| 摘要 |
PURPOSE:To simply and precisely discriminate the existence of a car by detecting the inductance change of an antenna loop as the phase change of current flowing into the loop antenna. CONSTITUTION:When a car exists close to a loop antenna 15 part, the inductance of the loop antenna 15 is changed and the waveform of an input frequency signal to an input terminal, i.e. a waveform shaping circuit 17, of the loop antenna 15 is changed at its phase. Consequently the time difference between the setting and resetting of a flip flop circuit 18, i.e. the time width of a gate signal supplied to a gate circuit 19, and the number of pulses applied to a pulse number comparator 20 is changed. The pulse number comparator 20 compares the number of supplied pulses with the set number of pulses from a pulse number setting circuit 21 and outputs a sensing signal for the discrimination of car existence. |
