Patent GB-802603-A (GB)
Title: Improvements in or relating to static electrical test equipment
Inventor: HARTLEY GEORGE CLIFFORD
IPC: H04M3/32
Filed: 1956-11-22
Abstract: 802,603. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Nov. 22, 1956, No. 35705/56. Class 40 (4). In a system like that of Specification 788,592, in which the speech path switches consist of two anode-one cathode tubes affording an anode-toanode speech path, a static electrical hunting circuit is provided for hunting among the outlets of a group of outlets accessible from several selectors of a switching stage, each group of selectors having access to x outlets of which y are individual to that group of selectors and the remainder are common to two or more groups, and each outlet being accessible for testing by the hunting circuit via a gating device operable from a single group of selectors or from two or more groups, respectively. The switches used are preferably in the form of multiple tubes having a number of two anode-one cathode units in a single envelope, strappings interconnecting a number of anodes, one from each pair of anodes to constitute the inlet of the switch. These interconnected anodes are indicated by a single anode in the drawings, in which the cathodes are not shown. Selector 13 is accessible from a number of groups of preceding selectors and on operation of an HA relay in such a group, say that of selector 14 in group 1, tube TA of that group is primed. Each selection operation occupies a period of time T (Fig. 5) and at thecommencement of such a period a pulse PT (Fig. 5) fires the primed tube TA and raises the potential of the group bus-bar G1. Positive potentials on G1 ... G4 thus indicate calls originating in the four groups Gp1 ... Gp4. In this system in any one switching stage selection takes place in respect of only one call at a time, so that only one of these bus-bars, say G1, goes positive. Assuming that a free outlet in level 1 is required the register (not shown) passes this information to the level. selection circuit (not shown) which raises the potential of lead 1 therefrom (Fig. 3). Gates GO 1 . . . GO5 are provided one per outlet, the outlets associated with GO1, GO2 and GO3 being available to group 1 only, those with GO4 to groups 1 and 2 (access gate GGI controlled by G1 or G2), and those with GO5 to all four groups (access gate GG3 controlled by any bus. bar G1 . . . G4. Thus all the gates GO1 . . .  GO5 have inputs from G1 and from level selection lead 1 and are opened in turn by pulses P1 to P10 (Fig. 5) and the output of each gate is connected to a tube such as TO. If selector 13 is busy, its relay H is operated, thus disabling tube TO; but if it is free, TO fires when pulse P3 is applied to gate GO3. All tubes TO controlled by the same lead from the level selection circuit have a common cathode resistor such as R which ensures that only one such tube fires. The rise in the cathode potential of the fired tube TO causes the relevant gap in selector 13 to ionize (W1 non-conductive), and H operates (after pulse P10), and disconnects the anode of TO which thereupon de-ionizes, the cathodes of all level 1 tubes then returning to ground potential. Pulse PT terminates before the end of period T and TA de-ionises. The equipment is then ready to deal with another selection operation. The anodes of all tubes TO are connected to pulse supply PT so that if a relay H fails to operate, the relevant tube TO is always doused at the end of that pulse so as to free the cathodes of other tubes of the same level. Specifications 734,345, [Group XL (a)], and 788,591 also are referred to.