Patent GB-803996-A (GB)
Title: Improvements in or relating to sequential selection or hunting arrangements
Inventor: PEARCE JAMES GORDON
IPC: H04Q3/00
Filed: 1954-12-07
Abstract: 803,996. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Oct. 28, 1955 [Dec. 7, 1954], No. 35345/54. Class 40 (4). In a hunting arrangement having a plurality of stages, each associated with one outlet of a group of outlets to be tested, which stages operate in succession in response to a signal applied to one of them from an external source, each stage causing either the seizure of the associated outlet if it is free, or the operation of another stage if it is busy, the outlets are normally tested in sequence from first to last, but, if a stage is faulty, the stages subsequent to the faulty one are caused to operate either by recommencing the hunt from the last outlet and operating the stages in the direction lastto-first, or by stepping past the faulty stage and continuing the hunt in the normal direction. First embodiment.-When the hunter (one stage of which is shown in Fig. 1) is to be operated, control equipment (not shown) applies H.T. to leads HT1 and HT2 of each stage, and also causes each idle outlet in the group to be tested to be identified by a striking voltage applied to the lead 10 of the associated stage. If the first outlet is idle, tubes VKMK and VKBB of the associated stage fire, the subsequent rise in potential at the junction of R3, R4 primes VKSZ, while that at the junction of R6, R7 backs off VKPR but is insufficient to fire VKSO. The control equipment applies firing potential to the lead 11 of the first stage, whereupon VKRO fires. The rise in potential at R13, R14 is ineffective on the backed-off VKPR, but that at R11, R12 fires VKSZ. The rise in potential on lead 12 may be used to effect seizure of the outlet by the selector under control (not shown), and that on lead 13 to operate a tube-extinguishing circuit (not shown) to remove H.T. from VKRO, VKPR and VKSO and thus stop the hunt. If the outlet is busy, VKMK and VKBB are not fired, and, when VKRO fires to the potential on lead 11, VKPR fires (instead of VKSZ) followed by VKSO which applies positive potential via MR1 and MR2 to leads 14 and 15 connected to the leads 11 of the preceding and succeeding stages, respectively. The first stage has no lead 14, and the last no lead 15, so firing of VKSO in the first stage fires VKRO in the second, and subsequent stages operate in like manner. The hunt proceeds in the forward direction as the tube VKRO of the preceding stage has in every case already been fired prior to the reversion of potential on lead 14. A timing circuit in the control equipment (not shown) is started when the potential is applied to lead 11 of the first stage and is disabled when an idle outlet is found. However, if the time taken to test all the outlets expires and no idle outlet has been found, the timing circuit applies the positive potential to lead 11 of the last stage, and hunting takes place in the reverse direction, thus allowing outlets associated with stages subsequent to a faulty stage to be tested. Second embodment.-Each stage is modified as shown in Fig. 2, the modification including the provision of an extra tube VKTD. Tube VKRO fires to the potential on lead 11 as before and the stage normally functions as already described. However, the potential on lead 11 also starts to charge C9. The time constant of C9, R27 is sufficient to cover the normal firing time of VKRO and VKSZ (outlet idle) or of VKRO, VKPR, and VKSO (outlet busy), but at the expiration of that time firing potential is applied to VKTD. The lead 16 is connected to lead 11 in the succeeding stage and the firing of VKSO (outlet busy) energizes that lead and backs off VKTD. Tube VKTD is also disabled if VKSZ fires (outlet free), by the disconnection of H.T. from HT2 (by means not shown). If, however, the stage fails to operate in the normal manner, VKTD fires after the period timed by C9, R27 and energizes lead 11 of the next stage, whereupon the hunt continues in the forward direction.