Patent GB-308609-A (GB)
Title: Improvements in or relating to selector testing circuits
IPC: H04Q3/00
Filed: 1929-03-22
Abstract: 308,609. Telefonaktiebolaget L. M. Ericsson, March 24, 1928, [Convention date]. Automatic exchange systems.-In a selector, the resistance of the testing circuit is increased as soon as the connection is made to a value that prevents a double connection being completed if a second selector should be testing the circuit at the instant of release. The invention is described in connection with power driven selectors with rotary and then radial movement in the same plane. The rotary motion is controlled by a register controller whilst the radial motion is automatic. When the switch GV1 is taken, a register RR is connected to the circuit and a contact is made by means cf a sequence switch extending a circuit through relay R0G3, resistances R1, R2, rotary off normal switch VO1, and radial off normal switch RO,. The register RR is set and when the setting is complete, a circuit is closed for R1G2 (VO1, R1G2, RR) which locks up at 3 and completes a circuit for high resistance relay R1G1. Relay R1G1 locks up independent of R1G2 at 5. The resistance R2 is thus removed from circuit R0G3 and replaced by R,G,. A circuit is also completed for relay CVG (9, 5) and for clutch magnet MHG (via contacts of CVG and R1G1) moving the switch in a rotary direction. During rotary motion the impulses are Sent back by 8 to RR and when the desired contact row is reached, R1G2 is de-energized stopping the rotary motion and allowing CRG (14, 9, 5) and MHG to energize to drive the wipers in a radial direction. When a free circuit GV2 is reached, R,G, is energized (VO1, 38, R1G3, C, R3, R4, etc.) breaking the circuit of CRG to stop the switch and completing a circuit for R1G4 (via CVG which latter does not energize) which locks up at 14, extends the calling circuit, and short-circuits the lower winding of R1 G3 marking the contact C busy to other selectors. The windings of relay R1G3 are differential making the relay insensitive if two such relays should be connected to the same contact C in parallel, i.e. if two hunting selectors should test the same free circuit simultaneously. The relay R2G2 of GV2 operates from battery at RR and selector GV2 is operated in a, similar manner extending the circuit to FL3. The resistance R4 in the testing circuit is replaced by high resistance relay R,G, in the same manner as R2 was replaced by R1G1 to prevent a second connection during release. When the called subscriber replies contact 29 is made for a short period which short-circuits R2G3. Earth is thus connected to contact C (R3, 30, 28, 39, VO2) and R1G3 is short-circuited which returns the shortcircuit to R0G3 (R1, 32, 33, 38) to meter the call. As the lower windings of R2G3 and R1G3 are short-circuited these relays re-energize in series with R3G1 and R2G1 respectively, when the earth at 29 is removed. When the subscribers replace their receivers, earth at 4 is removed and R1G1 falls back completing circuits for CRG and CVG in turn to co-operate with MVG to restore the selector to normal. It also breaks the circuit of R1G3 and releases R2G1 to restore GV2. Should another selector be testing GV2 as R,G, releases, earth might be extended to R,G, over R1G3 of the testing selector. As both windings of R1G3 of the testing selector would be connected in series however, the relay would not operate and the selector would pass on. During release, the circuit of R4 is broken at 40 and 41 and consequently connection to C is prevented until the switch is again in its normal position.