Patent GB-266270-A (GB)
Title: Improvements in testing of automatic and semi-automatic telephone exchanges
IPC: H04M3/08
Filed: 1925-11-17
Abstract: 266,270. Standard Telephones & Cables, Ltd., and Cameron, A. H. Nov. 17, 1925. Automatic exchange systems.-Routine-testing apparatus for applying a complete cycle of tests to each in turn of a group of automatic switches comprises a sequence switch which in its different positions controls the application of different tests and only moves on to the next testing position if the preceding tests has been successful. If any test is unsuccessful, the sequence switch remains in the position corresponding to that test and a characteristic signal is given to an attendant. The throwing of a manual key connects up a " fault clear " signal which is operated as soon as the fault has been rectified, and the restoration of the key then causes the sequence switch to move on to control the remainder of the test cycle. The testing apparatus is associated with the switches of the group in turn by a step-by-step switch which automatically advances one step at the end of each successful cycle, and means is also provided for setting or re-setting the step-by-step switch to test or re-test any of the switches at will. The apparatus shown in Figs. 1 and 2 is specially designed for testing line-switches of the standard type shown in Fig. 3, tests being performed in respect of the following: the continuity and polarity of the incoming and outgoing line conductors; the continuity of the test conductor and the meter connections; the adjustment of the line and cut-off relays: the hunting operations including the speed of hunting; and the electrical condition of the outgoing wipers during an incoming call. The incoming leads (on the right of Fig. 3) of the various line-switches of a group are connected to banks 1, 2. 5. 3 of the switch RLS1. Fig. 1, and the twenty-five multipled links outgoing from the switch are associated with the banks of a second step-by-step switch RLS2. Fig. 2. The step-by-step sequence switch SS1, Fig. l.. controlling the cams shown in that Figure, effects the main control of the testing operations, but a second step-by-step sequence switch SS2, Fig. 2. also comes into action during the testing of the outgoing links associated with the switch RLS2. Testing incoming line and test conductors and adjustment of line and cut-off relays. The operation of start key SK energizes relay CR which completes a circuit from cam A over back contacts of relay STR and key FK for relay SS1R which in turn energizes the sequence switch magnet. The latter interrupts the circuit of relay SS1R and upon its release the switch moves one step into position 1¢ in which earth over cams A, B, relay PR1 and wiper 3 of switch RLS1 is connected to the incoming test wire. If this wire is discontinuous, lamp AL is lit over a circuit from earth over cams A, B, back contact of relays PR13, PR2, ADR in series with alarm relay FAR which energizes an alarm bell. (The alarm-is given after a slight delay determined by a slow-release relay ADR which operates in parallel with relay SS1R). The attendant then throws key FK disconnecting the bell and connecting up a fault-clear buzzer FCB. When the fault is rectified relay PR1 energizes over the test wire in series with the cut-off relay COR and lineswitch magnet DM and closes a circuit for relay PR2 which is made quick-acting by means of a normally short-circuited winding. Relay PR2 transfers the circuit previously traced for lamp AL over 'its own front contact and back contact of relay STR to operate buzzer FCB, and the restoration of key FK completes the circuit for moving switch SS1 into position 2. (If the test wire had been continuous relays PR1, PR2 would have operated immediately to advance the switch to position 2.) A loop is now connected over the positive and negative lines, key LRK, jack LRTJ. relays SFR1, SLR and cam H. If either of the line conductors is discontinuous, relays SFR1, SLR do not operate and lamp BL is lit and the alarm bell rung. If the conductors are continuous but reversed, relay SLR operates but not polarized relay SFR1, and lamp CL is lit. If the conductors are correctly connected. relay SFR1 completes a circuit for driving switch SS1 into position 2¢. (The reversing key LRK is provided so that the remaining tests may be proceeded with if the conductors are found reversed.) In position 2¢ the current over the loop is such that the line relay LR should not operate. If it does operate the connection of earth to the test conductor energizes relay PR1 over cam G, and relay PR2 lights lamp DL. If the line relay is properly adjusted and does not operate, a circuit over cams A, C and back contacts of relays PR3, PR2 drives the sequence switch to position 3 in which a circuit for the cut-off relav COR is completed over relay PR1, resistance RC, cams B, A. This circuit persists over position 3¢ to which the switch moves over cam A and a front contact of relay CR. If relay COR