Patent GB-190925896-A (GB)
Title: Improvements in and relating to Electric Selective Devices especially applicable to Telephone Systems and the like.
IPC: H01H67/06
Filed: 1909-11-09
Granted: 1910-11-03
Abstract: 25,896. American Automatic Telephone Co., and Goodrum, C. L. Nov. 9. Electric selectors, automatic exchange systems.- The ratchet member of an electric step-by-step selector is propelled and released by two electromagnets, the circuits of which are controlled by a combination of quick and sluggish relays, the sluggish relay, when de-energized, directly closing the circuit of the release magnet. Fig. 2 shows the application of such a system in an automatic telephone exchange. The subscriber closes the metallic circuit 150, 151 by removing the telephone from its hook, and then operates the impulse counter 156 to produce in rapid succession the number of current-interruptions required for selection. The initial circuit-closure energizes a quick relay A<1> which breaks the circuit of the propeller magnet 127 at m<129>, and a sluggish relay B' which closes a second contact m<133> in the circuit of the propeller magnet and breaks the circuit of the release magnet 135 at r<4>. The sluggish relay B' remains energized during the rapid currentinterruptions employed for selection, but the quick relay A<1> makes and breaks the circuit of the propeller magnet 127, which oscillates its pawl and propels the selector ratchet 1 to the required point. The hanging-up of the telephone, after a conversation is ended, de-energizes the relays A', B', and the following circuit is completed through the release magnet 135, namely, battery x<1>, wire m<127>, springs 145, 146, magnet 135, contact r<4>, interrupter 164, and wire 151. The rotary interrupter 164 is connected in the circuit of the release magnet for a reason which will appear below when the construction of the ratchet and pawl mechanism is described. The operation of the release magnet allows a spring to return the ratchet to zero, and a pin 149 separates the springs 145, 146 so as to open the circuit of the release magnet, leaving the system in readiness for a fresh selective operation. Fig. 1 shows a modified system in which, when the ratchet 1 has been propelled to the required point, a second series of current-interruptions separated from the first series by a pause is without effect on the ratchet, and can be used for an independent operation. The initial closure of the line circuit 50, 51 energizes a quick relay A which closes at a<4> the circuit of a sluggish relay B, which in turn closes at b<1> the circuit of a sluggish relay C. The rapid current-interruptions produced by the subscriber's impulse wheel 56 act on the quick relay A to make and break the circuit of the propelling- magnet 27 at a', so as to move the ratchet 1 to the desired position. The circuit by which the sluggish relay C was primarily excited is broken by the separation of springs 45, 47 as soon as the ratchet makes its first step, but, as long as the current interruptions continue, the relay C receives intermittent currents from the back-contact a<3> of the relay A. These intermittent currents pass through the previously-closed self-holding contact c<1> and maintain the relay C in an energized condition. If however a prolonged current is now permitted in the line circuit, so that the self-holding circuit of the relay C is deprived of current for an abnormal interval, the relay C has time to become deenergized, and, by opening the contact m', permanently cuts out the propeller magnet 27. Any further current interruptions, produced for instance by a second movement of the impulsewheel 56, do not therefore cause any further movement of the ratchet 1. When finally the telephone is hung up again so as to break the line-circuit 50, 51, all three relays A, B, C are de-energized, and the following circuit is closed through the release magnet 35, namely, battery X, wire 58, springs 45, 46, contact r, contact b<2>, magnet 35, and interrupter 64. The devices then return to normal condition as described in connexion with Fig. 2. The construction of the ratchet selector is shown in Fig. 3, which shows the apparatus in its zero position with the propelling-pawl 21 held out of engagement with the ratchet teeth by a catch 32, and the detent pawl 28 held out of engagement by the propelling- pawl. The energization of the propeller magnet 27 sets both pawls free to engage with the ratchet teeth, the pawl 21 being moved to the right, and when the magnet 27 is de-energized the spring 22<b> causes the pawl 21 to move the ratchet the space of a tooth. By repeated energizations of the magnet 27, a pair of contacts 6 can be brought into connexion with any of the pairs of contacts 8. To withdraw the pawls 21, 28 so that the ratchet may be returned to zero position by its spring, it is necessary to energize and de-energize the release magnet 35, so as to lift the catch 32 into engagement with the projection 31 of the pawl 21 and then to withdraw it. This double motion is secured by the rotary interrupter 164, Fig. 2, or 64, Fig. 1, in the circuit of the release magnet.