| 摘要 |
A b s t r a c t A system for registrating an article passing a predetermined area, and comprising a transmitter and a receiver with a common aerial alternately transmitting and receiving electromagnetic signals. A marker is attached to each article and receives said signals and transmits in turn other signals at passage of the area. The common transmitting and receiving aerial is formed as a multipole loop, preferably looped as a figure-of-eight dipole loop located in one plane. The known systems are encumbered with the problem that the marker with some orientations can pass without being detected. According to the invention the transmitting period is followed by a first receiving period in which the number of wave peaks is counted, and at least one additional receiving period in which the number of peaks is counted too. If the number of peaks during the first receiving period is sufficiently high, and the following period does not include too many peaks, the presence of a marker in the area is indicated. This system is so sensitive that the weaker side areas of another orientation than the main area may be utilized too. As a result, the marker cannot pass the area without being detected irrespective of its orientation. |
