Patent GB-556922-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H01H67/12
Filed: 1942-04-20
Abstract: 556,922. Automatic exchange systems and switches. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and BAKER, G. T. April 20, 1942, No. 5219. [Class 40 (iv)] Switches for automatic exchange systems comprise a terminal bank built up from multipling strips and comb-like members, the teeth of which can be bent into engagement with the strips, and contact-selecting and operating sets which are jacked into the bank and comprise primary, secondary and release magnets but no separate control relays. First selectors are also provided with a control relay set which cooperates with all the magnets of a train of switches to cause them to act as group and ordinary or PBX final selectors. This arrangement is convenient also for trunk offering and testing and for causing group selectors under special control to behave like PBX final selectors. The jacked-in parts of all the switches may be identical, differences in behaviour being brought about by the action of the common control set in conjunction with characteristic potentials permanently connected at the jacking-in points. The arrangement eliminates most of the relay contacts normally present in the talking circuit. The contact-selecting and operating members are driven by a constantly acting source of power, e.g. an individual or common electric motor with the help of a special clutch and linkwork which convert the rotary movement of the motor into a smooth step-by-step movement of the selecting and operating member. The arrangement is such that if an impulse is able to initiate the stepping operation the step is completed however short the impulse may be, and the system may employ " flick impulses " derived from condenser discharges and having a constant length independent of the make-to-break ratio of the originating impulses. Features of the system are claimed in Specifications 556,918, 556,919, 556,920, 556,921. Specifications 545,634, 549,047, 551,187, 556,928 and 556,929 also are referred to. Switch construction.- The terminal banks of a number of switches are built up from vertical strips 23, Fig. 1, provided with silver contact points and connected to outgoing circuits and horizontal combs 24 provided with silver-tipped teeth and connected to the incoming circuits, of the switches. The selecting part of each switch is jacked in to the bank as at 37, Figs 8 and 17. It comprises a pair of contact operating arms 53, 54, which may also carry wiping contacts, on a primary carriage which is driven across the bankface to select a row of contacts and is supported by a secondary carriage which is then driven so that the arms enter the bank to select a particular set of contacts. The carriages run on magnetized rails. During the secondary movement, the release magnet 78 holds the contact-operating members clear of the contacts by means of a guide frame 34, 46. The driving arrangements are a development of those described in Specification 545,634. On the operation and release of the primary magnet 74, which is a standard type of relay with a latch 82 secured to its armature, a cam-shaped clutch disc 48 is brought into engagement with a constantly running disc 47 and reciprocates an arm 76 in the direction of its length. By means of an additional cam surface co-operating with the frame, the arm is also given a rocking movement so that a pin 87' on its end enters a slot in a ratchet member secured to the primary carriage at the beginning and leaves it at the end of each forward stroke. When the driving pin enters a slot, a holding pin 118 on a pivoted arm 43 is forced out of a retaining ratchet and vice versa. A double movement of the latch arm 82 is necessary for each step. A similar drive is employed for the secondary movement but, where this is a hunting movement, the'carriage is given two steps for each rotation of the driving cam and stepping is continuous while the secondary magnet is energized. When the release magnet is energized at the end of the primary movement, it withdraws a detent 38 from the holding ratchet of the secondary carriage. In the normal position of this carriage, a holding pin 122 on a pivoted arm 33 is held clear of the holding ratchet by engagement of a pivoted projection 39 with the frame, but the first secondary step causes the projection to tilt so that the holding pin operates during the stepping movement in the same way as the holding pin 118. At the end of the movement, the release magnet is released and tilts the arm 33 so as to disengage the pin 122 and allow the arm to latch itself in this position, the carriage being held lower by the pawl 38 controlled by the release magnet. Consequently when the release magnet is operated again, the secondary carriage is restored owing to the removal of this pawl. Restoration of the primary carriage results from engagement of a hook 44 on the retaining arm 43 with a fixed projection 42, Fig. 8b, when secondary restoration is complete, the