Patent GB-827174-A (GB)
Title: Improvements relating to telephone systems
Inventor: STALLWORTHY FRANK ALLEN
IPC: H04Q1/446
Filed: 1955-03-18
Abstract: 827,174. Automatic exchange systems. SIEMENS, EDISON SWAN Ltd. March 5, 1956 [March 18, 1955], No. 8009/55. Class 40 (4). An exchange connection is set up and controlled by signal pulses of a single voice frequency and utilizes a backward answer signal followed by repeated similar pulses until a forward acknowledgement pulse is received and is such that a non-repeated clear back signal is sent when the called party clears to which no farward acknowledgement is given. In this arrangement, if a forward acknowledgement to on answer signal is lost, the succeeding answer signal will be interpreted as a clear back signal but as no acknowledgement is given a further answer signal will be sent and will elicit a further forward acknowledgement signal which if successfully transmitted will establish the connection. If a clear back signal is lost, the subsequent receipt of an answer signal will be interpreted as a clear back signal and the succeeding answer signal will be interpreted correctly if not lost. Outgoing line circuit.-Figs. 1a, 1b, 1c. At the exchange side, to the left of the Figures, terminals 1 to 4 are connected to a manual board or to a selector outlet, while on the right of the Figures terminals 5 and 6 are connected to the inter-exchange line. The circuit has a voice frequency signal receiver with pentodes V1 and V2 which distinguishes between voice frequencies and the signal voice frequency of 2280 c.p.s. to control a normally-operated relay X. A discharge tube CT1 and a capacitor C2 are used to measure the length and spacing of signal pulses switched on to the line from leads 7 and 8 by tone sending relay TX, and guards the voice frequency receiver following each train of dialled impulses and also following the seizure of the circuit. Non-linear resistances RX serve to quench sparks at the contacts of relays X and A. Voice frequency receiver.-Pentode V1 amplifies audio frequency fed from the line by transformer TR1 and has the primary windings of transformers TR2 and TR3 in series in its anode load. Secondary winding II of TR3 is tuned by capacitor C15 (and tuning capacitors C16, C17, if necessary) to respond to the signal frequency. Secondary winding III provides selective feed-back to VI. The outputs of transformers TR2, TR3 are applied to voltage doublers connected to the grid of pentode V2 and acting in opposition. In quiescent conditions resistor R25 biases the voltage doubler of transformer TR2 so that the grid of V2 is held positive and relay X in its anode circuit is therefore normally operated. When a signal of 2280 c.p.s. is received the output from TR3 drives the grid of V2 to cut-off to release relay X, whereas if any other signal is received TR2 delivers an output that holds V2 conductive. A chain of resistors R22, R23, R24 and R27 enables the relative outputs of TR2, TR3 to be adjusted. Outgoing call.-When the outgoing line circuit is seized, relays A and B pull up to operate tone sending relay TX and signal guard relay SR over their first windings ; SR being delayed as its second winding is short-circuited. TX connects the line to an A.C. source of 2280 c.p.s. to transmit a pick-up signal. When finally made SR releases TX and operates an auxiliary guard relay BB to measure off a dial pauseguard period (at the end of which the line is extended by line-splitting relay SP) by connecting the cathode of discharge tube CT1 to negative potential over winding I of control relay CR. Capacitor C2 charges slowly through as many of resistors R28, R29 and R30, as are not bridged until it fires CT1 to operate CR which locks up over its second winding, connects resistor R12 across C2, operates linesplitting relay SP, and by means of the surge induced in its first winding extinguishes CT1. If dialled impulses are received before the end of the guard period, relay CD pulls up to open the cathode connection of CT1 and shunt C2, the impulses being repeated by tone-sending relay TX. When dialling is completed CD falls back and the dial pause guard period is measured off again until CT1 fires to lock up CR and operate SP. If impulses are dialled after CT1 fires and CR pulls up, relays SP and CR are released as soon as A falls back on the first digit while TX repeats the pulse slowly enough to allow SP to release first. Outgoing call answered.-When the called party replies answer pulses of 2280 c.p.s. are sent back over the line and assuming that the first pulse is effective the receiver at the outgoing line circuit causes relay X to fall back for the duration of the pulse, causing relay CD to respond and release SP if SP is operated and the dial pause-guard period over. In falling back, X releases SR which operates answer relay D and holds BB. SR cannot hold up over released contact x2 due to the rectifier MR1. Relay D reverses the line to repeat the answer signal to a preceding circuit. At the end of the answer signal X pulls up to operate CR, if not operated, and to operate SR which holds BB and energizes answer control relay DD which is slow to make. During the time taken for DD to operate TX is pulled up to send a forward acknowledgement signal which normally stops the backward answer signal. When made, DD releases CD to operate SP which connects up the line for conversation. Clearing by called party before caller clears.