GB732245A - Electrical control system - Google Patents

Abstract

732,245. Automatic temperature control systems. BLECKMANN, H., BLECKMANN, A., and DAMHOFER, E., [trading as BLECKMANN & CO. [Firm of]]. Sept. 15, 1952 [Oct. 9, 1951], No. 23132/52. Class 38 (4). [Also in Group XXXVII] An electric control system comprising an electromagnetic switching element partly controlled by a. variable to be controlled, e.g. an electric furnace 10, is characterized by an armature 5 which is movable towards an electromagnet 3 against the action of a spring 6 which is subjected to the action of means periodically moving the armature 5 towards the electromagnet 3 through the energizing coil 2 of which flows a current dependent on the variable to be controlled, in the case of an electric furnace 10 this current is derived from a thermocouple 1 associated therewith, a pair of contacts 7, 8 being provided which are moved with the armature and maintain closed the circuit controlling the variable to be controlled, which contacts can only be opened when the armature 5 adheres to the electromagnet 3 due to the magnetic force thereof exceeding the opposing force of the spring 6. The means periodically moving the armature 5 and the contacts 7, 8 comprises an electric motor 9 driving a worm and cam arrangement 4. When the temperature of the thermocouple 1 reaches the desired value-adjustable by movement of a core 11 of the electromagnet 3 or by altering the stress of the spring 6- the output thereof energizes the electromagnet such that it overcomes the force of the spring 6 and retains the armature 5 attracted thereto. Contacts 7, 8 are thus opened removing the supply from the furnace and the motor. In other embodiments the means periodically moving the armature are in the form of a direct-acting bi-metallic strip or a further electromagnet controlled by the bi-metallic strip. Other embodiments are envisaged in which the controlling elements are pressure gauges, thermometers, hydrometers and the like.