Patent GB-190702499-A (GB)
Title: Improvements in Automatic Telephone Exchanges Operating with Electromagnetically Controlled Selecting Devices.
Filed: 1907-01-31
Granted: 1907-10-24
Abstract: 2499. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. Jan. 31. Telephone systems.-In an automatic-exchange telephone system, the contact-arm of the selector switch is turned about a pivot by a ratchet mechanism, the pivot being carried by a spindle turned by a second ratchet mechanism on an axis at rightangles to the axis of the pivot. The speakiog connexion between two subscribers is effected by a switch, which is prevented from becoming operative by a retarding-device until there is a pause of predetermined length between the interruptions of the current that operates the contact-arm of the selector, the arrangement being such that the said switch, before it makes the speaking connexion, closes a circuit through an exchange connexion of the selected line and a relay,-so that if this line is engaged the relay is energized and causes the return of the selector to its normal position. In the form of switch shown in elevation in Fig. 1, the contact-arm 2 is pivoted at 1, and is moved over the contacts 25 by the ratchet 4, pawl 8, and armature of the magnet 5. The pivot 1 is fixed in the arm 16 of the spindle 18, which is mounted in bearings in the plates 11 and carries a ratchetwheel 19 rotated by the magnet 21. The magnet 5 moves the contact-arm 2 to the desired row of contacts, and the magnet 21 selects from that row the required individual contact. The retaining- detent 15 is carried by an arm 17 fixed to the spindle 18, so as to engage the ratchet 4 when the latter is moved away from its pawl by the rotation of the spindle 18. The return of the switch to its zero position is effected as follows : when the release magnet 28 withdraws a detent from the ratchet-wheel 19, the spring 26 returns the spindle 18 to its normal position; shortly before this spindle reaches its position of rest, a hook 33 on the spring 32 fixed to the lever 31 engages the tail end of the detent 15, and the arm 17 then presses the lever 31 so as to cause the spring 52 to disengage the detent 15 from the ratchet 4, which is then returned to zero by a spring 14. The hook 33 is disengaged from the detent by a projection 36 on the tail end of the ratchet 4. Fig. 5 is a plan of a modified form of switch in which a separate release magnet is not needed, the arrangement being such that a rapid succession of current impulses-through the magnet 21 is necessary to turn the wheel 19, while if there is a pause of sufficient duration the detent is removed from the wheel 19 and the switch restored to zero. To this end, the armature 22 is connected to a suitable damping-device, such as a pawl 38 engaging a ratchet-wheel 39 in gear with a clock-work escapement. When the current in the magnet 21 is interrupted for a sufficient time, the armature 22 is retracted by the spring 40 until the heel of the pawl 23 engages a stop 24, thus raising the pawl 23 and detent 41 so as to release the ratchet-wheel 19. During conversation, the magnet 21 remains energized to keep the detent 41 in engagement with the wheel 19. A second retarded device may be provided which, after the last current impulse has been sent and the magnet 21 remains energized, connects, in a known way, the leads of the selected subscriber with the calling subscriber, the object being to prevent the disturbance of subscribers who are already conversing by the noise of the contact-arm moving over their multipled contacts. This device is used to test the selected line, and to return the selector to zero if the line is engaged. When the calling subscriber T, Fig. 6, removes his receiver and closes the key 42, current passes from the grounded battery 44 through the magnets 21, 45, line 54, and microphone 58 to earth. The key 42 indicates the means by which the circuit just described is interrupted to step round the ratchet-wheel 19 and contact-arm 2. The means for rotating the arm 2 about its pivot is not shown, but is controlled by interrupting a circuit through the other line-wire. The energizing of the magnet 45 causes its armature to raise the plunger-rod of a dash-pot 47 ; to this rod is connected the switch lever 48, pivoted at 49 and having its two arms 50, 51 connected to the contacts 3 on the arm 2. The movement of the armature 46 pushes the arms 50, 51 towards the contacts 52, 53, but the short impulses that serve to turn the wheel 19 do not suffice to raise the plunger-rod of the dash-pot sufficiently to bring about this contact. When, however, the key 42 is held depressed, the armature 46 is fully attracted and the arms 50, 51 engage the contacts 52, 53. In this movement, the arm 50 passes over a contact 56 connected to the earthed relay 57, and thus serves as a " busy " test; for if the selected line is engaged, current flows from the selected contact through the contact 3, arm 2, rod 50, contact 56, and relay 57 to ground, thereby causing the relay 57 to shortcircuit the magnet 21 and return the switch to zero. Since the magnets 21, 45 are always energized together, and the armatures 22, 46 are always operated together, these parts may be replaced by a single magnet and a single retarded armature, as shown in Fig. 7. If subscriber T<4> wishes to call subscriber T<3>, he removes his receiver so that current from the grounded battery 44 flows through his magnet 21, line 54, key 42, and microphone 58 to earth. The energizing of the magnet 21 (1) closes the switch 59 ; (2) turns the ratchetwheel 19 one step to bring the contact-arm upon the first pair of contacts which, however, are not connected to any leads ; and (3) raises the plunger rod of the dash-pot by means of the spring-pressed finger 60 and projection 61, so as to bring the switch lever 48 into the position shown in dotted lines, but no higher, because the stop 63 strikes the projection 62 and pushes in the finger 60 until disengaged from the projection 61. The calling subscriber then operates the selecting-switch in the usual way. At the first interruption of the current passing through the magnet 21, the finger 60 passes below the projection 61 and rests against the lower projection 64. The plunger rod slowly descends while the magnet 21 is energized, but the successive current impulses cause the finger 60 to keep it raised until the current interruptions cease ; the plunger rod then descends, and the rod 50 passes over the contact 56. If the selected line is engaged, current flows from the grounded battery 44 through the magnet 21 and switch 59 of the selected line, and through the lead a, contact-arm 2, rod 50, and relay 57 to earth, thus energizing the relay 57, and short-circuiting the magnet 21 so as to return the selector switch to zero.