Patent GB-491901-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1937-04-13
Abstract: 491,901. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., BEALE, C. E., and RICHARDS, I. T. April 13, 1937, No. 10546. [Class 40 (iv)] In a system in which long distance connections are set up by operators, the impulse sending equipment includes means for signalling to an operator the approximate time of delay with respect to a group of trunks on which delay working is in force. In the trunk exchange system shown in Fig. 1, subscribers local to the area obtain access to an incoming line ILL by dialling O, whereupon finder CCF hunts for an idle " demand " position DP which on response by the operator is connected to a 1st selector S1 and over a hunting switch SH to a register-sender S. The operator obtains access to outgoing trunks by sending 4 digits, the first of which is O, since S1 over its first 9 levels gives access to local automatic subscribers. Selector S2 responds to the second digit and S3 to the last two, the last digit determining whether S3 is to hunt or select a particular trunk or hunt in a sub-group. Selector S3 may have call-storage or repeated searching facilities as described in Specifications 491,865 and 491,878. Associated with each sender S is a two-motion auxiliary switch AS which is set by marking from the registers of the 2nd and 3rd digits. Two banks of AS are adapted to provide alternative route markings for the sender switch and other banks are connected to the group busy equipments GBE of the various trunk groups and to the delay supervisor's position DS. The group busy equipments furnish signals to the sender as to the busy or " in delay " condition of the trunk groups of regular or alternative routes, and the supervisor signals to the switch the approximate time of delay which is repeated to the demand operator in the form of tone signals. If a regular trunk group has an idle trunk or is busy, but not in delay, or if an alternative route group is neither busy nor in delay, digit transmission takes place with preference for an idle regular route. Alternative routing, however, does not occur if the last digit is other than 1, i.e. if a particular trunk or sub-group is required. If the regular route is in delay and the alternative route busy or in delay, digit transmission is prevented and the time of delay signalled to the operator who informs the calling party and sends the ticket to the delay supervisor. The supervisor may detail an ordinary operator to clear up calls on waiting tickets, and it is arranged that a sender seized by an operator on this duty transmits digits for the regular route even if the route is in delay. Calls incoming on long distance trunks ITL are dealt with in a similar manner by operators TP, but when the call is to the local exchange (1st digit other than O), the auxiliary switch AS is not used. Specifications 391,123 and 459,803 also are referred to. Registration of digits. On seizure of the register-sender, SW, Fig. 5, is operated from the first selector followed bv B which causes digit distributer DDM to take one step to connect up the first register over DD3 ... 6 and operate BA over DD1. Relay BA locks up, grounds a holding wire 16 (wire 15 has also been grounded by B) and removes shunts from relays DSA, DSB in the in-pulsing leads. The digits are transmitted to the registers, as described in Specification 398,812, as combinations of + pulses and strong and weak - pulses, and are directed over DD3 ... 6 by metal rectifiers to the registers, the X and Z relays in each register being marginal to - pulses. The distributer is stepped on after each digit by the relapse of series relays DSA, DSB operated by the pulses. Setting the auxiliary two-motion switch, Figs. 4 and 7, in accordance with the wanted trunk or group. This switch is only required on outgoing trunk calls (1st digit O) and is set in accordance with the 2nd and 3rd digits. Relay TG, Fig. 6, operates when the 1st digit is O, so that when the 3rd digit has been registered (DD in position 5), FS (lower), Fig. 7, operates over DD2, completes a selfinterrupting circuit for VM and connects marking potential over contacts bw ... bz of the 2nd register to vertical bank VB. When the switch reaches the marked level, PA opens the stepping circuit and operates RS which locks quickly over a light armature, further opens the vertical stepping circuit, shunts down PA and connects it to wiper P of the rotary marking bank, all levels of which are connected in multiple to contacts of the 3rd register. The operation of RS also disconnects the marking contacts of the 2nd register and connects up those of the 3rd register, and the relapse of PA completes a self-interrupting circuit for RM. On the 1st rotary step, PA is disconnected from the vertical bank and its shunt ground removed, so that when the rotary marking is found, PA re-operates, opens the driving circuit and operates H over rotary off-normal contacts. Relay H locks up and releases