resulting removal of pin 118 allowing the primary carriage to return to normal. On reaching normal, it disengages the hook 44, Fig. 8a, in readiness for the next primary stepping action. In a modified arrangement, the projection 42 instead of being fixed is movable by the release magnet to bring it into engagement with the hook 44 without any movement of the secondary carriage. This enables primary release to be given by releasing the release magnet without any secondary movement and secondary release to take place without primary release (the energization of the release magnet being maintained in this case). As shown in Fig. 18, the switches may be arranged in sets of 20 one above the other. All the sets may be of one stage or they may consist respectively of first, second and final selectors. The switches may have individual motors or all those in a vertical row may have a common motor as shown. Sprockets are provided on the shafts so that two may be coupled together by bicycle chain if a motor fails. Each switch may be contained in a sealed cover from which projects a pinion which engages a corresponding pinion on the power shaft when the switch has been jacked in. The horizontal wiring is carried in three run-ways 91 ... 93. Common control circuit ; group selector. Figs. 22 and 19.-A simple circuit arrangement is described with reference to Figs. 6 and 7 (not shown) in which the switches test for busy ground and impulses are repeated to the switches in the ordinary way so that the secondary magnet of a final selector controls the clutch by a double-pin arrangement as shown for the primary magnet in Fig. 8. The control circuit shown in Fig. 22, however, sends an impulse of limited duration for each impulse received as described in Specification 549,047 so that a single pin on the clutch disc is sufficient, and the switches test for idle battery. When the control circuit is seized, line and release relays AA, BB come up and condenser QE is charged. Primary magnet 1VR in the group selector, Fig. 19, is operated over the negative wire to prepare the switch for operation and disconnect the marking battery from the P wire to busy the switch and control circuit. The first dialled impulse brings up E which energizes MD which locks. Each impulse discharges QE through HR which repeats the impulses over the negative wire to 1VR. At the end of the digit, QD, which was connected up by E and has been repeatedly discharged by HR, is enabled to charge sufficiently for the tube NT to break down and energize CC which locks and releases E. Battery over relay D is connected via wire Z to release-magnet 1ZR in the selector. D and 1ZR operate, the latter energizing the secondary magnet 1RR. The first step off-normal switches the circuit of 1RR over to the negative wire so that D releases and the switch hunts until the test wiper RW1 encounters battery on the terminal of an idle line whereupon test relay H disconnects the negative wire, the switch stops and release magnet 1ZR is released to lower the contact operating members and so effect the switch through. HR also releases CC (provided E has fallen back) and is itself released by the relapse of 1ZR. All trunks busy.-The switch is stopped in an extreme position and springs 1SI connect ground to the positive wire to operate G which locks and connects up busy tone. Regular final selector, Fig. 20.-Primary control is the same as that of the group selector. The secondary magnet 2RR, however, is connected to ground instead of to battery and therefore does not operate immediately on the operation of the release magnet 2ZR but waits for battery impulses from contact hr 3 Relay CC is thus released on the relapse of E, since relay D remains energized. At the end of the second digit, CC completes the test circuit over the positive wire and, since in this case the release magnet is not released on the termination of the secondary movement, the test circuit is closed long enough for the operation of H if the line is idle. Supply and control of ringing current.- On the operation of H, which locks up, 2ZR is shunted out to complete the circuit in the final selector and ringing current is sent out over F, and D is released. When the called party replies, F switches through and locks up, and D re-operates, releasing MD to complete a metering circuit. Busy signal.-If relay H fails to operate, the relapse of E followed by that of CC energizes G which connects up busy tone and causes the release of the final selector releasemagnet. No effect is produced on the existing connection, however, since the positive, negative and Z wires are all disconnected at G contacts. Release.-On the relapse of AA, E pulls up in series with BB which holds. After an interval timed by the condenser QD, CC comes up and releases E and BB whereupon H, F and D fall, releasing the primary magnets in the switch train and so operating their release magnets. If release occurs prematurely the most recently seized selector takes a primary step and a secondary step an