation signal output from said oscillation unit when said resonant unit sees an oscillation at an abnormal frequency.