Patent GB-741305-A (GB)
Title: Improvements relating to automatic telephone systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/42
Filed: 1952-12-29
Abstract: 741,305. Automatic exchange systems. SIEMENS BROS., & CO., Ltd. Dec. 11, 1953 [Dec. 29, 1952], No. 32893/52. Class 40 (4). A uniselector constituting a group or final selector is controlled by means of revertive impulses fed to an impulse counting chain of electronic devices. The drawings show a first group selector, Fig. 1, a second group selector, Fig. 3, a final selector, Fig. 4, a subscriber's line circuit, Fig. 5, and a register-controller, Figs. 2a-2d. The selectors are high-speed motordriven uniselectors, each having an individual electric motor controlled by a latch magnet. Each first group selector is associated with a line-finder (not shown) to form a finder-selector link. Arrangements (not shown) for homing the second group selectors and final selectors are similar to those described in Specification 726,969. When a call is initiated, a line-finder common control circuit (not shown) connects earth over a start wire WS, Fig. 2a, to a group of register-controllers. In each free registercontroller a start relay SA is operated to energize the latch magnet DLM of a coupling switch having wipers SD1-11 which now proceeds to hunt for the particular finder-selector link which is coupled to the line-finder common control circuit at this time. The relevant link is marked by negative battery on a wire WFD (Fig. 1) connected to a contact of bank SD1, and the coupling switch is stopped on the required outlet by the operation of a relay TAA which also marks the outlet busy and causes the line-finder common control circuit to remove the earth from wire WS, relay SA being held in consequence of the operation of a relay HD. An earth connection in the line-finder common control circuit is extended over a wire WFC and wiper SD2 to a relay TG which operates, followed by. relays AD and B (Fig. 2b) and a line relay A in the first group selector (Fig. - 1). This completes a circuit (not shown) for driving the associated line-finder to the calling line. Earth is then removed from wire WFC, releasing relay TG and leaving relay AD holding over the calling loop. The calling line is marked busy to final selectors by tone from wire WBT, and dialling tone is sent to the calling subscriber from wire WDS by transformer action of relay AD. Reception of dial impulses and setting of group selectors. Relay AD repeats the thousands digit impulse train over a transformer TRR to a first impulse-counting chain comprising ten cold-cathode gas-filled valves VFA, ... VFZ, which form a closed chain and fire in turn in response to the incoming impulses in known manner, the firing of each valve extinguishing the preceding valve in the chain. At the end of the digit, relay AD remains operated and a condenser QR is charged until a wire WD reaches a potential which causes the firing of a first digit-counting valve VDW which was biased against firing before the first impulsecounting chain was operated. A first digitcounting relay DW is energized and connects the input wire WQQ of an " impulse converter," comprising two hot-cathode gas-filled valves VP and VQ, over wiper SD9 to a first control wiper CA of the first group selector. Those bank contacts of wiper CA which are associated with outlets to second group selectors are connected over their latch magnets, such as LMB, to negative battery. Each group of such contacts, except the first, is preceded by a " pilot " contact which is connected to positive battery. The operation of the first digit-counting relay DW also completes a circuit over wiper SD8 for thelatch magnet LMA of the first group selector, which moves off-normal. Each time wiper GA encounters a " pilot contact, the " impulse converter " produces an impulse on its output wire WPP which operates the first impulsecounting chain. When this registers a total of 10, indicating that the first group selector has reached the required group, a valve VF is fired. This brings up a relay TW which makes the circuit of the latch magnet LMA dependent upon a relay T which at this time is connected to test over wiper SD11 and the private wiper PA of the first group selector for negative battery connected over a low-resistance in a free second group selector. If no such free outlet is found in the selected group, wiper CA reaches the next " pilot " contact and the resulting impulse fires a valve VH, bringing up a relay TD which stops the first group selector and energizes a relay BP followed by relays DZ and TT and by a relay HA in the first group selector (Fig. 1). This initiates release of the register-controller by breaking the calling loop circuit for relay AD, and the calling party receives busy tone from wire WBS by transformer action of relay A. If, however, a free second group selector is found, the operation of relay T stops the first group selector and brings up relay TT. The setting of the seized second group selector is now controlled in a similar manner to that of the first in response to the registration of the hundreds digit in a second impulse-counting chain, comprising valves VGA, ... , VGZ, followed by the operation of a second digitcounting valve VDX and relay DX. Valve VF is extinguished and relays TW and TT are released. When the second impulse-counting chain registers a total of 10, a valve VG is fired and a relay TX is energized. Relay T, which is now connected to test for positive battery, stops the second group selector on an outlet to a free final selector. Setting of final selector. The tens digit is registered in the first impulse-counting chain, bringing about the firing of a third digit-counting valve VDY and the energization of a relay DY, and the units digit is registered in the second impulse-counting chain. The consequent firing of a fourth digit-counting valve VDZ and operation of relay DZ extinguishes valve VG, releases relay TX, and energizes relay T. The input of the first impulse-counting chain is now connected to the cathode of the tenth valve VGZ of the second impulse-counting chain, a circuit for the final selector latch magnet LMC is completed over wiper SD10, and the input wire WQQ of the " impulse converter " is connected over wiper SD11 and the private wipers of the first and second group selectors to the private wiper PC of the final selector. The bank contacts of wiper PC are connected alternately to positive and negative battery in their associated line circuits, and the " impulse converter " is now connected so as to produce an impulse at each reversal of potential on WQQ. Thus the second impulse-counting chain is stepped on together with the final selector, and each time it registers a total of 10 an impulse is sent to operate the first impulsecounting chain. When the first chain registers a total of 10, valve VF is fired and a relay TY is operated, and the next time the second chain registers a total of 10 valve VG fires and relay TX is energized, stopping the final selector on the wanted line and bringing up relay TT which completes a tone-detecting circuit over wiper SD11 and also completes circuits over wipers S3 and SD7 for the operation of relays HA (slowoperating) and D respectively in the first group selector (Fig. 1). If the wanted line is busy, the tone-detecting circuit energizes a relay TB which prevents the operation of relay D, and the calling party receives busy tone from wire WBS. If, however, the wanted line is free, the operation of relay D applies ringing tone from wire WRS, ringing current from wire WRC, and busying tone from wire WBT. Relay HA disconnects the calling loop from relay AD, initiating release of the register-controller. Ring-trip relay F operates and switches through when the called subscriber replies. A group selector, Figs. 6a-6c (not. shown), for dealing with calls incoming over a junction from another exchange, combines features of the first group selector, Fig. 1, and the registercontroller, Figs. 2a-2d. Each of the impulsecounting chains consists of five (instead of ten) counting valves with an additional discriminating valve and relay which operate when the digit to be registered exceeds 5. The discriminating relays may be used to control wiper-switching operations at subsequent selectors, Figs. 8 and 9 (not shown), each provided with two sets of wipers. In a further modification, Fig. 10 (not shown), the speaking wires are used for reverting impulses from the selectors to the impulsecounting chains and for energizing the latch magnets.