GB743573A - Railway signalling system - Google Patents

Abstract

743,573. Magnetic amplifiers. SVENSKA AKTIEBOLAGET GASACCUMULATOR. Aug. 28, 1951 [Sept. 4, 1950], No. 20261/51. Class 40 (4). [Also in Group XXXVIII] Pulse-modulated alternating currents, e.g. for selective signalling, are derived from transductors each of which has two control windings, one series connected with a resistor and the other with an inductance, so that each transductor operates similarly to a blocking oscillator. Transmitter. As shown, transductors 4, 5 ... may be switched selectively into circuit by a switch 3 when the similar A.C. windings 10, 11 are series connected with the output transformer 6 across a 50-cycle supply 1-2. The windings 10, 11 conduct during alternate half-cycles of the supply by virtue of rectifiers 12, 13 and magnetize the core in the same sense, the reactance of these windings being varied periodically by similar opposed control windings 14, 16 fed from the rectified output of transformer 6, and series connected, respectively, with a resistor 15 and inductance 17, the modulating frequency being determined by the control circuit constants. The transductors 4, 5 modulate the 50-cycle input at different frequencies which are doubled in the rectifier bridge 7, the modulated output therefrom being fed through a series resonant filter 8 to the line R, R. An additional primary winding 18 of transformer 6, fed directly from the supply, compensates for the magnetizing current of the operative transductor so that in the line R, R the modulation is 100 per cent. Alternatively, a single transductor may be used, the coupling of which is changed by altering its control voltage or circuit elements to produce the desired modulation frequencies. Receiver, Fig. 2. The signal carrier frequency is filtered at 24 and applied through a rectifier 25 and amplifier 26 to relay coils 27, 28 over resonance circuits 29, 30 tuned respectively to the modulation frequencies of transductors 4, 5 and rectifiers 31, 32 so that relay 27 or 28 responds according to the transductor 4 or 5 connected in circuit at the transmitter. An L.C. combination 33, 34 filters out the D.C. and unwanted harmonics from the amplifier output. In a modification, Fig. 3 (not shown), the relay coils 27, 28 act on opposite ends of a bar armature pivoted at its centre to close one or the other of two control circuits. A third circuit may be closed by the armature in its neutral position. Alternatively the inductance 33 may function as a zero-current relay.