GB1511311A - Device for the recognition of objects of animals - Google Patents

Abstract

1511311 Transponders SOC ANON COTIBAR 24 April 1975 [25 April 1974] 17042/75 Heading H4L For recognition of objects or animals, each object carries a secondary circuit, Fig. la resonant at 1, 2,..., or n frequencies, there being 1, 2,..., or n branches l 1 c 1 :l 2 c 2 : .... l n c n , connected to inductance L 2 in use coupled by mutual inductance, to inductance L 1 , in a primary circuit and carrying a constant current whose frequency, frequency modulated at 1000 Hz, is swept through N > n predetermined frequencies, the voltage across the inductance L 2 being demodulated by circuit 17-19 or an integrated circuit (not shown), the reaction caused in the primary circuit by the resonance of L 2 with any of the secondary branches resulting in a substantial change in the demodulated signal amplitude, which, detected by unit 21, enables counter 22 counting the clipped cycles of the demodulated signal, Fig. 8 (not shown), the counter providing an output to storage 24 when a predetermined count is reached. At the end of a sweep, storage 24 accordingly stores a "1" for each of the 1, or 2,..., or n resonances detected, at one or other of the position(s) corresponding to the particular values of the N frequencies swept through at which the resonance(s) occurred, the content of storage 24 thus identifying the particular secondary circuit, and hence object, detected. The content of the storage may be converted into binary form using the arrangement of Fig. 12 (not shown), the binary identification being stored in unit (59) for display or transfer to a centralized control. Upon detection of the proximity of an object, bistable 29 operates to enable the storage in 24 of the detected resonances, and the generation of the sweep, the latter being generated by adding the outputs of ramp generator 4 and 1 KHz oscillator 6, the resultant passing to voltage to frequency converter 7 whose output is fed to current amplifier 8, feedback resistor R CR operating to ensure that the current in inductance L, remains constant.