| 摘要 |
PURPOSE:To grasp effectively features of pertinent signals to prevent malfunctions dependent upon disturbance by detecting an counting two kinds of frequency respectively. CONSTITUTION:Alarm signal (a) consists of two tones, and they are issued alternately periodically. These signals f1 and f2 output signals (b) and (c) corresponding to length of their periods by decision circuit 5. OR between outputs of decision circuit 5 is operated, and the output is inputted to pulse width check circuit 7 to check whether the alternate period of two tones is proper or not; and in case that this period is regular, signal (d) is issued. Meanwhile, outputs of decision circuit 5 are counted through J/KFF8. The number of signals continuing for a regular time and the number of alternate switchings from f1-f2 are conuted respectively; and if respective counted value within a fixed time reach prescribed values, alarm equipment 14 is operated. Consequently, effective detection with reduced malfunctions can be performed even for fading and noise. |
