Patent GB-446918-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1934-11-14
Abstract: 446,918. Exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, Westminster and DIXON, R. G., 162, Westmount Road, Eltham Park, London. Nov. 14, 1934, No. 32770. [Class 40 (iv)] In a system employing call finders taken into use by temporarily used common apparatus on receipt of a starting signal, the starting signal is removed and the common apparatus released if an idle finder is not available. The invention is described in connection with a system in which operators have access to groups of junctions to P.B.X.'s over jacks and jack finders taken into use and controlled by one or other of a pair of allotters. There may be one or more jacks for each P.B.X. group at each operator's position, but the jacks are not multipled over the positions. The group of finders to be searched by an allotter is determined by a marking applied from the jack circuit to commoned contacts of the group in some banks of the allotter, markings being also applied for control purposes to the first and last contacts in another bank. Both allotters are started in response to a call, the second after a delay sufficient to permit the first to search over the wanted group and, if successful, to busy the group and disable the group test circuit for the second allotter to prevent double connections. The second allotter may, however, take a under for a call in another group in the case of simultaneous calls in two groups. On reaching the last contacts of a group and if the last finder is busy, a signal is sent back to the cord circuit, Fig. 1, which operates as described in Specification 446,917 to send the busy signal to the calling party. To ensure that the allotter has searched over the whole of the group, the arrangements for stopping the allotter on the last contacts and sending the signal are made dependent on a relay which operates when the allotter arrives at first contacts of a group. Terminals AT, BT corresponding to the various P.B.X. lines are commoned in groups and connected to contacts of the S relays of corresponding jacks such as CJ. The contacts of finders in the banks of allotter FA are connected to terminal sets CT ... GT, CT being commoned in groups cross-connected to AT, DT having first and last finders of the groups cross connected to AT, ET having last finders only connected to BT, whereas FT and GT are commoned in groups. Two allotters of the homing type are provided, one FA being shown, the start circuits of this allotter and the other being indicated by dotted and chain lines respectively. When a jack is plugged, sleeve relay S pulls up, but M and N in the plug circuit remain inert. CS operates and energizes start relay SA of allotter FA over off-normal contacts ON2 in series of both allotters, and SA holds itself over ON2 of the other allotter. Relay A pulls up, locks, and operates B which closes the driving circuit of the allotter. When the allotter arrives at the first line of the group, high-speed relay E operates over FA7 and connects up high-speed relay F which is short-circuited until the allotter leaves the first line whereupon F pulls up in series with E and connects a further high-speed relay G to FA7 for use if busy conditions are encountered. The test circuit passes from ground over commoned group in CT, FA6, relay C, FA5 to battery over a contact of KC in the line circuit. When test relay C operates, the driving circuit is opened and LC (i), KC (i) pull up. Relay D also operates and connects ground to wiper FA8, the commoned group of which is connected over FT and wiper FA8 in the other allotter to its FA5 wiper to busy the group to the other allotter which is also prevented from testing this group by relay D grounding wiper FA9 so that the FA9 wiper of the other allotter will extend this ground to shunt its relay E. Relay D also closes testing and driving circuits for the jack finder JF over FA1 and FA2, the test circuit including an additional bank 4 of JF in which terminals corresponding to jacks of the group are connected to a common terminal MT to limit the test to this group. When the calling jack is reached, common high-speed test relay K pulls up and operates L which energizes the right-hand winding of switching relay H. Cut-off relay CO also operates, locks in series with left hand winding of H and connects its left hand winding to the jack sleeve in place of relay S thereby increasing the sleeve current to signal the operator. The holding ground connected up by relay H shunts down C over FA5, and the operation of L releases A so that B, D, E and F fall back, and as K is shunted by the right hand winding of H, L relapses to complete the homing circuit of the allotter. All lines of group busy. When the allotter reaches the last contacts of the group, G operates over FA7, DT and AT since E and F were operated when the allotter entered the group. The allotter stops and if the last line is busy, C does not operate so that J pulls up and connects ground over FA4 to the sleeve of the jack to initiate the backward transmission of busy tone from the cord circuit. Relay B falls back followed by J and if no other call is waiting, S, CS, SA, SB and A relapse and the allotter goes home. If a call is waiting, CS and A do not release and B re-operates on the relapse of J to re-start the allotter. Operation of second allotter. When the' first allotter is taken into use by the operation of CS, SA, relay SB pulls up after a delay and starts the second allotter. As previously explained, the group searched by the first allotter is busied to the second which is also prevented from testing this group. The second allotter rotates to its home position or searches in another group if one happens to be calling. When the second allotter was started, it opened the original starting circuit over ON2 of the first allotter consequently this allotter cannot be restarted until the second allotter has homed. Dealing with faults. The operation of B consequent on seizure of the allotter brings SS and ZZ under the control of timed pulses, and if the allotter does not release within a predetermined time, ZZ connects up visual and audible alarms, releases B to home the allotter, opens the circuit of A to prevent re-starting of the allotter until the fault has been attended to and ZZ released by short-circuiting at jack ZJ. The motor circuits of the allotters and jack finders also include a release alarm relay.