Patent GB-667630-A (GB)
Title: Apparatus for receiving and registering code combinations each comprising a sequenceof electric double current signals
IPC: H04Q1/38
Filed: 1950-03-03
Abstract: 667,630. Electric selective signalling systems. STANDARD TELEPHONES & CABLES, Ltd. March 3, 1950. [March 5, 1949] No. 5457/50. Class 40 (i). [Also in Groups XL (b) and XL (c)] Apparatus for receiving and registering code combinations each of which comprises a sequence of positive and negative current pulses is characterised by pairs of discharge tubes in sequence, the pairs being such that a positive signal always fires a particular tube of a pair, and a negative signal the other, in each case the unoperated tube remaining inactive or firing subsequently to the first fired tube. In one embodiment for a sequence of four pulses (Fig. 3), the signal impulses are fed through a transformer 101 when a positive impulse becomes a positive pulse at the leading edge and a negative pulse at the trailing edge (Fig. 2), and vice versa. The pulses are taken through a suppressor circuit comprising rectifiers 102-105, which only passes on those pulses which make the outer terminals of the transformer secondary positive with respect to the mid-point. Thus, positive pulses are fed along line 154 to the control electrodes of thyratrons CT1-CT4, and negative pulses are fed along line 155 to thyratrons CT<SP>1</SP>1,-CT<SP>1</SP>4. The first two thyratrons CT1, CT<SP>1</SP>1 have a positive bias on their control electrodes from potentiometers 122- 125, so that any incoming pulse will cause one tube to fire, thus raising the cathode voltage by the P.D. across resistance 143, and preventing subsequent firing of the other tube. This P.D. also biasses the following pair of tubes CT2, CT<SP>1</SP>2, so that the next pulse will fire one of these tubes and prevent the associate tube from firing, and so on, until the fourth impulse fires CT4 or CT<SP>1</SP>4, thus energizing relay NL or PL, followed by relay Tr, which connects the anodes of tnyratrons CT1-CT4 to registering relays R1r-R4r respectively, so that any tube CT1- CT4 which has been fired, and subsequently has a reduced anode voltage, causes energization of the corresponding registering relay, which makes its own holding circuit. Relay Tr also causes operation of slow releasing restoring relay RSr, which breaks the anode circuits to allow the tubes to de-ionise, and energizes marker switch MS which advances one step when RSr releases to introduce a new set of registering relays. In a modification (Fig. 4), the four impulses are sandwiched between a negative and positive pulse. The negative start impulse fires a thyratron CT0 which is initially braised, to prepare the first pair of tubes CT1, CT<SP>1</SP>1, whose cathodes are not interconnected, so that they fire in sequence on the first signal impulse, causing a discriminating tube DT1 to fire only if the signal impulse were positive. Similarly, each subsequent pair of tubes CT, CT<SP>1</SP> and associated discriminating tube DT is affected by the subsequent signal impulses, and the final positive stop impulse fires tube CTL to energize relays Lpr and RSr in order, and the registering relays Rr associated with the discriminating tubes DT that have fired are energized and operate. Restoring to prepare for the next signal code follows as before. Two such circuits may be combined to operate alternately (Fig. 5 not shown) to allow signals to be sent at shorter intervals than required for complete deionization of the tubes in each circuit. To ensure consistency in the duration and amplitude of each incoming impulse, a pulse shaping circuit (Fig. 6) may be used, wherein cold' cathode tubes LT, LT<SP>1</SP> clip the pulses to uniform amplitude, and restrict the duration of the pulse to the time required for them to be.charged up to firing point, longer pulses merely charging condensers 807, 809 which subsequently discharge through parallel resistances 808, 810. The invention is not restricted to signals comprising a sequence of four pulses.