GB308172A - Improvements in and relating to contact-making relays, particularly for electric signalling systems - Google Patents

Abstract

308,172. British Thomson-Houston Co., Ltd., (Assignees of Tolson, W. A.). March 17, 1928, [Convention date]. Relaying or repeating systems; thermionic relays; duplex signalling.- The contact of a relay is operated in response to the voltage across an impedance in a control circuit when the current in that circuit has risen only to a fraction of its normal value, further rises in the control current being substantially bye-passed by a shunt across the impedance. As shown in Fig. 1 two relaywindings 24, 26 are connected in the plate circuit of a valve 25, the grid circuit of which isconnected across a resistance 17 in the direct current control circuit 16. The relays 24, 26 respond to a small current in the control circuit (determined by the bias battery 27) but as the control current rises, grid current flows in the valve 25 and prevents a large drop of voltage in the resistance 17. In a modification shown in Fig. 2, the relay winding 24 is in the control circuit, and is shunted by a two-electrode valve 25<1> biased by a battery 27, the shunting effect being the same as described above. As shown in Fig. 1, the relays from part of a two-way high-frequency repeater and are employed to prevent singing. Two aerials or high-frequency lines 5, 6 are associated with the channels 1, 2 of the repeater by hybrid coils 3, 4 and balancing networks 7, 8. Signals arriving on the line 6 pass to a detector 19, and thence to a modulator 12 (where they are re-converted to highfrequency form) and to the line 5. Carrier current for the modulator 12 is generated by a valve oscillator 9, the plate current path of which includes the resistance 17 and a valve 14, normally non-conductive. When signals arrive at the detector 19 the grid of the valve 14 is rendered more positive, and allows the oscillator plate current to start up. This plate current passes through the resistance 17 and causes the relays 24, 26 to operate. The relay 26 opens a shortcircuit across the grid leak 28 of the oscillator and oscillations are consequently generated in the valve 9 and pass to the modulator 12 and line 5. A fraction of this modulated energy may reach the detector 21 in the other branch 2 of the repeater and may set up a re-entrant path through the oscillator-modulator 23, hybrid coil 4, and the repeater branch 1. To prevent this (which would result in singing of the repeater) the relay 24 disconnects and short-circuits the output circuit of the detector 21. In the branch 1, the output circuit of the detector 19 is similarly opened by a relay in the circuit 32 extending from the oscillator-modulator 23 of the branch 2, which comprises valves arranged similarly to the valves 9, 14, 25 of the branch 1.