| 摘要 |
PURPOSE:To improve the reliability of vehicle detection by an arrangement wherein equipment on a vehicle is so constructed that it transmits a vehicle detection signal with a square wave amplitude modulation wave of which mark time width is sufficiently larger than space time width. CONSTITUTION:While a vehicle 1 is not entering an enclosed area 2T, a signal inputted to a receiver 5 is only a check-up signal fCH. This check-up signal fCH is inputted to a level decision circuit 5a6 via a filter 5a1, an amplifier 5a2, a remitter 5a3, a demodulator 5a4, and a filter 5a5. The output of the circuit is used to excite a check-up relay CHR, so that an output deciding that the vehicle 1 has not entered the enclosed area 2T is obtained. When the front portion of the vehicle enters the enclosed area 2T, this causes an action suppressing the check-up signal fCH in the remitter 5a3 and the check-up relay CHR drops. The relation between the mark time width M and space time width S of vehicle detection signals f1, f2 is set to M>>S whereby the degree of suppressing the check-up signal fCH is made larger to improve the reliability of vehicle detection. |
