Patent GB-847099-A (GB)
Title: Improvements in or relating to circuit arrangements
Inventor: DENBY JAMES FREDERICK
IPC: H04Q3/00
Filed: 1957-01-19
Abstract: 847,099. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC do. Ltd. Dec. 10, 1957 [Jan. 19, 1957], No. 2050/57. Class 40 (4). A modification of the gas discharge tube hunting circuit described in Specification 765,928 gives different signals on completing successful and unsuccessful hunting operations. A hunting operation starts from the stage at which the previous operation ceased. If, in the case of a fault, neither signal is made within a predetermined time, the circuit hunts backwards from the same starting stage. Again, if no signal is made within a predetermined time, the circuit hunts in a forward direction starting at stage 1. The direction of hunting is controlled by the H.T. feed to lead HTG. The control circuit for leads HTA, HTB, HTE, HTG is not described. The circuit may be used to select control-circuits in a cross-bar system. General.-Three stages 1, 2, n are shown connected in a ring. Junction relay sets JRS1 to JRSn control two-state circuit elements SZ(1), RO(1) to SZ(n), RO(n). If set JRS1 is free, tubes MKJ(1), MK(1) conduct and condition SZ(1) to respond to any pulse from tube IN(1). If set JRS1 is busy, tube MKJ(1) does not conduct and RO(1) responds to the pulse. The last stage to seize a free relay set is marked by a conducting tube, say M(1), the tubes M(1) to M(n) being connected in a self-extinguishing circuit in which only one tube can conduct. H.T. is permanently connected to leads HTA. Successful hunting operation.-At the start of the operation, H.T. is connected to leads HTB, HTE and a pulse is applied to leads RB. Tube ST(1) primed by M(1) strikes and is followed by IN(2) in stage 2. If set, JRS2 is busy, IN(2) is followed by RO(2), SO(2) and IN(n) in the third stage. If set JRSn is free SZ(n), SZA(n), SZJ(n), M(n) strike to seize the set and OA, common to all the stages, signals a successful operation. H.T. is disconnected from leads HTB, HTE and only M(n) remains conducting. Unsuccessful hunting operation,-If JRS1 to JRSn are all busy, tubes FTR(1), AOB(1) primed by the conducting M(1), follow RO(1), SO(1) when the hunting operation reaches the first stage again and an unsuccessful operation is signalled over lead BL. H.T. is removed from leads HTB, HTE in response to the signal on BL. Faults, backward hunting.-If, after a predetermined time the end of the operation is not signalled, H.T. is connected to leads HTG and a pulse is applied to leads RB. The H.T. on lead. HTB, HTE is not interrupted. Tube TS(1), primed by M(1), strikes and is followed by IN(1) to test stage 1. If JRS1 is busy, tubes RO(1), SO(1), SB(1) and IN(n) strike to test the nth stage. On striking, SO(1) has no effect on IN(2) which already conducts. A free set may be seized as before but again, if the end of the operation is not signalled within a predetermined time of the commencement of backward hunting, H.T. is disconnected from lead HTG and a pulse is applied to lead FS to start forward hunting from the first stage. Multistage hunting circuit.-If relay sets and corresponding stages of the hunting circuit are distributed over a number of racks the M tubes of each rack may be arranged with an auxiliary tube in a self-extinguishing circuit individual to the rack. The circuits are coupled so that an M tube on striking, is followed by the auxiliary tubes in the other circuits thus extinguishing all other M tubes.