| 摘要 |
1,216,160. Level crossings. SOC. DE FABRICATION D'INSTRUMENTS DE MESURE. 17 Sept., 1969 [17 Sept., 1968], No. 45781/69. Heading B7N. The presence of a vehicle between the barriers 3, 4, 5, 6 of a level crossing is signalled by the interruption of one or more beams 7-10 &c. of electromagnetic radiation extending between emitters 11-14 &c. on barriers 5 and 6 to receivers on barriers 3 and 4. The beams which have a wavelength of 3 cm. are alternately vertically and horizontally polarized and similarly polarized beams are modulated at different frequencies. Each receiver has an associated relay and the relay contacts are connected in series to an alarm circuit. Relay time constants are adjusted to prevent detection of pedestrians. |
