| 摘要 |
PURPOSE:To improve the accuracy of detection by dividing the frequency of the waveform shaping output of a detected waveform, counting output pulses of a reference oscillator with the frequency division output, and performing correct/error decision based upon a counted number in the period of the detected waveform by using data in a ROM. CONSTITUTION:A signal V2 obtained by shaping 2 the waveform of a signal V1 from an AC power source 1 is supplied to the 1st frequency divider 11 to obtain a signal V3 of half frequency. Output pulses V11 of a crystal oscillator 12, on the other hand, are frequency-divided by the 2nd frequency divider 13 into a signal V12. A counter 14 is reset at the rise of the signal V3 to begin to count the signal V12, thereby counting one period of the AC waveform, i.e. from time o to T1. The waveform of the signal V1, however, is shorter in period and the counter 14 is reset at time T1, so the counted value C1 is used as an address to read data in the corresponding address of a ROM 15 right before the counter 14 is reset. Here, if switches S0, S1, and S2 among switches 16 are turned on, the output of an OR gate 17 becomes a signal F1 and a D-FF 18 is risen as shown by a signal F2 in synchronization with the signal V3, so abnormality is detected at the time T1.
|
