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The line induction motor (LIM) is widely used for its some virtues due to the development of the sinusoidal pulse width modulation (SPWM) and vector controller (VC) technologies. Both the position loop and current loop are the necessary feedback control elements for the motor controller for it is efficient, flexible and anti-interference. As usual, the position loop for the LIM can be fulfilled by the electromagnetic or photoelectric sensors. However, the photoelectric sensors are directly and inevitably influenced by the photochemical smog. Without special measures, the electromagnetic position sensors also are infused by the electromagnetic interference (EMI) though they can eliminate the effect of smog. With the development of the eddy current technologies, some novel sensors are invented and manufactured. I.e., the proximity switch centered on the eddy current sensor technology is a typical position sensor with excellent immunity of EMI. Researches indicate that the eddy current proximity switch (ECPS) can be adaptive to the LIM application for its anti-jamming and anti-smog ability. Accordingly, the ECPS is proposed to provide the position loop for the motor controller. The ECPS is composed of exciting wingding, detection winding and post process circuit. Some critical factors are analyzed to improve the reliability of the output waveform from the proximity switch. Some methods and design rules of selection of the post-processing circuit, and the proper pull up resistance are summarized, which will influence the close control accuracy of the motor controller. Analysis of the critical factors to affect the reliability of the output waveform can give some instructions to the proper operation of the eddy current proximity switch with appropriate quality ratio of the output waveform.