Patent GB-766935-A (GB)
Title: Circuit testing apparatus
IPC: G01R31/04
Filed: 1954-10-22
Abstract: 766,935. Circuit testing apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 22, 1954 [Oct. 26, 1953], No. 30456/54. Class 37. Relates to short-circuit and continuity testing of wiring networks before installation of the active components such as valves, resistors and condensers. Fig. 2 is an example of such a network or chassis 100 comprising electrodes or terminal lugs 108 along mounting strips 102- 105 and shows predetermined electrodes or lugs 109 and plug and socket terminals 111, 112 connected by jumper wires 113 to form nodes, i.e. electrically joined sub-combinations of electrodes to which the proper components are to be connected. The circuit of Fig. 10 shows X, Y and Z nodes under test; each node comprises electrodes 109 connected by jumper wires 113. The invention provides apparatus for testing a circuit network having a plurality of normally isolated nodes (e.g. X, Y and Z, as in Fig. 10), each comprising a plurality of normally connected junction electrodes (e.g. X1, &c. in the X-node), said apparatus comprising (i) means whereby the nodes are tested in succession so as to check the continuity of the individual interjunction connections in each node, and (ii) means whereby testing ceases automatically in response to a break in any one of said inter junction connections. The unit 100 is plugged into a receptor 119 in the test apparatus (Fig. 1) and the Specification includes constructional details referring to this receptor 119 and to test control panels &c and wiring runs to selector switches and relays. General description, Figs. 9 and 10.-In Fig. 9 the nodes X, Y, Z are associated with respective individual resistors Rx, Ry, Rz and with common resistor Rg and battery 114. The apparatus grounds X1 and if there is a short circuit between XI and the Y or Z-nodes the voltage Vg then occurring across Rg operates a relay to indicate the short circuit and stop the test. Simultaneously with grounding X1 relays are associated with X2-X5 and if there is a break between X1 and X5 these relays respond to indicate the location of the break and stop the test. The apparatus comprises multi-level rotary magnetic stepping switches whereby the X-node is first tested and then in sequence the Y and Z-nodes. The equipment shown in Fig. 10 is based on Fig. 9 and comprises 5-level (L1-L5) stepping switches S1, S4 together with short circuit relay M1 and open circuit relays M2-M5 and normally cut-off triode 182. In the pre-test condition the S1, S4 wipers are in the home or contact 1 position and relays M2-M5 are energized and relay M1 deenergized. To start the test the operator presses a start switch and S1 wipers then advance to contact 2 and ground is applied to X1 in the X-node through the S1 wiper on level L1 and if there is a short circuit between X1 and the Y or Z-node the increase in Vg voltage across common resistor Rg causes triode 182 to conduct and operate relay M1 to actuate stop-test means (see below). If an open circuit exists between X1 and X5 relays M2-M5 drop out selectively, i.e. M2-M5 if break is between X1 and X2, M3 to M5 if X2 and X3 and so on. The release of any relay M2-M5 actuates stop-test means (see below). The S1 wipers eventually reach contacts 3 and 4 whereby the Y- and Z-nodes are tested in the same manner as the X-node. The Z-node, however, comprises 13 electrodes and the stepping switch S4 is provided to complete the continuity test of the Z-node, i.e. test between Z5 and Z13. When the S1 wipers reach their home contacts 1 the S4 wipers step and the Z-node is again grounded (this time at Z5 via contact 2 of L1, S4) whereby relays M2-M5 hold-in provided no open circuit exists between Z5 and Z13. The contacts 2 to 3 on the S4 levels are connected to the electrodes Z5 to Z13 as shown and excess contact 4 is grounded to prevent false drop-out of the M relays. While only three nodes X, Y, Z are shown in Fig. 9 the equipment disclosed has a capacity for testing 150 nodes and accordingly comprises three 5- level switches S1, S2, S3 each having 52 contacts on each level (see Figs. 12A to 12C below). Test procedure, Figs. 12A to 12C and Fig. 8.- The operator throws in motor switch 210 (Figs. 8 and 12A) and momentarily actuates test-start push 186 so that cam 228 driven by motor 229 intermittently operates timer relay T via switch 227 and pulses are delivered via lines 225, 191 into stepping magnet S1S (Fig. 12B) which advances S1 following operation and lock-up of master relay A. An interrupter relay B (Fig. 12A) is associated with relay T and if as S1 sweeps round a short or open circuit is encountered in the node under test an M relay responds (as described in relation to Fig. 10 above) and relays T and B both lock up whereby (i) steady D.C. is delivered into S1S to halt S1, (ii) a buzzer 244 sounds, and (iii) a signal lamp 212 flashes to indicate the short circuit or one or more of the lamps 213-216 flashes to indicate an open circuit. By observing the lamps 212- 216 and switch dials of S1-S4 (S1 in this case) (see Fig. 8) and using a network chart the operator is informed where the break or short circuit exists. If it is desired to repair immediately any defect shown up the timer motor 229 is turned off by switch 210 and this removes the test voltage from the test network and the latter is then taken out of the apparatus and the defect repaired. Subsequently the stepping action of S1 is restored by momentarily throwing switch 208 to " advance " position to de-energize solenoid S1S whereby S1 advances one step and with switch 208 in run position and motor switch 210 closed and no further defects encountered S1 sweeps on to its home contact 1. If the nodes under test are fault free relay H1 following sweep of S1 operates and locks-up and solenoid S2S steps S2 and then with successive actuation and lock-up of relays H2-H4 and C2-C4 to feed pulses in turn to S3S and S4S the switches S3 and S4 sweep through their test cycles. When S4 reaches home contact 1 the master relay A drops out to light " test complete " lamp 209 and isolate the tested network. If desired the test network may be wholly tested and all defects corrected at test completion; each time a defect is encountered the " advance " switch 208 is actuated. The chassis frame 101 (Fig. 2) by connection to any convenient contact point on L1 of S1, S2 or S3 may be tested for possible short circuit to the network nodes. The buzzer 244 is silenced during network repairs by opening switch 206 (Fig. 12A). The " advance " position of switch 208 is not effective until 206 is closed so that the test cannot be re-started with the buzzer 244 disconnected. The stepping switches may be returned to starting position during a test run by opening run-reset switch 207 (Figs. 8 and 12A) to open circuit relay B. The short-circuit detecting circuit including tube 182 is tested for failure by throwing switch 208 to " short test " position (Figs. 8 and 12A) so as to simulate a node network short circuit and operate relay M1.