Patent GB-1380715-A (GB)
Title: Pulse train supply systems
IPC: G06F11/16
Filed: 1971-11-18
Abstract: 1380715 Automatic exchange system; pulse Circuits SIEMENS AG 18 Nov 1971 [4 Dec 1970] 53495/71 Headings H3T and H4K Two similar multi-phase pulse train generators are coupled to respective sides of a bi-stable circuit to indicate to a pulse receiving station which one is operating and which is standby so that the operating generator is selected at the receiving station. Fig. 1 shows two similar pulse generators TEI, TEII each comprising a twophase pulse oscillator TG and connected through transmission lines at K to a receiving station comprising two similar channels, one for each phase. The output of the pulse generators is monitored by devices TU1, TUII which control respective sides BKI, BKII of a hi-stable circuit, the output of which indicates which pulse generator is to be used and which is stand-by. This output is passed through respective signal generators SGI, SGII and through the transmission lines to respective input AND gates in both receiving units TVI, TVII, which gates also receive a respective one of the phases from the pulse generators. The outputs of these gates are applied through an OR element to delay circuits VZ and amplifiers VS to respective logic circuits TGE. When a monitor TU detects failure of either phase of a pulse generator or when any other pulse defect is detected the bi-stable circuit changes over and, via a transmission unit SG, causes the AND gate in both phases of the receiving station to be blocked. At the offset of the next pulse of the standby unit the other signal transmission unit SG issues a signal which enables the gate corresponding to the other pulse generator. By initiating operation at the trailing edge of the pulse sufficient time is allowed for the next pulse to be effective. The receiving station also includes a monitor TUIII and this is disabled, during changeover, by a comparator VG. The delay elements at the receiving station enable equalization for the delays in the transmission line. Fig. 2 shows the bi-stable and signal transmission units at the transmission station. The bi-stable circuit comprises gating units G1, G2 which are cross-coupled and which receive the output of the monitoring elements TUI, TUII. The transmission units SG are cross-connected and are such that when a fault occurs in generator TEI the monitor TUI, by a direct connection, switches over unit SGI and also changes over the bi-stable circuit GI, G2. The output of gate G2 prepares the transmission unit SGII so that the next TPII pulse switches transmission unit SGII to provide a signal at VBII. Changeover may be effected manually by switches TSI, TS2 and a further connection KA prevents both pulse generators coming into operation if a fault occurs in the interconnecting link. Resistors R ensure that if the power supply to one side fails, changeover occurs.  Fig. 8 shows a monitoring arrangement for the pulse generators. The two phases TPI, TP2 are supplied to an AND gate G12 to provide a chain of pulses of equal mark to space ratio. These trigger a monostable circuit G13, VZ to provide pulses of reference length to the bi-stable circuit K3 the combined pulses are also fed to the circuit. If the trailing edge of the voltage reference pulse f occurs after the pulse being monitored, a pulse appears at the output of K3 changing over a bi-stable circuit G17, G18 to provide a fault indication at h. Monitoring of the pulse intervals formed by the gate G12 takes place after invertion through the gate G19 in a monitoring circuit TUI. Terminal RE provides for resetting. The pulse delay circuit VZ of Fig. 1 (Fig. 5) may be formed by NAND gates G7, G8 to which one input is fed by a LC delay network so that the leading edge of the pulse output from the gate is delayed. The trailing edge is delayed by inverting the delayed pulse and applying it to a further delay circuit. Resistors R1 prevent ringing and these may be replaced by diodes (Fig. 6, not shown). Alternatively RC delay elements may be used, isolated from the input and output by emitter followers (Fig. 7, not shown).