Patent GB-257966-A (GB)
Title: Improvements in electric switches, specially applicable to press button and the likeautomatically operated switches
IPC: H01H51/08
Filed: 1925-04-08
Abstract: 257,966. Cox, F. B. April 8, 1925. Selective distant control systems. - ln an arrangement of electric switchgear a control switch is rotated step by step in one direction by the reciprocating movement imparted to the armature of an electro-magnet connected to a supply by switches automatically operated by the armature, the control switch making in succesion desired circuit connections and being arrested in any desired angular position by the operation, through the movement of the control switch, of a limit switch or switches, the pairs of contacts of which are connected in series with the winding of the actuating electro-magnet, said pairs of contacts being also connected to a shortcircuiting switch which when closed renders the corresponding limit switch inoperative to break the magnet circuit. As shown applied to a motor control circuit in Fig. 1, the rotary arm a6 of the control switch A is stepped round by the core b2 of the electro-magnet B to cut out sections of the resistance D in the circuit of the motor M which are connected to segments d1 - - d8. The armature b, is connected by a link b3 to a pivoted member a3 carrying a pawl a4 engaging the ratchet teeth a2 of a wheel secured to the arm a6. The core b2 in rising rotates a pivoted arm b14 connected to a spring b13 which when moved across the dead-centre position breaks the solenoid circuit at contacts b7 with a snap action. The core b2 at the end of its stroke also opens switch b5 and is returned by gravity. The strokes of the core may be regulated by placing a dashpot b6 between members b2 and b3 or by attaching a dashpot to the switch b5 and the solenoid may carry a few series turns. When the arm a6 reaches the running position in which it engages the segment d8 a projection a8 engages a limit switch E which by opening the solenoid circuit prevents any further stepping round of the contact arm. The contacts e may however be short-circuited by a switch F operated by a handle J so that the arm a6 is stepped round to engage contact d1 but is again held in this position by operation of a second limit switch G. Another switch R is also operated by the arm a6 at this point so completing the circuit of the line contactor 0 for the motor circuit, a maintaining circuit for this contactor beng completed at contacts T. If this. maintaining circuit is at any time interrupted either by operation of a stop switch S or an overload relay Q the contactor is opened and cannot be reclosed until the control switch regains its initial position. The stepping round again proceeds on release of switch J and " inching " of the motor may be effected by simultaneous operation of switches J and S. In a modified form shown in Fig. 2, the control switch A1 has two positions only. the arm a6 engaging in the " on " position a limit switch W and in the " off " position a limit switch V, the contacts of these switches being short-circuited at contacts w4 or v4 of a hand-operated two-way knife switch U. Alternatively the short-circuiting contacts w5, v5 (Fig.2A) may be controlled by electromagnetic switch w6, v6 energized in accordance with the movements of a motor-driven hydraulic accumulator or similar apparatus. If it is desired to have a number of circuit-controlling positions at any of which the control switch arm may be arrested, limit switches corresponding to each position are provided the short-circuiting of which may be effected by a master switch of the type shown in Fig. 3, which is so arranged that in any position all of the limit switch contacts are shunted except the one at the stop position. Thus if the switch is adjusted so that pairs of contacts 1<1>, 3<1> and 4<1> are bridged by members 5<1>, 7<1> and 8<1> on the shaft 9 the contacts 2<1> are not bridged by the member 6' so that when the contact arm in stepping round reaches the limit switch corresponding to 2<1> the circuit of the operating electro-magnet will be broken.