GB126113A - Improvements in or relating to Automatic Electric Switches for Furnace Control and other purposes. - Google Patents

Abstract

126,113. Coates, H., Norballe, H. J., and Watford Electric & Manufacturing Co. April 26, 1918. Electrode furnaces.-In an arrangement comprising an electrode-adjusting or other motor, in circuit with a " clapper " or other switch operated electro-magnetically through a relay switch and arranged so as, on movement, to de-energize or reverse the action of the relay switch in order to cause intermittent current supply to the motor, the motor switch is arranged sn as, in the initial part of the closing movement, to shunt the relay switch contacts F<1>, F<2> by auxiliary contacts H, J, between which the breakage of the relay circuit is subsequently effected. One contact of the relay switch may be moved to open the relay circuit in this way, while the other is adjusted by the current or pressure-sensitive device in the main circuit. In the arrangment illustrated with the motor circuit omitted, an electro-magnet supplied with current from a transformer in the electrode circuit operates a lever F with a cross-piece F<1>, the ends of which form contacts of relay switches. The co-operating contact F<2> or F<3> of each relay is formed by an arm of a lever H pivoted at H<1>. Movement of the lever F due to high or low electrode current causes closure of a switch from supply mains I, II through the operating coil A<1> or B' of one or other of two switches A, A<2>, or B, B<2>, to send current to the motor armature in the required direction. When either motor switch begins to move. it also opens a switch C or C' previously closing a short-circuit to a solenoid K<1>. The core of this solenoid is adjustably retarded by a dash-pot K<2>, and carries two adjustable disks K adapted to strike the levers H and break the relay circuit again after a predetermined interval. Previously to this, the motor switch A or B has caused the closure of a switch E or E', which places in parallel with the contact F' of the relay switch the contact J engaged by the roller contact H<2> carried by a spring-urged arm having limited movement on the lever H. Thus the relay circuit is broken at the auxiliary contact H<2>, J to protect the primary contacts F<1>, F. Each motor switch, as soon as it begins to close, opens a switch D or D<1> in the primary operating circuit of the other motor switch, to prevent simultaneous operation. When the electric pressure between the electrode and the hearth is very low, a shunt coil G allows an arm G<1> to fall onto a contact G and connect an electro-magnetic switch L across a resistance R' which is permanently in a circuit through an upper contact G<2> bearing on the arm G'. The switch L then sends current by the path x to the operating coil of the electrode-raising motor switch B without traversing the relay switch F', so that the motor current is continuous and the electrode is raised rapidly. A manual controller has contacts M - - M<3>, of which M and M<1> are connected for the automatic regulation described. The electrode-raising switch B supplies a higher electric pressure to the motor than does the other switch A.