Patent GB-1177376-A (GB)
Title: Improvements in or relating to Electric Signal Line Monitoring Arrangements
IPC: H04Q3/00
Filed: 1967-03-30
Abstract: 1,177,376. Automatic exchange systems; magnetic and dielectric storage arrangements. SIEMENS A.G. 30 March, 1967 [31 March, 1966], No. 14523/67. Headings H3B and H4K. For the purpose of supervising line current in general, or of detecting metering pulses on a line in particular, the line current is applied to a ferro-magnetic or ferro-electric device to bias that device into saturation, the device being interrogated by pulses of increasing amplitude or alternating polarity to determine whether the line current is zero, has a first value giving one bias, or has a second value giving a larger bias. The interrogation may be effected by a pulse pair; the second pulse of each pair being of greater amplitude than the first, if both pulses have the same polarity, but both pulses having the same amplitude if they are of opposite polarities. The interrogation may be effected by a single pulse with a staircase waveform, or by a single pulse with a sawtooth waveform. As shown in Fig. 1 where pulse pairs a, b are used for interrogation, a number of lines SL11- SLxy are supervised by saturable devices A11- Axy in. a matrix AM. A scanner TVZ reads out the rows of the matrix in sequence, outputs due to the first pulse a being registered on a buffer store E1 and outputs due to the second pulse b being registered in a buffer store E2. A scanner TVS reads out the buffer stores E1 and E2 serially and together so that the results of the a and b interrogations of each saturable device are presented simultaneously as outputs a1, a2. A circuit AW interprets the outputs a<SP>1</SP>, a<SP>2</SP> to provide outputs Z1, Z2, indicative of line condition. Fig. 3 shows the outputs a<SP>1</SP>,  a <SP>2</SP>, Z1 Z2, obtained from a saturable core which exhibits hysteresis. At I is shown the result of interrogation, with pulses a and b of increasing amplitudes but like polarity; (a) for no line current, the first pulse a finding the core at ,- Br or + Br; (b) for a bias sl; or (c) a bias s2. At II is shown the result of interrogation with pulses a and b of the same amplitude but different polarity. It is to be noted that the space between the pulses of an interrogation pulse pair is sufficient to enable the core to regain its static condition under bias before the second pulse of the pair is applied. Providing the core has pronounced saturation it need not exhibit hysteresis, line current bias holding one interrogation pulse or both such pulses of a pair below the knee of the magnetization curve (see Fig. 2, not shown). Instead of interrogation with pulse pairs the pulses with staircase or sawtooth waveform of Fig. 4 may be used, it being determined when, during the course of an interrogation pulse, an output as appears. With the staircase waveform the leading edge of each step may be differentiated to mark off the three phases of an interrogation. With a sawtooth waveform the phases have to be marked off by a separate generator as could be provided by three saturable cores restored from three graduated conditions of bias by the sawtooth waveform (see Fig. 7, not shown), such arrangement being independent of supply voltage fluctuations. Since line condition is determined as soon as output as appears, interrogation may be shortened by cutting off the interrogation pulse as soon as an output occurs. A matrix of saturable cores suitable for interrogation in this manner has a common blocking bias winding (Fig. 5, not shown), a common interrogation winding and a common output winding. To access a particular core half-strength unblocking currents are applied to a row and a column winding so as to leave the core at the cross point subject only to bias by current in the line it supervises. As soon as an output appears on the common output winding the interrogation pulse generator is cut. off and a fresh interrogation sequence started.