Patent GB-190406646-A (GB)
Title: An Improved Call System for Telephone Stations.
Inventor: AMMER VICTOR
Filed: 1904-03-18
Granted: 1905-03-18
Abstract: 6646. Ammer, V. March 18. Telephone systems; telephone calls.-Relates to a telephone-call system in which any one of a number of stations or exchanges may be called up from one apparatus. The selection is performed by the subscriber earthing one or both of his line wires, either directly or through one or more resistances, or by connecting the two lines directly. The selecting-mechanism comprises a number of relays, the armatures of which make contact with the various lines leading to the different stations. Fig. 1 shows a simple case in which three calls can be made by earthing one or both of the line wires 1, 2 by means of the keys D', D<2>. If key D<1> is depressed, current passes from the battery, through relay a, key D', and bell W to earth E. The attraction of the armature a' completes the calling-circuit of station Z<2> as follows-from battery, armature a<1>, line b<1>, bell Z<2>, back to armature f, and ground. If the key I)' is depressed, the armature f is attracted in the same way, and station Z<1> called, while, if both keys are depressed, both armatures are attracted and station Z<3> called. An extra call may be obtained by connecting the two line wires directly, and, in this case, an electromagnet of high resistance is connected in bridge across the two line wires and supplied with current from a separate battery. When the line wires are connected they form a short circuit round the magnet which then releases its armature to make the desired connection. In this case, the line wires must be connected to earth through resistances. Fig. 4 shows a more complex case in which the line wires may be earthed through resistances R, R<1> respectively. Line 1 leads through relays a, c, and line 2 through relays b, d, to the battery o, the relays a, b being sensitive to weak currents and relays c, d to strong currents. The relays b, c, d have respectively two, three, and five armatures which engage with contacts connected to the line wires as shown. If, for example, the subscriber wishes to call station Z<6>, he simultaneously connects line 2 directly to earth, and line 1 through resistance R<1> to earth. This causes a strong current to flow through line 2 and relays b, d, and a weak current through line 1 and relays a, c. In this way, the armatures of relays b, d, a, but not of relay c, are attracted, and a, call circuit through station Z<6> is completed as follows-from battery Q, armatures a', b<1>, d<1>, h to line o, call at station Z<6>, relay C<6> to earth, When the operator at station Z<6> inserts a plug in the jack, the wire 3 is connected to the wires 1, 2 and hence to the battery Q, so that the electromagnetic cut-out t is energized and breaks the connections between the line wires 1, 2, and the battery Q. In a modification, the relays a, b, c, d may be operated indirectly by other relays in the line circuits. In order to protect the more sensitive relays from the action of the stronger currents necessary to actuate the less sensitive relays, the latter may, by the attraction of their armatures, close shunt circuits round the more sensitive relays.