Patent GB-707493-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: FORSHAW GEOFFREY
IPC: H04M15/10
Filed: 1952-03-08
Abstract: 707,493. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Feb. 25, 1953 [March 8, 1952], No. 6085/52. Class 40 (4) Periods of time for metering purposes are measured by a group of relays in a connecting circuit such as an outgoing relay set, the relays responding in turn from a random starting point to timed pulses applied successively over corresponding conductors from common equipment. The common equipment includes a group of relays operated cyclically from a source of timed pulses. When a preceding group selector GS finds the outgoing relay set ORS idle, it operates BA while ORS returns battery over lead S to signal the register to send all further digits as trains of impulses. BA operates B to energize HA and disconnect lead T from idle-marking battery. HA connects the group selector over wires + and - to junction JN. When the last impulse train has been sent over this path, the register applies strong or weak battery to lead S to operate MCH and MCD or MCH alone according to whether the metering interval is to be 1¢ or 3 minutes. 3-minute metering interval.-Assuming first that only MCH operates, I operates across the loop to replace the loop from the register. The register now signals the call fee by light or heavy earth conditions to energize 1, 2 or 3 of relays MW, MX, MY, MZ which connect the appropriate meter pulse lead MP1-MP6 to contact MA3. The register now releases MCH to operate SW, which causes A to pull up to a temporary loop from the register. SW also releases BA and connects holding earth to the P lead. When the called party answers, reversal of potential energizes D which operates DD slowly to return reversed potentials to the register. DD also energizes PP and start relay STP in the common pulse relay set PRS if no other ORS has not already done so. PP operates ST so that the next " S " pulse on lead SP energizes MA which locks up. The next "Z" pulse on lead ZP energizes MB. At the end of the "Z" pulse MA falls back. The appropriate number of meter pulses is now applied from MP to J and returned to the register over the P lead. Meanwhile the operation of STP causes the application of a pulse every 15 secs. from lead CPL to energize DR and drive a counting chain CA-OF in the common pulse relay set PRS. F follows DR and energizes pulse distribution relays IDA- 6DA in succession. According to the condition of PRS when ORS makes connection to it, one of the relays 1DA-6DA at the next CPL pulse energizes one of relays AW-AZ, BW or BX, say AY, which locks up over dd4. At 15-second intervals the other relays in the set operate and hold. When all are operated, PP relapses slowly so that the next operation of F energizes CL which releases all the relays AWBX except that just energized by the corresponding relay IDA-6DA. F also operates ND. Release of F restores CL to operate TMF and reoperate PP. If conversation continues until PP releases again, time warning tone from lead PPT is connected to relay A and made audible to both parties. If the connection is not cleared the next operation of F defines the start of the next 3-minute period. and operates CL to shunt and release MB which releases TMF slowly. CL restores at the next release of F to reoperate PP so disconnecting time warning tone. "S" and "Z" pulses then control MA and MB to return metering pulses as before.  1¢-minute metering interval.-If both MCH and MCD operate, the process functions as above described except that MCD releases MB after 1¢ minutes while holding ND locked. Metering pulses are thus sent to the register each 1¢ minutes but time warning tone is still supplied at 3-minute intervals.