870,077. Automatic exchange systems. STANDARD TELEPHONE & CABLES Ltd. (Bell Telephone Manufacturing Co. S.A.). Sept. 12, 1958 [Sept. 13, 1957], No. 28971/57. Class 40 (4). In a system using time division multiplex signalling between registers and mechanical switches, false operation due to contact bounce is avoided by allotting free time positions for " continuity " testing and by delaying connection of the signal received in the register until eight " continuity " pulses have been counted. A cross-bar multi-switch has 100 outlets OT0 to OT99 and 36 inlets W1 to W36. Test wires e from the outlets control a scanner ESC (see also Fig. 4, later) in a common control circuit ESBO. In a cycle of 140 time positions, 100 positions are allotted to the 100 outlets and pulses are generated in the time positions allotted to free outlets. These pulses are sampled in one time position of a cycle of 11, the time position identifying the numerical group to which the switch belongs. The continuity pulses and the pulses identifying the free outlets and the switch group, are transmitted over the c, d wires to a continuity testing circuit CTC in the register REG1 associated with the inlet, the inlets W1, W36 being connected to the channel COM1, COM2. In a cycle of 1540 pulse positions there will be 1 pulse for each free line and 220 " continuity " pulses. The circuit CTC counts eight "continuity " pulses and brings up changeover relay SW to connect a circuit CR which compares the identifying pulses with pulses produced by circuit WPN in the time position of a wanted group. At a coincidence, circuit RD records the time position of the free outlet in the wanted group and generates pulses in that position. Relay RLD energizes slow-to-operate relay SO and connects battery to the b-wire to signal the common control circuit ESBO. At the circuit ESBO a detector DET operates a combination of relays A1-A4, B1-B4, C1- C3 to record the inlet. The detector DET brings up one of the horizontal magnets HM1- HM36 over a relay tree HST and connects transformer TRH to the appropriate a, b wires over relay trees DRA, DRB. When relay SO comes up in BEG1, the battery signal on the b-wire is cut off and pulses identifying the selected free outlet are transmitted over the a, b wires. An electronic recording circuit like the circuit described in Specification 716,784 records the time position of the selected outlet and controls a relay tree VST to bring up the appropriate one of the vertical magnets VM1 to VM100. When the tree VST is set, a monostable trigger circuit MO brings back normally operated relay CCR and cuts off " continuity " pulses from X (see also Fig. 4) long enough for a connection to be completed through the switch. The vertical magnet is de-energized and the connection is held by the horizontal magnet. Scanning circuit ESC, Figs. 3 and 4.-The circuit comprises rectifier gates grouped as shown and controlled by pulses Pa1 to Pa5, Pb1 to Pb7, Pc1 to Pc4 which form cycles of 5, 7 and 4 time positions respectively in a complete cycle of 140 time positions. Pulses Pb7 are used for " continuity " testing and are applied to lead PSL. They may be cut off by contact ccr. If an outlet is busy a relay contact ncl opens to disable the gate corresponding to the outlet. Continuity testing circuit CTC, Fig. 5.-Continuity pulses Pb7 received over the secondary winding SEC of transformer TRS are repeated by a cathode follower CF. Rectifiers MR1, MR2, MR3 constitute an AND gate responding to coincident Pb7 pulses from TRS and from a local source. Triode VT1 produces a negative pulse at each coincidence. The negative pulses are applied to a Miller integrator MI. Eight successive pulses are necessary to raise the anode potential of MI sufficiently to fire a gas tube LV and thereby to open gate GA leading to the circuit CR, Fig. 2, over lead OPL. When the register has completed its operation at the stage concerned, the circuit is interrupted at DIS to extinguish the tube LV. Specifications 682,985, 737,866 and 750,324 also are referred to.