First transponder reply delays other transponder replies in an electronic identification system

摘要

A transponder reader (10) has a transmitter (11) for transmitting a signal and each transponder (1, 2, 3) includes a receiver for receiving the reader signal and a transmitter for generating a transponder signal. When the reader (10) recognises a transponder signal from one of the transponders (1), the time to respond to the reader signal being set in each transponder by a random wait timer, it immediately issues a mute instruction, muting all other active transponders (2, 3) and passing control to the said transponder (1), without the need for a specifically timed acknowledgement to the said controlling transponder (1). The reader (10) issues a disable/wakeup instruction which disables the controlling transponder (1) once the response signal from the controlling responder has been successfully received, to reactivate all muted (but not disabled) transponders (2, 3). The disable/wakeup signal is a modification of the reader signal and is transmitter for a period less than the response period of a transponder.