GB892273A - Electrical identification system - Google Patents

Abstract

892,273. Electric-selective signalling systems. STANDARD TELEPHONES & CABLES Ltd. Jan. 15, 1960 [Jan. 19, 1959], No. 1493/60. Class 40 (1). In an electrical identification circuit for determining the state of mn open/closed switches kll, a freerunning multivibrator MV steps a ring counter CT to energize one of m oscillators OSC1 ... m to supply a frequency peculiar to that oscillator via output line OL to the inputs of mn field stations U11-Umn. Each field station, e.g. U11 comprises a tuned receiver REC11 &c., a switch k11 and an oscillator OSC11 &c. and is so arranged that receivers REC11-REC1n are tuned to oscillator OSC1, REC21-REC2n to OSC2, &c. Each station of the group U11-U1n has an output oscillator OSC11-OSC1n producing a unique frequency within this group. The outputs of each field station passes via a common line 1L to n tuned receivers REC1 to RECn at the central station. With the counter CT in the first position, frequency-significant A.C. from OSC1 passes to all the field stations, but only receivers REC11-REC1n of the first n field stations are tuned to this frequency, these respond and, where switches K11 &c, are closed, corresponding oscillators OSC11-OSC1n. Thus within this period up to n different frequencies will be simultaneously applied to line 1L, detected by tuned receivers REC1-RECn and corresponding signals, gated with outputs from the ring counter, registered in a device REG so as to indicate the state of switches K11-K1n. This process is repeated for each step of the counter CT. In a modification the lines OL, 1L are replaced by one single line, in which case the m frequencies from oscillators OSC1-OSCm must necessarily be different from the n frequencies from oscillators OSC11 &c. The circuit may be applied to railway control systems, the field stations U11 &c. preferably comprising reed relays and the switches K11 &c. being opened by the presence of a train in an associated section of track. The oscillators and receivers are preferably known types employing transistors. The frequencies utilized may range upwardly from 540 cycles per second in steps of 120 cycles per second.