| 摘要 |
PURPOSE:To perform a reliabile detection without the movement of harmful foreign matters to a low-electric field part or the dielectric breakdown due to their motion when an applied voltage is raised. CONSTITUTION:When an AC voltage is applied to an apparatus, a force F acts upon a foreign matter 11 in its electric field space against gravity, and the foreign matter 11 is floated up. When the applied voltage is an AC voltage (v) of a commercial frequency and the height of floating-up at a time t1 is denoted as h1 in this case, a height h2 of floating-up a time t2 is lower than the height h1 if the applied voltage is a high frequency voltage having the same crest value v0. The locus of the height h1 or h2 to a time (t) is a curve A in case of application of the commercial frequency voltage and is a curve B in case of application of the high frequency voltage, and the direction of the force F applied to the foreign matter is changed in every half cycle of the voltage waveform by the applied voltage, and therefore, the height h2 of floating-up of the foreign matter in case of application of the high frequency voltage is lower than the height h1 of floating-up in case of application of the commercial frequency voltage. Consequently, by making the applied voltage high-frequency, the voltage is raised to perform a safe and high-precision detection on a basis of ultrasonic waves generated by the motion of the foreign matter. |
