| 摘要 |
PURPOSE:To provide an on-vehicle polarity-change detector which does not detect a polarity change even when the frequency of a rail circuit current is varied from the fundamental frequency or when an instantaneous power interruption of a signal power source occurs. CONSTITUTION:The noise in the rail circuit currents received by a pair of antennas 11, 12 and added by a current adder 13 are removed by a band-pass filter 14, and its frequency is calculated by a frequency counter 21. The calculated frequency is compared with a set frequency value of a predetermined range by a frequency setter 28. When the variation of the frequency falls within the set value, '0' representing normal frequency is provided, and when it falls out of the set value, '1' representing abnormal frequency is provided. The results are stored in a first signal memory 32 and a second signal memory 33. A frequency variation detecting circuit 25 inputs signals from the memories 32, 33, and interrupts the operation of a waveform comparator 13 when at least one of them is abnormal. The maximum waveform value of the starting circuit current is similarly monitored, thereby preventing the erroneous judgment at the time of instantaneous power interruption. |
