| 摘要 |
PURPOSE:To eliminate the possibility of false announcing occurring in higher harmonic noises completely by using two signals of different frequencies as detection signals and making announcing only when the changes appear simultaneously in the two detection signals. CONSTITUTION:Oscillators 1a, 1b emit signals of frequencies f01, f02 respectively simultaneously, and after these outputs are mixed 1c, they are applied to an exciter. The spacing between these two signals f01, f02 is so selected that when one signal is in proximity to a higher harmonic noise b1, the frequency of the other signal comes roughly to the center of the other two adjacent higher harmonic noises b2, b3. On the reception side, on the other hand, the signal obtained by a detection line 3 is applied dividedly to BPFs 9a, 9b which are so designed as to permit the passage of only the signals of the frequencies f01, f02, respectively. Now, when a human body approaches to the line 3, changes appear in both of the two detection signals, and the two inputs of an AND circuit 10 assume both the detection state. However, when a beat is generated between the detection signals and the higher harmonic noise, the two inputs do not both assume the detection state. |
