| 摘要 |
PROBLEM TO BE SOLVED: To select synchronism which is precisely established from the other synchronism detection means even if erroneous synchronism detection exists by permitting a synchronism selection means to judge and select a detection result supplied from plural synchronism detection means at respective timings and permitting a synchronism protection means to protect synchronism. SOLUTION: The synchronism detection part 11 generates a synchronism non-detection pulse when a synchronous pattern is not detected in a position where it is to be detected by the control of front protection. A synchronism judgement part 13 judges step-out when the number of synchronism non-detection times, which is to be supplied, is counted to be continuous three times. When step-out is recognized, a selection signal is outputted to a synchronism selection part 13b so that the output of the synchronism detection part 12 is selected, and therefore output is switched from the synchronism detection part 11 to the synchronism detection part 12. Thus, synchronism establishment from the synchronism detection part 12 can immediately be used even if synchronism is once established and then step-out occurs by executing such operation. |