- A non-repeated pulse is sent back over the line and normally releases X which operates CD to release line splitting relay SP. X remains released sufficiently long to release SR which releases relay D to reverse the line on the exchange side and thereby repeat the clear back signal to a preceding circuit. When the clear back signals ceases, X re-operates to release CD and re-operate SR which releases DD. When released CD energizes SP so that the outgoing line circuit is in a condition to respond to further answer and clear back signals. If the caller now clears, relay A falls back and relays SP and CR release, while TX is operated together with CD which causes the slow release of B. TX switches a clear forward pulse on to the line for two seconds and repeats the pulse after 1 sec. intervals until a backward acknowledgement is received. When released, B takes busying earth from the private wire but releases CD to operate DB which re-connects earth to hold the circuit marked busy and connects up a delayed alarm circuit over a line 9 and a lamp L. During the short time that CD is operated resistance R12 is connected across capacitor C2 to ensure that it carries no charge when CD releases and connects up discharge tube CT1 and capacitor C2 which after 2 seconds gains sufficient potential to fire the tube. When the tube fires, CR operates and holds relay DB but releases BB and energizes CF which locks up over its second winding. CF releases TX to terminate the forward release signal, and the voltage surge induced when CF locks up extinguishes CT1. When the tube CT1 fired C2 was partially discharged between trigger anode and cathode so that BB in falling back re-connects CT1 and measures off a further interval of one second at the end of which CT1 fires to pull back CR, release CF, and discharge C2 over R12. Relay CF again extinguishes CT1, pulls up BB over its first winding, and operates TX to send the second 2 seconds clear forward signal at the end of which CF is again operated to provide an interval of one second. Relays CR and CF interact in this manner to send forward release signals until a backward acknowledgement is received during an interval in which event X falls back to release SR so that when CT1 fires at the end of the interval CR responds to release CF and discharge C2. When CF and CR release, CT1 is extinguished and the first winding of DB is disconnected so that when X restores at the end of the backward acknowledgement signal DB falls back and the outgoing line circuit is ready for normal use. If the caller clears first the above operation is modified only in that when A falls back CD does not operate and relay B releases relays D and DD. Incoming line circuit.-Figs. 2a, 2b, 2c. At the left of the Figures terminals 26 and 27 are connected to the inter-exchange line and the circuit has a voice-frequency receiver with pentodes V3 and V4 which control a relay XX in the same way as the receiver in the outgoing line circuit controls relay X. An attenuating pad R43 to R48 protects the receiver from a short circuit on the exchange side. Non- linear resistances RX serve to quench sparks at contacts of XX and relay DA. When the pick-up signal is received from the outgoing line circuit, XX releases to operate guard relay BH which causes impulsing relay AA to respond and close a calling loop over the line. Dialling relay CC also responds when XX releases and operates relay DA. When XX pulls up at the end of the signal BR responds to mark the circuit busy and relay CC falls back to operate line-splitting relay AX and to break the calling loop. XX responds to the dialled impulses which are repeated by AA, AX being released on the first impulse and CC being pulled up until the end of the impulse train. Answer by called party.-Current is reversed in the loop to operate relay DP which locks up and causes the slow release of DA and immediate release of AX to split the line. DP also connects up tone-sending relay SX which holds until DA falls back to send an answer signal. When SX falls back DR is operated and reoperates DA which initiates the slow release of DR. When DR releases it initiates the slow release of DA which causes the transmission of a further backward answer pulse. DA and DR interact until a forward acknowledgement signal is received to release XX and operate CC before DR releases. Relays DA and DR hold up and AK is operated to remove the attenuating pad from the line. When XX pulls up at the end of the signal CC falls back so that the circuit is ready for conversation. Called party clears first.-Reversal of current over the line re