Patent GB-861827-A (GB)
Title: Improvements in or relating to selector switches for use in automatic telephone switching systems or the like
Inventor: BEASLEY HAROLD ARTHUR
IPC: H04M3/523
Filed: 1958-11-11
Abstract: 861,827. Automatic exchange systems. AUTOMATIC TELEPHONES & ELECTRIC CO. Ltd. Oct. 29, 1959 [Nov. 11, 1958], No. 36138/58. Class 40 (4). A two-motion selector of the vertical and rotary type is provided with contacts which are mechanically operable when the wipers are set to a prescribed level to enable automatic hunting to proceed over all the outlets of the level, and is arranged where access is obtained to a single group of trunks over another level and the wipers are set in response to two digits on to the first outlet, which gives access to callstorage equipment, to be controlled by the callstorage equipment in such a manner that if one or more of the trunks of the group is or are idle automatic hunting over the group takes place, while if all the trunks are busy the wipers remain on the first outlet connected to the callstorage equipment until a trunk becomes available. The selector also has a " camp-on-busy " facility when it is set by two digits to an individual outlet. Seizure of selector.-When the selector is idle, a potential of- 100 volts is applied to the P- wire of the incoming conductors IC. When a preceding selector finds this, it stops hunting and applies a loop to the speech (- and +) wires. Relay A operates, followed by relays B, CD, and CA, so that busying earth is connected to the incoming P-wire and a path is prepared to the vertical magnet VM. Selector set by two digits to individual outlet.- The first digit is repeated by relay A to vertical magnet VM which raises the wipers to the corresponding level. Vertical off-normal contacts N1-N5 are operated, so that, when relay A remains energized at the end of the first digit, relay CD is shunted out, releasing relay CA which brings up relay E. This prepares a circuit for the rotary magnet RM and re-operates relays CD and CA. In response to the second digit, rotary magnet RM rotates the wipers to the wanted outlet, operating rotary off-normal contacts NR1-NR5 so that relays CD and CA fall back again at the end of the digit, thereby completing a test circuit for relay H over the P-wiper. Relay E is disconnected, but is slow to release. If the outlet is free, the P-wiper encounters a potential of - 100 volts and relay H operates, switching through the speech wires to seize the succeeding equipment which thereupon returns earth over the P-wiper to hold relay H on its left-hand winding. Relay H also prevents the operation of relay PB, brings up relay HF to switch through the N -, N + and S conductors, and releases relay A which causes the re-operation of relays CD and CA, reconnecting relay E before it can release. However, relay B falls back with a delay following the release of A, finally releasing relay E together with relays CD and CA and also switching through the P-wire. An outgoing magneto trunk line circuit has now been seized. Camping.-If the wanted outlet is busy, the P-wiper encounters earth and relay H is not operated. Thus when relay CA releases, relay PB is energized over wiper DS, followed by relay PC, and relay E releases after a delay. Relay G then operates, sending " flicker number unobtainable " tone from lead FNUT via relay A to the calling operator and reoperating relay E to restore the test circuit for relay H over the P-wiper. The selector remains set at the wanted outlet. When it becomes free, earth on the P-wiper is replaced by - 100 volts. Relays H and HF operate and A, B and E release as described above. As relay PC is energized, the potentials on the speech wires are reversed to give a supervisory condition at the calling operator's position. Relays G and PB being operated, the energization of relay HF connects flicker earth from lead FE to the incoming S conductor, flashing a lamp at the calling operator's position. The operator throws a key to connect resistance battery to the S conductor, bringing up relay SK. Relays PB, PC, G and SK then release, and the selector is switched through as described above. Delay working. A supervisor puts a trunk in delay working by means of a key which extends earth by way of call-storage equipment CS to the relevant GB bank contact. A call to such a trunk proceeds like one to an ordinary busy outlet, described above, until the operation of relay G causes relay DL to operate to the earth on wiper GB. This returns " number unobtainable " tone from lead NUT via relay A and connects intermittent earth from lead IE to the incoming S conductor, flashing the calling operator's lamp at a characteristic rate to indicate delay working. The operator clears down the call and the switch goes home. Spare outlets.