GB637051A - Temperature control system - Google Patents

Abstract

637,051. Induction motors; automatic temperature control systems. FLIGHT, T. N., and WILSON, W. H. Feb. 12, 1948, Nos. 4164 and 18427. [Classes 35 and 38 (iv)] [Also in Group XXXVII] In a heating system wherein a thermally sensitive switch 15, Fig. 1, determines the direction of rotation of a reversible electric motor 9 operating a valve 10 to maintain the temperature constant, the motor is energized intermittently for varying periods depending upon the departure of the controlled temperature from a predetermined value. The valve 10 may control the amount of hot and returning water in pipes 3 and 4 respectively in a hot water radiator system or it may control the passage of steam from a boiler to a heatexchanger (Fig. 2, not shown). The reversible motor may be a shaded pole induction motor 23, Fig. 3, having four main poles each having an energizing winding 28-31. Each pole is split into two legs, each leg being wound with a shading coil. Shading coils 41, 43, 45, 47 are connected in series and coils 40, 42, 44, 46 are also connected in series, the two circuits being made common at 48, and connected to the thermostat switch 50 and a motor switch 49. The opposite ends of the shading coil circuits are connected to contacts 53, 54 of the thermostat switch and contacts 51, 52 of the motor switch. The main windings of the motor are energized intermittently by means of contacts 56, 57 co-operating with a rotating segment 58, the contact 57 being adjustable to vary the lengths of period of operation. At the predetermined value of temperature both sets of shading coils are short-circuited and upon energization the motor remains stationary. Upon a departure of the temperature from the predetermined value the thermostatic switch open circuits one set of shading coils so that upon energization the motor will rotate to operate the valve in a sense to correct the deviation. If, however, a large deviation occurs, further contacts 59, 60, 62 of the thermostat switch operate to close a secondary motor energizing circuit, the motor remaining energized as long as the segment 58 is in contact with 56 independent of the position of the contact 57, so that the valve may be positioned more quickly. The motor switch 49 is geared to the motor so that upon complete closure or full opening of the valve both shaded windings become short-circuited, thereby stopping the motor. In a modification (Fig. 4, not shown), both sets of shading windings are permanently short-circuited, the motor having two separately wound stators, the direction of rotation being determined according to which stator is energized by means of the thermostat switch.