Patent GB-680822-A (GB)
Title: Improvements in and relating to automatic telephone exchanges
IPC: H04M11/02
Filed: 1949-11-11
Abstract: 680,822. Automatic exchange systems. AUTOPHONE, Ltd., and ROSENFELDER, R. I. Nov. 11, 1949, No. 28955/49. Class 40 (iv). In an automatic exchange having facilities for making a general call for a wanted party who is absent from his telephone, the general call being established by conditioning switching means in a first finder/connector link used in an attempt to set up the call, the wanted party on replying from a telephone other than his own seizes a second finder/connector link and on dialling a reply number (which may be his own number or a special number) into it, influences the switching means in the first finder/ connector link over the connector multiple in such a way as to terminate the general call and complete the connection. Normal call. The two-step line relay LA operates partially in series with relay A of the first idle link when the calling subscriber's loop is completed. Relay LA marks the calling line in the bank c2 (or c1) and A brings up B to connect the interrupter INT to the line-finder magnet MLF to initiate hunting. When the calling line is found test relay F (or E) operates in series with the right-hand winding of LA which pulls up fully and releases A. Relay F (or E) short circuits its high resistance winding to busy the calling line. When A operated it brought up by the impulsing relay J which was subsequently held over the calling subscriber's loop. Relay J brings up B and C. Relay F brings up M to step the chain circuit for allotting the next call, and also twostep relay D which operates fully. Relay M brings up K. If the first digit is 2 both O and N come up so that when C releases at the end of the train the second step contacts of D fall back, connecting resistance RW into its circuit to hold it partially operated, thereby connecting the link to the second group of wipers a2, b2, c2. If the first digit is 1 relay N does not operate and when C releases D the resistance RW is not switched in so that D releases fully and the link is connected to wipers a1, b1, cl. If the wanted line is in the first half of the two-hundred line group, one further digit only is dialled and J repeats the impulses to the connector magnet MCS. When C falls back at the end of the train M follows and initiates the release of K during whose slow period test relay T operates if the called line is free to connect up ringing current and ringing tone. Relay T short circuits its upper winding to busy the called line and bring up the line relay LB fully. Relay Y comes up to the answering subscriber's loop, short circuits T to interrupt the ringing tone and current and connects the low resistance relay Z in the test circuit, the latter operating and switching through. A subscriber in the second half of the two-hundred-line group is reached by dialling O followed by another digit. When the connector stops at the tenth position relays K and T are connected in a circuit over wiper c2 in which only K operates to maintain the stepping circuit and suppress the transmission of busy tone. When the next digit is dialled the connector is stepped again and the call proceeds as before. Calling an absent subscriber. Subscribers capable of being so called are connected in the second hundreds group with which is associated an additional connector switch wiper d1. A subscriber priveleged to initiate a general call for the wanted subscriber is provided with a key Eka which unbalances the speech wires to operate X and M which brings up K and holds P which was operated (without effect) during the slow release of K and then locked under control of T. Relay M cuts relays U and Z into the test circuit whose resistance is thereby increased to render the called line selectable by another link. Relay U connects battery through resistance t10 to the upper one of the speech conductors whose balance is disturbed to keep X operated. Relay U also brings up C to connect up a special tone over rc indicating that a general call is being made. Relay U finally brings up the wanted subscriber's general call relay S and the common relay Q. Relay S short circuits its upper winding to busy the general call circuit. Contacts of S are jumpered through to mercury contact relays MRI ... III in different combinations for each wanted subscriber and Q energizes the appropriate combination to light lamps RC and sound bells. The called subscriber then goes to any telephone and sets up a call to his own line over a second link. The unbalance of the speech wires is then transmitted to the second link to bring up X and M therein, the latter removing the short circuit about relays U and Z. The resistances of T, U and Z are so selected that only Z in the second link operates and busies the called line by putting its own low resistance in shunt with the test wiper. This releases U in the first link and T is thereby shunted down and C is released to complete the talking circuit. If the wanted subscriber answers from his own telephone, Y shorts out T and U, the latter releasing C to complete the speech circuit. Breaking in on busy connection. A privileged subscriber may, on receiving busy tone operate key Eka to energize differential relay X. Relay M follows to bring up P and K which complete the talking connection. When the third subscriber hangs up testing takes place as before and the conversation proceeds in the normal manner. Any subscriber may break in on a call on which a general call is being sent out. Congestion conditions. If all links are busy a fresh caller brings up G which connects up busy tone to the calling line. If an attempt to answer general call is made on any telephone except the called subscriber's when the last link is in use, G comes up, reverts busy tone and releases Q to interrupt the lamp signals. G also earths the test lead to release T, U and C and so disconnect the special tone sent to the caller. Alternative methods of establishing a general call. (1) By dialling a digit 1 or (preferably) more, relay M can be made to operate followed by P, K and U, whereby relay X is unbalanced and operate to hold M, whereupon the general call is initiated as before. (2) A thermal relay Th may be operated if relay T remains operated for more than a predetermined time. Th brings up M which initiates the general call as before. In a modification, arrangements may also be made for the called subscriber to dial a special general call circuit number instead of his own number. The circuit is then modified as shown in Fig. 2. When U has been energized as described above in answer to the operation of the calling subscriber's key Eka, the two-winding relay R is operated over its coil Rl and holds over its coil Rh. Relay R connects the calling link to the general call circuit RCL, earths c2 to busy the called line and connects the test circuit to the third wire of the general call circuit to bring up line relay LR. The latter inserts a resistor LRL in series with relay S, thereby preventing seizure of the general call circuit by another link when relay S has short circuited its other winding. The called subscriber dials a predetermined number to gain access to the general call circuit after which the call proceeds as described above.