Inductive proximity switch is composed of three parts: oscillator, switch circuit and magnified output circuit. The oscillator will generate an alternating electric field. When hemetal object approaches this electric field and reaches the induction distance, whirlpool will generate in metal object, resulting in attenuation of vibrati on and then stop. The changeof vibration and stop of oscillator is treated by begid stage magnified circuit and convertedto switching sign, triggering driving con-contact detection.