-If an operator dials a spare outlet, marked by resistance earth on the GB bank, the call proceeds as for a busy outlet until the operation of relay G causes relay NU to operate to this resistance earth, returning " number unobtainable " tone from lead NUT. Operation as group selector.-If the first digit sets the selector to a level at which the normal post springs NP1, NP2 operate, the relapse of relays CD and CA at the end of the digit brings up relay RH which re-operates CD and CA and completes a circuit for rotary magnet RM which, by self-interruption at RMC2, steps the wipers over the selected level. Relay H tests over the P-wiper as before. If all outlets of the level are busy, the selector reaches the eleventh step where contacts S1-S5 operate, returning busy tone from lead BT and connecting earth to the P-wiper. (This may be used to operate an overflow meter.) Relay H operates over contacts S5 and locks over contacts S2, bringing up relay HF and releasing relays CD and CA. Relay A holds over the speech wipers in the eleventh position. Freeing selector from faulty outlet.-If, during hunting, the selector connects to an idle outlet but, due to a fault, one of the outgoing speech wires is disconnected, the succeeding equipment is not seized and no busying earth is returned over the P-wiper to hold relay H on its left-hand winding. Instead, the P-wiper remains connected to the idle marking potential of - 100 volts, which produces a reverse flux in the lefthand winding of relay H so that the relay releases, followed by relay HF Relays A, CD and CA are re-energized and hunting is resumed. Call-storage.-The selector is enabled to hunt over a group of outlets occupying the whole of a level, the wipers being set by two digits to the first contact of the level, which gives access to call storage equipment. Each of terminals T1-T10 is strapped to the first contact of the corresponding level of the DS bank, so that a different combination of relays DW, DX, DY and DZ is brought into use according to the level to which the wipers are raised. Assuming that the selector is set to level 1, where all outlets are busy and call-storage is in operation, the relapse of relays CD and CA at the end of the second digit causes the operation of relay DW over terminal T1 and also initiates the slow operation of relay RN and the delayed release of relay E. The operation of relay RN connects the incoming S conductor to the S wiper by way of relay SK and causes relays GP and G to operate to earth returned over the GB wiper from the call-storage equipment. Relay GP connects resistance battery over the N + wiper to the call-storage equipment to enable it to determine the number of calls in storage and also extends to the calling operator the " flicker number unobtainable " tone returned from the call-storage equipment over the N-wiper, indicating that the call has reached storage. When relay E finally completes its release, relays CD and CA re-operate. The selector remains at the call-storage position. When an outlet in the level becomes idle, the call-storage equipment returns flicker earth over the S wiper to the calling operator's position, where a relay responds and lights a lamp. The operator then throws a key, causing relay SK to operate to the flicker earth. Relays GP and G fall back, bringing up relay RH to complete a self-interrupting circuit for rotary magnet RM, so that hunting is resumed. If several selectors are hunting for a single idle outlet in the same level, only one is enabled to switch to it, the others stepping on to the end of the level, restoring to normal and then automatically reentering the call-storage position. Thus, in the. present example, the opening of vertical offnormal contacts N2 when the selector returns to normal brings about the release of relay RN, followed by relay RH. This completes a selfinterrupting circuit for vertical magnet VM, which raises the wipers. At level 1, since relay DW is already operated, vertical auxiliary wiper AW completes a circuit for high-speed relay VT, which breaks the vertical magnet circuit and prepares a circuit for rotary magnet RM. The operation of vertical off-normal contacts N1-N5 causes the slow release of relays CD and CA, completing a circuit for rotary magnet RM and initiating the delayed operation of relay RN which releases relay VT and breaks the rotary magnet circuit, so that the selector takes one rotary step to the call-storage position, where the operation is as before. Call-storage position in delay working.-In this case the P-wiper will encounter earth on its first bank contact, so that the operation of relay GP brings up relay DL. " Number unobtainable " tone is returned from the call-storage equipment over wiper N - and relay A to the calling operator, and intermittent earth from lead IE is connected to the incoming S conductor to give a visible indication at the operator's position.