Patent GB-1284354-A (GB)
Title: Improvements in or relating to indirectly controlled exchange systems
IPC: H04Q3/00
Filed: 1970-05-27
Abstract: 1284354 Automatic exchange systems SIEMENS AG 27 May 1970 [28 May 1969] 25403/70 Heading H4K In an exchange in which a selected path is switched-through section-by-section, a test is made for unwanted potentials or currents as each section is switched through and before the full path is set-up. A further test for correct switch-through is made on the full path at which time the link busy relays are energized. A four stage network using relays with separate energizing and holding windings is described. The sections may comprise one or more stages. Fig. 3 depicts the holding wires h for an established connection between T1 and Z1 and for a to-beset-up connection between T2 and Z2. The relay contacts in the h wires are brought up by the energizing windings corresponding to holding windings 11A1a, 11A1b &c. and the windings BAB1, BBC1 &c. represent the link-busy relays. False potential test (1).-The holding wires are terminated by resistors RV1 and RV2. It is assumed that the first section to be switched comprises an A and a B stage relay, Fig. 2, not shown. Contact ht22 is closed. If no fault exists, as indicated by the appearance of full positive battery via (currentless) RV2 in tester Ph, the marker releases this section and switchesthrough the next section, e.g. the C and D stages whereupon a similar test using contact hz21 and earth potential is performed. If both tests are successful the full path is switched through. Suppose now that the short circuit s occurs between the existing hold wire and the to-be-switched hold wire. In this case current would flow via RV2 and the short circuit to earth on the existing hold wire and therefore a false potential would be detected by Ph whereby the marker would be advised to drop this path and to select another. False current test (1).-The holding wires are terminated by rectifiers RV1, RV2. After switchthrough of the A and B stages (see above), contact ht21 is temporarily closed so as to apply a reverse bias pulse to the associated rectifier RV2. If a short circuit, e.g. s is in existence then resultant current flow via s to earth is detected by Uh so as to inhibit the marker from setting up this path. If s does not exist, the reverse connection of the rectifier prevents current flow therethrough and so the test is considered successful. The use of rectifiers is in some ways preferable to the use of resistors since energy is not dissipated therein during holding of the path. Post-switch-through test.-The contacts ht21, hz22 are temporarily closed to inject a low level current pulse into the holding wire. If this current has the expected magnitude it is an indication that the path is switched-through. Thereafter a higher level pulse may be injected so as to bring-up the link busy relays, these then remaining held by the holding current already supplied to the cross-point relays. False potential test (2).-Each a speech wire (Fig. 4) of an existing connection is connectible via a resistor Rp to a test potential Ua during the setting-up of a new connection path. The a wire of the latter is simultaneously connected to a potential tester Pa. If a short circuit such as s exists the tester detects the potential and informs the marker accordingly. If no potential is detected the next section is switched-through and another test is carried out as indicated above.