| 摘要 |
PURPOSE:To prevent wrong decision caused by noises in a low rotating speed range by deciding the rotating speed of the engine from level variation of the output signal of a timer circuit. CONSTITUTION:When the rotation signal period of a signal generating device 11 is longer than a decision period tau1, the output of the device 11 goes up to H to turn on a switch SW12, and the rotation signal is inputted to the timer circuit 13 as shown by a waveform (c), but the period of output pulses of the circuit 13 is longer than the rotation period, so pulses of the circuit 13 are outputted continuously. When the rotating speed increases until the period of the rotation signal becomes shorter than the decision period tau1, the output of the device 11 goes sown to L and the SW12 is turned off. Therefore, no rotation signal is inputted to the circuit 13, but the circuit 13 is triggered with the rotation signal right before the SW12 is turned off and the pulse signal output is stopped a specific time later, so that it is decided that a specific high rotating speed is obtained. For example, a noise a' is generated in the rotation signal during low rotating speed operation and its period tau2 becomes shorter than the decision period tau1; and the output of the device 11 goes down to L temporarily as shown by a broken line (b) to turn off the SW12. In this case, the pulse signal is outputted from the circuit 13 continuously, so no wrong decision is caused by the noise a'. |
