Patent GB-693157-A (GB)
Title: Improvements in or relating to magnetic storage devices
IPC: H04Q3/42
Filed: 1951-12-11
Abstract: 693,157. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. Dec. 11, 1951 [Dec. 16, 1950], No. 28979/51. Class 40 (iv). The system described in Specification 684,079 is simplified by combining the pick-up and recording heads, so that early in the passage of an elemental area under the head, the signal recorded therein is read and, subject to certain conditions, the signal is reversed by the recording head before the elemental area passes on. The invention is applied to a call annunciator, a magnetic drum 104 being employed in common by 1000 subscribers. Pick-up coils 50, 51 generate timing and synchronizing pulses corresponding to the subscribers' lines and the zero position of the drum, respectively. A scanning electrode 25, surrounded by a screening shield 26, rotates with the drum past line electrodes 31, 32 separated by shielding segments 29. Assume that subscriber's line 14 is idle and that the related segmental areas in channels Al, A2 and B1 are magnetized in the one direction, i.e. that they carry an O signal. Then closure of the subscriber's loop reduces the voltage on segment 32 so that amplifier 20 produces a high voltage on lead SX and a low voltage on lead SO. At this time an O signal is being read by the pickup coil of head 111 to apply a high voltage to lead A10. The left-hand part of amplifier 121 responds to these high voltages on leads SX and A10 and the low voltage from timing amplifier 60 to cause the recording coil of the head 111 to reverse the magnetization in the elemental area, i.e. to record an X signal. If the loop is still closed when the segment is next scanned, the X signal produces a low voltage on lead A10 to inhibit re-recording of X. When the line 14 is opened, the voltages on leads SO, SX become high and low respectively. At the same time X is read by coil 111 so that the resulting low voltage on lead A10, after passing through phase inverter 141, produces a high voltage on lead A1X. Gate circuit 201 responds to the high voltages on leads A1X and SO to send a high voltage to the lower lefthand input of amplifier 122, which responds to the O signal read by pick-up 112 and the timing signal from amplifier 60 to cause recording coil 112 to record an X signal. The gate circuit also signals timing circuit 270, which operates in a manner described later. While the line remains open the record in channels A1, A2, B1 remains X, X, O. When the loop releases, high voltage appears on leads SX, A1X, A2X to energize gate circuit 202 which combines with the timing pulse from amplifier 60 and the O reading from pick-up 113 to record X in channel B1. Gate 202 also energizes the right-hand part of amplifier 122 to record O in channel A2. The record X, O, X remains in channels A1, A2, B1 as long as the loop remains closed. This is a calling condition which is recognized by the register and display apparatus, shown in the right-hand bottom corner of Fig. 1, which responds to the increased voltage on lead B1X in the manner described in Specification 684,079 to indicate the identity of the calling line. Accidental impulses. If the line is closed accidentally and then re-opened, timing circuit 270 is energized as described in Specification 684,079 and after a predetermined time applies high voltage to the upper right-hand inputs of amplifiers 121-123 to record O in the appropriate elemental areas.