| 摘要 |
<p>PURPOSE:To eliminate erroneous detection by storing a frequency signal and deciding the presence/absence of a metallic body based on the number of the frequency signals when the respective frequencies of alternative current signals to be successively outputted form a signal generating means are more than a threshold value set in advance. CONSTITUTION:A signal generating means 7 generates the reference alternative current signal and the generated reference alternative current signal is impressed to an LC oscillation circuit composed of a loop coil 2, frequency switcher 7 and generator 3. A control part 6 switches capacitor C0-Cn at fixed time intervals by a switch S of the switcher 5 and according to the switching, the plural frequencies are switched at the prescribed time intervals and turned around. These plural alternative current signals are outputted form the generator 3 to a frequency comparator 8a. Based on a period signal from the control part 6, the comparator 8a compares the respective frequencies of received signals outputted form the generator 3 with the threshold value for the frequency change stored in a threshold value storage part 8b corresponding to the respec tive frequencies.</p> |
