Patent GB-273786-A (GB)
Title: Improvements in telephone systems
IPC: H04Q1/22
Filed: 1926-03-31
Abstract: 273,786. Standard Telephones & Cables, Ltd., and Chanter, A. J. March 31, 1926. Automatic exchange systems in which the progress of calls in a number of offices can be observed at a central office have the following features : (1) Dialled impulses are repeated by a relay D, Fig. 2, bridged across the line under observation. This relay pulls up at each interruption of the loop and controls a relay I which at each energization cuts a resistance NR2 into the circuit of relay D to make it follow the dial accurately. (2) A speech current amplifier connected to VA is inserted between the line and the observation trunk. (3) The iunctions from the various offices are provided with two-step relays V for associating them with the observation equipment and which are unable to operate fully it two calls arrive simultaneously. Each line SL to be observed is provided with a relay L connected up by means of a shoe at the main irame and with a pair of relays A, B connected up at the intermediateframe. A single junction circuit, Fig. 2, is provided for the office. Connecting call to observation desk. On an outgoing call, relay L (energized over the calling loop) and relay A (energized by ground on the private wire P) connect the line and private wires to the junction equipment and energize the relays P, Q, therein. Relay B cannot pull up in series with relay A. Relay P holds relay A in series with relay Y which energizes relay C and relays Y1, Y2 &c. which as at 5, Fig. 1, short circuit the upper windings of all the relays A to prevent the association of any other line withthe junction. If one calls, its relay B locks it away from the junction until the end of the call. Relay F, energized by relay Q energizes relay G and completes a circuit for relay U at theother end of the junction in series with relay R which is unable to pull up in this circuit. Relay G lights a calling lamp and completes a circuit over a contact of relay X (which is energized while the position is attended) for relay V which pulls up its armature 13 and then, provided there is no other relay V in the same condition, all its armatures locking itself up, energizing relay K to mark the position busy lighting a further lamp, and switching the junction through to the telephone set and the relays H, K, cutting oft relay U. Relay H lights a lamp and energizes relay SB. Relay R. Fig. 2. is now able to pull up and holds up relay P before it has time to fall back in response to the energization of relay ( . On an incoming call, relays A, B, P, Y, C pull up, but not relays L, Q. Relay U is energized in series with relay S which does not pull up, until relay V connects up the relays H, K, in place of relay U, whereupon it energizes relays M, N. Observation signals. Relay D follows the dial as described in the opening paragraph and relay I repeats the digits to relay H which repeats them to a call indicator on CI. Relay T disconnects the lower junction wire during impulsing and at the end of each digit connects up a valve amplifier VA and the observation attendant hears any busy or ring-back tone. When the call is metered, booster battery on the c-wire energizes relay M which locks itself by shortcircuiting resistance NR1 and energizes relays S, K in series over the wire J+. Relay K gives a distinctive signal and relay S makes a new 'holding circuit for relay P. Relay M also energizes relay N and releases relay F which releases relay G. Between the energization of relay N and the relapse of relay G the repeating coils are disconnected and a tone signal is given from TL to the observation position. On the relapse of relay G the observation attendant can hear the conversation. When the subscriber hangs up, relays L, Q, B, M, H, and R fall back. The remaining relays hold up however until the attendant throws the key RLSE. whereupon relay RL unlocks relay V and cuts the junction to release relay S. After an interval, relay P releases relays A, Y and the remaining relays fall back. When an observed line replies to an incoming call, relay L energizes relay Q and relays R, H pull up in series giving a lamp signal.