Patent GB-277735-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M3/60
Filed: 1926-06-17
Abstract: 277,735. Siemens Bros. &. Co., Ltd., and Patterson, W. G. June 17, 1926. Semi-automatic exchange systems.-In a system in which operators set up calls and in which seizure of an outgoing line is visually indicated to all the operators, the indicators are under direct control of the release relay of the selector connected to the said line, and the indication persists after the plug has been withdrawn until the selector is at normal under control of the release magnet armature. The indicator lamps are lighted if the switch shaft is manually operated. The system described comprises a first code selector, seized on plugging in, which hunts for a free A digit selector and register-controller, the first routing digit sent out by the controller operating the first code selector, which repeats the remaining digits as usual to complete the connection. Lamp flash signal is sent back and a congestion meter operated should any selector fail to find a free outlet. Lamp flash signal is also sent back in case of incomplete or premature dialling. If the relay set of the selector is removed from its seating, contacts close to light the indicator lamps. Operator's cord circuit. The operator throws key K, Fig. 1, to the left, and ascertains the number required. She then plugs into an idle jack J. When dialling tone is heard, she throws key K to the right and dials the wanted number, after which the key is returned to mid-position. Relay I operates over the a and b wires, lighting lamp SL. When the called subscriber answers, relay D operates to extinguish the lamp. By throwing both keys K, K<1>, a ringing generator is connected to the cord circuit. Operation on plugging in. When an operator plugs into a jack connected to a first code selector, relay G, Fig. 2, operates over the sleeve of the plug and the back-contact m w controlled by the release magnet M M, feeding back earth over wire e to light lamps E L, E L<1>, Fig. 1, associated with the line and multipled. with the jacks, at the operators' positions. Relay L also energizes in a loop over the a and b wires including relays D(2), I. Relays A [battery, A, c2, k3, l2, ka4, h4, earth] and B [battery, B, g4, ka6, l3, earth] now operate. Relay C (1) energizes. The finder switch A<1> - - P<1> is now self-stepped to find a free " A " digit selector, first in a circuit [battery, magnet DM, dm, m6, lf6, c3, kb1, wiper C' and normal contact, c4, m5, b4, earth], and then to earth on bank contacts of busy selectors. Relay KA now energizes from battery at DM to earth at b4, its short-circuit being broken, and relay KB(1) operates and locks up. Relay L remains operated over contacts ka2, ka3. Dialling signals are now sent back from earth over a tone transformer over the wiper B<1> and the a wire, and relay A holds up from the said earth. Impulsing and completion of connections. Impulses are now repeated by relay L over wiper P<1>, and when the register controller sends out the first train of impulses to the relay A over wipers A<1> B<1>, the vertical magnet is operated [battery, VM, C (2), b3, c1, a1, h6, lf5, earth] as usual. The off-normal contacts k1 - - k3 change over, releasing relay winding C(1) at k1, so that relays C, A fall back in turn at the end of the first train. The rotary magnet operates over contact a1 to step the wipers A<2> - - C<2> on to the first link, and to connect relay A to wiper C<2> so that if the link is busy relay A operates over contact rm of the magnet armature, de-energizing magnet RM, which again opens the circuit of relay A, allowing the magnet to step the switch on again in similar manner until a free link is reached. Relay H, short-circuited during hunting, operates in .series with relay A, which does not energize over rm, locks up, releases magnet RM, and forms an impulsing circuit for the next switch [a wire, h2, g2, h4, ka4, loop over wipers A<1>, B<1>, ka5, kb7, b wire]. At the completion of impulse sending, the controller disconnects earth from wiper C<1> so that relay KA releases, connecting the operator's cord to the called line. Relay B holds up over g4, ka6, kb5, wiper D' to earth. When the called subscriber replies, relay D, Fig. 1, operates, extinguishing lamp SL. Release. When both parties clear, the operator withdraws the plug, and relay G releases, so that relay B de-energizes shortly after, releasing relay H, so that the release magnet is energized [battery, MM. m3, b2, k2, c1, a1, h6, lf5, earth]. The lamps EL, EL<1>, meanwhile are held over contacts b1 and mm in turn until the switch is at normal. Relay KB also releases and magnet DM steps the " A " digit finder to normal from earth over wiper D<1>. Busy test and signal from first code selector. If the first code selector cannot find a free link, it steps to 11th contacts, operating s1- - s3, disconnecting relay H from the test wiper at s1 so that it operates. Wiper C<2> is connected to earth to operate a congestion meter and relay LF operates and locks up. Relay KB is released at lf1, removing earth from wiper C' to release the ' A ' digit selector and the register-controller. A busy tone ' and ' lamp flash battery ' interrupter is now connected over relay KB(2) to earth at lf5, and relay KA is released. Busy tone is transmitted over contacts lf4, kb2 to the a wire, battery and earth being connected to the b and a wires respectively from relay L. Lamp flash battery operates relay KB (2), so that battery is connected from winding L(1) to both wires a, b. Relay I at the operator's cord is therefore intermittently energized to flash the lamp SL. Relay B is held over g4, ka6, kb5, and wiper D<1> during lamp flash battery.' Subsequent busy condition is similarly signalled. All register controllers busy. The A ' digit selector rotates to its last contacts and connects earth to wiper E<1> to operate relay LF, sending back the busy signal as above. Operator removes plug during lamp flash signal from subsequent switch. Relay G releases, and relays MHA, MHB operate from battery over the a and b wires in turn, relay B being held at mhb1 until lamp flash battery' is disconnected, when relays MHA, MHB, B release and release of the connection proceeds normally. Incomplete or premature dialling. Relay M is provided to release the connection when faulty conditions arise. Suppose only three digits are dialled, wiper P<1> is disconnected at the controller after an interval, releasing relay B. If the first code selector has found a free link, relav H will be operated. Relay M operates and locks up to wire e, short-circuiting relay H which releases, and releasing relay KA. Relay B thereon reoperates, and relay KB releases. Relay A is released at h5, and the selector is rotated to its last contacts as before to give the busy signal. Selector manually released. If the release magnet armature is depressed by hand, relay G is released, the contact mm holding the lamps EL, EL<1>, Selector manually operated. If the selector shaft is lifted by hand, contact k2 operates the magnet MM, so that the engaged lamps are lighted. Removal of selector relay set. The relay set when in position separates knife-edge contacts ve, Fig. 2; when the set is removed, the contacts earth the wire e to light the engaged lamps.