GB344481A - Improvements in or relating to temperature regulating means - Google Patents

Abstract

344,481. Thermostats. STOW, A. A. and JONES, E. H. P., 68, Willow Walk, Bermondsey, London. Nov. 28, 1929, No. 36495. [Class 64 (ii).] A thermal switch comprises concentric tubes of the metal known by the Registered Trade Mark of "Invar," and brass, the outermost tube being perforated, operating through a lever system to control a series of contacts in succession. The thermal element comprises tubes 3, of brass, the outer tube being perforated to permit access of hot gases from the oven 1, and a tube 4 of "Invar." The tubes are connected at opposite ends alternately, and the inner tube is connected by a rod 8 to the lever system. The rod 8 acts upon a lever 15 pivoted at 16 and having a knife-edge 17 acting on another lever with bifurcated arms 18 pivoted at 21. This lever is pressed upward by a knife-edge mounted on a spring pillar 14. The rod 8 is adjusted in relation to the lever 15 by a knob 26 having a screwthreaded stem 27 engaging the threaded end of the rod 8. The setting of the rod 8 is shown upon a dial 30 geared with the knob 26. Four contact arms 43 are pivoted on a bus-bar 40, and co-operate with contacts 47 towards which they are pressed by springs 50. Contact screws 51 are adjusted so that the arms 43 are actuated by the knife-edge 22 in succession. The contacts control heating resistances which may therefore be cut out in succession. If the heating current is large, sparking at the contacts is avoided by employing a relay for the main heating resistance only, the auxiliary heating resistances being connected directly to three of the contacts 47. In Fig. 3, the arm 43 is replaced by a lever 67 which operates between two contacts 68, 69, so that when the contact 68 is engaged the relay is energized to close the circuit of the main heater, and when the contact 69 is engaged by expansion of the thermal element 2 the action of the relay is reversed to open the circuit of the main heater. According to the Provisional Specification, the thermal element may be in the form of a grid, cage, or rectangle formed by bars or rods.