Patent GB-654165-A (GB)
Title: Improvements relating to coded signalling apparatus
IPC: B61L1/18
Filed: 1947-10-23
Abstract: 654,165. Railway signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. Oct. 23, 1947, No. 28330. Convention date, Nov. 9, 1946. [Class 105] Coded current is supplied to a circuit such as the track circuits of a railway signalling system under the control of a continuouslyoperating coder through the intermediary of a polarized relay which is operated by current pulses derived from a condenser or transformer fed alternately in opposite directions under the control both of the coder and of the polarized relay. The coded current is thereby made half rate. The coded current may be supplied over contacts both of the coder and of the polarized relay, the halfrate code pulses then having unequal " on " and " off " periods. As shown in Fig. 1 a contact 10 of a continuously-operating coder CT when in its lower position effects the charging of a condenser Q from a battery BA in one or other sense depending on the position of contacts 12, 14 of a polar stick relay PS, i.e. a relay, the contacts of which remain in their last operated position until current of the opposite sense is received. In the position shown, the contacts 12, 14 of the polarized relay PS are at normal so that the upper plate is charged positively; when the coder contact 10 moves to the upper position the condenser discharges to the relay PS, the current pulse passing from right to left in the relay PS, this energizing the relay in the reverse sense whereby the contacts 12, 14 are set to the right (reverse). When the coder contact 10 next moves to the lower position the condenser is charged positively on the lower plate and the subsequent pulse (when coder contact 10 moves to the upper position) passes from left to right in the relay PS energizing the relay in the normal sense, whereby the contacts 12, 14 are set to the left (normal). When the coder contact 10 next makes its lower contact the apparatus is again in the position shown. Thus the polar relay PS has made one cycle of operation during two cycles of the coder CT. Application of a battery ATB to the track circuit is effected at a front contact 30 of a code-transmitting relay CTM which is energized for that period when a contact 26 of the coder CT is in its lower position and a contact 24 of the polar relay PS is at reverse; thus the track battery is applied only for a quarter period of the cycle of polar relay PS. The control of the signals at each end of the track section is effected by code-following relays ATR, BTR operated by the code pulses. These relays are responsive only to current in the direction shown by their arrows. With relay CTM closing its front contact 30 the battery ATB is applied to the track circuit, the current flow being from +ve through the front contact 30,'rail 1, relay BTR (in the operative direction), back contact 31 of a relay IR, rail 2, relay ATR (in the inoperative direction), to - ve. The closure of front contact 34 of relay BTR gives a current pulse in the secondary winding 37 of a transformer IT but this pulse is in the ineffective direction for relay IR. After the quarter period the code-transmitting relay CTM drops its contact 30 so that the relay BTR drops, whereby at back contact 34 a pulse is given to the secondary winding 37 to energize the relay IR in the operative direction. Relay IR at its front contact 31 then applies a battery IB to the track circuit from +ve through front contact 31, relay BTR (in the ineffective direction), rail 1, back contact 30, relay ATR (in the effective direction), rail 2 to - ve. The relay IR in due course drops and the apparatus is again in the position shown. Thus during the cycle (of the relay PS) relays ATR and BTR are each energized for a period and dropped for the remainder of the cycle. The movement of a contact such as 40 of the relay ATR energizes slow relays AFSA, ABSA to light the clear signals G at each end of the section. Entry of a train will shunt the current from the relay BTR so that this remains dropped and no current will be applied by the battery IB (this current would in any case be shunted from the relay ATR); relay ATR periodically receives current from the battery ATB but this is in the ineffective direction. Thus contact 40 of relay ATR remains dropped so that the slow relays AFSA, ABSA drop and the danger signals R are lit at each end of the section. Fig. 3 shows the polar stick relay PS as pulsed in the normal and reverse directions by the secondary winding 61 of a transformer, the primary winding 62 of which is centre-tapped to the - ve side of a battery and the ends of which alternately receive current over contact 64 in the normal and reverse positions. The polar relay is changed over only when coder contact 10 opens; this is because when contact 10 again makes its lower contact the feed is to the other end of the primary and this gives a pulse in the secondary which is of the same polarity as on the preceding break pulse. Arrangements are also described in which a relay (with front and back contacts) with a second winding and a stick circuit therefor is used instead of the polarized relay PS with normal and reverse setting armatures, Figs. 2 and 4 (not shown). Apparatus as above may be arranged cascade-fashion to sub-divide the coding speed still further.