GB943808A - Improvements in or relating to elicerical signalling systems - Google Patents

Abstract

943,808. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. March 16, 1962 [March 17, 1961], No. 9863/61. Addition to 869,373. Drawing to Specification. Heading H4K. Despite mutilation metering pulses are detected by a scanning circuit which requires that for a pulse to be regarded as genuine the number of scans which find a pulse present should exceed by a given number the number of scans which find the pulse absent and that subsequently the number of absences should exceed by a given number the number of presences. Pulses are continuously reviewed in this way by adding 1 to a five-stage counter each time a scan indicates the pulse present and by subtracting 1 when the pulse is found absent. The counter comprises five consecutive storage areas TA1 to TA5 on a magnetic drum track. The storage areas of the drum track normally register 0 and, when a scan detects the presence of a signal, 1 is written into the first storage area found to hold 0 as the areas are examined from TA1 to TA5. When a scan detects the absence of the signal a 0 is written into the first storage area found to hold a 1 unless this is the last storage area TA5. When presences are in excess of absences sufficient to write 1 in storage area TA5, the signal satisfies the conditions for a metering pulse and it is necessary to effect the addition of 1 to the subscriber's meter store which is also contained on the drum. Before collecting the pulse for such registration, which collection is effected periodically after every so many scans, a sufficient number of absences of the signal must be detected to write 0 in all the storage areas TA1 to TA4. With TA5 the only area holding 1 collection ensues and a sixth storage area TA6 has 1 written in it to provide a guard period by blocking the scanning signal for the duration of one collection cycle.