operates (incorrectly) at this time it opens the line loop and the release of relays SLR, ASLR lights lamp EL. If relay COR does not operate, the sequence switch moves to position 4 over cams A, C and a front contact of relay ASLR. The resistance RC is now removed from the circuit of the cut-off relay which should therefore operate and by breaking the loop cause the switch to move to position 4¢. If the cut-off relay does not operate. lamp FL lights. In position 4¢ a circuit over the right-hand locking winding of relay SS1R controlled by relay ADR provides a pause for the cut-off relay to release completely. The switch SS1 moves to position 5 over cam A and a front contact of relay CR, and in this position the resistances RA, RB are removed from the loop circuit and the line relav LR should therefore energize. If it does not, lamp GL lights over cams B, A. If the line relay operates, the connection of earth to the test conductor energizes relays PR1, PR2 to drive the switch to position 5¢. Testing hunting operation and speed. In position 5¢, the operation of the line relay causes the switch to start hunting and this goes on continuously since all the test conductors are earthed, the earth for the last conductor in the bank P25 being supplied over a front contact of relay PR13 and cams A, D, whilst the remaining test conductors are earthed over cams F, A. When the wipers pass over the last line in the bank, relay PR3 operates and energizes relay PR4 which completes a circuit over cams A, D, Y for the switch SS1. If the line switch fails to hunt, lamp HL is lit. The switch SS1 moves out of position 6 over cams A, C and back contacts of relays PR3, PR2 and thereafter moves to position 11 under the control of the upper right-hand contact of cam A. If the line switch is too fast, the last terminal of the bank is reached again before the sequence switch reaches position 8¢, relays PR3, PR4 are operated and lamp OL is lit in series with relay STR which opens the sequenceswitch driving circuit, and rings the alarm bell. If the switch is too slow, the last terminal is not reached when the sequence switch reaches position 9¢ and lamp PL is lit in this position over a back contact of relay PR4. In position 10¢ the earth is removed from the last test terminal P25 and the switch therefore comes to rest on the last line and the cut-off relay operates and locks over the test wiper, relay PR3 and a front contact of relay FR, which has operated over the loop comprising cams T, W, wipers 2. 3 of switch RLS2, wipers 1, 2 of the switch RLS1, relays SFR1, SLR, and cam H. The speed test is repeated later as referred to in a later paragraph. Testing meter connections. In position 11, a circuit is completed over cams A, E to an armature of relay MR. If either the meter line or the last meter link is disconnected, lamp JL is lit, but if continuous, relay MR is operated over the metering wiper of the line switch and wiper 4 of switch RLS2 and the sequence switch moves to position 11¢ and thence over the upper right contact of cam A to position 12. Testing incoming-call conditions. In position 12, the cut-off relay is energized over relay PR1 and cams B, A and relay FR is released. The switch moves to position 12¢ over cam D, back contact of relay FR, front contact of relay PR1, and battery is connected to the positive line from cam G over key LSRK, front contact of relay PR1 and wiper 1 of switch RLS1. If the cutoff relay has closed its front contacts (which it should not do for an incoming call) this circuit will be extended over the positive line wiper to the left winding of relay FR which will light lamp KL indicating that the positive wiper is not dead. A similar circuit over the other winding of relay FR tests the condition of the negative wiper. If the test wiper is not dead, lamp KL is lit over a back contact of relay PR1, but if the test wiper is dead, relay PR1 operates and moves switch SS1 to position 13. Testing outgoing links. The control relay SS2R of the second sequence switch SS2 is energized over cams A, F, front contact of relay CR and cam S and moves the switch to position 1¢ in which earth at cam T is placed upon the negative line to energize the line relay LR. The operation of the line and cut-off relays then extends this circuit over relays SFR2. FR, cam W. positive line, to battery on cam 2. If either of the outgoing line conductors is discontinuous, relay FR does not energize and lamp LL is lit. If the conductors are continuous but reversed, relay FR operates and lights lamp ML. If the conductors are continuous and of correct polarity, relay SFR2 also operates and moves switch SS2 into position 2 in which the outgoing test conductor is connected to relav PR3. If the conductor is open, relay PR3 does not operate and lamp QL lights over cams U, V, F. but if the conductor is continuous relays PR3, PR4 operate and the switch moves to position 2¢ in which the outgoing meter link is tested. If this is faulty, lamp NL is lit but if continuous, relay MR is operated