Patent GB-683847-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04Q3/00
Filed: 1950-09-05
Abstract: 683,847. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., and SCOWCROFT, J. Aug. 14, 1951 [Sept. 5, 1950], No. 21884/50. Class 40 (iv). A switching set terminating at a group centre a junction from a dependent exchange comprises a switch which receives the first digit dialled after seizure of the set and subsequently transfers it to a register when an idle one is found. This switch is thereafter used to select a required group of outgoing junctions, to determine the charge rate for the call, and to time the call for metering purposes. Reception of dial impulses. When a subscriber at a dependent exchange dials a first digit causing the seizure of a junction to the group centre, relays A, B, C, and CA are energized. Switch RH hunts for an idle register which returns battery over wiper RH4 to bring up relay K, followed by KR. Meanwhile the second dialled digit is repeated by relay A to switch MK. At the end of the digit, relay C falls back and applies earth to contact banks MK2, MK3, MK4 in order to transfer the second digit to the seized register. Relay CA releases slowly and completes a circuit via wiper MK8 for the switch MK to step to its 12th contacts. Subsequent dialled digits are received in the register. Establishment of connection and metering. The register translates the first two digits received, i.e. the second and third dialled digits, into four coded digits. On completion of dialling, the register pulses out the first coded digit over wiper RH6, stepping switch MK and bringing up relays CC and CA which fall back at the end of the pulse train. Switch DS then hunts in a group of outgoing junctions marked by wiper MK9, an idle junction returning battery over wiper DS3 to energize relays KA and KAR. The latter relay completes a circuit over wiper MK8 for the switch MK to step to its 25th contacts. Relays CC and CA are re-operated by the second coded digit which steps the switch MK to a position corresponding to the charge rate for the call. At the end of the digit the relapse of relay CC, before the delayed release of relay CA, applies earth to wipers MK5 and MK6, thereby operating a combination of relays MA, MB, MC to determine the number of metering pulses to be transmitted. The register now sends two routing digits and the four uncoded digits of the wanted number over wipers RH8, RH9, DS1, DS2, and thereafter applies earth to wiper RH7. This brings up relay CO which frees the register and releases relays K and KR. When the called subscriber answers, battery reversal brings up relay D, and relay DA is operated by the first S-pulse. The following Z-pulse brings up relay DB, and the predetermined number of metering pulses is sent over the incoming P-wire to the calling subscriber's meter or to a ticketing- machine. Relay DA falls back at the end of the Z-pulse and connects intermittent earth to switch magnet MK which moves its wipers one step every six seconds, relay DB holding over wiper MK1. After twenty steps (two minutes), if the call has not terminated, relay DB releases and completes a circuit over wiper MK8 for switch MK to step to its 25th contacts. The next S-pulse re-operates relay DA, and another metering cycle begins. All registers busy. If switch RH fails to find an idle register so that relays K and KR are not operated, the relapse of relay C at the end of the second dialled digit brings up relay RE which generally applies busy tone to the calling line. If, however, the second dialled digit is 3, busy tone is cut off by the operation of relay G over wiper MK7. The relapse of relay CA causes switch MK to step to its 12th contacts as previously described, and relay C re-operates over wiper MK8 so that the third dialled digit is repeated by relay A to switch MK. Relay C then falls back and is generally followed by relay G to apply busy tone. If, however, the third dialled digit as well as the second is 3, denoting a local call which can be completed without the use of a register, relay G holds over wiper MK9 at its 15th contact and the relapse of relay C causes switch DS to hunt for an idle outlet in a local group marked by wiper MK9 as previously described. The remaining dialled digits are repeated by relay A to subsequent switching stages and the call proceeds substantially in the manner previously described, relay G having selected the number of metering pulses required for a local call. Outgoing junctions or local switches busy. If switch DS fails to find an idle outlet in the marked group, it steps on to its 25th contacts so that relays KA and BT are energized in series to stop the switch and apply busy tone.