Patent GB-892012-A (GB)
Title: Improvements in supervisory arrangements for carrier current signalling systems
Inventor: SLOW JOHN LEONARD
IPC: H04J1/14
Filed: 1958-11-13
Abstract: 892,012. Carrier transmission. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. Nov. 9, 1959 [Nov. 13, 1958], No. 36568/58. Class 40 (4). Duplicate carrier supplies are continuously maintained in operative condition, changeover from the effective supply to the standby supply taking place automatically if the effective supply develops a fault; if both sets of equipment become faulty, supply is given by the equipment having the less serious fault if the other equipment is completely disabled or by the equipment operative when the second fault develops if the faults on the two equipments are similar. As shown, the A equipment includes six carrier sources CSA1-CSA6 and the B equipment has six similar sources CSB1-CSB6, The sources are connected through AND gates to transistors TR1 and TR3. When the supplies are working normally, transistors TR1 and TR3 are conductive and relays MA, MB, ALA and ALB are operated. Differential relay Y is energized over its left-hand winding and therefore operates, but differential relays P, X and Q are energized over both windings and do not operate. Thus switching relays R1A, R2A, &c., are operated but not relays R1B, R2B, &c., so that the A carrier supplies are connected to their respective outputs CS1, CS2, &c., Fig. 3, while suitable terminations are connected across the B carrier supplies. The A equipment is therefore supplying the system. Fault on one carrier frequency generator in A equipment.-Transistor TR1 is cut off, so that relay MA releases, followed by relay ALA which lights an alarm lamp LP5 and initiates an alarm over extension loops 12, 13 and 14, 15. Differential relays P and X operate, releasing differential relay Y. Thus switching relays R1B, R2B, &c. are operated in place of relays R1A, R2A, &c. and the B supply (assumed to be in order) replaces the defective A supply. To cut off the alarm the operator momentarily operates key KK to bring up relay COA which opens the alarm extension loops 12, 13 and 14, 15. When the fault has been dealt with, normal conditions may be restored by operating reset key KR which causes transistor TR1 to conduct, operating relay MA. Restoration of key KR brings up relay ALA and releases differential relay P. The system will continue to be supplied by the B equipment as long as it is in order, but a change back to the A supply may be effected if desired by closing manuallyoperated contacts SWA, thereby releasing differential relay X to operate differential relay Y and effect the changeover to the A equipment. Failure of direct current supply to A equipment.-This releases all the A switching relays and relays MA, ALA and Y. Relays P and X are now operated from the B supply, re-operating relay Y and bringing up the switching relays in the B equipment which thus takes over the carrier supply. Failure of one carrier supply in B equipment following changeover from faulty A equipment.- In either of the situations described in the preceding two paragraphs, relays P and X are operated so that the release of relays MB and ALB will not affect the switching relays and the B equipment will continue to supply the system with such carrier supplies as are available. Failure of direct current supply to B equipment following failure of one carrier supply in A equipment.-Relays MB and ALB and the B switching relays are released, while relays Q and Y are operated from the A supply so that the A switching relays are operated in spite of the released condition of relays MA and ALA and transfer takes place back to the A equipment although this is partly faulty. B equipment becomes faulty while A equipment is carrying the load.-Relays MB and ALB are released, giving the usual alarms and bringing up relay Q which maintains the circuit for the A switching relays even if the A equipment subsequently suffers a carrier failure. Removal of equipment from rack.-This removes a link from one of two series circuits SC1 and SC2 and is signalled as a fault. Supervisory lamps.-LP1 is lit when the A equipment is in use and LP2 when it is faulty, LP4 and LP3 respectively giving corresponding indications for the B equipment. Lamp LP5 lights when either equipment is faulty. The arrangements for the B equipment are similar to those for the A equipment, and neither equipment has precedence over the other. Dry-reed relays are used throughout.