| 摘要 |
PURPOSE:To securely decide the rotational speed of a rotary body even if a reference signal for rotation decision making is interrupted by detecting at least two kinds of signals having periods corresponding to the rotational speed of the rotary body. CONSTITUTION:A signal passage limiting circuit 8 inhibits an ignition signal S4 from being passed for a specific time T after the reference signal S1 is inputted. This signal S1 when outputted normally and continuously or the signal S4 when the specific time T is elapsed after the signal S1 is interrupted is used as a signal for detecting the abnormality of the rotation of an engine. Further, the specific time T is shorter than the period wherein an inhibiting signal is outputted by an engine rotation decrease deciding circuit 3 and longer than the reference signal period of the lowest rotational speed at which engine rotations can be maintained. Thus, the signal S1 or S4 is inputted to a period arithmetic circuit 2 through an OR circuit 9 to calculate the period, which is then decided by the circuit 3; when the period is longer than a specific reference value, the inhibiting signal is outputted to inhibit data in a storage circuit from being updated.
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