GB1277604A - Improvements relating to position-locating means - Google Patents

Abstract

1277604 Inductive signalling; transponders FERRANTI Ltd 21 Sept 1970 [11 Nov 1969] 55048/69 Headings H4L and H4U A means for automatically determining the position of each one of a plurality of objects within a given area, comprises a number of inductive loops together dividing the area into separate regions, means for applying to each loop a plurality of groups of coded signals, a transponder located with each object and responding only to a predetermined one of the coded signals and receiving means responsive to the signal from the transponder to indicate the identity of the object and the region within which it is located. As described, each group of signals consists of a transponder address signal followed by a loop identifying signal and the objects to be identified are located in a warehouse which is subdivided into four regions, each surrounded by an inductive loop, Fig. 1 (not shown). Each loop is fed via its own amplifier with a low-frequency carrier modulated with the coded signals under the control of a common control unit and each object carries a transponder receiving signals from an inductive loop and transmitting a modulated radio-frequency carrier as a response signal which is received and identified by a radio receiver. In operation, initially switches S1 to S4 of the control unit are in the position shown and a pulse code generator 58 which produces a repeated sequence of address codes, supplies the address code of one of the transponders to modulators 52 to modulate a low frequency carrier from 51 for transmission to the loops via amplifiers 53. This signal is received by the transponders, Fig. 3, and detected at 62, a unit 63 in the appropriate transponder recognizing the address signal and operating a switch 65 to connect the detector 62 to the transmitter modulator 67 for a predetermined period. The control unit 59 at the interrogator then changes over the switches S1 to S4 and causes the code generators 54 to 57 to supply loop identifying signals to the respective loops 21 to 24 to which only the transponder prepared by the preceding address signal will respond by retransmitting the corresponding loop identifying signal. This signal is received by the common radio receiver which may have a display panel or print-out indicating the location of each transponder. The loops may be energized one at a time instead of simultaneously to avoid difficulties when a transponder is located at the boundary between two loops.