Patent GB-839627-A (GB)
Title: Improvements in or relating to multi-stage sequential testing devices
Inventor: FOSTER HENRY THOMAS VINCENT
IPC: H04Q3/00
Filed: 1955-11-04
Abstract: 839,627. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Nov. 2, 1956 [Nov. 4, 1955], No. 31529/55. Class 40 (4). In a high-speed hunting or finding device having a plurality of stages, one per circuit to be tested, which stages become effective in succession, each stage includes two cold-cathode tubes (A, B) forming a mutually-extinguishing pair, and the condition of the two tubes (A, B) of the pair in any stage determines whether the striking of a third tube (RO) in that stage can or cannot be effective on the succeeding stage. Each stage is associated with equipment (such as the outlet of a selector) and the circuit finds a calling or a marked equipment, or the first free equipment of a group. Each stage consists of a marking circuit MKC and a repeating circuit HCT, the marking circuits of all stages of the device being connected to a common control circuit HCC (not shown). When the particular equipment, e.g. an outlet of a selector, associated with the stage shown, applies positive potential to lead 10, tube ST fires and its positive cathode potential is applied to HCC over leads 11 and 13, the component values being such that tube A does not fire. HCC applies positive potential to lead 12 to fire the tube B in all the stages, and subsequently to lead 13 to back off MR3 in all stages. In the stage shown, this results in the firing of A by the cathode potential of the fired tube ST, and, since A and B have a common anode load resistor, this douses B. The positive cathode potential of the fired tube A is applied via MR5 to the cathode load circuit of the relevant tube RO (OT does not fire). The control circuit HCC then applies positive potential to the start lead 14. If the first stage is not operated, the positive cathode potential of B backs off MR8 and the positive cathode potential resulting from the firing of RO fires the RO tube of the next stage via MR9 and lead 21. Succeeding stages operate in a similar manner until the operated stage is reached. In that stage, the positive cathode potential of the fired A tube is applied to the cathode of RO but this is insufficient to back off RO which fires to the positive potential on its trigger. The positive cathode potential of RO backs off MR5, thus enabling that of A to fire OT. MR8 is conducting to the cathode of the doused tube B and hence the cathode potential of RO does not fire the RO tube of the next stage. The positive cathode potential of OT is applied to lead 16 to initiate the preparation of succeeding equipment for connection to that of the operated marking circuit, and over lead 15 to HCC. When the succeeding equipment signals to the control circuit that the required connection has been established, the H.T. is removed from common lead 17, whereupon the fired tubes ST, A, OT, RO and B in all the stages are doused, and the device is again idle. Faulty operation of a stage.-If, in any marking circuit, tubes A and B conduct simultaneously, then the positive cathode potential of A backs off MR10, and that of B is effective on lead 18 to cause HCC to remove H.T. from lead 17, whereupon the device is reset and the sequence is recommenced. If the fault persists and connection to the succeeding equipment is not obtained within a predetermined time, alarms (not shown) within the equipment associated with the operated marking circuit operate and inter alia remove the potential from lead 10 of that marking circuit and busy the associated equipment, so that subsequent operations of the device are not interrupted. Alternatively, if one of the tubes A, B fails to function correctly, both of these tubes may be doused when the start condition is applied to lead 14. The RO tubes will fire in succession until the marking circuit in which the tube B is not fired is reached, but (due to A not being fired either) OT cannot fire, and the sequence cannot continue. To deal with this type of fault the control circuit starts a timer coincidently with applying potential to lead 14 which timer, after a time slightly in excess of that required for all the RO tubes to fire, applies positive potential to lead 19, unless it is prevented from so doing by the firing of an OT tube. MR 12 is thus backed off and the positive cathode potential of RO fires tube LO in the faulty marking circuit, thus backing off MR8 and allowing the RO tube of the next stage to be fired. Lead 20 from the anodes of the LO tubes is connected (in HCC) through an alarm device to its H.T. supply so that the fired tube LO remains conducting to busy out that stage and to indicate the faulty stage. If the stage affected was operated, the alarms in the associated equipment operate after a delay to remove the potential from lead 10 and to busy the equipment. Operated marking circuit not detected.-If the RO tube of the last stage fires and no OT tube has been fired, a reset device in HCC removes H.T. from lead 17 and then re-applies it to initiate a second test.