| 摘要 |
PURPOSE:To discriminate automatically a fault with high accuracy by arranging a mutual discrimination circuit comparing mutually plural reference frequencies and a self-discrimination circuit counting its own reference frequency with a prescribed period of window so as to discriminate the fault. CONSTITUTION:When a reference frequency 3a is high in excess of a permissible range or a reference frequency 3b or 3c is low below the permissible range in the mutual discrimination circuit comprising a self system counter 12a, a cross system counter 13a and a comparator 14a, a control signal S1 goes to a low level when the count of the counter 13a is a prescribed value or below, and a control signal S4 increments a 16-adic counter 23a by 1. The detected fault is added by the counter 23a similarly in a converse signal level, and if the fault takes place consecutively for a prescribed number of times, it is informed externally. Even after other reference frequency 3b or 3c is failed in the self-discrimination circuit comprising the self system and cross system window generators 16a, 17a, the circuit itself detects the frequency fluctuation regardless of a low accuracy. |
