| 摘要 |
PURPOSE:To bring a metal detecting apparatus to asymmetric error even if each detecting coil is scanned by a transmission signal with same frequency, in an apparatus for detecting an automobile at a railroad crossing, by respectively changing a transmitting side and a receiving side by switch circuits having a symmetric error characteristic and an asymmetric error characteristic. CONSTITUTION:Detecting circuits 11, 12... are successively scanned by change-over circuit 3 of a scanning signal generator 4 to apply the transmitting signal with same frequency from a generator 2 to the detection coils of the bridge circuits 11 of the circuits 11, 12... and, when a vehicle such as an automobile approaches a railroad crossing, the output of the corresponding detection circuit 14 is brought to a low level. This generator 4 and the circuit 3 are constituted so as to obtain outputs of symmetric error characteristics to a circuit obstacle and, if the transmitting signal is not inputted to all or either one of the circuits because of the obstacles of the generator 4 and the circuit 3, output corresponding to either one of the circuits 11, 12... is generated. On the other hand, each logical circuit 15 for performing the change-over of a receiving side has an asymmetric error characteristic. Therefore, an asymmetric error showing the presence of the vehicle is obtained to the obstacles of the circuits 14, 15 of the receiving side and a metal detecting apparatus with high safety is formed. |
