Patent GB-190516484-A (GB)
Title: Improvements in Call Signal Apparatus for Group-calling in Telephone Installations.
Filed: 1905-08-14
Granted: 1906-01-11
Abstract: 16,484. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. Aug. 14. Telephone systems; telephone calls.-Relates to means for group-calling in exchange systems, the calling subscriber being enabled to give a selected one of two or more signals according as the wanted subscriber is in one or other of two or more groups. The arrangement may be such that the call remains under the control of the subscriber, who can withdraw it by hanging up his receiver. In the arrangement shown in Fig. 1, the reference letter f denotes the subscriber's receiver, m the microphone, w and z the call bell and condenser or polarization cell, and t<1>, t' the two group-signalling keys. If the subscriber wishes to call group No. 1, of which L<1> is the calling-lamp, he takes his receiver from the hook and depresses the key t<1>. Current then passes from the battery B' to earth through the relay winding a and line 1, the armature d being attracted against the tension of its controlling. spring. The coil e of the reversing- relay R<2> is short-circuited through the contacts e', c' and armature d when the last-named is attracted, and the contact at c closes the circuit of the lamp L<1> through the contact c<5>. When the key t<1> is released, the current flows through the microphone and both coils a, b of the relay R, the armature of which remains attracted owing to the greater air space between the armature and core on the side of the winding b. If the subscriber hangs up his receiver, the relay R<1> is de-energized and the lamp L<1> extinguished. In order to call group No. 2, the subscriber unhooks his receiver and depresses the key t<2>, thus connecting both lines 1, 2 to earth through the resistance r. The current in the line 1 divides, one part passing through the resistance r to earth and the remainder through the line 2 and coils b, e. The current in the coil b is too weak to neutralize the effect of that in the coil a, and the armature d is attracted. The relay R' being energized, the armature x makes contact at c' instead of c<5>, and the lamp L<2> is consequently lighted. The simultaneous excitation of the relays R', R<2> in this case prevents the short-circuiting of the latter at the contact c. The calling of group No. 1 may be effected by a direct earth connexion without breaking the microphone circuit. The extinction of the lamps when the operator responds to the call may be effected by disconnecting the relays from the lines, but, in the arrangement shown in Fig. 1, an earth battery B<3> connected with the cord circuit S', S' sends current through the coils b, e, so as to bring the armature d into the normal position and so extinguish the lamps. The devices X, Y serve to connect with a testing-circuit and play no part in the operation of the system described. Fig. 4 shows an arrangement in which three groups can be called, the opposition of two batteries of different strengths being utilized to effect the third call. The calling-relay R<2> is polarized, the armature d' making contact at d<3> or d<4> according to the direction of the current. On depression of the key t<1> the relay R<1> is energized, and the circuit of the lamp L<1> closed through the contacts c<3>, d<2>. If the key t<2> is depressed, the relay R' is energized and contact is made at d<1>, d<3>, the lamp L<2> being lighted. If the call is made by means of the key t<3>, the batteries B', B<2> are opposed, the relays R', R' being both energized, but the current in the latter is reversed. The contacts made in this case are at c', c<3> and at d<4>, d', the lamp L<3> being lighted. Two branch stations N', N', speaking to each other, can be supplied with current from the line-wires through resistances w<1>, w<2> without actuating a call signal, for contact is in that case made at c<1>, c<3> and d<1>, d<3>, thus cutting out all the lamps. The arrangement may be reversed, the branch stations being fed through the lines connected in series, and the calling of the third group being effected through both lines and earth. In a modification, two non-polarized relays control the lamps L', L<2>, and a polarized relay in series with one of them is used to control the lamp L<3>. In the arrangement shown in Fig. 6, the relay R<3> is doubly wound, and the relays R', R<2> have retaining-coils v<3>, v<4>, and a common armature c. If the key t<1> or t<2> is depressed, the lamp L<1> or L<2> is lighted. If the key t<3> is depressed, the armature c is unattracted, but the current in the coils r', r<2> due to the opposed batteries B', B' causes the attraction of the armature d, the coils being so wound as to assist each other's action in these circumstances. The lamp L<3> is, thus lighted. When supplying current to the, branch stations N<1>, N<2>, the coils r<1>, r<2>oppose each other, and no signal is given. At each call of the group No. 1 or No. 2, the armature. d is also attracted, but the resistances e, e<3> are so chosen, that the shunt current through the lamp L<3> when the lamp L<1> or L<2> is in use is not sufficient to cause it to glow. The circuit of the retaining-coils v<3>, v' is automatically broken between the battery B<3> and the armature c by the exchange operator in taking up the call.