RS. Digit transmission, regular route available without delay. After keying 4 digits, the operator presses the start key which connects up a particular pulse code resulting in the operation of EW, EY, EZ in the 5th register, whereupon, if H has operated (auxiliary switch set), SS pulls up. If a different number of digits were required, another of the registers or relays HW, HX would be used to respond to the start signal. Relay SS disconnects the in-pulsing leads, puts marking ground on wiper CN2 of the control switch and releases FS slowly, whereupon IG connects impulse springs MIS to magnet SM of the sending switch. After S has taken three steps, the loop springs LIS are connected up and impulses transmitted until SZ pulls up over contacts of the first register and bank S4. Relay IG falls back and the sender proceeds by self-interruption of SM to position 20. In the meantime, during the release period of IG, PC has operated over its lower winding and connected its upper inefficient winding in the outgoing loop so that it holds until the loop is momentarily interrupted by the switch-through at the selector, the sender then stepping to normal by further self-interruption of' SM. This provides an inter-digital pause depending on the hunting time of the selector. If PC does not relapse due to non-response to the signal or to absence of a signal, e.g. between the two digits for a final selector, IG pulls up again in position 20 and S is stepped by the impulse springs to 24 and then to normal by self-interruption. If an extended hunting operation is required between the stages, relay D in the loop is operated by battery reversal and holds up the sender. SZ held over S3 then relapses, CN takes a step and succeeding digits are transmitted in similar manner. The third selector is arranged to hunt over the selected level in response to an unbalance signal which is sent in the present case if the 4th keyed digit is 1 resulting in the operation of relay AR. At the end of the 3rd digit with CN in position 3, ground over CN1 applied to the + out wire provides the signal and shunts down PC so that S is stepped rapidly to normal by selfinterruption. When SZ relapses, CN goes to position 4 and then immediately to position 5 owing to the operation of AR, the fourth digit being thereby skipped. With CN in this position, digit transmission is terminated and CO is operated over contacts of the 5th register and disconnects the holding ground from wire 15 whereupon the register relays release and all the switches restore, DD being provided with a second normal position at contacts 13. Digit cancellation. The cancel key applies heavy - to both in-leads and operates all the relays of the register which is connected up. CK (lower) is therefore operated to make a homing circuit for distributer magnet DDM including the upper holding winding of this relay which also releases the registers and opens the in-pulsing wires until DD is normal. Regular route engaged or in delay, alternative routing. The route-busy equipment grounds the contact of wiper R of the two-motion switch and during the release period of FS following the operation of sending start relay SS, GE pulls up, locks, and operates GR which disconnects the marking contacts of the second and third registers and connects up wipers C1, C2 of the two motion switch, the corresponding banks being connected over a translating frame to sending control bank S4 to provide alternative routing digits. This, however, only occurs if the 4th digit is 1 (AR operated), indicating that the 3rd selector is to hunt over the selected level. If this digit other than 1, indicating that the operator desires a particular high grade trunk or hunting in a sub-group, alternative routing would defeat the aim of the operator and, therefore, if AR is not operated, AGE pulls up to prevent it as will appear below. Regular and alternative routes both busy or in delay. If both routes are busy and the regular route not in delay, GE and AGE are both operated by ground on the banks of wipers R and A so that GR remains inert, the alternative route markings are not applied, and the regular route code is transmitted. The third selector stores the call or hunts repeatedly as the case may be. If the regular route is in delay and the alternative route busy or in delay, DR (lower) also operates, holds over its upper winding, disconnects the holding windings of GE, AGE and connects the other windings of these relays to wipers Dl, D2 of the two-motion switch. Tone transformer TR is connected across the in-pulsing leads, and relay IG is disconnected to prevent out-pulsing. Delays of 20, 40 or 60 minutes on a route are indicated by ground placed on D1, D2 or both, whereby GE, AGE or both these relays operate to select a tone lead 10-12 for connection to the primary of the tone transformer. The keying operator informs the calling party of the delay and sends the call ticket to the delay supervisor. Delay working. An ordinary position with a " delay " ke