Patent GB-190504883-A (GB)
Title: Improvements in or relating to Central Station Telephone Systems working with a Common Battery.
Inventor: BIRNBAUM ISIDORE BERNARD
Filed: 1905-03-08
Granted: 1905-10-26
Abstract: 4883. Birnbaum, I. B., and Bell, F. G. March 8. Telephone systems.-In a common battery exchange system, drop indicator coils are employed to give both the line indicating and clearing-out signals and operate also as impedance coils, and, if desired, as translators and as self-inductors for a special vibratory calling-apparatus. Jacks and plugs and a back-contact giving an audible clearing-out signal are also described. Fig. 1 shows two subscribers' sets I, II, each having at the exchange a jack possessing three fixed contacts d, e, g and two spring contacts c, f together with a collar l. The spring f and collar l are connected to the line a, the former through the indicator coil. When the instrument is lifted from the hook at the station I, the indicator coil is energized through the contact of the springs f, c with the fixed contacts e, d ; at the same time, an audible signal relay n is operated. The operator then inserts her plug, Fig. 2, into the jack and depresses the key q ; her apparatus contains an impedance coil j connected as indicated to the zinc or negative pole of the common battery o. The set of connexions are then as shown in Fig. 4, the indicator coil m playing the part of one of the impedance coils. To call subscriber II, she inserts her plug into the corresponding jack and rings up by means of the generator w When his indicator has also fallen, she inserts the plugs 1, 2, Fig. 3, into the two jacks. The plug 1 has the usual tip p and sleeve s, but the plug 2 has a ring w, sleeve s, and a tip p. The tip has no electric connexions, and merely forces the spring f of a jack away from the contact e and into connexion with the contact g. The ring w of the plug 2 is connected to the sleeve of the plug 1, and the sleeve of the plug 2 to the tip of the plug 1. The circuits of the two subscribers are then as indicated by Fig. 5, the two indicator. coils m playing the part of two impedance coils, the currents through these two coils being in opposite directions owing to the action of the tip of the plug 2 on the spring f of its jack. If, then, only one subscriber puts his instrument on its hook, neither indicator will be restored ; when both instruments are put up, the two indicators will be silently restored. In order to operate the buzzer or audible signal relay n, back-contacts 10 are introduced. The armatures 9 are connected directly to the - pole through the coil n, and through the contact 10 to the spring c and the line b. The contact 9 10 will only be made so long as both subscribers' instruments are on their hooks, and if at the same time the plugs 1, 2 be in the jacks an audible clearing-out signal will be given by the relay n, the circuit being from the + pole through the contact e, f (of the jack in which the plug 1 has been inserted), coil m, collar l, sleeve s, ring w, spring c, contact 10, and the relay n to the - pole. Only one drop is restored, the buzzer and the other drop being restored only by the pulling out of the plugs. The system can be arranged with a third wire or common earth return for calling. Further, the indicator coils may be "split" and used as translators, Fig. 8. A vibratory calling-device is indicated in Fig. 11 to dispense with a generator. The operator inserts her plug and presses the key 4, thus energizing the electromagnetic coils 5, and causing a vibratory armature 6 to set up self-induced currents in the circuit containing the impedance coils m, j and the call bell and condenser at the called station. In a modified arrangement, the key 4 is replaced by employing a back-stop with which the key q is normally in contact, so that the mere insertion of the plug actuates the call.