GB305618A - Improvements in or relating to telephone systems - Google Patents

Abstract

305,618. Automatic Telephone Manufacturing Co., Ltd., and Passmore, W. O. Nov. 8, 1927. Automatic exchange systems.-In a small system of ony ten lines, a Strowger-type switch hunts vertically for the calling line and is then stepped horizontally by impulses into engagement with the wanted line. The switch has two sets of wipers, the banks of one set which engages the calling line being multipled horizontally so that during the numerical operation contact is maintained with the calling line, whilst the banks of the other set which engages the wanted line are multipled vertically. Busy tone, dialling tone, and cabling howler currents which operate the wanted party's receiver are generated by relay interrupting arrangements, Fig. 3, the calling and busy tones being periodically interrupted by a series of relays I<1> - - I<3>. Hunting. When a subscriber, Fig. 1, removes the receiver, start relay S energizes over the loop, and selectable potential over earthed armature 13 and the loop is placed upon a terminal in the bank of a special vertical wiper 21. Relay S energizes relay D which is slow-to-release owing to a short-circuit at armature 38 around its upper winding. Relay D energizes the vertical magnet VM which lifts the wipers and deenergizes relay D. Intermittent operation of relay D and magnet VM thus continues until the marked level is reached when relay FG operates, disconnects the vertical magnet, and connects up the rotary magnet RM which rotates the wipers one step, releasing FG. Relay CO operates over wiper 17, releasing relay S. Numerical operation. Relay A now operates over the calling loop and energizes BA, B, the last-named extending the start circuit over lead 77 to the next switch. At the same time dialling tone from lead 75 is connected up. Since the switch has already taken one rotary step, the first impulse is absorbed by two-step relay PA which is operated over contacts 23, 25, 58, and transfers the impulsing circuit to the rotary magnet at armature 37. During the rotary movement relay E connects relay FG to the test wiper 60 and if the wanted line is busy, FG locks up on the release of E and connects busy-tone lead 76 to the a-lead. If the wanted line is idle, switching relay H energizes over wiper 60 and connects up ringing lead 74 which supplies a ' howler ' tone to the called party's receiver. When the called party replies, relay F operates and relay D acts as a feed on the called side. Dialling-tone, busy-tone, and ringing-current arrangements, Fig. 3. When relay B operates it connects earth over lead 78 to relay BR, V which respectivety generate busy-tone, and dialling and calling current. Earth on lead 78 also energizes relay I<3> which locks up and energizes P, this in turn locking up and energizing I<1>. The three relays are then in turn short-circuited and the whole cycle is repeated, relays I<2> and I<3> at contacts 72, 73 effecting periodic interruptions in the ringing and busy-tone leads, respectively.