| 摘要 |
PURPOSE:To shorten the time required for anomaly detection, by switching current and auxiliary units when the time change rate of the output level of the LPF exceeds a fixed value in respect to current and auxiliary units for fundamental frequency generation dependent upon a PLL circuit. CONSTITUTION:In current and auxiliary fundamental frequency generating units consisting of main oscillators 1 and 1' and PLL circuits 2 and 2', outputs of LPFs 22 and 22' are subjected to A/D conversion by converters 6 and 6' and are stored in memories 7 and 7'. Digital values stored in memories and digital values of A/D converters are compared with each other by comparators 8 and 8'. If memories and comparators use fundamental frequencies fi and fi' of main oscillators as sampling pulses, comparators detect equivalently the difference between two digital values different in period, namely, the time change rate of the LPF output signal level. In case that this difference exceeds a fixed value, change-over switches 3 and 3' are switched through control circuit 5 to perform switching from the current unit to the auxiliary unit or from the auxiliary unit to the current unit. |
