GB787255A - Improvements in or relating to high-speed hunting circuits - Google Patents

Abstract

787,255. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Oct. 6, 1955 [Nov. 25, 1954], No. 34143/54. Class 40 (4). In a hunting arrangement two groups of serially-arranged gas discharge tubes are provided, one tube from each group forming a stage, and successive operation of the stages takes place in one direction by the application of a potential to the tube of one group in the first stage and alternatively in the other direction by the application of a potential to the tube of the other group in the last stage. First embodiment, Fig. 1. V2 and V4 supply H.T. to the even- and odd numbered tubes, respectively. A hunting operation is started by a mark on terminal HSH which strikes forward hunt tube STF, which marks run forward lead RF to fire IROF. If outlet 1 is busy tube 1M is not conducting. Resistor R1 is chosen to be much smaller than R2 so that very little potential is applied to the seize lead or to the grid of V1 which remains at cut-off. Striking of 1ROF, however, strikes 2ROF. Assume that outlet 2 is idle so that a potential on its mark lead has struck 2M. Rectifier MR6 is therefore blocked and potential is applied to the seize lead and the grid of V3. V3 therefore conducts to cut off V4 which cuts off H.T. from the odd-numbered tubes to prevent 3ROF striking and stop the hunting. If, on the other hand, hunting stops because of a faulty stage then backward hunt tube STB fires after a delay determined by R and C. STB then marks run backward control lead RB so that hunting takes place through tubes 4ROB-IROB in turn. Second embodiment, Fig. 3. The outlets may be divided into two groups 1 to 4 and N-3 to N. According to whether a marking potential is applied from an outlet in the first or the second group so a forward or a backward start circuit STF or STB is operated. If hunting in the one direction fails to find a marked outlet then EPF or EPB is operated to cause hunting in the reverse direction. If a faulty stage is encountered then hunting in the reverse direction takes place after a predetermined time. This is achieved by applying a start condition over lead ST1 or ST2 to delay circuit DC as well as to STF or STB. After the predetermined time D.C. energizes both start circuits, that one previously energized being ineffective so that hunting takes place in reverse. If simultaneous start conditions are applied to both start circuits it is arranged that one has preference. over the other.