440,678. Automatic exchange switches. BRANDER, B. J., 10, Dannemoragatan, Stockholm. Oct. 19, 1934, No. 30016. [Class 40 (iv)] Brush-choosing switches of the panel type are driven by individual two-phase synchronous motors fed, as regards numerical operation, by direct-current impulses generated by impulse-receiving relays and, as regards non-numerical operation, by twophase alternating current. The invention is described with reference to circuits for final selectors set by two digits each impulse of which is converted into a set of pulses equivalent collectively to two alternating currents with a phase difference of 90‹. Features of the switch construction form the subjectmatter of Specification 440,709. Construction of switches, Fig. 2. Two switch-supporting plates s are mounted horizontally on either side of a flat bank e and are held by springs m. Each switch comprises a slide Y movable on rollers relatively to the plate s and carrying five sets of brushes a normally held out of engagement with the bank by springs r which also supply current. A further slide rod Z movable relatively to slide Y has an extension z provided with a rack geared to the armature 3 of a twophase synchronous motor M. During the selecting operations, the slide Z is first moved to the left to render a particular set of brushes operative by engagement of a stud f with a lug g. The direction of the motor is then reversed and the engagement of a pawl k with a rack l causes the slides Y, Z to move together to the right, the selected set of brushes making contact with the lines of the wanted group. Off-normal contacts n are separated by a stud o when slides Y, Z are in their normal relative positions and contacts p are closed by a stud q when the slide Z reaches its extreme left position. Final selector, Fig. 4. Line and release relays R1, R3 operate and current from positive battery at contact 35 is supplied to armature 3 and field coils 1, 2. At the first impulse of the tens digit, the release of R1 connects negative battery to coils 2 causing the armature to make a quarter revolution. Shortly afterwards, relay R2 operates connecting negative battery to coils 1 so that the armature makes a second quarter revolution. Similarly two further quarter revolutions are made by the response of R1 and the subsequent release of R2 at the end of the impulse. The armature thus makes a complete revolution in response to each impulse. At the end of the digit, the relapse of relay R7 completes the circuit of relay R5 which was prepared by off-normal relay R4, the operation of R5 reversing the connections to coils 1 and 2 so that in response to the units impulses the motor is driven in the reverse direction. At the end of this digit, test relay R8 is connected up and testing and ringing takes place in known manner. During conversation, the selector may be held locked by passage of continuous current through coils 1, 2 and armature 3 in series with a resistance 17. To prevent unnecessary current consumption, this locking circuit may be made dependent on a contact 26 controlled by a door or lid giving access to the switches so that the circuit is only closed when interference is likely. At the end of conversation when R3 releases, relays R2 and R1 (over a third winding 22) interact to drive the motor in a manner similar to that employed during impulsing. Slides Y, Z move together to the left until Y reaches stop-pin i, Fig. 2, when Z continues to move alone until stud q closes contacts p which operate reversing relay R5. Slide Z then moves to the right back to normal position where contacts n are opened, the pawl k moving along the under-side of rack l during this operation. In a modification, Fig. 5 (not shown), the relay R2 is dispensed with, the two-phase effect from a single directcurrent impulse being obtained by associating with one pair of motor field coils a delay device such as an inductance or condenser. Restoration is effected by single-phase A.C. made effectively two-phase by the same means. In a further modification, Fig. 6, (not shown), employing a battery earthed at its positive pole, the stator comprises four pairs of oppositely-wound coils, the members of the pairs being alternately energized by connections to the negative pole under control of the impulse relay. The two-phase effect is again produced by a delay device which may comprise a double-wound inductance coil with or without associated condensers or resistances with a high - temperature coefficient. Specification 252,934, [Class 40 (iv)], is referred to.