| 摘要 |
PROBLEM TO BE SOLVED: To make a decision whether a measured AC signal is synchronized or not accurately by convering the output signal from a limiter circuit into a DC signal having a voltage level proportional to the phase difference between first and second SC signals and outputting an asynchronous signal if the voltage level of the DC signal is higher than that of a synchronism decision signal. SOLUTION: A filter circuit 4 converts the output signal V7 from a limiter circuit 8 into a DC signal V8 having a voltage level proportional to the phase difference between a synchronism reference signal VS and an inner sine wave signal Vc . A comparator 6 compares the voltage level of the DC signal V8 from the filter circuit 4 with that of a synchronism decision signal VR1 from a reference power supply 5 and outputs an asynchronism signal V9 if the former is higher. Since the phase difference between the synchronism reference signal VS and the inner sine wave signal VC is replaced directly by the variation amount of signal voltage level, malfunction due to harmonic or noise can be suppressed. Consequently, a decision can be made accurately whether the synchronism reference signal VS and the inner sine wave signal Vc are synchronized or not. |
